157 research outputs found
Coherent Beam-Beam Tune Shift of Unsymmetrical Beam-Beam Interactions with Large Beam-Beam Parameter
Coherent beam-beam tune shift of unsymmetrical beam-beam interactions was
studied experimentally and numerically in HERA where the lepton beam has a very
large beam-beam parameter (up to ). Unlike the symmetrical case of
beam-beam interactions, the ratio of the coherent and incoherent beam-beam tune
shift in this unsymmetrical case of beam-beam interactions was found to
decrease monotonically with increase of the beam-beam parameter. The results of
self-consistent beam-beam simulation, the linearized Vlasov equation, and the
rigid-beam model were compared with the experimental measurement. It was found
that the coherent beam-beam tune shifts measured in the experiment and
calculated in the simulation agree remarkably well but they are much smaller
than those calculated by the linearized Vlasov equation with the single-mode
approximation or the rigid-beam model. The study indicated that the single-mode
approximation in the linearization of Vlasov equation is not valid in the case
of unsymmetrical beam-beam interactions. The rigid-beam model is valid only
with a small beam-beam parameter in the case of unsymmetrical beam-beam
interactions.Comment: 32 pages, 13 figure
Stability of the selfsimilar dynamics of a vortex filament
In this paper we continue our investigation about selfsimilar solutions of
the vortex filament equation, also known as the binormal flow (BF) or the
localized induction equation (LIE). Our main result is the stability of the
selfsimilar dynamics of small pertubations of a given selfsimilar solution. The
proof relies on finding precise asymptotics in space and time for the tangent
and the normal vectors of the perturbations. A main ingredient in the proof is
the control of the evolution of weighted norms for a cubic 1-D Schr\"odinger
equation, connected to the binormal flow by Hasimoto's transform.Comment: revised version, 36 page
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 a narrow charmonium-like state in exclusive B+ -> K+ pi+pi- J/psi decays
We report the observation of a narrow charmonium-like state produced in the
exclusive decay process B+ -> K+ pi+pi- J/psi. This state, which decays into
pi+pi- J/psi, has a mass of 3872.0+-0.6(stat)+-0.5(syst) MeV, a value that is
very near the M_D + M_D* mass threshold. The results are based on an analysis
of 152M B-Bbar events collected at the Upsilon(4S) resonance in the Belle
detector at the KEKB collider. The statistical significance of the signal is in
excess of 10 sigma.Comment: 10 pages 4 figures, submitted to Physical Review Letter
Observation of B0->pi0pi0
We report the first observation of the decay B0->pi0pi0, using a 253/fb data
sample collected at the Upsilon(4S) resonance with the Belle detector at the
KEKB e+e- collider. The measured branching fraction is BF(B0->pi0pi0) = {2.32
+0.4-0.5(stat) +0.2-0.3(syst)} x 10^-6, with a significance of 5.8 standard
deviations including systematic uncertainties. We also make the first
measurement of the direct CP violating asymmetry in this mode.Comment: 6 pages, 2 figures, submitted to ICHEP04, Beijing and Physical Review
Letters. v2: a possible pile-up background is checked and a systematic error
for it is include
Hamiltonian 2-forms in Kahler geometry, III Extremal metrics and stability
This paper concerns the explicit construction of extremal Kaehler metrics on
total spaces of projective bundles, which have been studied in many places. We
present a unified approach, motivated by the theory of hamiltonian 2-forms (as
introduced and studied in previous papers in the series) but this paper is
largely independent of that theory.
We obtain a characterization, on a large family of projective bundles, of
those `admissible' Kaehler classes (i.e., the ones compatible with the bundle
structure in a way we make precise) which contain an extremal Kaehler metric.
In many cases, such as on geometrically ruled surfaces, every Kaehler class is
admissible. In particular, our results complete the classification of extremal
Kaehler metrics on geometrically ruled surfaces, answering several
long-standing questions.
We also find that our characterization agrees with a notion of K-stability
for admissible Kaehler classes. Our examples and nonexistence results therefore
provide a fertile testing ground for the rapidly developing theory of stability
for projective varieties, and we discuss some of the ramifications. In
particular we obtain examples of projective varieties which are destabilized by
a non-algebraic degeneration.Comment: 40 pages, sequel to math.DG/0401320 and math.DG/0202280, but largely
self-contained; partially replaces and extends math.DG/050151
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
Evidence for B0->pi0pi0
We report evidence for the decay B0->pi0pi0. The analysis is based on a data
sample of 152million BBbar pairs collected at the Upsilon(4s) resonance with
the Belle detector at the KEKB e+e- storage ring. We find
25.6+9.3/-8.4(stat)+1.6/-1.4(syst) B0->pi0pi0 signal events with a significance
of 3.4 standard deviations. We measure the branching fraction to be
(1.7+-0.6(stat)+-0.2(syst))*10^{-6}.Comment: Submitted to PR
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