From Bjorken Scaling to p QCDExperimental techniques from

From Bjorken Scaling to p. QCD--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 1

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

BBK 1971 S. M. Berman, J. D. Bjorken and J. B. Kogut, Phys. Rev. D 4, 3388 (1971) • BBK calculated for p+p collisions, the inclusive reaction A+B C + X when particle C has p. T>> 1 Ge. V/c • The charged partons of DIS must scatter electromagnetically “which may be viewed as a lower bound on the real cross section at large p. T. ” BNL-Seminar-Dec 7, 2004 3

CCR at the CERN-ISR Discovery of high p. T production in p-p F. W. Busser, et al. , CERN, Columbia, Rockefeller Collaboration Phys. Lett. 46 B, 471 (1973) Bj scaling BBK scaling • e-6 p. T breaks to a power law at high p. T 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 4

BBK scaling with n=8, not 4 Inspires Constituent Interchange Model Berman, Bjorken, Kogut, PRD 4, 3388 (1971) x. T=2 p. T/ 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. 42 B, 461(1972) BNL-Seminar-Dec 7, 2004 5

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

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

n(x. T, s) WORKS n 5=4++ QCD: Cahalan, Geer, Kogut, Susskind, PRD 11, 1199 (1975) Same data Ed 3 /dp 3(x. T) ln-ln plot BNL-Seminar-Dec 7, 2004 8

ISR Expt’s more interested in n(x. T, s) than absolute cross section Athens BNL CERN Syracuse Collaboration, C. Kourkoumelis, et al Phys. Lett. 84 B, 279 (1979) But n(x. T, s) agrees cross sections vary by factor of 2 BNL-Seminar-Dec 7, 2004 9

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

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

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

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 13

THE UA 2 Jet-Paris 1982 From 1980 --1982 most high energy physicists doubted jets existed because of the famous NA 5 ET spectrum which showed NO JETS. This one event changed everybody’s opinion. BNL-Seminar-Dec 7, 2004 14

Also Paris 1982 -Jets in ET distribution CCOR Jets after 8 orders of mag. PL 126 B, 132 (1983) 1980 ICHEP-NA 5 No Jets 7 orders of magnitude BNL-Seminar-Dec 7, 2004 15

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

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

<ztrig> measured at ISR DATA: CCOR NPB 209, 284 (1982) ztrig=p. Ttrig/p. Tjet=p. Ttrig+1. 5 px 0. 3 Ge. V/c<p. T | | <0. 7 | |< 60 o • <ztrig> ~ 0. 8 -0. 9 at ISR, n~ 11 • <ztrig> x. T scales BNL-Seminar-Dec 7, 2004 18

How everything you want to know about JETS was measured with 2 -particle correlations CCOR, A. L. S. Angelis, et al Phys. Lett. 97 B, 163 (1980) Physica. Scripta 19, 116 (1979) p. Tt p. T pout=p. T sin x. E p. Tt > 7 Ge. V/c vs p. T BNL-Seminar-Dec 7, 2004 19

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

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

j. T, k. T, x. E, pout definitions all in plane transverse to beam direction p. Tt p. T pout=p. T sin x. E p. Tt pout 2 =x. E 2 2 k. Ty 2 + j. Ty 2 • j. T is parton fragmentation transverse momentum • k. T is transverse momentum of a parton in a proton (2 protons) • x. E=-p. Tt/|p. Tt|2 represents away jet fragmentation z • pout is component of away p. T perpendicular to trigger p. Tt BNL-Seminar-Dec 7, 2004 22

x. E distribution measures fragmentation fn. x. E ~ z/<ztrig>=0. 85 measured* Dq (z)~e-6 z • independent of p. Tt See M. Jacob’s talk EPS 1979 Geneva * but we did learn something new on this issue in PHENIX. BNL-Seminar-Dec 7, 2004 23

