Tagged: CERN ALICE Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 2:17 pm on October 17, 2017 Permalink | Reply
    Tags: , , CERN ALICE, HBOOK and PAW and ROOT and GEANT, , , , , René Brun   

    From ALICE at CERN: “40 Years of Large Scale Data Analysis in HEP: Interview with René Brun” 

    CERN
    CERN New Masthead

    16 October 2017
    Virginia Greco

    1
    Over 40 years of career at CERN, René Brun developed a number of software packages that became largely used in High Energy Physics. For these fundamental contributions he was recently awarded a special prize of the EPS High Energy Particle Physics Division. We have talked with him about the key events of this (hi)story.

    1
    René Brun giving a seminar at CERN (on October 4, 2017) about “40 Years of Large Scale Data Analysis in HEP – the HBOOK, Paw and Root Story”. [Credit: Virginia Greco]

    It is hard to imagine that one same person can be behind many of the most important and largely used software packages developed at CERN and in high-energy physics: HBOOK, PAW, ROOT and GEANT. This passionate and visionary person is René Brun, now honorary member of CERN, who was recently awarded a special prize of the EPS High Energy Particle Physics Division “for his outstanding and original contributions to the software tools for data management, detector simulation, and analysis that have shaped particle and high energy physics experiments for many decades”. Over 40 years of career at CERN, he worked with various brilliant scientists and we cannot forget that the realization of such endeavors is always the product of a collaborative effort. Nevertheless, René has had the undoubtable merit of conceiving new ideas, proposing projects and working hard and enthusiastically to transform them in reality.

    One of his creations, ROOT, is a data analysis tool widely used in high energy and nuclear physics experiments, at CERN and in other laboratories. It has already passed beyond the limits of physics and is now being applied in other scientific fields and even in finance. GEANT is an extremely successful software package developed by René Brun, which allows simulating physics experiments and particle interactions in detectors. Its latest version, GEANT4, is currently the first choice of particle physicists dealing with detector simulations.

    But previous to ROOT and GEANT4, which are very well known among the youngest as well, many other projects had been proposed and software tools had been developed. It is a fascinating story, which René was invited to tell in a recent colloquium, organized at CERN by the EP department.

    As he recounts, all started in 1973, when he was hired in the Data Handling (DD) division at CERN to work with Carlo Rubbia in the R602 experiment at the ISR. His duty was to help developing a special hardware processor for the online reconstruction of the collision patterns. But since this development was moving slowly and was not occupying much of his work time, René was asked to write some software for the event reconstruction in multiwire proportional chambers. “At that time, I hated software,” René confesses smiling, “I had written software during my PhD thesis, while studying in Clermont-Ferrand and working at CERN during the weekends, and I hadn’t really enjoyed it. I had joined Rubbia’s group with the ‘promise’ that I would work on hardware, but very quickly I became a software guy again…”

    In short time, René implemented in software (programming in Fortran4) what they could not realize via hardware and, in addition, he developed a histogram package called HBOOK. This allowed realizing a very basic analysis of the data, creating histograms, filling them and sending the output to a line printer. He also wrote a program called HPLOT which was specialized in drawing histograms generated by HBOOK.

    At that time, there were no graphic devices, so the only way to visualize histograms was printing them using a line printer, and programs were written in the form of punched cards.

    René remembers with affection the time spent punching cards, not for the procedure itself, which was slow and quite tedious, but for the long chats he used to have in the room where the card punchers and printers of the DD department were sitting, as well as in the cafeteria nearby. In those long hours, he could discuss ideas and comment on new technologies with colleagues.

    A huge progress was made possible by the introduction of the teletype, which replaced card punchers. Users could generate programs on a disk file and communicate with a central machine, called FOCUS, while – at the same time – seeing on a roll of paper what they were doing as in a normal type machine. “The way it worked can make people smile today,” René recounts, “To log in the FOCUS, one had to type a command which caused a red light to flash in the computer centre. Seeing the light, the operator would mount into the memory of the machine the tape of the connected person, who could thus run a session on the disk. When the user logged out, the session was again dumped on tape. You can imagine the traffic! But this was still much faster than punching cards.”

    Some time later, the teletype was in turn replaced by a Tektronix 4010 terminal, which brought in a big revolution, since it gave the possibility to display results in graphic form. This new, very expensive device allowed René to speed up the development of his software: HBOOK first, then another package called ZBOOK and the first version of GEANT. Created in 1974 with his colleagues in the Electronic Experiments (EE) group, GEANT1 was a tool for performing simple detector simulations. Gradually, they added features to this software and were able to generate collision simulations: GEANT2 was born.

    In 1975 René joined the NA4 experiment, a deep inelastic muon scattering experiment in the North Area, led by Carlo Rubbia. There he collaborated on the development of new graphic tools that allowed printing histograms using a device called CalComp plotter. This machine, which worked with a 10-meter-long roll of paper, granted a much better resolution compared with line printers, but was very expensive. In 1979 a microfilm system was introduced: histograms saved on the film could be inspected before sending them to the plotter, so that only the interesting ones were printed. This reduced the expenses due to the use of the CalComp.

    René was then supposed to follow Rubbia in the UA1 experiment, for which he had been doing many simulations – “Without knowing that I was simulating for UA1,” René highlights. But instead, at the end of 1980, he joined the OPAL experiment, where he performed all the simulations and created GEANT3.

    While working on the HBOOK system, in 1974 René had developed a memory management and I/O system called ZBOOK. This tool was an alternative to the HYDRA system, which was being developed in the bubble chambers group by the late Julius Zoll (also author of another management system called Patchy).

    Thinking that it was meaningless to have two competing systems, in 1981, the late Emilio Pagiola proposed the development of a new software package called GEM. While three people were working hard on the GEM project, René and Julius together started to run benchmarks to compare their systems, ZBOOK and HYDRA, with GEM. Through these tests, they came to the conclusion that the new system was by far slower than theirs.

    In 1983 Ian Butterworth, the then Director for Computing, decided that only the ZBOOK system would be supported at CERN and that GEM had to be stopped, and HYDRA was frozen. “My group leader, Hans Grote, came to my office, shook my hand and told me: ‘Congratulations René, you won.’ But I immediately thought that this decision was not fair, because actually both systems had good features and Julius Zoll was a great software developer.”

    In consequence of this decision, René and Julius started a collaboration and joined forces to develop a package integrating the best features of both ZBOOK and HYDRA. The new project was called ZEBRA, from the combination of the names of the two original systems. “When Julius and I announced that we were collaborating, Ian Butterworth immediately called both of us to his office and told us that, if in 6 months the ZEBRA system was not functioning, we would be fired from CERN. But indeed, less than two months later we were already able to show a running primary version of the ZEBRA system.”

    At the same time, histogram and visualization tools were under development. René put together an interactive version of HBOOK and HPLOT, called HTV, which run on Tektronix machines. But in 1982 the advent of personal workstations marked a revolution. The first personal workstation introduced in Europe, the Apollo, represented a leap in terms of characteristics and performance: it was faster, had more memory and better user interface than any other previous device. “I was invited by the Apollo company to go to Boston and visit them,” René recounts. “When I first saw the Apollo workstation, I was shocked. I immediately realized that it could speed up our development by a factor of 10. I put myself at work and I think that in just three days I adapted some 20000 lines of code for it.”

