Baryon Production in Heavy Ion Collisions Baryon Production in Heavy Ion Collisions Paul Sorensen manifestations of multi-parton dynamics

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Baryon Production Baryon Production in Heavy Ion in Heavy Ion

CollisionsCollisions

Paul Sorensen

manifestations of multi-parton dynamicsmanifestations of multi-parton dynamics

San Diego — March 2006

2

heavy-ion collisionsheavy-ion collisions

Quark-hadron transition Hadrons form - protons & neutrons

t = 10-6 sec

T=1 GeV

t = 51017 secT=1 meV

The Planck epoch

Today Nucleus-nucleus collisions may probe the physics of this quark-hadron transition197Au

197Au

UrQMD Group – Frankfurt

√sNN=200 GeV


3

centrality dependencecentrality dependenceRCP is the number of particles produced in head-on collisions divided by the number produced in grazing collisions (expected increase with system size scaled out)

For intermediate hadron probes, RCP depends on the number of quarks in the hadron.

Production increases more quickly for hadrons with three instead of two quarksCentral: head-onhigher density

fireball

Peripheral: grazingless dense

pT indicates the length scale the hadron can probe

0.6 < pT/n (GeV/c) < 2.0

0.33 > (fm) > 0.1


4identified particle identified particle RRAAAA/R/RCPCP

A large suppression of hadrons is observed• Measurements interpreted in terms of energy-loss for quarks and gluons in medium

The suppression patterns depend on particle-type• Baryons exhibit less suppression• Measurements interpreted several ways: hydro-like flow, protons scaling with N-binary, coalescence/recombination, gluon junctions etc.

e-Print Archive: nucl-ex/0510052


5

baryon to meson ratiobaryon to meson ratio

the faster increase of baryon production is common to many systems: it can’t be q vs. g fragmentation multi-parton dynamics (power corrections, higher

twist)before being applied in Au+Au factorization should be established

experimentally


6

// expectations expectations

the expectation for Ω/ is probably not correct given the power-law shape in p+p

Oregon Reco.

ratios may depend on flavor


7

lower √slower √sNNNN

is the baryon enhancement just a lack of baryon suppression?

at lower √sNN the RCP of baryons is

above unity


8anti-baryon to baryon anti-baryon to baryon ratiosratios

gluon vs quark hadronization predictions don’t work in A+A or p+p collisions“soft” physics extends quite high in pT


9implications for “charm” implications for “charm” RRAAAA

charmelectron branching ratios depend on the hadron type: c decays yield electrons less frequently than D0 decays.

when using non-photonic electrons to look for charm, charm can hide in the c

A baryon enhancement in the charm sector can result in a non-photonic electron suppression


10

an examplean example• consider a charm spectrum that follows a power law• for Au+Au modify the default c/D ratio to match the /KS (while holding the total number charm hadrons fixed)• compare the decay electron spectra in p+p and Au+Au

The ratio shows that when c/D has the same form as /KS, even if the charm yield follows Nbin scaling, the electron spectrum will be

suppressed

decay electron RAA


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example 2example 2

• The resulting electron RAA is below preliminary measurements!• Implies energy loss for charm quarks may be smaller than for light quarks

Consider c/D similar to /KS and charm RAA similar to light hadron RAA

Data are above the curve

we cannot say charm quarks are suppressed as much as light quarks

decay electron RAA


12

preferred charm Rpreferred charm RAAAAA 2 analysis shows that for this scenario, preliminary PHENIX data

prefer charm hadron RAA = 1.35 light hadron RAA

decay electron RAA


13

higher phigher pTT

A charm baryon enhancement as parameterized by /KS does not change the non-photonic electron RAA above 5 GeV/c

but what pT would a c/D enhancement persist to? We should measure c.

bottom contribution is highly uncertain and not considered here?

decay electron RAA


14

what about Dwhat about Dss/D/D00

enhance the Ds yield by 50% (for this plot the Ds/D0 ratio is taken to be pT independent, not really a good assumption)

Depending on the poorly known branching ratio, a Ds enhancement can also contribute to an electron suppression

decay electron RAA


15

azimuthal dependence: vazimuthal dependence: v22azimuthal momentum-space anisotropy: a self

quenching probe of early interactions

x

zNon-central Collisions

€

The initial spatial anisotropy evolves

( )via interactions and density gradients

into a momentum space anisotropy

Ed3N

d3p=

1

2π

d2N

pTdpTdy1+ 2vn cos nΔϕ( )

n=1

∞

∑ ⎛

⎝ ⎜

⎞

⎠ ⎟

v0 "radial flow" , v1"directed flow"

v2 "elliptic flow" (largest).

in-plane

out-of-plane

y

Au nucleus

Au nucleus

sensitivity to the system geometry can arise through secondary rescattering, soft-

gluon radiation, etc.


