Ⅱ-4. Hadron Physics

RIKEN Accel. Prog. Rep. 47 (2014)

Status of the charm and bottom measurement with PHENIX-VTX
T. Hachiya,∗1 A. Adare,∗2 Y. Akiba,∗1 R. Akimoto,∗1 H. Asano,∗1 S. Bathe,∗1 J. Bryslawskyj,∗3 A. Dion,∗4
T. Koblesky,∗2 M. Kurosawa,∗1 M. McCumber,∗5 D. McGlinchey,∗2 T. Moon,∗1 H. Nakagomi,∗1 R. Nouicer,∗6H. Sako,∗7 S. Sato,∗7 M. Shimomura,∗8 T. Sumita,∗1 A. Taketani,∗1 H. Torii,∗1 and the PHENIX VTX groupthe ideal curve.
(3) DCA decomposition method:
The charm and bottom yields were obtained byﬁtting the measured DCA distribution with theDCA templates of charms and bottoms3) . The
DCA templates are correlated with the shapeof their transverse momentum (pT ) distribution
since the DCA is determined by convolution of
two eﬀects: the decay length of the parent particle and pT kick relative to the parent momentum. In order to include this eﬀect, we ﬁt boththe DCA and pT distribution of electrons simultaneously. We are testing the several methods
to decompose charm and bottom components.

Heavy quarks (bottom and charm) are one of theclean probes for studying properties of hot dense
medium created in the high energy heavy ion collisions.
Due to their large mass, heavy quarks are mainly produced though the initial hard scattering. Once produced, the heavy quarks traverse and interact withthe medium. Therefore, the modiﬁcation of their production yield and emission angle reﬂects the medium
properties.
The PHENIX experiment1) installed a silicon vertex tracker (VTX)2) and collected a large amount of√p + p, Au+Au and Cu+Au collision events at sN N =200 GeV successfully in the past three years. TheVTX provides a clear separation of charm and bottom quarks via measurement of distance of the closest
approach of electrons relative to the collision vertex(DCA).
The preliminary results of the fraction of (b →e)/(b → e + c → e) and the azimuthal anisotropy ofcharms were already reported3,4) . In order to improve
the DCA measurement, we recently updated the following items in the analysis:(1) Hot and dead channel status on the sensor:
The bad channels that have extremely higher
and lower hit rate were masked. In addition,
the unstable channels that changed the hit rateby time were also newly masked. Figure 1 shows
the map of the hot and dead channels for a readout chip. The colored channels indicate the badchannels caused by the faulty bump bonding between the sensor and the readout chip.
(2) Parameter tuning of the track association between the VTX hits and the track measured in
the central arm:
The angular resolution of tracks measured in thecentral arm was an input for the χ2 calculationof the track ﬁtting between VTX hits and thetrack. This resolution was updated to be realistic (1m rad.). The blue histogram and black
curve in Fig. 2 show the χ2 distribution for thereconstructed proton in simulation and the ideal
χ2 function. The histogram suitably reproduces
∗1
∗2
∗3∗4
∗5
∗6
∗7
∗8Fig. 1. Hot and dead channels for a readout chip. The
colors indicate the bad statuses mostly due to faulty
bump bonding.

Fig. 2. The χ2 distribution of proton in simulation. The
histogram suitably reproduces the ideal curve.

We are working to complete the Au+Au and p + p
analysis for publication. The Cu+Au analysis is alsoin progress and we aim to show the ﬁrst Cu+Au resultin 2014.

RIKEN Nishina Center
University of Colorado
City University of New York
Department of Physics and Astronomy, Stony Brook University
Oak Ridge National Laboratory
Brookhaven National Laboratory
Japan Atomic Energy Agency
Iowa State University

References
1) K. Adcox et al.: Nucl. Inst. Meth. A 499, 469 (2003).
2) R. Nouicer et al.: Proc. of Sci. (Vertex2007), 042 (2007).
3) R. Akimoto et al.: RIKEN Accel. Prog. Rep. 46, 60(2013).
4) M. Kurosawa et al.: RIKEN Accel. Prog. Rep. 46, 61(2013).

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