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  • richardmitnick 11:59 am on March 22, 2017 Permalink | Reply
    Tags: , , CERN ATLAS, , , Quest for the lost arc   

    From ATLAS: “Quest for the lost arc” 

    CERN ATLAS Higgs Event

    CERN/ATLAS
    ATLAS

    21st March 2017
    ATLAS Collaboration

    1
    Figure 1: ATLAS simulation showing a hypothetical new charged particle (χ1+) traversing the four layers of the pixel system and decaying to an invisible neutral particle (χ10) and an un-detected pion (π+). The red squares represent the particle interactions with the detector. (Image: ATLAS Collaboration/CERN)

    Nature has surprised physicists many times in history and certainly will do so again. Therefore, physicists have to keep an open mind when searching for phenomena beyond the Standard Model.

    ..
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    Some theories predict the existence of new particles that live for a very short time. These particles would decay to known particles that interact with the sophisticated “eyes” of the ATLAS detector. However, this may not be the case. An increasingly popular alternative is that some of these new particles may have masses very close to each other, and would thus travel some distance before decaying. This allows for the intriguing possibility of directly observing a new type of particle with the ATLAS experiment, rather than reconstructing it via its decay products as physicists do for example for the Higgs boson.

    2
    Figure 2: The number of reconstructed short tracks (tracklets) as a function of their transverse momentum (pT). ATLAS data (black points) are compared with the expected contribution from background sources (gray solid line shows the total) . A new particle would appear as an additional contribution at large pT, as shown for example by the dashed red line. The bottom panel shows the ratio of the data and the background predictions. The error band shows the uncertainty of the background expectation including both statistical and systematic uncertainties. (Image: ATLAS Collaboration/CERN)

    An attractive scenario predicts the existence of a new electrically charged particle, a chargino (χ1±), that may live long enough to travel a few tens of centimetres before decaying to an invisible neutral weakly interacting particle, a neutralino (χ10). A charged pion would also be produced in the decay but, due to the very similar mass of the chargino and the neutralino, its energy would not be enough for it to be detected. As shown in Figure 1, simulations predict a quite spectacular signature of a charged particle “disappearing” due to the undetected decay products.

    ATLAS physicists have developed dedicated algorithms to directly observe charged particles travelling as little as 12 centimetres from their origin. Thanks to the new Insertable B-Layer, these algorithms show improved performance reconstructing such charged particles that do not live long enough to interact with other ATLAS detector systems. So far, the abundance and properties of the observed particles are in agreement with what is expected from known background processes.

    New results presented at the Moriond Electroweak conference set very stringent limits on what mass such particles may have, if they exist. These limits severely constrain one important type of Supersymmetry dark matter. Although no new particle has been observed, ATLAS physicists continue the search for this “lost arc”. Stay tuned!

    See the full article here .

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

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  • richardmitnick 1:08 pm on March 21, 2017 Permalink | Reply
    Tags: 30 million collision events, , CERN ATLAS, , ,   

    From ATLAS: “Particle-hunting at the energy frontier” 

    CERN ATLAS Higgs Event

    CERN/ATLAS
    ATLAS

    20th March 2017
    ATLAS Collaboration

    1
    Fig. 1: The highest-mass dijet event measured by ATLAS (mass = 8.12TeV). Green lines indicate tracks of charged particles. Green and yellow blocks show the energy of the two back-to-back jets deposited in the calorimeters. (Image: ATLAS Collaboration/CERN)

    There are many mysteries the Standard Model of particle physics cannot answer. Why is there an imbalance between matter and anti-matter in our Universe? What is the nature of dark matter or dark energy? And many more. The existence of physics beyond the Standard Model can solve some of these fundamental questions. By studying the head-on collisions of protons at a centre-of-mass energy of 13 TeV provided by the LHC, the ATLAS Collaboration is on the hunt for signs of new physics.

    2
    Fig. 2: Dijet resonance search results. (Image: ATLAS Collaboration/CERN)

    A newly released ATLAS search studies approximately 30 million collision events that produce two high-energy sprays of particles in the final state. These sprays are known as “jets” or, when seen in pairs as in this case, “dijets” (Figure 1). Jets with extraordinarily high energies – copiously produced due to the strong interactions of quarks and gluons – probe the highest energy scales of all processes at the LHC. These jets can provide a window into new physics phenomena, and allow ATLAS physicists to search for mediators between Standard Model and dark matter particles or other hypothetical objects such as non-elementary quarks, heavy “partners” of known Standard Model particles or miniature quantum black-holes (a phenomenon of strong gravity predicted in models with additional spatial dimensions). They can even be used to search for very heavy particles with masses beyond the LHC collision energies, through models known as contact interactions (similar to the Fermi model for weak interactions).

    The dijet search described here consists of two complementary analyses: the resonance analysis and the angular analysis. The resonance analysis looks for a localized excess in the dijet mass spectrum. In the absence of a heavy resonance, the mass distribution is well described by a smooth, monotonically falling function. A statistically significant bump would signify a new particle with mass near the measured bump. The histogram in Figure 2 displays the results of the resonance analysis. The x-axis represents the dijet mass (mjj) and the y-axis (shown with a logarithmic scale) represents the number of observed events. The solid black dots show the data, the red curve represents the fit of a smooth function to the data, and the open green dots show how two non-elementary (“excited”) quark signals might look like. The second panel shows how significant the deviations in the data are as compared to the smooth background fit. The vertical blue lines show the region with the largest significance. A statistical analysis results in a probablility value of 0.63 which means that there is no significant deviation from the Standard Model. The third panel compares the data to the dijet mass prediction; again, no significant deviation from the Standard Model expectation is seen.

    See the full article here .

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

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  • richardmitnick 8:51 pm on March 10, 2017 Permalink | Reply
    Tags: , , CERN ATLAS, , , , , , , The strong force (strong interaction)   

    From Symmetry: “A strength test for the strong force [strong interaction]” 

    Symmetry Mag

    Symmetry

    03/10/17
    Sarah Charley

    1
    Science Saturday

    New research could tell us about particle interactions in the early universe and even hint at new physics.

    Much of the matter in the universe is made up of tiny particles called quarks. Normally it’s impossible to see a quark on its own because they are always bound tightly together in groups. Quarks only separate in extreme conditions, such as immediately after the Big Bang or in the center of stars or during high-energy particle collisions generated in particle colliders.

    Scientists at Louisiana Tech University are working on a study of quarks and the force that binds them by analyzing data from the ATLAS experiment at the LHC. Their measurements could tell us more about the conditions of the early universe and could even hint at new, undiscovered principles of physics.


