1,659 research outputs found
Precision weak boson production cross-section measurements at LHCb
Precision measurements of weak boson production cross-sections at the Large Hadron Collider (LHC) allow the Standard Model to be tested and parton distribution functions to be constrained. To achieve this goal an absolute precision of 2% or better is desirable on the experimental measurement. We present how such accuracy on the luminosity determination at a hadron collider is achieved in the LHCb experiment. The LHCb measurements are unique in that they combine two methods, the classical van der Meer method and a novel method based on beam-gas
interactions. The impact of these precise luminosity measurements on the LHCb analyses of electroweak production measurements are presented
Spin dependence of the antinucleon-nucleon interaction
The status of our present knowledge on the antinucleon-nucleon interaction at
low and medium energies is discussed. Special emphasis is put on aspects
related to its spin dependence which are relevant for experiments planned by
the PAX collaboration. Predictions for the spin-dependent antiproton-proton
cross sections sigma_1 and sigma_2 are presented, utilizing antinucleon-nucleon
potential models developed by the Juelich group, and compared to results based
on the amplitudes of the Nijmegen partial-wave analysis.Comment: 8 pages, 4 figures, to appear in the proceedings of the 19th
International Spin Physics Symposium, September 27 - October 2, 2010,
Juelich, German
Spin-dependent pbar-d cross sections at low and intermediate energies
Antiproton-deuteron () scattering is calculated at beam energies
below 300 MeV within the Glauber approach, utilizing the amplitudes of the
J\"ulich models. A good agreement is obtained with available
experimental data on upolarized differential and integrated cross
sections. Predictions for polarized total cross sections are
presented, obtained within the single scattering approximation including
Coulomb-nuclear interference effects. It is found that the total longitudinal
and transversal cross sections are comparable in absolute value to
those for scattering.
The kinetics of polarization buildup is considered.Comment: 8 pages, 5 figures, to appear in proceedings of the 19th
international Spin Physics Symposium, September 27 - October 2, 2010,
Juelich, German
The polarised internal target for the PAX experiment
The PAX (Polarized Antiproton eXperiment) collaboration aims to polarise antiproton beams stored in ring by means of spin-filtering. The experimental setup is based on a polarised internal gas target, surrounded by a detection system for the measurement of spin observables. In this report, we present results from the commission of the PAX target (atomic beam source, openable cell, and polarimeter)
Measurement of the Spin-Dependence of the pbar-p Interaction at the AD-Ring
We propose to use an internal polarized hydrogen storage cell gas target in
the AD ring to determine for the first time the two total spin-dependent pbar-p
cross sections sigma_1 and sigma_2 at antiproton beam energies in the range
from 50 to 450 MeV. The data obtained are of interest by themselves for the
general theory of pbar-p interactions since they will provide a first
experimental constraint of the spin-spin dependence of the nucleon-antinucleon
potential in the energy range of interest. In addition, measurements of the
polarization buildup of stored antiprotons are required to define the optimum
parameters of a future, dedicated Antiproton Polarizer Ring (APR), intended to
feed a double-polarized asymmetric pbar-p collider with polarized antiprotons.
Such a machine has recently been proposed by the PAX collaboration for the new
Facility for Antiproton and Ion Research (FAIR) at GSI in Darmstadt, Germany.
The availability of an intense stored beam of polarized antiprotons will
provide access to a wealth of single- and double-spin observables, thereby
opening a new window on QCD spin physics.Comment: 51 pages, 23 figures, proposal submitted to the SPS committee of CER
Measurement of the ratio of branching fractions BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma)
The ratio of branching fractions of the radiative B decays B0 -> K*0 gamma
and Bs0 -> phi gamma has been measured using 0.37 fb-1 of pp collisions at a
centre of mass energy of sqrt(s) = 7 TeV, collected by the LHCb experiment. The
value obtained is BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma) = 1.12 +/- 0.08
^{+0.06}_{-0.04} ^{+0.09}_{-0.08}, where the first uncertainty is statistical,
the second systematic and the third is associated to the ratio of fragmentation
fractions fs/fd. Using the world average for BR(B0 -> K*0 gamma) = (4.33 +/-
0.15) x 10^{-5}, the branching fraction BR(Bs0 -> phi gamma) is measured to be
(3.9 +/- 0.5) x 10^{-5}, which is the most precise measurement to date.Comment: 15 pages, 1 figure, 2 table
Observation of two new baryon resonances
Two structures are observed close to the kinematic threshold in the mass spectrum in a sample of proton-proton collision data, corresponding
to an integrated luminosity of 3.0 fb recorded by the LHCb experiment.
In the quark model, two baryonic resonances with quark content are
expected in this mass region: the spin-parity and
states, denoted and .
Interpreting the structures as these resonances, we measure the mass
differences and the width of the heavier state to be
MeV,
MeV,
MeV, where the first and second
uncertainties are statistical and systematic, respectively. The width of the
lighter state is consistent with zero, and we place an upper limit of
MeV at 95% confidence level. Relative
production rates of these states are also reported.Comment: 17 pages, 2 figure
Search for CP violation in decays
A model-independent search for direct CP violation in the Cabibbo suppressed
decay in a sample of approximately 370,000 decays is
carried out. The data were collected by the LHCb experiment in 2010 and
correspond to an integrated luminosity of 35 pb. The normalized Dalitz
plot distributions for and are compared using four different
binning schemes that are sensitive to different manifestations of CP violation.
No evidence for CP asymmetry is found.Comment: 13 pages, 8 figures, submitted to Phys. Rev.
Differential branching fraction and angular analysis of the decay B0→K∗0μ+μ−
The angular distribution and differential branching fraction of the decay B 0→ K ∗0 μ + μ − are studied using a data sample, collected by the LHCb experiment in pp collisions at s√=7 TeV, corresponding to an integrated luminosity of 1.0 fb−1. Several angular observables are measured in bins of the dimuon invariant mass squared, q 2. A first measurement of the zero-crossing point of the forward-backward asymmetry of the dimuon system is also presented. The zero-crossing point is measured to be q20=4.9±0.9GeV2/c4 , where the uncertainty is the sum of statistical and systematic uncertainties. The results are consistent with the Standard Model predictions
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