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  • richardmitnick 1:00 pm on April 4, 2013 Permalink | Reply
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    From CERN at Quantum Diaries: “Grey matter confronted to dark matter” 

    THIS QUANTUM DIARIES POST IS PRESENTED IN ITS ENTIRETY BECAUSE OF ITS IMPORTANCE.

    April 4th, 2013
    Pauline Gagnon

    Pauline Gagnon

    “After 18 years spent building the experiment and nearly two years taking data from the International Space Station, the Alpha Magnetic Spectrometer or AMS-02 collaboration showed its first results on Wednesday to a packed audience at CERN. But Prof. Sam Ting, one of the 1976 Nobel laureates and spokesperson of the experiment, only revealed part of the positron energy spectrum measured so far by AMS-02.

    Positrons are the antimatter of electrons. Given we live in a world where matter dominates, it is not easy to explain where this excess of positrons comes from. There are currently two popular hypotheses: either the positrons come from pulsars or they originate from the annihilation of dark matter particles into a pair of electron and positron. To tell these two hypotheses apart, one needs to see exactly what happens at the high-energy end of the spectrum. But this is where fewer positrons are found, making it extremely difficult to achieve the needed precision. Yesterday, we learned that AMS-02 might indeed be able to reach the needed accuracy.

    graph
    The fraction of positrons (measured with respect to the sum of electrons and positrons) captured by AMS-02 as a function of their energy is shown in red. The vertical bars indicate the size of the uncertainty. The most important part of this spectrum is the high-energy part (above 100 GeV or 102) where the results of two previous experiments are also shown: Fermi in green and PAMELA in blue. Note that the AMS-02 precision exceeds the one obtained by the other experiments. The spectrum also extends to higher energy. The big question now is to see if the red curve will drop sharply at higher energy or not. More data is needed before the AMS-02 can get a definitive answer.

    Only the first part of the story was revealed yesterday. The data shown clearly demonstrated the power of AMS-02. That was the excellent news delivered at the seminar: AMS-02 will be able to measure the energy spectrum accurately enough to eventually be able to tell where the positrons come from.

    But the second part of the story, the punch line everyone was waiting for, will only be delivered at a later time. The data at very high energy will reveal if the observed excess in positrons comes from dark matter annihilation or from “simple” pulsars. How long will it take before the world gets this crucial answer from AMS-02? Prof. Ting would not tell. No matter how long, the whole scientific community will be waiting with great anticipation until the collaboration is confident their measurement is precise enough. And then we will know.

    If AMS-02 does manage to show that the positron excess has a dark matter origin, the consequences would be equivalent to discovering a whole new continent. As it stands, we observe that 26.8% of the content of the Universe comes in the form of a completely unknown type of matter called dark matter but have never been able to catch any of it. We only detect its presence through its gravitational effects. If AMS-02 can prove dark matter particles can annihilate and produce pairs of electrons and positrons, it would be a complete revolution.”

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  • richardmitnick 11:15 am on February 1, 2013 Permalink | Reply
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    From Pauline Gagnon at Quantum Diaries: "What’s coming up at CERN in 2013?" 

    Pauline Gagnon
    Pauline Gagnon

    “The Year of the Dragon (2012) came with a roar: a wonderful discovery and a greater understanding of how matter works. What might 2013, the Year of the Serpent, have in store for CERN? The serpent could very well represent the long and winding road of the many new upgrades ahead.

    On Monday 11 February at 6 am Geneva time, the Large Hadron Collider (LHC) will stop producing collisions, marking the start of a major overhaul for all accelerators at CERN. This will be the first in a series of three long-shutdowns to allow a complete refurbishing of the main accelerator, the LHC. The goal is to be able to increase its energy from the actual 8 TeV to 13 or even 14 TeV. This means an increased reach for new particles.

    acc

    This is not just to play a game of ‘my particle is bigger than yours’, but rather an attempt at finding the passageway to new theories. Since energy (E) and mass (m) are two forms of the same essence, as stated by the famous equation E = mc2, where c2 acts as a conversion factor between the two, increasing the accelerator energy will give us the possibility to create particles more massive than we have ever been able to produce before. It will also enhance the production rate of known particles – like the newly discovered boson – to better study them.

    It is foreseen that the accelerator complex will come back to life in 2014, with the LHC becoming operational again in 2015.”

    See the full article here.