    ATLAS at the LHC

    The particles that stick quarks together are aptly named “gluons.” Gluons carry the strong force, one of four fundamental forces in the universe that govern how particles interact and behave. The strong force binds quarks into particles such as protons, neutrons and atomic nuclei.

    As its name suggests, the strong force [strong interaction] is the strongest—it’s 100 times stronger than the electromagnetic force (which binds electrons into atoms), 10,000 times stronger than the weak force (which governs radioactive decay), and a hundred million million million million million million (1039) times stronger than gravity (which attracts you to the Earth and the Earth to the sun).

    But this ratio shifts when the particles are pumped full of energy. Just as real glue loses its stickiness when overheated, the strong force carried by gluons becomes weaker at higher energies.

    “Particles play by an evolving set of rules,” says Markus Wobisch from Louisiana Tech University. “The strength of the forces and their influence within the subatomic world changes as the particles’ energies increase. This is a fundamental parameter in our understanding of matter, yet has not been fully investigated by scientists at high energies.”

    Characterizing the cohesiveness of the strong force is one of the key ingredients to understanding the formation of particles after the Big Bang and could even provide hints of new physics, such as hidden extra dimensions.

    “Extra dimensions could help explain why the fundamental forces vary dramatically in strength,” says Lee Sawyer, a professor at Louisiana Tech University. “For instance, some of the fundamental forces could only appear weak because they live in hidden extra dimensions and we can’t measure their full strength. If the strong force is weaker or stronger than expected at high energies, this tells us that there’s something missing from our basic model of the universe.”

    By studying the high-energy collisions produced by the LHC, the research team at Louisiana Tech University is characterizing how the strong force pulls energetic quarks into encumbered particles. The challenge they face is that quarks are rambunctious and caper around inside the particle detectors. This subatomic soirée involves hundreds of particles, often arising from about 20 proton-proton collisions happening simultaneously. It leaves a messy signal, which scientists must then reconstruct and categorize.

    Wobisch and his colleagues innovated a new method to study these rowdy groups of quarks called jets. By measuring the angles and orientations of the jets, he and his colleagues are learning important new information about what transpired during the collisions—more than what they can deduce by simple counting the jets.

    The average number of jets produced by proton-proton collisions directly corresponds to the strength of the strong force in the LHC’s energetic environment.

    “If the strong force is stronger than predicted, then we should see an increase in the number of proton-protons collisions that generate three jets. But if the strong force is actually weaker than predicted, then we’d expect to see relatively more collisions that produce only two jets. The ratio between these two possible outcomes is the key to understanding the strong force.”

    After turning on the LHC, scientists doubled their energy reach and have now determined the strength of the strong force up to 1.5 trillion electronvolts, which is roughly the average energy of every particle in the universe just after the Big Bang. Wobisch and his team are hoping to double this number again with more data.

    “So far, all our measurements confirm our predictions,” Wobisch says. “More data will help us look at the strong force at even higher energies, giving us a glimpse as to how the first particles formed and the microscopic structure of space-time.”

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 10:04 am on March 10, 2017 Permalink | Reply
    Tags: , , , , CERN ATLAS, , , , , , Xiaofeng Guo   

    From Brookhaven: Women in STEM – “Secrets to Scientific Success: Planning and Coordination” Xiaofeng Guo 

    Brookhaven Lab

    March 8, 2017
    Lida Tunesi

    1
    Xiaofeng Guo

    Very often there are people behind the scenes of scientific advances, quietly organizing the project’s logistics. New facilities and big collaborations require people to create schedules, manage resources, and communicate among teams. The U.S. Department of Energy’s Brookhaven National Laboratory is lucky to have Xiaofeng Guo in its ranks—a skilled project manager who coordinates projects reaching across the U.S. and around the world.

    Guo, who has a Ph.D. in theoretical physics from Iowa State University, is currently deputy manager for the U.S. role in two upgrades to the ATLAS detector, one of two detectors at CERN’s Large Hadron Collider that found the Higgs boson in 2012.


    CERN ATLAS Higgs Event


    CERN/ATLAS detector

    Brookhaven is the host laboratory for both U.S. ATLAS Phase I and High Luminosity LHC (HL-LHC) upgrade projects, which involve hundreds of millions of dollars and 46 institutions across the nation. The upgrades are complex international endeavors that will allow the detector to make use of the LHC’s ramped up particle collision rates. Guo keeps both the capital and the teams on track.

    “I’m in charge of all business processes, project finance, contracts with institutions, baseline plan reports, progress reports—all aspects of business functions in the U.S. project team. It keeps me very busy,” she laughed. “In the beginning I was thinking ‘in my spare time I can still read physics papers, do my own calculations’… And now I have no spare time!”

    Guo’s dual interest in physics and management developed early in her career.

    “When I was an undergraduate there was a period when I actually signed up for a double major, with classes in finance and economics in addition to physics,” Guo recalled. “I’m happy to explore different things!”

    Later, while teaching physics part-time at Iowa State University, Guo desired career flexibility and studied to be a Chartered Financial Analyst. She passed all required exams in just two years but decided to continue her research after receiving a grant from the National Science Foundation.

    Guo joined Brookhaven Lab in 2010 to fill a need for project management in Nuclear and Particle Physics (NPP). The position offered her a way to learn new skills while staying up-to-date on the physics world.

    Early in her time at Brookhaven, Guo participated in the management of the Heavy Flavor Tracker (HFT) upgrade to the STAR particle detector at the Relativistic Heavy Ion Collider (RHIC), a DOE Office of Science User Facility for nuclear physics research. The project was successfully completed $600,000 under budget and a whole year ahead of schedule.


    BNL/RHIC Star Detector

    “This was a very good learning experience for me. I participated in all the manager meeting discussions, updated the review documents, and helped them handle some contracts. Through this process I learned all the DOE project rules,” Guo said.

    While working on the HFT upgrade, Guo also helped develop successful, large group proposals for increased computational resources in high-energy physics and other fields of science. She joined the ATLAS Upgrade projects after receiving her Project Management Certification, and her physics and finance background as well as experience with large collaborations have enabled her to orchestrate complex planning efforts.

    For the two phases of the U.S. ATLAS upgrade, Guo directly coordinates more than 140 scientists, engineers, and finance personnel, and oversees all business processes, including finance, contracts, and reports. And taking her job one step further, she’s developed entirely new management tools and reporting procedures to keep the multi-institutional effort synchronized.

    “Dr. Guo is one of our brightest stars,” said Berndt Mueller, Associate Lab Director of NPP. “We are fortunate to have her to assist us with many challenging aspects of project development and execution in NPP. In the process of guiding the work of scores of scientists and engineers, she has single-handedly created a unique and essential role in the development of complex projects with an international context, demonstrating skills of unusual depth and breadth and the ability to apply them across a wide array of disciplines.”

