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M. J. Tannenbaum Brookhaven National Laboratory Upton, NY 11973 USA

From Bjorken Scaling to pQCD---Experimental techniques from p-p collisions of the 1970’s with application to Au+Au collisions at RHIC. M. J. Tannenbaum Brookhaven National Laboratory Upton, NY 11973 USA. Nuclear Physics Seminar Physics Department, BNL December 7, 2004.

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M. J. Tannenbaum Brookhaven National Laboratory Upton, NY 11973 USA

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  1. From Bjorken Scaling to pQCD---Experimental techniques from p-p collisions of the 1970’s with application to Au+Au collisions at RHIC M. J. Tannenbaum Brookhaven National Laboratory Upton, NY 11973 USA Nuclear Physics Seminar Physics Department, BNL December 7, 2004 BNL-Seminar-Dec 7, 2004

  2. Phys. Rev. 179, 1547 (1969) Phys. Rev. 185, 1975 (1969) Bjorken Scaling in Deeply Inelastic Scattering and the Parton Model---1968 BNL-Seminar-Dec 7, 2004

  3. BBK 1971 S.M.Berman, J.D.Bjorken and J.B.Kogut, Phys. Rev. D4, 3388 (1971) • BBK calculated for p+p collisions, the inclusive reaction • A+B C + Xwhen particle C has pT>> 1 GeV/c • The charged partons of DIS must scatter electromagnetically “which may be viewed as a lower bound on the real cross section at large pT.” BNL-Seminar-Dec 7, 2004

  4. CCR at the CERN-ISRDiscovery of high pT production in p-p F.W. Busser, et al., CERN, Columbia, Rockefeller Collaboration Phys. Lett. 46B, 471 (1973) Bj scaling  BBK scaling • e-6pT breaks to a power law at high pT with characteristic s dependence • Large rate indicates that partons interact strongly (>> EM) with other. • Data follow BBK scaling but with n=8!, not n=4 as expected for QED BNL-Seminar-Dec 7, 2004

  5. BBK scaling with n=8, not 4 Inspires Constituent Interchange Model Berman, Bjorken, Kogut, PRD4, 3388 (1971) xT=2pT/s n=4 for QED or vector gluon n=8 for quark-meson scattering by the exchange of a quark CIM-Blankenbecler, Brodsky, Gunion, Phys.Lett.42B,461(1972) BNL-Seminar-Dec 7, 2004

  6. State of the Art Fermilab 1977 D. Antreasyan, J. Cronin, et al., PRL 38, 112 (1977) Beautiful xT scaling at all 3 fixed target energies with n=8 Totally Misleading--Not CIM or QCD but kT BNL-Seminar-Dec 7, 2004

  7. CCOR 1978--Discovery of “REALLY high pT>7 GeV/c” at ISR CCOR A.L.S. Angelis, et al, Phys.Lett. 79B, 505 (1978) See also A.G. Clark, et al Phys.Lett 74B, 267 (1978) • Agrees with CCR, CCRS (Busser) data for pT < 7 GeV/c. • Disagrees with CCRS fit pT > 7 GeV/c • New fit is: BNL-Seminar-Dec 7, 2004

  8. QCD: Cahalan, Geer, Kogut, Susskind, PRD11, 1199 (1975) n(xT, s) WORKS n5=4++ Same data Ed3/dp3(xT) ln-ln plot BNL-Seminar-Dec 7, 2004

  9. ISR Expt’s more interested in n(xT,s) than absolute cross section Athens BNL CERN Syracuse Collaboration, C.Kourkoumelis, et al Phys.Lett. 84B, 279 (1979) But n(xT,s) agrees cross sections vary by factor of 2 BNL-Seminar-Dec 7, 2004

  10. Status of ISR single particle measurements 1978 kT is what made n=4++ n=8 BNL-Seminar-Dec 7, 2004

  11. Status of QCD Theory in 1978 BNL-Seminar-Dec 7, 2004

  12. C A a c X b B d LO-QCD in 1 slide BNL-Seminar-Dec 7, 2004

  13. QCD and Jets are now a cornerstone of the standard model • Incredibly at the famous Snowmass conference in July 1982, many if not most people were skeptical • The International HEP conference in Paris, three weeks later, changed everything. BNL-Seminar-Dec 7, 2004

  14. THE UA2 Jet-Paris 1982 From 1980--1982 most high energy physicists doubted jets existed because of the famous NA5 ET spectrum which showed NO JETS. This one event changed everybody’s opinion. BNL-Seminar-Dec 7, 2004

