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

JetsCritical--Jyv--March, 2007 M. J. Tannenbaum 1/62

Hard-scattering and Jets Hard-scattering and Jets from RHIC to LHC: from RHIC to LHC:

a critical review a critical review

M. J. TannenbaumBrookhaven National Laboratory

Upton, NY 11973 USA

High pT physics at LHC University of Jyväskylä, Finland

March 23-27 , 2007


Jets in Hadron Collisions are very Jets in Hadron Collisions are very complicated with a long learning complicated with a long learning

curve. Probably worse in RHI curve. Probably worse in RHI physics. Hard scattering is better physics. Hard scattering is better

learned with single particle and few learned with single particle and few particle correlation measurements. particle correlation measurements. The main advantage of jets is rate The main advantage of jets is rate

at large pat large pTT


BDMPS 1997-1998BDMPS 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

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R = (Δη )2 + (Δφ)2

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.


4%

0.5%

Au+Au EAu+Au ETT spectra at AGS and RHIC are the same shape!!! 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

16003200 LHC ?


Non-Random Fluctuations of ENon-Random Fluctuations of ETT measured in measured in

PHENIX (a nice jet cone) ~1% ~ 15 GeV LHCPHENIX (a nice jet cone) ~1% ~ 15 GeV LHC

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

compare Data to Mixed events

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

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


EETT/Jets/hard-scattering/Jets/hard-scattering

Lessons from Lessons from ISR/FNAL/SPSISR/FNAL/SPS

or why nobody of a or why nobody of a certain age believes certain age believes

“proof by Monte Carlo”“proof by Monte Carlo”e.g. see M. D. Corcoran, Phys. Rev. D32 (1985)592-603

or my colloquium here Friday, March 23, 2007


THE UA2 Jet-Paris 1982THE UA2 Jet-Paris 1982From 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.


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

Jets not apparent in EJets not apparent in ETT distributions distributions

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

s=540 GeV


New STAR “Jet” measurement in p-p New STAR “Jet” measurement in p-p collisions---first at RHIC-hep-ex/0608030collisions---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?


cf. Single particle inclusive pcf. Single particle inclusive pTT spectrum spectrum

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

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

Classical

New


LO-LO-QQCCDD in 1 sli in 1 sliddee

A

B

a

bc

d

C

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faA (x1) D cC /

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fbB (x2) D dD /

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dσ

dˆ t X


abab(cos (cos **) and Spin Asymmetry -- ) and Spin Asymmetry -- Fundamental predictions of Fundamental predictions of QQCCDD


• 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:

When dealing with Jets it is important to When dealing with Jets it is important to remember that remember that QQCCD D couples to color not flavorcouples to color not flavor

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gg → gg

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gg → uu

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gg → dd

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gg → bb

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gg → cc

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

...


j

CDF jet measurement in p-p collisions CDF jet measurement in p-p collisions reads like a legal contractreads 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)[25]F.Abe, et al, Phys Rev D45, 1448 (1992)


continuedcontinued

etcetera...


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

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

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


Part of the learning curve CDF 1996Part 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


Inclusive invariant Inclusive invariant 00 spectrum is power law spectrum is power law for pfor pTT3 GeV/c n=8.13 GeV/c n=8.10.1 in p+p and Au+Au0.1 in p+p and Au+Au

Nuclear Modification Factor

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RBA =d2NBA

π /dpT dydNBAinel

[ ]

TBA × d2σ ppπ /dpT dy[ ]

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RBA =d2NBA

π /dpT dydNBAinel

[ ]Ncoll

σ ppinel × d2σ pp

π /dpT dy[ ]

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)

sNN=200 GeV


RRAAAA: : 00 and non-identified charged are different and non-identified charged are different for pfor pTT <6 GeV/c, dubbed “Intermediate p <6 GeV/c, dubbed “Intermediate pTT””

Au Au sNN=200 Gev-run 4

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


xxTT scaling scaling ssNNNN=200/130 AuAu shows h=200/130 AuAu shows h are anomalous 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 RAA=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<pThis is the Baryon Anomaly 2<pTT<4.5 GeV/c <4.5 GeV/c

p are not suppressedp/ 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 Rcp of Baryons & mesons become equal ((fragmentation) for pfragmentation) for pTT>6 GeV/c at 200 GeV>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 !!


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


To test details of TheoryTo test details of TheoryRRAAAA((, p, pTT)-)-00


Au+Au collisions at 200GeVRAA is absolute, v2 is relative

L = distance from edge to center calculated in Glauber model

Little/no energy loss for L < 2 fm

0-10%

50-60%

nucl-ex/0611007

(submitted to Phys. Rev. C.)

RRAAAA 00 vs. Reaction Plane-learn something new! vs. Reaction Plane-learn something new!

L


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 ) =d2Y AA /dpT dy

TAA d2σ NN /dpT dy

TAA = Ncoll /σ inel.


RHIC-PHENIX year-5RHIC-PHENIX year-5direct photon cross-sectiondirect 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.

q

qg

q

q g

isolatedphotons

Compton

Annihilation

small-ignore


Direct photon production-simple theory hard experimentDirect photon production-simple theory hard experiment

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

q

qg

q

q g

isolatedphotons

Compton

Annihilation

small-ignore

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

Substitution and Jacobean gives:


d+Au Direct PHENIX Prelim

State of RState of RdAdA in d+Au at in d+Au at ssNNNN=200 GeV=200 GeV

Both Direct and 0 consistent with 1


Direct Direct is“EMC effect” for gluons 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

Eskola, Kolhinen, Vogt hep-ph/0104124

x pT(RHIC) pT (LHC)

0.02 2 GeV/c 60 GeV/c0.002 0.2 GeV/c 6 GeV/c

€

RgA (x,Q2)=

100 xT


For Au+Au min bias RFor Au+Au min bias RAAAA is also simple is also simple

100 xT

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. B535(1998)351


Central Collisions---no theory counterpart-yetCentral Collisions---no theory counterpart-yetAu+Au Central Collisions

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


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

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

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

PHENIX direct-PHENIX direct- v v22 QM2006 QM2006


MJT-This is a great measurement for LHCMJT-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


CorrelationsCorrelations


A very interesting formulaA very interesting formula

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.



measured Ratio of jet transverse momenta


Shape of xShape of xEE distribution depends on distribution depends on

and and nn but not on but not on bb

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ˆ x h

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ˆ x h

1.0

0.8

0.6

0.4

0.2

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n = 8.1


The formula works in p+pThe formula works in p+p

PHENIX p+p PRD 74, 072002

(2006)




PHENIX p+p PRD PHENIX p+p PRD 7474, 072002 (2006) , 072002 (2006)


ApplicationApplication2-particle 2-particle

correlations in correlations in Au+AuAu+Au


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


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


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

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


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

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ˆ x h

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ˆ x h

€

ˆ x h

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

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

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xE / ˆ x h

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

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

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ˆ x h

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ˆ p Ta

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ˆ p Tt


Also--PHENIX QM2006-JJia Cu+CuAlso--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

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ˆ x h

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ˆ x h

€

ˆ x h

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


ConclusionsConclusions

• 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.

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ˆ x h

€

ˆ x h

€

ˆ p Tt


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

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

Thanks to Dan Magestro for table of data pointsSTAR, J. Adams, D. Magestro, et al PRL 97, 162301 (2006)


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


Normalize 064018 to PRL95 by eyeNormalize 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


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


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...


STAR PRL 91, 072304 (2003)

h± --- h±

C: 20-60%T: 4-6

P: 2-PT Trig

h± --- h± C: 30-40%T: 2.5 - 4 P: 1 - 2.5

45o

45o 60o

60o


2-particle correlations AuAu at intermediate p2-particle correlations AuAu at intermediate pTT

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 < pT,trigger < 4.0 GeV1.0 < pT,assoc < 2.5 GeV

Conical emission: Mach cone? Cherenkov? Other mechanisms?

PHENIXPRL97(2006)052301


Interaction with medium? Interaction with medium? Where does the lost energy go? Where does the lost energy go?

Mach Cone? Ridge?Mach Cone? Ridge?If it is a medium effect look at If it is a medium effect look at particles with velocity of the particles with velocity of the

mediummedium


Frankly, until we figure out all these Frankly, until we figure out all these unexplained results at RHIC in the unexplained results at RHIC in the 0.1--10 GeV/c range, I’m not very 0.1--10 GeV/c range, I’m not very interested in ~100 GeV jets at LHC interested in ~100 GeV jets at LHC

nor do I expect much influence of the nor do I expect much influence of the medium to be observable medium to be observable

at such large pat such large pTT


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

• RAA vs. Npart

NA50 at SPS

• 0<y<1 PHENIX at RHIC

• |y|<0.35

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

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


ENDEND


STAR-New 2-particle results-HP2006STAR-New 2-particle results-HP20062.5 < pT,trigger< 4 GeV 6 < pT,trigger< 10 GeV

STAR preliminary STAR preliminary1 < pT,assoc < 2.5 GeV

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?


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

PHENIX Preliminary

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

( ) ( )( ) ( ) ( )σ −+++= AJGausscBC NearNear ;2cos21 1,2

( ) ( ) ( )⎥⎥⎦

⎤

⎢⎢⎣

⎡

⎭⎬⎫

⎩⎨⎧ +−−+

⎭⎬⎫

⎩⎨⎧ −−−≡−

2

2

2

2

2exp

2exp

2 AAA

A DDSAJ

σ

πϕ

σ

πϕ

σππϕ

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

• The dashed red line is the v2 component.

PHENIX low pPHENIX low pTT correlations-QM2006 correlations-QM2006


One of the few definitive resultsOne 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


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

hep-ex/0609010

hep-ex/0609010 PRL 97, 252002 (2006)

Theoretical Uncertainty Band

nucl-ex/0611018(submitted to Phys. Rev. Lett.


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

Au+Au 20-30%

a

b

c c

ba) Near-side jet-like corrl.

+ ridge-like corrl. + v2 modulated bkg.

b) Ridge-like corrl. + v2 modulated bkg.

c) Away-side corrl.+ v2 modulated bkg.

STARSTAR

STAR-HardProbes 06


Centrality Dependence of the RidgeCentrality 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

preliminary(J+R) method

(J) method

(J) methodyiel

d

,

)

Npart

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

STARSTAR


Conical Flow vs Deflected JetsConical Flow vs Deflected Jets

away

nea

r

Med

ium

mach

cone

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

Med

ium aw

ay

nea

r

deflect

ed jets

0 1

2 0

Central Au+Au 0-12% triggered

HP2006QM2005

3 < pT,trigger < 4 GeV1 < pT,assoc < 2 GeV

ZYAM/Purdue normalization

Not obviously the best projection-difficult to understand


PHENIX-Polar co-ordinates-wrt ConePHENIX-Polar co-ordinates-wrt Cone

φ

12

13

1213φφφ−=

Trigger

Associated

Method being developed in PHENIX-Better Projection?

Motivation: cone ‘lives’ at constant

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

VanLeeuwen-Ajitnand-HP2006

Combinatorialbackground

Cone simulation

Deflected Jet simulation

More strength at =0 for deflected

=180° swamped?


θ = 120

Uncorrected, no v2 subtraction

*0180=

*00.0=

0110φ=

= 0

Cent: 0-5%PHENIX Preliminary

PHENIX Acceptance

*2φ=

N.N. Ajitanand’s Hard Probes 2006

3 < pT,trigger < 4 GeV1 < pT,assoc < 2 GeV

Experimental results: PHENIXExperimental results: PHENIX

Cone simulation Deflected Jet simulationMiddle of

Long Learning Curve


My parting adviceMy parting advice

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


Backup, Extras, Backup, Extras, what couldn’t fit what couldn’t fit


PHENIX preliminary

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 shapeRP dependence confirms corrected Jet function shape

2222tatavvvv<>≈<><>

• 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


OutlineOutline• 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 isn’t 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 haven’t seen flow put in neither the ridge.


IssuesIssues• 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


8 < pT(trig) < 15 GeV/c

Width of Away-Side PeaksWidth of Away-Side Peaks

• away-side widths similar for central and peripheral

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

STAR nucl-ex/0604018 STARSTAR


PHENIX d+Au resultsPHENIX d+Au results

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

PHENIX, PRC 73, 054903 (2006)


PHENIX d+Au PRC73PHENIX d+Au PRC73

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


• 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

ConclusionsConclusions

€

ˆ x h


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


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 nucl-ex/0603017


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

Correlations in d+Au


jjTT k kT T inin

p+p d+Aup+p d+AuCronin EffectCronin EffectJ/J/ vs D-Y vs D-Y


A few complications for kA few complications for kTT

€

ˆ p Tt (1− ˆ x h ) zt ,a

€

ˆ x h−1 zt kT

2 = xh−1 pout

2 − jTy2 (1+ xh

2)

Jet imbalance due to kT smearing <zt,a> vary with pTt pTa


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.

ISR

PHENIX


We did (re)learn a few things at RHICWe did (re)learn a few things at RHIC• FFF’s formula was really:

• Jan Rak discovered this by insisting to rederive all the formulas, but it was in FFF’s paper.

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

pout2 =xE22 kTy zt 2 + jt

Ty 2+ jaTy 2

CCOR NPB 209, 284 (1982)


<z<ztrigtrig> measured at ISR> measured at ISR

• <ztrig> ~ 0.8-0.9 at ISR, n~ 11

• <ztrig> xT scales

DATA: CCOR NPB 209, 284 (1982)

pTjet=pTtrig+1.5px

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

ztrig=pTtrig/pTjet


kkTT is not a parameter, it can be measured is not a parameter, it can be measured


Feynman Feynman Field & FoxField & Fox to the rescue to the rescue


• 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

jjTT, k, kTT, x, xEE, p, poutout definitions all definitions all

in plane transverse to beam directionin plane transverse to beam direction

pout2 =xE22 kTy 2 + jTy 2+ jTy 2

xE pTt

pout=pT sin

pTt pT


Early theoretical attempt to understand kEarly theoretical attempt to understand kTT

• Modern work falls under the subject “resummation”

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


A puzzle from RHIC: why does A puzzle from RHIC: why does NLO-QCD fit the p-p NLO-QCD fit the p-p 00 spectrum with no k spectrum with no kTT??

Data: PHENIX PRL 91, 241803 (2003)

Theory: W.Vogelsang, see B.Jager, A.Schafer, M.Stratmann,W.Vogelsang PRD67,054005(2003)


kkTT and NLO are distinct---e.g. Drell Yan and NLO are distinct---e.g. Drell Yan

A.S.Ito, et al, PRD23,604 (1981)

Note Gaussian shape, no power-law tail!

J.K.Yoh, et al, CFS, PRL 41, 684 (1978)

A.L.S.Angelis, et al, CCOR, PLB 87, 398 (1979)


<p<pTT>(=>(=2k2kTT) vs ) vs s in Drell-Yans in Drell-Yan

CMOR, NPB348, 1 (1991)


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

ISR CDF


D-Y has Similar Scaling to xD-Y has Similar Scaling to xTT scaling scalingC

FS

, P

RL

41,

684

(19

78)

CMOR, NPB 348, 1 (1991)


But First another lesson But First another lesson from the same period. from the same period.

Why you should Why you should beware of theory curves beware of theory curves

on your dataon your data


Discovery of `Drell-Yan’ and the `Theory’Discovery of `Drell-Yan’ and the `Theory’

Christenson, Lederman…PRL 25, 1523 (1970) `Theory’ Altarelli, Brant Preparata PRL 26 42 (1971)

p+U+-+X

sNN=7.4 GeV


The truth 1974 and laterThe truth 1974 and later

NA50 PLB 477, 28 (2000)

E70 PRL 39 252 (1977)


kkTT and NLO II and NLO II

``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) doesn’t measure kT they derive it by kT-smearing NLO cross predicitons to agree with measurements. See also hep-ex/0407011.

In George Sterman’s words 12/3/04:In George Sterman’s words 12/3/04:


Application to RHICApplication to RHIC


Inclusive single hadron high pInclusive single hadron high pTT spectra in p-p all spectra in p-p all ss


xxTT scaling in p-p collisions x~0.05-0.10 scaling in p-p collisions x~0.05-0.10

xT


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

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


M. May, M. May, et al.,et al.,


High pHigh pTT in A+B collisions--- in A+B collisions---TTABAB Scaling Scaling

view along beam axis

• 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

looking down


PHENIXPHENIXSemi-Semi-

Inclusive Inclusive 00

Au+Au Au+Au ssNNNN=130 and =130 and

200 GeV200 GeVvs pvs pTT

Peripheral 60 -- 80%

Central 0-10%

S.S.Adler, et al, PRC 69, 034910 (2004)


Same data vs xSame data vs xTT on log-log plot on log-log plot


Recall Recall 00: n=5.1 works better for x: n=5.1 works better for xTT> 0.2> 0.2

n=6.3 n=5.1


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

PHENIX preliminary 0 d+Au vs centrality for DNP2003


UA2 results on cosUA2 results on cos* and k* and kTT in direct in direct

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


Comparison with Other ExperimentsComparison with Other Experiments

Preliminary

Systematic errors are not shown

Preliminary

proton-proton collisions proton-antiproton collisions


DATA: CCOR NPB 209, 284 (1982)

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

00 correlations correlations

QQCCDD


QQCCDD follows x follows xT T scaling-very powerful tool scaling-very powerful toolLOQCD, QED: n=4

QCD

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


For A+A: RFor A+A: RAAAA1 before RHIC1 before RHIC

• The importance of comparison data!


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

€

C2(Au + Au) = C2(p + p) + A * (1+ 2v2( pTt )v2( pTa )cos(2Δφ))

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

Co

nd

itio

nal

Pro

bab

ilit

y


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

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

Co

nd

itio

nal

Pro

bab

ilit

y

€

C2(Au + Au) = C2(p + p) + A * (1+ 2v2( pTt )v2( pTa )cos(2Δφ))


Great PR-Is it great Science?Great PR-Is it great Science?

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

Did the away jet vanish in Au+Au? Did the away jet vanish in Au+Au?

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


STAR J. Adams, et al.,

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


Normalized data with PRL95 curveNormalized data with PRL95 curve


PHENIX and E802 EPHENIX and E802 ETT compared compared

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

PHENIX preliminary

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

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