HARA Kazuhiko University of Tsukuba, Institute of Physics, Assistant Professor, 物理学系, 講師 (20218613)
KIM Shinhong University of Tsukuba, Institute of Physics, Professor, 物理学系, 教授 (50161609)
TAKIKAWA Koji University of Tsukuba, Institute of Physics, Professor, 物理学系, 教授 (00011635)
SEIYA Yoshihiro University of Tsukuba, Institute of Physics, Assistant Professor, 物理学系, 講師 (80251031)
|Budget Amount *help
¥8,000,000 (Direct Cost: ¥8,000,000)
Fiscal Year 2002: ¥2,600,000 (Direct Cost: ¥2,600,000)
Fiscal Year 2001: ¥5,400,000 (Direct Cost: ¥5,400,000)
The research has been conducted by studying proton-antiproton collisions and B-hadron signals observed and reconstructed with the CDF detector at the Tevatron collider at Fermi National Accelerator Laboratory in USA. The CDF Run-II experiment started in 2001. Since then the accelerator performance has improved steadily, achieving a best instantaneous luminosity of L = 4.7 x 10^<31> cm^<-2> s^<-1>. And CDF has thus far accumulated 170 pb^<-1> of data, surpassing that of Run I (1992 - 1996), 110 pb^<-1>. The CDF detector, after a major upgrade, has been operational smoothly after the initial commissioning and calibration phases.
The B-physics capability of CDF has been enhanced as well. In the studies of B hadron decays, precision track reconstruction using silicon micro-strip detectors, and particle identification, are important. In CDF Run II, a device called Silicon Vertex Trigger (SVT) has been introduced, which uses information of the silicon detectors at the second level of the trig
ger. It has enabled us to collect efficiently the decay products of long-lived particles such as B and charm hadrons. With this, we are now able to trigger on decay modes consisting of only hadrons, such as B^^-^0_s → D^+_sπ^- and B^0/B^^-^0 → π^+π^-. As for particle identification, a time-of-flight (TOF) system has been added. It has achieved a time resolution of 110 ps, close to the design value of 100 ps. It provies a kaon-pion separation at low momentum regions. The main purpose of the TOF system is to use charged kaons for the identification of initial flavor of the B mesons. Also, the TOF system should be useful in achieving a high signal-to-noise ratio in the B^0_s reconstruction, because there is a high probability that a K^+K^- pair is produced in the B^0_s meson decays. At higher momentum regions the dE/dx information from the main tracking chamber provides a 1.2-σ K-π separation.
Analyses of collision data are in progress, and we expect in the near future several results, including the measurements of the B^0_s meson lifetime and the branching fraction of the B^^-^0_s → D^+_sπ^- relative to B^^-^0 → D^+π^-, and the search for the lifetime difference between the two mass eigenstates of the B^0_sB^^-^0_s system. And then we will look for the B^0_sB^^-^0_s oscillations after optimizing flavor tagging algorithms. In a longer term, we will perform measurements of CP-violating asymmetries in the decays B^0_s/B^^-^0_s → J/ψφ and B^0_s/B^^-^0_s → K^+K^-. Less