  15. CCOR Jets after 8 orders of mag. PL 126B, 132 (1983) Also Paris 1982-Jets in ET distribution 1980 ICHEP-NA5 No Jets 7 orders of magnitude BNL-Seminar-Dec 7, 2004

  16. Also Paris1982-first measurement of QCD subprocess angular distribution using 0-0 correlations DATA: CCOR NPB 209, 284 (1982) QCD BNL-Seminar-Dec 7, 2004

  17. The leading-particle effect a.k.a. trigger bias • Due to the steeply falling power-law spectrum of the scattered partons, the inclusive particle pT spectrum is dominated by fragments biased towards large z. This was unfortunately called trigger bias by M. Jacob and P. Landshoff, Phys. Rep. 48C, 286 (1978) although it has nothing to do with a trigger. Fragment spectrum given pTq Fragment spectrum given pT BNL-Seminar-Dec 7, 2004

  18. <ztrig> measured at ISR DATA: CCOR NPB 209, 284 (1982) ztrig=pTtrig/pTjet pTjet=pTtrig+1.5px • <ztrig> ~ 0.8-0.9 at ISR, n~ 11 • <ztrig> xT scales 0.3 GeV/c<pT || <0.7 ||< 60o BNL-Seminar-Dec 7, 2004

  19. pTt pT pout=pT sin xE pTt How everything you want to know about JETS was measured with 2-particle correlations CCOR, A.L.S.Angelis, et al Phys.Lett. 97B, 163 (1980) PhysicaScripta 19, 116 (1979) pTt > 7 GeV/c vs pT BNL-Seminar-Dec 7, 2004

  20. kT is not a parameter, it can be measured BNL-Seminar-Dec 7, 2004

  21. Feynman Field & Fox to the rescue BNL-Seminar-Dec 7, 2004

  22. pTt pT pout=pT sin xE pTt jT, kT, xE, pout definitions all in plane transverse to beam direction pout2 =xE22  kTy2 +  jTy2+  jTy2 • jT is parton fragmentation transverse momentum • kT is transverse momentum of a parton in a proton (2 protons) • xE=-pTpTt/|pTt|2 represents away jet fragmentation z • pout is component of away pT perpendicular to trigger pTt BNL-Seminar-Dec 7, 2004

  23. xE distribution measures fragmentation fn. xE ~ z/<ztrig> <ztrig>=0.85 measured* Dq(z)~e-6z • independent of pTt See M. Jacob’s talk EPS 1979 Geneva *but we did learn something new on this issue in PHENIX. BNL-Seminar-Dec 7, 2004

  24. CCOR <|pout|>2 vs x2E pout2 =xE22  kTy2 +  jTy2+  jTy2 CCOR, A.L.S.Angelis, et al Phys.Lett. 97B, 163 (1980) BNL-Seminar-Dec 7, 2004

  25. jT is constant-independent of pTt and s Characteristic of jet fragmentation • it took the e+ e- people several more years to get this correct---because they didn’t understand the seagull effect: (jT < pT) BNL-Seminar-Dec 7, 2004

  26. kT varies with pTt and s--not intrinsic BNL-Seminar-Dec 7, 2004

  27. We did (re)learn a few things at RHIC pout2 =xE22  kTyzt 2 +  jtTy2+  jaTy2 FFF’s formula was really: Jan Rak discovered this by insisting to rederive all the formulas, but it was in FFF’s paper. <zt> depends on pTa as well as pTt but may be too confusing for this talk CCOR NPB 209, 284 (1982) BNL-Seminar-Dec 7, 2004

  28. kT Phenomenology-I BNL-Seminar-Dec 7, 2004

  29. L.Apanasevich, et al, PR D59 074007 (1999) kT Phenomenology-II BNL-Seminar-Dec 7, 2004

  30. Early theoretical attempt to understand kT  <kT>=3.5/2=2.5 GeV/c • Modern work falls under the subject “resummation” BNL-Seminar-Dec 7, 2004

  31. Gaussian Integrals-I Nicely covered in L.Apanasevich, et al, PR D59 074007 (1999), covered here for convenience and completeness BNL-Seminar-Dec 7, 2004

