collision geometry and suppression what is happening at high pt?

Collision Geometry and SuppressionWhat is happening at high pT?

Jiangyong JiaState University of NewYork at StonyBrook@High pT

19th Winter Workshop on Nuclear Dynamics 2/11/2003 2 Jiangyong Jia@High pT

Outline

Introduction Jet tomography of Quark Matter

Quick overview of high pT results from 200GeV Jet-like angular correlation and spectra shape at high pt High pT suppression continues to highest pT measured Large v2 at high pT Mysterious scaling behavior for baryon at high pt

Comparison with simple geometrical model calculation. Consistent with high pT yield and di-jet suppression Insufficient to describe v2 and baryon yield

Conclusion


jet cross section can be calculated in pQCD for nucleon-nucleon collisions

jets are “calibrated” probe for dense nuclear matter created at RHIC

e

e

DELPHI

RHIC

jet example:

e+e annihilation into two ~50 GeV jets

Jets — a Unique Observable for Heavy Ion Physics

e

e q

q


q

q

hadronsleadingparticle

leading particle

schematic view of jet production

hadrons

q

q

hadrons

hadrons

leadingparticle

jet production in quark matter

leadingparticle

q

q

hadronsleadingparticle

jet production in quark matter

Jets—New Penetrating Probe at RHIC

jets are important particle production mechanism at RHIC energies

hard to observe directly in A-A collisions indirect measurements through

high pT leading particles azimuthal correlation

jet tomography of quark matter

in colored “quark matter” partons expected to lose significant energy via gluon bremsstrahlung attenuation or absorption of jets “jet quenching” suppression of high pT hadrons modification of angular correlation changes of particle composition

Positron Emission Tomography of the Brain


Direct evidence of jets Leading particle + angular correlation

Both STAR and PHENIX identify the jet signal jet like near angle correlation for p+p and Au+Au

Similar width(STAR,PHENIX) Similar +/- ratio(STAR) jet fragmentation not modified much?

STAR Preliminary Au+Au @ 200 GeV/c4<pT(trig)<6 GeV/c

2<pT(assoc.)<pT(trig)PHENIX Preliminary

raw differential yields2-4 GeV

Pair distribution

Subtracted distribution

Mixed distribution

20-40%


The yield per trigger

Compare the yield per trigger for ~0 and ~ (Au+Au – flow) / p+p per trigger. Near angle ~ 1,

pT>4 GeV/c, large fraction come from jet.

Back angle correlation decrease with centralityDisappearance of away side

jet.

Away side jet are absorbed or mono-jet production?

?


Charged Hadron Spectra

Preliminary sNN = 200 GeV


200 GeV results from all experiments


Charge spectra shape at high pT

Inverse slope increase with pT Spectra is more power law

<pTtrunc> = pT - pT

min as

function of centrality Nearly flat at high pT

Slope~constant at high pT

Low pT ‘flow’ pattern


Charge spectra shape at high pT

Inverse slope increase with pT Spectra is more power law

<pTtrunc> = pT - pT

min as

function of centrality Nearly flat at high pT

AuAu Yield 200GeV/130GeV Compare UA1(200)/Extrap(130)

for || < 0.5(blue lines) Consistent with pQCD calculation?

pT>4 ~5 GeV/c are jet like

3


1


Centrality dependence of high pT suppression

But when we compare with pp, jet production are strongly suppressed Suppression continues decrease as function of centrality Charged : factor ~3.5 from peripheral to central 0 : factor ~5 from peripheral to central Interesting to see STAR data on Ks and

Nuclear Modification Factor as a function of Npart

Binary-scaled yield as a function of Npart

PHENIX Preliminary

4 < pT < 6 GeV/c

3.5 5

h+ + h- 0


High pt particles have strong anisotropical flow!

Both STAR and PHENIX showed v2 saturates finite value at high pT Hydro : v2 created by pressure, only applicable to low pt (<3GeV/c) Saturation : insufficient to produce v2 To produce v2, jets have to be strongly influenced by geometry. This qualitatively

goes in the direction of jet quenching Different energy loss along different path—jet tomography But current models in market are not enough to produce observed v2

Decrease at high pTSensitive to geometrical profile

M. Gyulassy, I. Vitev and X.N. Wang

PRL 86 (2001) 2537

Cylindrical

Woods-Saxon

STAR preliminary


At medium pt, particle compositions are very different from elementary collisions

p/ ratio for AuAu at pT>2GeV/c ~ 1 in central collisions ~ 0.4 in peripheral collisions ~ 20% lower for anti-proton

Above gluon jet value

Not normal fragmentation


Identified particle suppression

Suppression behaviors are very different at medium pt If suppressions merge at high pt, particle composition will be

similar to peripheral collision— like pp What mechanism affects 2-5GeV/c region? Flow? Baryon

transport? Jet Suppression + Quark recombination?

s

PHENIXSTAR h++h-

k

p+pbar %9260%50

Note that there are difference in centrality selectionPHENIX curve just show the trend and can have large uncertainty at high pt


Jet Suppression + Quark recombination?

