Carl Gagliardi – d+Au Collisions at STAR – DIS’06 1
d+Au Collisions at STAR
Outline
• d+Au collisions and saturation physics at RHIC• Recent STAR results• STAR plans for the future
Carl A. GagliardiTexas A&M University
for the CollaborationSTARSTAR
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 2
E-M Calorimeter
Time of Flight
Projection Chamber
STAR detector
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 3
Mid-rapidity p+p at RHIC and NLO pQCDPRL 91, 241803
PHENIX π0
Calculations byW. Vogelsang
At 200 GeV, pQCD does a very good job describing mid-rapidity yields
STAR (h++h-)/2BRAHMS (h++h-)/2
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 4
Mid-rapidity d+Au
PRL 91, 072304
Pedestal&flow subtracted
Inclusive yields and back-to-back di-hadron correlations are very similar in p+p and d+Au collisionsIn contrast, Au+Au collisions are very different from p+p and d+Au – but that’s not the subject of this talk
STARSTAR
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 5
Mid-rapidity vs. forward rapidity
MidRapidity
ForwardRapidity
CTEQ6M• Gluon density can’t grow forever.• Saturation may set in at forward rapidity when gluons start to overlap.• Can be explored by comparing p(d)+A to p+p.
yT es
px 2~
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 6
Forward particle production in d+Au collisionsBRAHMS, PRL 93, 242303
Sizable suppression in charged hadron production in d+Au collisions relative to p+p collisions at forward rapidity
BRAHMS
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 7
ln 1x related to rapidity of
produced hadrons.
As y grows
Expectations for a color glass condensate
D. Kharzeev, hep-ph/0307037
Iancu and Venugopalan, hep-ph/0303204
Are the BRAHMS data evidence for gluon saturation at RHIC energies?
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 8
Recent saturation model calculation
Very good description of the pT dependence of the BRAHMSd+Au → h− + X cross section at η = 3.2
(Dumitru, Hayashigaki, and Jalilian-Marian, NP A765, 464)
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 9
Is saturation really the explanation?
Difficult to explain BRAHMS results with standard shadowing, but in NLO pQCD calculations <xg> ~ 0.02 is not that small
(Guzey, Strikman, and Vogelsang, PL B603, 173)
In contrast, <xg> <~ 0.001 in CGC calculations(Dumitru, Hayashigaki, and Jalilian-Marian, NP A765, 464 )
Basic difference: pQCD: 2 2 CGC: 2 1
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 10
Do we understand forward π0 production in p + p?
Bourrely and Soffer, EPJ C36, 371: NLO pQCD calculations underpredict the data at low s from ISR Ratio appears to be a function of angle and √s, in addition to pT
√s=23.3GeV √s=52.8GeV
xF xF
Ed3
dp3 [
b/G
e V3 ]
Ed3
dp3 [
b/G
eV3 ]
NLO calculations with different
scales:
pT and pT/2
Data-pQCD differences
at pT=1.5GeV
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 11
The error bars are statistical plus point-to-point systematic
Consistent with NLO pQCD calculations at 3.3 < η < 4.0
Data at low pT trend from KKP fragmentation functions toward Kretzer. PHENIX observed similar behavior at mid-rapidity.
p+p +X at 200 GeVnucl-ex/0602011
STARSTAR
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 12
d+Au +X at 200 GeV
pT dependence of d+Au π0 cross section at <η> = 4.0 is best described by a LO CGC calculation.
(Dumitru, Hayashigaki, and Jalilian-Marian, NPA 765, 464)
nucl-ex/0602011
STARSTAR
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 13
dependence of RdAu
nucl-ex/0602011
STARSTAR
pp
dAudAuR
197*21
• Observe significant rapidity dependence.
• pQCD calculations significantly over predict RdAu.
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 14
Any difference between p+p and d+Au?
Kharzeev, Levin, McLerran gives physics picture (NPA748, 627)
d+Au: Mono-jet?
PT is balanced by many gluons
Dilute parton system
(deuteron)
Dense gluonfield (Au)
Color glass condensate predicts that the back-to-back correlation from p+p should be suppressed
p+p: Di-jet
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 15
Back-to-back correlations with the color glass
(Kharzeev, Levin, and McLerran, NP A748, 627)
The evolution between the jets makes the correlations disappear.
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 16
25<E<35GeV
35<E<45GeV
• HIJING predicts similar correlations in d+Au as PYTHIA predicts for p+p.
• Only significant difference is combinatorial background level.
Forward + mid-rapidity di-hadron correlations
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 17
STARSTAR• are suppressed at small <xF> and <pT,π>
consistent with CGC picture
• are similar in d+Au and p+p at larger <xF> and <pT,π>
as expected by HIJING
25<E<35GeVFixed as E & pT grows
Forward + mid-rapidity correlations in d+Au
nucl-ex/0602011
π0: |<η>| = 4.0h±: |η| < 0.75; pT > 0.5 GeV/c
<pT,π> ~1.0 GeV/c
<pT,π> ~1.3 GeV/c
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 18
STAR Forward Meson Spectrometer
• FMS increases areal coverage of forward EMC from 0.2 m2 to 4 m2
• Addition of FMS to STAR provides nearly continuous EMC from -1<η<+4
• Available for Run 7
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 19
p+p and d+Au ++X correlations with forward
hep-ex/0502040p+p in PYTHIA d+Au in HIJING
Conventional shadowing will change yield, but not angular correlation. Saturation will change yield and modify the angular correlation.
