arXiv subjects

M. Nakao

Publications and source records attributed to M. Nakao.

139 records · Page 8Linked to original sources

arXiv2010

First Measurement of Inclusive B -> X_s eta Decays

We report a first measurement of inclusive B -> X_s eta decays, where X_s is a charmless state with unit strangeness. The measurement is based on a pseudo-inclusive reconstruction technique and uses a sample of 657 x 10^6 BB-bar pairs accumulated with the Belle detector at the KEKB e^+e^- collider. For M_{X_s} < 2.6 GeV/c^2, we measure a branching fraction of (26.1 +/- 3.0 (stat) +1.9 -2.1 (syst) +4.0 -7.1 (model)) x 10^-5 and a direct CP asymmetry of A_{CP} = -0.13 +/- 0.04 +0.02 -0.03. Over half of the signal occurs in the range M_{X_s} > 1.8 GeV/c^2.

hep-ex↗

arXiv2010

Measurement of branching fractions, isospin and CP-violating asymmetries for exclusive \boldmath$b \to dγ$ modes

We report new measurements of the decays $B\toρ^+ γ$, $B \to ρ^0 γ$ and $B \to ωγ$ using a data sample of $657 \times 10^6$ $B$ meson pairs accumulated with the Belle detector at the KEKB $e^+ e^-$ collider. We measure branching fractions ${\cal B}(B^+ \to ρ^+ γ) = (8.7^{+2.9}_{-2.7}{}^{+0.9}_{-1.1})\times 10^{-7}$, ${\cal B}(B^0 \to ρ^0 γ) = (7.8^{+1.7}_{-1.6}{}^{+0.9}_{-1.0}) \times 10^{-7}$ and ${\cal B}(B^0 \to ωγ) = (4.0^{+1.9}_{-1.7} \pm 1.3) \times 10^{-7}$. We also report the isospin asymmetry $Δ(ργ) = -0.48^{+0.21}_{-0.19}{}^{+0.08}_{-0.09}$; and the first measurement of the direct CP-violating asymmetry $A_{CP}(B^+ \to ρ^+ γ) = -0.11\pm{0.32}\pm{0.09}$, where the first and second errors are statistical and systematic, respectively.

hep-ex↗

arXiv2010

KEKB Beam Collision Stability at the Picosecond Timing and Micron Position Resolution as observed with the Belle Detector

Using the Belle detector we study the characteristics of beam collisions at the KEKB 3.5 GeV $e^+$ on 8 GeV $e^-$ asymmetric energy collider. We investigate the collision timing {\tip} and its $z$-coordinate along the beam axis {\zip} as a function of the position of the colliding bunch in a beam train. The various {\tip} and {\zip} behaviors observed by Belle are attributed to beam loading effects in the radio frequency cavities that accelerate the beams with a beam abort gap. We report these results in detail and discuss the prospects for the SuperKEKB collider.

physics.ins-det↗

arXiv2010

Physics at Super B Factory

This report presents the results of studies that investigate the physics reach at a Super $B$ factory, an asymmetric-energy $e^+e^-$ collider with a design luminosity of $8 \times 10^{35}$ cm$^{-2}$s$^{-1}$, which is around 50 times as large as the peak luminosity achieved by the KEKB collider. The studies focus on flavor physics and CP violation measurements that could be carried out in the LHC era. The physics motivation, key observables, measurement methods and expected precisions are presented.

hep-ex↗

arXiv2008

sBelle Design Study Report

In this note, we compile results of various simulation studies for the upgrade of the Belle detector. Based on these studies, we propose a set of optimum or appropriate parameters of the detector.

hep-ex↗

arXiv2008

Search for B+ -> D*+ pi0 decay

We report on a search for the doubly Cabibbo suppressed decay B+ -> D*+ pi0, based on a data sample of 657 million BBbar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric energy e+ e- collider. We find no significant signal and set an upper limit of Br(B+ -> D*+ pi0) < 3.6 x 10^-6 at the 90% confidence level. This limit can be used to constrain the ratio between suppressed and favored B -> D* pi decay amplitudes, r < 0.051, at the 90% confidence level.

hep-ex↗

arXiv2008

B, D and K decays

With the advent of the LHC, we will be able to probe New Physics (NP) up to energy scales almost one order of magnitude larger than it has been possible with present accelerator facilities. While direct detection of new particles will be the main avenue to establish the presence of NP at the LHC, indirect searches will provide precious complementary information, since most probably it will not be possible to measure the full spectrum of new particles and their couplings through direct production. In particular, precision measurements and computations in the realm of flavour physics are expected to play a key role in constraining the unknown parameters of the Lagrangian of any NP model emerging from direct searches at the LHC. The aim of Working Group 2 was twofold: on one hand, to provide a coherent, up-to-date picture of the status of flavour physics before the start of the LHC; on the other hand, to initiate activities on the path towards integrating information on NP from high-pT and flavour data.

