Jana Bielcikova (Yale University) High-p T physics at LHC, Jyväskylä March 23-27, 2007 Strange...

Jana Bielcikova (Yale University)

High-pT physics at LHC, Jyväskylä March 23-27, 2007

Strange particle correlations – coalescence at RHIC and LHC

Jana Bielcikova High-pT physics at LHC 2

Outline:

• Why recombination/coalescence? • Correlations with strange particles at

RHIC• What do we expect at the LHC?


RCP (Nbin scaled central-to-peripheral ratio)• intermediate pT (pT = 2-5 GeV/c) : baryon/meson splitting independent of strangeness content

• high pT (pT > 5 GeV/c) : all particles have similar RCP and appear to show similar suppression

Baryon anomaly at intermediate pT


• large enhancement of B/M ratio in Au+Au relative to p+p collisions - reaches maximum at pT~3 GeV/c• jet fragmentation is not a dominant source of particle production

Baryon/meson ratios at RHIC

STAR, PRL 97 (152301) 2006

Au+Au: p/ ~ 1 Λ/K0S ~ 1.8

p+p: p/ ~ 0.3 Λ/K0S

~ 0.6e++e-: p/ ~ 0.1-0.2


cartoon

Parton recombination at intermediate pT

• in vacuo fragmentation of a high momentum quark to produce hadrons competes with in medium recombination of lower momentum quarks to produce hadrons

•6 GeV/c particle via : fragmentation from high pT

meson - 2 quarks at pT~3 GeV/c baryon - 3 quarks at pT~2 GeV/cRecombination produces more baryons than mesons at intermediate pT

R.J. Fries et al., PRL 90 (202303) 2003V. Greco et al., PRL 90 (202302) 2003

baryon

meson


Elliptic flow: constituent quark scaling

mesons

baryons

scaling v2 and mT-m0 by quark content nq (baryon: nq= 3, meson: nq=2)

resolves baryon-meson separation

20

2TT mpm


Intermediate pT: recombination

• Naively expected behavior of observables:

• Observed at RHIC: - soft physics extends up to pT=4-6 GeV/c

- but ideal hydrodynamics works only for pT<2 GeV/c

0 1 2 3 4 5 6 7 8 9 10 11 12 GeV/c

soft/hydropQCD

0 1 2 3 4 5 6 7 8 9 10 11 12 GeV/c

pQCDrecombination

hydro


Correlations with identified particles

provide additional information on:• baryon/meson enhancement • medium modification of jet shape • particle production mechanisms

coalescence/recombination mechanisms

and/or (modified) fragmentation of high-pT partons?

parton

hadrons

hadrons

Λ, Λ, K0S, γ … ?

Λ, Λ, K0S, γ … ?

parton

Jana BielcikovaHigh-pT physics at LHC 9

Jet-like correlations

Full jet reconstruction in A+A collisions at RHIC difficult due to underlying background:

azimuthal correlations of high-pT particles

p+p

A+A

flow

near-side away-side

TriggerAssociated

Associated


Correlations at near-side

a.u.

pTtrig=3-6 GeV/c, 1.5 GeV/c <pT

assoc< pTtrig

h-h, Au+Au (0-10%)

ridge

ridge

jetjet+ridge

after v2 subtraction

jetridge

v2 + away-side peak

Au+Au: ‘long-range’ correlations at near side (“the ridge”)

Near-side yield : Δɸ (J+R) = Δɸ (J) + Δɸ (R) Jet yield : Δɸ (J) = Δɸ (|Δη| < 0.7) - Δɸ (|Δη| > 0.7) Ridge yield : Δɸ (R) = Δɸ (J+R) - Δɸ(J)

J+RR/2

R/2


• steep increase of near-side yield with centrality in Au+Au• ratio of yields in central Au+Au/d+Au ~ 4-5

-> “jet” yield is independent of centrality and agrees with d+Au

JetJet + Ridge

-> “ridge” yield increases with centrality ridge of K0

S < ridge of Λ

Ridge

Centrality dependence of near-side yield

Jet

J.B. (STAR), QM2006


pTtrigger dependence of jet and ridge

yields

• near-side associated yield is ridge dominated at intermediate pT

• jet yield: - increases steeply with pT

trigger

- smaller for Λ-triggers than for K0S-triggers ?