    Guo’s management of Phase I won great respect for the project from the high-energy physics community and the Office of Project Assessment (OPA) at the DOE’s Office of Science. The OPA invited her to participate in a panel discussion to share her expertise and help develop project management guidelines that can be used in other Office of Science projects. Guo also worked with BNL’s Project Management Center to help the lab update its own project management system description to meet DOE standards and lay down valuable groundwork for future large projects.

    As the ATLAS Phase I upgrade proceeds through the final construction stage, Guo is simultaneously managing the planning stages of HL-LHC.

    “We haven’t completely defined the project timeline yet, but it’s projected to go all the way to the end of 2025,” Guo said.

    Like Phase I, HL-LHC will ensure ATLAS can perform well while the LHC operates at much higher collision rates so that physicists can further explore the Higgs as well as search for signs of dark matter and extra dimensions.

    Although she admits to missing doing research herself, Guo is not disheartened.

    “I’m still in the physics world; I’m still working with physicists,” she said. “I enjoy working and interacting with people. So I’m happy.”

    Brookhaven’s work on RHIC and ATLAS is funded by the DOE Office of Science.

    See the full article here .

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    BNL Campus

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
    i1

     
  • richardmitnick 3:56 pm on February 17, 2017 Permalink | Reply
    Tags: , Bjorken x variable, CERN ATLAS, , HERA collider, How strange is the proton?, , , , , , Strong interactions   

    From CERN ATLAS: “How strange is the proton?” 

    CERN ATLAS Higgs Event

    CERN/ATLAS
    ATLAS

    25th January 2017
    ATLAS Collaboration

    1
    Figure 1: The data ellipses illustrate the 68% CL coverage for the total uncertainties (full green) and total excluding the luminosity uncertainty (open black). Theoretical predictions based on various PDF sets are shown with open symbols of different colours. (Image: ATLAS Collaboration/CERN)

    The protons collided by the LHC are not elementary particles, but are instead made up of quarks, antiquarks and gluons. The theory of the strong interactions – quantum chromodynamics (QCD) – does not allow physicists to calculate the composition of protons from first principles. However, QCD can connect measurements made in different processes and at different energy scales such that universal “parton density functions” (PDFs) can be extracted. These determine the dynamic substructure of the proton.

    The discovery of quarks as the elements of the partonic structure of the proton dates about 50 years. Soon after QCD was born and the existence of gluons inside the proton was established. Much has since been learned through a combination of new experimental data and theoretical advances. At the LHC, reactions involve quarks or gluons that carry a certain fraction x of the proton’s momentum, expressed through the Bjorken x variable. Below x of 0.01, the proton constituents are mainly gluons and a sea of quark-antiquark pairs.

    Electron-proton scattering data from the HERA collider has constrained the gluon and the sum of all quarks weighted by the square of their electric charge.

    3
    Data from the HERA collider live on (Image: DESY Hamburg)

    4
    DESY map

    But the low x sea-quark composition – expressed in terms of the lighter quarks named up, down and strange quarks – is still not well understood. New data from the ATLAS experiment shows, with unprecedented precision, the production of W and Z bosons through the weak interaction. This sheds new light on the question: how “strange” the proton is at small x?

    The W production is detected through its decay into a charged lepton (electron or muon) and a neutrino, while the Z boson produces an electron-positron (or muon-antimuon) pair. The experimental detection of electrons and muons poses different challenges and thus the simultaneous measurement in both channels provides an important cross-check of the results, thus improving the final precision achieved. The integrated cross sections for Z boson and W boson production are measured with a precision of 0.3% and 0.6%, respectively, and with an additional common normalisation uncertainty from the luminosity determination of 1.8%. Differential cross sections are also measured in a variety of kinematic regions and about half of the measurement points have a precision of 1% or better.

    2
    Figure 2: Determination of the relative strange-to-light quark fraction R_s. Bands: Present result and its uncertainty contributions from experimental data, QCD fit, and theoretical uncertainties. Closed symbols with horizontal error bars: predictions from different NNLO PDF sets. Open square: previous ATLAS result. (Image: ATLAS Collaboration/CERN)

    The measurements are then compared to state-of-the-art QCD expectations using different PDF sets. Because the production of W and Z bosons through the weak interaction has a different dependence on the specific quark flavours compared to the electromagnetic interaction seen in electron-positron scattering at HERA, analysing both data sets gives new access to the strange quark content of the proton.

    As is shown in Figure 1, the measured production rate of W bosons is very similar for all PDF sets, in good agreement with the data. In contrast, the rate for Z boson production is underestimated significantly for most PDF sets. A dedicated analysis enables this deficit to be attributed to a too small strange quark contribution in most PDF sets. The new PDF set, which this paper presents, requires the strange quark sea to be of a similar size as the up and down quark sea. This is summarised by the quantity RS, which is the ratio of the strange quark sea to the up and down quark sea, and which is found to be close to one, as shown in Figure 2. This result is a striking confirmation of the hypothesis of a light-flavour symmetry of proton structure at low x. This result will generate many further studies, because hitherto there had been indications from low energy neutrino-scattering data that favoured a suppressed strange-quark contribution with respect to the up and down quark parts, leading to an RS close to 0.5.

    The analysis also shows that the potential to which precise W and Z cross sections can provide useful constraints on PDFs is not limited by the now very high experimental precision, but rather by the uncertainty of the currently available theory calculations. The salient results of this paper are thus of fundamental importance for forthcoming high-precision measurements, such as the mass of the W boson, and also represent a strong incentive for further improving the theory of Drell-Yan scattering in proton-proton collisions.

    Links:

    Precision measurement and interpretation of inclusive W+, W− and Z/γ∗ production cross sections with the ATLAS detector, https://arxiv.org/abs/1612.03016

    See the full article here .

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

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  • richardmitnick 2:30 pm on January 25, 2017 Permalink | Reply
    Tags: , CERN ATLAS, HERA at DESY, Parton density functions (PDFs), ,   

    From CERN ATLAS: “How strange is the proton?” 

    CERN ATLAS Higgs Event

    CERN/ATLAS
    ATLAS

    25th January 2017
    ATLAS Collaboration

    1
    Figure 1: The data ellipses illustrate the 68% CL coverage for the total uncertainties (full green) and total excluding the luminosity uncertainty (open black). Theoretical predictions based on various PDF sets are shown with open symbols of different colours. (Image: ATLAS Collaboration/CERN)

    The protons collided by the LHC are not elementary particles, but are instead made up of quarks, antiquarks and gluons. The theory of the strong interactions – quantum chromodynamics (QCD) – does not allow physicists to calculate the composition of protons from first principles. However, QCD can connect measurements made in different processes and at different energy scales such that universal “parton density functions” (PDFs) can be extracted. These determine the dynamic substructure of the proton.

