115 research outputs found
Transverse spin effects in hadron-pair production from semi-inclusive deep inelastic scattering
First measurements of azimuthal asymmetries in hadron-pair production in
deep-inelastic scattering of muons on transversely polarised ^6LiD (deuteron)
and NH_3 (proton) targets are presented. The data were taken in the years
2002-2004 and 2007 with the COMPASS spectrometer using a muon beam of 160 GeV/c
at the CERN SPS. The asymmetries provide access to the transversity
distribution functions, without involving the Collins effect as in single
hadron production. The sizeable asymmetries measured on the NH_ target indicate
non-vanishing u-quark transversity and two-hadron interference fragmentation
functions. The small asymmetries measured on the ^6LiD target can be
interpreted as indication for a cancellation of u- and d-quark transversities.Comment: 13 pages, 4 figures, updated to the published versio
Double parton correlations and constituent quark models: a light front approach to the valence sector
An explicit evaluation of the double parton distribution functions (dPDFs), within a relativistic Light-Front approach to constituent quark models, is presented. dPDFs encode information on the correlations between two partons inside a target and represent the non-perturbative QCD ingredient for the description of double parton scattering in proton-proton collisions, a crucial issue in the search of new Physics at the LHC. Valence dPDFs are evaluated at the low scale of the model and the perturbative scale of the experiments is reached by means of QCD evolution. The present results show that the strong correlation effects present at the scale of the model are still sizable, in the valence region, at the experimental scale. At the low values of x presently studied at the LHC the correlations become less relevant, although they are still important for the spin-dependent contributions to unpolarized proton scattering
Correlations in double parton distributions: perturbative and non-perturbative effects
Measurement of unpolarized semi-inclusive pi+ electroproduction off the proton
Semi-inclusive pi+ electroproduction on protons has been measured with the
CLAS detector at Jefferson Lab. The measurement was performed on a
liquid-hydrogen target using a 5.75 GeV electron beam. The complete five-fold
differential cross sections were measured over a wide kinematic range including
the complete range of azimuthal angles between hadronic and leptonic planes,
phi, enabling us to separate the phi-dependent terms. Our measurements of
phi-independent term of the cross section at low Bjorken x were found to be in
fairly good agreement with pQCD calculations. Indeed, the conventional current
fragmentation calculation can account for almost all of the observed cross
section, even at small pi+ momentum. The measured center-of-momentum spectra
are in qualitative agreement with high energy data, which suggests a surprising
numerical similarity between the spectator diquark fragmentation in the present
reaction and the anti-quark fragmentation measured in e+e- collisions. We have
observed that the two phi-dependent terms of the cross section are small.
Within our precision the cos(2phi) term is compatible with zero, except for
low-z region, and the measured cos(phi) term is much smaller in magnitude than
the sum of the Cahn and Berger effects.Comment: 42 pages, 30 figure
Erratum to: Determination of the integrated luminosity at HERA using elastic QED compton events
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