Ⅱ-4. Hadron Physics

RIKEN Accel. Prog. Rep. 49 (2016)

Current status of open heavy flavor measurements in
RHIC-PHENIX RUN14K. Nagashima,∗1,∗2 A. Adare,∗2 Y. Akiba,∗1 H. Asano,∗1,∗4 S. Bathe,∗1,∗5 J. Bryslawskeyj,∗5 T. Hachiya,∗1T. Koblesky,∗3 M. Kurosawa,∗1 D. Mcglinchey,∗3 T. Moon,∗1,∗6 H. Nakagomi,∗7 R. Nouicer,∗8 T. Rinn,∗9Z. Rowan,∗5 T. Sumita,∗1 and A. Taketani∗1The Quark Gluon Plasma (QGP) existed in the early
universe. We are studying the physical property of theQGP at RHIC-PHENIX. It can be characterized by thequark energy loss mechanism. Especially heavy quarks(charm and bottom) are important probes of the QGP.
They are predominantly produced during hard scattering in the initial stage of a heavy-ion collision producesthem dominantly, since the charm and bottom masses
are larger than the temperature of the QGP. Additionally the energy loss of heavy quarks would be expected to be smaller than that of light quarks due tolower collisional energy loss and the Dead-Cone-Eﬀect
that leads to a strong suppression of small angle gluonradiation. The silicon vertex tracker (VTX) was installed and used to measure the ﬁrst data in 2011. It
can separate the charm and bottom hadron decay electrons with the distance of closest approach (DCA). The
DCA of a track is calculated separately in the transverse plane (DCAT ) and the beam direction (DCAL )as shown in Fig.1.

Fig. 1. DCAT is defined as DCAT = L - R in the transverse(bending) plane

We focus on DCAT for the analysis because DCAT
has a better resolution than DCAL in the design performance. In order to estimate the charm and bottom
hadron invariant yields separately, we use a DCA cocktail method subtracting all background components es∗1∗2∗3∗4∗5∗6∗7∗8∗9RIKEN Nishina Center
Department of Physics, Hiroshima University
Department of Physics, University of Colorado, Boulder
Department of Physics, Kyoto University
Department of Natural Science, Baruch College, CUNY
Department of Physics, Yonsei University
Department of Physics, University of Tsukuba
Brookhaven National Laboratry
Department of Physics, Iowa State University

timated by simulations and data, and a Bayesian inference technique based on a Markov Chain Monte Carlo(MCMC).
PHENIX reported the nuclear modiﬁcation factor
RAA of electrons from charm and bottom hadron de√cays separately based on Au+Au collisions at sN N =1,2)
200 GeV recorded in 2004 and 2011.
We found thatsuppression of electrons from bottom hadron decays
is lesser than that from charm for the region 3 < pT
< 4 GeV/c.3,4) Accordingly, we plan to measure thecentrality dependence of RAA over a broader pT range
with high statistics data recorded in 2014. It is expected to have 10 times more statistics than the data
recorded in 2011. VTX performances was the same in2014 and 2011, as a result of comparing DCAT resolutions as shown in Fig.2. We ﬁnished the calibration

Fig. 2. DCAT resolution as a function of pT in Run14
AuAu (blue) and Run11 AuAu (read). The comparison
shows that detector performances are much the same.

and quality assurance of the 2014 data and obtained
the electron DCAT distribution in each centrality bin.
The next step is to estimate the normalization andshape of all background components in order to decomvolute the electron DCAT distribution. Eventually we will obtain the invariant cross section of bothcharm and bottom hadrons, and compare it with thep+p collision data recorded in 2015 to estimate RAA .
References
1) A. Adare et al; Phys. Rev. C 84, 044905 (2011).
2) A. Adare et al; arXiv:1509.04662.
3) T. Hachiya et al: In this report.
4) H. Asano et al: In this report.

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