# Presentation: 678900

## A critical review of Jet Physics from ISR/FNAL/SpS to LHC

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

- International Workshop on Jet Physics in Heavy Ion collisions at the LHC     ECT* Trento, Italy                          September 1, 2006

## Jets in Hadron Collisions are very complicated with a long learning curve. Probably worse in RHI physics. Hard scattering is better learned with single particle and few particle correlation measurements. The main advantage of jets is rate at large pT

## BDMPS 1997-1998

- 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

- 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.
-  For LHC Morsch (HP2006) gives ~ 1500 GeV for R=1 at sNN=5500 GeV, a factor of 5 increase, recent predictions [PHENIX PRC**71**(2005)034908, Busza nucl-ex/0410035] give a ratio as low as 2 compared to RHIC.

**Notes:**
I should make up a new slide saying that BDMPS predicted energy loss due to a coherent LPM effect of brems of a colored gluon on the unscreened color charges in the medium. de/dx propto L, so is coherent. This opened the way to use hard scattering as a probe of unscreened color charge density. Then mention that R. Baier asked me if we could find jets and jet phenomena at RHIC in 1998, since in RHI collisions.... Of courseI said we could do it with single and 2 particle correlation techniques we developed in the original high pT discovery at the CERN ISR

## PHENIX and E802 ET compared

- PHENIX and E802 ET compared

- E877 dET/d=200 GeV@sNN=4.8 GeV    PHENIX dET/d~680 GeV@sNN=200 GeV

- PHENIX preliminary

## Au+Au ET spectra at AGS and RHIC are the same shape!!!

- Au+Au ET spectra at AGS and RHIC are the same shape!!!

_****__**      **__****_

******/8     0.76**

******/4     0.76**

**3********/8     0.76**

******/2     0.76**

**5********/8     0.76**

**1600**
**3200**

- LHC ?

## ET/Jets/hard-scatteringLessons from ISR/FNAL/SPSor why nobody of a certain age believes “proof by Monte Carlo”

- [e.g. see M. D. Corcoran, Phys. Rev. D**32 **(1985)592-603]

## Bjorken Scaling in Deeply Inelastic Scattering and the Parton Model---1968

## 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 + X*     when 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 p**T**.”*

## CCR at the CERN-ISRDiscovery of high pT 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 BBK scaling but with n=8!, not n=4 as expected for QED

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

- Bj scaling  BBK scaling

## BBK scaling with n=8, not 4 Inspires Constituent Interchange Model

- Berman, Bjorken, Kogut, PR**D4**, 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)

## 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

## 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:

## n(xT, s) WORKS n5=4++

- Same data Ed3/dp3(xT)   ln-ln plot

## ISR Expt’s more interested in n(xT,s) than absolute cross section

- cross sections vary by factor of 2

- Athens BNL CERN Syracuse Collaboration,  C.Kourkoumelis, et al Phys.Lett. **84B**, 279 (1979)

- But n(xT,s) agrees

## Status of ISR single particle measurements 1978

- kT is what made n=4++  n=8

## Status of QCD Theory in 1978

## 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.

## Why nobody (in the U.S.) believed in jets

- In 1972-73, soon after hard-scattering was discovered in p-p collisions, Bjorken PRD**8** (1973) 4098 and Willis (ISABELLE Physics Prospects-BNL-17522) proposed 4 hadron calorimeters to search for jets from fragmentation of scattered partons with large pT realizing that a substantial increase in rate would be expected in measuring the entire jet at a given pT rather than just the leading fragment. (Bjorken’s parent-child effect)
-  It took until 1980 to get a full azimuth ~0.88 (~45o) calorimeter but meanwhile experiments were done with smaller back-to-back calorimeters each with aperture ~45o ~0.55 and many new trigger biases were discovered, for instance, jets wider than the calorimeter aperture would deposit less energy than narrow jets of the same pT and be suppressed by the steeply falling spectrumjet structure is dominated by the calorimeter geometry  [e.g. see M. Dris NIM **158** (1979) 89]

## (In)famous FNAL E260 found “Jets” (1977) 

- (In)famous FNAL E260 found “Jets” (1977)

-  In each of 2 back to back calorimeters with ~45o ~0.36 (same as PHENIX) the invariant cross section of several particles with a vector sum pT is much larger than a single particle of the same pT. The authors took this as evidence for the exactly back-to-back in azimuth jets of constituent scatteringNever let an interested theorist collaborate on an experiment.