16in-plane baryon in-plane baryon enhancementenhancement• At intermediate pAt intermediate pTT, v, v22 of hadrons display of hadrons display quark number quark number

dependencedependence• Baryon yields have more in-plane enhancement than meson Baryon yields have more in-plane enhancement than meson yieldsyields


17

quark-number scalingquark-number scaling

PR

L 92

(20

04

) 05

23

02

; PR

L 91

(20

03

) 18

23

01

Since hadronization is a soft process, it can be modified by the presence of a QGP.

Simple models of hadronization by coalescence relate quark and hadron v2:

v2q = v2

h(pT/n)/n,

n is the number of quarks in the hadron

Models imply

v2 is developed before hadrons form

deconfinement: long range interactions amongst quarks not hadrons


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run 4 vrun 4 v22(p(pTT/n)/n update/n)/n updateWith higher precision, fine structure is observed: the scaling doesn’t follow NCQ (3 vs 2) exactly

Is this related to a jet component, a breakdown of simple approximations, or something new?

Q: Are coalescence models invalidated?

A: Not necessarily. Imperfect v2/n was also anticipated within ReCo models.

STAR Preliminary


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a closer looka closer lookInclusion of gluons in recombination was

predicted to lead to a larger meson v2/n than baryon

v2/n:B.Müller, et al. nucl-th/0503003

Including contributions from sea quarks and gluons

should cause deviations from v2/n

To 1st order: the constituents look like massive valence quarks with no sub-structure

gProbing more deeply reveals substructure in the form of sea quarks or gluons

Further daughter partons are revealed as the scale Q2 is increased

g qq

STAR Preliminary


20comparisons to comparisons to predictionspredictionsInclusion of gluons in

recombination was predicted to lead to a larger

meson v2/n than baryon v2/n:

B.Müller, et al. nucl-th/0503003

Tantalizing indication for the fate of gluons and the nature of the constituents

Systematic errors on the data and calculations need to be carefully addressed


21comparisons to comparisons to predictionspredictions

Effect of the quark momentum distribution

inside the hadron:V.Greco, et al.

Phys.Rev.C70:024901,2004

A momentum distribution within hadrons leads to v2/n breaking similar to data.

Fragmentation component may be necessary at higher pT


22comparisons to comparisons to predictionspredictions

The original parton v2 is not recovered from scaling so the opacity puzzle remains.

Calculation fails for p/ and RCP but it does predict the gradual drop in v2 at high pT.

MPC + Coalescence/Jetset: jet fragmentation

contribution + spatial correlations also can distort

the scaling of v2/n:D. Molnar nucl-th/0406066

pT/n


23

from hadronic x-sections?from hadronic x-sections?

here, larger proton v2 is from the additive quark model for hadronic cross-sections

/ ratio should distinguish hadronic cross-sections from coalescence.

Is there a duality between the pictures?

• interacting co-moving quarks form a hadron• interacting hadrons described by the sum of their constituent quarks

Both yield ~NCQ scaling.

Y. Lu, et. al.


24

CoronaCoronaDemonstrates that the corona effect can yield interesting pT and particle type dependences

What about a “corona” in e+e-will the simple parameterization of the core get the K* or v2 and

RCP?


25

another B/M enhancementanother B/M enhancement

The large away-side B/M ratio also points to multi-gluon/quark dynamics:

wherever the density of comoving constituents is largerin-plane: v2

central vs. peripheral: RCP and in the “wake” of quenched jets, it becomes easier to produce baryons.

near-sidelike p+p

away-side: comoving q/g enhance the

probability for baryon production


26Conclusions:Conclusions:

the baryon enhancement in e+e-ggg seems to rule out a quark vs gluon jet fragmentation explanation: pbar/p ratios also confirm this

a mass hypothesis is strongly disfavored by , , , and RCP and v2 (corona?)

Baryon junctions may be disfavored by the enhancements at √sNN=17 GeV (Nbin)

The baryon enhancement is generic to many systems (e+e-, d+Au): does v2/n point to interactions within a deconfined phase!?

Some open questions:Some open questions:Do diquarks play a role in our observations?

Why does the [MPC + Coalescence/Jetset + spatial correlations] model fail to describe the data? Which part is wrong?

How much do hadronic cross sections contribute to the species dependence? Definitely shouldn’t be overlooked!

Outlook:Outlook:changes in hadronization induced by high energy densities may be a valuable tool to study -symmetry and confinement

Documents

Baryon Production in Heavy Ion Collisions Baryon Production in Heavy Ion Collisions Paul Sorensen manifestations of multi-parton dynamics