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# Hard-scattering and Jets from RHIC to LHC: a critical review - PowerPoint PPT Presentation

Hard-scattering and Jets from RHIC to LHC: a critical review. M. J. Tannenbaum Brookhaven National Laboratory Upton, NY 11973 USA. High p T physics at LHC University of Jyväskylä, Finland March 23-27 , 2007.

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Hard-scattering and Jets from RHIC to LHC: a critical review

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### Hard-scattering and Jets from RHIC to LHC: a critical review

M. J. Tannenbaum

Brookhaven National Laboratory

Upton, NY 11973 USA

High pT physics at LHC University of Jyvskyl, Finland March 23-27 , 2007

JetsCritical--Jyv--March, 2007

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

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• 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.

• For LHC Morsch (HP2006) gives ~ 1500 GeV for R=1 at sNN=5500 GeV, a factor of 5 increase, recent predictions [PHENIX PRC71(2005)034908, Busza nucl-ex/0410035] give a ratio as low as 2 compared to RHIC.

JetsCritical--Jyv--March, 2007

4%

0.5%

### 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 ?

JetsCritical--Jyv--March, 2007

J. T. Mitchell, BNL 7/21/2006

### Non-Random Fluctuations of ET measured in PHENIX (a nice jet cone) ~1% ~ 15 GeV LHC

compare Data to Mixed events

Random Fluctuations: ~5-8%~75-120 GeV

Are the fluctuations identical in adjacent patches of R=1 ?

JetsCritical--Jyv--March, 2007

### ET/Jets/hard-scatteringLessons from ISR/FNAL/SPSor why nobody of a certain age believes proof by Monte Carlo

e.g. see M. D. Corcoran, Phys. Rev. D32 (1985)592-603 or my colloquium here Friday, March 23, 2007

JetsCritical--Jyv--March, 2007

### 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 everybodys opinion.

JetsCritical--Jyv--March, 2007

CCOR Jets after 8 orders of mag. PL 126B, 132 (1983)

### Jets not apparent in ET distributions

s=540 GeV

UA2-Jets after 5-6 orders of magnitude PLB 138, 430 (1984)

JetsCritical--Jyv--March, 2007

### 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 PRD55 (1997) 7183 for a critical review of jet algorithms

I guess that they missed my colloquium and the period 1978-82 or I have to read the fine print more carefully-triggered by cluster not unbiased?

JetsCritical--Jyv--March, 2007

### cf. Single particle inclusive pT spectrum

Classical

New

Hard scattering evident after only 3-4 orders of magnitude pT>2 GeV/c

NLO-pQCD precison agreement Strattmann Vogelsang hep-ph/0702083

JetsCritical--Jyv--March, 2007

C

A

a

c

X

b

B

d

### LO-QCD in 1 slide

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### ab(cos *) and Spin Asymmetry -- Fundamental predictions of QCD

JetsCritical--Jyv--March, 2007

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

• LHC physicists seem to think that because they have a better chance at measuring jets than at RHIC due to the much larger rate and pT range, they may be able to study the structure of jets and separate medium radiation from normal fragmentation.

• 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:

...

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

JetsCritical--Jyv--March, 2007

j

### CDF jet measurement in p-p collisions reads like a legal contract

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

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].

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

JetsCritical--Jyv--March, 2007

### continued

etcetera...

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### 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 corrections are taken into account.