**C.Bromberg et al E260, PRL 38 (1977)1447, NPB134 (1978) 189**

## But, experiments with different apertures got different results

-  The first 4 experiment was a bubble chamber(!) 110 GeV/c K- on p [M. Deutschmann, et al, ABCCLVW collab, NPB**155** (1979)307]

-  multiparticle cross section for pT> 1.5 GeV/c >> single particle
-  Data extrapolate nicely to those of E260 [8] in slope and magnitude.
-  But ``principal axis” analysis of the data shows “the vast majority of events with large pT multiparticle systems DO NOT exhibit jet-like structure.”

## NA5-the coup-de-grâce to jets (1980)

-  Full azimuth calorimeter -0.88<*<0.67 ( NA35, NA49)

-  plus triggered in two smaller apertures corresponding to E260.
-  No jets in full azimuth data
- All data way above QCD predictions
-  The large ET observed is the result of “a large number of particles with a rather small transverse momentum”--the first ET measurement in the present terminology.

- K. Pretzl, Proc 20th ICHEP (1980)          C. DeMarzo et al NA5, PLB**112**(1982)173

- For more on ET see MJT IJMPA **4 **(1989)3377

## Back to-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 from UA2 in 1982 changed everybody’s opinion.

## Also Paris 1982-Jets in ET distribution

- Also Paris 1982-Jets in ET distribution

- NA5-1980 ICHEP-No Jets 7 orders of magnitude

- s=24.3 GeV

## LO-QCD in 1 slide

- LO-QCD in 1 slide

## Also Paris1982-first measurement of QCD subprocess angular distribution using      0-0 correlations

- DATA: CCOR NPB 209, 284 (1982)

- Also Paris1982-first measurement of QCD subprocess angular distribution using      0-0 correlations

- QCD

## Eventually this was measured with di-jets

- see L. Di Lella ARNPS** 35** (1985) 107--134

## When dealing with Jets it is important to remember that QCD couples to color not flavor 

-  The high jet cross section may not be good news. NLO, NNLO, NN....NLO may cause lots of multi jets instead of di-jets.
-  Also jets will be produced by many different subprocesses:

- When dealing with Jets it is important to remember that QCD couples to color not flavor

- With all these subprocesses contributing roughly equally at large pT, the jet structure might be quite complicated to understand.

- ...

## CDF made such a measurements in p-p collisions but it reads like a legal contract

- The energy of a jet is defined as the sum of the energies of the towers belonging to the corresponding cluster. Corrections are applied to compensate for the non-linearity and non-uniformity of the energy response of the calorimeter, the energy deposited inside the jet cone from sources other than the parent parton, and the parent parton energy that radiates out of the jet cone. Full details of this procedure can be found in [25].

- CDF PRD **68** (2003) 012003-jT distribution in di-jets

## [25]F.Abe, et al, Phys Rev D45, 1448 (1992)

## continued

- etcetera...

## Jet measurements of QCD in pp collisions are now standard after a ~30 year learning curve

- The measured crosssection is in agreement with NLO pQCD predictions after the necessary nonperturbative parton-to-hadron correction sare taken into account.