hep-ph↗

arXiv2007

New Measurements Using External Photon Conversion at a High Luminosity B Factory

We propose two novel methods for testing the standard model using external photon conversion at a high-luminosity e^+e^- B factory proposed recently. The first method is to measure the mixing-induced CP-violation parameter S_{pi^0pi^0} in B^0 --> pi^0 pi^0 decays. The precision of S_{pi^0pi^0} is estimated to be 0.23 from a Monte Carlo study for a data sample containing 50 x 10^9 BBbar pairs. We demonstrate that this measurement is crucial for reducing the discrete ambiguity of the Cabibbo-Kobayashi-Maskawa angle phi_2 determined from the isospin analysis with B --> pi pi decays. The second method is to measure photon polarization in B^0 --> K^{*0}(--> K^+ pi^-) gamma decays using the external photon conversion, and combine it with S_{K^{*}gamma} from B^0 --> K^{*0}(--> K^0_S pi^0) gamma decays. This offers a promising way of determining the hypothetical right-handed current amplitude and phase beyond the standard model.

hep-ex↗

arXiv2004

Physics at Super B Factory

This report presents the results of studies that investigate the physics reach at a Super B factory, an asymmetric-energy e^+e^- collider with a design luminosity of 5 x 10^35 cm^-2s^-1, which is around 40 times as large as the peak luminosity achieved by the KEKB collider. The studies focus on flavor physics and CP violation measurements that could be carried out in the LHC era. The physics motivation, key observables, measurement methods and expected precisions are presented. The sensitivity studies are a part of the activities associated with the preparation of a Letter of Intent for SuperKEKB, which has been submitted recently.

hep-ex↗

arXiv2003

Belle Results on b --> s ell+ ell- and b --> gamma

We discuss the latest results and future prospects of the Belle experiment on the electroweak and radiative processes b --> s ell+ ell-, b --> s gamma and b --> d gamma. In particular, the first measurement of the inclusive rate for B --> X(s) ell+ ell- provides a new constraint on the physics beyond the Standard Model. The yet to be measured decay B --> rho gamma is expected to provide a new constraint on the CKM matrix element |V(td)| in the near future.

hep-ex↗

arXiv2003

Observation of B+ -> rho+ rho0

We report the first observation of the charmless vector-vector decay process B+ ->rho+ rho0. The measurement uses a 78 fb^{-1} data sample collected with the Belle detector at the KEKB asymmetric e+e- collider operating at the Upsilon(4S) resonance. We obtain a branching fraction of Br(B+ ->rho+ rho0)=(31.7+-7.1(stat.)+3.8-6.7(sys.))*10^{-6}. An analysis of the rho helicity-angle distributions gives a longitudinal polarization of Gamma_{L}/Gamma=(94.8+-10.6(stat.)+-2.1(sys.))%.

hep-ex↗

arXiv2003

The Data Acquisition System Based on PMC Bus

High energy physics experiments in KEK/Japan rush into over KHz trigger stage. Thus, we need a successor of the data acquisition(DAQ) system that replaces the CAMAC or FASTBUS systems. To meet these needs, we have developed a DAQ system which includes a crate, base-board modules, daughter cards for front-end A/D or T/D conversion, and back-end communication cards for data transfer and timing control. The size of the crate is for the 9U Euro-cards with the standard VME32 bus and extension connectors for power supply. The base-board comprises of a local bus with the sequencer connected to the front-end daughter cards via event buffering FIFOs, and the standard PMC (PCI mezzanine card) bus to be set a PMC processor unit to reduce data size from the front-end daughter cards. A data transfer module, which is connected to the event building system, and a trigger control unit, which communicates with the central timing controller are installed on the back-end communication card connected to the rear end of the base-board. We describe the design of this DAQ system and evaluate the performance of it.

physics.ins-det↗

arXiv2003

Development of a PCI Based Data Acquisition Platform for High Intensity Accelerator Experiments

Data logging at an upgraded KEKB accelerator or the J-PARC facility, currently under commission, requires a high density data acquisition platform with integrated data reduction CPUs. To follow market trends, we have developed a DAQ platform based on the PCI bus, a choice which permits a fast DAQ and a long expected lifetime of the system. The platform is a 9U-VME motherboard consisting of four slots for signal digitization modules, readout FIFOs for data buffering, and three PMC slots, on one of which resides a data reduction CPU. We have performed long term and thermal stability tests. The readout speed on the platform has been measured up to 125 MB/s in DMA mode.

hep-ex↗