[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
[email protected] 2Bad Honnef, 27/06/[email protected] Bad Honnef, 27/06/08
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?
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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
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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
)/(
)/(
,
,
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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
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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]
[email protected] 10Bad Honnef, 27/06/[email protected] Bad Honnef, 27/06/08
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
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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
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Simulation steps
1. baseline: pp @ 200 GeV NPE (PYTHIA)
2. add c/D enhancement
3. add energy loss
4. add electrons from B decay
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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
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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
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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)
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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)
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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
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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
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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
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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