Transcript The hemisphere problem revisited

Suppression of Hadrons
at Forward Rapidity at RHIC
M. Grosse Perdekamp, UIUC
STAR
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
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
observed final state
initial state
partonic
matter
Au
hadronization
Au
CYM & LGT
time
Suppression of Hadrons at Forward Rapidity at RHIC
2
J/ψ Production: Some Relevant Cold Nuclear
Matter Effects in the Initial State
(I) Shadowing (from fits to DIS
data or model calculations)
RGPb
(II) Dissociation of cc
into two D mesons by
nucleus or co-movers
D
cc
co-movers
D
(III) Gluon saturation from non-linear
gluon interactions for the high
gluon densities at small x
K. Eskola H. Paukkumen, C. Salgado
JHEP 0807:102,2008
low x
high x
 DGLAP LO analysis of nuclear pdfs
GPb (x,Q2)=RGPb(x,Q2) Gp (x,Q2)
Suppression of Hadrons at Forward Rapidity at RHIC
3
J/ψ : Most of the Suppression in A-A is from Cold
Nuclear Matter Effects found in d-A Collisions
EKS shadowing + dissociation:
use d-Au data to determine
break-up cross section
EKS shadowing + dissociation:
from d-Au vs Au-Au data
at mid-rapidity
forward-rapidity
PRC 77,024912(2008)
Suppression of Hadrons at Forward Rapidity at RHIC
4
(III) cont’d
The Color Glass Condensate
see for example, F. Gelis, E. Iancu, J. JalilianMarian, R. Venugopalan, arXiv:1002.0333
gluon density n(Y , kT ) saturates for
CGC:
effective
large an
densities
at field
smalltheory:
x:
Small-x gluons are described as the
Non-linear
evolution
color
fields radiated
byeqn.
fast color
sources
at higher rapidity. This EFT
n
2
2 2
 the
n



n

μα
describes
saturated
gluons
S
S t
S n(slow
Y
partons)
as a Color Glass Condensate.
diffusion
g-ginvariant,
merging
g emission
The EFT
provides a gauge
universal distribution, W(ρ):
 1a
g-g merging
large if αtoS nfind
W(ρ) ~ probability
configuration ρ of color sources
in a nucleus.
saturation
scale
QS in kT of
so W(ρ)
thatnis
(Y described
, kT )  1 by
The evolution
αS
the JIMWLK equation.
QS, nuclear enhancement ~ A1/3
Suppression of Hadrons at Forward Rapidity at RHIC
5
CGC Expectations for Nuclear Modification of
Hadron Cross Sections in d-Au Collisions
Nuclear
Modification
Factor:
RdA
d 2 N dA / dpT d
RdA ( pT ) 
TdAd 2 pp / dpT d
CGC-based expectations
Kharzeev, Kovchegov, and Tuchin,
Phys.Rev.D68:094013,2003
rapidity, y
gluon saturation at low x
 RdAu decreases
at forward rapidity
measure RdAu for
different hadrons:
h+,-, π0, J/ψ
pT
Suppression of Hadrons at Forward Rapidity at RHIC
6
BRAHMS d+Au Cross Sections Decrease with
Increasing Rapidity and Centrality
RdAu
BRAHMS, PRL 93, 242303
Hadron production is suppressed at large rapidity
consistent with saturation effects at low x in the
Au gluon densities  CGC
Similar results from PHOBOS, STAR and PHENIX
Suppression of Hadrons at Forward Rapidity at RHIC
7
Theory vs Data  CGC
J. Albacete and C. Marquet, PLB687, 184
p+p
d+Au
Not bad! However, different K factors
for h+,- in BRAHMS and π0 in STAR
Suppression of Hadrons at Forward Rapidity at RHIC
8
Theory vs Data  Cronin +
Shadowing + E-loss
I.Vitev, T. Goldman, M.B. Johnson,
JW. Qiu, Phys. Rev. D74 (2006)
Not bad either!
RdA results alone do not uniquely demonstrate gluon
saturation. Competing explanations can account for
observed hadron suppression in d-Au at forward rapidity !
Suppression of Hadrons at Forward Rapidity at RHIC
9
Probing for Gluon Saturation Effects with
Hadron-Hadron Correlations in d+Au
dilute parton
system -- d
dense gluon
field -- Au
pT is balanced by
many gluons
jet with
trigger hadron
jet with
associated hadron
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
Experimental signature:
Angular correlation
between hadrons in opposing
hemispheres
widening 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
Suppression of Hadrons at Forward Rapidity at RHIC
10
PHENIX Muon Piston Calorimeter
Technology  ALICE(PHOS)
PbWO4
avalanche photo diode readout
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
Assembly at UIUC
Acceptance:
MPC integrated in the
piston of the muon
spectrometer magnet.
11
Suppression of Hadrons at Forward Rapidity at RHIC
11
Use of Forward Calorimeter for the Measurement
of di-Hadron Correlations
merged p0s PHENIX central
spectrometer magnet
ϕ
Muon Piston
Calorimeter (MPC)
d
p0
MPC
PbWO4
mid-fwd
xgluon ~ 10-2
fwd-fwd
xgluon ~ 10-4-10-3
trigger
EM-cluster
3.1<η<3.9
Au
asssociated
asssociated
p0
p0 or EM-clusters
3.1
3.1<<ηη<<3.9
3.9
trigger
p0 or h+/|η|<0.35
Backward direction
(South) 
Forward direction
(North) 
Side View
Suppression of Hadrons at Forward Rapidity at RHIC
12
Npair
Di-Hadron Conditional Yield CY and JdA
mid-fwd
Conditional Yield
Correlated
CY pp ,dAu 
pp , dAu
N pair
pp , dAu
N trig
 assoc
Df
Di-Hadron Nuclear
Modification factor
J dA
J dA
pair
/  dA
1  dA

