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

From the ISR to RHIC--- Measurements of Hard Scattering and Jets using Inclusive Single Particle Production and 2-Particle Correlations. M. J. Tannenbaum Brookhaven National Laboratory Upton, NY 11973 USA.

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

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  1. From the ISR to RHIC---Measurements of Hard Scattering and Jets using Inclusive Single Particle Production and 2-Particle Correlations M. J. Tannenbaum Brookhaven National Laboratory Upton, NY 11973 USA Correlations and Fluctuations in Relativistic Nuclear Collisions, MIT April 21-23, 2005 MIT-Correlations-April 22, 2005

  2. In 1998 at the QCD workshop in Paris, Rolf Baier asked me whether jets could be measured in Au+Au collisions because he had a prediction of a QCD medium-effect on colored partons in a hot-dense-medium with lots of unscreened color charge. • As the expected energy in a typical jet cone BDMPS 1997-1998 • is  R2 x1/ 2 x dET/d= R2/2 x dET/d ~ 300 GeV for R=1 at sNN=200 GeV where the maximum Jet energy is 100 GeV, Jets can not be reconstructed in Au+Au central collisions at RHIC. • But hard-scattering can be well studied by single inclusive and 2-particle correlation measurements as it was discovered at the CERN ISR in the 1970’s • And it just so happened that the PHENIX detector was designed to trigger, measure and separate  and 0 out to pT> 25 GeV/c ! MIT-Correlations-April 22, 2005

  3. Phys. Rev. 179, 1547 (1969) Phys. Rev. 185, 1975 (1969) Bjorken Scaling in Deeply Inelastic Scattering and the Parton Model---1968 MIT-Correlations-April 22, 2005

  4. 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.” MIT-Correlations-April 22, 2005

  5. 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 MIT-Correlations-April 22, 2005

  6. 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) MIT-Correlations-April 22, 2005

  7. 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 MIT-Correlations-April 22, 2005

  8. 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: MIT-Correlations-April 22, 2005

  9. QCD: Cahalan, Geer, Kogut, Susskind, PRD11, 1199 (1975) n(xT, s) WORKS n5=4++ Same data Ed3/dp3(xT) ln-ln plot MIT-Correlations-April 22, 2005

  10. 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 MIT-Correlations-April 22, 2005

  11. Status of ISR single particle measurements 1978 kT is what made n=4++ n=8 MIT-Correlations-April 22, 2005

  12. Status of QCD Theory in 1978 MIT-Correlations-April 22, 2005

  13. C A a c X b B d LO-QCD in 1 slide MIT-Correlations-April 22, 2005

  14. 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. MIT-Correlations-April 22, 2005

  15. 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. MIT-Correlations-April 22, 2005

  16. 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 MIT-Correlations-April 22, 2005

  17. Also Paris1982-first measurement of QCD subprocess angular distribution using 0-0 correlations DATA: CCOR NPB 209, 284 (1982) QCD MIT-Correlations-April 22, 2005

  18. 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 MIT-Correlations-April 22, 2005

  19. <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 MIT-Correlations-April 22, 2005

  20. 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 MIT-Correlations-April 22, 2005

  21. kT is not a parameter, it can be measured MIT-Correlations-April 22, 2005

  22. Feynman Field & Fox to the rescue MIT-Correlations-April 22, 2005

  23. 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 MIT-Correlations-April 22, 2005

  24. 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. MIT-Correlations-April 22, 2005

  25. 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) MIT-Correlations-April 22, 2005

  26. 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) MIT-Correlations-April 22, 2005

  27. kT varies with pTt and s--not intrinsic MIT-Correlations-April 22, 2005

  28. 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) MIT-Correlations-April 22, 2005

  29. kT Phenomenology-I MIT-Correlations-April 22, 2005

  30. L.Apanasevich, et al, PR D59 074007 (1999) kT Phenomenology-II MIT-Correlations-April 22, 2005

  31. Early theoretical attempt to understand kT  <kT>=3.5/2=2.5 GeV/c • Modern work falls under the subject “resummation” MIT-Correlations-April 22, 2005

  32. Gaussian Integrals-I Nicely covered in L.Apanasevich, et al, PR D59 074007 (1999), covered here for convenience and completeness MIT-Correlations-April 22, 2005

  33. Gaussian Integrals--II MIT-Correlations-April 22, 2005

  34. Conclusions from ISR MIT-Correlations-April 22, 2005

  35. 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) MIT-Correlations-April 22, 2005

  36. 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) MIT-Correlations-April 22, 2005

  37. <pT>(=2kT) vs s in Drell-Yan CMOR, NPB348, 1 (1991) MIT-Correlations-April 22, 2005

  38. N.B.-- Lots of Drell-Yan Measurements at Colliders: all you need is luminosity. ISR CDF MIT-Correlations-April 22, 2005

  39. 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. MIT-Correlations-April 22, 2005

  40. Application to RHIC MIT-Correlations-April 22, 2005

  41. 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) MIT-Correlations-April 22, 2005

  42. Inclusive single hadron high pT spectra in p-p all s MIT-Correlations-April 22, 2005

  43. xT scaling in p-p collisions x~0.05-0.10 xT MIT-Correlations-April 22, 2005

  44. -A DIS at AGS (1973)--Hard-Scattering is pointlike M. May, et al, (M.Murtagh, T.Kirk, MJT) PRL 35, 407 (1975) MIT-Correlations-April 22, 2005

  45. M. May, et al., MIT-Correlations-April 22, 2005

  46. 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 MIT-Correlations-April 22, 2005

  47. 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) MIT-Correlations-April 22, 2005

  48. For A+A: RAA1 before RHIC • The importance of comparison data! MIT-Correlations-April 22, 2005

  49. 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 MIT-Correlations-April 22, 2005

  50. 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) MIT-Correlations-April 22, 2005

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