- baryon jet is wider than meson jet• jet/ridge ratio increases with pT

trigger

Jet + Ridge Ridge Jet

J.B. (STAR), QM2006


pT-distribution of associated particles

Trigger particle T(ridge) MeV T (jet) MeV

h+/- 438 ± 4 (stat.) 478 ± 8

K0S 406 ± 20 (stat.) 530 ± 61

Λ 416 ± 11 (stat.) 445 ± 49

STAR preliminary“jet” sloperidge slopeinclusive slope

J. Putschke (STAR), QM’06

h-h correlationspT

associated>2GeV/c

• Ridge spectra similar to particles from the bulk• Jet spectra are harder(T increases steeply with pT

trig)

J.B. (STAR), QM’06


What does a parton recombination model predict?

jet

ReCo: R. Hwa, Z.Tan: PRC72 (057902) 2005 • central-to-peripheral ratio (“ICP”):

- jet yield is independent of centrality “ICP” is driven by long-range Δη correlations

- qualitative agreement between data and model BUT!

• quantitative agreement requires same centrality and pT selection• check required on how well the “ridge” is reproduced by the model

J.B. (STAR), QM2006


Particle composition in the ridge

/K0S ratio:

in the ridge: ~ 1.0 similar to that from inclusive pT spectra in the jet: ~ 0.5 consistent with p+p

|Δη|<2.0 |Δη|<0.7

STAR preliminary STAR preliminary

J.B. (STAR), WWND07


1) Parton radiation and its coupling to the longitudinal flow

•gluon bremsstrahlung of hard-scattered parton

•radiated gluon contributes to broadening

2) Medium heating and parton recombination Chiu & Hwa Phys. Rev. C72:034903,2005

•hard parton enhances thermal parton distribution (ΔT=15 MeV)

recombination of thermal partons forms a pedestal (ridge) •enhanced baryon/meson ratio

3) Longitudinal broadening of quenched jets in turbulent color field

A. Majumder, B. Mueller, S.A.Bass, hep-ph/0611135

•plasma instabilities in expanding medium broadening of jet cone

wide ridge in rapidity at low pTassoc

4) Radial flow + trigger bias S.Voloshin, nucl-th/0312065, Nucl. Phys. A749, 287 (2005)

Quantitative calculations needed !

What is the origin of the ridge ?

Armesto et al, PRL 93 (2004)


Testing recombination with and

The production of and Ω is almost exclusively from thermal

s-quarks even out to pT = 6-8 GeV/c(shower = “jet” contributions are

strongly suppressed)

Prediction:1. Ω/ratio should rise linearly

with pT

2. There should be no Ω or di-hadron correlations at near side!

R. Hwa, C.B. Yang , nucl-th/0602024

S = shower (“jet”)

T = thermal


Test 1: Ω/ ratio

• Ω/ ratio turns over

• the position of the “turn-over”point in pT shifts to higher pT ascentrality increases

•ReCo based on coalescence of thermal s-quarks describes the data well up to pT~4 GeV/c

Note: theory curves are for central Au+Au collisions only

S. Blyth (STAR), QM2006


Comparison of baryon/meson ratios

• all measured baryon/mesonratios have the “turn-over”

• Does the position of the “turn-over” point shift to higher pT as the strangeness content increases ?

• In general, all ratios have the turn-over point at lower pT than predicted by ReCo

S. Blyth (STAR), QM2006

turn-over locationp/

Λ/K


Test 2: correlations with multi-strange particles

There is a near-side peak for and -triggered correlations and its magnitude is independent of strangeness content !This is in disagreement with the recombination picture.

B. Abelev (PhD 2007, Yale), J.B. (STAR) QM2006


Some thoughts on recombination at RHIC

• Recombination is:- simple (“intuitive”) phenomenological model - does not predict dynamics in the parton phase

- successful for single inclusive measurements and elliptic flow- challenged by two-particle correlations

What is the ridge? How far does the ridge extend in ? How well are the ridge properties described by ReCo models?

-triggered correlations: is it all in the ridge?


Coalescence at LHC energies

Fries and Mueller, EJP C34, S279 (2004)

- calculation depends on transverse radial flow extrapolation- thermal parton phase temperature: T=175 MeV- parton energy loss: Vitev+Gyulassy, PRL 89, 252301 (2002)

r=0.65 r=0.75

r=0.85

includes parton energy loss


p/ ratio from thermal recombination at the LHC

Fries and Mueller, EJP C34, S279 (2004)

Crossover between recombination and pQCD:

RHIC LHC 4 GeV/c 6 GeV/cp 6 GeV/c 8 GeV/c

LHC vs RHIC: amplitude of B/M ratio is the same, but the limit is pushed to larger pT.

