Suppression of Hadrons at Forward Rapidity at RHIC

Suppression of Hadrons at Forward Rapidity at RHIC

47th Recontres De Moriond QCD and High Energy

Interactions La Thulie March 10h–17th 2012


Final State of a Au-Au

Collision in STAR

STAR

M. Grosse Perdekamp, UIUC

Suppression of Hadrons at Forward Rapidity at RHIC 2

Outline: Hadron Suppression at Forward Rapidities Initial State in HI Collisions

o A-A Collisions at RHIC and the Initial State Jet quenching, Elliptic flow, J/ψ

o Studying the Initial State in d-A Collisions Hadron cross sections, hadron pair correlations

o Summary & Outlook: p-A at LHC and e-A at EIC

PCM & clust. hadronization

NFD

NFD & hadronic TM

PCM & hadronic TM

CYM & LGT

string & hadronic TMAu Autime

initial statepartonic matter

hadronization

observed final state


J/ψ Production: Some Relevant Cold Nuclear Matter Effects in the Initial State

(I) Shadowing (from fits to DIS data or model calculations)

high x low x

D

Dcc moversco-

(II) Dissociation of into two D mesons by nucleus or co-movers

cc

(III) Gluon saturation from non-linear gluon interactions for the high gluon densities at small x

K. Eskola H. Paukkumen, C. SalgadoJHEP 0807:102,2008 DGLAP LO analysis of nuclear pdfs

RGPb

GPb (x,Q2)=RGPb(x,Q2) Gp (x,Q2)


J/ψ : Most of the Suppression in A-A is from Cold Nuclear Matter Effects found in d-A

CollisionsEKS shadowing + dissociation: use d-Au data to determine break-up cross section

PRC 77,024912(2008)

EKS shadowing + dissociation: from d-Au vs Au-Au data at mid-rapidity

EKS shadowing + dissociation: from d-Au vs Au-Au data at forward-rapidity


(III) cont’d The Color Glass Condensate see for example, F. Gelis, E. Iancu, J. Jalilian-Marian, R. Venugopalan, arXiv:1002.0333

gluon density saturates forlarge densities at small x :

222 nμαnnYn

StSS

g emissiondiffusion

g-g merging

),( TkYn

g-g merging large if

saturation scale

QS, nuclear enhancement ~ A1/3

1nαS

STTS αkYnkQ 1),( that so in

Non-linear evolution eqn.

CGC: an effective field theory:Small-x gluons are described as the color fields radiated by fast color sources at higher rapidity. This EFT describes the saturated gluons (slow partons) as a Color Glass Condensate.

The EFT provides a gauge invariant,universal distribution, W(ρ): W(ρ) ~ probability to find a configuration ρ of color sources in a nucleus.

The evolution of W(ρ) is described bythe JIMWLK equation.


CGC Expectations for Nuclear Modification of Hadron Cross Sections in

d-Au Collisions 2

2

/( )/

dAT

dA T ppdA T

d N dp dR pT d dp d

Nuclear Modification Factor:

CGC-based expectationsKharzeev, Kovchegov, and Tuchin, Phys.Rev.D68:094013,2003

RdA

pT

rapidity, y

gluon saturation at low x RdAu decreases at forward rapidity measure RdAu for different hadrons: h+,-, π0, J/ψ


BRAHMS, PRL 93, 242303

RdA

uBRAHMS d+Au Cross Sections Decrease with Increasing Rapidity and Centrality

Hadron production is suppressed at large rapidityconsistent with saturation effects at low x in the Au gluon densities CGC

Similar results from PHOBOS, STAR and PHENIX

7


Theory vs Data CGC

Not bad! However, different K factorsfor h+,- in BRAHMS and π0 in STAR

p+p d+Au

J. Albacete and C. Marquet, PLB687, 184

8


Theory vs Data Cronin + Shadowing + E-loss I.Vitev, T. Goldman, M.B. Johnson,

JW. Qiu, Phys. Rev. D74 (2006)

RdA results alone do not uniquely demonstrate gluon

saturation. Competing explanations can account for observed hadron suppression in d-Au at forward rapidity !