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

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

JetsCritical--Jyv--March, 2007

### Part of the learning curve CDF 1996

In PRL 77, 438 (1996) CDF reported that Jet cross section deviates from QCD at large pT. Figure looks exactly like 1983 Figure of Paige and Tannenbaum (BNL-33119, 1983) proposing to detect quark substructure via parity violation following [Eichten,Lane, Peskin, PRL 50, 811 (1983)]. PV would be a clear signature of new physics! CDF deviation from QCD was explained by invoking an even better than new Gluon structure function CTEQ4HJ [Huston, et al, PRL 77, 444 (1996)] Do you believe this? Needs to be checked with direct measurements with x>0.25

JetsCritical--Jyv--March, 2007

### Inclusive invariant 0 spectrum is power law for pT3 GeV/c n=8.10.1 in p+p and Au+Au

Nuclear Modification Factor

sNN=200 GeV

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)

JetsCritical--Jyv--March, 2007

RAA: 0 and non-identified charged are different for pT <6 GeV/c, dubbed Intermediate pT

Au Au sNN=200 Gev-run 4

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

JetsCritical--Jyv--March, 2007

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

PHENIX, PRC 69, 034910 (2004)

• 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 RAA=constant as observed!

• (h+ + h-)/2 xT scales in peripheral same as p-p but difference between central and peripheral is significant

JetsCritical--Jyv--March, 2007

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

PHENIX PRL 91(2003) 172301

p/ ratio much larger than from jet fragmentation

p are not suppressed

Is this recombination QGP: Fries,Muller, Nonaka PRL 90 202303 (2003)

JetsCritical--Jyv--March, 2007

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

• In agreement with recombination predictions

• Balance between recombination and fragmentation should be different at LHC

• 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 producedp have no associated jet structure !!

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

STAR-Jana Bielcikova Hard Probes 2006

JetsCritical--Jyv--March, 2007

MJT

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

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?

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### To test details of TheoryRAA(, pT)-0

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50-60%

0-10%

Le

RAA0vs. Reaction Plane-learn something new!

nucl-ex/0611007

(submitted to Phys. Rev. C.)

Au+Au collisions at 200GeV

RAA is absolute, v2 is relative

Le = distance from edge to center calculated in Glauber model

Little/no energy loss for Le< 2 fm

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### The biggest result at QM2006??!

QM2005

-I wanted to make a T-shirt

pp dir reference is pQCD

QM2006-

pp dir reference is run 5 msmt

If RAA= RAA the whole concept of energy loss changes: perhaps no effect for pT>20 GeV

JetsCritical--Jyv--March, 2007

isolatedphotons

q

Compton

g

q

q

Annihilation

g

q

### RHIC-PHENIX year-5direct photon cross-section

• PHENIX Year-5 preliminary result.

• pT region is extended up to 24GeV/c.

• Good reference for the evaluation of nuclear effect for high-pT direct photon production at RHIC.

small-ignore

JetsCritical--Jyv--March, 2007

isolatedphotons

q

Compton

g

q

q

Annihilation

g

q

### 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:

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d+Au Direct PHENIX Prelim

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

Both Direct g and p0 consistent with 1

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Eskola, Kolhinen, Vogt hep-ph/0104124

100 xT

Direct isEMC effect for gluons

Nuclear Modification Factor-Min Bias

=

x pT(RHIC) pT (LHC)

Consistent with 1 No modification within the error

This is first measurement of EMC effect for gluons

0.02 2 GeV/c 60 GeV/c

0.002 0.2 GeV/c 6 GeV/c

JetsCritical--Jyv--March, 2007

100 xT

### For Au+Au min bias RAA is also simple

Au+Au minimum bias

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

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

JetsCritical--Jyv--March, 2007

100 xT

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

Au+Au Central Collisions

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) Emelyanov, et al. PRC 61, 044904 (2000) and references therein.

