5,783 research outputs found
On The Expected Photon Spectrum in B -> X_s + gamma and Its Uses
Measuring the photon energy spectrum in radiative B decays provides essential
help for gaining theoretical control over semileptonic B transitions. The
hadronic recoil mass distribution in B -> X_u \ell\nu promises the best
environment for determining |V_ub|. The theoretical uncertainties are largest
in the domain of low values of the lepton pair mass q^2. Universality relations
allow to describe this domain reliably in terms of the photon spectrum in B ->
X_s + \gamma. A method is proposed to incorporate 1/m_b corrections into this
relation. The low-E_\gamma tail in radiative decays is important in the context
of extracting |V_ub|. We argue that CLEO's recent fit to the spectrum
underestimates the fraction of the photon spectrum below 2 GeV. Potentially
significant uncertainties enter in the theoretical evaluation of the integrated
end-point lepton spectrum or the B -> X_u \ell\nu width with a too high value
of the lower cut on q^2 in alternative approaches to |V_ub|.Comment: 24 pages, 6 figures, LaTeX. Revised: Complete version. Numerical
predictions are improved and the estimate for the decay fraction revised. The
theoretical expectations for the decay fraction and the spectrum itself are
given on the plot
The Presampler for the Forward and Rear Calorimeter in the ZEUS Detector
The ZEUS detector at HERA has been supplemented with a presampler detector in
front of the forward and rear calorimeters. It consists of a segmented
scintillator array read out with wavelength-shifting fibers. We discuss its
desi gn, construction and performance. Test beam data obtained with a prototype
presampler and the ZEUS prototype calorimeter demonstrate the main function of
this detector, i.e. the correction for the energy lost by an electron
interacting in inactive material in front of the calorimeter.Comment: 20 pages including 16 figure
Reducing theoretical uncertainties in mb and lambda1
We calculate general moments of the lepton energy spectrum in inclusive
semileptonic B -> X_c l \nu decay. Moments which allow the determination of
mb^{1S} and lambda1 with theoretical uncertainties Delta(mb^{1S}) ~ 0.04 GeV
and Delta(lambda1) ~ 0.05 GeV^2 are presented. The short distance 1S mass is
used to extract a mass parameter free of renormalon ambiguities. Moments which
are insensitive to mb and lambda1 and therefore test the size of the 1/mb^3
matrix elements and the validity of the OPE are also presented. Finally, we
give an expression for the total branching ratio with a lower cut on the lepton
energy, which allows one to eliminate a source of model dependence in current
determinations of |Vcb| from B -> X_c l \nu decay.Comment: 8 pages, one figur
Subleading shape functions in B -> X_u l \nu and the determination of |Vub|
We calculate the subleading twist contributions to the endpoint of the
inclusive lepton energy spectrum in B -> X_u l \nu. We show that the same two
subleading twist functions that appear in the decay B -> X_s \gamma govern the
subleading effects in this decay. Using these results we find large
O(Lambda/mB) corrections to the determination of |Vub| from the endpoint of the
charged lepton spectrum. Using a simple model for the relevant subleading shape
functions, we estimate the uncertainty in |Vub| from Lambda/mb corrections to
be at the ~ 15% level for a lower lepton energy cut of 2.2 GeV.Comment: 6 pages, 2 figure
Direct CP Violation, Branching Ratios and Form Factors , in Decays
The and transitions involved in hadronic B decays are
investigated in a phenomenological way through the framework of QCD
factorization. By comparing our results with experimental branching ratios from
the BELLE, BABAR and CLEO Collaborations for all the B decays including either
a pion or a kaon, we propose boundaries for the transition form factors and depending on the CKM matrix element parameters and
. From this analysis, the form factors required to reproduce the
experimental data for branching ratios are and
. We calculate the direct CP violating asymmetry
parameter, , for and decays, in the case where mixing effects are taken into
account. Based on these results, we find that the direct CP asymmetry for
, ,
, and , reaches its maximum when the invariant mass is
in the vicinity of the meson mass. The inclusion of
mixing provides an opportunity to erase, without ambiguity, the phase
uncertainty mod in the determination of the CKM angles in case
of and in case of .Comment: 74 pages, 15 figures, 8 tables. A few misprints corrected, two
references adde
in the Standard Model with Flavor Symmetry
The observed branching ratios for decays are much larger than
factorization predictions in the Standard Model (SM). Many proposals have been
made to reconcile the data and theoretical predictions. In this paper we study
these decays within the SM using flavor U(3) symmetry. If small annihilation
amplitudes are neglected, one needs 11 hadronic parameters to describe decays where can be one of the , , and nonet
mesons. We find that existing data are consistent with SM with flavor U(3)
symmetry. We also predict several measurable branching ratios and CP
asymmetries for , decays.