pair
N coll  pp
/  pp
CYdAu
trig

 RdA
CYpp
RdA
Sgl-Hadron Nuclear
Modification factor
sgl
/  dA
1  dA

sgl
N coll  pp
/  pp
Possible indicators of nuclear effects
JdA < 1, RdA < 1 ( only mono-jets  JdA ~ 0 )
angular de-correlation of widths
Suppression of Hadrons at Forward Rapidity at RHIC
13
STAR 2008 d-Au
π0 Forward - Forward Correlations
pp data
(rad)
Strong azimuthal broadening from pp to
dAu for away side, while near side remains
unchanged.
(rad)
dAu data
(dAu)- (pp)=0.52±0.05
Suppression of Hadrons at Forward Rapidity at RHIC
14
Comparison to CGC Prediction
CGC prediction for b=0
(central collisions)
by Cyrille Marquet
Nucl.Phys.A796:41-60,2007
dAu Central
Strong suppression of away
side peak in central dAu is
consistent with CGC prediction
Suppression of Hadrons at Forward Rapidity at RHIC
15
PHENIX
PHENIXJJdAdA Strong
vs xfrag Suppression
no Suppression
for Central
for
Peripheral
CollisionsCollisions
at Low xfrag
! !
Forward-Forward
Mid-Forward
60-88%
(Peripheral)
Trig pT: 1.1-2.0 GeV/c
Trig pT: 0.5-7 GeV/c
0-20%
(Central)
frag
x Au

pT 1 e
 1
 pT 2 e
 2
Back-to-back hadron (jet)
suppression is large at low-x
for central collisions
 mono-jet like ?!
 CGC ? Shadowing + E-loss?
s
PHENIX Phys.Rev.Lett. 107 (2011) 172301
Note: points for mid-fwd JdA are offset for visual clarity
Suppression of Hadrons at Forward Rapidity at RHIC
16
JdA vs pQCD, Shadowing and Energy Loss
Z.-B.Kang, I. Vitev, H. Xing arXiv:1112.6021
JdAu
pQCD + shadowing
+ initial and final
state energy loss
JdA < 1 is not
a unique CGC
signature
Suppression of Hadrons at Forward Rapidity at RHIC
17
Leading Order JdA ~
RGAU
xGAu ( x, Q 2 )
R ( x, Q ) 
AxGp ( x, Q 2 )
Au
G
2
Eskola , Paukkunen, Salgado, JHP04 (2009)065
Mid-Forward
Forward-Forward
60-88%
(Peripheral)
0-20%
(Central)
b=0-100%
Q2 = 4 GeV2
EPS09 NLO gluons
xAu
 ab cd
pairs
b
 dAu
/  dAu
f da ( xd )  f Au
( x Au )  
 D z , z d 
J dA 

