unresolved issues in hard- scattering at rhic

ETD-HIC2007 M. J. Tannenbaum 1/31

Unresolved issues in hard- Unresolved issues in hard- scattering at RHICscattering at RHIC

M. J. TannenbaumBrookhaven National Laboratory

Upton, NY 11973 USAEarly Time Dynamics in Heavy Ion Collisions

McGill University Montreal, Canada

July 16-19, 2007


BDMPS 1997-1998BDMPS 1997-1998In 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 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.

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R = (Δη )2 + (Δφ)2

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: “Everything you want to know about JETS can be measured with two particle correlations.”

And it just so happened that the PHENIX detector was designed to trigger, measure and separate and 0 out to pT> 25 GeV/c !


““Everything” was correct except that in p-p correlations the Everything” was correct except that in p-p correlations the away side xaway side xEE distribution does not measure the fragmentation distribution does not measure the fragmentation function* It measures the ratio of pfunction* It measures the ratio of pTT of away jet to trigger jet of away jet to trigger jet

Corrected for acceptance

N

A

€

ˆ x h =1.0

€

ˆ x h = 0.8

kT smearing

n is the power of invariant pTt spectrum

trigger (pTt) away (pTa) Ratio of pTa to pTt of away side to trigger particles

Ratio of jet transverse momenta

* contradicts Feynman, Field and Fox, Nucl. Phys. B128(1977)1-65

PHENIX PRD74, 072002 (2006)


19% norm uncertainty

p-p collisions at RHIC: p-p collisions at RHIC: 00 production (PHENIX) production (PHENIX)

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e−5.6 pT

No surprise (to me) that NLO pQCD agrees with dataarXiv:0704.3599v1 [hep-ex]


CCOR A.L.S. Angelis, et al, Phys.Lett. 79B, 505 (1978)

p-p

ISR ISR 00 vs RHIC p-p vs RHIC p-p RHIC pp vs AuAu RHIC pp vs AuAu

Nuclear Modification Factor

0 are suppressed in Au+Au eg 200 GeV

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RAA ( pT ) =d2NAA

π /dpT dyNAAinel

TAA d2σ ppπ /dpT dy0 invariant cross section in p-p at s=200 GeV is a pure

power law for pT > 3 GeV/c, n=8.100.05. New 62.4 GeV measurement agrees with CCOR shifted up in pT by 3.3%


THE major discoveries at RHICTHE major discoveries at RHIC

1) 0 suppressed by a factor of 5 compared to point-like scaling for 3< pT<20 GeV/c

2)h and 0 behave differently at intermediate pT 2--6 GeV/c

latest preprint nucl-ex/0611007

Discovery-PHENIX PRL 88 (2002) 022301

p/ ratio much larger than from jet fragmentation: The Baryon

Anomaly-still not understood ps: If this is ‘recombination’ QGP: Fries,Muller, Nonaka PRL 90 202303 (2003)

PHENIX PRL 91(2003) 172301


Anisotropic (Elliptic) Transverse Flow--an Anisotropic (Elliptic) Transverse Flow--an Interesting complication in AA collisionsInteresting complication in AA collisions

px

py

• spatial anisotropy momentum anisotropy

x

yz

Reaction Plane

x

y

p

patan=φ

•Perform a Fourier decomposition of the momentum space particle distributions in the x-y plane

v2 is the 2nd harmonic Fourier coefficient

Directed flow zero at midrapidity

Elliptical flow dominant at midrapidity


Universal Scaling

Don’t forget large asimuthal isotropy Don’t forget large asimuthal isotropy is it a perfect liquid?is it a perfect liquid?

Nice plots from Arkadij Taranenko-PHENIX-QM2006

D.Teaney,

PRC68, 034913 (2003)

Any viscosity damps v2 fpr pT> 1.7 GeV/c


Direct are not suppressed. 0 and suppressed even at high pT

Implies a strong medium effect (energy loss) since not affected. Suppression is flat at high pT. Are data flatter than theory?

Status of RStatus of RAAAA in AuAu at in AuAu at ssNNNN=200 GeV QM05=200 GeV QM05

MJT


Comparison with theory including systematic errorComparison with theory including systematic error

⎥⎥

⎦

⎤

⎢⎢

⎣

⎡+

−++=− ∑

=

2

12

222 )(ln2 ε

σ

μσσεn

i i

icbi iy

L

Model values from C.Loizides hep-ph/0608133v2

Presented at QM2006. Journal article to be submitted soon.