    The work of René in adapting HTV for the Apollo workstation attracted the interest of the late Rudy Böck, Luc Pape and Jean-Pierre Revol from the UA1 collaboration, who also suggested some improvements. Therefore, in 1984 the three of them elaborated a proposal for a new package, which would be based on HBOOK and ZEBRA, that they called PAW, from Physics Analysis Workstation.

    2
    The PAW team: (from the left) René Brun, Pietro Zanarini, Olivier Couet (standing) and Carlo Vandoni.

    After a first period of uncertainties, the PAW project developed quickly and many new features were introduced, thanks also to the increasing memory space of the workstations. “At a certain point, the PAW software was growing so fast that we started to receive complaints from users who could not keep up with the development,” says René smiling. “Maybe we were a bit naïve, but certainly full of enthusiasm.”

    The programming language generally used for scientific computing was FORTRAN. In particular, at that time FORTRAN 77 (introduced in 1977) was widespread in the high-energy physics community and the main reason for its success was the fact that it was well structured and quite easy to learn. Besides, very efficient implementations of it were available on all the machines used at the time. As a consequence, when the new FORTRAN 90 appeared, it seemed obvious that it would replace FORTRAN 77 and that it would be as successful as the previous version. “I remember well the leader of the computing division, Paolo Zanella, saying: ‘I don’t know what the next programming language will do but I know its name: FORTRAN.’”

    In 1990 and 91 René, together with Mike Metcalf, who was a great expert of FORTRAN, worked hard to adapt the ZEBRA package to FORTRAN 90. But this effort did not lead to a satisfactory result and discussions raised about the opportunity to keep working with FORTRAN or moving to another language. It was the period when object-oriented programming was taking its first steps and also when Tim Berners Lee joined René’s group.

    Berners-Lee was supposed to develop a documentation system, called XFIND, to replace the previous FIND that could run only on IBM machines, which had to be usable on other devices. He believed, though, that the procedure he was supposed to implement was a bit clumsy and certainly not the best approach to the problem. So, he proposed a different solution with a more decentralized and adaptable approach, which required first of all a work of standardization. In this context, Berners-Lee developed the by-now-very-famous idea of the World Wide Web servers and clients, developed using an object-oriented language (Object C).

    It was a very hot period, because the phase of design and simulation of the experiments for the new accelerator LHC had been launched. It was important to take a decision about the programming language and the software tools to use in these new projects.

    At the workshop of ERICE, organized by INFN in November 1990, and then at the Computing in High Energy Physics (CHEP) conference in Annecy (France), in September 1992, the high-energy physics “software gurus” of the world gathered to discuss about programming languages and possible orientations for software in HEP. Among the many languages proposed, there were also Eiffel, Prolog, Modula2 and others.

    In 1994 two Research and Development (RD) projects were launched: RD44, with the objective of implementing in C++ a new version of GEANT (which will become GEANT4), and RD45, aiming to investigate object-oriented database solutions for the LEP experiments.

    According to René, his division was split in three opinion groups: those who wanted to stay with FORTRAN 90, those who bet on C++ and those who were interested in using commercial products. “I presented a proposal to develop a package that would take PAW to the OO word. But the project, which I called ZOO, was rejected and I was even invited to take a sabbatical leave” René admits.

    This blow, though, proved later to be indeed a strike of luck for René. He was suggested by his division leader, David Williams, to join the NA49 experiment in the North Area, which needed somebody to help developing the software. At first, he refused. He had been leading for years both the GEANT and the PAW projects and making simulation or developing software for different groups and applications, thus accepting to go back working in a specific experiment appeared to him as a big limitation.

    But he gave it second thoughts and realized that it was an opportunity to take some time to develop new software, with total freedom. He went to visit the NA49 building in the Prevessin site and, seeing from the windows pine trees and squirrels, he felt that it was indeed the kind of quiet environment he needed for his new project. Therefore, he moved his workstation from his office to the Prevessin site (“I did it during a weekend, without even telling David Williams”) and, while working for NA49, he taught himself C++ by converting in this new OO language a large part of his HBOOK software.

    At the beginning of 1995, René was joined in NA49 by Fons Rademakers, with whom he had already collaborated. The two of them worked very hard for several months and produced the first version of what became the famous ROOT system. The name comes simply from the combination of the starting letter of the email addresses of the two founders (René and Rdm, for Rademakers), the double O of Object Oriented and the word Technology. But the meaning or the word ‘root’ also fitted well with its being a basic framework for more software to be developed and with the use of tree structures in its architecture.

    In November of the same year, René gave a seminar to present the ROOT system. “The Computing Division auditorium was unexpectedly crowded!” René recalls, “I think it was because people thought that Fons and I had disappeared from the software arena, while all of a sudden we were back again!” And actually the ROOT system generated considerable interest.

    But while René and Fons were completely absorbed by the work on their new software package, the RD45 project, which had the mandate to decide what new software had to be adopted by the new LHC experiments, had proposed to use the commercial product “Objectivity” and a lot of work was ongoing to develop applications to meet the HEP needs. According to René, there was a clear intention to obstruct the development and diffusion of ROOT. In spring 1996 the CERN director for computing, Lorenzo Foa, declared that the ROOT project was considered as a private initiative of NA49 which was not supported by the CERN management and that the official line of development was the one around Objectivity.

    “I think that the LHC Computing Board didn’t have the right insight into the architecture of these software tools to be able to judge which solution was the best. Thus, they had to trust what they were told,” René comments. “It is always a problem when there is such a divide between the experts – and users – working on something and the people who are to take important decisions.”

    Nevertheless, René and Fons continued developing ROOT and implementing new features, taking advantage of the lessons learnt with the previous software packages (in particular the requests and criticisms of the users). In addition, they followed closely the development of the official line with Objectivity, in order to know what people using it were looking for and what the problems or difficulties were. “The more we looked into Objectivity, the more we realized it could not meet the needs of our community,” René adds, “we knew that the system would fail and that eventually people would realize it. This gave us even more energy and motivation to work hard and improve our product.”

    They had continuous support from the NA49 and ALICE collaborations, as well as from many people in ATLAS and CMS, who saw good potentiality in their software package. At the time, René was collaborating with many people in both experiments, including Fabiola Gianotti and Daniel Froidevaux, in particular for detector simulations. Besides, many users trusted them for the relationship created along many years through the user support of PAW and GEANT.

    Things started to change when interest for ROOT raised outside CERN. In 1998, the two experiments of Fermilab, CDF and D0, decided to discuss about the future of their software approach, in view of the soon-coming Run II of the Tevatron. Hence, they opened two calls for proposals of software solutions, one for data storage and one for data analysis and visualization. René submitted ROOT to both calls. During the CHEP conference in Chicago the proposals were discussed and the last day it was publicly announced that CDF and D0 would adopt ROOT. “I was not expecting it,” says René, “I remember that when the communication was given, everybody turned their face and looked at me.” Soon later, the experiments of RHIC at the Brookhaven National Laboratory took the same decision. The BaBar experiment at SLAC, after years spent attempting to use Objectivity, had realized that it was not as good a system as expected, so moved to ROOT as well.