Experimentalists: RHIC p+A, eRHIC

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

JetsCritical--Jyv--March, 2007

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

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

JetsCritical--Jyv--March, 2007

### 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

JetsCritical--Jyv--March, 2007

PHENIX direct- v2 QM2006

PHENIX preliminary

Needs big improvement. We just have installed a new reaction plane detector for coming high luminosity Au+Au run7 for rare probe v2 measurement at PHENIX

JetsCritical--Jyv--March, 2007

### MJT-This is a great measurement for LHC

• /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

CERN Yellow Report-hep-ph/0311031

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### Correlations

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### A very interesting formula

Ratio of jet transverse momenta

measured

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

1.0

0.8

0.6

0.4

0.2

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### The formula works in p+p

PHENIX p+p PRD 74, 072002 (2006)

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### PHENIX p+p PRD 74, 072002 (2006)

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### Application2-particle correlations in Au+Au

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### STAR showed that the away jet really didnt vanish--it just lost energy and widened

STAR-PRL91(2003)072304 4< pTt< 6 GeV/c 2<pTa<pTt xh=pTa/pTt~0.5

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

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### I applied my xE formula to STAR PRL 95 yields

pp, AuAu sNN=200 GeV

4 < pTt < 6 GeV/c <pTt>=4.56 GeV/c

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

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### It works for STAR p+p and:

a) * means data normalized to agree with hep-ex/0605039-PRD 74, 072002

b)

JetsCritical--Jyv--March, 2007

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

• consistent with increase of energy loss with distance traversed in medium

### STAR Au+Au--Clear effect with centrality

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

JetsCritical--Jyv--March, 2007

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

0 (pTt>5 GeV/c)--h

JetsCritical--Jyv--March, 2007

### Conclusions

• Both the STAR data (FQ.Wang) and PHENIX QM2006 data nicely exhibit the xE/scaling in the range 0.2 <xE<0.6 as the dominant feature. Thus, in my opinion, the simple scaling formula adjusted to fit the data in the range 0.2 <xE<0.6 is a simple and elegant way to characterize the xE distributions in A+A collisions which gives a quantitative estimate of the relative energy loss of away-jets triggered by a high pTt hadron (e.g. 0).

• This is a decent estimate of the energy loss of jets passing through the medium since trigger jets are surface biased due to an effect similar to trigger bias--jets emitted closer to the surface which have not lost energy are favored over jets emitted deeper in the medium with higher which have lost energy.

• Help on this issue from theorists would be appreciated.

JetsCritical--Jyv--March, 2007

### Newer STAR data AuAu: nucl-ex/0604018

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

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

Thanks to Dan Magestro for table of data points

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

JetsCritical--Jyv--March, 2007

### Normalize 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

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

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

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

JetsCritical--Jyv--March, 2007

### 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...

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h --- h

C: 20-60%

T: 4-6

P: 2-PTTrig

h --- h

C: 30-40%

T: 2.5 - 4

P: 1 - 2.5

45o

60o

STAR PRL 91, 072304 (2003)

45o

60o

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### 2-particle correlations AuAu at intermediate pT

2.5 < pT,trigger < 4.0 GeV

1.0 < pT,assoc < 2.5 GeV

PHENIX

PRL97(2006)052301

Status at QM05:PHENIX PRELIMINARY

Strong away-side broadening seen at low pT,assoc

Is there a dip at the away-side?

Conical emission: Mach cone? Cherenkov? Other mechanisms?

Also note: systematic uncertainties should not be disregarded

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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

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Frankly, until we figure out all these unexplained results at RHIC in the 0.1--10 GeV/c range, Im 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

JetsCritical--Jyv--March, 2007

### What I still dont understand-I

• After 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.

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What I still dont understand-II

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.

JetsCritical--Jyv--March, 2007

What I still dont understand-III

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 isnt 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.

JetsCritical--Jyv--March, 2007

NA50 at SPS (0<y<1)

PHENIX at RHIC (|y|<0.35)

### J/ Suppression--RAAPHENIX mid-rapidity (e+e-) the same as NA50!!!

• RAA vs. Npart

• NA50 at SPS

• 0<y<1

• PHENIX at RHIC

• |y|<0.35

Bar: uncorrelated error

Bracket : correlated error

Global error = 12% is not shown

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### END

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### STAR-New 2-particle results-HP2006

6 < pT,trigger< 10 GeV

2.5 < pT,trigger< 4 GeV

STAR preliminary

1 < pT,assoc < 2.5 GeV

STAR preliminary

Systematic study of intermediate pT,assoc under way

Broadening persists to higher pT,trigger, but not dip

What happens to the away-side at intermediate pT?