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{−2lnL}min −{−2lnL}min−overall

2

1

= 2(1)


QM05-06: Direct eQM05-06: Direct e in Au+Au indicate a theoretical crisis in Au+Au indicate a theoretical crisis

heavy quarks suppressed the same as light quarks, and they flow, but less. This disfavors the energy loss by gluon bremsstrahlung in medium hypothesis but brings string theorists into the game.

p-p beautiful agreement of e with c b production PHENIX PRL97(2006)252002

Au+Au PHENIX PRL 98 (2007)172301

Au+Aup-p


RRAAAA 00 in AuAu in AuAu ssNNNN=200 GeV vs. Reaction Plane =200 GeV vs. Reaction Plane to probe details of the theory-learn something new!to probe details of the theory-learn something new!

L

PHENIX nucl-ex/0611007

(submitted to Phys. Rev. C.)

Little/no energy loss for L < 2 fm

L = distance from edge to center of participants calculated in Glauber model

RAA is absolute, v2 is relative so no hint of this in v2 measurements. This result also suggests that v2 for pT>2GeV/c is due to anisotropic energy loss not flow.

RAA() vs. centrality varies density of and distance through medium

3 < pT < 5 GeV/c


Direct Direct with respect to the reaction plane with respect to the reaction planeTurbide, Gale & Fries, PRL 96 (2006) 032303 predict that if jet(parton) suppression is due to g+q-->g+q (+g) in the medium then the reaction g+q--> +q should create a source of direct photons proportional to the distance traversed through the medium-fewer on the mid-plane more vertical, the opposite of 0 and other hadronic jet

fragments

PHENIX preliminary

Not seen to within errors. Same sign of v2 for and 0 more likely from present data.


CGC?CGC?‘Monojets’ in d+Au?‘Monojets’ in d+Au?

“We see how Carlo Rubbia wheels and deals in order to raise multimillion-dollar funding for his work, and to publish his results first so as to maintain his dominance in the field and secure the Nobel Prize. We also witness Rubbia’s anxious futile attempts, once he has won the Nobel Prize, to prove a highly speculative new theory called supersymmetry”.


Brahms RBrahms RdAudAu, R, RCPCP in d+Au vs rapidity in d+Au vs rapidity

BIG effect in RCP; some tendency in RdAu. BRAHMS PRL93 242303


d+Au is it CGC?d+Au is it CGC?`Monojets’? `Monojets’? correlations correlations

widths and conditional yields the same for triggers in all 3 spectrometers for pp and dAu

trigger

away

PHENIX PRL 96 (2006) 222301


STARSTAR

Statistical errors only

• are suppressed at small <xF> and <pT,>

Spp-SdAu= (9.0 ± 1.5) %

consistent with CGC picture

• are consistent in d+Au and p+p at larger <xF> and <pT,>

as expected by HIJING

25<E<35GeV

35<E<45GeV

Fixed as

E & pT grows

STAR Preliminary

STAR Preliminary

STAR Preliminary

STAR Preliminary

STAR-Correlations in d+Au PRL 97, 152302 (2006)


Correlations-one of the first definitive resultsCorrelations-one of the first definitive results

Trigger mesons and baryons in the region of the baryon anomaly both show the same trigger (near) side and away side jet structure. This ‘kills’ the elegant recombination model of the baryon anomaly

PHENIX PRC 71 051902 2.4<pTt<4 GeV/c 1.7< pTa<2.5 GeV/c


STAR PRL95 showed that the away jet really STAR PRL95 showed that the away jet really didn’t vanish--it just lost energy and wideneddidn’t vanish--it just lost energy and widened

STAR-PRL91(2003)072304 4< pTt< 6 GeV/c 2<pTa<pTt

xEpTa/pTt~0.5

STAR-PRL95(2005)152301 4< pTt< 6 GeV/c 0.15<pTa<4 GeV/c xE pTa/pTt~0.04


Shape of xShape of xEE distribution depends on distribution depends on

and and nn but not on but not on bb

€

ˆ x h

€

ˆ x h

1.0

0.8

0.6

0.4

0.2

€

n = 8.1

Measured ratio of particles pTa/pTt xE

Ratio of jet transverse momenta

€

ˆ p Ta / ˆ p Tt ≡ ˆ x h

PHENIX PRD74, 072002 (2006)


