# Presentation: 470914

## Measurements of Hard-Scattering by PHENIX at RHIC

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

- Hadron Collider Physics Symposium         La Biodola, Isola d’Elba, Italy                          May 20-26, 2007

- For the PHENIX Collaboration

## The CERN ISR was the first Hadron Collider and made many discoveries and developed many techniques which are in use in Au+Au and p-p collisions at RHIC today. 

-  Proof using same-side and away side two particle correlations that high pT particles in p-p collisions are produced from states with two roughly back-to-back jets which are the result of scattering of constituents of the nucleons as described by QCD, which was developed during the course of these measurements.

- G. Giacomelli and M. Jacob, Phys. Rept. **55** (1979) 1-132 M. Jacob and K. Johnsen, CERN Yellow Report 84-13

-  The rapidity plateau (although several of my RHI colleagues  don’t believe in a plateau). Will not be discussed in this talk.

-  Hard scattering in p-p collisions via particle production at large pT which proved that the partons of DIS strongly interacted with each other. xT scaling measurements to find the underlying physics.

## CERN-ISR Discoveries, cont’d

-  direct lepton (e) production from the decay of (unknown at that time-1974) particles composed of b and c quarks.
-  first and only J/Psi cross section measurement for all pair pT  0 at a hadron collider, until PHENIX at RHIC [PRL **92** (2004) 051802]   and CDF [PRD **71**(2005) 032001 (15 years after their first publication)]
-  direct photon production

- J/Psi suppression has been the gold plated signature for the quark gluon plasma in AA

## Three things are dramatically different in Relativistic Heavy Ion Physics                       than in p-p physics

-  the multiplicity is ~A~200 times larger in AA central collisions than in p-p huge energy in jet cone: 300 GeV for R=1 at sNN=200 GeV

-  huge azimuthal anisotropies which don’t exist in p-p which are interesting in themselves, and are useful, but sometimes troublesome.

-  space-time issues both in momentum space and coordinate space are important in RHI : for instance what is the spatial extent of parton fragmentation, is there a formation time/distance?

## High Energy Nucleus-Collisions provide the means of creating Nuclear Matter in conditions of Extreme Temperature and Density

-  At large energy or baryon density, a phase transition is expected from a state of nucleons containing confined quarks and gluons to a state of “deconfined” (from their individual nucleons) quarks and gluons covering a volume that is many units of the confinement length scale.

## One Big Grape

-  (1 - e-r)/r

- Rep. Prog. Phys. **63** (2000) 1511

## The Quark Gluon Plasma (QGP)

-  The QCD confinement scale---when the string breaks---is order:

-  1/QCD ~1/m=1.4 fm

-  The QCD potential becomes screened with increasing temperature, T, in analogy to increasing Q2: s(T) becomes smaller, reducing the binding energy, and the string tension (T) becomes smaller, increasing the confinement radius.

-  For  r < 1/ a quark does feel the full color charge but for         r >1/ the quark is free of the potential, effectively deconfined

## ICHEP-Paris1982: first unbiased jet (UA2)   +first measurement of QCD subprocess angular distribution using 0-0 correlations (CCOR)

- DATA: CCOR NPB 209, 284 (1982)

- ICHEP-Paris1982: first unbiased jet (UA2)   +first measurement of QCD subprocess angular distribution using 0-0 correlations (CCOR)

- QCD

**p-p**

## AuAu Central Collisions cf. p-p

- STAR-Jet event in pp

- STAR Au+Au central

- PHENIX Au+Au central

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

-  spatial anisotropy momentum anisotropy

- 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

## Elliptic Flow v2 in AuAu Central 200 GeV   Universal in constituent quark Kinetic Energy

- Elliptic Flow v2 in AuAu Central 200 GeV   Universal in constituent quark Kinetic Energy

- large v2 for high and low pT, plateaus for pT>2 GeV/c for mesons, scales in KE/constituent quark                                             -meson (not shown) follows same scaling: further implies flow is partonic not hadronic                                                KE scaling suggests Hydrodynamic origin.                          v2 for pT>2 GeV/c suggests low viscosity, D.Teaney, PRC**68 **(2003**) **034913, ``the perfect fluid’’??

