Of Particular Significance

Jets: Article Updated

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 10/31/2011

I’m hoping to focus this week on updating and improving some of the background articles on the website, rather than updating the latest news (unless something really crucial happens.)   I’ve just put up an improved version of my article on one of the most important aspects of the physics of the Large Hadron Collider, and indeed of any modern high-energy particle collider: jets, the experimental manifestation of high-energy quarks, anti-quarks, and gluons.  The article, which explains why a high-energy quark created in a particle collision is measured as a spray (or “jet”) of hadrons, now has figures and an accompanying text that should make it much clearer.  Comments welcome, as always.

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8 Responses

  1. Hi Dilation,

    Prof Matt Strassler: “Again, you’d better distinguish proton-proton collisions (in which no quark-gluon plasma [QGP] is created) from the collisions of large atomic nuclei. Otherwise you will end up very deeply confused about what’s happening in the two cases…”

    It has been difficult understanding the depth of particle research so I am listening and fully acknowledge the confusion Prof Matt Strassler is telling me to be aware of. I fully admonish this and this displays my inexperience.

    It goes back to what Leon Ledermen ( http://3.bp.blogspot.com/_cldxKGOzgeM/SbGmLsx9Q4I/AAAAAAAACEc/soFdhnmNsY0/s400/symmetry1.JPG ) has spoken about in terms of symmetry and how I have read of many scientist along the way who are taking a stance in the idea of an asymmetrical expression since the beginning of the universe as contained in the idea of what this beginning amounts too, can it be looked at when looking at particle research?

    As strange as it may sound from theoretical position I understand what string theory may or may not be saying, with regard to what we are seeing in those valleys. For me such expression is contained in the idea of a Jet expression so yes I need to understand this better.


  2. “A basic process in QCD is the energy loss of a fast parton in a medium composed of colour charges. This phenomenon, “jet quenching”, is especially useful in the study of the QGP, using the naturally occurring products (jets) of the hard scattering of quarks and gluons from the incoming nuclei. A highly energetic parton (a colour charge) probes the coloured medium rather like an X-ray probes ordinary matter. The production of these partonic probes in hadronic collisions is well understood within perturbative QCD. The theory also shows that a parton traversing the medium will lose a fraction of its energy in emitting many soft (low energy) gluons. The amount of the radiated energy is proportional to the density of the medium and to the square of the path length travelled by the parton in the medium. Theory also predicts that the energy loss depends on the flavour of the parton.” See: ALICE enters new territory in heavy-ion collisions- http://cerncourier.com/cws/article/cern/46055


    1. This process does not occur (measurably) within the collision of two protons. You need the dense environment of the fireball created by the collision of two large atomic nuclei to see it. I haven’t addressed that at all in this article; it’s really a separate topic.

    2. Be patient Plato,
      maybe Matt will write about the QGP in the future if he finds time for it …?
      I would like and appreciate that too 😉

  3. Prof Matt Strassler,

    “historical development syntactically constructed.”

    Through following the successes of LHC there is one thing that stands out for me when it comes too, “Jet Quenching.” The QGP “had been a theoretical question in relation too, gas or fluid,” and now we can say indeed, it is a fluid?


    ” At the recent seminar, the LHC’s dedicated heavy-ion experiment, ALICE, confirmed that QGP behaves like an ideal liquid, a phenomenon earlier observed at the US Brookhaven Laboratory’s RHIC facility. This question was indeed one of the main points of this first phase of data analysis, which also included the analysis of secondary particles produced in the lead-lead collisions. ALICE’s results already rule out many of the
    existing theoretical models describing the physics of heavy-ions. ”


    See: 2010 ion run: completed!- http://cdsweb.cern.ch/journal/CERNBulletin/2010/50/News%20Articles/1312215?ln=en

    I appreciate your demonstrations in related article to previous question of
    http://arxiv.org/abs/1110.6461. A Thank you, to you and your colleagues.

    I must say following string theory has brought me to this point about the nature and beginnings of our universe. Can we say that the collision process is being representative by the microanalyses of using experimental procedures in correlation with the LHC when looking at the universe?


    1. Again, you’d better distinguish proton-proton collisions (in which no quark-gluon plasma [QGP] is created) from the collisions of large atomic nuclei. Otherwise you will end up very deeply confused about what’s happening in the two cases… they are quite different. In this article, I have focused on what happens in the absence of a quark-gluon plasma. If you add one, then quite a lot of what I have written in this article needs to be modified. But that is a very long story, demanding its own article.

  4. Prof Matt Strassler,

    I again appreciate the ongoing information data that you are reconstructing.

    Does your historical developmental line syntactically constructed eventually lead to what Lubos Motl’s describing in context of the collision process?

    CMS: a very large excess of diphotons- http://motls.blogspot.com/2011/11/cms-very-large-excess-of-diphotons.html

    Especially the paper linked here:

    Measurement of the Production Cross Section for Pairs of Isolated Photons in pp collisions at sqrt(s) = 7 TeV- http://arxiv.org/abs/1110.6461


    1. See today’s post; though I’m not sure what you mean by “historical development syntactically constructed.” In any case, Lubos is a string theorist and has never written papers on LHC physics, so buyer beware.

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