Near future experiments can provide important tests for the Standard Model with
flavor U(3) symmetry.Comment: 13 pages, 4 table
Measurement of the B-Meson Inclusive Semileptonic Branching Fraction and Electron-Energy Moments
We report a new measurement of the B-meson semileptonic decay momentum
spectrum that has been made with a sample of 9.4/fb of electron-positron
annihilation data collected with the CLEO II detector at the Y(4S) resonance.
Electrons from primary semileptonic decays and secondary charm decays were
separated by using charge and angular correlations in Y(4S) events with a
high-momentum lepton and an additional electron. We determined the semileptonic
branching fraction to be (10.91 +- 0.09 +- 0.24)% from the normalization of the
electron-energy spectrum. We also measured the moments of the electron energy
spectrum with minimum energies from 0.6 GeV to 1.5 GeV.Comment: 36 pages postscript, als available through
http://w4.lns.cornell.edu/public/CLNS/, Submitted to PRD (back-to-back with
preceding preprint hep-ex/0403052
Study of tau Decays to Four-Hadron Final States with Kaons
The tau decays to four hadrons have been studied with the CLEO III detector
at the Cornell Electron Storage Ring (CESR) using (7.56 +- 0.15) fb^{-1} of
data collected near the Y(4S) resonance. We present the first statistically
significant measurements of B(tau- -> K- pi+pi- pi0 nu, excluding K^0) = (7.4
+- 0.8 +- 1.1) x 10^{-4} and B(tau--> K- K+ pi- pi0 nu) = (5.5 +- 1.4 +- 1.2) x
10^{-5}, including the first observation of the decay, tau- -> K- omega nu,
with branching fraction (4.1 +- 0.6 +- 0.7) x 10^{-4}. We also publish the
first upper limit for B(tau- -> K- K+ K- pi0 nu) < 4.8 (6.1) x 10^{-6} at 90%
(95%) confidence level (C.L.).Comment: 9 pages postscript, also available from
http://www.lns.cornell.edu/public/CLNS/2004/, submitted to PR
The Search for eta(1440) --> K^0_S K^pm \pi^mp in Two-Photon Fusion at CLEO
We analyze 13.8 \rm fb^{-1} of the integrated e^+e^- luminosity collected at
10.6 GeV center-of-mass energy with the CLEO II and CLEO II.V detectors to
study exclusive two-photon production of hadrons with masses below 1.7{\rm \
GeV/c^2} decaying into the K^0_S K^\pm \pi^\mp final state. We observe two
statistically significant enhancements in the \eta(1440) mass region. These
enhancements have large transverse momentum which rules them out as being due
to pseudoscalar resonances but is consistent with the production of
axial-vector mesons. We use tagged two-photon events to study the properties of
the observed enhancements and associate them with the production of f_1(1285)
and f_1(1420). Our non-observation of \eta(1440) is inconsistent by more than
two standard deviations with the first observation of this resonance in
two-photon collisions by the L3 experiment. We present our estimates for 90%
confidence level upper limits on the products of two-photon partial widths of
pseudoscalar hadrons and their branching fractions into
K^0_S(\pi^+\pi^-)K^\pm\pi^\mp.Comment: 24 pages postscript,also available through
http://www.lns.cornell.edu/public/CLNS/2004/, submitted to PR
Photon transitions in Upsilon(2S) and Upsilon(3S)
We have studied the inclusive photon spectra in Upsilon(2S) and \Upsilon(3S)
decays using a large statistics data sample obtained with the CLEO III
detector. We present the most precise measurements of electric dipole (E1)
photon transition rates and photon energies for Upsilon(2S)->gamma chi_bJ(1P)
and Upsilon(3S)->gamma chi_bJ(2P) J=0,1,2. We measure the rate for a rare E1
transition Upsilon(3S)->gamma chi_b0(1P) for the first time. We also set upper
limits on the rates for the hindered magnetic dipole (M1) transitions to the
eta_b(1S) and eta_b(2S) states.Comment: 10 pages postscript,also available through
http://www.lns.cornell.edu/public/CLNS/2004/, submitted to PR
- …