[email protected] Honnef, 27/06/[email protected] Honnef, 27/06/08 1 Consequences of a c /D enhancement effect

[email protected] 1Bad Honnef, 27/06/[email protected] Bad Honnef, 27/06/08

Consequences of a c/D enhancement effect on the non-photonic electron nuclear modification

factor in central heavy-ion collisions at RHIC

G. Martinez-Garcia, S. Gadrat and P. Crochet, Phys. Lett. B 663 (2008) 55

also P. Sorensen and X. Dong, Phys. Rev. C 74 (2006) 024902

Outline

1. Non-photonic electron (NPE) RAA @ RHIC

2. “anomalous” baryon/meson enhancement @ RHIC

3. Putting 1. & 2. together or how a charm baryon/meson enhancement lowers the NPE RAA


NPE RAA @ RHIC

PHENIX: A. Adare et al., Phys. Rev. Lett. 98 (2007) 172301, STAR: B. I. Abelev et al., Phys. Rev. Lett. 98 (2007) 192301

• charm & bottom energy loss via NPE RAA

• pt < 3-4 GeV/c: NPE RAA < 0 RAA, as expected (color charge & dead-cone)

• pt > 4-5 GeV/c: NPE RAA ~ 0 RAA, puzzling…

• quantitative agreement between PHENIX & STAR

PHENIX STAR

tepp

teAA

coll

eAA dpdN

dpdN

NR

/

/1

• NPE RAA vs hadron RAA?

• b vs c contributions?





What if this applies also to the c/D ratio?

• sizeable yield of c w.r.t. D mesons in pp @ 200GeV

• BR(c e+X) < BR(D e+X)

• a c/D enhancement lowers the yield of NPE in HIC

• NPE RAA is not exclusively sensitive to heavy quark dE/dx


The proof in numbers

ss

cc

cc

DDDDDD

D NNNNNN

NNNN

00

/,

ppDee

ppDee

ppD

ppD

AA NN

NNC

NNC

NNR

c

c

cc

cc

)/(1

)/(1

)/(1

)/(1

,

,

ss

cccc

c

DDDDDDDDDDD

D

Dee BRNNBRNNBRNN

BRNNNN

)/()/()/(

)/(/

0000 ,,

,,

%63.31

%63.31

%3.71

%3.71

C

CRAA

assumptions:

• binary scaling

• same relative yield of D mesons in pp & AA collisions

with C the c/D enhancement factor

and

pp collisions @ 200 GeV (with particle yield from PYTHIA)

RAA = 0.90(0.79) for c/D = 0.35(0.84) i.e. C = 5(12)

ppD

AAD

NN

NNC

cc

cc

)/(

)/(

,

,


Differences light vs heavy for recombination process

• transverse momentum (I)

• pt of a light meson(baryon) = 2(3) times pt of the valence quarks

• pt of a heavy (simple) hadron ~ pt of the heavy quark

• transverse momentum (II)

for the same velocity, pt of a light(heavy) quark is small(large)

recombination of heavy quark appears at larger pt?

• the light(heavy) quark fragmentation time is large(small)

~ 25, 1.6 & 0.4 fm/c for a 10 GeV/c , D & B meson*

recombination of light & heavy quarks qualitatively different

*A. Adil & I. Vitev, Phys. Lett. B 649 (2007) 139


Predictions on c/D enhancement

diquark

correlations

quark recombination

percolation of strings

• recombination & percolation agree quantitatively: c/D ~ 0.3 @ pt ~ 5-6 GeV/c

• diquark correlations predict larger enhancement

L. Cunquiero et al., Eur. Phys. J. C 53 (2008) 585, C. Pajares, private communication, V. Greco, http://alice.pd.infn.it/quenchingDay.html,

S.H. Lee et al., arXiv:0709.3637v2 [nucl-th]


First study on c/D enhancement vs NPE RAA

~20%~20%

P. Sorensen and X. Dong, Phys. Rev. C 74 (2006) 024902

main assumption: c/D(pt) identical to measured

/K0s(pt)

• large enhancement (a factor 20)

• located at low pt (< 5GeV/c)

20% suppression at pt ~ 2.5 GeV/c


The approach revisited

S. Sorensen and X. Dong, Phys. Rev. C

74 (2006) 024902

our study, Phys. Lett. B

663 (2008) 55

c/D shape in AuAu as /K0S data Gaussian

c/D shape in pp as /K0S data PYTHIA

maximum of c/D ratio ~1.7 at pt ~3 GeV/c ~0.9 at pt ~5 GeV/c

energy loss hadron shape scalingS.Wicks et al., Nucl.

Phys. A 784 (2007) 426

electrons from B decay no yes


Simulation steps

1. baseline: pp @ 200 GeV NPE (PYTHIA)

2. add c/D enhancement

3. add energy loss

4. add electrons from B decay


1) PYTHIA: pp collisions @ 200 GeV

PYTHIA using PHENIX tuning (Phys. Rev. Lett. 88 (2002) 192303)

• PYTHIA slightly softer than PHENIX & agrees with FONLL (as in PRL 97 (2002) 252002)

• decay electrons from c have a softer spectrum than decay electrons from D

suppression of NPE in AA collisions is further enhanced for pt >~ 2 GeV/c


2) folding-in the c/D enhancement

• pt-differential charm cross-section is conserved

• RAA = (dN/dpt with c/D enhanc.) / (dN/dpt w/o c/D enhanc.)

assumption for c/D vs pt:Gaussian with mean=5 GeV/c,

cte=0.9, =2.9 GeV/c


NPE RAA with c/D enhancement (only NPE from charm here)

• c/D enhancement results in ~ 40% of suppression for pt ~ 2-4 GeV/c

• smaller suppression (20%) at large pt (due to the Gaussian shape)

• comparison limited to pt > 2 GeV/c (shadowing not included)


3) including energy loss (only NPE from charm here)

• rad. & col. energy loss from S. Wicks et al., Nucl. Phys. A 784 (2007) 426

• suppression from col. energy loss ~ suppression from c/D enhancement

• RAA with all effects ~ 0.2 for pt > 3 GeV/c (similar to that of light hadrons)


4) including electrons from B decay

theoretical uncertainties in mQ, F/0, R/0, PDF

charm/bottom crossing point from 2.5 to 10.5 GeV/c (central value ~ 4.5 GeV/c)

FONLL calculations from M. Cacciari et al., Phys. Rev. Lett. 95 (2005) 122001

pp @ 200GeV, FONLL


NPE RAA with c/D enhancement, dE/dx & e B

• 2 scenarios ptCP = 4.5 GeV/c (central) & pt

CP = 10.5 GeV/c (highest)

• c/D enhancement is responsible for 10(25) % of the suppression for a charm/bottom crossing-point at 4.5(10.5) GeV/c


Summary

a c/D enhancement, as observed for p/+, /Ks0 & /,

lowers the non-photonic electron RAA at intermediate pt by 10-25% because

• BR(c e+X) smaller than BR(D e+X)

• pt(e c) softer than pt(e D)

measurement of c/D urgently needed before solid conclusions from non-photonic electrons RAA can be drawn

more details in Phys. Lett. B 663 (2008) 55


Outlooks: c/D enhancement & NPE flow

toy model:

• build a sample of D0 & c

• give them elliptic flow with PHENIX/STAR nq scaling

• let them decay

• get decay electron v2 vs. pt for different % of D0 & c

c/D enhancement increases NPE v2

detailed (PYTHIA) simulations in progress

Documents

[email protected] Honnef, 27/06/[email protected] Honnef, 27/06/08 1 Consequences of a c /D enhancement effect