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The Weak Decay of Helium Hypernuclei
A {Lambda} hyperon replaces a neutron in a nucleus to form a hypernucleus via the {sup A}X(K{sup {minus}}, {pi}{sup {minus}}) {sub {Lambda}}{sup A}X reaction at 750 MeV/c (Brookhaven Experiment 788). The free {Lambda} decay rates {Gamma}({Lambda} {yields} p{pi}{sup {minus}}) and {Gamma}({Lambda} {yields} n{pi}{sup 0}) are diminished due to Pauli blocking; but a non-mesonic decay mode, nucleon stimulated decay N{Lambda} {yields} Nn, is present and is detected via the energetic decay nucleon(s) ({approx} 400MeV/c). Measurements of the various hypernuclear decay rates {Gamma}({Lambda} {yields} p{pi}{sup {minus}}), {Gamma}({Lambda} {yields} n{pi}{sup 0}) and {Gamma}({Lambda}n {yields} nn) provides insight into the strong modification of the weak interaction such as the baryon-baryon {Delta}I ={1/2} rule. The hypernuclear state is isolated by momentum analysis of (K{sup {minus}}, {pi}{sup {minus}}) target reaction. Out-of-beam large volume scintillation detectors and tracking chambers axe used to make particle identification of the hypernuclear decay products by time-of-flight, dE/dx, and range. The kinetic energy of the decay neutrons are measured by time of flight using the large volume 100 element neutron detector system. The hypernuclear lifetime is directly measured using precision scintillator counters and tracking chambers. Measurements of the various decay rates as well as the total lifetime are discussed for {sub {Lambda}}{sup 4}He
Weak decays of 4He-Lambda
We measured the lifetime and the mesonic and non-mesonic decay rates of the
4He-Lambda hypernucleus. The hypernuclei were created using a 750 MeV/c
momentum K- beam on a liquid 4He target by the reaction 4He(K-,pi-)4He-Lambda.
The 4He-Lambda lifetime was directly measured using protons from Lambda p -> n
p non-mesonic decay (also referred to as proton-stimulated decay) and was found
to have a value of tau = 245 +/- 24 ps. The mesonic decay rates were determined
from the observed numbers of pi-'s and pi0's as Gamma_pi-/Gamma_tot = 0.270 +/-
0.024 and Gamma_pi0/Gamma_tot = 0.564 +/- 0.036, respectively, and the values
of the proton- and neutron-stimulated decay rates were extracted as
Gamma_p/Gamma_tot = 0.169 +/- 0.019 and Gamma_n/Gamma_tot <= 0.032 (95% CL),
respectively. The effects of final-state interactions and possible 3-body
Lambda N N decay contributions were studied in the context of a simple model of
nucleon-stimulated decay. Nucleon-nucleon coincidence events were observed and
were used in the determination of the non-mesonic branching fractions. The
implications of the results of this analysis were considered for the empirical
Delta I = 1/2 rule and the decay rates of the 4H-Lambda hypernucleus.Comment: 15 pages, 11 figures, published in PRC, revised content to match
published versio
Impact of D0-D0bar mixing on the experimental determination of gamma
Several methods have been devised to measure the weak phase gamma using
decays of the type B+- --> D K+-, where it is assumed that there is no mixing
in the D0-D0bar system. However, when using these methods to uncover new
physics, one must entertain the real possibility that the measurements are
affected by new physics effects in the D0-D0bar system. We show that even
values of x_D and/or y_D around 10^{-2} can have a significant impact in the
measurement of sin^2{gamma}. We discuss the errors incurred in neglecting this
effect, how the effect can be checked, and how to include it in the analysis.Comment: 18 pages, Latex with epsfig, 8 figure
Cabibbo-suppressed non-leptonic B- and D-decays involving tensor mesons
The Cabibbo-suppressed non-leptonic decays of B (and D) mesons to final
states involving tensor mesons are computed using the non-relativistic quark
model of Isgur-Scora-Grinstein-Wise with the factorization hypothesis. We find
that some of these B decay modes, as B --> (K^*, D^*)D^*_2, can have branching
ratios as large as 6 x 10^{-5} which seems to be at the reach of future B
factories.Comment: Latex, 11 pages, to appear in Phys. Rev.