Probing baryon/meson differences at the LHC implies particle identification over a large pT range


ALICE PID capability at mid−rapidityFrom Physics Performance Report Vol.II

1 year of Pb+Pb data taking (=107 central Pb+Pb events)


• 1-dimensional model: recombination in the direction of the detected hadron

• pT spectrum depends on 2 parameters:

ξ: suppression factor (ξRHIC = 0.07, ξ LHC = 0.01-0.03)

Γ: overlap factor of shower partons from neighbouring jets

• numerical estimates done for shower parton distributions generated by a gluon

Coalescence in high jet density environmentR.C. Hwa and C.B. Yang, PRL 97, 042301 (2006)

),p(H),p(Hdpp

dNT

)2(hT

)1(h

TT

h

1-jet contribution=fragmentation2-jet contribution

jet overlap factor

higher probability to form p than 13.0)2/1z(S

3.0)3/1z(Sqg

qg


pT spectra in high jet density environment

Γ(pT) ~ pT-7

Γ(pT) ~ pT-7

Γ=0.1 at pT=10 GeV/cfor N(jets)~100 in ||<0.5Γ(pT) ~ pT

-7

pT~20 GeV/c:pion:insignificant contribution from 2-jet recombination

xproton:2-jet recombinationcontribution higher than 1-jet contribution

Note: unfortunately the figures do not show the 1-jet contribution


Consequence #1: large p/ ratio

R(p/) = 5-20 It is huge!

• pT>20 GeV/c: N(jet)<2 in ||<0.5 Γ will decrease faster than pT

-7

• p and distributions ~ξ2

R(p/) is independent of ξ• Γ(pT) cancels out

How does it relate to Fries+Mueller prediction (see slide 23)? - it corresponds to fragmentation term and Γ=0

Γ(pT) ~ pT-7


Consequence #2: no structures intwo-particle correlations

• high density of jets at the LHC:

- jets are part of the background - hadron with pT=10-20 GeV/c is a recombination product rather than a fragmentation product of higher pT parton

“Triggering” on hadrons in pT=10-20 GeV/c range does not select any special subset of jet-like events no peaks expected in two-particle correlations!

This is in a sharp contrast to the situation at RHIC!

• pT spectrum depends on 2 parameters:

ξ: suppression factor, ξRHIC = 0.07, ξ LHC = 0.01-0.03)

Γ: overlap factor of shower partons from neighbouring jets

• numerical estimates done for shower parton distributions generated by a gluon


• thermal recombination pushes to higher pT~2-10 GeV/c

• shower recombination in high jet density environment significant

out to pT~20 GeV/c

Observables:• surprisingly large p/ ratio (5-20)• no associated particles in azimuthal correlations

These predictions can be easily experimentally tested (in ALICE).

BUT: jet quenching will populate the recombination region at the LHC

and thus complicate the intepretation of the data.

Summary: recombination at the LHC


BACKUP


Analysis method

raw data correlation mixed events correlation corrected data correlation

h-K0S, 3 < pT

trig < 6 GeV/c, 2 < pTassoc < 3 GeV/c

ridge jetAu+Au, 0-10%


before elliptic flow subtraction

Correlations with strange particle triggers in Au+Au at 200 GeV

Selection criteria:• 3.0 GeV/c < pT

trigger < 3.5 GeV/c • 1 GeV/c < pT

associated < 2 GeV/c• || < 1

Correlation function:• normalized per trigger particle• corrected for reconstruction efficiency of associated charged particles• acceptance corrected

STAR preliminarySTAR preliminary

STAR preliminarySTAR preliminarySTAR preliminarySTAR preliminary

STAR preliminarySTAR preliminary

trigger: baryon/meson baryon/antibaryon

after elliptic flow subtraction (using ZYAM method) Ajitanand et al, PRC72 (2005) 011902

systematic errors due to v2 uncertainty ~ 30%

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Jana Bielcikova (Yale University) High-p T physics at LHC, Jyväskylä March 23-27, 2007 Strange...

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