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### PHENIX low pT correlations-QM2006

0.2 < pT,1 < 0.4 GeV/c, 0.2 < pT,2 < 0.4 GeV/c, |Dh|<0.7

200 GeV Au+Au, 0-5% Central, Like-Sign Pairs

• The blue line is a fit to a function with a v2 component, a near-side Gaussian at Df=0 and an away-side Gaussian at Df=p-D

• The dashed red line is the v2 component.

PHENIX Preliminary

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### One of the few definitive results

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

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

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JetsCritical--Jyv--March, 2007

hep-ex/0609010

PRL 97, 252002 (2006)

Theoretical Uncertainty Band

### Suppression of Direct (non-photonic) Electrons pT>3 GeV/c implies suppression of c and b quarks

nucl-ex/0611018

(submitted to Phys. Rev. Lett.

hep-ex/0609010

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Au+Au 20-30%

a

b

b

c

c

STAR

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

Near-side jet-like corrl.+ ridge-like corrl. + v2 modulated bkg.

Ridge-like corrl. + v2 modulated bkg.

Away-side corrl.+ v2 modulated bkg.

STAR-HardProbes 06

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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

3 < pt,trigger < 4 GeV and pt,assoc. > 2 GeV

yield,)

(J+R) method

(J) method

(J) method

preliminary

Npart

STAR

### Centrality Dependence of the Ridge

JetsCritical--Jyv--March, 2007

near

near

HP2006QM2005

Central Au+Au 0-12% triggered

20

Medium

Medium

ZYAM/Purdue normalization

away

away

3 < pT,trigger < 4 GeV

1 < pT,assoc < 2 GeV

0 1

deflected jets

mach cone

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

### Conical Flow vs Deflected Jets

Not obviously the best projection-difficult to understand

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q

### PHENIX-Polar co-ordinates-wrt Cone

Method being developed in PHENIX-Better Projection?

Trigger

Cone simulation

Combinatorialbackground

Associated

More strength at Df =0 for deflected

Df=180 swamped?

Motivation: cone lives at constant q

Deflected Jet simulation

Cone is not back-to-back with trigger in 3-space

Must distinguish hollow from solid moving cone

VanLeeuwen-Ajitnand-HP2006

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= 120

Deflected Jet simulation

Cone simulation

### Experimental results: PHENIX

PHENIX Acceptance

PHENIX Preliminary

Cent: 0-5%

Df = 0

3 < pT,trigger < 4 GeV

1 < pT,assoc < 2 GeV

Uncorrected, no v2 subtraction

Middle of

Long Learning Curve

N.N. Ajitanands Hard Probes 2006

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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.

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### Backup, Extras, what couldnt fit

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PHENIX preliminary

### Reaction Plane dependence same data

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

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### RP dependence confirms corrected Jet function shape

Correlation Function

Jet Function corrected for v2

• Shoulder and dip of wide away jet seen in all bins

• The dip is significant for bin 4 where the v2 systematic is small

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### Outline

• Start from ISR, FNAL hard scat, early jet no jet ->jet then interesting diversion on jet results I like PV xT at beginning give ET. RHIC ET plot and increase to LHC jet bkg 1.5 TeV in cone Morsch-check 300 GeV again and use LHC extrapolations.

• show jet finding and correcting from cdf paper show cdf jT and humpback results. New star results--comment on the long learning curve and problems of normalizing response and pT scale use lower pT as scale calibration as CDF/D0 did in tests of high pT tail.