    The discovery of quarks as the elements of the partonic structure of the proton dates about 50 years. Soon after QCD was born and the existence of gluons inside the proton was established. Much has since been learned through a combination of new experimental data and theoretical advances. At the LHC, reactions involve quarks or gluons that carry a certain fraction x of the proton’s momentum, expressed through the Bjorken x variable. Below x of 0.01, the proton constituents are mainly gluons and a sea of quark-antiquark pairs.

    Electron-proton scattering data from the HERA collider has constrained the gluon and the sum of all quarks weighted by the square of their electric charge.

    3
    The electron(positron)-proton collider HERA was shut down at the end of June 2007. HERA was a unique instrument which made a major contribution to high energy particle physics and, in particular, to confirming aspects of quantum chromodynamics (QCD). The knowledge obtained with HERA will be essential for discovering the meaning of data obtained from the large hadron Collider (LHC) at CERN in Geneva. http://www.desy.de/~mpybar/endofHERA.html

    But the low x sea-quark composition – expressed in terms of the lighter quarks named up, down and strange quarks – is still not well understood. New data from the ATLAS experiment shows, with unprecedented precision, the production of W and Z bosons through the weak interaction. This sheds new light on the question: how “strange” the proton is at small x?

    The W production is detected through its decay into a charged lepton (electron or muon) and a neutrino, while the Z boson produces an electron-positron (or muon-antimuon) pair. The experimental detection of electrons and muons poses different challenges and thus the simultaneous measurement in both channels provides an important cross-check of the results, thus improving the final precision achieved. The integrated cross sections for Z boson and W boson production are measured with a precision of 0.3% and 0.6%, respectively, and with an additional common normalisation uncertainty from the luminosity determination of 1.8%. Differential cross sections are also measured in a variety of kinematic regions and about half of the measurement points have a precision of 1% or better.

    2
    Figure 2: Determination of the relative strange-to-down sea quark fractions r_s (left) and R_s (right). Bands: Present result and its uncertainty contributions from experimental data, QCD fit, and theoretical uncertainties. Closed symbols with horizontal error bars: predictions from different NNLO PDF sets. Open square: previous ATLAS result. (Image: ATLAS Collaboration/CERN)

    The measurements are then compared to state-of-the-art QCD expectations using different PDF sets. Because the production of W and Z bosons through the weak interaction has a different dependence on the specific quark flavours compared to the electromagnetic interaction seen in electron-positron scattering at HERA, analysing both data sets gives new access to the strange quark content of the proton.

    As is shown in Figure 1, the measured production rate of W bosons is very similar for all PDF sets, in good agreement with the data. In contrast, the rate for Z boson production is underestimated significantly for most PDF sets. A dedicated analysis enables this deficit to be attributed to a too small strange quark contribution in most PDF sets. The new PDF set, which this paper presents, requires the strange quark sea to be of a similar size as the up and down quark sea. This is summarised by the quantity RS, which is the ratio of the strange quark sea to the the up and down quark sea, and which is found to be close to one, as shown in Figure 2. This result is a striking confirmation of the hypothesis of a light-flavour symmetry of proton structure at low x. This result will generate many further studies, because hitherto there had been indications from low energy neutrino-scattering data that favoured a suppressed strange-quark contribution with respect to the up and down quark parts, leading to an RS close to 0.5.

    The analysis also shows that the potential to which precise W and Z cross sections can provide useful constraints on PDFs is not limited by the now very high experimental precision, but rather by the uncertainty of the currently available theory calculations. The salient results of this paper are thus of fundamental importance for forthcoming high-precision measurements, such as the mass of the W boson, and also represent a strong incentive for further improving the theory of Drell-Yan scattering in proton-proton collisions.

    Links:

    Precision measurement and interpretation of inclusive W+, W− and Z/γ∗ production cross sections with the ATLAS detector, https://arxiv.org/abs/1612.03016

    See the full article here .

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

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  • richardmitnick 1:14 pm on December 16, 2016 Permalink | Reply
    Tags: CERN ATLAS, The Trouble with Terabytes, Worldwide LHC Computing Grid   

    From CERN ATLAS: “The Trouble with Terabytes” 

    CERN ATLAS Higgs Event

    CERN/ATLAS
    ATLAS

    14th December 2016
    Katarina Anthony

    2
    Computing at CERN

    2016 has been a record-breaking year. The LHC surpassed its design luminosity and produced stable beams a staggering 60% of the time – up from 40% in previous years, and even surpassing the hoped for 50% threshold.

    While all of the ATLAS experiment rejoiced – eager to analyse the vast outpouring of data from the experiment – its computing experts had their work cut out for them: “2016 has been quite a challenge,” says Armin Nairz, leader of the ATLAS Tier-0 operations team. Armin’s team is in charge of processing and storing ATLAS data in preparation for distribution to physicists around the world – a task that proved unusually complex this year. “We were well prepared for a big peak in efficiency, but even we did not expect such excellent operation!”

    “Data-taking conditions are constantly changing,” says Armin. “From the detector alignment to the LHC beam parameters, there is never a ‘standard’ set of conditions. One of our key roles is to process this information and provide it along with the main event data.” This job, called the ‘calibration loop’, can take up to 48 hours. Countless teams verify and re-verify the calibrations before they are applied in subsequent bulk reconstruction of the physics data.

    Before 2016, the Tier-0 team would have a 10 to 12 hour break between each LHC beam fill. This gave their servers some breathing room to catch up with demand. “In the weeks leading up to the ICHEP conference, the LHC was working almost too perfectly,” says Armin. “At one point, it operated at 80% efficiency. This meant there were very short breaks between runs; just 2 hours between a beam dump and the next fill.”

    The CERN IT department provided an extra 1000 cores to help the ATLAS team cope with ever-growing demand. However, it soon became clear that that would not be enough: “We had to come up with a new strategy,” explains Armin. “We needed a way to grow Tier-0 without relying on more computers on-site.” Their solution: outsource the data reconstruction to the Worldwide LHC Computing Grid.

    To accomplish this feat, Armin’s Tier-0 team joined forces with the ATLAS Distributed Computing group and the Grid Production team. “Together, we had to train the Grid to process data with a Tier-0 configuration in the much-needed short time scale,” says Armin. “We experimented with lots of different configurations, trying to steer the jobs to the most appropriate sites (i.e. those with the best, quickest machines).”

    This was quite an arduous task for an already-busy team, though it proved very effective. “Despite overwhelming demand during ICHEP, we were able to shepherd copious amounts data into physics results,” says Armin. “In the end, the data presented at the conference was just 2 weeks old!”