CCOR <|pout|>2 vs x 2 E pout 2 =x. E 2 2 k. Ty 2 + j. Ty 2 CCOR, A. L. S. Angelis, et al Phys. Lett. 97 B, 163 (1980) BNL-Seminar-Dec 7, 2004 24

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

k. T varies with p. Tt and s--not intrinsic BNL-Seminar-Dec 7, 2004 26

We did (re)learn a few things at RHIC • FFF’s formula was really: pout 2 =x. E 2 2 k. Ty zt 2 + jt. Ty 2 + ja. Ty 2 • Jan Rak discovered this by insisting to rederive all the formulas, but it was in FFF’s paper. • <zt> depends on p. Ta as well as p. Tt but may be too confusing for this talk CCOR NPB 209, 284 (1982) BNL-Seminar-Dec 7, 2004 27

k. T Phenomenology-I BNL-Seminar-Dec 7, 2004 28

k. T Phenomenology-II L. Apanasevich, et al, PR D 59 074007 (1999) BNL-Seminar-Dec 7, 2004 29

Early theoretical attempt to understand k. T <k. T>=3. 5/ 2=2. 5 Ge. V/c • Modern work falls under the subject “resummation” BNL-Seminar-Dec 7, 2004 30

Gaussian Integrals-I Nicely covered in L. Apanasevich, et al, PR D 59 074007 (1999), covered here for convenience and completeness BNL-Seminar-Dec 7, 2004 31

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

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

A puzzle from RHIC: why does NLO-QCD fit the p-p 0 spectrum with no k. T? Data: PHENIX PRL 91, 241803 (2003) Theory: W. Vogelsang, see B. Jager, A. Schafer, M. Stratmann, W. Vogelsang PRD 67, 054005(2003) BNL-Seminar-Dec 7, 2004 34

k. T 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) Note Gaussian shape, no power-law tail! A. S. Ito, et al, PRD 23, 604 (1981) BNL-Seminar-Dec 7, 2004 35

<p. T>(= 2 k. T) vs s in Drell-Yan CMOR, NPB 348, 1 (1991) BNL-Seminar-Dec 7, 2004 36

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

k. T 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 k. T in direct photon production that I know of, see UA 2 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 D 59 074007 (1999) doesn’t measure k. T they derive it by k. T-smearing NLO cross predicitons to agree with measurements. See also hep-ex/0407011. BNL-Seminar-Dec 7, 2004 38

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

RHIC pp spectra s=200 Ge. V nicely illustrate hard scattering phenomenology p-p • Good agreement with NLO p. QCD ü 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. 0 Thermallyshaped Soft Production: e -6 p. T indep. s • Reference for A+A and p+A spectra ü Hard Scattering -varies with s 0 measurement in same experiment allows us the study of nuclear effect with less systematic uncertainties. PHENIX (p+p) PRL 91, 241803 (2003) BNL-Seminar-Dec 7, 2004 40

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

x. T scaling in p-p collisions x~0. 05 -0. 10 x. T BNL-Seminar-Dec 7, 2004 42

-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 43

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

High p. T 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 ü A for p+A, AB for A+B for the total rate ü TAB the overlap integral of the nuclear profile functions, as a function of impact parameter b BNL-Seminar-Dec 7, 2004 45

What really Happens: for p+A RA > 1! The anomalous nuclear enhancement a. k. a. the Cronin effect-due to multiple scattering of initial nucleons (or constituents) • Known since 1975 that yields increase as A , > 1 =1. 15 0. 01 • J. W. Cronin et al. , Phys. Rev. D 11, 3105 (1975) • D. Antreasyan et al. , Phys. Rev. D 19, 764 (1979) BNL-Seminar-Dec 7, 2004 46

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

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

PHENIX Semi. Inclusive 0 Au+Au s. NN=130 and 200 Ge. V vs p. T Peripheral 60 -- 80% Central 0 -10% S. S. Adler, et al, PRC 69, 034910 (2004) BNL-Seminar-Dec 7, 2004 49