Fragmentation : minijet partons combine with q,qbar from vacuum to form hadron Recombination: minijet partons combine with q,qbar from QGP soup Pt<4GeV/c dominated by recombination — p/ anomaly. Pt>6GeV/c dominated by fragmentation — particle composition like pp

By B.Muller. et al. nucl-th/0301087

qq

q

Fragmentation

q q

q q q

Recombination

1MesonBaryon

1MesonBaryon

V.Creco. et al. nucl-th/0301093


however

Flow, baryon transport, or recombination are not jets! STAR’s correlation measurement is in favor of jets even in 3-4GeV/c

region

Need to better quantify how much contribution are from jets in these pt range and study PID dependence of the angular correlation


What do we learn?

High pt particle production are really hard — jets Strong centrality dependence of suppression, v2, away side jets at high pT

Suggestive of “surface emission” of jets or mono-jet production? In qualitative agreement with jet quenching model Saturation model is insufficient to produce large v2

Anomalous proton/ yield at medium pt 2-4GeV/c Soft or hard or in between? Back to back correlation using identified leading particle should be able to tell us

whether they are from jets. At pt>5 GeV/c particle composition might approach composition for pp Jet suppression + quark recombination

Inspired by E. Shuryak Phys.Rev. C66 (2002) 027902 Which effect can be explained by jet absorption and collision geometry?

Consistent with high pT yield and di-jet suppression. Insufficient to describe v2

?


Simple Toy Geometrical Model for Jet absorption

Jets are absorbed in overlap region according to

Density of matter in transverse plane determined by participant density

Azimuth isotropic di-jets production

according to binary collision profile

Hadron spectra are related to jet distribution via parton-hadron duality

dlk

ef

~ Npart

Ncoll


Density distribution calculated from glauber model

0-5% 75-80%

Woods-saxon nuclear density profile

Npart

Ncoll


Model Assumptions to Compare with Data

Model is simplistic and can only describes main features of geometry Assume all particles above 4 GeV/c from jets Assume jets are back-to-back Ignore the fragmentation Contains no pT and s and flavor dependence

Try different kind of absorption :

is the only free parameter

Adjust absorption strength k to reproduce suppression factor of 3.5(charged) and 5() in most central collisions.

Predict centrality dependence of yield suppression Predict centrality dependence of di-jet suppression Predict centrality dependence of v2

iIkef

0

1),( yxdlI

0

2),( yxldlI

00

0

3),( yx

lll

dlI

Normal nuclear absorption

Energy loss style absorption

Absorption + expansion, l0 ~ 0.2 fm


Scaling behavior of the yields

Qualitatively describe the centrality dependence of the yield

Not sensitive to the absorption pattern

0

1),( yxdlI

0

2),( yxldlI

00

0

3),( yx

ll

ldlI

Ncoll

Npart/2

Solid line factor 3.5, dash line factor 5

• h, 4-8 GeV/c

0, 4.5-5 GeV/c

ppAuAu

AuAu

yperiy

NpartybSy

or )(

)()(


Centrality dependence of back-back jets

Compare STAR back-back jet measurement for 4 <pT<6 GeV/c By construction, same side jet will always be 1 Qualitatively describe the centrality dependence of the away side


Centrality dependence of v2

NB: in these models,v2 are purely geometrical origin, does not consider detailed modification of momentum distribution

Geometrical anisotropy is insufficient to produce observed v2 by jet absorption V2 is sensitive to absorption model, smallest for longitudinal expanding source V2 will increase using hard sphere or cylindrical nuclear profile, but unphysical


Varying

Maximum v2 produce by surface. Different geometrical profile have

different geometrical limit. v2 is below geometrical limit at

experimental observed suppression value

Geometrical limit for WS profile is less than observed v2

•Suppression factor for 0-5% centrality

V2 for 50-55% centrality

Away side jet for 0-5% centrality

hard sphere profileFor sphere, surface volume is

%26~3

3/4

43

2

R

d

R

dR

6/)2sin(max

v :profile cyl

cylindrical profile

S. Voloshin

ws profile


Conclusion

Exciting high pT results from 200GeV AuAu Direct observation of jets Strong high pT suppression and suppression of away side jet Qualitatively consistent with jet quenching and saturation model

Puzzle1 : Large v2 at high pT Puzzle2: High pT proton and

Binary scaling between 2-4GeV/cMysterious particle composition at same pt range.Jet suppression + quark recombination

Jet absorption gives characteristic centrality dependence of observables Consistent with high pT yield and di-jets suppression Insufficient to describe v2 and proton yield

collision geometry and suppression what is happening at high pt?

Documents

high pt yield

high ptcomparison

high pthigh pt suppression

highest pt measuredlarge

rhic jets

star preliminary au

gev jets

jet signaljet