    The Tier-0 team will be ready should such a situation arise again. “Although this solution took enormous effort, it was ultimately successful,” concludes Armin. “However, ATLAS computing management are now preparing to add new computing resources in 2017, in the hopes of avoiding a similar situation. We have also used this experience to help improve our reconstruction software and workflow, bettering our performance as the year went on.” After all, an experiment is only as valuable as the data it collects!

    About the Grid

    The Worldwide LHC Computing Grid is a global collaboration of computer centres. It is composed of four levels, or “Tiers”. Each Tier is made up of several computer centres and provides a specific set of services. Between them the tiers process, store and analyse all the data from the Large Hadron Collider.

    ATLAS Tier-0, located at the CERN data centre, has about 800 machines, with approximately 12,000 processing cores. This allows 12,000 jobs to run in parallel, and up to 100,000 jobs are run per day. During data-taking, the ATLAS online data-acquisition system transfers data to Tier-0 at about 2 GB/s, with peaks of 7 GB/s.

    See the full article here .

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

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  • richardmitnick 4:25 pm on December 6, 2016 Permalink | Reply
    Tags: 2016: an exceptional year for the LHC, , , , CERN ATLAS, , ,   

    From CERN: “2016: an exceptional year for the LHC” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    CERN

    6 Dec 2016
    Corinne Pralavorio

    1
    This proton-lead ion collision in the ATLAS detector produced a top quark – the heaviest quark – and its antiquark (Image: ATLAS)

    It’s the particles’ last lap of the ring. On 5 December 2016, protons and lead ions circulated in the Large Hadron Collider (LHC) for the last time. At exactly 6.02am, the experiments recorded their last collisions (also known as ‘events’).

    When the machines are turned off, the LHC operators take stock, and the resulting figures are astonishing.

    The number of collisions recorded by ATLAS and CMS during the proton run from April to the end of October was 60% higher than anticipated. Overall, all of the LHC experiments observed more than 6.5 million billion (6.5 x 1015) collisions, at an energy of 13 TeV. That equates to more data than had been collected in the previous three runs combined.

    3
    One of the first proton-lead ion collisions at 8.16 TeV recorded by the ALICE experiment. (Image: ALICE/CERN)

    In technical terms, the integrated luminosity received by ATLAS and CMS reached 40 inverse femtobarns (fb−1), compared with the 25fb−1 originally planned. Luminosity, which measures the number of potential collisions in a given time, is a crucial indicator of an accelerator’s performance.

    “One of the key factors contributing to this success was the remarkable availability of the LHC and its injectors,” explains Mike Lamont, who leads the team that operates the accelerators. The LHC’s overall availability in 2016 was just shy of 50%, which means the accelerator was in ‘collision mode’ 50% of the time: a very impressive achievement for the operators. “It’s the result of an ongoing programme of work over the last few years to consolidate and upgrade the machines and procedures,” Lamont continues.

    4
    An event recorded by the CMS experiment during the LHC’s proton-lead ion run for which no fewer than 449 particles tracks were reconstructed. (Image: CMS/CERN)

    For the last four weeks, the machine has turned to a different type of collision, where lead ions have been colliding with protons. “This is a new and complex operating mode, but the excellent functioning of the accelerators and the competence of the teams involved has allowed us to surpass our performance expectations,” says John Jowett, who is in charge of heavy-ion runs.

    With the machine running at an energy of 8.16 TeV, a record for this assymetric type of collision, the experiments have recorded more than 380 billion collisions. The machine achieved a peak luminosity over seven times higher than initially expected, as well as exceptional beam lifetimes. The performance is even more remarkable considering that colliding protons with lead ions, which have a mass 206 times greater and a charge 82 times higher, requires numerous painstaking adjustments to the machine.

    The physicists are now analysing the enormous amounts of data that have been collected, in preparation for presenting their results at the winter conferences.

    6
    A proton-lead ion collision recorded by the LHCb experiment in the last few days of the LHC’s 2016 run. (Image: LHCb)

    Meanwhile, CERN’s accelerators will take a long break, called the Extended Year End Technical Stop (EYETS) until the end of March 2017. But, while the accelerators might be on holiday, the technical teams certainly aren’t. The winter stop is an opportunity to carry out maintenance on these extremely complex machines, which are made up of thousands of components. The annual stop for the LHC is being extended by two months in 2017 to allow more major renovation work on the accelerator complex and its 35 kilometres of machines to take place. Particles will return to the LHC in spring 2017.

    7
    The integrated luminosity of the LHC with proton-proton collisions in 2016 compared to previous years. Luminosity is a measure of a collider’s efficiency and is proportional to the number of collisions. The integrated luminosity achieved by the LHC in 2016 far surpassed expectations and is double that achieved at a lower energy in 2012. (Image : CERN)

    See the full article here.

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    Meet CERN in a variety of places:

    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New

    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

    CERN LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles

    Quantum Diaries

     
  • richardmitnick 11:47 am on October 17, 2016 Permalink | Reply
    Tags: , CERN ATLAS, , Dr Michel Della Negra, Dr Peter Jenni, , Sir Tejinder (Jim) Virdee, W.K.H. Panofsky Prize   

    From ICL: “Fathers of Higgs boson detectors awarded particle physics prize” 

    Imperial College London
    Imperial College London

    17 October 2016
    Hayley Dunning

    1
    Professor Sir Tejinder Virdee (L) and Dr Michel DellaNegra (R)

    2
    Dr Peter Jenni

    Two Imperial physicists share in a prize for experimental physics for their work masterminding the CMS and ATLAS experiments

    The W.K.H. Panofsky Prize in Experimental Particle Physics, awarded by the American Physical Society, has this year been given to three scientists, “For distinguished leadership in the conception, design, and construction of the ATLAS and CMS detectors, which were instrumental in the discovery of the Higgs boson.”

    Receiving the honours are Professor Sir Tejinder (Jim) Virdee FRS from the Department of Physics at Imperial, Dr Michel Della Negra from CERN, who is also a Distinguished Research Fellow at Imperial, and Dr Peter Jenni from CERN and Albert-Ludwigs-University Freiburg.

    In July 2012, scientists using the Compact Muon Solenoid (CMS) and A Toroidal LHC Apparatus (ATLAS) experiments operating at the Large Hadron Collider (LHC) at CERN announced the discovery of the Higgs boson.

    CERN/CMS Detector
    CERN/CMS Detector

    CERN CMS Higgs Event
    CERN CMS Higgs Event

    CERN/ATLAS detector
    CERN/ATLAS detector

    CERN ATLAS Higgs Event
    CERN ATLAS Higgs Event

    This new particle, whose associated field gives mass to the fundamental particles, is the last missing link of the Standard Model of particle physics.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth

    Professor Jordan Nash, head of the Department of Physics at Imperial, said: “I’m delighted to see that Jim and Michel have been awarded this year’s Panofsky prize. Their dedication for more than two decades to the design, construction, and operation of the CMS detector has been essential to enabling the wonderful science and discoveries we have seen at the LHC.”