Not bad either!

9


Idea:Presence of dense gluon field in the Au nucleus leads to scattering of multiple gluons and parton can distribute its energy to many scattering centers Mono-jet signature ! D. Kharzeev, E. Levin, L. McLerran, Nucl.Phys.A748:627-640,2005

dilute parton system -- d

dense gluon field -- Au

Probing for Gluon Saturation Effects with Hadron-Hadron Correlations in d+Au

Experimental signature:Angular correlation between hadrons in opposing hemisphereswidening of correlation

width of d-Au compared to pp reduction in associated

yield of hadrons on the away site

Effects large at low x forward rapidity forward EMC upgrades in STAR : 2 < η < 4 PHENIX : 3.1 < |η| < 3.8

jet withtrigger hadron

jet with associated hadron

pT is balanced by many gluons

10

Suppression of Hadrons at Forward Rapidity at RHIC11

PHENIX Muon Piston CalorimeterTechnology ALICE(PHOS)

PbWO4 avalanche photo diode readout

Acceptance: 3.1 < η < 3.9, 0 < φ < 2π -3.7 < η < -3.1, 0 < φ < 2π

Both detectors were installed for 2008 d-Au run.

PbWO4 + APD + Preamp

Asse

mbl

y at

UIU

C

MPC integrated in thepiston of the muonspectrometer magnet.

11


Use of Forward Calorimeter for the Measurement of di-Hadron Correlations

d Auasssociatedp0 or EM-clusters3.1 < η < 3.9

PHENIX central spectrometer magnet

Backward direction (South)

Forward direction (North)

Muon Piston Calorimeter (MPC)

triggerp0 or h+/-

|η|<0.35

Side View

mid-fwd xgluon ~ 10-2

fwd-fwd xgluon ~ 10-4-10-3

trigger EM-cluster 3.1<η<3.9

asssociated p0 3.1 < η < 3.9

mid-fwd xgluon ~ 10-2merged p0s

p0MPCPbWO4

ϕ

12


Df

mid-fwd

assocdAupp

trig

dAupppair

dAupp NN

CY,

,

,

Cor

rela

ted

Npair Conditional Yield

Di-Hadron Nuclear Modification factor

trigdA

pp

dAudA R

CYCYJ

Possible indicators of nuclear effects JdA < 1, RdA < 1 ( only mono-jets JdA ~ 0 ) angular de-correlation of widths

pppairpp

dApairdA

colldA N

J

//1

pp

sglpp

dAsgldA

colldA N

R

//1

Sgl-Hadron Nuclear Modification factor

Di-Hadron Conditional Yield CY and JdA

13


pp data dAu data

(dAu)- (pp)=0.52±0.05Strong azimuthal broadening from pp to dAu for away side, while near side remains unchanged.

(rad)(rad)

STAR 2008 d-Au π0 Forward - Forward

Correlations

14


Comparison to CGC Prediction

CGC prediction for b=0 (central collisions)by Cyrille MarquetNucl.Phys.A796:41-60,2007

dAu CentralStrong suppression of away side peak in central dAu is consistent with CGC prediction

15


PHENIX JdA vs xfrag no Suppression for Peripheral Collisions !

sepep

x TTfragAu

2121

Note: points for mid-fwd JdA are offset for visual clarity

60-88%(Peripheral)

Trig pT: 1.1-2.0 GeV/c Trig pT: 0.5-7 GeV/c

Forward-Forward Mid-Forward

0-20%(Central)

PHENIX JdA Strong Suppression for Central Collisions at Low xfrag !

Back-to-back hadron (jet) suppression is large at low-xfor central collisions mono-jet like ?! CGC ? Shadowing + E-loss?