**At RHIC, inclusive single particles provide a precision pQCD probe, well calibrated in pp, dAu... collisions **

- A. Abulencia, et al, CDF PRL 96 (2006) 122001-kT algorithm

## 0's in p+p: Data vs. pQCD

- Result from run2 published-a classic
- PRL91 (2003) 241803
- New result from run5
- preliminary
- Comparison of 0 cross section
- Next-to-leading order(NLO) pQCD
- CTEQ6M + KKP or Kretzer
- Matrix calculation by Aversa, et. al.
- Renormalization and factorization scales are set to be equal and set to
- 1/2pT, pT, 2pT
- Calculated by W.Vogelsang

- Theorists have a tough job---Experimentalists can use scaling rules

- NLO-pQCD described very well
- down even to *p**T* ~ 1 GeV/*c*

## QCD follows xT  scaling-very powerful tool

- QCD follows xT  scaling-very powerful tool

- LOQCD, QED: n=4
- QCD

- Structure and Fragmentation fns., which `scale’,  i.e. are functions only of ratios of momenta, are in F (G)

## Inclusive invariant 0 spectrum is power law for pT3 GeV/c n=8.10.1 in p+p and Au+Au

- Inclusive invariant 0 spectrum is power law for pT3 GeV/c n=8.10.1 in p+p and Au+Au

**Nuclear Modification Factor**** **

- Impossible to distinguish reduction in the number of partons (due to e.g. stopping in medium) from fractional downshift in spectrum (due to e.g. energy loss of parton in medium)

******s****NN****=200 GeV**

## RAA: 0 and non-identified charged are different

- RAA: 0 and non-identified charged are different

**Au Au ********s****NN****=200 Gev-run 4**

- Does either obey QCD?  We tried xT scaling AuAu 200 cf 130 GeV

## 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
-  (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)

## Rcp of Baryons & mesons become equal (fragmentation) for pT>6 GeV/c at 200 GeV

- STAR-Jana Bielcikova Hard Probes 2006

-  In agreement with recombination predictions

-  Balance between recombination and fragmentation should be different at LHC

-  Very important to measure at LHC--needs pid over a large pT range

-  Hwa & Yang nucl-th/0603053 predict *p*/~10 out to pT~20 GeV/c at LHC due to recombination of  partons from the many jets produced *p* have no associated jet structure !!

## New direct 's in p+p: Data vs. pQCD

**PHENIX run3 preliminary result.**
**Recent Update down to 3GeV/c**
**Publication is coming soon.**
**NLO-pQCD calculation**
**Private communication with W.Vogelsang**
**CTEQ6M PDF.**
**Sum of direct ******** +**** ****Bremsstrahlung ******
**3 scales (****1/2****pT,1pT,2 pT)**

- New direct 's in p+p: Data vs. pQCD

- Previous results for pT> 5GeV/c new results pT>3 GeV/c

## Comparison with other data and pQCD

- PHENIX data clarifies longstanding data/theory puzzle

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

## Comparison with Other Experiments

- Systematic errors are not shown

- proton-proton collisions

- proton-antiproton collisions

## xT scaling: a) Direct-   b) Jets

- xT scaling: a) Direct-   b) Jets

- Direct  n5

- _Jets-Ratio of Scaled Cross Sections 630/1800_

- Jets n4.5

- G.C.Blazey & B.L.Flauger, ARNPS **49**, 633 (99)

## New: STAR xT scaling result for (anti-)protons in p+p collisons sNN=200 GeV

- New: STAR xT scaling result for (anti-)protons in p+p collisons sNN=200 GeV

-  n=6.8  0.5

*p, *     n =6.5  1.0

- STAR, nucl-ex/0601033. It appears that Brodsky, et al PLB**637**, 58 are likely wrong

## New STAR Jet measurement in p-p collisions---first at RHIC-hep-ex/0608030

- “Jets were reconstructed using a midpoint-cone algorithm”

- See Kilgore, Giele PRD**55 **(1997) 7183 for a critical review of jet algorithms

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

- 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

## To test details of TheoryRAA(, pT)-0

- To test details of TheoryRAA(, pT)-0

## For A+A: RAA1 before RHIC

-  The importance of comparison data!