I applied my xI applied my xEE formula to STAR PRL 95 yields formula to STAR PRL 95 yields

STAR, J. Adams, Fuqiang Wang, et al PRL 95, 152301 (2005)

4 < pTt < 6 GeV/c <pTt>=4.56 GeV/c pp, AuAu sNN=200 GeV

p+p

=1.0

AuAu 40-80

=0.75

AuAu00-05

=0.48€

ˆ x h

€

ˆ x h

€

ˆ x h

• Away jet /trigger jet ( ) decreases with increasing centrality

€

ˆ x h

€

ˆ p Ta

€

ˆ p Tt


Newer STAR data AuAu: PRL 97Newer STAR data AuAu: PRL 97

8 < pTt < 15 GeV/c <pTt>=9.38 GeV/c

Thanks to Dan Magestro for table of data points

STAR, J. Adams, D. Magestro, et al PRL 97, 162301 (2006)

PRL 97: narrow jets punch through for pTt>8 GeV/c

STAR PRL 97 data has much too flat shape, an apparent sharp break, and disagrees in normalization with STAR PRL95. Is it two components?


If this is punch-through due to tangential If this is punch-through due to tangential emission, why does it depend on pemission, why does it depend on pTT??

Tangential emission

We must carefully map out how this effect depends on pTt and pTa and particle type and angle to the reaction plane...


AuAu 200 0-5% like sign0.2< pT,1 pT,2< 0.4 GeV/c

Away side correlations in Au+Au much wider than in p-pAway side correlations in Au+Au much wider than in p-p

D

Away side distribution much wider in A+A than p-p in correlation fn. C() Subtraction of v2 (flow?) effect J() causes a dip at 180o which gives 2 peaks at D~1 radian independent of system and centrality for Npart >100. This is also seen for (auto) correlations of low pT particles. Is this the medium reaction to the passage of a color-charged parton? Stay tuned, much more study needed.

PHENIX AuAu PRL 98 (2007)

232302


The biggest result at QM2006??!The biggest result at QM2006??!

QM2006-QM2006-pp dir pp dir reference is run 5 msmt reference is run 5 msmt If RIf R

AAAA= R= RAA AA the whole concept the whole concept

of energy loss changes: perhaps of energy loss changes: perhaps no effect for pno effect for pTT>20 GeV >20 GeV

QM2005QM2005-I wanted to make a T-shirt-I wanted to make a T-shirtpp dir pp dir reference is pQCD reference is pQCD

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RAA ( pT ) =d2NAA

π /dpT dyNAAinel

TAA d2σ ppπ /dpT dy


Eskola et al. NPA696 (2001) 729

gluons in Pb / gluons in p

x

AntiShadowing

Shadowing

For Au+Au min bias direct For Au+Au min bias direct R RAAAA is simple is simpleAu+Au minimum bias at mid-rapidity

Do the structure function ratios actually drop by ~20% from x=0.1 to x=0.2?

Eskola,Kolhinen,Ruuskanen Nucl. Phys. B535(1998)351

100 xT


Central Collisions---no theory counterpart-yetCentral Collisions---no theory counterpart-yetAu+Au Central Collisions at mid-rapidity

Nobody has seriously measured nor calculated structure function ratios as a function of centrality!!!

Theorists, HELP!

100 xT

Very few attempts so far for structure function measurements or theory as a function of impact parameter: E665, ZPC 65, 225 (1995) Li and Wang, PLB 527, 85 (2002) Klein and Vogt PRL 91, 142301 (2003) Emel’yanov, et al. PRC 61, 044904 (2000) and references therein.

Experimentalists: RHIC p+A, eRHIC


What I still don’t understand-IWhat I still don’t understand-IAfter 6 runs at RHIC, many discoveries have been made in Au+Au collisions but there is much that is still not known or understood:• Is the nuclear modification factor RAA for 0 really constant at a factor of 5 suppression over the range 3< pT< 20 GeV/c which would occur for a constant-fractional energy loss analogous to bremsstrahlung, or does the suppression tend to vanish at larger pT? Is dE/dx constant or a constant fraction or something else?• Does RAA for direct- really approach that of 0 at large pT~20 GeV/c as indicated by preliminary data? If true this would argue that the suppression due to a medium effect vanishes at large pT> 20 GeV/c and the effect observed is due to the structure function. If this is confirmed, it would be VERY BAD for LHC.• The detailed mechanism of jet suppression due to interaction with the medium is not understood. It is not known whether partons lose energy continuously or discretely, whether they stop in the medium so that the only observed jet fragments are those emitted from the surface or whether partons merely lose energy exiting the medium such that those originating from the interior of the medium with initially higher pT are submerged (due to the steeply falling pT spectrum) under partons emitted at the surface which have not lost energy. In either case, there is a surface bias.