- STAR-PRC**72** (2005) 014904

- PHENIX PRL**98** (2007) 162301

## p-p collisions at RHIC: 0 production (PHENIX) 

- p-p collisions at RHIC: 0 production (PHENIX)

- No surprise (to me) that NLO pQCD agrees with data

- arXiv:0704.3599v1 [hep-ex]

## CCR at the CERN-ISRDiscovery of high pT 0 production in p-p 

-  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 xT=2pT/s scaling but with *n*eff=8!, not *n*eff=4 as expected for QED

-  F.W. Büsser, *et al., *
- CERN, Columbia, Rockefeller Collaboration
-  Phys. Lett. **46B**, 471  (1973)

- Bjorken scaling PR**179**(1969)1547  BermanBjKogut scaling PRD4(71)3388  Blankenbecler, Brodsky, Gunion xT=2pT/s Scaling PL **42B**, 461 (1972)

*n*eff gives the form of the force-law between constituents: *n*eff=4 for QED

## CCOR 1978--Discovery of “REALLY high pT>7 GeV/c” at ISR

- CCOR 1978--Discovery of “REALLY high pT>7 GeV/c” at ISR

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

*n*eff=5 (=4++) as predicted for QCD

- QCD: Cahalan, Geer, Kogut, Susskind, PR**D11**, 1199 (1975)

- 8

- 5

## CCRS-1974 Discovery of direct e~10-4 at ISR not due to internal conversion of direct photons

- CCRS PLB**53**(1974)212; NPB**113**(1976)189

- Data points (e++e-)/2 lines 10-4 (++-)/2

- Farrar and Frautschi PRL**36**(1976)1017 proposed that direct leptons are due to internal conversion of direct photons with /~10-20% to e+e- (d/dm~1/m) for pT>1.3 GeV/c. CCRS looks, finds very few events, sets limits excluding this.

- p.s. these direct e are due to semi-leptonic decay of charm particles not discovered until 1976, 2 year later: Hinchliffe and Llewellyn-Smith NPB**114**(1976)45

## J/Psi and direct e 

- CSZ NPB**142**(1978)29 pT=1.100.05 GeV/c

- CCRS NPB**113**(1976)189 direct e not due to J/

- First

- Best

- Not cause of direct e

- CCRS PLB**56**(1975)482 2nd J/ in Europe

## ISR direct photon production + correlations

- See the classic paper of Fritzsch and Minkowski, PLB **69** (1977) 316-320

- No evidence for bremss. contribution to direct --same side correlation is zero--see CMOR NPB**327**, 541 (1989) for full list of references.

## From ISR to RHIC

## ISR 0 vs RHIC p-p  RHIC pp vs AuAu

- ISR 0 vs RHIC p-p  RHIC pp vs AuAu

- Nuclear Modification Factor** **

******0**** are suppressed in Au+Au eg 200 GeV**

- 0 invariant cross section in p-p at s=200 GeV is a pure power law for pT > 3 GeV/c, n=8.10.1

## Suppression of 0 is arguably the major discovery at RHIC. Energy loss in medium?

- Suppression of 0 is arguably the major discovery at RHIC. Energy loss in medium?

**Au Au ********s****NN****=200 GeV-QM 2005**

- Non-identified h and 0 different pT<6GeV/c. Does either obey QCD?  xT scaling AuAu 200 cf 130 GeV showed 0 xT scaling  Energy loss scales. h do not xT scale: baryons not suppressed for 2 < pT < 6 GeV/c--This is called the baryon anomaly, still not understood.

- NO suppression in A+A collisions at lower c.m. energies. Suppression is unique at RHIC-**different** from low sNN

- Original 0 discovery, PHENIX PRL **88 **(2002)022301; latest preprint nucl-ex/0611007

## RAA vs. Npart integrated over pT
 NA50 at SPS 
 0<y<1
 PHENIX at RHIC
 |y|<0.35

- Bar: uncorrelated error
- Bracket : correlated error
**Global error = 12% is not shown**

- RAA vs. Npart integrated over pT
-  NA50 at SPS
-  0<y<1
-  PHENIX at RHIC
-  |y|<0.35

- BUT-J/ Suppression--RAA is the **same** for  PHENIX mid-rapidity (e+e-) as at lower sNN!!!