## State of RdA in d+Au at sNN=200 GeV

- State of RdA in d+Au at sNN=200 GeV

**Both Direct ******** and ********0**** consistent with 1  **

## Direct  is“EMC effect” for gluons  

- Consistent with 1  No modification within the error
- This is first measurement of ‘EMC effect’ for gluons

- Nuclear Modification Factor-Min Bias

- _x    p__T__(RHIC)     p__T__ (LHC)_

**0.02    2 GeV/c   60 GeV/c**

**0.002  0.2 GeV/c  6 GeV/c**

- =

## AA measurements at LHC probably useless without pp and pA (dA) comparison data  

- Predictions from CERN-Yellow-report-hep-ph/0308248

- AA measurements at LHC probably useless without pp and pA (dA) comparison data

-  For pp make sure to run at 900 GeV and 14000 GeV. Interpolation +QCD might be adequate to believe 5500 GeV

-  LHC could be the CGC factory. Rg(x,Q2) not known for any A or any x or Q2. Forward d+Au measurements at RHIC will be useful.

-  Need d+Pb or p+Pb runs at sNN=5500 GeV, unless direct  are not suppressed in Pb+Pb. Direct  much harder at LHC than at RHIC

## Direct  with respect to the reaction plane

- Direct  with respect to the reaction plane

- Turbide, 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

## MJT-This is a great measurement for LHC

- CERN Yellow Report-hep-ph/0311031

-  /0 much smaller at LHC compared to RHIC.  Measurement with real photons is much harder

-  use external or internal  conversions to low mass e+e- pairs for pT <5 GeV/c (contains 0 and all other decay photon)---nice measurement of hadron v2>0

-  compare to low mass +- pairs, which have no 0 and minimal  and should have v2<0 if medium regeneration theory is correct

- Opposite v2 for ee and  would indicate dramatic physics without need to know all the backgrounds in detail

## Correlations

## 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 *p*Tt is weighted to high *z*t by *z*tn-2

## p.s.-The same math shows that surface bias is identical for jets and single particle triggers

- i.e. I don’t agree if jets fragment outside of medium which they must by Quantum Mechanics

- MJT simplistic calc for a uniform opaque medium (*x*=fraction of energy lost from center to surface1): RAA(x=1) =1/(n-1) or 1/(n-2), n=8.1 RHIC,          LHC n~6.5 less suppression!? Corona Effect?                            To theorists: please improve my result.

**R****AA**

## 2 particle Correlations

- (1)

## 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

## Feynman, Field and Fox said that xE distribution from single particle or Jet measures D(z)

- Feynman, Field and Fox said that xE distribution from single particle or Jet measures D(z)

- “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 (hep-ex/0605039) found this is wrong

- Following FFF and CCOR PLB**97**(1980)163-168 we were trying to measure the net transverse momentum of the di-jet (2 x <kT>)

-  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

- We needed <zt> to solve for kT. Tried to get it from xE dist.

## Fit xE distributions to form of D(z) used by LEP measurements by integrating Eq (1) numerically  

- Fit xE distributions to form of D(z) used by LEP measurements by integrating Eq (1) numerically

- D(z)=exp(-10z)

- D(z)=exp(-20z)

- After many convergence difficulties, two vastly different fragmentations  Functions triedNo effect on calculated xE distributions---Mike, can you check this analytically?!

## Amazingly, I got a simple, interesting formula

- Measured ratio of particle pTa, pTt         Ratio of jet transverse momenta

## Shape of xE distribution depends on         and n but not on b

- Shape of xE distribution depends on         and *n* but not on *b*

- 1.0
- 0.8
- 0.6
- 0.4
- 0.2

## Does the formula work?

-  PHENIX p+p   hep-ex/0605039

## It works for PHENIX p+p hep-ex/0605039

- nb: vertical scale labels on this and similar plots should be multiplied by 10

## PHENIX o - h  correlation functionsp+p s=200 GeV hep-ex/0605039

- d+Au

- N   *j*T   jet fragmentation transverse momentum-measure directly
- F   *k*T  parton transverse momentum-more complicated.