• The reason why heavy quarks appear to lose the same energy as light quarks is not understood. • It is not known whether a parton originating at the center of the medium can exit the medium without losing any energy. • It is not known where the energy from the absorbed jets or parton energy loss goes or how it is distributed.• The surface bias discussed above complicates the use of two-particle correlations of hard-scattered partons to probe the medium since detecting a particle from an away-side parton changes the surface bias of the trigger parton. This means that detection of both a trigger and away side particle is required in order to constrain the hard-scattering kinematics and the position of the origin of the hard-scattered parton-pair within the nuclear matter. Then, the main correlation information with relatively stable kinematics and origin is obtained by studying correlations with an additional 1 or two particles, i.e. a total of 3 or 4 particle correlations, which is much more complicated and requires much more data than the same studies in p+p collisions.

What I still don’t understand-IIWhat I still don’t understand-II


• The baryon anomaly, the increase of the p±/± ratio in the range 2<pT <6 GeV/c in Au+Au collisions from the value given by parton-fragmentation in this pT range in p+p collisions, is not understood. Elegant recombination models fail to explain the similar jet activity correlated to the p and triggers in this “intermediate” pT range. • The wide away-side non-identified hadron correlations for triggers in the intermediate range 2<pT <6 GeV/c in Au+Au collisions, with a possible dip at 180o which causes apparent peaks displaced by ~60o, is not understood. It could represent a Mach cone due to the analogy of a sonic-boom of the parton passing through the medium faster than the speed of sound, or it could indicate jets with large deflections. The effect may be related to the baryon anomaly, which occurs in this pT range; or the peaks, which are seen also for much softer trigger particles, may not be a hard-scattering effect. • The ridge is not understood. What causes it? What are its properties? How does it depend on pTt, angle to reaction plane etc? Why isn’t there an away-side ridge?• Finally, J/ suppression, which for more than 20 years has represented the gold-plated signature of deconfinement, is not understood.

What I still don’t understand-IIIWhat I still don’t understand-III


NA50 at SPS (0<y<1)PHENIX at RHIC (|y|<0.35)

Bar: uncorrelated errorBracket : correlated errorGlobal error = 12% is not shown

J/J/ Suppression--R Suppression--RAAAA

PHENIX mid-rapidity (e+e-) the same as PHENIX mid-rapidity (e+e-) the same as NA50!!!NA50!!!

Suppression increases at more forward rapidity PHENIX PRL 98, 232301 (2007)


ENDEND


DATA: CCOR NPB 209, 284 (1982)

ICHEP-Paris1982: first measurement of QCD ICHEP-Paris1982: first measurement of QCD subprocess angular distribution using subprocess angular distribution using 00--00

correlations-Rutherford Scattering of quarkscorrelations-Rutherford Scattering of quarks

QQCCDDp-p


00 R RAAAA 62.4 GeV : NEW!! 62.4 GeV : NEW!!

• “Old”: p+p reference from fit to ISR data-good effort, bad idea. • “New”: p+p reference measured at RHIC!• Suppression in 62.4 GeV is now more similar to that for 200 GeV


Comparison with theory including systematic error-2Comparison with theory including systematic error-2

⎥⎥

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⎤

⎢⎢

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⎡+

−++=− ∑

=

2

12

222 )(ln2 ε

σ

μσσεn

i i

icbi iy

L


€

{−2lnL}min −{−2lnL}min−overall = 2(1)

I.Vitev, PLB 639, 38 (2006)


Comparison with theory including systematic error-3Comparison with theory including systematic error-3

⎥⎥

⎦

⎤

⎢⎢

⎣

⎡+

−++=− ∑

=

2

12

222 )(ln2 ε

σ

μσσεn

i i

icbi iy

L


€

{−2lnL}min −{−2lnL}min−overall = 2(1)

Wicks, Horowitz, Djordjevic,Gyulassy NPA783, 493 (2007)


