830 research outputs found
Graviton as a Goldstone boson: Nonlinear Sigma Model for Tensor Field Gravity
Spontaneous Lorentz invariance violation (SLIV) realized through a nonlinear
tensor field constraint H_{}^2=\pm M^2 (M is the proposed scale for Lorentz
violation) is considered in tensor field gravity theory, which mimics
linearized general relativity in Minkowski space-time. We show that such a SLIV
pattern, due to which the true vacuum in the theory is chosen, induces massless
tensor Goldstone modes some of which can naturally be associated with the
physical graviton. When expressed in terms of the pure Goldstone modes, this
theory looks essentially nonlinear and contains a variety of Lorentz and CPT
violating couplings. Nonetheless, all SLIV effects turn out to be strictly
cancelled in all the lowest order processes considered, provided that the
tensor field gravity theory is properly extended to general relativity (GR).
So, as we generally argue, the measurable effects of SLIV, induced by
elementary vector or tensor fields, are related to the accompanying gauge
symmetry breaking rather than to spontaneous Lorentz violation. The latter
appears by itself to be physically unobservable, only resulting in a
non-covariant gauge choice in an otherwise gauge invariant and Lorentz
invariant theory. However, while Goldstonic vector and tensor field theories
with exact local invariance are physically indistinguishable from conventional
gauge theories, there might appear some principal distinctions if this local
symmetry were slightly broken at very small distances controlled by quantum
gravity in an explicit, rather than spontaneous, way that could eventually
allow one to differentiate between them observationally.Comment: 15 pages, some minor additions mad
Bottomonium(-like) state spectroscopy at B-factories
Bottomonium spectroscopy is a key source necessary for understanding of Quantum Chromodynamics. The expected results of this endeavor will provide important tests for various theoretical approaches to understanding quarkantiquark interaction dynamics. Recent results in bottomonium spectroscopy are presented
Phase Difference Between the Electromagnetic and Strong Amplitudes for psi(2S) and J/psi Decays into Pairs of Pseudoscalar Mesons
Using the data for 24.5x10^6 psi(2S) produced in e^+e^- annihilations at
sqrt{s}=3686 MeV at the CESR-c e^+e^- collider and 8.6x10^6 J/psi produced in
the decay psi(2S)->pi^+pi^-J/psi, the branching fractions for psi(2S) and J/psi
decays to pairs of pseudoscalar mesons, pi^+pi^-, K^+K^-, and K_S K_L, have
been measured using the CLEO-c detector. We obtain branching fractions
Br(psi(2S)->pi^+pi^-)=(7.6+-2.5+-0.6)x10^-6,
Br(psi(2S)->K^+K^-)=(74.8+-2.3+-3.9)x10^-6, Br(psi(2S)->K_S
K_L)=(52.8+-2.5+-3.4)x10^-6, and Br(J/psi->pi^+pi^-)=(1.47+-0.13+-0.13)x10^-4,
Br(J/psi->K^+K^-)=(2.86+-0.09+-0.19)x10^-4, Br(J/psi+-K_S
K_L)=(2.62+-0.15+-0.14)x10^-4, where the first errors are statistical and the
second errors are systematic. The phase differences between the amplitudes for
electromagnetic and strong decays of psi(2S) and J/psi to 0^{-+} pseudoscalar
pairs are determined by a Monte Carlo method to be
\delta(psi(2S)_{PP}=(110.5^{+16.0}_{-9.5})^o and
\delta(J/psi)_{PP}=(73.5^{+5.0}_{-4.5})^o. The difference between the two is
\Delta\delta = \delta(psi(2S))_{PP}-\delta(J/psi)_{PP}
=(37.0^{+16.5}_{-10.5})^o.Comment: 16 pages, 5 figures, submitted to PR
Measurement of the branching ratio of the decay KL -> pi e nu and extraction of the CKM parameter |Vus|
We present a new measurement of the branching ratio R of the decay KL -> pi e
nu (Ke3), relative to all charged KL decays with two tracks, based on data
taken with the NA48 detector at the CERN SPS. We measure R = 0.4978 +- 0.0035.
From this we derive the Ke3 branching fraction and the weak coupling
parameter |Vus| in the CKM matrix. We obtain |Vus|f+(0) = 0.2146 +- 0.0016,
where f+(0) is the vector form factor in the Ke3 decay.Comment: 18 pages, 8 figures. accepted by Phys Lett.
Measurement of the Ratio Gamma(KL -> pi+ pi-)/Gamma(KL -> pi e nu) and Extraction of the CP Violation Parameter |eta+-|
We present a measurement of the ratio of the decay rates Gamma(KL -> pi+
pi-)/Gamma(KL -> pi e nu), denoted as Gamma(K2pi)/Gamma(Ke3). The analysis is
based on data taken during a dedicated run in 1999 by the NA48 experiment at
the CERN SPS. Using a sample of 47000 K2pi and five million Ke3 decays, we find
Gamma(K2pi)/Gamma(Ke3) = (4.835 +- 0.022(stat) +- 0.016(syst)) x 10^-3. From
this we derive the branching ratio of the CP violating decay KL -> pi+ pi- and
the CP violation parameter |eta+-|. Excluding the CP conserving direct photon
emission component KL -> pi+ pi- gamma, we obtain the results BR(KL -> pi+ pi-)
= (1.941 +- 0.019) x 10^-3 and |eta+-| = (2.223 +- 0.012) x 10^-3.Comment: 20 pages, 7 figures, accepted by Phys. Lett.
First observation of the KS->pi0 gamma gamma decay
Using the NA48 detector at the CERN SPS, 31 KS->pi0 gamma gamma candidates
with an estimated background of 13.7 +- 3.2 events have been observed. This
first observation leads to a branching ratio of BR(KS->pi0 gamma gamma) = (4.9
+- 1.6(stat) +- 0.9(syst)) x 10^-8 in agreement with Chiral Perturbation theory
predictions.Comment: 10 pages, 4 figures submitted to Phys. Lett.
A new measurement of direct CP violation in two pion decays of the neutral kaon
The NA48 experiment at CERN has performed a new measurement of direct CP
violation, based on data taken in 1997 by simultaneously collecting K_L and K_S
decays into pi0pi0 and pi+pi-. The result for the CP violating parameter
Re(epsilon'/epsilon) is (18.5 +/- 4.5(stat)} +/- 5.8 (syst))x10^{-4}.Comment: 18 pages, 6 figure
Search for CP violation in K0 -> 3 pi0 decays
Using data taken during the year 2000 with the NA48 detector at the CERN SPS,
a search for the CP violating decay K_S -> 3 pi0 has been performed. From a fit
to the lifetime distribution of about 4.9 million reconstructed K0/K0bar -> 3
pi0 decays, the CP violating amplitude eta_000 = A(K_S -> 3 pi0)/A(K_L -> 3
pi0) has been found to be Re(eta_000) = -0.002 +- 0.011 +- 0.015 and
Im(eta_000) = -0.003 +- 0.013 +- 0.017. This corresponds to an upper limit on
the branching fraction of Br(K_S -> 3 pi0) < 7.4 x 10^-7 at 90% confidence
level. The result is used to improve knowledge of Re(epsilon) and the CPT
violating quantity Im(delta) via the Bell-Steinberger relation.Comment: 18 pages, 7 figures, submitted to Phys. Lett.
- …