3,779 research outputs found
An imaging time-of-propagation system for charged particle identification at a super B factory
Super B factories that will further probe the flavor sector of the Standard
Model and physics beyond will demand excellent charged particle identification
(PID), particularly K/pi separation, for momenta up to 4 GeV/c, as well as the
ability to operate under beam backgrounds significantly higher than current B
factory experiments. We describe an Imaging Time-of-Propagation (iTOP) detector
which shows significant potential to meet these requirements. Photons emitted
from charged particle interactions in a Cerenkov radiator bar are internally
reflected to the end of the bar, where they are collected on a compact image
plane using photodetectors with fine spatial segmentation in two dimensions.
Precision measurements of photon arrival time are used to enhance the two
dimensional imaging, allowing the system to provide excellent PID capabilities
within a reduced detector envelope. Results of the ongoing optimization of the
geometric and physical properties of such a detector are presented, as well as
simulated PID performance. Validation of simulations is being performed using a
prototype in a cosmic ray test stand at the University of Hawaii.Comment: 3 pages, 5 figures, submitted to TIPP09 proceeding
The D0 Run IIb Luminosity Measurement
An assessment of the recorded integrated luminosity is presented for data
collected with the D0 detector at the Fermilab Tevatron Collider from June 2006
to September 2011 (Run IIb). In addition, a measurement of the effective cross
section for inelastic interactions, also referred to as the luminosity
constant, is reported. This measurement incorporates new features that lead to
a substantial improvement in the precision of the result. A luminosity constant
of \sigma_{LM} = 48.3\pm1.9\pm0.6 mb is obtained, where the first uncertainty
is due to the accuracy of the inelastic cross section used by both CDF and D0,
and the second uncertainty is due to D0 sources. The recorded luminosity for
the highest E_T jet trigger is L_rec = 9.2 \pm 0.4 fb^{-1}, with a relative
uncertainty of 4.3%.Comment: 20 pages, 23 figure
Cross-talk suppressed multi-anode MCP-PMT
We have developed a 4-channel multi-anode MCP-PMT, SL10, which exhibits a
performance of sigma_TTS ~ 30 ps for single photons with G ~ 10^6 and QE=20%
under a magnetic field of B <= 1.5 T. The cross-talk among anodes has been
extensively studied. We have taken two measures to suppress it: one is to
configure the SL10 to an effectively independent 4 small pieces of MCP-PMT's by
segmenting an electrode of the second MCP-layer; the other is to use a constant
fractional discriminator. Remarkable improvement has been achieved.Comment: 14 pages, 14 figure
Structural comparison of the free and DNA-bound forms of the purine repressor DNA-binding domain
AbstractBackground: The purine repressor (PurR) regulates genes that encode enzymes for purine biosynthesis. PurR has a two domain structure with an N-terminal DNA-binding domain (DBD) and a C-terminal corepressor-binding domain (CBD). The three-dimensional structure of a ternary complex of PurR bound to both corepressor and a specific DNA sequence has recently been determined by X-ray crystallography.Results We have determined the solution structure of the PurR DBD by NMR. It contains three helices, with the first and second helices forming a helix-turn-helix motif. The tertiary structure of the three helices is very similar to that of the corresponding region in the ternary complex. The structure of the hinge helical region, however, which makes specific base contacts in the minor groove of DNA, is disordered in the DNA-free form.Conclusion The stable formation of PurR hinge helices requires PurR dimerization, which brings the hinge regions proximal to each other. The dimerization of the hinge helices is likely to be controled by the CBD dimerization interface, but is induced by specific-DNA binding
\tau^- \to \mu^- \pi^0(\eta,\eta') Decays in New Physics Scenarios beyond the Standard Model
The semileptonic decays could be
sensitive probe for new physics scenarios with lepton flavor violation(LFV).
Motivated by the recent Belle measurement, we investigate these decays in type
III two-Higgs-doublet model (2HDM III), R-parity violating supersymmetric
models(RPV SUSY) and flavor changing models with family non-universal
couplings, respectively. In these new physics scenarios, there are LFV
couplings at tree level. Our results have shown that the decays are very
sensitive to the LFV couplings and could be enhanced to the present
experimental sensitivities. We have derived strong bounds on relevant couplings
of these models, which may be useful for further relevant studies.Comment: 18 pages, 7 eps figures. Hadronic uncertainties considered and
references adde
Spectral Correlation in Incommensurate Multi-Walled Carbon Nanotubes
We investigate the energy spectra of clean incommensurate double-walled
carbon nanotubes, and find that the overall spectral properties are described
by the so-called critical statistics of Anderson metal-insulator transition. In
the energy spectra, there exist three different regimes characterized by
Wigner-Dyson, Poisson, and semi-Poisson distributions. This feature implies
that the electron transport in incommensurate multi-walled nanotubes can be
either diffusive, ballistic, or intermediate between them, depending on the
position of the Fermi energy.Comment: final version to appear in Phys. Rev. Let
Study of B -> \rho \pi decays at Belle
This paper describes a study of B meson decays to the pseudoscalar-vector
final state \rho\pi using 31.9\times 10^6 B\bar{B} events collected with the
Belle detector at KEKB. The branching fractions B(B^+ \to \rho^0\pi^+) =
(8.0^{+2.3+0.7}_{-2.0-0.7}) \times 10^{-6} and B(B^0 -> \rho^{+-} \pi^{-+}) =
(20.8^{+6.0+2.8}_{-6.3-3.1}) \times 10^{-6} are obtained. In addition, a 90%
confidence level upper limit of B(B^0 \to \rho^0\pi^0) < 5.3 \times 10^{-6}is
reported.Comment: 14 pages, 3 figures, to be submitted to Phys. Lett.
Search for the Lepton-Flavor-Violating Decay at Belle
We have searched for the Lepton Flavor Violating decay using a data sample of 84.3 fb accumulated with the Belle detector
at KEK. The -meson was detected through the decay modes: and . No signal candidates are found, and we
obtain an upper limit for the branching fraction at the 90% confidence level.Comment: Submitted to Phys.Rev.Let
Observation of the DsJ(2317) and DsJ(2457) in B decays
We report the first observation of the B --> Dbar DsJ(2317) and B --> Dbar
DsJ(2457) decays based on 123.8 10^6 BBar events collected with the Belle
detector at KEKB. We observe the DsJ(2317) decay to Ds pi0 and DsJ(2457) decay
to the Ds* pi0 and Ds gamma final states. We also set 90% CL upper limits for
the decays DsJ(2317) --> Ds* gamma, DsJ(2457) --> Ds* gamma, DsJ(2457) --> Ds
pi0 and DsJ(2457) --> Ds pi+ pi-.Comment: 6 pages, 3 figures. A few minor corrections. Replaced by version
accepted to publication in Phys. Rev. Let
Observation of Large CP Violation in the Neutral B Meson System
We present a measurement of the Standard Model CP violation parameter sin
2phi_1 based on a 29.1 fb^{-1} data sample collected at the Upsilon(4S)
resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider.
One neutral B meson is fully reconstructed as a J/psi Ks, psi(2S) Ks, chi_c1
Ks, eta_c Ks, J/psi K_L or J/psi K^{*0} decay and the flavor of the
accompanying B meson is identified from its decay products. From the asymmetry
in the distribution of the time intervals between the two B meson decay points,
we determine sin 2phi_1 = 0.99 +- 0.14(stat) +- 0.06(syst). We conclude that we
have observed CP violation in the neutral B meson system.Comment: 4 figures, to appear in Phys. Rev. Letter
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