The leading-particle effect a.k.a. trigger biasThe 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 pTt is weighted to high zt by zt

n-2

( <z>=1/b )


Continuing as in PRD Continuing as in PRD 7474, 072002 (2006), 072002 (2006)We can integrate over the trigger jet zt and find the inclusive pion cross section:

Bjorken parent-child relation: parton and particle invariant pT spectra have same power n

Inclusive high pT particle has n-1 times larger <z> than unbiased fragmentation, <z>=1/b


2 particle Correlations2 particle Correlations

(1)

Prob. that you make a jet with which fragments to a with zt=pTt/

€

ˆ p Tt

€

ˆ p Tt

Prob. that away jet with fragments to a with za=pTa/

€

ˆ p Ta

€

ˆ p Ta

Appears to be sensitive to away jet Frag. Fn.


PHENIX-compared measured xPHENIX-compared measured xEE distribution to numerical distribution to numerical

integral using LEP fragmentation functions-not sensitive!integral using LEP fragmentation functions-not sensitive!

• independent of pTt

xE ~ pTa/pTt ~z/<ztrig>

<ztrig>=0.85 measured

Dq

(z)~e-6z

ISR-CCOR 1979

LEP

PHENIX PRD 74 (2006) 072002

bq=8.2

bg=11.4


Amazingly, I got a neat analytical resultAmazingly, I got a neat analytical result

Take:

Using: Where (a,0)= (a)=(a-1) (a)

(1)

(2)


The final resultThe final result

Where B/b<m>b is the mean charged multiplicity in the jet


Why dependence on the Frag. Fn. vanishesWhy dependence on the Frag. Fn. vanishes

• The only dependence on the fragmentation function is in the normalization constant B/b which equals <m>, the mean multiplicity in the away jet from the integral of the fragmentation function.

• The dominant term in the xE distribution is the Hagedorn function … so that at fixed pTt the xE distribution is predominantly a function only of xE and thus exhibits xE scaling, as observed.

• The reason that the xE distribution is not sensitive to the shape of the fragmentation function is that the integral over zt in (1, 2) for fixed pTt and pTa is actually an integral over jet transverse momentum .. . However since the trigger and away jets are always roughly equal and opposite in transverse momentum (in p+p), integrating over … simultaneously integrates over … . The integral is over zt, which appears in both trigger and away side fragmentation functions in (1).


Oh yes--PHENIX Oh yes--PHENIX oo - h - h correlation functions correlation functionsp+p p+p s=200 GeV: PRD s=200 GeV: PRD 7474, 072002 (2006), 072002 (2006)

d+Au

N jT jet fragmentation transverse momentum-measure directly

F kT parton transverse momentum-more complicated.

Corrected for acceptance

N

A


Results RMS kResults RMS kTT in p+p @ 200 GeV in p+p @ 200 GeV

Main contribution to the systematic errors comes from unknown ratio gluon/quark jet => D(z) slope =><m>

ISR

PHENIX


A very interesting formulaA very interesting formula

measured Ratio of jet transverse momenta


Does the formula work?Does the formula work?

PHENIX p+p PRD 74, 072002

(2006)


It works for PHENIX p+p PRD It works for PHENIX p+p PRD 7474, 072002 , 072002

xh=0.8 due to kT smearing


Formula works in Au+Au: Away-side yield vs pFormula works in Au+Au: Away-side yield vs pTaTa/p/pTtTt is is

steeper in Au+Au than p-p indicating energy losssteeper in Au+Au than p-p indicating energy loss

h(3<pTt<4 GeV/c)--h

Measured ratio of particle pTa/pTt xE Ratio of jet transverse momenta

€

ˆ p Ta / ˆ p Tt ≡ ˆ x h

in Au+Au indicates that away jet has lost energy relative to trigger jet.