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

n(x. T) point-by-point 200/130 • 0 x. T scales in both peripheral and central Au+Au with same value of n=6. 3 as in p-p • (h+ + h-)/2 x. T scales in peripheral same as p-p but difference between central and peripheral is significant BNL-Seminar-Dec 7, 2004 51

x. T scaling of direct in p-p PHENIX preliminary, K. Okada, H. Torii, et al, SPIN 2004, JPS 2004 BNL-Seminar-Dec 7, 2004 52

Recall 0: n=5. 1 works better for x. T> 0. 2 n=6. 3 n=5. 1 BNL-Seminar-Dec 7, 2004 53

x. T scaling with Jets at the Tevatron a failure of QCD? Ratio of Scaled Cross Sections 630/1800 • Exp’t J. Huston, Proc. ICHEP 98, World Scientific also see CDF qcd www pages and G. C. Blazey & B. L. Flauger, ARNPS 49, 633 (99) n 4= 0. 448 n=4. 45 • Theory n 4= 0. 559 n=4. 56 • Either just outside or just touching the systematic errors? BNL-Seminar-Dec 7, 2004 54

BNL-Seminar-Dec 7, 2004 55

Backup with PHENIX highlights BNL-Seminar-Dec 7, 2004 56

Central Spectrum is suppressed---is this due to a shift caused by energy loss central Ncoll = 975 94 TAA = 22. 8 1. 6/mb BNL-Seminar-Dec 7, 2004 57

RAA : High PT Suppression to at least 10 Ge. V/c Peripheral Au. Au - consistent with Ncoll scaling (large systematic error) Binary scaling Factor 5 Large suppression in central Au. Au - close to participant scaling at high PT Participant scaling PRL 91 (2003) 072301 BNL-Seminar-Dec 7, 2004 58

Cronin effect observed in d+Au at RHIC s. NN=200 Ge. V PHENIX preliminary 0 d+Au vs centrality for DNP 2003 BNL-Seminar-Dec 7, 2004 59

Nuclear modification factor: s. NN dependence for A+B collisions CERN: Pb+Pb ( s. NN ~ 17 Ge. V), + ( s. NN ~31 Ge. V): all previous msmts B+A-Cronin enhancement RAA ~ 2. 0 A. L. S. Angelis PLB 185, 213 (1987) WA 98, EPJ C 23, 225 (2002) PHENIX, PRL 88 022301 (2002) D. d'E. PHENIX Preliminary QM 2002 RAA ~1. 5 RAA ~ 0. 4 RAA~0. 2 Ncollision scaling Npart scaling RHIC Au+Au s. NN=130 and 200 Ge. V HUGE SUPPRESSION---Major Discovery 2001 -2 BNL-Seminar-Dec 7, 2004 60

Spectra are suppressed for more central collisions--is this due to a shift caused by energy loss? • RAA(p. T)=constant for p. T> 4 • d /p. Tdp. T is p. T-8. 1 • p. T for d /dp. T BNL-Seminar-Dec 7, 2004 61

|k. Ty| from pp and d. Au k. T-broadening increases with p. Ttrig as as at lower s no difference in d. Au and pp! z =0. 75 taken as constant BNL-Seminar-Dec 7, 2004 need lots more data in both pp and p(d)+Au 62

|j. Ty| and z |k. Ty| in Au+Au PHENIX preliminary QM 2004 (2. 5 p. Ttrigg 4. 0) (1. 0 p. Tassoc 2. 5) (3. 0 p. Ttrigg 5. 0) (1. 5 p. Tassoc 3. 0) pp <z><|k. Ty|> pp <|j. Ty|> There seems to be significant broadening of the away-side correlation peak which persists also at somewhat higher p. T range. BNL-Seminar-Dec 7, 2004 63

UA 2 results on cos * and k. T in direct R. Ansari, et al, UA 2, ZPC 41, 395 (1988) BNL-Seminar-Dec 7, 2004 64