# Presentation: 080195

## Consequences of a c/D enhancement effect on the non-photonic electron nuclear modification factor in central heavy ion collisions at RHIC energies

- Gines Martinez-Garcia*, Sebastien Gadrat*,#, and Philippe Crochet&
- (*) Subatech, Nantes, France
- (&) LPC Clermont Ferrand, France
- (#) Now at LPSC, Grenoble, France

- Hot Quarks 2008, Estes Park, Colorado, USA.

- More details in Physics Letter **B**663 (2008) 55.

## Outline of the talk

- Physics Motivations:
- Non-photonic electron nuclear modification factor (RAA) at RHIC energies;
- Enhancement of baryon/meson ratio at RHIC energies;
- Enhancement of the c/D ratio in HIC:
- Model to compute the consequences on the non-photonic electron RAA;
- Considering all ingredients:
- c/D enhancement;
- Quark energy loss;
- Beauty contribution.

- Sébastien Gadrat, Hot Quarks 08

## Non-photonic electron RAA @ RHIC

- Non-photonic electrons are assumed to arise from the semi-leptonic decay of charm and beauty hadrons;
- Suppression increases with the centrality of the collision;
- Suppression similar to light hadron suppression at high pT;
- Radiative energy loss is not enough to explain the data.

- PHENIX, PRL 172301 (2007)

- STAR, PRL 192301 (2007)

- Sébastien Gadrat, Hot Quarks 08

## e± RAA @ RHIC understood ?

- Sébastien Gadrat, Hot Quarks 08

## Baryon/meson enhancement @ RHIC

- STAR, nucl-ex/0703040
- STAR, nucl-ex/0701052 STAR, nucl-ex/0703033

-  already observed for light (u, d) and strange species ;
-  the heavier the baryon, the higher in pT the maximum occurs (Ω/Φ) ;
-  quark coalescence models qualitatively describe the data (PRC65, PRL90, PRC68, PRC67, JPG30, PRC70).

- Sébastien Gadrat, Hot Quarks 08

## BR(c  e anything) is smaller than any BR(D  e anything)

A relative enhancement of the c/D would lead to a « natural » single electrons suppression with respect to p+p scaling !

 e± RAA not exclusively sensitive to heavy quarks dE/dx !

|  | 
D0, D0 | 
D+, D- | 
Ds+, Ds- | 
c+, c-  |
| --- | --- | --- | --- | --- |
| 
BR (Xe)
in % | 
6.71  0.29
 | 
17.2  1.9 | 
8 +6-5 | 
4.5  1.7 |

- BR(c  e anything) is smaller than any BR(D  e anything)
- A relative enhancement of the c/D would lead to a « natural » single electrons suppression with respect to p+p scaling !
-  e± RAA not exclusively sensitive to heavy quarks dE/dx !

- Sébastien Gadrat, Hot Quarks 08

## Proof in numbers...

**with C the ********c****/D enhancement factor**

**and**

**pp collisions @ 200 GeV :**

**Perfect binary scaling**
**S****a****me D****0****,D****+****,D****s**** relative yields**

- RAA=0.90 (0.79) for c/D=0.35(0.84)  C=5 (12)

- Yields (Pythia phenix settings) c/D ~ 0.073

- Sébastien Gadrat, Hot Quarks 08

## Theoretical predictions

- V. Greco, Private communication & Quenching Day, INFN (2005)

- L. Cunqueiro & C. Pajares, Private communication &
- Eur. Phys J C53 585 (2008), arXiv:0712.0509v1 [hep-ph]

- Enhancement of c/D is expected in HIC;
- Maximum at 5-6 GeV/c;
- Existence of diquarks correlations in the sQGP;

- S. Yasui et al., arXiv:0803.1366v1 [nucl-th]
- S. H. Lee et al., arXiv:0709.3637v2 [nucl-th]

- Recombination

- Percolation of strings

- Diquark correlations

- Sébastien Gadrat, Hot Quarks 08

## First study of this effect done by                P. Sorensen and X. Dong

- New RAA including c/D effect

- Results:
-  enhancement effect for low pT:           2 ≾ pT ≾ 5 GeV/c;
-  high value for the max c/D ratio required (~ 1.7 taken from the /Ks0);
-  suppression less than 20%.

- Assumptions:
-  use /Ks0 measured shapes as a reference for c/D ones;
-  the charm RAA is similar to light hadrons RAA.