€

ˆ x h = 0.66 ± 0.04

The away side pTa/pTt xE distribution triggered by a leading particle with pTt was thought to be equal to the fragmentation function but we found that it is NOT sensitive to the shape of the fragmentation function but only to the shape of the inclusive pTt spectrum with power n (=8.1). Formula derived in PRD 74 (2006) 072002 works for pp and AA


Direct Direct - h - h correlations in p+p correlations in p+p s=200 GeV s=200 GeV New PHENIX preliminary resultNew PHENIX preliminary result

0 Direct

In order to understand whether away side xE distribution from a direct is the (quark) fragmentation function must understand kT smearing for direct . Next step is to measure kT for direct

q

qg

q

q g

Compton

Annihilation


Direct Direct 's in p-p 's in p-p s=200 GeV: Data vs. pQCD s=200 GeV: Data vs. pQCD

Published results 3<pT<15 GeV/c

PHENIX PRL 98 (2007) 012002

p-pp-p

Preliminary results for 5<pT<24 GeV/c


Aurenche et al Eur. Phys. JC9 (1999)107

PHENIX data clarifies

longstanding data/theory puzzle

Comparison with other data and pQCDComparison with other data and pQCD

Talk by Monique Werlen at RHIC&AGS users meeting 2005


<TAB>

2004--Direct Photons in Au+Au 200 GeV: follow T2004--Direct Photons in Au+Au 200 GeV: follow TABAB scaling from p-p for all centralities-no suppressionscaling from p-p for all centralities-no suppression

Direct photons unaffected by QCD medium in Au+Au

0 suppression is medium effect

1) Proves that initial state Au structure function is simply a superposition of p-p structure functions including g(x).

PHENIX PRL94 (2005) 232301

gAu+Au

Centrality


QM2005-direct QM2005-direct in AuAu via internal in AuAu via internal conversionconversion

Kroll Wada PR98(1955) 1355q

g q

e+

e-PHENIX NPA774(2006)403

Eliminating the 0 background by going to 0.2<mee<0.3 GeV enables direct signal to be signal to be

measured for 1<pmeasured for 1<pTT <3 GeV/c in Au+Au. It is exponential, does that mean it is thermal. We <3 GeV/c in Au+Au. It is exponential, does that mean it is thermal. We

must see whether p-p direct must see whether p-p direct is gaussian as p is gaussian as pTT 0 as in Drell-Yan or exponential like for 0 as in Drell-Yan or exponential like for 0


Everything you want to know about JETS can Everything you want to know about JETS can be measured with 2-particle correlationsbe measured with 2-particle correlations--NOT

CCOR, A.L.S.Angelis, et al Phys.Lett. 97B, 163 (1980) PhysicaScripta 19, 116 (1979)

pTt > 7 GeV/c vs pT

xE pTt

pout=pT sin

pTt pT

From RHIC97--QCD98


xxEE distribution measures fragmentation fn distribution measures fragmentation fn.-NOT

Dq(z)~e-6z

• independent of pTt

<ztrig>=0.85 measured

See M. Jacob’s talk EPS 1979 Geneva

From RHIC97--QCD98

xE ~ pTa/pTt ~z/<ztrig>


Where did I (and everybody in HEP) get Where did I (and everybody in HEP) get this idea?---from Feynman, Field and Foxthis idea?---from Feynman, Field and Fox

“There is a simple relationshipbetween experiments done with single-particle triggers and those performed with jet triggers. The only difference in the opposite side correlation is due to the fact that the ‘quark’, from which a single-particle trigger came, always has a higher p than the trigger (by factor 1/ztrig). The away-side correlations for a single-particle trigger at p should be roughly the same as the away side correlations for a jet trigger at p (jet)= p (single particle)/ <ztrig>”.

FFF Nucl.Phys. B128(1977) 1-65


As measured at the ISR by Darriulat, etc.As measured at the ISR by Darriulat, etc.P. Darriulat, et al, Nucl.Phys. B107 (1976) 429-456

Figures from P. Darriulat, ARNPS 30 (1980) 159-210 showing that Jet fragmentation functions in p, e+e- and pp (CCOR) are the

same with the same dependence of b (exponential slope) on “ ”

€

ˆ s


PHENIX PreliminarysNN=200GeV Au+Au

Direct Photon Direct Photon vv22


PHENIX PreliminarysNN=200GeV Au+Au

Direct Photon Direct Photon vv2 2

Run7: PHENIX new Reaction Plane Detector


STAR 0604018 AuAu central flatter than STAR 0604018 AuAu central flatter than PHENIX 0605039 p+p for xPHENIX 0605039 p+p for xEE>0.5!>0.5!

Can still fit, but curves too flat xh>1, but still decreases with increasing centrality

Norm (data) Norm fit hatx_hData*0.6 Fit*0.500 1.300Data*0.6 Fit*0.350 1.200Data*0.6 Fit*0.300 0.850

unresolved issues in hard- scattering at rhic

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