  32. Gaussian Integrals--II BNL-Seminar-Dec 7, 2004

  33. Conclusions from ISR BNL-Seminar-Dec 7, 2004

  34. A puzzle from RHIC: why does NLO-QCD fit the p-p 0 spectrum with no kT? Data: PHENIX PRL 91, 241803 (2003) Theory: W.Vogelsang, see B.Jager, A.Schafer, M.Stratmann,W.Vogelsang PRD67,054005(2003) BNL-Seminar-Dec 7, 2004

  35. Note Gaussian shape, no power-law tail! kT and NLO are distinct---e.g. Drell Yan J.K.Yoh, et al, CFS, PRL 41, 684 (1978) A.L.S.Angelis, et al, CCOR, PLB 87, 398 (1979) A.S.Ito, et al, PRD23,604 (1981) BNL-Seminar-Dec 7, 2004

  36. <pT>(=2kT) vs s in Drell-Yan CMOR, NPB348, 1 (1991) BNL-Seminar-Dec 7, 2004

  37. N.B.-- Lots of Drell-Yan Measurements at Colliders: all you need is luminosity. ISR CDF BNL-Seminar-Dec 7, 2004

  38. kT and NLO II In George Sterman’s words 12/3/04: ``Every final state in hard scattering carries the imprint of QCD dynamics at all scales.’’ • For the only measurement of kT in direct photon production that I know of, see UA2 Collaboration, ZPC 41, 395 (1988) • They also measure cos* distribution for + Jet production and show that it is flatter than Jet+Jet (Compton-like). • L.Apanasevich, et al, PR D59 074007 (1999) doesn’t measure kT they derive it by kT-smearing NLO cross predicitons to agree with measurements. See also hep-ex/0407011. BNL-Seminar-Dec 7, 2004

  39. Application to RHIC BNL-Seminar-Dec 7, 2004

  40. p-p Thermally-shaped Soft Production: e-6pT indep. s Hard Scattering -- varies with s RHIC pp spectra s=200 GeV nicely illustrate hard scattering phenomenology • Good agreement with NLO pQCD • this is no surprise for `old timers’ (like me) since as I just explained, single particle inclusive spectra were what proved QCD in the late 1970’s before jets. • Reference for A+A and p+A spectra • p0 measurement in same experiment allows us the study of nuclear effect with less systematic uncertainties. p0 PHENIX (p+p) PRL 91, 241803 (2003) BNL-Seminar-Dec 7, 2004

  41. Inclusive single hadron high pT spectra in p-p all s BNL-Seminar-Dec 7, 2004

  42. xT scaling in p-p collisions x~0.05-0.10 xT BNL-Seminar-Dec 7, 2004

  43. -A DIS at AGS (1973)--Hard-Scattering is pointlike M. May, et al, (M.Murtagh, T.Kirk, MJT) PRL 35, 407 (1975) BNL-Seminar-Dec 7, 2004

  44. M. May, et al., BNL-Seminar-Dec 7, 2004

  45. High pT in A+B collisions---TAB Scaling view along beam axis looking down • For point-like processes, the cross section in p+A or A+B collisions compared to p-p is simply proportional to the relative number of pointlike encounters • A for p+A, AB for A+B for the total rate • TAB the overlap integral of the nuclear profile functions, as a function of impact parameter b BNL-Seminar-Dec 7, 2004

  46. The anomalous nuclear enhancement a.k.a. the Cronin effect-- due to multiple scattering of initial nucleons (or constituents) What really Happens: for p+A RA > 1! • Known since 1975 that yields increase as A,  > 1 =1.150.01 • J.W. Cronin et al.,Phys. Rev. D11, 3105 (1975) • D. Antreasyan et al.,Phys. Rev. D19, 764 (1979) BNL-Seminar-Dec 7, 2004

  47. For A+A: RAA1 before RHIC • The importance of comparison data! BNL-Seminar-Dec 7, 2004

  48. RAA at RHIC--Suppression to at least 10 GeV/c Peripheral AuAu - consistent with Ncoll scaling (large systematic error) Binary scaling Factor 5 Large suppression in central AuAu - Never seen previously!! A breakdown of QCD??? Participant scaling PHENIX, PRL 91 (2003) 072301 BNL-Seminar-Dec 7, 2004

  49. PHENIXSemi-Inclusive 0Au+Au sNN=130 and 200 GeVvs pT Peripheral 60 -- 80% Central 0-10% S.S.Adler, et al, PRC 69, 034910 (2004) BNL-Seminar-Dec 7, 2004

  50. Same data vs xT on log-log plot BNL-Seminar-Dec 7, 2004

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