280 research outputs found
Linearly polarised photon beams at ELSA and measurement of the beam asymmetry in pi^0-photoproduction off the proton
At the electron accelerator ELSA a linearly polarised tagged photon beam is
produced by coherent bremsstrahlung off a diamond crystal. Orientation and
energy range of the linear polarisation can be deliberately chosen by accurate
positioning of the crystal with a goniometer. The degree of polarisation is
determined by the form of the scattered electron spectrum. Good agreement
between experiment and expectations on basis of the experimental conditions is
obtained. Polarisation degrees of P = 40% are typically achieved at half of the
primary electron energy. The determination of P is confirmed by measuring the
beam asymmetry, \Sigma, in pi^0 photoproduction and a comparison of the results
to independent measurements using laser backscattering.Comment: 9 pages, 10 figures, submitted to EPJ
Measurement of ϒ production in pp collisions at √s = 2.76 TeV
The production of ϒ(1S), ϒ(2S) and ϒ(3S)
mesons decaying into the dimuon final state is studied with
the LHCb detector using a data sample corresponding to an
integrated luminosity of 3.3 pb−1 collected in proton–proton
collisions at a centre-of-mass energy of √s = 2.76 TeV. The
differential production cross-sections times dimuon branching
fractions are measured as functions of the ϒ transverse
momentum and rapidity, over the ranges pT < 15 GeV/c
and 2.0 < y < 4.5. The total cross-sections in this kinematic
region, assuming unpolarised production, are measured to be
σ (pp → ϒ(1S)X) × B
ϒ(1S)→μ+μ−
= 1.111 ± 0.043 ± 0.044 nb,
σ (pp → ϒ(2S)X) × B
ϒ(2S)→μ+μ−
= 0.264 ± 0.023 ± 0.011 nb,
σ (pp → ϒ(3S)X) × B
ϒ(3S)→μ+μ−
= 0.159 ± 0.020 ± 0.007 nb,
where the first uncertainty is statistical and the second systematic
Study of the doubly charmed tetraquark T+cc
Quantum chromodynamics, the theory of the strong force, describes interactions of coloured quarks and gluons and the formation of hadronic matter. Conventional hadronic matter consists of baryons and mesons made of three quarks and quark-antiquark pairs, respectively. Particles with an alternative quark content are known as exotic states. Here a study is reported of an exotic narrow state in the D0D0π+ mass spectrum just below the D*+D0 mass threshold produced in proton-proton collisions collected with the LHCb detector at the Large Hadron Collider. The state is consistent with the ground isoscalar T+cc tetraquark with a quark content of ccu⎯⎯⎯d⎯⎯⎯ and spin-parity quantum numbers JP = 1+. Study of the DD mass spectra disfavours interpretation of the resonance as the isovector state. The decay structure via intermediate off-shell D*+ mesons is consistent with the observed D0π+ mass distribution. To analyse the mass of the resonance and its coupling to the D*D system, a dedicated model is developed under the assumption of an isoscalar axial-vector T+cc state decaying to the D*D channel. Using this model, resonance parameters including the pole position, scattering length, effective range and compositeness are determined to reveal important information about the nature of the T+cc state. In addition, an unexpected dependence of the production rate on track multiplicity is observed
"Table 21" of "Photoproduction of mesons off protons and neutrons"
Inclusive differential cross-sections of mesons produced off the free proton versus and versus the momentum transfer to the nucleon, , for incident photon energy = 1.250-1.300 GeV
"Table 21" of "Photoproduction of mesons off protons and neutrons"
Inclusive differential cross-sections of mesons produced off the free proton versus and versus the momentum transfer to the nucleon, , for incident photon energy = 1.250-1.300 GeV
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