(di)-hadron production in d+au collisions at rhic
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(di)-Hadron Production in d+Au Collisions at RHIC
Mickey Chiu
2
PHENIX
SOUTH MPC
NORTH MPC
)( 43 yyTd ee
s
px )( 43 yyT
Au ees
px
•Fwd-Fwd, x~(0.001,0.005)•Mid-Fwd, x~(0.008,0.040)•Mid-Bwd, x~(0.050,0.100)
d(forward) Au(backward)
Span rapidity, constrain x regions
•Large suppression in RdA•That increases with centrality•And increases with larger rapidity
•Consistent with previous measurements•However, x covered by single inclusive measurement is over wide range
•Includes shadowing, anti-shadowing, (EMC effect)
RdAu in 2 forward rapidity Bins
Guzey, Strikman, Vogelsang, PLB603, 173
Guzey, Strikman, Vogelsang, PL B603, 173
Di-hadron Measurement
Peripheral d+Au Correlation Function
CORRELATED
Npair
“Di-Hadron Nuclear Modification factor”
• Possible indicators of nuclear effects
• JdA < 1
• Angular decorrelation of widths
pppairpp
dApairdA
colldA N
J
/
/1
Notes:
1. Low pT (but back-to-back peak is selected so possibly clean hard signal, and low pT is desired if one wants to cross over into Qs regime)
2. Pedestal Determination (Assumed up to twice the width as a systematic).
3. Di-Hadrons instead of di-jets (but ok if fragmentation unmodified)
Underlying
event
0 (trigger,central)/0 (associate,forward)
p+p
d+Au 0-20%
d+Au 60-88%
pTt, 0
pTa, 0
mid-fwd
NO SIGN OF RIDGE
d
cdab
pbpp
ap
d
cdab
Aub
Auda
d
pppairsppcoll
dAupairsdAu
dA
zzDxfxf
zzDxfxf
NJ
c
c
,)()(
,)()(
/
/
Large Suppression in Central d+Au
b=0-100%Q2 = 4 GeV2
xAu
EPS09 NLO gluonsEskola , Paukkunen, Salgado, JHP04 (2009)065
),(
),(),(
2
22
QxAxG
QxxGQxR
p
AuAuG
Low x, mostly gluons JdA RGAuHigh x, mostly quarks
Weak effects expected
Counting Nucleons in Path
d Au
bnucleon
bnucleon
From Glauber Monte Carlo we can determine the number of nucleons in the path of each nucleon in the deuteron, and correlate that with some measurement in our detector that is correlated to centrality (South BBC, Au-going side).
“wee partons” overlap?
Centrality60-88%40-60%20-40%0-20%
Centrality, or b Dependence
AugdA RJ ~
•If we are measuring gluons w/ JdA, then we can perhaps extract impact parameter and x dep of
Qs, and possibly extract the value of Qs at RHIC?•Since Ncoll~L~A1/3 ~TA we might be able to understand how gluons recombine with N nucleons?
•eg, from above data are we seeing an approx linear dependence on length????
xfrag ~ 1.6x10-2
xfrag ~ 5x10-3
xfrag ~ 5x10-4
0
22
2 ~),,(1
)(x
xNQbxxG
RbQ coll
AusSb dependent:
Impact Parameter Dependent pdf’s
•New impact parameter dependent PDF’s where
•N=1 in EPS09 (pdf’s are linearly suppressed with T), N=4 in EPS09s.
EPS09s and Pythia Calculation
•Using PYTHIA and EPS09s one can extract the JdA expected from nuclear shadowing, and thus extract pdf’s at low x.•EPS09s seems to be a little above the data
•Additional suppression of pdf’s in most central collisions
EPS09s Mid-Rapidity
•Perhaps somewhat surprisingly, EPS09s + standard pQCD works well at mid-rapidity, even though other nuclear effects like Cronin are ignored. •In any case, agreement is pretty good and Cronin is not too large (~10% effects)
EPS09s Forward Rapidity
•Same pQCD calculation for forward inclusive hadrons fails•“Problem” with inclusion of Brahms charged pion data in EPS08…•New physics has to come into play at forward rapidity? Why?