    Gradually, it was clear that the HEP community was ‘naturally’ going towards ROOT, so the CERN management had to accept this situation and, eventually, support it. But this happened only in 2002. With more manpower allocated to the project, ROOT continued developing fast and the number of users increased dramatically. It also started to spread to other branches of science and into the financial world. “In 2010, we had on average 12000 downloads per month of the software package and the ROOT website had more visitors than the CERN one”.

    3
    The logo of the ROOT software package.

    René retired in 2012, but his two most important brainchildren, ROOT and GEANT, keep growing thanks to the work of many young scientists. “I think that it is essential to have a continuous stimulus that pushes you to improve your products and come out with new solutions. For this, the contribution of young people is very important,” comments René. But, as he admits, what really made him and his colleagues work hard for so many years is the fact that the software packages they were developing had always some competitors and, in many cases, they were challenged and even obstructed. “When you are contrasted, but you know you are right, you are condemned to succeed.”

    The great attention to the users’ needs has also been very important, because it helped to shape the software and build a trust relationship with people. “I have always said that you have to put the user support at the highest priority,” René explains. “If you reply to a request in 10 minutes you get 10 points, in one hour you get 2 points, and in one day you go already to -10 points. Answering questions and comments is fundamental, because if the users are satisfied with the support you give them, they are willing to trust what you propose next.”

    Now that he is retired, René still follows the software development at CERN, but only as an external observer. This does not mean that he has left apart his scientific interests, on the contrary he is now dedicating most of his energies to a more theoretical project, since he is developing a physics model. In his spare time, he likes gardening. He loves flowers, but he cannot avoid looking at them with a scientific eye: “A colleague of mine, who is mathematician, and I developed a mathematical model about the way flowers are structured and grow.”

    Brilliant minds are always at work.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Meet CERN in a variety of places:


    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS
    ATLAS
    CERN/ATLAS detector

    ALICE
    CERN ALICE New

    CMS
    CERN/CMS Detector

    LHCb

    CERN/LHCb

    LHC

    CERN/LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles


    Quantum Diaries

    Advertisements
     
  • richardmitnick 1:59 pm on October 17, 2017 Permalink | Reply
    Tags: , , CERN ALICE, Eliane Epple, , , ,   

    From ALICE at CERN: Women in STEM – “Focus on Eliane Epple” 

    CERN
    CERN New Masthead

    16 October 2017
    Virginia Greco

    1
    Eliane Epple
    A postdoctoral researcher at Yale University, Eliane is working on an analysis involving hard scattering events that produce direct photons and has recently done her first shift as Run Manager for ALICE.

    When she started studying physics in Stuttgart, her hometown, Eliane Epple was already passionate about particle physics. But since it was not possible to specialize in this field at her university, after two years she moved to Munich and attended the Technical University Munich (TUM). Here, she followed courses for two more years before joining a research project led by Prof. Laura Fabbietti, who had just received a big grant and was starting her research group. The subject of Eliane’s Diploma thesis was the study of the interactions of kaons – and other particles containing strange quarks – with nuclear matter (protons and neutrons). More in detail, for her Diploma she analyzed the decay products of a resonance called Λ(1405), which is by some theories treated as a molecular bound state of an anti-kaon and a nucleon. Its is in this sense a pre-stage of a kaonic nuclear cluster that she later studied during her PhD, still working with Prof. Fabbietti.

    In particular, Eliane and colleagues were investigating the possible existence of anti-kaonic bound-states formed by, for example, two nucleons and one anti-kaon.­ Besides Fabbietti’s team, other groups all over the world were working on this topic, since a number of theoretical physicists had hypothesized that the attraction between nucleons and anti-kaons should be strong enough to give rise to this bound state, at least for a short time. “I analyzed data from the High Acceptance Di-Electron Spectrometer (HADES) at GSI.

    GSI HADES

    In particular, I looked for particles produced in p+p collisions that could originate bfrom the decay of this anti-kaon-nucleon bound state,” explains Eliane. “It was a very controversial topic at the time, because there were groups that, analyzing a certain set of data, could see a signal compatible with the detection of such bound state, while others couldn’t. I didn’t find any signal proving this hypothesis, but at the same time my results set un upper limit for the existence of this bound state at the beam energy of 3.5 GeV.”

    “In order to set a limit,” Eliane continues, “you compare the result of your data analysis with the outcome of a simulation, performed assuming the hypothesis that the signal you are looking for but didn’t see exists. In other words, you develop a model for this case and study how much signal you can introduce and still keep consistency with your data. You proceed to add more and more signal strength to your model in little steps, until you reach a threshold: if you overcome it, the model doesn’t fit anymore with the data. This threshold is an upper limit.”

    She also combined her results with data from other experiments and showed that it was very unlikely that the signal seen by some other groups could be due to an anti-kaon-nucleon bound state. “Actually, I think that this signal exists because there are many compelling reasons from our theory colleagues, but it is very challenging to see, first of all because the production cross section of this state is probably very small, which means that it occurs rarely, so we need to take a lot of data. In addition, it might be a very broad state, so we are not going to find a narrow peak. As a consequence, understanding the background well is essential.”

    When she completed her PhD in 2014, she decided to change field. “In that situation, you have two possible choices,” explains Eliane, “either you stay on the same topic and become an expert in a very specific field, or you change and broaden your horizon. In this second case, you do not become a specialist of one topic but rather increase your ‘portfolio’. I preferred to go for this second option and do something completely new. This way is much harder because you basically start from the beginning but I think it benefits a researcher in the long term to look at a field, in this case QCD, from many perspectives. I thus also encourage some young researchers to give low energy QCD research a chance and see what people do beyond the TeV scale.” Therefore, she joined the research group led by John Harris and Helen Caines at Yale University, in New Haven (US), where she has been working for two and a half years now, and entered the ALICE collaboration.

    Her present research activities focus on hard probes in high-energy collisions. “The proton is a very fascinating object, there is a lot going on in it,” Eliane comments. “When you scatter two protons at low energy (an energy range where I have previously been working on), you see how the ‘entire’ proton behaves, you are not able to distinguish its internal structure. On the contrary, at the high energies of LHC, when you collide two protons you start seeing what happens inside, you can observe how partons collide with each other.”

    In these hard scattering events, particles with a high transverse momentum are present in the final state. Eliane is analyzing Pb-Pb events in which a parton and a photon (a gamma) are produced. Photons do not interact with strongly-interacting matter, hence, when the Quark Gluon Plasma (QGP) is created in ALICE by smashing lead nuclei, a photon produced in the collision can traverse this medium and get out unaffected. In the opposite direction, a parton moves away from the collision vertex and fragments into a particle shower. The sum of the momenta of the particles in this shower have to balance the momentum of the photon (combining these fragments with the gamma on the other side is called gamma-hadron correlation), and altogether they carry the total momentum of the mother parton.

    The objective of this research is measuring the fragmentation function, which describes the correlation between the momentum of the mother and those of each particle in the shower. Normally, most of the daughter particles carry a small fraction (less than 20%*) of the momentum of the mother, whereas very few of them have a high fraction of this momentum. “By studying the behaviour of the particle shower in Pb-Pb collisions, in comparison with pp and p-Pb collisions, we can understand how the QGP medium modifies it,” explains Eliane. “We may have, for example, fewer of these very high momentum fragments and therefore more of the low momentum ones, or the shower might be broader. This study gives information about the properties of the medium that is created.”

