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RIKEN Nishina Center for Accelerator-Based Science Experimental Group

Group Leader: Yasuyuki Akiba (D.Sc.)

Research Summary

Yasuyuki  Akiba(D.Sc.)

RIKEN BNL Research Center (RBRC) Experimental Group studies the strong interactions (QCD) using RHIC accelerator at Brookhaven National Laboratory, the world first heavy ion collider and polarized p+p collider. We have three major activities: Spin Physics at RHIC, Heavy ion physics at RHIC, and detector upgrades of PHENIX experiment at RHIC. We study the spin structure of the proton using the polarized proton-proton collisions at RHIC. This program has been promoted by RIKEN’s leadership. The first focus of the research is to measure the gluon spin contribution to the proton spin. Our recent data analysis has shown that the spin of gluons in the proton is polarized. We also measure the spin of anti-quarks in the proton through measurements of W bosons.
We collected a large amount of data for W measurement in the 2013 RUN, and we are now analyzing the data. The aim of Heavy ion physics at RHIC is to re-create Quark Gluon Plasma, the state of Universe just after the Big Bang. Two important discoveries, jet quenching effect and strong elliptic flows, have established that new state of dense matter is indeed produced in heavy ion collisions at RHIC.We are proceeding to understand the nature of the matter. Recently, we have measured direct photons in Au+Au collisions for 1<pT<3 GeV/c, where thermal radiation from hot QGP is expected to dominate. The comparison between the data and theory calculations indicates that the initial temperature of 300 MeV to 600 MeV is achieved. These values are well above the transition temperature to QGP, which is calculated to be approximately 160 MeV by lattice QCD calculations. In order to advance the QGP study at RHIC, we constructed a silicon vertex tracker (VTX) and installed it in PHENIX in 2010.With this new detector we are measuring production of heavy quarks (charm and bottom) in pp and AA collisions. We recorded approximately 40 billion Au+Au collision events in 2014 and 2016.

Main Research Fields

  • Mathematical & Physical Sciences


  • Quark
  • High temperature and high density matter
  • Nucleon structure
  • Spin

Selected Publications

  • 1.PHENIX Collaboration (A. Adare et al.):
    "Inclusive cross section and double-helicity asymmetry for pi0 production at midrapidity in p+p collisions at sqrt(s)=510 GeV"
    Phys. Rev. D93, 011501 (2016)
  • 2.PHENIX Collaboration (A. Adare et al.):
    "Observation of direct-photon collective flow in sqrt(s_NN)=200 GeV Au+Au collisions"
    Phys. Rev. Lett. 109, 122302 (2012)
  • 3.PHENIX Collaboration (A. Adare et al.):
    "Cross Section and Parity-Violating Spin Asymmetries of W Boson Production in polarized p+p Collisions at sqrt(s)=500 GeV"
    Phys. Rev. Lett. 106, 062001 (2011)
  • 4.PHENIX Collaboration (A. Adare et al.):
    "Enhanced Production of Direct Photons in Au+Au Collisions at sqrt(s_NN)=200 GeV and Implications for the Initial Temperature"
    Phys. Rev. Lett. 104, 132301 (2010)
  • 5.PHENIX Collaboration (Stephen Scott Adler et al.):
    "Measurement of direct photon production in p + p collisions at s**(1/2) = 200-GeV."
    Phys.Rev.Lett.98:012002 (2007)
  • 6.PHENIX Collaboration (A. Adare et al.):
    "J/psi Production vs Centrality, Transverse Momentum, and Rapidity in Au+Au Collisions at s(NN)**(1/2) = 200-GeV."
    Phys.Rev.Lett.98:232301 (2007)
  • 7.PHENIX Collaboration (A. Adare et al.):
    "Energy Loss and Flow of Heavy Quarks in Au+Au Collisions at s(NN)**(1/2) = 200-GeV"
    Phys.Rev.Lett.98:172301 (2007)
  • 8.PHENIX Collaboration (Adcox, K. et al.):
    "Formation of dense partonic matter in relativistic nucleus-nucleus collisions at RHIC: Experimental evaluation by the PHENIX collaboration"
    Nucl.Phys., A757, 184-283 (2005).
  • 9.PHENIX Collaboration (Adler, S.S.et al.):
    "Midrapidity Neutral Pion Production in Proton-Proton Collisions at s**(1/2)=200 GeV"
    Phys.Rev.Lett., 91, 241803 (2003).
  • 10.PHENIX Collaboration (Adcox, K. et al.):
    "Suppression of hadrons with large transverse momentum in central Au+Au collisions at s(NN)**(1/2) = 130-GeV"
    Phys.Rev.Lett., 88, 022301 (2002).

Related Links

Lab Members

Principal investigator

Yasuyuki Akiba
Group Leader

Core members

Yasushi Watanabe
RBRC Researcher
Atsushi Taketani
RBRC Researcher
Yuji Goto
RBRC Researcher
Satoshi Yokkaichi
RBRC Researcher
Takashi Hachiya
RBRC Researcher
Itaru Nakagawa
RBRC Researcher
Seidl Ralf
RBRC Researcher
Takahito Todoroki
RBRC Researcher
Takashi Ichihara
Special Temporary Research Scientist

Contact Information

2-1 Hirosawa,
Wako, Saitama
351-0198, Japan
Email: akiba [at] bnl.gov