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Using Jets to See Into Quark Matter

Using Jets to See Into Quark Matter. David Morrison Brookhaven National Laboratory. people were trying to understand origins of so many discovered particles Gell-Mann and Zweig propose quarks as underlying structure quark concept focuses on kinship relations among particles. Back to 1964.

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Using Jets to See Into Quark Matter

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  1. Using Jets to See Into Quark Matter David Morrison Brookhaven National Laboratory

  2. people were trying to understand origins of so many discovered particles Gell-Mann and Zweig propose quarks as underlying structure quark concept focuses on kinship relations among particles Back to 1964 hadrons quarks mesons baryons pions, kaons, ... protons, neutrons, ...

  3. Feynman, in 1969, proposes “partons” as way to explain experimental results from SLAC at Stanford parton concept focuses on dynamics, the way things behave when then interact With advent of QCD in 1973 partons are identified with quarks and gluons While others were at Woodstock hadron hadron pT pL

  4. partons quarks gluons nucleons protons neutrons Some more terminology hadrons quarks mesons baryons pentaquark pions, kaons, ... protons, neutrons, ... , –, ...

  5. Strong nuclear force has some very unusual properties doesn’t get weaker with distance! So what happens when you try to send two quarks flying apart? Free quarks? quark anti-quark EM force decreases with distance

  6. Force between two quarks gluons quark quark Compare to gravitational force at Earth’s surface Quarks exert 16 metric tons of force on each other!

  7. A directed “spray” of particles pion • as connection between quarks breaks up, most of the motion stays close to direction of the original quarks • the fragmented bits appear as normal subatomic particles • pions, kaons, protons, ... pion pion kaon

  8. “sprays” of particles had been seen in experiments before original term “core”, came from cosmic ray experiments first use of “jet” seems to be by Bjorken in 1970 Origin of the word “jet” high-energy proton 14N core core

  9. Jet properties • cone-like spray of particles surrounding direction of each outgoing parton • quark-quark scattering leads to back-to-back structure • high-energy parton-parton interaction can be calculated with precision

  10. Many sources of low pT particles • many ways to create particles in electron-positron or proton-proton collisions that don’t involve jets • typical transverse momentum (pT) few hundred MeV/c

  11. At low energy, jets hard to discern ?

  12. At higher energy, jets stand out !

  13. First evidence for jets was subtle • By 1975 at SLAC (DESY too) energy of electron-positron collisions high enough for jets to appear ... statistically • As collision energy was raised, average “sphericity” decreased • Gradual appearance of back-to-back jets in Mark I experiment sphericity collision energy

  14. Jets in electron-positron collisions

  15. e+e- one thing; hadron collisions another incoming partons vary International conference on high-energy physics, Paris, 1982 Results from CERN experiment UA2 really convinced everyone that jets in hadron-hadron collisions had been seen Jets & proton-antiproton collisions

  16. Very selective timeline partons 1969 quarks 1964 “jets” 1970 Fermilab (NAL) CERN SPS CERN ISR UA2 jets in p +p 1982 jets in e+e– 1975 QCD 1973

  17. Jets and the period 1969-1982 • It took time for suitable facility to be available • high enough energy for jets to stand out • It took time to design and build the right sort of experiment • Fundamental theory was developed part-way through the period

  18. RHIC Physics Program • RHIC proposed 1983 • One of the main emphases is study of properties of matter under extreme conditions • huge energy densities • enormous temperatures (over 1 trillion C) • To achieve these conditions we collide heavy nuclei at very high energies • Extremely useful to have probes with known properties

  19. 1984 BNL note about RHIC physics Jets in nuclear collisions

  20. Jets at RHIC • Not starting at “square one” • properties of jets in electron-positron, proton-proton, proton-antiproton collisionswell-measured • relying on over 30 years of jet physics results • Energy high enough that jets not too rare • Experiments designed with jets in mind • The plan in a nutshell • show that RHIC experiments can “see” jets • look for changes in expected jet properties

  21. PHOBOS BRAHMS PHENIX STAR

  22. RHIC from Space Brookhaven National Laboratory New York City

  23. RHIC from Space

  24. STAR PHENIX Each collaboration about 400 physicists and engineers Much of the research driven by students

  25. Finding jets using correlations photons trigger particle • Method 1 • find a high-momentum charged particle and look nearby for others • Method 2 • main particle in jet is very often a pion • a 0 usually decays into photons • find a high-energy photon and look nearby for others pion pion, kaon, ...