**~20%**

- PRC74 024902 (2006), SQM06 & HQ06

- Sébastien Gadrat, Hot Quarks 08

## A more detailed study of the charm enhanced B/M effect on the non-photonic RAA 

|  | Sorensen and Dong | Our study |
| --- | --- | --- |
| c/D shape in Au+Au | as /Ks0 | Gaussian |
| c/D shape in p+p | as /Ks0 | from Pythia |
| Maximum of the c/D ratio | ~ 1.7 (from the /Ks0) for pT ~ 3 GeV/c | ~ 1 for pT ~ 6 GeV/c |
| Energy loss | From the scaling of the hadron shape | From S. Wicks et al., NPA 784(07)426 |
| Beauty contribution | No | Yes |

- Sébastien Gadrat, Hot Quarks 08

## Pythia:  p+p at 200 GeV

- PHENIX data are well reproduced by Pythia (tuned according to PRL88 192303 (2002)) though Pythia spectrum slightly softer;
- Decay electrons from c exhibit a softer spectrum:
-  suppression of non-photonic electrons is further enhanced !

- Sébastien Gadrat, Hot Quarks 08

## c/D enhancement hypothesis

** ****p****T**** differential cross section is conserved ;**
**	****     ****dN/dp****T**** with nuclear effects**
** ****R****AA**** =**
**	****    ****dN/dp****T**** w/o any nuclear effect**

-  Shape of the c/D (pT) enhancement

- Sébastien Gadrat, Hot Quarks 08

## RAA(pT) from c/D enhancement

- Natural suppression of the non-photonic electron till 40% in the pT region 2-4 GeV/c;
- Suppression of 20% up to pT~9 GeV/c;

- Attention ! Shadowing has not been taken into account but only relevant for pT < 2GeV/c.

**N****on-photonic electrons from charm**

- Sébastien Gadrat, Hot Quarks 08

## RAA(pT) with c/D enhancement and charm energy loss

- Collisional energy loss leads to a similar effect as c/D enhancement (light blue vs red);
- Suppression 0.2 level, like light quarks seen for pT>3 GeV/c (blue);

- Sébastien Gadrat, Hot Quarks 08

## Beauty contribution

- Not well known from experimental data;
- Large uncertainty from theory (mc, mb, Qr, Qf);

- T. Ullrich, Hard Probes 08

- Crossing-points:
- 4.5 and 10.5 GeV/c

- Sébastien Gadrat, Hot Quarks 08

## RAA (pT) with all the effects

- Additional suppression of the non-photonic electrons of 10(25)% due to c/D enhancement for a charm vs beauty crossing point of 4.5 (10.5) GeV/c;

- Sébastien Gadrat, Hot Quarks 08

## Conclusions

- Enhancement of the c/D ratio in HIC would lead to a suppression of non-photonic electrons;
- Assuming an enhancement similar to light hadrons with a maximum at pT=5 GeV, as expected from recombination models, the suppression of non-photonic electrons is increased by 10-25% in the pt range 4-9 GeV;
- Direct measurement of open heavy flavour production are imperative before solid conclusion on the e± RAA can be drawn.

- Sébastien Gadrat, Hot Quarks 08

## Perspectives

- R. Averbeck, QM2008

- Role of the c/D enhancement on the elliptic flow of non-photonic electron has to be understood ...

- Simulation in progress...

- Sébastien Gadrat, Hot Quarks 08

## Back up

- Sébastien Gadrat, Hot Quarks 08

## Other effects related to the chemical composition of heavy flavoured hadron 

- Enhancement of Ds meson production:
- BR in the semi-leptonic channel is not well known 8+6-5 %. However, similar BR expected from the spectator model;
- Small effect expected with this BR.
- Enhancement of beauty B/M ratio:
- The mass of the beauty quark being higher,  beauty semi-leptonic decays exhibit similar behaviour in beauty hadrons. Expected from the spectator model;
- Large enhancement is expected form diquarks correlations (factor 10);

- S. H. Lee et al., arXiv:0709.3637v2

- Sébastien Gadrat, Hot Quarks 08

## Qualitative differences: light vs heavy quark recombination

- For the same velocity, the pT of the heavy quark is larger, ~ mQ/mq factor:
- Recombination extend to higher pT;
- Estimation pTc~1 GeV x mc/mq = ~4 GeV (mc=1.25 GeV, mq=300 MeV);
- Full pT :
**Light:** pT of the hadron (2 or 3) times the pT of the quarks;
**Heavy:** pT of the hadron slightly higher than the pT of the heavy quark;
- The light (heavy) quark fragmentation time is long (short):
- 20, 1.5 & 0.4 fm/c for a 10 GeV/c , D & B meson (hep-ph/0611109)

- Sébastien Gadrat, Hot Quarks 08

## New parameterisation

- Gaussian shape centred at ~7 GeV, maximum of 0.9 and  =2.9 GeV.

- 40%

- Sébastien Gadrat, Hot Quarks 08

## New parameterisation

- 10(25)% up to pT ~9 GeV/c for a charm vs beauty crossing point at 4.5(10.5) GeV/c!

- Sébastien Gadrat, Hot Quarks 08