    There are measurements of gamma-hadron correlations performed in PHENIX,

    BNL RHIC PHENIX

    at 200 GeV which show that in gold-gold collisions the fragmentation function changes, giving fewer particles with high momentum fractions and many more particles having a low momentum fraction. ALICE is investigating what happens at higher energies.

    Eliane is now working in collaboration with a graduate student at her institute and other colleagues in Berkeley. “We are performing a very complex analysis. In our events, we have to identify gammas on one side and the hadron showers on the other. But gammas can also be decay products of other particles, such as pions and other mesons. Thus, it is important to avoid this background signal and take into consideration only events in which the gamma is produced in the primary vertex. This is not easy and requires a number of following steps.”

    Eliane will continue working at Yale for some time. Then, she will either look for another post-doctoral position in ALICE or will directly apply for some grants, most likely in Europe. “There are various opportunities in Germany to get research funding to start your own research group.”

    Even though she likes her present topic of analysis, in the future she might change for something more basic: the substructure and dynamic of the proton. “The proton is a very complex and fascinating object in its own right, we still do not know much about its internal dynamics,” she highlights. In any case, the most important thing for her is to settle on a research topic that will give her deeper insight into QCD properties — something she is very intrigued by.

    In addition to doing data analysis, Eliane coordinates the activities of the EMCal calibration group and EMCal photon object group and, lately, has been Run Manager for the data taking. With so much work and a four-year-old daughter, there is not much time left. Nevertheless, when she can, she attends classes of modern dance to de-stress and relax.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Meet CERN in a variety of places:


    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS
    ATLAS
    CERN/ATLAS detector

    ALICE
    CERN ALICE New

    CMS
    CERN/CMS Detector

    LHCb

    CERN/LHCb

    LHC

    CERN/LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles


    Quantum Diaries

     
  • richardmitnick 8:18 am on October 4, 2017 Permalink | Reply
    Tags: , CERN ALICE, , , , ,   

    From ALICE: Women in STEM – “Focus on Ester Casula” 

    CERN
    CERN New Masthead

    18 September 2017 [Just found in social media.]

    1
    Ester Casula

    Ester Anna Rita Casula is a postdoctoral researcher at the Italian National Institute of Nuclear Physics (INFN) of Cagliari – her hometown.

    1

    NAZIONALI del GRAN SASSO, located in L’Aquila, Italy

    She has been ALICE Run Manager for two weeks between June and August of this year.

    During her second week of shift, I meet Ester at point 2, where she spends most of her time monitoring the data taking and making sure everything runs smoothly.

    Sitting with me in the kitchen next to the control room, she talks smiling and laughing. I can see that she has a very extroverted personality. Besides telling me about her work, she unveils an uncommon passion of hers…

    What’s you background and your career path up to now?

    I have studied Physics at the University of Cagliari, in Italy, and I have been a member of the ALICE collaboration since when I was working on my Bachelor’s Degree thesis. At that time, we didn’t have data yet, so I used Monte Carlo simulations. Then, for my Master’s Degree thesis and during my PhD I focused on the analysis of low masses in the di-muon channel – thus, mainly the F – in pp, Pb-Pb and p-Pb collisions at all of the energies we have taken data with. I started with the data from pp collisions at 7 TeV – for my Master’s thesis – and then continued with the other energies and with p-Pb and Pb-Pb data (in detail: pp at 2.76 and 5 TeV, p-Pb at 5 TeV, Pb-Pb at 2.76 and 5 TeV).

    After completing my PhD in 2014, I started a first postdoc with the University of Cagliari and now I am concluding a second postdoc with the INFN in the same town.

    I am based in Cagliari, but in the last months I have spent most of my time at CERN and, in particular, in the control room, since I have also followed some runs as a shift leader.

    How do you like being the run manager?

    It is an interesting experience: every day you might have to face a different problem. For example, during my shift once we were called by the LHC control room to be informed that ALICE was causing the dump of the beam. Of course, we had to solve the issue very quickly. It happened in the dead of the night and I was at home. As soon as I received the call by the shift leader I got up and went to the control room. Luckily I am staying nearby, in Saint-Genis.

    In situations like this you have to react quickly, try to understand the issue as fast as you can and take decisions. In this specific case, the problem was caused by the threshold of the Beam Control Monitors (BCM), which are basically protection devices. We called the expert on call for the BCM, who checked the situation and fixed this issue. Even though the problem seemed to be solved, I kept staying in the control room until 5 am, because I was worried that something else could happen.

    What do you like the most of this role?

    Certainly this, the fact that you need to keep under control and solve different kinds of issues. In addition, you have to give instructions and take decisions: this is quite challenging, if you are not used to it. Actually, you start training in taking responsibilities already when you are the shift leader. When you become run manager, you go a little step forward. I spend a lot of time in the control room and, when I am at home, I check continuously the electronic log to know how the run is proceeding. When I wake up in the morning, the first thing I do – even before standing up – is checking online the status of the accelerator, to know if it is working, and of the experiment.

    It sounds a bit stressing…

    Well, it can be stressing sometimes, indeed. In particular because you have to be ready and react quickly; but, actually, I am finding it easier this week, since it is my second time as run manager.

    You can count on the run coordinator anyway, right?

    Sure. But we call her only if something very important happens. For normal issues, such as a shift leader having some doubts about the operations to perform, the run manager takes on the responsibility. Certainly, it is important to know what the most common issues are. That is why, before starting my first shift, I overlapped with the previous run manager for some days.

    What’s your main field of interest?

    I work on the analysis of the F in Pb-Pb collisions. An article on this topic based on data at 2.75 TeV is in preparation and now we are analyzing data from collisions at 5 TeV. I am quite specialized on this topic.

    Would you like to change topic to do something different?

    Yes, why not?

    Actually, when I was doing my first steps in the analysis, I made some study on the U, but it was based on simulations only, so it was more of an exercise than a real analysis.

    Anyway, I will see. I will have to evaluate the opportunities.

    What are your plans for the future?

    My postdoctoral contract at INFN will get to an end soon, so I will have to look for another job. I would prefer to keep staying in Cagliari, but I am also taking into consideration the possibility to make an experience in another country.

    Where? Or where absolutely not?

    Well, preferably in Europe, but not necessarily. Certainly I would avoid cold places… [She laughs].

    Would you like to teach?

    I don’t know. I have been a tutor for two courses at the University, which means that I helped the professor with the laboratory lessons. It was an interesting experience, but I am not particularly attracted to teaching, mainly because it takes a lot of time to prepare classes and find the right way to explain complex topics.

    Thus, I guess you would prefer to work for a Laboratory, as you are doing at INFN?

    Ideally yes, I would prefer to focus only on research.

    Nevertheless, I don’t exclude the academic career either. I think that I can enjoy part of the process of training students, even though I think it can be hard and tiring.

    What are your interests outside work?

    Well, my main hobby is breeding dogs. I raise them and make them compete in dog shows, which are dog beauty contests. [She laughs.]

    How many dogs do you have?

    I have three at my place, in Cagliari. Three more are looked after by some friends of mine but I make them participate in competitions as well.