16PHENIX Phys.Rev.Lett. 107 (2011) 172301


JdA vs pQCD, Shadowing and Energy Loss

17

Z.-B.Kang, I. Vitev, H. Xing arXiv:1112.6021

pQCD + shadowing+ initial and final state energy loss

JdA < 1 is not a unique CGC signature

JdAu


d

cdab

pbpp

ap

d

cdab

AubAud

ad

pppairsppcoll

dAupairsdAu

dA

zzDxfxf

zzDxfxfN

J

c

c

,)()(

,)()(/

/

Leading Order JdA ~ RGAU

xAu

EPS09 NLO gluons

Eskola , Paukkunen, Salgado, JHP04 (2009)065

Low x, mostly gluons JdA ~ RGAu

High x, mostly quarksWeak effects expected

60-88%(Peripheral)

0-20%(Central)

Forward-Forward Mid-Forward

b=0-100%Q2 = 4 GeV2

),(),(),( 2

22

QxAxGQxxGQxR

p

AuAuG

18


Summary & Future Steps Towards GA(x) and knowing the Initial State of HI Collisions

19

o RHIC data on single and di-hadron suppression suggest large nuclear effects in the initial state of HI collisions.o A detailed theoretical analysis of the available data yet has to be carried out.o Next: Hadron and Jet measurements in p-Pb at the LHCo Future: GA(x) measurements at an electron-ion collider

eRHIC: 10 GeV + 100 GeV/n - estimate for 10 fb-1

e+A whitepaper (2007)

Precise extractionof GA(x,Q2) fromFL measurementsat EIC

will be able to dis-criminate betweendifferent models


Backup Slides


21

Why Study Nuclear Effects in Nucleon Structure in Particular the Nuclear Gluon Distribution GA(x) ?

General interest:• Extend Understanding of QCD into the non- perturbative regime of high field strengths

and large gluon densities.• Search for universal

properties of nuclear matter at low x and

high energies.

Heavy Ion Collisions:• Understand the initial

state to obtain quantitative

description of the final state

in HI-collisions.

• Establish theoretical framework to describe initial state of HI-collisions based

on measurements of GA (x) in p/d-A or e-A.


Jet Quenching: Initial State Saturation of GA(x) or QGP Final State Effect ?

PHENIX RAuAu and RdAu for π0 (from 2002 Au-Au and 2003 d-Au runs)

Nuclear modification factor:

Quantify nuclear effects in hadron production

RAuAu < 1

RdAu ~ 1

ddpNdddpNd

N Tpp

inel

TAA

coll //1

2

2

RAA

Two explanations for RAuAu < 1

(I) suppression of nuclear GA (x) (II) final state effects of strongly interacting partonic matter

Control measurement of RdAu ~ 1 final state effect!

22


Elliptic Flow v2 : Choice of Initial State GA(x) has Large Impact on Hydro

Calculations

Color Glass Condensate

T. Hirano, U. Heinz, D. Kharzeev,R. Lacey, Y. NaraPhys.Lett.B636:299-304,2006

PHOBOS v2 vs Hydro Calculations

Brodsky-Gunion-Kuhn Model Phys.Rev.Lett.39:1120

Knowledge of the initialstate is important for thequantitative interpretation of experimental results inheavy ion collisions!

23


Probing Low x with Correlation Measurements for Neutral Pions

PYTHIA p+p study, STAR, L. Bland

FTPC

TPCBarrel EMC

FMS

asso gives handle on xgluon

Trigger forward p0

Forward-forward di-hadron correlations reach down to <xg > ~ 10-3

With nuclear enhancement xg ~ 10-4


Alternative Explanation of Rapidity-Separated di-Hadron correlations in d+Au

Complete (coherent + multiple elastic scattering) treatment of multiple parton scattering gives suppression of pairs with respect to singles for mid-rapidity tag!

However, small for forward trigger particle!

