Radiation Laboratory

Nucleons, such as protons and neutrons, are a bound state of constituent quarks glued together with gluons. The detail structure of nucleons, however, is not well understood yet. Especially the mechanism to build up the spin of proton, which is 1/2, is a major problem in physics of the strong force. The research goal of Radiation Laboratory is to solve this fundamental question using the world first polarized-proton collider, realized at RHIC in Brookhaven National Laboratory (BNL) in USA. RHIC stands for Relativistic Heavy Ion Collider, aiming also to create Quark Gluon Plasma, the state of Universe just after the Big Bang. RIKEN-BNL Research Center (RBRC) directed by N. Samios carries our core team at BNL for those exciting researches using the PHENIX detector. We have found that the proton spin carried by gluons is indeed small, which is a very striking finding beyond our expectations. Recently we successfully identified W boson in the electron/positron decay channel, with which we established the method to determine how much anti-quarks carry the proton spin. Other than the activities at RHIC we are preparing new experiments at SPring-8, J-PARC and Fermilab to study the nature of hadron. We are also performing technical developments such as novel ion sources, fine pitch pixel detectors and neutron optical devices.

Research Subjects

• Spin physics with relativistic polarized-proton collisions at RHIC
• Study of nuclear matter at high temperature and/or at high density
• Technical developments on radiation detectors and accelerators

Publications

1. PHENIX Collaboration (A. Adare et al.):
   "Measurements of Higher-Order Flow Harmonics in Au+Au Collisions at sqrt(sNN) = 200 GeV."
   Phys. Rev. Lett. 107:252301(2011)
2. T. Nakamura, H. En'yo, T. Ichihara, Y. Watanabe, S. Yokkaichi,:
   "Data oriented job submission scheme for the PHENIX user analysis in CCJ"
   J. Phys. Conf. Ser.331:072025(2011)
3. PHENIX Collaboration (A. Adare et al.):
   "Enhanced Production of Direct Photons in Au þ Au Collisions at sqrt(s_NN) = 200 GeV and Implications for the Initial Temperature"
   Phys. Rev. Lett. 104, 132301 (2010)
4. PHENIX Collaboration (A. Adare et al.):
   "Cross Section and Parity-Violating Spin Asymmetries of W Boson Production in Polarized p t p Collisions at sqrt(s)=500 GeV"
   Phys. Rev. Lett. 106, 062001 (2011)
5. A. Bazilevsky et al.:
   "Single Transverse-Spin Asymmetry in Very Forward and Very Backward Neutral Particle Production for Polarized Proton Collisions at s**(1/2) = 200-GeV."
   Phys.Lett.B650:325-330 (2007)
6. PHENIX Collaboration (A. Adare et al.):
   "Inclusive cross-section and double helicity asymmetry for pi0 production in p + p collisions at s**(1/2) = 200-GeV: Implications for the polarized gluon distribution in the proton"
   Phys.Rev.D76:051106 (2007)
7. A. Bazilevsky et al.:
   "Single Transverse-Spin Asymmetry in Very Forward and Very Backward Neutral Particle Production for Polarized Proton Collisions at s**(1/2) = 200-GeV."
   Phys.Lett.B650:325-330 (2007)
8. 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)
9. PHENIX Collaboration (Stephen Scott Adler et al.):
   "Measurement of density correlations in pseudorapidity via charged particle multiplicity fluctuations in Au+Au collisions at s(NN)**(1/2) = 200-GeV."
   Phys.Rev.C76:034903(2007)
10. KEK-PS-E325 Collaboration (R. Muto et al.):
    "Evidence for in-medium modification of the phi meson at normal nuclear density."
    Phys.Rev.Lett.98:042501 (2007)