    I get a litter of puppies once every three years and I keep some of them. They are all Italian Greyhounds with pedigree. I own the mother and select a father when I decide to have new puppies. [She laughs again.]

    What moves you to do this?

    I love them. I have even created the world online database of the Italian hounds, which didn’t exist before. I started it by myself, then I got some help from other three breeders in US and France. We have registered about 60,000 dogs. Unfortunately, we could go backward only till the end of the 19th century. Lately, the national dog clubs are putting information online, but in order to collect old data I had to rely on the original documentation. So, I went personally to the headquarters of the Italian National Dog Institution (ENCI) in Milan and photocopied all the certificates they have, from 1912 up to now.

    This is cool, but why did you do it?

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Meet CERN in a variety of places:


    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS
    ATLAS
    CERN/ATLAS detector

    ALICE
    CERN ALICE New

    CMS
    CERN/CMS Detector

    LHCb

    CERN/LHCb

    LHC

    CERN/LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles


    Quantum Diaries

     
  • richardmitnick 12:16 pm on August 12, 2017 Permalink | Reply
    Tags: ALPIDE chip, , CERN ALICE, Desk cosmic ray detector, , , The ALPIDE chip is a CMOS monolithic active pixel sensor   

    From ALICE at CERN: “A desk cosmic ray detector for schools using the ALPIDE chip” 

    CERN
    CERN New Masthead

    11 August 2017
    Virginia Greco

    An educational and outreach project conceived by the ALICE ITS team is now moving forward rapidly thanks to Matthew Aquilina, who has joined the collaboration as a summer student, and his supervisors Magnus Mager and Felix Reidt.

    1
    Magnus Mager (left) and Matthew Aquilina (right). In the center, a prototype of compact cosmic ray detector based on the ALPIDE chip. [Credits: Virginia Greco]

    Would you like to have your own cheap and compact cosmic ray detector, sitting right on your desk? It sounds much like a nerdy fantasy, but indeed such a device can be realized and become a very useful educational and outreach tool.

    This was the idea inspiring the ALICE ITS team at CERN, who decided to use the pixel sensor chip (ALPIDE) to build a small and easy-to-operate cosmic ray detector. The project is now taking off thanks to the involvement of Matthew Aquilina – a summer student from Malta who joined the group at the end of June – and his supervisors Magnus Mager and Felix Reidt.

    The ALPIDE chip is a CMOS monolithic active pixel sensor being developed for the upgrade of the ITS of the ALICE experiment and characterized by very high detection efficiency.

    Some spare ALPIDE chips could be diverted to this pedagogical project, in which they are used to detect muons and electrons from cosmic rays. By making a stack of up to four chips, connected one-to-one, it is possible to reconstruct the trajectory of a particle crossing them. Considering an average rate of one cosmic ray per square centimeter per minute, with its active area of 1.4cm x 3cm, the ALPIDE chip registers a hit every few seconds. Because of the acceptance limitation in terms of solid angle due to the setup, the reconstruction rate is around 1 cosmic ray track per minute.

    “The ALPIDE chip is very good for this application since it has very low noise,” explains Magnus. “In addition, it has a multiple-event buffer that allow acquiring new data while we are reading out the previous, so essentially it is dead-time free.”

    2
    In order to target educational and outreach activities, a dedicated, cost-effective, and easy to use readout system was devised. It was decided to interface the chip to an Arduino microprocessor board, which is largely used for being very versatile and easy to program.

    The setup of the compact cosmic ray detector, thus, includes an Arduino card and up to four boards hosting each an ALPIDE chip, one on top of the other. “Programming the Arduino microprocessor to communicate with the chips turned out to be fairly easy,” Magnus comments, “but we still needed an interface to allow people having no specific technical expertise to operate the system.”

    Here is when Matthew came in. His main task, in fact, is to develop a user-friendly interface to control the system, with the aim to make it ‘plug and play’. He is employing the Unity platform, which is free software meant for developing 3D games but can also be used to make interfaces with 3D objects and operation menus. In this specific case, the user will be able to see on the screen the four detector planes, the pixel detectors on them and, when a cosmic ray crosses their active area, the corresponding hit in each plane. The work is still in progress but is moving forward rapidly.

    “When I started, first of all I had to study the Arduino-ALPIDE communication protocol, which meant going through the 110-page ALPIDE manual,” Matthew explains; “during the second week, I interfaced the microprocessor with Unity and then I started developing the user-friendly interface”. Indeed, he was chosen by Magnus and his colleagues among many candidates for his previous experience with the Unity software, which he had gained by developing a 3D game with it.

    A potential future development for the project is to allow data saving in exportable file formats to be read by other programs, so that some data analysis – such as angular distribution of the cosmic rays, day/night dependence and season dependence – could be performed.

    Once the user-friendly interface is done, it will be time to ‘advertise’ the project and make the system available to teachers and students. Some channels to take into consideration are the CERN teacher programmes and the CERN S’Cool Lab. “This device can be useful both for computer science and physics classes,” adds Magnus, “because students can learn about cosmic rays and detectors as well as how to program Arduino to communicate with a custom chip.”

    It can also be used for outreach purposes in some special event, such as the CERN open days.

    Matthew, on his side, is already profiting of this project, since he is enhancing his programming skills and is learning about physics and electronics. At the fourth year of his undergraduate engineering course at the University of Malta, Matthew applied to the CERN summer student programme attracted by the perspective of spending some time at CERN and because he was willing to have an experience outside his country.

    “I think I will continue my studies enrolling in a Master’s and a PhD programme, but I am not sure about the topic yet,” he declares. “Actually, at high-school I studied mainly chemistry and biology, then at the University I switched to engineering. I think I will continue with something that incorporates programming and electronics, such as robotics”.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Meet CERN in a variety of places:


    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS
    ATLAS
    CERN/ATLAS detector

    ALICE
    CERN ALICE New

    CMS
    CERN/CMS Detector

    LHCb

    CERN/LHCb

    LHC

    CERN/LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles


    Quantum Diaries

     
  • richardmitnick 2:18 pm on July 3, 2017 Permalink | Reply
    Tags: A new Fast Interaction Trigger (FIT) system, , ALICE detector upgrades enter production phase, ALICE will be able to further investigate the properties of Quark-Gluon Plasma in pp p-Pb and Pb-Pb collisions, ALPIDE pixel chips will guarantee higher granularity and reduced material budget, CERN ALICE, Introduction of a Muon Forward Tracker (MFT), Replacement of the Inner Traking System (ITS), Run 3 of LHC after the two-year long shut down (LS2) that will start at the end of 2018, Upgrade of the Time Projection Chamber (TPC)   

    From ALICE at the LHC at CERN: “ALICE detector upgrades enter production phase” 

    CERN
    CERN New Masthead

    16 June 2017
    Virginia Greco

    The activities for the upgrade of the ALICE detector and instrumentation proceed on schedule. Validated the prototypes, now the components have to be produced, assembled and tested in order to be ready for installation during the next 2-year long shut down of LHC (2019-2020).

    1
    Scheme of the upgrade of the ALICE detector. [From Zhongbao Yin’s talk at the LHCP2017 Conference]

    While the extended end-of-year shutdown has concluded and the LHC has been switched on again, the activities for the upgrade of the ALICE detector have entered a new phase. The prototypes of the various new components have been tested and validated, so that now production can start.