    Hayley Dunning talked to Professor Virdee about his latest award, chasing the Higgs and the future of the Large Hadron Collider.

    You’ve won a few prizes for your work – how does it feel to win the W.K.H. Panofsky Prize?

    It is a great honour to receive this prize and it is particularly pleasing to get this recognition from our peers. Even though the past 25 years have been long and not without many difficulties, it has nevertheless led to a fantastic result for all of us at the LHC – the discovery of the Higgs boson.

    This award is also acknowledgement of the huge experimental effort that led to the discovery of the Higgs boson. This wouldn’t have been possible without the contributions of thousands of scientists and engineers from around the world. On a personal note, I have enjoyed the enormous support of my exceptional colleagues at Imperial as well as the many others in the CMS Collaboration.

    What attracted you to particle physics and big experiments like the LHC?

    Particle physics is a modern-day name for the centuries-old effort to understand the fundamental laws of nature. I was intrigued to find out more: how nature really works at the most fundamental level, and I’ve always felt that this has to be one of the most exciting of human endeavours.

    Particle physicists didn’t really set out to do ‘big’ experiments. I, like my colleagues, were not attracted by the magnitude of the experiment, but by the magnitude and importance of the questions for which we were searching answers. CMS has the size it has due to the huge power of its ‘microscope’ to examine physics at the smallest distance scales offered for study by the highest accelerator energy so far achieved.

    And this can be seen in the history of this endeavour: twenty-five years ago, we started CMS with a handful of physicists and engineers. The enormity of the detectors that were necessary to answer these enormous questions meant that the collective talents and resources of a worldwide effort would be necessary. Now, CMS has over 3,000 scientists and engineers and involves 40 countries.

    Did you always believe you would be able to find the Higgs boson with CMS and ATLAS?

    In retrospect, and not overlooking the open mind that we all physicists have to have, I did believe, that if the Higgs boson were a true constituent particle of nature, we would find it sooner or later at the LHC. It has to be remembered that mass is a fundamental attribute of fundamental particles and is what gives our universe substance.

    At the time of conception of the CMS detector, a few of us paid particular attention to conjectures that suggested the mass of the Higgs boson could lie in the range where, years later, in 2012, it was eventually found. In this range the electromagnetic calorimeter, which I pioneered, played a vital role. Similarly, other parts of CMS were conceived, designed and constructed so as to ensure that the Higgs boson would be found if it were at other masses.

    Luckily, it turned out that the Higgs boson is a choice of nature. What was less of a stroke of luck is that we found it – given that it is a real element of nature.

    What are you working on now, and what do you hope for the future of the LHC experiments?

    My current work involves the in-depth study of the properties of the newly found Higgs boson, the search for widely anticipated physics beyond the Standard Model, and the design of the upgrades to the CMS detector for very high luminosity (implying very high proton-proton interaction rate) LHC running, due to start in the mid-2020s.

    In the context of this upgrade, a year or so ago I began another exciting project to develop a novel technique to replace a part of CMS. The goal is to increase the physics reach of the next phase of the LHC and take us into the 2030s. In 2015 I was awarded an EU-ERC Advanced grant to carry out the research, development and prototyping of this novel project.

    See the full article here .

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    Imperial College London

    Imperial College London is a science-based university with an international reputation for excellence in teaching and research. Consistently rated amongst the world’s best universities, Imperial is committed to developing the next generation of researchers, scientists and academics through collaboration across disciplines. Located in the heart of London, Imperial is a multidisciplinary space for education, research, translation and commercialisation, harnessing science and innovation to tackle global challenges.

     
  • richardmitnick 8:46 am on October 13, 2016 Permalink | Reply
    Tags: , , CERN ATLAS, , ,   

    From Harvard: “They ponder the universe” 

    Harvard University

    Harvard University

    October 12, 2016
    Alvin Powell

    Harvard students join faculty at CERN in Europe to tackle physics’ mysteries


    Access mp4 video here .

    Once you know enough math, Harvard Ph.D. student Tony Tong said, you get to know physics. And physics, he said, is simply amazing.

    “[Physics] is always helpful to answer the question of ‘Why?’ Why the skies are blue, why the universe is so big, basic stuff,” Tong said. “I’m always curious about those questions and the solution is always so beautiful.”

    Tong, it seems, had come to the right place. He was speaking on a warm July day in a small courtyard at the European Organization for Nuclear Research, known as CERN, the scientific campus on the outskirts of Geneva that is the world’s beating heart for high-energy particle physics.

    CERN/LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

    Home of the world’s most powerful particle accelerator, the Large Hadron Collider (LHC), CERN made world headlines in 2012 when scientists announced the discovery of the Higgs boson, the final undiscovered particle in the theoretical framework of the universe called the Standard Model.

    CERN CMS Higgs Event
    CERN CMS Higgs Event

    CERN ATLAS Higgs Event
    CERN ATLAS Higgs Event

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    The eyes of the scientific world remain focused on CERN today because the LHC is back in operation after a major upgrade that boosted its energy to 13 tera electron volts, allowing it to crash beams of protons into each other more powerfully than ever before. Now that the Standard Model is complete, scientists are looking for what’s still mysterious, sometimes called the “new physics” or “physics beyond the Standard Model.” Its form, presumably, would involve a particle born of these high-energy collisions, one that points the way to an even broader understanding of the universe, shedding light on such puzzling areas as dark matter, supersymmetry, dark energy, and even gravity, which has stubbornly refused to fit neatly into our understanding of the universe’s basic forces.

    Standard model of Supersymmetry DESY
    Standard model of Supersymmetry DESY

    CERN fired up its first accelerator in 1957. Among its milestone discoveries are the elementary particles called W and Z bosons, antihydrogen — the antimatter version of the common element — and the creation of the World Wide Web to share massive amounts of information among scientists, scattered at institutions around the world.

    The CERN campus, which straddles the Switzerland-France border amid breathtaking views of the distant Alps, produces more than just science, however. In ways technological, theoretical, educational, and inspirational, it also produces scientists.


    Access mp4 video here .
    Inside the Antimatter Factory at CERN, the ATRAP antimatter experiment seeks to slow and trap antimatter for comparison with ordinary matter.

    CERN ATRAP New
    CERN ATRAP

    “Those four years at CERN doing research were a very important part of my training,” said Harvard Physics Department chair Masahiro Morii, who was a research scientist at CERN early in his career. “It taught me things that are a bit difficult to quantify, but changed my perspective very drastically on what it means to be a scientist, what it means to be a high-energy physicist.”

