3,026 research outputs found
Feasibility studies of the time-like proton electromagnetic form factor measurements with PANDA at FAIR
The possibility of measuring the proton electromagnetic form factors in the
time-like region at FAIR with the \PANDA detector is discussed. Detailed
simulations on signal efficiency for the annihilation of into a
lepton pair as well as for the most important background channels have been
performed. It is shown that precision measurements of the differential cross
section of the reaction can be obtained in a wide
angular and kinematical range. The individual determination of the moduli of
the electric and magnetic proton form factors will be possible up to a value of
momentum transfer squared of (GeV/c). The total cross section will be measured up to (GeV/c).
The results obtained from simulated events are compared to the existing data.
Sensitivity to the two photons exchange mechanism is also investigated.Comment: 12 pages, 4 tables, 8 figures Revised, added details on simulations,
4 tables, 9 figure
Technical Design Report for the PANDA Solenoid and Dipole Spectrometer Magnets
This document is the Technical Design Report covering the two large
spectrometer magnets of the PANDA detector set-up. It shows the conceptual
design of the magnets and their anticipated performance. It precedes the tender
and procurement of the magnets and, hence, is subject to possible modifications
arising during this process.Comment: 10 pages, 14MB, accepted by FAIR STI in May 2009, editors: Inti
Lehmann (chair), Andrea Bersani, Yuri Lobanov, Jost Luehning, Jerzy Smyrski,
Technical Coordiantor: Lars Schmitt, Bernd Lewandowski (deputy),
Spokespersons: Ulrich Wiedner, Paola Gianotti (deputy
Precision measurement of the branching fractions of J/psi -> pi+pi-pi0 and psi' -> pi+pi-pi0
We study the decays of the J/psi and psi' mesons to pi+pi-pi0 using data
samples at both resonances collected with the BES III detector in 2009. We
measure the corresponding branching fractions with unprecedented precision and
provide mass spectra and Dalitz plots. The branching fraction for J/psi ->
pi+pi-pi0 is determined to be (2.137 +- 0.004 (stat.) +0.058-0.056 (syst.)
+0.027-0.026 (norm.))*10-2, and the branching fraction for psi' -> pi+pi-pi0 is
measured as (2.14 +- 0.03 (stat.) +0.08-0.07 (syst.) +0.09-0.08 (norm.))*10-4.
The J/psi decay is found to be dominated by an intermediate rho(770) state,
whereas the psi' decay is dominated by di-pion masses around 2.2 GeV/c2,
leading to strikingly different Dalitz distributions.Comment: 15 pages, 2 figure
Measurement of azimuthal asymmetries in inclusive charged dipion production in annihilations at = 3.65 GeV
We present a measurement of the azimuthal asymmetries of two charged pions in
the inclusive process based on a data set of 62
at the center-of-mass energy GeV collected with
the BESIII detector. These asymmetries can be attributed to the Collins
fragmentation function. We observe a nonzero asymmetry, which increases with
increasing pion momentum. As our energy scale is close to that of the existing
semi-inclusive deep inelastic scattering experimental data, the measured
asymmetries are important inputs for the global analysis of extracting the
quark transversity distribution inside the nucleon and are valuable to explore
the energy evolution of the spin-dependent fragmentation function.Comment: 7 pages, 5 figure
Measurement of the quasi-elastic axial vector mass in neutrino-oxygen interactions
The weak nucleon axial-vector form factor for quasi-elastic interactions is
determined using neutrino interaction data from the K2K Scintillating Fiber
detector in the neutrino beam at KEK. More than 12,000 events are analyzed, of
which half are charged-current quasi-elastic interactions nu-mu n to mu- p
occurring primarily in oxygen nuclei. We use a relativistic Fermi gas model for
oxygen and assume the form factor is approximately a dipole with one parameter,
the axial vector mass M_A, and fit to the shape of the distribution of the
square of the momentum transfer from the nucleon to the nucleus. Our best fit
result for M_A = 1.20 \pm 0.12 GeV. Furthermore, this analysis includes updated
vector form factors from recent electron scattering experiments and a
discussion of the effects of the nucleon momentum on the shape of the fitted
distributions.Comment: 14 pages, 10 figures, 6 table
Measurement of the Cross Section between 600 and 900 MeV Using Initial State Radiation
We extract the cross section in the energy
range between 600 and 900 MeV, exploiting the method of initial state
radiation. A data set with an integrated luminosity of 2.93 fb taken at
a center-of-mass energy of 3.773 GeV with the BESIII detector at the BEPCII
collider is used. The cross section is measured with a systematic uncertainty
of 0.9%. We extract the pion form factor as well as the
contribution of the measured cross section to the leading order hadronic vacuum
polarization contribution to . We find this value to be
.Comment: 14 pages, 7 figures, accepted by PL
Study of
We present an analysis of the decay based
on data collected by the BESIII experiment at the resonance. Using
a nearly background-free sample of 18262 events, we measure the branching
fraction . For GeV/ the partial branching fraction is
. A partial wave analysis shows that the dominant
component is accompanied by an \emph{S}-wave contribution accounting for
of the total rate and that other components are
negligible. The parameters of the resonance and of the
form factors based on the spectroscopic pole dominance predictions are also
measured. We also present a measurement of the helicity
basis form factors in a model-independent way.Comment: 17 pages, 6 figure
Observation of in
Using a sample of events recorded with
the BESIII detector at the symmetric electron positron collider BEPCII, we
report the observation of the decay of the charmonium state
into a pair of mesons in the process
. The branching fraction is measured for the first
time to be , where the first uncertainty is
statistical, the second systematic and the third is from the uncertainty of
. The mass and width of the are
determined as MeV/ and
MeV.Comment: 13 pages, 6 figure
Observation and study of the decay
We report the observation and study of the decay
using events
collected with the BESIII detector. Its branching fraction, including all
possible intermediate states, is measured to be
. We also report evidence for a structure,
denoted as , in the mass spectrum in the GeV/
region. Using two decay modes of the meson ( and
), a simultaneous fit to the mass spectra is
performed. Assuming the quantum numbers of the to be , its
significance is found to be 4.4, with a mass and width of MeV/ and MeV, respectively, and a
product branching fraction
. Alternatively, assuming , the
significance is 3.8, with a mass and width of MeV/ and MeV, respectively, and a product
branching fraction
. The angular distribution of
is studied and the two assumptions of the
cannot be clearly distinguished due to the limited statistics. In all
measurements the first uncertainties are statistical and the second systematic.Comment: 10 pages, 6 figures and 4 table
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