## Results RMS kT in p+p @ 200 GeV

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

## LHC prediction from many talksSchutz, Gustaffson, Morsch ...

**Hmmm!**

## Application2-particle correlations in Au+Au

## STAR-Peripheral Au+Au data vs. pp+flow

- STAR-QM2002-Hardke  4< pTt< 6 GeV/c  2<pTa<pTt

**Conditional Probability**

## STAR-Central Au+Au data vs. pp+flow

- STAR-QM2002-Hardke  4< pTt< 6 GeV/c  2<pTa<pTt

**Conditional Probability**

## Great PR-Is it great Science?

- STAR-PRL**91**(2003)072304  4< pTt< 6 GeV/c  2<pTa<pTt

- Did the away jet vanish in Au+Au?

- Also serious issues with exact v2 to use, and exact background level

## I-Reaction plane dependence of jet correlation 

- I-Reaction plane dependence of jet correlation

- Jet energy loss depends on path-length through the medium

- Methodology of J. Bielcikova, S.Esumi, K. Filimonov, S. Voloshin, J.P. Wurm, PRC 69 (2004) 021901(R)

- 4< pTt< 6 GeV/c  2<pTa<pTt

## II-Going to lower pTa showed that the away jet didn’t vanish it just lost energy and widened

- II-Going to lower pTa showed that the away jet didn’t vanish it just lost energy and widened

- STAR-PRL**91**(2003)072304  4< pTt< 6 GeV/c  2<pTa<pTt  xh=pTa/pTt~0.5

- STAR-PRL**95**(2005)152301         4< pTt< 6 GeV/c  0.15<pTa<4 GeV/c xh=pTa/pTt~0.04

## I applied my xE 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

## Clear           scaling effect with centrality

| p+p | data*0.6 | fit*1.0 |        =1.0 |
| --- | --- | --- | --- |
| AuAu40-80 | data*0.6 | fit*1.75 |         =0.75 |
| AuAu00-05 | data*0.6 | fit*4.0 |        =0.48
 |

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

## Emergence of narrow Di-Jets pTa>3 GeV/c---Is the trick pTt>8 GeV/c? or ?? 

**8 < p****T****(trig) < 15 GeV/c**

**STAR nucl-ex/0604018**

- Remember, charged hadrons are anomalous for pT 6 GeV/c

- ~0.375

- ~0.5

- ~0.75

## Away side yields from nucl-ex/0604018 

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

- Thanks to Dan Magestro for table of data points

## I find that STAR(nucl-ex/0604018)  differs from     STAR (PRL95) in normalization and SHAPE

- nb: vertical scale labels on these and similar plots should be multiplied by 10    STAR* 0604019 label should be STAR* 0604018

## I Normalized 064018 to PRL95 by eye

- If this is a real discontinuity in the xE distribution it could indicate softer away jets that interact and harder jets that have punched through

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

- Tangential emission

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

**Notes:**
Start off with 2 assoc, then move to 6 assoc

## 2-particle correlations AuAu at intermediate pT

- 2-particle correlations AuAu at intermediate pT

**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**

## Reaction Plane dependence same data 

- Reaction Plane dependence same data

- clear variation of correlation function and phase and magnitude of v2 with angle to reaction plane

## RP dependence confirms corrected Jet function shape

-  Shoulder and dip of wide away jet seen in all bins
-  The dip is significant for bin 4 where the v2 systematic  is small

- Correlation Function

- Jet Function corrected for v2

## STAR-New 2-particle results-HP2006

**2.5 < p****T,trigger****< 4 GeV**

**6 < p****T,trigger****< 10 GeV**

**STAR preliminary**

**STAR preliminary**

**1 < p****T,assoc**** < 2.5 GeV**

- Systematic study of intermediate pT,assoc under way

**Broadening persists to higher p****T,trigger****, but not ‘dip’**

- What happens to the away-side at intermediate pT?

