# Presentation: 658198

##  STAR measurements of  open charmproduction in dAu collisions at √sNN=200 GeV                          An Tai                                            For the STAR Collaboration

- (1) Motivations
- (2) Data analysis
- (3) Results and Conclusions

## Motivations:

- Study heavy quark dynamic in medium, such as heavy quark energy loss in dense matter, and probe medium properties through heavy quarks
- Gluon structure function of nuclei
-   Comparing ratios of different open charm
-        species with the statistical model prediction--- is the charm quark hadronization modified by the thermal medium ?

- dAu provides an important reference to study
-       heavy flavor production in Au+Au

-                            (9.1%)

- we also measure D from its semi-leptonic decay to electrons in both dAu and pp collisions at √sNN=200 GeV

- Decay channels used in this analysis

- (6.2%)

- About 15  M  dAu minbias events are used in the analysis

## Mass plots from dAu data using event-mixing technique

- 8.5< pt<11.0 GeV/c

-   D*±   Signal

- D0  from D*  decay (tagged D0)

## Results

- Assuming   σ(D*) = σ(D±)  and scale σ(D*) and σ(D±) to match  D0   by D*/D0=0.40

***dAu minbias at ******√s=200 GeV***

-          = 1.12 ± 0.20 ± 0.37 mb

-           = dn/dy*42*4/7.5

*STAR preliminary*

- total multiplicity=4*dn/dy(|y|<0.5)

##  The measurements of open charms are   consistent with background-subtracted electron data in STAR !

**Lijuan Ruan’s talk (Thursday afternoon)**

*STAR preliminary*

- A combined fit using D0  and the electron data leads**     **
**     **
**       ****=1.36± 0.20 ± 0.39 mb**

-  The measurements of open charms are   consistent with background-subtracted electron data in STAR !

**The band is obtained from D decay based on the power-law fit to the measured open charm spectrum.**

## STAR background-subtracted electrons by EMC   first time seeing beauty at RHIC !

##               ratios --- consistent with other experiments

*STAR preliminary*

**CDF:   hep-ex/0307080**
**HERA:   www-h1.de/h1/www/publications/conf_list.html**
**e+e-: hep-ph/0312054**
**Statistical model: A. Andronic etc. nucl-th/0209035 and private communication.**

##  Open charm spectrum is hard !

*STAR preliminary*

**Phenix: Phys. Rev. Lett. 88, 192303(2002)**
** ****D. Kharzeev,hep-ph/0310358**

## Charm quark hadronization at RHIC

- NLO pQCD predictions are provided by R. Vogt,   Int. J. Mod. Phys. E12 (2003) 211

- bare c-quark spectrum, normalized to measured dn/dy

-  D spectrum would be drop by a factor of 3 at pt~10GeV/c when Peterson fragmentation function is set in.
-  Harder fragmentation function, like, δ(z-1), is needed
-  c-quark may hadronize through recombination mechanism.

## Conclusion I

**D0,D* and D****±****  are first measured in dAu run at ****√s****=200 GeV using STAR TPC with a p****T**** coverage of 0<pt<11 GeV/c**
**       ****=****1.12 ± 0.20 ± 0.37 mb from directly-measured open charm and         =****1.36± 0.20 ± 0.39 mb from D****0**** and the single electron measurement**
**D*/D****0****= 0.40±0.09(stat)±0.13(sys), consistent with other experimental results.**

## Conclusion II

**STAR measured D spectrum and single electron are consistent.**
**The measured D pt spectrum coincides with the bare-quark distribution from the NLO calculation.**
**A hard D meson p****T**** spectrum may be obtained from k****T ****factorization scheme (Kharzeev et al), or charm quark recombination or very hard charm fragmentation function (****δ****(z-1) function****). **

## Slide 14

##       broadening and c-quark fragmentationat fixed target experiment

- Bare c-quark spectrum

- After       and fragmentation
-  ε=0.06

-   π+A scattering at 350 GeV/c

**momentum loss due to fragmentation can be counter-balanced by initial**** ****   **

## Charm quark hadronization at RHIC ----harder fragmentation function or c-quark recombination ??

- NLO pQCD predictions are provided by R. Vogt

- bare c-quark spectrum, normalized to measured dn/dy

## Analysis procedure

- Put M(Kππ~) into D± histogram

- If(0.1<p(π~)<1.0 GeV/c && p(Kπ)/p(π~))>7.0, π~πs

##  D± signal is real

-  D± signal is real

- 0-40% centrality

- D±

**K-****π****+****π****- ---wrong charge combination**
**No signal !**

- Raw countings are close for D+ and D-

- D-

- D+

##      signal from                                 

- BR=6.2%

**0.53GeV < m(****ρ****) < 0.95GeV**

- 8.5< pt<11.0 GeV/c

##      signal is real 

-             0-40% centrality

- wrong charge combination
- No signal !

##              ratios

- (1) Assume D*=D0(dir)
- D0=D0(dir)+0.68D*± +D*0
- D*/D0=0.37
- (2) Assume D*=3D0(dir)
- D0=D*/3+0.68D*±+D*0
- D*/D0=0.50

**CDF:   hep-ex/0307080**
**HERA:   www-h1.de/h1/www/publications/conf_list.html**
**e+e-: hep-ph/0312054**
**Statistical model: A. Andronic etc. nucl-th/0209035 and private communication.**

*STAR preliminary*

## Mass and width: Measured vs Monte Carlo                          ------Agree wellwidth is dominated by detector resolutions

## Pythia parameters

- Phenix-tuned pythia parameters:
- <kt>=1.5 GeV/c, mc=1.25 GeV/c^2
- K-factor=3.5, CTEQ5L, PARP(67)=1
- σ(ccbar)=653μb
- STAR tuned pythia parameters <kt>=2.0 GeV/c, mc=1.7 GeV/c^2,
- K-factor=2.2, CTEQ5M1, PARP(67)=4
- σ(ccbar)=1078 μb