3,707 research outputs found
Role of Vector Mesons in High-Q^2 Lepton-Nucleon Scattering
The possible role played by vector mesons in inclusive deep inelastic
lepton-nucleon scattering is investigated. In the context of the convolution
model, we calculate self-consistently the scaling contribution to the nucleon
structure function using the formalism of time-ordered perturbation theory in
the infinite momentum frame. Our results indicate potentially significant
effects only when the vector meson---nucleon form factor is very hard.
Agreement with the experimental antiquark distributions, however, requires
relatively soft form factors for the , and vertices.Comment: 22 pages, 9 figures (available upon request); accepted for
publication in Phys.Rev.D, ADP-92-197/T12
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Inclusive J/Ï production at mid-rapidity in pp collisions at âs = 5.02 TeV
Inclusive J/Ï production is studied in minimum-bias proton-proton collisions at a centre-of-mass energy of s = 5.02 TeV by ALICE at the CERN LHC. The measurement is performed at mid-rapidity (|y| < 0.9) in the dielectron decay channel down to zero transverse momentum pT, using a data sample corresponding to an integrated luminosity of Lint = 19.4 ± 0.4 nbâ1. The measured pT-integrated inclusive J/Ï production cross sec- tion is dÏ/dy = 5.64 ± 0.22(stat.) ± 0.33(syst.) ± 0.12(lumi.) ÎŒb. The pT-differential cross section d2Ï/dpTdy is measured in the pT range 0â10 GeV/c and compared with state-of- the-art QCD calculations. The J/Ï ăpTă and ăpT2ă are extracted and compared with results obtained at other collision energies. [Figure not available: see fulltext.]
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Measurement of electrons from heavy-flavour hadron decays as a function of multiplicity in p-Pb collisions at âsNN = 5.02 TeV
The multiplicity dependence of electron production from heavy-flavour hadron decays as a function of transverse momentum was measured in p-Pb collisions at sNN = 5.02 TeV using the ALICE detector at the LHC. The measurement was performed in the centre-of-mass rapidity interval â1.07 < ycms< 0.14 and transverse momentum interval 2 < pT< 16 GeV/c. The multiplicity dependence of the production of electrons from heavy-flavour hadron decays was studied by comparing the pT spectra measured for different multiplicity classes with those measured in pp collisions (QpPb) and in peripheral p-Pb collisions (Qcp). The QpPb results obtained are consistent with unity within uncertainties in the measured pT interval and event classes. This indicates that heavy-flavour decay electron production is consistent with binary scaling and independent of the geometry of the collision system. Additionally, the results suggest that cold nuclear matter effects are negligible within uncertainties, in the production of heavy-flavour decay electrons at midrapidity in p-Pb collisions. [Figure not available: see fulltext.
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Measurement of charged jet cross section in pp collisions at s =5.02 TeV
The cross section of jets reconstructed from charged particles is measured in the transverse momentum range of
Search for the QCD critical point in nuclear collisions at the CERN SPS
Pion production in nuclear collisions at the SPS is investigated with the aim
to search, in a restricted domain of the phase diagram, for power-laws in the
behavior of correlations which are compatible with critical QCD. We have
analyzed interactions of nuclei of different size (p+p, C+C, Si+Si, Pb+Pb) at
158 GeV adopting, as appropriate observables, scaled factorial moments in a
search for intermittent fluctuations in transverse dimensions. The analysis is
performed for pairs with invariant mass very close to the two-pion
threshold. In this sector one may capture critical fluctuations of the sigma
component in a hadronic medium, even if the -meson has no well defined
vacuum state. It turns out that for the Pb+Pb system the proposed analysis
technique cannot be applied without entering the invariant mass region with
strong Coulomb correlations. As a result the treatment becomes inconclusive in
this case. Our results for the other systems indicate the presence of power-law
fluctuations in the freeze-out state of Si+Si approaching in size the
prediction of critical QCD.Comment: 31 pages, 11 figure
Transverse lattice calculation of the pion light-cone wavefunctions
We calculate the light-cone wavefunctions of the pion by solving the meson
boundstate problem in a coarse transverse lattice gauge theory using DLCQ. A
large-N_c approximation is made and the light-cone Hamiltonian expanded in
massive dynamical fields at fixed lattice spacing. In contrast to earlier
calculations, we include contributions from states containing many gluonic
link-fields between the quarks.The Hamiltonian is renormalised by a combination
of covariance conditions on boundstates and fitting the physical masses M_rho
and M_pi, decay constant f_pi, and the string tension sigma. Good covariance is
obtained for the lightest 0^{-+} state, which we identify with the pion. Many
observables can be deduced from its light-cone wavefunctions.After perturbative
evolution,the quark valence structure function is found to be consistent with
the experimental structure function deduced from Drell-Yan pi-nucleon data in
the valence region x > 0.5. In addition, the pion distribution amplitude is
consistent with the experimental distribution deduced from the pi gamma^* gamma
transition form factor and diffractive dissociation. A new observable we
calculate is the probability for quark helicity correlation. We find a 45%
probability that the valence-quark helicities are aligned in the pion.Comment: 27 pages, 9 figure
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Measurement of Î (1520) production in pp collisions at âs=7TeV and pâPb collisions at âsNN=5.02TeV
The production of the Î (1520) baryonic resonance has been measured at midrapidity in inelastic pp collisions at s=7TeV and in pâPb collisions at sNN=5.02TeV for non-single diffractive events and in multiplicity classes. The resonance is reconstructed through its hadronic decay channel Î (1520) â pK - and the charge conjugate with the ALICE detector. The integrated yields and mean transverse momenta are calculated from the measured transverse momentum distributions in pp and pâPb collisions. The mean transverse momenta follow mass ordering as previously observed for other hyperons in the same collision systems. A Blast-Wave function constrained by other light hadrons (Ï, K, KS0, p, Î) describes the shape of the Î (1520) transverse momentum distribution up to 3.5GeV/c in pâPb collisions. In the framework of this model, this observation suggests that the Î (1520) resonance participates in the same collective radial flow as other light hadrons. The ratio of the yield of Î (1520) to the yield of the ground state particle Î remains constant as a function of charged-particle multiplicity, suggesting that there is no net effect of the hadronic phase in pâPb collisions on the Î (1520) yield
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