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  • richardmitnick 4:19 pm on December 10, 2012 Permalink | Reply
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    From Quantum Diaries – Pauline Gagnon : “Gluino, Higgsino, bingo!” 

    Pauline Gagnon
    Dr. Pauline Gagnon

    Gluinos and Higgsinos are some of the many undiscovered particles we may find at the Large Hadron Collider (LHC) if a theory called supersymmetry, also known as SUSY, turns out to be true. This theory is built on the Standard Model, the current theoretical model of particle physics.

    Standard Model

    The Standard Model relies on the Higgs boson to hold true. But even with this boson, physicists know that this model cannot be the final answer as it has a few shortcomings. For example, it fails to provide an explanation for dark matter or why the masses of fundamental particles such as electrons and muons are so different. This theory of supersymmetry is one of the most popular and most promising ways to extend the Standard Model, but it has yet to manifest itself.

    SUSY is very popular since it brings lots of harmony in the world of sub-atomic particles. In the Standard Model, there are two types of particles: fermions and bosons. The fermions include quarks and leptons and are the building blocks of matter. These particles have “spin” values of ½. The force carriers are bosons, the other family of particles. They have integer values of spin, that is, 0 or 1.

    Supersymmetry would blend fermions and bosons together by associating partners to each particle: a fermion would be paired with a boson, and vice-versa. For example, each quark would come with a “squark,” the name given to the supersymmetric partners of quarks. The squarks would be bosons rather than fermions and would carry spin 0. The same thing goes for leptons. Likewise, the known bosons (gluons, Higgs, W, Z and photons) would come with fermion superpartners with half spin values. These would be the gluinos, Higgsinos, winos, zinos and photinos. A mixture of the force carrier superpartners (all except the gluinos) gives charginos and neutralinos, the latter being particles that would be the perfect candidates for dark matter….”

    And, now, it gets interesting. Dr Gagnon is a great communicator. Please read the full post here.

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  • richardmitnick 6:22 pm on September 28, 2012 Permalink | Reply
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    From CERN Blog at Quantum Diaries: “How is new physics discovered?” 

    IT HAS BEEN A WHILE SINCE I HAVE BEEN ABLE TO PRESENT A POST FROM QUANTUM DIARIES. MY AUDIENCE IS A MORE GENERALIST PUBLIC – INTERESTED, EDUCATED, BUT NOT PROFESSIONAL SCIENTISTS. NOW COMES A POST WHICH I BELIEVE MIGHT BE APPROACHABLE FOR MY READERS.

    pg
    Pauline Gagnon

    2012.09.28
    Pauline Gagnon

    “Finding an experimental anomaly is a great way to open the door to a new theory. It is such a good trick that many of us physicists are bending over backward trying to uncover the smallest deviation from what the current theory, the Standard Model of particle physics, predicts.

    sm
    Standard Model

    This is the approach the LHCb collaboration at CERN is pursuing when looking at very rare decays. A minute deviation can be more easily spotted for rare processes. One good place to look is in the rate of K meson decays, a particle made of one strange quark s and one anti-down quark d.

    Recently, the LHCb collaboration has turned its attention to measuring the decay rate of the short-lived kaons K0S, the only K mesons decaying fast enough to be seen with precision in their detector.”

    I hope that is enough to entice you to read further.

    LHCB
    LHCb Collaboration

    Pauline Gagnon is a very good writer. Read and enjoy the rest of her post here. While you are at it, look around at the various Quantum Diary blogs, Twitter feeds,member organization web sites.

    Participants in Quantum Diaries:

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    US/LHC Blog

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  • richardmitnick 2:13 pm on March 2, 2012 Permalink | Reply
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    From Pauline Gagnon at CERN via Quantum Diaries: “All on the Higgs for (nearly) everyone” 

    “Like most of my colleagues, the most frequently asked question I get from friends and family these days is: what is this Higgs boson business? Here is what I hope will help not only family members but also struggling physicists. It is not the simplest but it is complete and accurate.

    First of all, let’s clarify one point: it has nothing to do with God. This “God’s particle” business has got to go. It was just a bad joke to start with and like any joke, it gets stale fast.

    And we need to talk about three separate aspects: the Higgs mechanism*, the Higgs field and the Higgs boson.

    See Pauline’s very thorough discussion here.

    *Link is to Wikipedia with which some might object

    Participants in Quantum Diaries:

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    US/LHC Blog


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    Brookhaven Lab

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