70 research outputs found
Proton Structure Functions from Chiral Dynamics and QCD Constraints
The spin fractions and deep inelastic structure functions of the proton are
analyzed using chiral field theory involving Goldstone bosons. A detailed
comparison with recent chiral models sheds light on their successful
description of the spin fractions of the proton as being due to neglecting
helicity non-flip chiral transitions. This approximation is valid for zero mass
quarks but not for constituent quarks. Since the chiral spin fraction models
with the pure spin-flip approximation reproduce the measured spin fractions of
the proton, axialvector constituent-quark-Goldstone boson coupling is found to
be inconsistent with the proton spin data. Initial quark valence distributions
are then constructed using quark counting constraints at Bjorken and
Regge behavior at . Sea quark distributions predicted by chiral field
theory on this basis have correct order of magnitude and shape. The spin
fractions agree with the data.Comment: 30 pages, 2 tables, 10 figure-ps files, LaTex. Accepted by Int. J.
Mod. Phys. A. More details added on polarized chiral splitting function
Measurement of the charge asymmetry in B±→ϕK±B±→ϕK± and search for B±→ϕπ±B±→ϕπ± decays
The CP-violating charge asymmetry in B±→ϕK±B±→ϕK± decays is measured in a sample of pp collisions at 7 TeV centre-of-mass energy, corresponding to an integrated luminosity of 1.0 fb−1 collected by the LHCb experiment. The result is ACP(B±→ϕK±)=0.022±0.021±0.009ACP(B±→ϕK±)=0.022±0.021±0.009, where the first uncertainty is statistical and the second systematic. In addition, a search for the B±→ϕπ±B±→ϕπ± decay mode is performed, using the B±→ϕK±B±→ϕK± decay rate for normalization. An upper limit on the branching fraction B(B±→ϕπ±)<1.5×10−7B(B±→ϕπ±)<1.5×10−7 is set at 90% confidence level
Many-Body Currents and the Strange-Quark Content of 4he
Meson-exchange current (MEC) contributions to the parity-violating (PV)
asymmetry for elastic scattering of polarized electrons from He are
calculated over a range of momentum transfer using Monte Carlo methods and a
variational He ground state wavefunction. The results indicate that MEC's
generate a negligible contribution to the asymmetry at low-|\qv|, where a
determination of the nucleon's mean square strangeness radius could be carried
out at CEBAF. At larger values of momentum transfer -- beyond the first
diffraction minimum -- two-body corrections from the - \lq\lq
strangeness charge" operator enter the asymmetry at a potentially observable
level, even in the limit of vanishing strange-quark matrix elements of the
nucleon. For purposes of constraining the nucleon's strangeness electric form
factor, theoretical uncertainties associated with these MEC contributions do
not appear to impose serious limitations.Comment: 32 TEX pages and 7 figures (not included, available from authors upon
request), CEBAF Preprint #TH-94-1
Measurement of violation parameters and polarisation fractions in decays
The first measurement of asymmetries in the decay and an updated measurement of its branching fraction and polarisation fractions are presented. The results are obtained using data corresponding to an integrated luminosity of of proton-proton collisions recorded with the LHCb detector at centre-of-mass energies of and . Together with constraints from , the results are used to constrain additional contributions due to penguin diagrams in the -violating phase , measured through decays to charmonium
Precise measurements of the properties of the and states and observation of mass structures
Invariant mass distributions of B+pi- and B0pi+ combinations are investigated in order to study excited B mesons. The analysis is based on a data sample corresponding to 3.0 fb-1 of pp collision data, recorded by the LHCb detector at centre-of-mass energies of 7 and 8 TeV. Precise measurements of the masses and widths of the $B_1 (5721)^{0,+} and B_2*(5747)^(0,+) states are reported. Clear enhancements, particularly prominent at high pion transverse momentum, are seen over background in the mass range 5850--6000 MeV in both B+pi- and B0pi+ combinations. The structures are consistent with the presence of four excited B mesons, labelled B_J(5840)^(0,+) and B_J(5960)^(0,+), whose masses and widths are obtained under different hypotheses for their quantum numbers
First observation and amplitude analysis of the decay
The decay is observed in a data sample corresponding to of collision data recorded by the LHCb experiment during 2011 and 2012. Its branching fraction is measured to be where the uncertainties are statistical, systematic and from the branching fraction of the normalisation channel , respectively. An amplitude analysis of the resonant structure of the decay is used to measure the contributions from quasi-two-body , , and decays, as well as from nonresonant sources. The resonance is determined to have spin~1
Spin asymmetries A(1) of the proton and the deuteron in the low x and low Q(2) region from polarized high energy muon scattering (vol 60, pg 072004 1999)
Contains fulltext :
129035.pdf (publisher's version ) (Open Access
The spin-dependent structure function g(1)(x) of the proton from polarized deep-inelastic muon scattering
Contains fulltext :
129126.pdf (publisher's version ) (Open Access
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