Suppression of Hadrons at Forward Rapidity at RHIC
47th Recontres De Moriond QCD and High Energy
Interactions La Thulie March 10h–17th 2012
Suppression of Hadrons at Forward Rapidity at RHIC
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
Suppression of Hadrons at Forward Rapidity at RHIC 3
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)
Suppression of Hadrons at Forward Rapidity at RHIC 4
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
Suppression of Hadrons at Forward Rapidity at RHIC 5
(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.
Suppression of Hadrons at Forward Rapidity at RHIC 6
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
Suppression of Hadrons at Forward Rapidity at RHIC
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
Suppression of Hadrons at Forward Rapidity at RHIC
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
Suppression of Hadrons at Forward Rapidity at RHIC
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
Suppression of Hadrons at Forward Rapidity at RHIC
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
Suppression of Hadrons at Forward Rapidity at RHIC
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
Suppression of Hadrons at Forward Rapidity at RHIC
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
Suppression of Hadrons at Forward Rapidity at RHIC
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
Suppression of Hadrons at Forward Rapidity at RHIC
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
Suppression of Hadrons at Forward Rapidity at RHIC
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
Suppression of Hadrons at Forward Rapidity at RHIC
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
Suppression of Hadrons at Forward Rapidity at RHIC
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
Suppression of Hadrons at Forward Rapidity at RHIC
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
Suppression of Hadrons at Forward Rapidity at RHIC 20
Backup Slides
Suppression of Hadrons at Forward Rapidity at RHIC
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.
Suppression of Hadrons at Forward Rapidity at RHIC
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
Suppression of Hadrons at Forward Rapidity at RHIC
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
Suppression of Hadrons at Forward Rapidity at RHIC
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
Suppression of Hadrons at Forward Rapidity at RHIC
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
Suppression of Hadrons at Forward Rapidity at RHIC
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
Suppression of Hadrons at Forward Rapidity at RHIC
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
Suppression of Hadrons at Forward Rapidity at RHIC
• 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
Suppression of Hadrons at Forward Rapidity at RHIC 29
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
Suppression of Hadrons at Forward Rapidity at RHIC 30
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
Suppression of Hadrons at Forward Rapidity at RHIC
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
Suppression of Hadrons at Forward Rapidity at RHIC
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
Suppression of Hadrons at Forward Rapidity at RHIC
dAu all data
Centrality Dependence
dAu central
Azimuthal decorrelations show significant dependence on centrality!
dAu peripheral
Suppression of Hadrons at Forward Rapidity at RHIC
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
Suppression of Hadrons at Forward Rapidity at RHIC 35
CGC Calculations K. Tuchin arXiv:09125479
pp
dAu
dAu-centraldAu-peripheral
Suppression of Hadrons at Forward Rapidity at RHIC 36
• 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