- PHENIX nucl-ex/0611020 to appear PRL

- This was CERN-Heavy Ion’s main claim to fame in the infamous press conference of 2000 claiming observations ``consistent with the predicted signatures of a QGP.’’ Will have to wait for LHC to find out whether J/ merely act like ordinary hadrons low pT or whether they are actually probes of deconfinement as predicted by Matsui and Satz PLB**178**(1986)416. Also see discussion by MJT in Rep.Prog.Phys. **69 **(2006)2005

**Au+Au**

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

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

- Published results 3<pT<15 GeV/c

- PHENIX PRL **98** (2007) 012002

**p-p**

**p-p**

- Preliminary results for 5<pT<24 GeV/c

## Comparison with other data and pQCD

- Aurenche et al  Eur. Phys. JC**9** (1999)107

- PHENIX data clarifies longstanding data/theory puzzle

- Talk by Monique Werlen at RHIC&AGS users meeting 2005

## 2004--Direct Photons in Au+Au 200 GeV: follow TAB scaling from p-p for all centralities-no suppression

**2004--Direct Photons in Au+Au 200 GeV: follow T****AB**** scaling 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 PRL**94** (2005) 232301

**Au+Au**

## QM2005-direct  in AuAu via internal conversion

- QM2005-direct  in AuAu via internal conversion

- Kroll Wada PR**98**(1955) 1355

- PHENIX NPA**774**(2006)403

- Eliminating the 0 background by going to 0.2<mee<0.3 GeV enables direct  signal to be measured for 1<pT <3 GeV/c in Au+Au. It is exponential, does that mean it is thermal. We must see whether p-p direct  is gaussian as pT 0 as in Drell-Yan or exponential like for 0

## Status of RAA in AuAu at sNN=200 GeV QM05

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

- Status of RAA in AuAu at sNN=200 GeV QM05

## QM2006-Direct e 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 PRL**97**(2006)252002

**Au+Au **PHENIX   PRL **98 **(2007)172301

**Au+Au**

**p-p**

##  RAA 0 in AuAu sNN=200 GeV vs. Reaction Plane to probe details of the theory-learn something new!

**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

## The biggest result at QM2006??!

- QM2006-
- pp dir  reference is run 5 msmt
- If RAA= RAA the whole concept of energy loss changes: perhaps no effect for pT>20 GeV

- QM2005
- -I wanted to make a T-shirt
- pp dir  reference is pQCD

## For Au+Au min bias direct  RAA is simple

- For Au+Au min bias direct  RAA is simple

- Au+Au minimum bias

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

- Eskola,Kolhinen,Ruuskanen Nucl. Phys. B**535**(1998)351

## Central Collisions---no theory counterpart-yet

- Au+Au Central Collisions

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

- Theorists, HELP!

- 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

## 2-particle correlations AuAu at intermediate pT are very different from p-p

- 2-particle correlations AuAu at intermediate pT are very different from p-p

**Status at QM05:**** **PHENIX PRELIMINARY

- Is there a ’dip’ at the away-side?

- Strong away-side broadening seen at low pT,assoc

- Also note: systematic uncertainties should not be disregarded

**2.5 < p****T,trigger**** < 4.0 GeV**
**1.0 < p****T,assoc**** < 2.5 GeV**

- Conical emission: Mach cone? Cherenkov? Other mechanisms?

**PHENIX**
**PRL97(2006)052301**

**Au+Au**

## Latest PHENIX Result-PRL June 1, 2007

- 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.

## Away-side yield  vs pTa/pTt is steeper in Au+Au than p-p indicating energy loss AND learn something new in p-p

- h(3<pTt<4 GeV/c)--h

- 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

## Many discoveries at RHIC             Lead to many new open questions Like at the ISR in the early 1970’s

## Feynman, Field and Fox said that xE distribution from single particle or Jet measures D(z)-we found not true

- Feynman, Field and Fox said that xE distribution from single particle or Jet measures D(z)-we found not true

- “There is a simple relationship
- between 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.

- P. Darriulat, et al,  Nucl.Phys. **B107 **(1976) 429-456

## PHENIX-compared measured xE distribution to numerical integral using LEP fragmentation functions-not sensitive!

-  independent of pTt

- See M. Jacob’s talk EPS 1979 Geneva

- xE ~ pTa/pTt ~z/<ztrig>

- <ztrig>=0.85 measured

- Dq (z)~e-6z

**ISR-CCOR**

**LEP**

- PHENIX PRD** 74** (2006) 072002

- 

## Extras

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

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

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

- PHENIX PRL** 96 **(2006)** **222301

## Many new Explanations.
One example:Grandchamp, Rapp, Brown; PRL 92, 212301 (2003)
In-media dissolution
Plus regeneration from “off-diagonal”  c-cbar pairs