Decay constants, semi-leptonic and non-leptonic decays in a Bethe-Salpeter Model
We evaluate the decay constants for the B and mesons and the form factors
for the semileptonic decays of the B meson to and mesons in a
Bethe-Salpeter model. From data we extract from and from decays. The form factors are then used to obtain non-leptonic
decay partial widths for and in the
factorization approximation.Comment: 15 Pages, 3 Postscript figures (available also from [email protected]
Resummation of Running Coupling Effects in Semileptonic B Meson Decays and Extraction of
We present a determination of from semileptonic B decays that
includes resummation of supposedly large perturbative corrections, originating
from the running of the strong coupling. We argue that the low value of the BLM
scale found previously for inclusive decays is a manifestation of the
renormalon divergence of the perturbative series starting already in third
order. A reliable determination of from inclusive decays is possible
if one either uses a short-distance b quark mass or eliminates all unphysical
mass parameters in terms of measured observables, such that all infra-red
contributions of order cancel explicitly. We find that using the
running mass significantly reduces the perturbative
coefficients already in low orders. For a semileptonic branching ratio of
we obtain from
inclusive decays, in good agreement with the value extracted from exclusive
decays.Comment: 37 pages + 4 figures, final version accepted for publication in Phys.
Rev.
A new method for extracting the weak phase gamma from B ---> D K(*) decays
A new method to extract the weak phase is suggested by exploiting B
---> D K^{(*)} decay modes that are not Cabibbo suppressed, using the isospin
relations, and ignoring the annihilation diagram as usual. Assuming pair at factories, one can determine with
accuracy for 80^o D K modes and for
50^o D K^* modes.Comment: 10 pages with 2 figure
Lattice QCD calculation of decay form factors at zero recoil
A lattice QCD calculation of the decay form factors
is presented. We obtain the value of the form factor at the
zero-recoil limit with high precision by considering a ratio of
correlation functions in which the bulk of the uncertainties cancels. The other
form factor is calculated, for small recoil momenta, from a similar
ratio. In both cases, the heavy quark mass dependence is observed through
direct calculations with several combinations of initial and final heavy quark
masses. Our results are and
. For both the first error is statistical,
the second stems from the uncertainty in adjusting the heavy quark masses, and
the last from omitted radiative corrections. Combining these results, we obtain
a precise determination of the physical combination , where the mentioned systematic errors are added in
quadrature. The dependence on lattice spacing and the effect of quenching are
not yet included, but with our method they should be a fraction of .Comment: 32 pp, 10 figs; final, published versio
Study of the B^0 Semileptonic Decay Spectrum at the Upsilon(4S) Resonance
We have made a first measurement of the lepton momentum spectrum in a sample
of events enriched in neutral B's through a partial reconstruction of B0 -->
D*- l+ nu. This spectrum, measured with 2.38 fb**-1 of data collected at the
Upsilon(4S) resonance by the CLEO II detector, is compared directly to the
inclusive lepton spectrum from all Upsilon(4S) events in the same data set.
These two spectra are consistent with having the same shape above 1.5 GeV/c.
From the two spectra and two other CLEO measurements, we obtain the B0 and B+
semileptonic branching fractions, b0 and b+, their ratio, and the production
ratio f+-/f00 of B+ and B0 pairs at the Upsilon(4S). We report b+/b0=0.950
(+0.117-0.080) +- 0.091, b0 = (10.78 +- 0.60 +- 0.69)%, and b+ = (10.25 +- 0.57
+- 0.65)%. b+/b0 is equivalent to the ratio of charged to neutral B lifetimes,
tau+/tau0.Comment: 14 page, postscript file also available at
http://w4.lns.cornell.edu/public/CLN
Further Search for the Two-Photon Production of the Glueball Candidate
The CLEOII detector at the Cornell e+ e- storage ring CESR has been used to
search for the two-photon production of the decaying into pi+ pi-.
No evidence for a signal is found in data corresponding to an integrated
luminosity of 4.77/fb and a 95% CL upper limit on of 2.5 eV is set. If this result is combined with the BES Collaboration's
measurement of in radiative decay, a 95% CL
lower limit on the stickiness of the of 73 is obtained. If the
recent CLEO result for \Gamma_{two-photon} * BR{\K_S K_S} is combined with
the present result, the stickiness of the is found to be larger
than 102 at the 95% CL. These results for the stickiness (the ratio of the
probabilities for two-gluon coupling and two-photon coupling) provide further
support for a substantial neutral parton content in the .Comment: 8 pages, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
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