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

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

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

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  1. 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 • Non-photonic electron (NPE) RAA @ RHIC • “anomalous” baryon/meson enhancement @ RHIC • Putting 1. & 2. together or how a charm baryon/meson enhancement lowers the NPE RAA

  2. NPE RAA @ RHIC STAR PHENIX • 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 ~ 0RAA, puzzling… • quantitative agreement between PHENIX & STAR • NPE RAA vs hadron RAA? • b vs c contributions? PHENIX: A. Adare et al., Phys. Rev. Lett. 98 (2007) 172301, STAR: B. I. Abelev et al., Phys. Rev. Lett. 98 (2007) 192301

  3. 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  What if this applies also to the c/D ratio?

  4. assumptions: • binary scaling • same relative yield of D mesons in pp & AA collisions The proof in numbers 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)

  5. 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

  6. Predictions on c/D enhancement quark recombination percolation of strings • recombination & percolation agree quantitatively: c/D ~ 0.3 @ pt ~ 5-6 GeV/c • diquark correlations predict larger enhancement diquark correlations 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]

  7. First study on c/D enhancement vs NPE RAA 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 ~20%

  8. The approach revisited

  9. Simulation steps • baseline: pp @ 200 GeV  NPE (PYTHIA) • add c/D enhancement • add energy loss • add electrons from B decay

  10. 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

  11. 2) folding-in the c/D enhancement assumption for c/D vs pt: Gaussian with mean=5 GeV/c, cte=0.9, =2.9 GeV/c • pt-differential charm cross-section is conserved • RAA = (dN/dpt with c/D enhanc.) / (dN/dpt w/o c/D enhanc.)

  12. 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)

  13. 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)

  14. 4) including electrons from B decay pp @ 200GeV, FONLL 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

  15. NPE RAA with c/D enhancement, dE/dx & e  B • 2 scenarios ptCP = 4.5 GeV/c (central) & ptCP = 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

  16. 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

  17. 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

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