    This major upgrade will increase the performance of the detector in order to fully exploit the higher interaction rate of about 50 kHz that is expected in Run 3 of LHC, after the two-year long shut down (LS2) that will start at the end of 2018.

    The upgraded ALICE detector will be able to cope with the increased readout rate and will provide better vertex resolution and tracking efficiency at low pT. At the same time, it will preserve its excellent particle identification properties.

    The upgrade programme foresees the replacement of the Inner Traking System (ITS) associated to a new beam pipe with a smaller diameter, the introduction of a Muon Forward Tracker (MFT), the upgrade of the Time Projection Chamber (TPC), and the substitution of the V0 and T0 detectors with a new Fast Interaction Trigger (FIT) system. The readout electronics has also been partially redesigned, together with the Central Trigger Processor (CTP) and the DAQ and Offline Data systems.

    The new ITS will be a 7-layer barrel structure made of carbon fiber and equipped with dedicated silicon pixel sensors (ALPIDE), replacing the previous 6-layer detector that used strip, drift and pixel sensors. Being smaller (approximately 30 um x 30 um), thinner (50 um on the inner barrel and 100 um on the outer) and monolithic (sensor and readout chip are integrated in the same silicon structure), the ALPIDE pixel chips will guarantee higher granularity and reduced material budget. As a result, the track position resolution at the primary vertex will be improved by a factor of 3 with respect to the present detector.

    The ALPIDE chip is employed as well in the Muon Forward Tracker (MFT), which is a new vertex detector for muons; combined with the existing Muon Spectrometer, it will allow precise identification of secondary vertices and better mass resolution. Composed of 5 disks of silicon pixel detectors, it will be placed between the central barrel detector and the hadron absorber of the Muon Spectrometer.

    The upgrade of the TPC involves replacing the multi-wire chambers, which limit the event readout rate to 3.5 kHz, with quadruple-GEM chambers designed to minimize ion back-flow and to allow continuous, untriggered readout. New front-end electronics will be also needed. The new TPC will be able to operate at 50 kHz preserving its current performance in terms of tracking, momentum resolution and particle identification.

    The FIT will be dedicated to forward trigger and to the measurement of a number of parameters, including luminosity, collision time, as well as multiplicity and centrality of heavy ion collisions. This new detector, which will replace the existing V0 and T0, will consist of two arrays of Cherenkov radiators, equipped with micro-channel plate detectors and photomultipliers, and of a single, large-size scintillator ring. The FIT will provide larger acceptance and finer segmentation than the present two, without compromising the time resolution.

    As a consequence of the increased luminosity and interaction rate of LHC, a significantly larger amount of data will have to be processed and selected. Thus, a new Central Trigger Processor and a powerful data processing system integrating some online and offline functionalities have been designed as well.

    With this upgraded detector and instrumentation, ALICE will be able to further investigate the properties of Quark-Gluon Plasma in pp, p-Pb and Pb-Pb collisions. In particular, the goal for next runs is to perform high-precision measurements that will shed light on thermodynamics, evolution and flow of the QGP, as well as on parton interactions with the medium.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Meet CERN in a variety of places:

    CernCourier
    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS
    ATLAS
    CERN/ATLAS detector

    ALICE
    CERN ALICE New

    CMS
    CERN/CMS Detector

    LHCb

    CERN/LHCb

    LHC

    CERN/LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles


    Quantum Diaries

     
  • richardmitnick 2:18 pm on June 18, 2017 Permalink | Reply
    Tags: , , CERN ALICE, First collisions of 2017 in ALICE: ready to go, , , ,   

    From ALICE: “First collisions of 2017 in ALICE: ready to go” 

    CERN
    CERN New Masthead

    16 June 2017
    Virginia Greco

    1
    No image caption or credit

    After the long winter shut-down, on May 23 the first proton-proton collisions with stable beams of 2017 were delivered by LHC and detected by the four experiments. The ALICE detector was fully operative and took great snapshots of these collisions (as the event display in the picture).

    The accelerator is now in the intensity ramp-up phase: it started injecting only few bunches and is gradually increasing the number in subsequent fills. It is expected to reach the nominal working conditions towards the beginning of July.

    In reality, the very first collisions were delivered a week before the official date, but they were not in optimal conditions, since the beams were not stable. During this phase, which is called ‘quiet beam’, the experts of LHC perform tests and make adjustments to the various components of the accelerator.

    ALICE used the quiet beam collisions to perform some performance tests, in particular on the forward detectors (AD, V0) and the Electro-Magnetic Calorimeter (EMCAL), but only a minor part of the whole apparatus was switched on. This is because the quiet beam is not totally safe for the instrumentation: when the experts of LHC change the settings of the machine and make adjustments, there is the risk of beam losses hitting directly the detectors, and thus damaging them. In particular, the parts that need to stay off are those closest to the beam line, such as parts of the inner tracking system and the gas detectors.

    When collisions with stable beams were delivered, ALICE started its data-taking programme. The LHC ramp-up plan started with three circulating bunches per beam, and moved on to about 12, 75, 300, 600.

    Even if at the beginning the collision rate was very low, a number of operations could be performed, such as a trigger alignment scan for the pixel detector and a high-voltage scan for the V0 and AD sub-detectors to find the optimal work voltage.

    In order to have precise information on the alignment of the central barrel detectors, data were taken with different polarities of the dipole and the solenoid (specifically, minus-minus, plus-plus and no magnetic fields). This information will be used to reconstruct the data that will be collected along the whole year.

    Following the requirements of some physics group, run of data taking at low rate – with the whole detector on – were also performed, as well as at high interaction rate (150kHz, the nominal one) with the Time Projection Chamber (TPC). This was particularly important, since during the shut-down the gas mixture filling the TPC was changed from Ar-CO2 to Ne- CO2-N2. In this test, the detector showed high performance, as expected.

    Finally, during the 300-bunches fill ALICE took data with a reduced (halved) magnetic field of the solenoid, since these conditions are recommended to study the low mass di-muon spectrum.

    “The restart has been great,” comments Grazia Luparello, run coordinator of ALICE, “in just a few fills of the accelerator we managed to perform all the tests and the special data taking included in our programme; we are satisfied and ready to go for physics”.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Meet CERN in a variety of places:

    CernCourier
    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS
    ATLAS
    CERN/ATLAS detector

    ALICE
    CERN ALICE New

    CMS
    CERN/CMS Detector

    LHCb

    CERN/LHCb

    LHC

    CERN/LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles


    Quantum Diaries

     
  • richardmitnick 1:10 pm on May 19, 2017 Permalink | Reply
    Tags: , CERN ALICE, , Installing new equipment in preparation for the LHC Run 3 upgrade., ,   

    From ALICE: “Installing new equipment in preparation for the LHC Run 3 upgrade.” 

    CERN
    CERN New Masthead

    Installing new equipment in preparation for the LHC Run 3 upgrade.

    1

    The big cube on the back (the one with the door at the corner carrying the “blue man” sticker) is the clean room where ALICE detectors are assembled in dust-free environment. All the material that enters in that room has to be cleaned beforehand and people going inside it must wear protective clothing (to avoid bringing dust into the room).

