effects of minijet degradation on hadron observables in heavy-ion collisions lilin zhu sichuan...

Effects of minijet degradation on hadron

observables in heavy-ion collisions

Lilin Zhu

Sichuan University

QPT2013, Chengdu

QPT2013, Chengdu

Outline

Introduction

Physics ideas of the recombination model

New property of minijet distribution

Hadronic spectra

Conclusion

Lilin Zhu 2

Lilin Zhu QPT2013, Chengdu 3

Transverse momentum spectra

pT2 6

low intermediate

high

pQCDhydro

no rigorous theoretical framework

At intermediate pT recombination model has been successful.

That is where abundant experimental data exist.

Lilin Zhu CPOD2011, Wuhan 4

ReCo models

Duke group: I. 6-dimensional phase spaceII. using Wigner function from density matrix

Texas A&M/BudapestI. Monte Carlo implementationII. Soft and hard partonsIII. Soft-hard coalescence is allowed

Oregon group:I. one-dimensional momentum spaceII. using phenomenological recombination function

PRL90,202301(03), PRC68,044902(03),ArXiv:1102.5723.

PRL90,202302(03), PRC68,034904(03).

PRC67,034902(03), PRC70,024905(04).Hwa, QGP4, p.267.

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Oregon recombination model

pT distributions of and p Recombination functions

Hwa, Phys. Rev. D (1980).

S : shower parton

T : thermal parton = T T + T S + SS

==T T T T T T + + T T S T T S + + T SS T SS + + SSSSSS

fragmentation

Lilin Zhu 5

Parton distributions before recombination

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Parton distributions

Thermal partons:

Shower distribution

Lilin Zhu 6

SPD, Obtained from FF, Hwa-Yang (04)

T is the inverse slope parameter, not the hydro temperature

let’s see how to take parton momentum degradation into account

hard and semihard parton distributions at the medium surface. Integrated over all initial creation points.

Lilin Zhu

p2dynamical path length

Fries, et al PRC(03)

The process of momentum degradation

parton distribution at creation point

Calculation in pQCD is not reliable at intermediate q and difficult to account for the nuclear complications at various c and

The degradation of momentum from k to q can be written as a simple exponential Hwa-Yang(10)

Nuclear complicatioin is in the determination of

7QPT2013, Chengdu


The probability of having at and c in the medium

Since depends on the nuclear medium and the azimuthal angle, so we could express in terms of angle and centrality c.

That is contained in the probability function in relating to

Mean dynamical path length

As the system expands, the density D decreases but t1 increases, so is not very sensitive to the expansion dynamics.

probability of production of a (semi)hard parton at creation point x0 and y0

The dynamical effect of energy loss per unit length i=g, q.

Whereas depends on , c implicitly, the mean depends on them explicitly.

determined by fitting nuclear modification factor

The geometrical path length is weighted by the local density along the trajectory marked by t.

not time

Hwa-Yang(10)


Mean dynamical path length

Points determined from calculation that account for nuclear complications.


For calculating the pT spectra of any hadron produced later, we make averaged over

No momentum degradation

More suppression for gluons than for quarks throughout the whole region.

Minijet distribution at RHIC

minijet distribution, averaged over , initial creation points.

Minijet Degradation Factor

QPT2013, ChengduLilin Zhu

Increase is rapid at low q.

Rg is roughly half of Rq, but q and c dependencies are similar in shape.

12

It is analogous to the nuclear modification factor RAA for , but for minijets.

parametrization for


Tsallis distribution could fit the minijet distribution very well

Tt=0.32 is universal;

ni depends on parton type.

pion production


The formalism for recombination of thermal and shower partons has been developed previously. Hwa-Yang, PRC(04)

Hwa-Zhu, PRC(11)Now we generalize to non-central collisioins, especially show the contributions from various species of semihard partons

Zhu-Hwa , 1307.3328

The two shower partons are from the same minijet with momentum q

TT

TS

SS

proton production


TTT

TTS

SSS

TSS

pion at central collision


The inverse slope is adjusted to fit the low pT behavior.

T=0.283 GeV.

It’s the same value for all hadrons at low pT.

The pT of TS and SS are fixed by minijets, whose magnitudes depend on .

TTTS

SS

QPT2013, ChengduLilin Zhu

Zhu-Hwa, 1307.3328

17

pion

Only vary C(Npart) for the thermal partons. No parameters are adjusted for the shape of the pT distribution at intermediate and high pT region at all centralities.

proton


It is our prediction for proton pT>5 for c > 20%.

Quark minijets are more influential than gluons in the proton distribution at high pT.

Kaon


Good fit out to 9 GeV/c for all centralities.

p/pi at RHIC

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For 0-10% the ratio is very well reproduced. For 20-40% not as well around the peak.

Lilin Zhu 20


at LHC

pion

Hwa-Zhu, PRC (11)


Pb-Pb collisions at 2.76 TeV

At LHC minijets are pervasive and their effects dominate the spectra at the low and intermediate pT range.

TS>TT at pT>0.5 GeV/c.

RHIC

TT

TS

SS

Zhu-Hwa, 1307.3328


K/p/Λ spectra (0-5% Central)

T=0.38 for thermal partons is higher than 0.283 at RHIC.

For p and Λ, TTS>TTT

0-5％0-5％

0-5％

Hwa-Zhu, PRC(11)

Lilin Zhu QPT2013, Chengdu

effect of minijets at LHC

T=0.38 GeV at LHC

T=0.283 GeV at RHIC

24

Due to the abundant production of minijet,TS is elevated going from RHIC to LHC

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Summary & outlook

new features of momentum degradation of minijets produced at intermediate q before hadronization.

pT and c dependencies of hadronic observables are well

reproduced-- by the minijet approach in the framework of the recombination model

Extension of the study to hyperons production, such as: Omega.

Hadron production at LHC.

Lilin Zhu 25

QPT2013, Chengdu

Thank you!

Lilin Zhu 26

QPT2013, Chengdu

backup

Lilin Zhu 27

Hwa-Zhu, (12)

QPT2013, ChengduLilin Zhu 28

The good fits support our minijet approach to the treatment of azimuthal anisotropy.


Determining RFs

R p was determined from CTEQ From the parton distributions in proton a=b=1.755, c=1.05 at Q2=1GeV2

R was determined from Drell-Yan processes a=b=0 See Phys. Rev. C 66, 025204


Recombination functions

Given by the valon distribution of the hadrons

1 2

1 2 3

, ,...1 2 1 2 1 2

, ,...1 2 3 1 2 3 1 2 3

( , ) ( , )

( , , ) ( , , )

KQ Q

p nQ Q Q

R y y y y G y y

R y y y y y y G y y y

1 2

1 2 3

1 2 1 2 1 2

1 2 3 1 2 3 1 2 3

( , ) ( 1)

( , , ) ( 1)

a bQ Q

a b cQ Q Q

G y y y y y y

G y y y y y y y y y


Recombination model for fragmentation

Fragmentation function known from fitting e+e- annihilation data S V G S K G K

Biennewies, Kniehl, KramerKniehl, Kramer, Pötter

Recombination function known in the recombination model

Hwa, Phys. Rev. D (1980).

Shower parton distributions

K, L, G, Ls, Gs

Hwa and Yang, PRC70,024904(2004)

effects of minijet degradation on hadron observables in heavy-ion collisions lilin zhu sichuan...

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