Abstracts for DNP (fall meeting) 2010 (Nov. 2-6, 2010, Santa Fe, NM)

• Wenqin Xu

Title: Extracting bottom quark production cross section from p+p collisions at RHIC

The STAR collaboration has measured the non-photonic electron (NPE) production at high transverse momentum (pT ) at middle rapidity in p + p collisions at sqrt(s) = 200 GeV at the Relativistic Heavy Ion Collider (RHIC). The relative contributions  of bottom and charm hadrons to NPE have also been obtained through electron hadron azimuthal 
correlation studies. Combining these two,  we are able to determine the high pT mid-rapidity electron spectra 
from bottom and charm decays, separately.

PYTHIA with different tunes and FONLL calculations have been compared  with this measured electron spectrum
from bottom decays to extract the bb-bar differential cross section after normalization to the measured spectrum.
The extrapolation of the total bb-bar production cross section in the whole kinematic range and its dependence
on spectrum shapes from model calculations will also be discussed.

• Yifei Zhang

Title: Open charm hadron reconstruction via hadronic decays in p+p collisions at $sqrt{s}$ = 200 GeV

Heavy quarks are believed to be an ideal probe to study the properties of the QCD medium produced in the relativistic heavy ion collisions. Heavy quark production in elementary particle collisions is expected to be better calculated in the perturbative QCD. Precision understanding on both the charm production total cross section and the fragmentation in p+p collisions is a baseline to further explore the QCD medium via open charm and charmonium in heavy ion collisions.
Early RHIC measurements in p+p collisions which were carried out via semi-leptonic decay electrons provides limited knowledge on the heavy quark production due to the incomplete kinematics, the limited momentum coverage and the mixed contribution from various charm and bottom hadrons in the electron approach. In this talk, we will present
the reconstruction of open charm hadrons (D0 and D*) via the hadronic decays in p+p collisions at $sqrt{s}$ = 200 GeV in the STAR experiment. The analysis is based on the large p+p minimum bias sample collected in RHIC Run9. The Time-Of-Flight detector, which covered 72% of the whole barrel in Run9, was used to improve the decay daughter
identification. Physics implications from this analysis will be presented.

• Xin Li

Title: Non-photonic Electron Measurements in 200 GeV p+p collisions at RHIC-STAR

Compared to the light quarks, heavy quarks are produced early in the collisions and interact very differently with the strongly couple QGP(sQGP) created at RHIC. In addition, their large masses are created mostly from the spontaneous symmetry breaking. All these features make heavy quark an ideal probe to study the sQGP. One of the critical references in these studies is the heavy quark production in p+p collisions, which also provides a crucial test to the pQCD. Measuring electrons from heavy quark semi-leptonic decay (non-photonic electron) is one of the major approaches to study heavy quark production at RHIC.

We will present STAR measurements on the mid-rapidity non-photonic electron production at pT>2 GeV/c in 200 GeV p+p collisions using the datasets from the 2008 and 2005 runs, which have dramatically different photonic backgrounds. We will compare our measurements with the published results at RHIC and also report the status of the analysis at pT<2 GeV/c using the dataset from the 2009 run.

• Jonathan Bouchet

Title: Reconstruction of charmed decays using microvertexing techniques with the STAR Silicon Detectors

Due to their production at the early stages, heavy flavor particles are of interest to study the properties of the matter created in heavy ion collisions. Direct topological reconstruction of $D$ and $B$ mesons, as opposed to indirect methods using semi-leptonic decay channels [1], provides a precise measurement and thus disentangles the $b$ and $c$ quarks contributions [2].

In this talk we present a microvertexing technique used in the reconstruction of $D^{0}$ decay vertex ($D^{0} \rightarrow K^{-}\pi^{+}$) and its charge conjugate. The significant combinatorial background can be reduced by means of
secondary vertex reconstruction and other track cut variables. Results of this method using the silicon detector information of the STAR experiment at RHIC will be presented for the Au+Au system at $\sqrt{s_{NN}}$ = 200 GeV.

[1]A. Abelev et al., Phys. Rev. Lett. {\bf 98} (2007) 192301
[2]N. Armesto et al., Phys. Lett. B{\bf 637} (2006) 362-366.