• LHC- lots of jets but also lots of multijets NNLO, etc, main problem with jet algorithms

• issues: comparison data--pp probably good enough to run 900 GeV and 14 TeV and interpolate. However theorists used wrong value of jT in their present calculation. Morsch misstates the n value at LHC give the correct n value

• Morsch error: surface bias is the same for jets as for single particles

• pAu is the real issue due to low x regime. give constituent kinematic.s comment on people who say nothing will be observed CGC is big issue as shadowing

• opportunities: v2 gamma via mu mu if medium is black. Soft medium effects e.g. p/pi where does it go to fragmentation value, surface effect isnt different jets-inclusive, humpback or jT measurements--why none at RHIC

• biggest lesson learned at RHIC: Flow is a major complication to measuring jets via 2 particle correlations. ---same for jet plots at LHC---I havent seen flow put in neither the ridge.

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### Issues

• Surface bias same for jets and fragmentsis the same if fragmentation takes place outside medium

• wide away jets indicate kT effect, Should do carefully as a function of pTt pTa identified particles. Compare widths of same and away side peaks

• if STAR punchthrough is a surface effect, why does it depend on pT

• medium effect should reflect properties of the medium e.g. flow velocity. Thus heavier particles may show medium effect at larger pT

• if away jet cone is due to medium effect should also be seen on same side since correlation to parton is much better

• Although RAA persists to 20 GeV/c and shows no sign of changing, effect may go away at higher pT, e.g. if energy loss is like ionization loss dE/dx~constant

• if jets fragment outside medium will be very hard to see medium modification. Also with high energy jets soft gluons due to LPM radiation may be well outside jet cone or at too low a pT

• The high jet cross section may not be good news. Could be lots of NN....NLO multi jets. Also jets will be produced by gg->gg, u\bar{u}, d\bar{d} c\bar{c}, b\bar{b}---QCD couples to color, not flavor.

• gluon structure function at low x is not known. Not well known in nuclei at any x. pA or dA runs are vital to understand this and to test for CGC

• smaller increases in dn/deta e.g 2 from RHIC to LHC may not be good because in GLV this determines the gluon density and thus the suppression

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STAR

### Width of Away-Side Peaks

8 < pT(trig) < 15 GeV/c

STAR nucl-ex/0604018

• away-side widths similar for central and peripheral

• Away-side width INCREASES with increasing pTa??!!!

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### PHENIX d+Au results

PHENIX, PRC 73, 054903 (2006)

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

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### PHENIX d+Au PRC73

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

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• Nice fit of 1/(1+y)n=8.1with to PHENIX hep-ex/0605039 and PRC73; and STAR PRL95 xE distributions. But STAR nucl-ex/0604018 d+Au much flatter than PHENIX d+Au PRC73,054903 (2006)

• Both STAR Au+Au measurements show a decrease in the ratio of the transverse momentum of the away jet relative to the trigger jet with increasing centrality. For both data sets decreases by a factor of ~2 from p+p (dAu) to Au+Au central collisions. Much more info than IAA.

• New STAR punchthrough data has much too flat shape, an apparent sharp break, and disagrees in normalization with STAR PRL95.

• Comparison of two STAR data sets would benefit by going lower in pTa (zT) for the data of nucl-ex/0604018 to see whether slope is really steeper at low zT, with dramatic break and (unreasonable in my opinion) flattening of the zT distribution for zT 0.5

### Conclusions

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### CGC?Monojets in d+Au?

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

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

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away

trigger

### 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

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STAR

Fixed h, as

E & pT grows

Correlations in d+Au

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

• Spp-SdAu= (9.0 1.5) %

• consistent with CGC picture

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

• as expected by HIJING

STAR Preliminary

STAR Preliminary

25<Ep<35GeV

STAR Preliminary

STAR Preliminary

35<Ep<45GeV

Statistical errors only

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### jT kT inp+p d+AuCronin EffectJ/ vs D-Y

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### A few complications for kT

<zt,a> vary with pTt pTa

Jet imbalance due to kT smearing

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PHENIX

ISR

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

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

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## We did (re)learn a few things at RHIC

pout2 =xE22 kTyzt 2 + jtTy2+ jaTy2

FFFs formula was really:

Jan Rak discovered this by insisting to rederive all the formulas, but it was in FFFs paper.