    The boxes in front of the room, including the Air Conditioning unit that was installed yesterday, provide the services that are needed in the Clean Room.

    For reference, the AC unit is up to ISO 8 standard (https://www.mssl.ucl.ac.uk/…/clean…/cr_standards.html…).

    The Clean Room will be used to assemble the new Time Projection Chamber (TPC) which will be installed inside the L3 magnet during Long Shutdown 2 (mid 2018 – end 2019).

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Meet CERN in a variety of places:

    CernCourier
    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS
    ATLAS
    CERN/ATLAS detector

    ALICE
    CERN ALICE New

    CMS
    CERN/CMS Detector

    LHCb

    CERN/LHCb

    LHC

    CERN/LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles


    Quantum Diaries

     
  • richardmitnick 2:25 pm on April 24, 2017 Permalink | Reply
    Tags: , CERN ALICE, , , ,   

    From Symmetry: “A tiny droplet of the early universe?” 

    Symmetry Mag

    Symmetry

    04/24/17
    Sarah Charley

    Particles seen by the ALICE experiment hint at the formation of quark-gluon plasma during proton-proton collisions. [ALREADY COVERED WITH AN ARTICLE FROM CERN HERE.]

    1
    Mona Schweizer, CERN

    About 13.8 billion years ago, the universe was a hot, thick soup of quarks and gluons—the fundamental components that eventually combined into protons, neutrons and other hadrons.

    Scientists can produce this primitive particle soup, called the quark-gluon plasma, in collisions between heavy ions. But for the first time physicists on an experiment at the Large Hadron Collider have observed particle evidence of its creation in collisions between protons as well.

    The LHC collides protons during the majority of its run time. This new result, published in Nature Physics by the ALICE collaboration, challenges long-held notions about the nature of those proton-proton collisions and about possible phenomena that were previously missed.

    “Many people think that protons are too light to produce this extremely hot and dense plasma,” says Livio Bianchi, a postdoc at the University of Houston who worked on this analysis. “But these new results are making us question this assumption.”

    Scientists at the LHC and at the US Department of Energy’s Brookhaven National Laboratory’s Relativistic Heavy Ion Collider, or RHIC, have previously created quark-gluon plasma in gold-gold and lead-lead collisions.

    BNL RHIC Campus

    BNL/RHIC Star

    BNL RHIC PHENIX

    CERN/LHC Map

    CERN LHC Tunnel


    CERN LHC

    In the quark gluon plasma, mid-sized quarks—such as strange quarks—freely roam and eventually bond into bigger, composite particles (similar to the way quartz crystals grow within molten granite rocks as they slowly cool). These hadrons are ejected as the plasma fizzles out and serve as a telltale signature of their soupy origin. ALICE researchers noticed numerous proton-proton collisions emitting strange hadrons at an elevated rate.

    “In proton collisions that produced many particles, we saw more hadrons containing strange quarks than predicted,” says Rene Bellwied, a professor at the University of Houston. “And interestingly, we saw an even bigger gap between the predicted number and our experimental results when we examined particles containing two or three strange quarks.”

    From a theoretical perspective, a proliferation of strange hadrons is not enough to definitively confirm the existence of quark-gluon plasma. Rather, it could be the result of some other unknown processes occurring at the subatomic scale.

    “This measurement is of great interest to quark-gluon-plasma researchers who wonder how a possible QGP signature can arise in proton-proton collisions,” says Urs Wiedemann, a theorist at CERN. “But it is also of great interest for high energy physicists who have never encountered such a phenomenon in proton-proton collisions.”

    Earlier research at the LHC found that the spatial orientation of particles produced during some proton-proton collisions mirrored the patterns created during heavy-ion collisions, suggesting that maybe these two types of collisions have more in common than originally predicted. Scientists working on the ALICE experiment will need to explore multiple characteristics of these strange proton-proton collisions before they can confirm if they are really seeing a miniscule droplet of the early universe.

    “Quark-gluon plasma is a liquid, so we also need to look at the hydrodynamic features,” Bianchi says. “The composition of the escaping particles is not enough on its own.”

    This finding comes from data collected the first run of the LHC between 2009 and 2013. More research over the next few years will help scientists determine whether the LHC can really make quark-gluon plasma in proton-proton collisions.

    “We are very excited about this discovery,” says Federico Antinori, spokesperson of the ALICE collaboration. “We are again learning a lot about this extreme state of matter. Being able to isolate the quark-gluon-plasma-like phenomena in a smaller and simpler system, such as the collision between two protons, opens up an entirely new dimension for the study of the properties of the primordial state that our universe emerged from.”

    Other experiments, such as those using RHIC, will provide more information about the observable traits and experimental characteristics of quark-gluon plasmas at lower energies, enabling researchers to gain a more complete picture of the characteristics of this primordial particle soup.

    “The field makes far more progress by sharing techniques and comparing results than we would be able to with one facility alone,” says James Dunlop, a researcher at RHIC. “We look forward to seeing further discoveries from our colleagues in ALICE.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 1:25 pm on April 24, 2017 Permalink | Reply
    Tags: , CERN ALICE, , New ALICE results show novel phenomena in proton collisions, , , , Strange quark   

    From ALICE at CERN: “New ALICE results show novel phenomena in proton collisions” 

    CERN
    CERN New Masthead

    CERN ALICE Icon HUGE

    24 Apr 2017.
    Harriet Kim Jarlett

    1
    As the number of particles produced in proton collisions (the blue lines) increase, the more of these so-called strange hadrons are measured (as shown by the orange to red squares in the graph) (Image: ALICE/CERN)

    In a paper published today in Nature Physics , the ALICE collaboration reports that proton collisions sometimes present similar patterns to those observed in the collisions of heavy nuclei. This behaviour was spotted through observation of so-called strange hadrons in certain proton collisions in which a large number of particles are created. Strange hadrons are well-known particles with names such as Kaon, Lambda, Xi and Omega, all containing at least one so-called strange quark. The observed ‘enhanced production of strange particles’ is a familiar feature of quark-gluon plasma, a very hot and dense state of matter that existed just a few millionths of a second after the Big Bang, and is commonly created in collisions of heavy nuclei. But it is the first time ever that such a phenomenon is unambiguously observed in the rare proton collisions in which many particles are created. This result is likely to challenge existing theoretical models that do not predict an increase of strange particles in these events.

    “We are very excited about this discovery,” said Federico Antinori, Spokesperson of the ALICE collaboration. “We are again learning a lot about this primordial state of matter. Being able to isolate the quark-gluon-plasma-like phenomena in a smaller and simpler system, such as the collision between two protons, opens up an entirely new dimension for the study of the properties of the fundamental state that our universe emerged from.”

    The study of the quark-gluon plasma provides a way to investigate the properties of strong interaction, one of the four known fundamental forces, while enhanced strangeness production is a manifestation of this state of matter. The quark-gluon plasma is produced at sufficiently high temperature and energy density, when ordinary matter undergoes a transition to a phase in which quarks and gluons become ‘free’ and are thus no longer confined within hadrons. These conditions can be obtained at the Large Hadron Collider by colliding heavy nuclei at high energy. Strange quarks are heavier than the quarks composing normal matter, and typically harder to produce. But this changes in presence of the high energy density of the quark-gluon plasma, which rebalances the creation of strange quarks relative to non-strange ones. This phenomenon may now have been observed within proton collisions as well.