LHC mid-y, RHIC fwd-y, same x
•At LHC mid-rapidity (5 TeV), xT is 25 times lower than at RHIC for the same hadron pT
•LHC hadron pT = 2 GeV, y = 0, should reach same x as at forward y at RHIC, x ~ 10-3
•Why no suppression?
Wherefore forward rapidity?Au
bnucleon
Au
bnucleon
•Must look at parton rapidity…•Particles at mid-rapidity come from partons of moderate x, while forward particles come from high x•Forward rapidity partons have stronger “coherence” effects due to bigger boost.
Lab frame Nucleus frame
L/ ~ 0.1 fm
x mid-rapidity
x fwd-rapidity
“pQCD” ApproachKang, Vitev, Xing [arxiv:1112.6021]
•Perturbative approach incorporates ISI and FSI for momentum imbalance (multiple scattering broadening), plus energy loss and coherent power corrections
CGC ApproachesLappi and Mantsaari, arxiv:1209.2853Stasto, Xiao, Yuan [arxiv:1109.1817]
•Another way the “coherence” effects can manifest itself at forward rapidities is in the Color Glass Condensate
•Merger of gluons competing with splitting of gluons, enhanced at large rapidity.
•Much work being done and formalism being worked out.
Hybrid rcBK Approach
Summary•There seem to be some interesting effects in the Au nucleus at x of about 10-3
•Rapidity dependence is very important•Larger “coherence” effects at higher rapidities, since one selects higher rapidity partons•“Coherence” = gluon saturation? Or something else?•Also possibly other explanations (Eloss, eg, rapidity shift)
•Single Inclusive vs Di-Hadron•Di-Hadron seems superior
•Better control of parton kinematics in di-hadron•Better control of backgrounds•Ability to probe down to lower pT, and therefore Qs
•Important: Impact Parameter Dependence starting to be probed•Nuclear thickness dependence crucial
•LHC p+A already provides interesting results that one can then test against ideas from what we know already at RHIC
Backup Slides
MPC Performance
North MPC
Decay photon impact positions for low and high energy 0s. The decay photons from high energy 0s merge into a single cluster
Sometimes use (EM) clusters, but always corrected to 0 energy
Clusters 80% 0 (PYTHIA)
“Trigger”Near
Far
Jet1
Jet2
CNM effects: dynamical shadowing, Energy Loss, Cronin
RdA Past, di-Hadron Future
Kharzeev, NPA 748, 727 (2005)
•Di-Hadron Correlations allow one to select out the di-jet from the underlying event•Constrains x range (probe one region at a time)•Probe predicted angular decorrelation of di-jets (width broadening)
Kharzeev, Levin, McLerran Nucl. Phys. A748 (2005) 627
Color Glass Condensate
(Qiu, Vitev PLB632:507,2006)
di-Hadron Signal
Peripheral d+Au Correlation Function
d
dN
NN
NCY
assoc
trigassoctrig
pair 1
CORRELATED
Npair
“Di-Hadron Nuclear Modification factor”
trigdA
trigdAdA RIJ
• Possible indicators of nuclear effects
• JdA < 1, RdA < 1
• Angular decorrelation of widths
pppairpp
dApairdA
colldA N
J
/
/1
ppsglpp
dAsgldA
colldA N
R
/
/1
“Sgl-Hadron Nuclear Modification factor”
“Conditional Yield”
Number of di-jet particle pairs per trigger particle after corrections for efficiencies, combinatoric background, and subtracting off pedestal
Caveats:
1. Low pT (but back-to-back peak is selected)
2. Pedestal Determination (Assumed up to twice the width as a systematic).
3. Di-Hadrons instead of di-jets (but ok if fragmentation unmodified)
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