<zt> depends on pTa as well as pTt but may be too confusing for this talk

CCOR NPB 209, 284 (1982)

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### <ztrig> measured at ISR

DATA: CCOR NPB 209, 284 (1982)

ztrig=pTtrig/pTjet

pTjet=pTtrig+1.5px

• <ztrig> ~ 0.8-0.9 at ISR, n~ 11

• <ztrig> xT scales

0.3 GeV/c<pT || <0.7 ||< 60o

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### kT is not a parameter, it can be measured

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### Feynman Field & Fox to the rescue

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pTt

pT

pout=pT sin

xE pTt

### jT, kT, xE, pout definitions all in plane transverse to beam direction

pout2 =xE22 kTy2 + jTy2+ jTy2

• jT is parton fragmentation transverse momentum

• kT is transverse momentum of a parton in a proton (2 protons)

• xE=-pTpTt/|pTt|2 represents away jet fragmentation z

• pout is component of away pT perpendicular to trigger pTt

JetsCritical--Jyv--March, 2007

### Early theoretical attempt to understand kT

<kT>=3.5/2=2.5 GeV/c

• Modern work falls under the subject resummation

JetsCritical--Jyv--March, 2007

### 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)

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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)

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### <pT>(=2kT) vs s in Drell-Yan

CMOR, NPB348, 1 (1991)

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### N.B.-- Lots of Drell-Yan Measurements at Colliders: all you need is luminosity.

ISR

CDF

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### D-Y has Similar Scaling to xT scaling

CFS, PRL 41, 684 (1978)

CMOR, NPB 348, 1 (1991)

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### But First another lesson from the same period. Why you should beware of theory curves on your data

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### Discovery of Drell-Yan and the Theory

p+U+-+X

sNN=7.4 GeV

Christenson, LedermanPRL 25, 1523 (1970)

Theory Altarelli, Brant Preparata PRL 26 42 (1971)

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### The truth 1974 and later

NA50 PLB 477, 28 (2000)

E70 PRL 39 252 (1977)

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### kT and NLO II

In George Stermans 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) doesnt measure kT they derive it by kT-smearing NLO cross predicitons to agree with measurements. See also hep-ex/0407011.

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### Application to RHIC

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### Inclusive single hadron high pT spectra in p-p all s

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### xT scaling in p-p collisions x~0.05-0.10

xT

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-A DIS at AGS (1973)--Hard-Scattering is pointlike

M. May, et al, (M.Murtagh, T.Kirk, MJT) PRL 35, 407 (1975)

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### M. May, et al.,

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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

JetsCritical--Jyv--March, 2007

## 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)

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## Same data vs xT on log-log plot

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n=6.3

n=5.1

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

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

PHENIX preliminary 0 d+Au vs centrality for DNP2003

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

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

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Preliminary

Preliminary

### Comparison with Other Experiments

Systematic errors are not shown

proton-proton collisions

proton-antiproton collisions

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

DATA: CCOR NPB 209, 284 (1982)

QCD

JetsCritical--Jyv--March, 2007

### 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)

JetsCritical--Jyv--March, 2007

## For A+A: RAA1 before RHIC

• The importance of comparison data!

JetsCritical--Jyv--March, 2007

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

Conditional Probability

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

JetsCritical--Jyv--March, 2007

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

Conditional Probability

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

JetsCritical--Jyv--March, 2007

### Great PR-Is it great Science?

Did the away jet vanish in Au+Au?

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

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

JetsCritical--Jyv--March, 2007

### 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

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### Normalized data with PRL95 curve

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### PHENIX and E802 ET compared

PHENIX preliminary

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

JetsCritical--Jyv--March, 2007