J. Qiu, I. Vitev, Phys.Lett.B632:507-511,2006


Forward Meson Spectrometer (FMS) Pb-glass EM calorimeter ~x50 more acceptance

STAR

BEMC: -1.0 < < 1.0 TPC: -1.0 < < 1.0 FMS: 2.5 < < 4.1

The STAR FMS Upgrade and Configuration for Run 2008 see A. Ogawa

H2, Sunday 11:57


IdAu from the PHENIX Muon ArmsObservations at PHENIX using the 2003 d-Au sample:

– Left: IdA for hadrons 1.4 < || < 2.0 , PHENIX muon arms. correlated with h+/- in || < 0.35, central arms.– Right: Comparison of conditional yields with different trigger

particle pseudo-rapidities and different collision centralities No significant suppression or widening seen within large

uncertainties !

Phys.Rev.Lett. 96 (2006) 222301

Trigger pT range

pTaassociated

0-40% centrality

40-88% centralityIdA

IdA

pTa, h+/-

pTt, hadron


• The MPC can reliably detect pions (via p0g g) up to E =17 GeV• To go to higher pT, use single clusters in the calorimeter

– Use p0s for 7 GeV < E < 17 GeV– Use clusters for 20 GeV < E < 50 GeV

• Correlation measurements are performed using p0s, clusters• Use event mixing to identify pions: foreground photons from same event background photons from different events

MPC Pion/Cluster Identification

N

South MPC

Minv (GeV/c2)

12 < E < 15Foreground

Background

Yield


MPC Pion Selection• Cuts

– Cluster Cuts• Cluster ecore > 1.0 (redundant w/ pion assym and energy

cuts)– Pi0 pair

• E > 6 GeV• Asym < 0.6• Separation cuts to match fg/bg mass distribution• Max(dispx, dispy) < 2.5

• Use mixed events to extract yields– Normalize from 0.25-0.4 presently

5.1)()( 221

221 iyiyixix

cmyyxxdr 5.3)()( 221

221


MPC/CA Cuts• MPC pi0 ID

– Mass window of 0.1-0.2 GeV + previously shown cuts– 7 – 17 GeV energy range– Max(dispx,dispy) <= 2.5

• Charged Hadron ID Track Quality == 31 or 63– n0 <0 Rich cut– pT < 4.7 GeV– pc3 sdz and sdphi matching < 3 – -70 < zed < 70

• EMC pi0– Alpha < 0.8– PbGl min E = 0.1, PbSc min E = 0.2– Chi2 cut of 3, prob cut of 0.02– Sector matching– Mass window 0.1-0.18– Trigger bit check


PRL 94, 082302

Suppression in the d direction and enhancement in the Au fragmentation region

Similar Results from STAR, PHENIX and PHOBOS

d x1 Au x2

x1 >> x2 for forward particle, xg = x2 0


pp data dAu data

(dAu)- (pp)=0.52±0.05Strong azimuthal broadening from pp to dAu for away side, while near side remains unchanged.

(rad)(rad)

STAR Run8 FMS : π0 Forward - Forward

Correlations


dAu all data

Centrality Dependence

dAu central

Azimuthal decorrelations show significant dependence on centrality!

dAu peripheral


Comparison to CGC prediction

CGC prediction for b=0 (central)by Cyrille MarquetNucl.Phys.A796:41-60,2007

dAu CentralStrong suppression of away side peak in central dAu is consistent with CGC prediction


CGC Calculations K. Tuchin arXiv:09125479

pp

dAu

dAu-centraldAu-peripheral


• Momentum distribution of gluons in nuclei? Extract via scaling violation in F2 Direct Measurement: FL ~ xG(x,Q2) Inelastic vector meson production Diffractive vector meson production• Space-time distribution of gluons in nuclei? Exclusive final states Deep Virtual Compton Scattering F2, FL for various impact parameters• Role of colour-neutral (Pomeron) excitations? Diffractive cross-section Diffractive structure functions and vector meson productions Abundance and distribution of rapidity gaps• Interaction of fast probes with gluonic medium? Hadronization, Fragmentation Energy loss CGC EFT: will it be possible to carry out a global analysis of RHIC d+A, LHC p+A and EIC e+A to extract W(ρ) and thus demonstrate universality of W(ρ) ?

EIC: 4 Key Measurements in e+A Physics

Documents

Suppression of Hadrons at Forward Rapidity at RHIC