## Interaction with medium? Where does the lost energy go? Mach Cone? Ridge?If it is a medium effect look at particles with velocity of the medium

## Near-Side Long-Range  Correlation: the Ridge

**Near-side jet-like corrl.****+ ridge-like corrl. ****+ v****2 ****modulated bkg.**** **
**Ridge-like corrl. ****+ v****2 ****modulated bkg.**** **
**Away-side corrl.****+  v****2 ****modulated bkg.**

- STAR-HardProbes 06

## Centrality Dependence of the Ridge

- yield of associated particles can be separated into a jet-like yield and a ridge yield
- jet-like yield consistent in  and  and independent of centrality
- ridge yield increases with centrality

## Conical Flow vs Deflected Jets

**STAR 3 particle : Given a trigger, plot plot ********1**** vs ********2**** for 2 away particles**

**Not obviously the best projection-difficult to understand**

## PHENIX-Polar co-ordinates-wrt Cone

- Trigger

- Associated

- Method being developed in PHENIX-Better Projection?

- Motivation: cone ‘lives’ at constant 

- Cone is not back-to-back with trigger in 3-space
- Must distinguish hollow from solid moving cone

- VanLeeuwen-Ajitnand-HP2006

- Combinatorialbackground

- Cone simulation

- Deflected Jet simulation

- More strength at  =0 for deflected

- =180° swamped?

## Experimental results: PHENIX

- Uncorrected, no v2 subtraction

- = 0

- Cent: 0-5%

**PHENIX *****Preliminary***

**PHENIX Acceptance**

- N.N. Ajitanand’s Hard Probes 2006

- 3 < pT,trigger < 4 GeV
- 1 < pT,assoc < 2 GeV

- Middle of
- Long Learning Curve

## Frankly, until we figure out all these unexplained results at RHIC in the   0.1--10 GeV/c range, I’m not very interested in ~100 GeV jets at LHC nor do I expect much influence of the medium to be observable                     at such large pT

## My parting advice

- A big lesson learned at RHIC was that flow or anisotropy with respect to the reaction plane is a major complication to jets (via 2-particle correlations). Most likely it is the same for jets at LHC. Then there is the ridge and .... Expect a new long learning curve.

## Backup, Extras,        what couldn’t fit 

## STAR PRL 91, 072304 (2003)

**45****o**

**45****o**

**60****o**

**60****o**

## 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

## Width of Away-Side Peaks

- away-side widths similar for central and peripheral
- Away-side width INCREASES with increasing pTa??!!!

**STAR nucl-ex/0604018**

## Normalized data with PRL95 curve

## STAR 0604018 AuAu central flatter than PHENIX 0605039 p+p for xE>0.5!

- STAR 0604018 AuAu central flatter than PHENIX 0605039 p+p for xE>0.5!

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

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

## PHENIX d+Au results

-  Beautiful p+p and dAu results with pTt in STAR punchthrough range.

- PHENIX, PRC 73, 054903 (2006)

## PHENIX d+Au PRC73

-  STAR 0604018 AuAu0-5 flatter than all published p+p and d+Au data ????

## It works for STAR p+p and:

-   a) * means data normalized w.r.  to hep-ex/0605039

- b)

## Conclusions

## CGC?‘Monojets’ in d+Au?

## Brahms RdAu, RCP in d+Au vs rapidity

- Brahms RdAu, RCP in d+Au vs rapidity

- BIG effect in RCP; some tendency in RdAu. BRAHMS PRL**93** 242303

## 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 nucl-ex/0603017**

## Correlations in d+Au

- Statistical errors only

-  are suppressed at small <xF> and <pT,>**      **
**S****pp****-S****dAu****= (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**

**STAR Preliminary**

**STAR Preliminary**

**STAR Preliminary**

**STAR Preliminary**

**Correlations in d+Au**

## Recall 0: n=5.1 works better for xT> 0.2

## Cronin effect observed in d+Au at RHIC sNN=200 GeV

- PHENIX preliminary 0 d+Au vs centrality for DNP2003

## UA2 results on cos* and kT in direct 

- R. Ansari, et al, UA2, ZPC **41**, 395 (1988)

## xE distribution measures fragmentation fn.

- xE distribution measures fragmentation fn.

- xE ~ z/<ztrig>

- Dq(z)~e-6z

-  independent of pTt

- <ztrig>=0.85 measured

- See M. Jacob’s talk EPS 1979 Geneva

- From MIT 2005

## Why 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).