Search results for "gluon"
showing 10 items of 697 documents
Dimensionally regularized box and phase-space integrals involving gluons and massive quarks
1999
The basic box and phase space integrals needed to compute at second order the three-jet decay rate of the Z-boson into massive quarks are presented in this paper. Dimensional Regularization is used to regularize the infrared divergences that appear in intermediate steps. Finally, the cancellation of these divergences among the virtual and the real contributions is showed explicitly.
Top quark tensor couplings
2011
We compute the real and imaginary parts of the one-loop electroweak contributions to the left and right tensorial anomalous couplings of the $tbW$ vertex in the Standard Model (SM). For both tensorial couplings we find that the real part of the electroweak SM correction is close to 10$%$ of the leading contribution given by the QCD gluon exchange. We also find that the electroweak real and imaginary parts for the anomalous right coupling are almost of the same order of magnitude. The one loop SM prediction for the real part of the left coupling is close to the 3$\sigma$ discovery limit derived from $b\rightarrow s \gamma$. Besides, taking into account that the predictions of new physics int…
Equation of state and transverse expansion effects in heavy ion collisions
1992
The effects of the equation of state on the expansion of hadronic matter and on the dilepton production rates in heavy ion collisions are studied. We have used two widely different descriptions of the hadron phase and considered scenarios with and without phase transition. The hadron phase is treated either as a gas of ideal massless pions or, more realistically, as a gas of different kinds of massive hadrons with finite size.
SUSY Ward identities for multi-gluon helicity amplitudes with massive quarks
2006
We use supersymmetric Ward identities to relate multi-gluon helicity amplitudes involving a pair of massive quarks to amplitudes with massive scalars. This allows to use the recent results for scalar amplitudes with an arbitrary number of gluons obtained by on-shell recursion relations to obtain scattering amplitudes involving top quarks.
New Results on Charm Production at HERA
2014
The copious production of charm quarks at HERA yielded measure- ments of the charm contribution to the proton structure and of the charm mass and fragmentation parameters of charmed hadrons. Several measure- ments of charm production in deep inelastic scattering from the H1 and ZEUS collaborations as well as combined data are presented. They provide a powerful vindication of the form of the gluon density in the proton de- rived from scaling violations of inclusive deep inelastic scattering data. A QCD fit to the charm data leads to a measurement of the charm mass and provides precise predictions e.g. for W and Z production at the LHC. In ad- dition, charm fragmentation fractions in photopro…
Measurement of the fraction oftt¯production via gluon-gluon fusion inpp¯collisions ats=1.96 TeV
2009
We present a measurement of the ratio of the tt production cross section via gluon-gluon fusion to the total tt production cross section in pp collisions at √s=1.96 TeV at the Tevatron. Using a data sample with an integrated luminosity of 955 pb-1 recorded by the CDF II detector at Fermilab, we select events based on the tt decay to lepton+jets. Using an artificial neural network technique we discriminate between tt events produced via qq annihilation and gg fusion, and find Gf=σ(gg→tt )/σ(pp →tt )<0.33 at the 68% confidence level. This result is combined with a previous measurement to obtain the most stringent measurement of this quantity by CDF to date, Gf=0.07-0.07+0.15.
First measurement of the Sivers asymmetry for gluons using SIDIS data
2017
The Sivers function describes the correlation between the transverse spin of a nucleon and the transverse motion of its partons. It was extracted from measurements of the azimuthal asymmetry of hadrons produced in semi-inclusive deep inelastic scattering of leptons off transversely polarised nucleon targets, and it turned out to be non-zero for quarks. In this letter the evaluation of the Sivers asymmetry for gluons in the same process is presented. The analysis method is based on a Monte Carlo simulation that includes three hard processes: photon-gluon fusion, QCD Compton scattering and leading-order virtual-photon absorption process. The Sivers asymmetries of the three processes are simul…
Multi-strange baryon production at mid-rapidity in Pb-Pb collisions at root s(NN)=2.76 TeV
2014
The production of − and − baryons and their anti-particles in Pb–Pb collisions at √sNN = 2.76 TeV has been measured using the ALICE detector. The transverse momentum spectra at mid-rapidity (|y| < 0.5) for charged and hyperons have been studied in the range 0.6 < pT < 8.0 GeV/c and 1.2 < pT < 7.0 GeV/c, respectively, and in several centrality intervals (from the most central 0–10% to the most peripheral 60–80% collisions). These spectra have been compared with the predictions of recent hydrodynamic models. In particular, the Kraków and EPOS models give a satisfactory description of the data, with the latter covering a wider pT range. Mid-rapidity yields, integrated over pT, have been determ…
Suppression of Λ(1520) resonance production in central Pb-Pb collisions at sNN=2.76 TeV
2019
The production yield of the Λ(1520) baryon resonance is measured at midrapidity in Pb-Pb collisions at sNN = 2.76 TeV with the ALICE detector at the Large Hadron Collider (LHC). The measurement is performed in the Λ(1520)→pK− (and charge conjugate) hadronic decay channel as a function of the transverse momentum (pT) and collision centrality. The ratio of the pT-integrated production of Λ(1520) baryons relative to Λ baryons in central collisions is suppressed by about a factor of 2 with respect to peripheral collisions. This is the first observation of the suppression of a baryonic resonance at the LHC and the first 3σ evidence of Λ(1520) suppression within a single collision system. The mea…
Quark degrees of freedom in hadronic systems
2000
Quantum Chromodynamics (QCD) is the theory of the strong interactions. We review descriptions of hadronic systems motivated by QCD, analyzing the recent controversy between gluonic and bosonic degrees of freedom under the prism of the Cheshire Cat Principle. Our analysis leads to an optimal scheme to study hadronic properties. We proceed to extend this low energy descriptions to the deep inelastic regime.