  26. An algorithm • a way to locate the running of the bulls in Pamplona, Spain: • start by finding one high-momentum bull • look others moving in roughly the same direction • if the bull density is high, you might reconsider the place you’ve chosen to stand The next step is simple: just replace “bull” by “particle”

  27. PHENIX

  28. See a pattern consistent with jets! particle track density - + angle of track away from photon

  29. Jets in RHIC p+p collisions PHENIX STAR

  30. RHIC proton-proton collisions • We haven’t discovered jets; we’ve shown that the experiments can detect the expected jets • Provide a solid baseline for studying nucleus-nucleus collisions • Fine-tune techniques and the understanding of detectors to prepare for finding jets in nuclear collisions

  31. Collisions of larger objects

  32. Collision geometry gold is a large nucleus, lots of partons (quarks, anti-quarks and gluons) gold nucleus “pancake” thin due to special relativity gold nucleus

  33. A “peripheral” (glancing) collision jet quark quark a bit like a proton-proton collision jet

  34. jet? quark quark jet? A “central” (head-on) collision

  35. Single pions and energy loss PHENIX Preliminary probability of creating 0

  36. “is this thing on?” if you detect one beam, at least know the source is on intensity of the “other” beam tells you a lot Case study: opacity of fog

  37. High-energy physics in vacuum parton parton parton parton focus is on understanding interactions between elementary particles

  38. High-energy physics in medium parton parton parton hot, dense system of quarks, gluons parton focus is on understanding nature of created medium

  39. jet? quark quark jet? High-energy physics in cold nuclear matter deuteron (bound state of neutron and proton) gold provides a crucial “control” experiment–what does a parton do passing through normal nuclear matter?

  40. Pedestal&flow subtracted same direction opposite direction intensity angle away from initial high momentum particle

  41.   Quantifying the effect jet “strength” glancing head-on type of collision STAR results: PRL 90, 082302 (2003)

  42. Interpreting the observation jet! quark quark The “stuff” created during collision is very unusual, very unlike normal nuclear matter. Energy loss of parton ~5 GeV/fm. Compare with results from e+A at HERA: 0.3 GeV/fm.

  43. A (very) loose comparison accelerator RF cavity: 10 MV/m parton in hot, dense “QCD matter”: 5 GeV/fm factor of 500 quadrillion different

  44. z y x Determining the reaction plane Initial asymmetry in coordinate space leads to asymmetry in pressure leads to asymmetry in momentum space–which can be detected

  45. pTtrigger=4-6 GeV/c, 2<pTassociated<pTtrigger, ||<1 STAR Preliminary Aihong Tang, January 16, 2004 at Quark Matter conference

  46. Exploring different territories PET biological tissues RHIC dense mix of quarks, gluons particles g nuclear collision brain g particles

  47. Parallels with 1970’s high-energy • RHIC is creating nuclear collisions at particle physics energies • The experiments have been designed with the benefit of previous efforts • acceptance, resolution, calorimetry, particle identification • Very active exchanges between experiment and theory; active development of theory

  48. Fin • RHIC experiments detect jets convincingly • Jet measurements contributing to very lively interplay between theory and experiment • quark-gluon plasma, color-glass condensate, color-flavor locked matter, color superconductivity • Jets used as sophisticated probe of very complex environment of nuclear collision • only the more straightforward jet analyses have been published so far • di-hadron correlations, –jet studies, high pT identified particles, many more to come!

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