Sensitive down to xg ~ 10-3 in pQCD scenario; few x 10-4 in CGC scenario.
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 20
Conclusions
• Forward rapidity inclusive π0 production at RHIC is well described by pQCD calculations
• d+Au results at RHIC provide hints that saturation effects are becoming important
• Future STAR measurements will elucidate the dynamics underlying forward inclusive particle suppression at RHIC
• RHIC may be the ideal accelerator to explore the onset of saturation
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 21
The STARSTAR CollaborationU.S. Labs:
Argonne, Lawrence Berkeley, and Brookhaven National Labs
U.S. Universities: UC Berkeley, UC Davis, UCLA, Caltech, Carnegie Mellon, Creighton, Indiana, Kent State, MIT, MSU, CCNY, Ohio State, Penn State, Purdue, Rice, Texas A&M, UT Austin, Washington, Wayne State, Valparaiso, Yale
Brazil: Universidade de Sao Paolo
China: IHEP - Beijing, IPP - Wuhan, USTC,Tsinghua, SINAP, IMP Lanzhou
Croatia: Zagreb University
Czech Republic: Nuclear Physics Institute
England:University of Birmingham
France: Institut de Recherches Subatomiques Strasbourg, SUBATECH - Nantes
Germany: Max Planck Institute – Munich University of Frankfurt
India:Bhubaneswar, Jammu, IIT-Mumbai, Panjab, Rajasthan, VECC
Netherlands:NIKHEF/Utrecht
Poland:Warsaw University of Technology
Russia: MEPHI – Moscow, LPP/LHE JINR – Dubna, IHEP – Protvino
South Korea:Pusan National University
Switzerland:University of Bern
STARSTAR
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 22
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 23
Pseudo-rapidity yield asymmetry vs pT
Back/front asymmetry in 200 GeV d+Au consistent with general expectations of saturation or coalescence; doesn’t match pQCD prediction.
Au direction / d direction
PRC 70, 064907STARSTAR
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 24
Nuclear Gluon Density
World data on nuclear DIS constrains nuclear modifications to gluon density only for xgluon > 0.02
e.g., see M. Hirai, S. Kumano, T.-H. Nagai, Phys. Rev. C70 (2004) 044905 and data references therein
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 25
One calculation within the saturation picture
RdAu
RCP
Saturation model calculation with additional valence quark contribution (Kharzeev, Kovchegov, and Tuchin, PL B599, 23)
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 26
x values in saturation calculations
In CGC calculations, the BRAHMS kinematics corresponds to <xg> <~ 0.001 (Dumitru, Hayashigaki, and Jalilian-Marian, NP A765, 464 )
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 27
Many recent descriptions of low-x suppression
Saturation (color glass condensate)● Jalilian-Marian, NPA 748 (2005) 664.● Kharzeev, Kovchegov, and Tuchin, PLB 599 (2004) 23; PRD 68 (2003) 094013.● Armesto, Salgado, and Wiedemann, PRL 94 (2005) 022002.● Dumitru, Hayashigaki, and Jalilian-Marian, NPA 765 (2006) 464
Multiple scattering● Qiu and Vitev, PRL 93 (2004) 262301; hep-ph/0410218.
Shadowing● R. Vogt, PRC 70 (2004) 064902.● Guzey, Strikman, and Vogelsang, PLB 603 (2004) 173.
Parton recombination● Hwa, Yang, and Fries, PRC 71 (2005) 024902.
Factorization breaking● Kopeliovich et al., PRC 72 (2005) 054606.● Nikolaev and Schaefer, PRD 71 (2005) 014023.
Others?
A short list (probably incomplete)
● ...
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 28
<z>
<xq>
<xg>
NLO pQCD
S. Kretzer
p p 0, 3.8, s 200GeV
Forward π0 production at a hadron collider
• Large rapidity π production (η~4) probes asymmetric partonic collisions
• Mostly high-x quark + low-x gluon• 0.3 < xq< 0.7
• 0.001< xg < 0.1• <z> nearly constant and high ~ 0.7-0.8
• A probe of low-x gluons
NN
q
g
s 2EN
ln(tan(2
))
xq xF / zENxqp xgp
xF 2E
s
z E
Eq
xg pT
se g
EN
(collinear approx.)
Carl Gagliardi – d+Au Collisions at STAR – DIS’06 29
Constraining the x-values probed in hadronic scatteringGuzey, Strikman, and Vogelsang, Phys. Lett. B 603, 173
Measure two particles in the final state to constrain the x-values probed
Log 10
(xG
luon
)
Gluon
TPC
Barrel EMC
FTPC FTPC
FPDFPD
For 22 processes
• FPD: || 4.0
• TPC and Barrel EMC: || < 1.0
• Endcap EMC: 1.0 < < 2.0
• FTPC: 2.8 < < 3.8
Collinear partons:
● x+ = pT/s (e+1 + e+2) ● x = pT/s (e1 + e2)
Log10(xGluon)
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