pairs
 ab cd
N coll  pp /  pp
f pa ( x p )  f pb ( x p )  
 D z , z d 
c
c
High x, mostly quarks
Weak effects expected
Low x, mostly gluons  JdA ~ RGAu
Suppression of Hadrons at Forward Rapidity at RHIC
18
Summary & Future Steps Towards GA(x) and
knowing the Initial State of HI Collisions
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 LHC
o Future: GA(x) measurements at an electron-ion collider
e+A whitepaper (2007)
Precise extraction
of GA(x,Q2) from
FL measurements
at EIC
will be able to discriminate between
different models
eRHIC: 10 GeV + 100 GeV/n - estimate for 10 fb-1
Suppression of Hadrons at Forward Rapidity at RHIC
19
Backup Slides
Suppression of Hadrons at Forward Rapidity at RHIC
20
Why Study Nuclear Effects in Nucleon Structure in
Particular the Nuclear Gluon Distribution GA(x) ?
General interest:
Heavy Ion Collisions:
• Extend Understanding
of QCD into the nonperturbative regime of
high field strengths and
large gluon densities.
• Understand the initial state
to obtain quantitative
description of the final state
in HI-collisions.
• Search for universal
properties of nuclear
matter at low x and high
energies.
• 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
21
Jet Quenching: Initial State Saturation
of GA(x) or QGP Final State Effect ?
Quantify nuclear
effects in hadron
production
Nuclear
modification
factor:
1 d 2 N A A / dpT d
RAA 
p p
Ncoll d 2 Ninel
/ dpT d
PHENIX RAuAu and RdAu for π0
Two explanations for RAuAu < 1
(from 2002 Au-Au and 2003 d-Au runs)
RdAu ~ 1
(I) suppression of nuclear GA (x)
(II) final state effects of strongly
interacting partonic matter
Control measurement of
RdAu ~ 1  final state effect!
RAuAu < 1
Suppression of Hadrons at Forward Rapidity at RHIC
22
Elliptic Flow v2 : Choice of Initial State GA(x) has
Large Impact on Hydro Calculations
PHOBOS v2 vs Hydro Calculations
Color Glass Condensate
Brodsky-Gunion-Kuhn Model
Phys.Rev.Lett.39:1120
T. Hirano, U. Heinz, D. Kharzeev,
R. Lacey, Y. Nara
Phys.Lett.B636:299-304,2006

Knowledge of the initial
state is important for the
quantitative interpretation
of experimental results in
heavy ion collisions!
Suppression of Hadrons at Forward Rapidity at RHIC
23
Probing Low x with Correlation Measurements
for Neutral Pions
PYTHIA p+p study, STAR, L. Bland
Trigger forward p0
Forward-forward di-hadron
correlations reach down
to <xg > ~ 10-3
FMS
TPC
Barrel EMC
FTPC
asso gives handle on xgluon
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 midrapidity 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
STAR
The STAR FMS Upgrade and
Configuration for Run 2008
see A. Ogawa
H2, Sunday 11:57
BEMC: -1.0 <  < 1.0
TPC: -1.0 <  < 1.0
FMS: 2.5 <  < 4.1
Forward Meson Spectrometer (FMS)
Pb-glass EM calorimeter
~x50 more acceptance
Suppression of Hadrons at Forward Rapidity at RHIC
IdAu from the PHENIX Muon Arms
pTa, h+/-
Observations at PHENIX using the 2003 d-Au sample:
pTt, hadron
– 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 !
0-40% centrality 40-88% centrality
IdA
Trigger pT
range
IdA
pTaassociated
Phys.Rev.Lett. 96 (2006) 222301
Suppression of Hadrons at Forward Rapidity at RHIC
MPC Pion/Cluster Identification
•
•
•
•
The MPC can reliably detect pions (via p0g 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
Foreground 12 < E < 15
Background
N
Yield
Minv (GeV/c2)
Suppression of Hadrons at Forward Rapidity at RHIC
South MPC
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
dr  ( x1  x2 ) 2  ( y1  y2 ) 2  3.5cm
(ix1  ix2 ) 2  (iy1  iy2 ) 2  1.5
•
Use mixed events to extract yields
– Normalize from 0.25-0.4 presently
Suppression of Hadrons at Forward Rapidity at RHIC
29
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
30
Similar Results from
STAR, PHENIX and PHOBOS
PRL 94, 082302
Suppression in the d direction and
enhancement in the Au fragmentation region
d  x1
Au  x2
x1 >> x2 for forward particle, xg = x2  0
Suppression of Hadrons at Forward Rapidity at RHIC
STAR Run8 FMS :
π0 Forward - Forward Correlations
pp data
(rad)
Strong azimuthal broadening from pp to
dAu for away side, while near side remains
unchanged.
(rad)
dAu data
(dAu)- (pp)=0.52±0.05
Suppression of Hadrons at Forward Rapidity at RHIC
Centrality Dependence
dAu all data
dAu peripheral
dAu central
Azimuthal
decorrelations show
significant dependence
on centrality!
Suppression of Hadrons at Forward Rapidity at RHIC
Comparison to CGC prediction
CGC prediction
for b=0 (central)
by Cyrille Marquet
Nucl.Phys.A796:41-60,2007
dAu Central
Strong suppression of away
side peak in central dAu is
consistent with CGC prediction
Suppression of Hadrons at Forward Rapidity at RHIC
CGC Calculations K. Tuchin arXiv:09125479
dAu
pp
dAu-peripheral
dAu-central
Suppression of Hadrons at Forward Rapidity at RHIC
35
EIC: 4 Key Measurements in e+A Physics
• 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) ?
Suppression of Hadrons at Forward Rapidity at RHIC
36