Jet Physics at RHIC

1. Jet Physics at RHIC Focusing high-energy tools on nuclear collisions

2. The BNL lecture last month … PET Imaging by Dave Schlyer photon electron positron 2 mm photon E = 500,000 eV David Morrison

3. The BNL lecture this month … photon quark quark 2 mm photon E = 500,000 eV David Morrison

4. The BNL lecture this month … quark quark quark 2 mm quark E = 500,000 eV David Morrison

5. The BNL lecture this month … quark quark quark 2 mm quark E > 5,000,000,000 eV David Morrison

6. The BNL lecture this month … quark quark quark 0.000000000002 mm quark E > 5,000,000,000 eV David Morrison

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

8. 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, ... David Morrison

9. 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 David Morrison

10. 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

11. q q q q q q q q q q Fragmentation quarks, anti-quarks appear, break original connection into more and more and more particles q q David Morrison

12. 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 David Morrison

13. “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 David Morrison

14. 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 David Morrison

15. Many sources of low pT particles • many ways to create particles in electron-positron or proton-proton collisions that don’t involve jets • e.g., create an unstable particle that then decays • typical transverse momentum (pT) few hundred MeV/c David Morrison

16. At low energy, jets hard to discern ? David Morrison

17. At higher energy, jets stand out ! David Morrison

18. 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 David Morrison

19. Jets in electron-positron collisions David Morrison

20. 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 David Morrison

21. 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 David Morrison

22. 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 David Morrison

23. 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 David Morrison

24. 1984 BNL note about RHIC physics Jets in nuclear collisions

25. 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 David Morrison

26. PHOBOS BRAHMS PHENIX STAR you are here David Morrison

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

28. 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, ... David Morrison

29. Correlations outside particle physics • One way to find “el encierro” (the running of the bulls) in Pamplona, Spain: • start by finding one high-momentum bull • look near that bull for others moving in the same direction • if the bull density is high, you’re likely standing in the middle of the bull run David Morrison

30. PHENIX David Morrison

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

32. Candidate jets in RHIC p+p collisions PHENIX STAR David Morrison

33. Collisions of larger objects David Morrison

34. Hiding in plain sight Au+Au at full RHIC energy in STAR detector gold ion jets can be difficult to find, even when you know they’re there gold ion David Morrison

35. What is a nucleus? If you ask a very high energy proton, it’s a huge collection of partons David Morrison

36. 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 David Morrison

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

38. jet? quark quark jet? A “central” (head-on) collision David Morrison

39. Single pions and energy loss PHENIX Preliminary probability of creating 0 David Morrison

40. A “lighthouse” of parton fragments David Morrison

41. Using this tool to study QCD “fog” • seeing one beam, know the other should be there • collide two fog banks, wait for spontaneous appearance of working lighthouse • look for changes • intensity • wavelength • angular spread David Morrison

42. High-energy physics in vacuum parton parton parton parton David Morrison

43. High-energy physics in medium parton parton parton hot, dense system of quarks, gluons parton David Morrison

44.   What about the other jet? jet “strength” glancing head-on type of collision STAR results: PRL 90, 082302 (2003) David Morrison

45. Interpreting the observation jet! quark quark strongly suggests that “stuff” created during collision is very unusual, very unlike normal nuclear matter David Morrison

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

47. Parallels with 1970’s high-energy • RHIC is creating nuclear collisions at particle physics energies • C-AD runs a machine with unprecedented capabilities • 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 David Morrison

48. Fin • RHIC experiments detect jets convincingly • Jets used as sophisticated probe of very complex environment of nuclear collision • study of jets also important for spin physics! • Only the more straightforward jet analyses have been published so far • Jet measurements contributing to very lively interplay between theory and experiment David Morrison

50. We’d like to “X-ray” nuclear collisions • However, analogy is slightly flawed • Medical X-ray source is (usually) outside the system being studied • Properties of X-ray beam can be prepared precisely • Can study X-ray photos with and without a sample in place David Morrison