    Year-round, the graduate students and postdoctoral fellows taking their initial career steps work among established scientists, learning and gaining experience difficult to get outside of CERN or a handful of other facilities around the world. Harvard’s Donner Professor of Science John Huth said what becomes apparent is science’s messiness.

    “They see the process as it unfold with all its warts. Science is pretty messy when you get into the nitty-gritty,” Huth said. “It’s just an invaluable experience. Even if you become a scientist in a different discipline or you leave science entirely, understanding that intrinsic messiness is really important.”

    In an environment focused on the practice of physics rather than the teaching of it, CERN puts the onus for learning onto the student, Morii said. Students build and test equipment, make sure what’s installed is running properly, and pluck the most meaningful pieces from the resulting data tsunami. They analyze it at all hours of the day and sometimes deep into the night, since there’s always someone awake and logged onto Skype to answer a question or share an insight.

    “People are really passionate, so it doesn’t really feel like you’re up until 11 doing your job. Maybe you’re thinking about something on the train home and you wanted to look into it. It’s not regular hours, but I don’t think that deters anyone,” said Harvard physics Ph.D. student Julia Gonski. “People like the work and it’s fun. Twenty-four hours a day, you can get on Skype and someone you know is on Skype and working.”

    While fellows and graduate students are at CERN year-round, each summer the campus’ population swells as undergraduates eager to take part in the world’s most famous science experiment step off the plane in Geneva.

    At CERN, they become part of a unique city of physicists from around the world, with different educational and cultural backgrounds but the same passions and similar goals.

    “It was this enormous scientific laboratory, with thousands of people working all hours of the night trying to understand the fundamentals of the universe, as corny as that is to say,” said Harvard postdoctoral fellow Alexander Tuna, who first came to CERN as a summer undergrad from Duke University in 2009. “It was really immersive and fun. There’s always someone around with an interesting insight or an answer to a question.”

    The secrets of the universe

    As a visitor approaches CERN, the giant brown orb of the multistory Globe of Science and Innovation comes into view.

    The globe, looking like an enormous particle half-buried in the earth, serves as a CERN welcome center and is far more visually appealing than the main campus across the street. Protected by fences with access limited through guard stations, the campus’ narrow, twisting roadways wind between boxy, industrial-looking buildings numbered instead of named, as if creativity there is reserved for science instead of infrastructure. Even the cafeteria that serves as a central gathering spot is named simply “Restaurant 1.”

    “It was different than I expected,” said Harvard junior Matthew Bledsoe. “I figured a place on the forefront of physics would look fresher and newer, new buildings and stuff. But [they are] 1950s and ’60s-era buildings, so the buildings are pretty old. It looks like a factory.”

    Visitors quickly learn to look past the boxy exteriors to what’s inside. There they find thousands of people working on 18 experiments, seven associated with the LHC and the others with smaller accelerators and a decelerator, which is used for antimatter experiments like those run by Harvard Physics Professor Gerald Gabrielse’s ATRAP collaboration.

    ATRAP, short for “antihydrogen trap,” relies on the LHC’s high energy to make protons collide with a target to create antiprotons. The experiment then cools and slows the antiprotons, and combines them with positrons, the antimatter equivalent of electrons, to create antihydrogen for study and comparison with ordinary hydrogen. Gabrielse, who pioneered antimatter experiments at CERN, said that for students who want to go into high-energy physics, getting a taste of the enormous collaborations that are behind such experiments is key.

    “If you’re interested in making a career in doing those kinds of things [experimental particle physics], it’s extremely important to have this experience,” Gabrielse said.

    The LHC, with its potential to pierce the veil between the known world of the Standard Model and the mysteries that the model does not address, takes center stage. Yet to visitors wandering the halls and sidewalks of CERN, the LHC is nowhere to be seen.

    That’s because the LHC is buried 300 feet underground in a massive tunnel that runs 17 miles from Switzerland into France and back again. Its twin proton beams circle in opposite directions, crossing four times on their journey. At those crossings are four major particle detectors, one of which is ATLAS, a massive machine backed by a worldwide collaboration in which Harvard scientists play lead roles, and which was one of two experiments to detect the Higgs boson.

    CERN/ATLAS detector
    CERN/ATLAS detector

    2
    Outside the ATLAS control room at the LHC. Joe Sherman/Harvard Staff Photographer

    “You can think of it (ATLAS) as a really large camera surrounding the collision point where protons collide,” Tuna said.

    ATLAS, which stands for A Toroidal LHC Apparatus, is 180 feet long, 82 feet in diameter, and weighs 7,000 tons. When the proton beams collide, they scatter particles in all directions. ATLAS dutifully records these collisions, producing far more data than current computing technology can store, so filters are employed that screen out more mundane results and keep only the most promising for analysis.

    The complex undertaking requires a collaboration that is as massive as the task the researchers have set for themselves. It includes about 3,000 physicists from 175 institutions in 38 countries.

    “This is the center of particle physics right now,” said Harvard Ph.D. student Karri DiPetrillo. “As a scientist, you like asking nature questions and seeing what the answer is. Because we have thousands of people working on a single experiment, you know we’re asking some of the hardest questions in the universe. If it takes thousands of people to find the answer, you know that it’s a good question.”

    For decades, physicists exploring the most basic particles that make up the universe were guided by the Standard Model, which held that everything is made of a limited number of quarks, leptons, and bosons. Over the years, one by one, experimental physicists, including Harvard faculty members, found the particles predicted by the theory: bottom quark, W boson, Z boson, top quark. In 2012, they found the Higgs boson, the last theorized particle.

    When the huge hubbub over the Higgs discovery faded, particle physicists began to assess the field’s new reality. After decades in which theoretical physicists were leading, telling experimental physicists what new particle to look for, the roles are now reversed.

    As reliable as the Standard Model has been, it doesn’t explain everything. And, while theoretical physicists have several ideas of where those mysteries might fit into current knowledge, no evidence exists to tip the scales toward one idea or another.

    Even the Higgs boson still holds secrets, as detecting it didn’t completely explain it. Scientists who continue to probe the Higgs boson hope that the particle may yet reveal clues — inconsistencies from what is expected from the Standard Model — that will outline the broader path forward.

    “There are really two paths. One path is to really push on what we understand about the Higgs boson because that has the strangest properties associated with it and if you push the theory at all the Higgs creates the most problems for it,” Huth said. “The other is the discovery region for something new, like dark matter.”

