524 research outputs found
Search for Lepton Flavor-Violating "tau -> mu gamma" decay
We search for the lepton flavor-violating "tau -> mu gamma" decay using 29.7
million tau pairs accumulated by the Belle experiment. The main background
sources are found to be tau pairs with "tau -> mu nu nu" decay and radiative
dimuon events. One event is observed in the signal region, while 2.5 +- 0.6
background events are expected. A preliminary upper limit Br(tau -> mu gamma) <
6 x 10^{-7} at the 90% confidence limit is obtained.Comment: Invited talk at the Seventh International Workshop on Tau Lepton
Physics (TAU02), Santa Cruz, Ca, USA, Sept 2002, 6 pages, LaTeX, 13 eps
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
Seesaw and Lepton Flavour Violation in SUSY SO(10)
That and are sensitive probes of
SUSY models with a see-saw mechanism is a well accepted fact. Here we propose a
`top-down' approach in a general SUSY SO(10) scheme. In this framework, we show
that at least one of the neutrino Yukawa couplings is as large as the top
Yukawa coupling. This leads to a strong enhancement of these leptonic flavour
changing decay rates. We examine two `extreme' cases, where the lepton mixing
angles in the neutrino Yukawa couplings are either small (CKM-like) or large
(PMNS-like). In these two cases, we quantify the sensitivity of leptonic
radiative decays to the SUSY mass spectrum. In the PMNS case, we find that the
ongoing experiments at the B-factories can completely probe the spectrum up to
gaugino masses of 500 GeV (any tan ). Even in the case of CKM-like
mixings, large regions of the parameter space will be probed in the near
future, making these two processes leading candidates for indirect SUSY
searches.Comment: 22 pages with 2 figures. Figures for \tau -> \mu \gamma decay
corrected after typo found in the program. Decay \mu -> e gamma completely
unchanged and conclusions basicaly unchange
An Improved Standard Model Prediction Of BR(B -> tau nu) And Its Implications For New Physics
The recently measured B -> tau nu branching ratio allows to test the Standard
Model by probing virtual effects of new heavy particles, such as a charged
Higgs boson. The accuracy of the test is currently limited by the experimental
error on BR(B -> tau nu) and by the uncertainty on the parameters fB and |Vub|.
The redundancy of the Unitarity Triangle fit allows to reduce the error on
these parameters and thus to perform a more precise test of the Standard Model.
Using the current experimental inputs, we obtain BR(B -> tau nu)_SM = (0.84 +-
0.11)x10^{-4}, to be compared with BR(B -> tau nu)_exp = (1.73 +-
0.34)x10^{-4}. The Standard Model prediction can be modified by New Physics
effects in the decay amplitude as well as in the Unitarity Triangle fit. We
discuss how to disentangle the two possible contributions in the case of
minimal flavour violation at large tan beta and generic loop-mediated New
Physics. We also consider two specific models with minimal flavour violation:
the Type-II Two Higgs Doublet Model and the Minimal Supersymmetric Standard
Model.Comment: 7 pages, 13 figures, 1 table. v2: added references and discussion of
B -> D tau nu in the 2HDM. v3: added Bs->mumu in the 2HDM. Final version to
appear in PL
Evidence for CP Violation in B0 -> D+D- Decays
We report measurements of the branching fraction and CP violation parameters
in B0 -> D+D- decays. The results are based on a data sample that contains 535
x 10^6 BBbar pairs collected at the Upsilon(4S) resonance, with the Belle
detector at the KEKB asymmetric-energy e+e- collider. We obtain [1.97 +- 0.20
(stat) +- 0.20 (syst)] x 10^(-4) for the branching fraction of B0 -> D+D-. The
measured values of the CP violation parameters are: S = -1.13 +- 0.37 +- 0.09,
A = 0.91 +- 0.23 +- 0.06, where the first error is statistical and the second
is systematic. We find evidence of CP violation in B0 -> D+D- at the 4.1 sigma
confidence level. While the value of S is consistent with expectations from
other measurements, the value of the parameter A favors large direct CP
violation at the 3.2 sigma confidence level, in contradiction to Standard Model
expectations.Comment: 12 pages, 3 figures, submitted to PR
Search for the h_c meson in B^+- ->h_c K^+-
We report a search for the meson via the decay chain , \etac \gamma with and
. No significant signals are observed. We obtain upper limits on the
branching fractions for in bins of the
invariant mass. The results are based on an analysis of 253
fb of data collected by the Belle detector at the KEKB
collider.Comment: 12 pages, 6 figures, submitted to Phys. Rev.