    In particular, the new results show that the production rate of these strange hadrons increases with the ‘multiplicity’ – the number of particles produced in a given collision – faster than that of other particles generated in the same collision. While the structure of the proton does not include strange quarks, data also show that the higher the number of strange quarks contained in the induced hadron, the stronger is the increase of its production rate. No dependence on the collision energy or the mass of the generated particles is observed, demonstrating that the observed phenomenon is related to the strange quark content of the particles produced. Strangeness production is in practice determined by counting the number of strange particles produced in a given collision, and calculating the ratio of strange to non-strange particles.

    Enhanced strangeness production had been suggested as a possible consequence of quark-gluon plasma formation since the early eighties, and discovered in collisions of nuclei in the nineties by experiments at CERN’s Super Proton Synchrotron.

    CERN Super Proton Synchrotron

    Another possible consequence of the quark gluon plasma formation is a spatial correlation of the final state particles, causing a distinct preferential alignment with the shape of a ridge. Following its detection in heavy-nuclei collisions, the ridge has also been seen in high-multiplicity proton collisions at the Large Hadron Collider, giving the first indication that proton collisions could present heavy-nuclei-like properties. Studying these processes more precisely will be key to better understand the microscopic mechanisms of the quark-gluon plasma and the collective behaviour of particles in small systems.

    The ALICE experiment has been designed to study collisions of heavy nuclei. It also studies proton-proton collisions, which primarily provide reference data for the heavy-nuclei collisions. The reported measurements have been performed with 7 TeV proton collision data from LHC run 1.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Meet CERN in a variety of places:

    CernCourier
    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS
    ATLAS
    CERN/ATLAS detector

    ALICE
    CERN ALICE New

    CMS
    CERN/CMS Detector

    LHCb

    CERN/LHCb

    LHC

    CERN/LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles


    Quantum Diaries

     
  • richardmitnick 2:30 pm on February 14, 2017 Permalink | Reply
    Tags: , , CERN ALICE, ,   

    From CERN ALICE: “QGP: 17 years after the public announcement…” 

    CERN
    CERN New Masthead

    CERN ALICE Icon HUGE

    31 January 2017
    Virginia Greco

    Interview with Luciano Maiani, DG of CERN from 1999 to 2003, who gave the announcement talk of the discovery of QGP at the SPS.

    CERN  Super Proton Synchrotron
    CERN Super Proton Synchrotron

    3
    About 25 years after its first theoretical prediction, the new state of matter called quark-gluon plasma (QGP) was observed at CERN’s SPS. The public announcement was made on the 10th of February 2000 by Luciano Maiani, Director General of CERN back then. At the event organized by ALICE to celebrate the 30-year anniversary of the first heavy-ion collisions at the SPS, Maiani gave his account of this piece of history of physics.

    We had an interview with him after the seminar.

    After one year of mandate as DG of CERN you had the honour and the responsibility to announce that evidence of the existence of QGP had been found at the SPS. How did you live these happenings?

    At that time I was not an expert in heavy ion physics, because I hadn’t worked in the field. Nevertheless, I was aware of the phase transition issue and of the two existing visions about what happens to nuclear matter at very high temperature. On one side there was the theory that matter would break down into a gas of quarks and gluons (and temperature could be freely increased), on the other side the model of Hagedorn about the existence of an upper limit of the temperature reachable, which could be estimated from the hadron spectrum to be 170-180 MeV.

    With the development of QCD it was possible to combine these two models. In particular, in 1975 Nicola Cabibbo and Giorgio Parisi suggested that the Hagedorn limit temperature is just the critical temperature of a phase transition from a gas of hadrons, made of confined quarks, to a gas of deconfined quarks and gluons (the QGP). These works had convinced the experts in the field.

    When the moment came to decide whether to make a public announcement about what the SPS had found, I discussed with many of the people involved, such as Claude Detraz, who was Director for Fixed Target and Future Programmes during my mandate, Reinhard Stock and Hans Specht. After examining the data and collecting opinions, I concluded that we had convincing signals that what we were observing was indeed the quark-gluon plasma.

    But the public announcement was cautious, wasn’t it? Was there still some doubt?

    I think that the announcement was quite clear. I have the text of it with me, it reads: “The data provide evidence for colour deconfinement in the early collision stage and for a collective explosion of the collision fireball in its late stages. The new state of matter exhibits many of the characteristic features of the theoretically predicted Quark-Gluon Plasma.” The key word is “evidence”, not discovery, and the evidence was there, indeed.

    In the talk I gave at that time I also described the concept of quark deconfinement using an analogy with the snow on the Jura Mountain, which I particularly like. We can consider a quark as a skier: when the temperature is not very low, on the mountain there are only patches of snow in which the skier can move. When the temperature decreases and the snow increases, the skier can move along bigger and bigger spaces, up to a point where he or she can freely sweep long distances. The same can be said for a quark confined in a hadron (the patch), which becomes free when temperature increases.

    Of course at that moment the idea still popular was that we were dealing with a phase transition to a gaseous state in which quarks and gluons would be asymptotically free. Later RHIC showed that the situation is more complicated and that this new state is much more like a liquid with very low viscosity rather than like a gas.

    The announcement came just a few months before the start of the programme of RHIC. Were there some polemics about this “timing”?

    3
    The Solenoidal Tracker at the Relativistic Heavy Ion Collider (RHIC)

    We were almost at the conclusion of a long and accurate experimental programme at the SPS, so making a summing up was needed. In addition, as I said, we thought there were the elements for a public announcement. And this has been proved right by later experiments.

    Somebody thought that it would make RHIC, which was going to enter in operation, appear useless. But that was not the case, since much more was left to study. Indeed in the same announcement talk I said: “the higher energies of RHIC and LHC are needed to complete the picture and provide a full characterization of the Quark-Gluon Plasma”.

    In your opinion, what is the future of this branch of research?

    Well, there are still many open problems, things that need to be studied further.

    It is very important to explore the properties of this new state of matter and the connected phenomena, to get a more precise physical picture of the new state.

    Personally, I think that there is also another possible line of research in this field: to study the production of those exotic hadronic resonances that are not included in the scheme of baryons and mesons (i.e. three quarks or quark-antiquark structures). These resonances have been observed in CMS and LHCb in pp collisions, and it would be interesting to study how they are produced in heavy-ion collisions. It could give us indications about what these objects are, tell us if they are molecules made of colourless hadrons or new states which are configurations of quarks and antiquarks (different from mesons) that include subcomponents connected by colour bounds.

    ALICE could provide an important contribution to this research. It is not easy to observe such exotic states in heavy-ion collisions but I think it is worth trying.

    4
    No image caption. No image credit.

    An iconic view of the universe
    Inflationary Universe. NASA/WMAP
    Inflationary Universe. NASA/WMAP

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Meet CERN in a variety of places:

    CernCourier
    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS
    ATLAS
    CERN/ATLAS detector

    ALICE
    CERN ALICE New

    CMS
    CERN/CMS Detector

    LHCb

    CERN/LHCb

    LHC

    CERN/LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles


    Quantum Diaries

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
%d bloggers like this: