19 November 2004RHIC-II workshop, BNL 1

Forward PhysicsForward Physicsat RHIC and LHCat RHIC and LHC

report from the Lawrence Workshopreport from the Lawrence Workshop

F.VidebækF.Videbæk

BNLBNL

19 November 2004RHIC-II workshop, BNL 2

Program of meetingProgram of meetinghttp://agenda.cern.ch/fullAgenda.php?ida=a044385

Color Glass CondensateA.Mueller – Review of HERA dataR.Debbe -BRAHMS forward programB.Wysloch -The forward detectors of CMSL.McLerran -Color Glass Condensate. Physical Picture and

simple questionsP.Armesto -geometric ScalingK.Tuchin – Forward Physics at RHIC. Onset of SaturationR.Hwa – Forward Production by Parton RecombinationD.Kahana - - Initial thoughts for D+A

Heavy Ion systematicI.Bearden – BRAHMS Au-Au resultsR.Hollis – limiting fragmentationG.Stephans – fixed target at RHIC

SPINF.Videbaek – BRAHMS spinJ.Qiu – RHIC spinJ.Ralston – disentangling forward physics

19 November 2004RHIC-II workshop, BNL 3

McLerran: Phase Space of Interesting Physics

Small x: Potentially large region in Q

Matter has universal properties at small x:Only variable is the saturation momentum!

Is this true?

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Crucial Observations:

Geometric Scaling in epLimiting Fragmentation

Renormalization Group

Are these connected by universal QCD properties at large y.

19 November 2004RHIC-II workshop, BNL 5

Developing Theoretical Story:Developing Theoretical Story:

Fluctuations are important:Evolution equations from low density to high density

are fluctuation dominated.

Event by event studies with wide coverage in x and/or pT?What are predictions for fluctuation spectra in observables?

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Deep Inelastic Scattering eA has no direct access (first order) to the gluon PDF it measures q - qbar

To access gluon PDF the preferred system would be p+A thru “gluon-initiated” g+q or g +g interactions.

The “benefits” of p+A systemsThe “benefits” of p+A systems

R.Debbe

19 November 2004RHIC-II workshop, BNL 9

At 4 degrees (y~3 for pions) and pT = 1 GeV/c one can reach to values as low of x2 ~ 10-4

But one has to remember that that low number is a lower limit, not a typical value.

From Gusev, Strickman, and Vogelsang.

Most of the data collected at 4 degrees would have x2~0.01

19 November 2004RHIC-II workshop, BNL 10

K.TuchinK.TuchinForward Physics at RHIC onset of saturationForward Physics at RHIC onset of saturation

19 November 2004RHIC-II workshop, BNL 11

Scaling of charm spectra with atomic Scaling of charm spectra with atomic number number AA(Kharzeev)(Kharzeev)

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Forward Production by Parton Recombination

Rudolph C. Hwa -- conclusionNo change of physics from <0 to >0.No multiple scattering or gluon saturation put in explicitly.Behaviors to checkβ, dependences pT spectra (a) pions

(b) protons If p/> 0.2, difficult forfragmentation

RCP well reproduced with only the recombination of

soft and shower partons.•Back-to-back jets•Di-hadron correlations

No conflict between CGC and recombination, only question is where?

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• Different rapidities provide different densities of the medium: Sensitive to the dynamics

• Largest medium effect at mid-rapidity?

• Rapidity dependent high-pT suppression factors: provide information on dynamical medium effect

Rapidity Dependent High-pRapidity Dependent High-pTT MeasurementMeasurement

Nucl-th/0108056, Polleri and Yuan

at fixed time

y~0

high-y

Nu

cle

ar

Mod

ificati

on

Facto

rBRAHMS forward rapidity

19 November 2004RHIC-II workshop, BNL 16

Rcp for hRcp for h++ and h and h-- at at ~3.2~3.2 Rcp at ~3.2 for charged

hadrons

Strong centrality dependence:

Rcp(0-10%) < Rcp(20-40%)

No significant dependence

in 0<<3.2

Maximum at pT~2GeV/c

(rapidity independent soft-hard

transition?)

Systematic Errors

- 10-15% overall

- 10% p-by-p

Is this understood?

~3.2

~2.2~0

BRAHMS PRL 91 (2003)

BRAHMS Preliminary

19 November 2004RHIC-II workshop, BNL 17

3D-Hydro+Jet3D-Hydro+Jet

PRC 68 (2003) 064902 Hirano and Nara

3D Hydrodynamic Simulation with Jet (pQCD/PYTHIA)

Qualitatively describe data with pseudo-rapidity dependence

19 November 2004RHIC-II workshop, BNL 18

Divergence at higher y :Associated K+ productionNo single source with

unique T and B

Strangeness with KaonsStrangeness with Kaons

RAPIDITY DEPENDENCE

High rapidity equivalent in certain ways to lower energy data at mid-rapidity? Can be used to explore baryon high-density matter ?

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p+p, d-Ap+p, d-A

UA5 (200-900) → Z.Phys.C 43 (1989) 1ISR (23.6,45.2) → Nucl.Phys B129 365 (1977)

d+Au data from nucl-ex/0409021p+Em referenced therein

Limiting Fragmentation Observations at PHOBOSLimiting Fragmentation Observations at PHOBOS Richard S Hollis, UICRichard S Hollis, UIC

19 November 2004RHIC-II workshop, BNL 20

Questions raisedQuestions raised

Several questions remainCentrality dependence for whole rangeCollision species dependenceWill Cu+Cu fit into Au+Au data systematics?Is this observation specific to η?Original hypothesis was for rapidity distributionsDoes each particle species exhibit the same features?Limiting fragmentation also seen for v2.

Should these measurements be done for identified hadrons?

19 November 2004RHIC-II workshop, BNL 21

RHIC spin – Jianwei Qiu, Iowa S.U.RHIC spin – Jianwei Qiu, Iowa S.U.

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NN = -0.08 +- = -0.08 +- 0.005 +- [0.015] in 0.17 < x0.005 +- [0.015] in 0.17 < xFF < < 0.320.32

The SSA needs xf-pt coverage to disentangle phenomena (Collins, Sievers…)Jet-correlations studies important.

19 November 2004RHIC-II workshop, BNL 23

Multiplicity and hermetic coverage to |Multiplicity and hermetic coverage to |ηη|<7|<7 Zero Degree EnergyZero Degree Energy Physics:Physics:

– CentralityCentrality– Limiting FragmentationLimiting Fragmentation– Peripheral and ultra-peripheral collisionsPeripheral and ultra-peripheral collisions– Low-x, Color-Glass CondensateLow-x, Color-Glass Condensate– DCC, Centauros, StrangeletsDCC, Centauros, Strangelets

Forward Region:B.Wyslouch

19 November 2004RHIC-II workshop, BNL 24

Emerging ThemesEmerging Themes

(Armesto) To clarify the role of saturation (scaling): To clarify the role of saturation (scaling): more data needed, e.g. more data needed, e.g.

• pp, pA and AA at 0 < y < 5 (Y -scan of Qs2).• pA with several A at b = 0 (A-scan of Qs2 ).• AA at different b (centrality evolution of multiplicities).• Correlations in pA for the same and different rapidities.

(Mueller) Need to understand the early times.• measurements from initial system ( jets, photons, di-leptons)

19 November 2004RHIC-II workshop, BNL 25

(Tuchin) At RHIC we are starting to see a novel effects due to a quasi-classical regime of QCD - the Color Glass Condensate, first signatures of which where observed at HERA.

Future tests of CGC at RHIC y À 1: inclusive hadrons (V) open charm ? hidden charm ? di-leptons ? correlations and Fluctuations ?(McLerran) Fluctuations are important:Evolution equations from low density to high densityare fluctuation dominated.

Event by event studies with wide coverage in x and/or pT?What are predictions for fluctuation spectra in observables?

19 November 2004RHIC-II workshop, BNL 26

(J.Qiu) RHIC spin

(discussion) -Can the connection between saturation and limiting fragmentation be clarified by additional high-y measurements for identified particles.•Should the options to investigate systems with large baryon density vs. rapidity or fixed target at lower energy be explored?•How firm is the evidence for CGC at RHIC?

19 November 2004RHIC-II workshop, BNL 27

The pitch for Forward PhysicsThe pitch for Forward Physics

Many of the issues brought up at the workshop are Many of the issues brought up at the workshop are central to an enhanced forward physics program.central to an enhanced forward physics program.

The RHIC program The RHIC program isis on its way to implement this on its way to implement this for upgrades, and possible future detector.for upgrades, and possible future detector.

There are good reasons this should be a There are good reasons this should be a motivation and an integral part for the RHIC-II motivation and an integral part for the RHIC-II program.program.

Many of the points here have also been addressed in the Letter of Many of the points here have also been addressed in the Letter of Intent of a new detector for RHIC Intent of a new detector for RHIC http://www.bnl.gov/henp/pac0904.asphttp://www.bnl.gov/henp/pac0904.asp

Low-x physics will be important too at LHC. The Low-x physics will be important too at LHC. The opportunities for systematic measurements at opportunities for systematic measurements at RHIC with pA, AA makes it competitive.RHIC with pA, AA makes it competitive.