    The undergraduate summer

    A scientist’s path to CERN usually starts with a passion for physics. Graduate student Nathan Jones credits a family road trip to Colorado during which he read a library book about the universe. Undergrad Bledsoe was wowed by a trip to Fermilab outside Chicago as a high school freshman, while grad student Gonski traces it to the annoyance she felt when she learned her high school chemistry teacher had gotten the science wrong.

    “I remember being in chemistry class in high school when they told us protons and neutrons are indivisible,” said Gonski, who learned otherwise from Stephen Hawking’s “A Brief History of Time.” “I was so offended … I remember being frustrated and asking my parents, ‘Did you guys know?’ At that point I wanted to see how far down we can go [in particle size].”

    After that initial spark, students take classes and often work in a campus laboratory before heading overseas. Some undergraduates go to CERN through the Undergraduate Summer Research Experience program run by the University of Michigan for students across the country. Several Harvard students benefitted instead from the Weissman International Internship Program Grant, established in 1994 to provide faraway opportunities for them.


    Access mp4 video here .
    A field of sunflowers stands at the roadside on the approach to CERN.

    Once the funding is set, there’s nothing left but the plane ride and moving into their new digs. Undergraduates live in settings ranging from downtown Geneva to the French countryside. Last summer, three Harvard students — Ben Garber ’17, Gary Putnam ’17, and Bledsoe — rented an apartment over the border in France and commuted to work each day by bike, while Katie Fraser ’18 stayed closer, at CERN’s on-campus hostel.

    Days consisted of morning lectures on topics relevant to their work. After those lectures — and the occasional pickup basketball game at lunchtime — they’d spend afternoons working on a project. Garber worked with Tuna and DiPetrillo on an analysis of Higgs boson decay (the particle itself exists for a tiny period of time) into two W bosons. Bledsoe worked on hardware, building and testing a circuit board to be used in the planned 2018 ATLAS upgrade, in the cavernous Building 188 under the tutelage of Theo Alexopoulos from the Technical University of Athens. Wherever they were, whether doing project tasks or having cafeteria conversations, the students were steeped in physics.

    “It was a lot of fun, different than I expected. You learn stuff just by being there, pick up vocabulary in lunchtime conversations,” Fraser said. “It definitely solidified my desire to go into high-energy physics.”

    Melissa Franklin, Mallinckrodt Professor of Physics, said lessons can be found behind almost every door at CERN.

    “I was just amazed, it was unbelievable,” said Franklin, who first visited between her undergraduate and graduate years. “I went to every place I could on site and just knocked on doors and bugged people … You learn so much by osmosis. You have to learn to hang around and ask good questions.”

    Jennifer Roloff, a Harvard physics Ph.D. student, first came to CERN in 2011 as an undergraduate and has been back every summer. Now she helps manage the University of Michigan summer undergraduate program, which gives her a broad view of the student experience.

    “There are definitely some students who do miss home,” Roloff said. “For a lot of them it’s the first time out of the country [or] the first time long-term out of the country. For a lot of them, they realize this is not what they want to do. CERN is not for everyone. There are challenges and difficulties that are not in other physics.”

    That understanding, Gabrielse said, is as important a lesson as finding your intellectual home.

    “Some decide, based on it, to go into the field. Some decide not to,” Gabrielse said. “That guidance too is valuable.”

    Yet being at CERN is not just about science. Students have their weekends free and can explore their new surroundings. Some hike the Alps or the closer Jura Mountains. Others walk the ancient streets of Geneva, visiting its lakefront, restaurants, museums, and other attractions. Putnam loved a park near the University of Geneva where people played on large chessboards with giant pieces. He also soaked up the area’s natural splendor.

    “It’s so beautiful here,” Putnam said. “Sometimes I forget and do the normal thing of looking down and not paying attention, but being able to look up and see the mountains is really special.”

    On call for a particle emergency

    Life at CERN as graduate students is not quite so fancy-free. Visits are limited to summers early in graduate careers as they complete coursework, but once that’s done, they can come and stay to conduct dissertation research.

    To keep the ATLAS collaboration running, graduate students are required to spend a year of research time doing work to benefit the experiment itself, to ensure that high-quality data is collected, for example, or that potentially significant collision events aren’t lost in the data.

    “We have to make sure the data we’re receiving is like you expect it, ready for analysis,” DiPetrillo said. “[It’s taken] probably half of my time in the last year; the other half has been working on Standard Model measurement of the Z boson.”

    5
    A little physicist humor written on a CERN blackboard. Joe Sherman/Harvard Staff Photographer

    Part of DiPetrillo’s duty is assisting in ATLAS’ day-to-day operation, working in the ATLAS control room — with its Mission Control feel, and dominated by a wall-sized screen — and monitoring one of several subsystems that make the whole operation work. Monitoring those subsystems makes ATLAS a 24/7 proposition.

    In addition to working overnight in the control room, DiPetrillo is often on call to back up someone on site. While on call, she has to stay near her phone and within an hour’s drive of the facility in case something goes wrong. If that happens, she troubleshoots the problem with the person in the control room or pushes the problem up to someone more senior.

    “You can think of ATLAS as always taking data so we always need people watching it, making sure ATLAS is working in a way that we want [it] to, that the detector is working … and that data looks the way we expect,” DiPetrillo said.

    When not on call or manning the control room overnight, a graduate student’s life at CERN is full of meetings to share and hear the latest findings, and of hours poring over the latest data looking for the kind of statistical bump that might indicate a new particle — or a new something else.

    The LHC’s recent upgrade has made scientists hopeful that a new particle will be discovered soon. But if not, another upgrade planned for about 2018 may do the trick. While the recent upgrade made the energy of the proton beam higher, the next one will increase luminosity, or the number of protons in the beam, multiplying the number of collisions at any given moment and improving the odds of detecting extremely rare events.

    “We’re all here to … discover stuff, but it’s so difficult. It’s impossible to do as one person,” Gonski said. “I would love to be one person on the 500-person team to discover [supersymmetry’s] stop quark. It’d be great for physics if we all discovered this and for me to say I want to do this — be a tiny fraction of a large group effort.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

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    Harvard University campus

    Harvard is the oldest institution of higher education in the United States, established in 1636 by vote of the Great and General Court of the Massachusetts Bay Colony. It was named after the College’s first benefactor, the young minister John Harvard of Charlestown, who upon his death in 1638 left his library and half his estate to the institution. A statue of John Harvard stands today in front of University Hall in Harvard Yard, and is perhaps the University’s best known landmark.

    Harvard University has 12 degree-granting Schools in addition to the Radcliffe Institute for Advanced Study. The University has grown from nine students with a single master to an enrollment of more than 20,000 degree candidates including undergraduate, graduate, and professional students. There are more than 360,000 living alumni in the U.S. and over 190 other countries.

     
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