- One example:Grandchamp, Rapp, Brown; _[PRL 92, 212301 (2003)](http://arxiv.org/abs/hep-ph/0306077)_
- In-media dissolution
- Plus regeneration from “off-diagonal”  c-cbar pairs

- J/ Suppression--My Nightmare Scenario

- The Nightmare is that nobody will believe this. Must see J/ enhancement to believeWait for LHC result

## Direct photon production-simple theory hard experiment

- See the classic paper of Fritzsch and Minkowski, PLB **69** (1977) 316-320

- small-ignore

- Compton distribution is much flatter than scattering and peaked backwards from gluon

- Substitution and Jacobean gives:

## xT scaling sNN=200/130 AuAu shows h are anomalous

-  0 xT scales in both peripheral and central Au+Au with same value of n=6.3 as in p-p. Indicates that structure and fragmentation fns. (including any energy loss) *scale *in AuAu i.e. energy loss is fractional.     _Note: a constant fractional energy loss and a power law spectrum implies that R__AA__=constant as observed!_
-  (h+ + h-)/2 xT scales in peripheral same as p-p but difference between central and peripheral is significant

- PHENIX, PRC **69**, 034910 (2004)

## This is the Baryon Anomaly 2<pT<4.5 GeV/c 

- p are not suppressed

- p/ ratio much larger than from jet fragmentation

- PHENIX PRL 91(2003) 172301

- Is this ‘recombination’  QGP: Fries,Muller, Nonaka PRL **90** 202303 (2003)

## One of the few 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

## Near side and away side correlations the same for meson and baryon triggers

- doi:10.1016/j.physletb.2003.10.071

- http://dx.doi.org/

- PHENIX PLB (2007) in press

## For Au+Au min bias direct  RAA is simple

- For Au+Au min bias direct  RAA is simple

- Au+Au minimum bias

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

- Eskola,Kolhinen,Ruuskanen Nucl. Phys. B**535**(1998)351

## PHENIX QM2006-AuAu h (3<pTt<4 GeV/c) -h  

| p+p pTt=3.3 | N=0.45 |        =1.0 |
| --- | --- | --- |
| AuAu00-20 | N=1.25 |       =0.65 |

## PHENIX QM2006-Chun Zhang AuAu

| p+p pT=4.4 | data*1.0 | fit*0.35 |        =1.10 |
| --- | --- | --- | --- |
| AuAu00-20 | data*1.0 | fit*1.25 |         =0.45 |

## PHENIX QM2006-Chun Zhang AuAu

| p+p pT=2.3 | data*1.0 | fit*0.35 |        =1.30 |
| --- | --- | --- | --- |
| AuAu00-20 | data*1.0 | fit*5.25 |         =0.60 |

-  pp curve is too flat at this low pT ???
-  All AuAu curves roughly a factor two smaller      .     for central Au+Au than p-p indicating energy loss of away jet relative to trigger.
-  For CuCu central the ratio is 2/3 rather than 1/2.

## Also--PHENIX QM2006-JJia Cu+Cu

| p+p | data*1.0 | fit*0.5 |        =0.90 |
| --- | --- | --- | --- |
| CuCu60-89 | data*1.0 | fit*0.7 |         =0.70 |
| CuCu00-20 | data*1.0 | fit*0.7 |        =0.57
 |

- 0 (pTt>5 GeV/c)--h

## “Mike, is there a ‘real collider detector’ at RHIC?”---J. Steinberger 

** ****PHENIX is picturesque because it is not your father’s solenoid collider detector**
** ****Special purpose detector designed and built to measure  *****rare processes***** involving *****leptons and photons***** at the *****highest luminosities.***
*** ******possibility of zero magnetic field on axis ***
***minimum of material in aperture 0.4% X******o***
*** ******EMCAL RICH e************ i.d. and lvl-1 trigger***

*** ************ ************0****** separation up to p******T****** ~ 25 GeV/c***
*** ******EMCAL and precision TOF for h************ ******pid ***

## PHENIX

## Detecting electrons means detecting all particles=PHENIX

- Detecting electrons means detecting all particles=PHENIX

**Notes:**
I should give pizero gamma separation range  and hadron pid range on this slide for both emcal and precision tof as I was asked this question by Chris Schmid, a theorist.

## PHENIX J/ peaks in Au+Au sNN=200 GeV

## Two-spin Asymmetry ALL of 0 at mid-rapidity constrains integrated gluon spin structure function G of proton

- PHENIX arXiv:0704.3599v1 [hep-ex] Subm. PRD Rapid Comm