(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)