Study of the Baryon-Antibaryon Low-Mass Enhancements in Charmless Three-body Baryonic B Decays
The angular distributions of the baryon-antibaryon low-mass enhancements seen
in the charmless three-body baryonic B decays B+ -> p pbar K+, B0 -> p pbar Ks,
and B0 -> p Lambdabar pi- are reported. A quark fragmentation interpretation is
supported, while the gluonic resonance picture is disfavored. Searches for the
Theta+ and Theta++ pentaquarks in the relevant decay modes and possible
glueball states G with 2.2 GeV/c2 < M-ppbar < 2.4 GeV/c2 in the ppbar systems
give null results. We set upper limits on the products of branching fractions,
B(B0 -> Theta+ p)\times B(Theta+ -> p Ks) Theta++
pbar) \times B(Theta++ -> p K+) G K+) \times
B(G -> p pbar) < 4.1 \times 10^{-7} at the 90% confidence level. The analysis
is based on a 140 fb^{-1} data sample recorded on the Upsilon(4S) resonance
with the Belle detector at the KEKB asymmetric-energy e+e- collider.Comment: 14 pages, 13 figure files, update of hep-ex/0409010 for journal
submisssio
Measuring V_ub and probing SUSY with double ratios of purely leptonic decays of B and D mesons
The experimental prospects for precise measurements of the leptonic decays
B_u -> tau nu / mu nu, B_s -> mu+ mu-, D -> mu nu and D_s -> mu nu / tau nu are
very promising. Double ratios involving four of these decays can be defined in
which the dependence on the values of the decay constants is essentially
eliminated, thus enabling complementary measurements of the CKM matrix element
V_ub with a small theoretical error. We quantify the experimental error in a
possible future measurement of |V_ub| using this approach, and show that it is
competitive with the anticipated precision from the conventional approaches.
Moreover, it is shown that such double ratios can be more effective than the
individual leptonic decays as a probe of the parameter space of supersymmetric
models. We emphasize that the double ratios have the advantage of using |V_ub|
as an input parameter (for which there is experimental information), while the
individual decays have an uncertainty from the decay constants (e.g. f_B_s),
and hence a reliance on theoretical techniques such as lattice QCD.Comment: 21 pages, 4 figure
Evidence of the Purely Leptonic Decay B- --> tau- nu_tau-bar
We present the first evidence of the decay B- --> tau- nu_tau-bar using 414
fb^-1 of data collected at the Upsilon(4S) resonance with the Belle detector at
the KEKB asymmetric-energy e+e- collider. Events are tagged by fully
reconstructing one of the B mesons in hadronic modes. We detect the signal with
a significance of 3.5 standard deviations including systematics, and measure
the branching fraction to be Br(B- --> tau- nu_tau-bar) = (1.79
+0.56-0.49(stat) +0.46-0.51(syst))*10^-4. This implies that f_B = 0.229
+0.036-0.031(stat) +0.034-0.037(syst) GeV and is the first direct measurement
of this quantity.Comment: 6 pages, 3 figures, to appear in Physical Review Letter
Observation of B+->Lambda_c+Lambda_c-K+ and B0->Lambda_c+Lambda_c^-K0 decays
We report first measurements of the doubly charmed baryonic B decays
B->Lambda_c+Lambda_c-K. The B+->Lambda_c+Lambda_c-K+ decay is observed with a
branching fraction of (6.5+1.0-0.9+-1.1+-3.4)x10^{-4} and a statistical
significance of 15.4sigma. The B0->Lambda_c+Lambda_c-K0 decay is observed with
a branching fraction of (7.9+2.9-2.3+-1.2+-4.2)x10^{-4} and a statistical
significance of 6.6sigma. The branching fraction errors are statistical,
systematic, and the error resulting from the uncertainty of Lambda_c+->pK-pi+
decay branching fraction. The analysis is based on 357fb-1 of data accumulated
at the Y(4S) resonance with the Belle detector at the KEKB asymmetric e+e-
collider.Comment: 10 pages, 3 figure
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