320 research outputs found
Scalar mesons moving in a finite volume and the role of partial wave mixing
Phase shifts and resonance parameters can be obtained from finite-volume
lattice spectra for interacting pairs of particles, moving with nonzero total
momentum. We present a simple derivation of the method that is subsequently
applied to obtain the pi pi and pi K phase shifts in the sectors with total
isospin I=0 and I=1/2, respectively. Considering different total momenta, one
obtains extra data points for a given volume that allow for a very efficient
extraction of the resonance parameters in the infinite-volume limit.
Corrections due to the mixing of partial waves are provided. We expect that our
results will help to optimize the strategies in lattice simulations, which aim
at an accurate determination of the scattering and resonance properties.Comment: 19 pages, 12 figure
Photoproduction of scalar mesons on protons and nuclei
We study the photoproduction of scalar mesons close to the threshold of
f_0(980) and a_0(980) using a unitary chiral model. Peaks for both resonances
show up in the invariant mass distributions of pairs of pseudoscalar mesons. A
discussion is made on the photoproduction of these resonances in nuclei, which
can shed light on their nature, a subject of continuous debate.Comment: 25 pages, 9 figures, accepted for publication in Phys Rev
The preliminary lattice QCD calculation of meson decay width
We present a direct lattice QCD calculation of the meson decay width
with the s-wave scattering phase shift for the isospin pion-kaon () system. We employ a special finite size formula, which is the extension of
the Rummukainen-Gottlieb formula for the system in the moving frame, to
calculate the scattering phase, which indicates a resonance around
meson mass. Through the effective range formula, we extract the effective
coupling constant GeV and
decay width MeV. Our simulations are done with the MILC
gauge configurations with flavors of the "Asqtad" improved staggered
dynamical sea quarks on a lattice at and lattice spacing fm.Comment: To make it concise. arXiv admin note: text overlap with
arXiv:1110.1422, but much of v1 text overlap with articles by same and other
authors remove
A Precursor of Chiral Symmetry Restoration in the Nuclear Medium
Spectral enhancement near the 2m_{\pi} threshold in the I=J=0 channel in
nuclei is shown to be a distinct signal of the partial restoration of chiral
symmetry. The relevance of this phenomenon with the possible detection of
2\pi^{0} and 2\gamma in hadron-nucleus and photo-nucleus reactions is
discussed.Comment: Revtex, 4 pages, 3 eps figures, title and introduction changed, to
appear in Phys. Rev. Let
Finite volume treatment of pi pi scattering and limits to phase shifts extraction from lattice QCD
We study theoretically the effects of finite volume for pipi scattering in
order to extract physical observables for infinite volume from lattice QCD. We
compare three different approaches for pipi scattering (lowest order
Bethe-Salpeter approach, N/D and inverse amplitude methods) with the aim to
study the effects of the finite size of the box in the potential of the
different theories, specially the left-hand cut contribution through loops in
the crossed t,u-channels. We quantify the error made by neglecting these
effects in usual extractions of physical observables from lattice QCD spectra.
We conclude that for pipi phase-shifts in the scalar-isoscalar channel up to
800 MeV this effect is negligible for box sizes bigger than 2.5m_pi^-1 and of
the order of 5% at around 1.5-2m_pi^-1. For isospin 2 the finite size effects
can reach up to 10% for that energy. We also quantify the error made when using
the standard Luscher method to extract physical observables from lattice QCD,
which is widely used in the literature but is an approximation of the one used
in the present work.Comment: 10 pages, 8 figure
Hidden beauty baryon states in the local hidden gauge approach with heavy quark spin symmetry
Using a coupled-channel unitary approach, combining the heavy quark spin symmetry and the dynamics of the local hidden gauge, we investigate the meson-baryon interaction with hidden beauty and obtain several new states of N around 11 GeV. We consider the basis of states eta (b) N, I'N, BI > (b) , BI pound (b) , B (*) I > (b) , B (*) I pound (b) , B (*) I pound (b) (*) and find four basic bound states which correspond to BI pound (b) , BI pound (b) (*) , B (*) I pound (b) and B (*) I pound (b) (*) , decaying mostly into eta (b) N and I'N and with a binding energy about 50-130 MeV with respect to the thresholds of the corresponding channel. All of them have isospin I = 1/2 , and we find no bound states or resonances in I = 3/2 . The BI pound (b) state appears in J = 1/2 , the BI pound (b) (*) in J = 3/2 , the B (*) I pound (b) appears nearly degenerate in J = 1/2 , 3/2 and the B (*) I pound (b) (*) appears nearly degenerate in J = 1/2 , 3/2, 5/2. These states have a width from 2-110 MeV, with conservative estimates of uncertainties, except for the one in J = 5/2 which has zero width since it cannot decay into any of the states of the basis chosen. We make generous estimates of the uncertainties and find that within very large margins these states appear bound
Eta, eta-prime photoproduction and electroproduction off nucleons
The photo- and electroproduction of eta, eta-prime mesons on nucleons are
investigated within a relativistic chiral unitary approach based on coupled
channels. The s-wave potentials for electroproduction and meson-baryon
scattering are derived from a chiral effective Lagrangian which includes the
eta-prime as an explicit degree of freedom and incorporates important features
of the underlying QCD Lagrangian such as the axial U(1) anomaly. The effective
potentials are iterated in a Bethe-Salpeter equation and cross sections for
eta, eta-prime photo- and electroproduction from nucleons are obtained. The
results for the eta-prime photoproduction cross section on protons reproduce
the appearance of an S_{11} resonance around 1.9 GeV observed at ELSA. The
inclusion of electromagnetic form factors increases the predicted eta
electroproduction cross sections on the proton, providing a qualitative
explanation for the hard form factor of the photocoupling amplitude observed at
CLAS.Comment: 26 page
The network of photodetectors and diode lasers of the CMS Link alignment system
The central feature of the CMS Link alignment system is a network of Amorphous Silicon Position Detectors distributed throughout the muon spectrometer that are connected by multiple laser lines. The data collected during the years from 2008 to 2015 is presented confirming an outstanding performance of the photo sensors during more than seven years of operation. Details of the photo sensor readout of the laser signals are presented. The mechanical motions of the CMS detector are monitored using these photosensors and good agreement with distance sensors is obtained
A study of charged kappa in
Based on events collected by BESII, the decay
is studied. In the invariant mass
spectrum recoiling against the charged , the charged
particle is found as a low mass enhancement. If a Breit-Wigner function of
constant width is used to parameterize the kappa, its pole locates at MeV/. Also in this channel,
the decay is observed for the first time.
Its branching ratio is .Comment: 14 pages, 4 figure
Performance of the CMS Cathode Strip Chambers with Cosmic Rays
The Cathode Strip Chambers (CSCs) constitute the primary muon tracking device
in the CMS endcaps. Their performance has been evaluated using data taken
during a cosmic ray run in fall 2008. Measured noise levels are low, with the
number of noisy channels well below 1%. Coordinate resolution was measured for
all types of chambers, and fall in the range 47 microns to 243 microns. The
efficiencies for local charged track triggers, for hit and for segments
reconstruction were measured, and are above 99%. The timing resolution per
layer is approximately 5 ns
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