Search results for " phenomenology"
showing 10 items of 3693 documents
Semi-inclusive deep inelastic lepton scattering off complex nuclei
1999
It is shown that in semi-inclusive deep inelastic scattering (DIS) of electrons off a complex nucleus A, the detection, in coincidence with the scattered electron, of a nucleus (A-1) in the ground state, as well as of a nucleon and a nucleus (A-2), also in the ground state, may provide unique information on several long standing problems, such as : i) the nature and the relevance of the final state interaction in DIS; ii) validity of the spectator mechanism in DIS; iii) the medium induced modifications of the nucleon structure function; iv) the origin of the EMC effect.
Relativity and constituent quark structure in model calculations of parton distributions
2004
According to recent studies, Parton Distribution Functions (PDFs) and Generalized Parton Distributions (GPDs) can be evaluated in a Constituent Quark Model (CQM) scenario, considering the constituent quarks as composite objects. In here, a fully covariant model for a system of two particles, together with its non relativistic limit, are used to calculate PDFs and GPDs. The analysis permits to realize that by no means the effects of Relativity can be simulated taking into account the structure of the constituent particles, the two effects being independent and necessary for a proper description of available high energy data in terms of CQM.
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.
Deeply virtual electroproduction of photons and mesons on the nucleon : leading order amplitudes and power corrections
1999
We estimate the leading order amplitudes for exclusive photon and meson electroproduction reactions at large Q^2 in the valence region in terms of skewed quark distributions. As experimental investigations can currently only be envisaged at moderate values of Q^2, we estimate power corrections due to the intrinsic transverse momentum of the partons in the meson wavefunction and in the nucleon. To this aim the skewed parton distribution formalism is generalized so as to include the parton intrinsic transverse momentum dependence. Furthermore, for the meson electroproduction reactions, we calculate the soft overlap type contributions and compare with the leading order amplitudes. We give firs…
Heavy quarks and tau leptons: New physics opportunities
2014
In this talk I discuss the role of heavy quarks in new physics searches with tau leptons. I focus on new physics effects associated to the scalar sector which are naturally enhanced for the heaviest fermions due to the large hierarchy of the fermion masses. I will discuss two topics within this context: lepton flavour violation in the $\tau - \ell$ ($\ell=e,\mu$) sector and violations of lepton universality in tauonic $B$ decays.
Generalized parton distributions and constituent quarks
2002
An approach is described to calculate Generalized Parton Distributions (GPDs) in Constituent Quark Models (CQM). The GPDs are obtained from wave functions to be evaluated in a given CQM. The general relations linking the twist-two GPDs to the form factors and to the leading twist quark densities are recovered. Results for the leading twist, unpolarized GPD in the Isgur and Karl model are presented.
NO nu A plus T2K: The race for the neutrino mass hierarchy
2006
The determination of the ordering of the neutrino masses (the hierarchy) is probably a crucial prerequisite to understand the origin of lepton masses and mixings and to establish their relationship to the analogous properties in the quark sector. Here, we follow an alternative strategy to the usual neutrino--antineutrino comparison in long baseline neutrino oscillation experiments: we exploit the combination of the neutrino-only data from the NOvA and the T2K experiments by performing these two off-axis experiments at different distances but at the same $/L$, where $$ is the mean neutrino energy and $L$ is the baseline. This would require a minor adjustment to the proposed off-axis angle fo…
Tensor charges of light baryons in the Infinite Momentum Frame
2007
We have used the Chiral-Quark Soliton Model formulated in the Infinite Momentum Frame to investigate the octet, decuplet and antidecuplet tensor charges up to the 5Q level. Using flavor SU(3) symmetry we have obtained for the proton $\delta u=1.172$ and $\delta d=-0.315$ in fair agreement previous model estimations. The 5Q allowed us to estimate also the strange contribution to the proton tensor charge $\delta s=-0.011$. All those values have been obtained at the model scale Q^2=0.36 GeV^2.
Accommodating three low-scale anomalies (g-2, Lamb shift, and Atomki) in the framed standard model
2019
The framed Standard Model (FSM) predicts a [Formula: see text] boson with mass around 20 MeV in the “hidden sector,” which mixes at tree level with the standard Higgs [Formula: see text] and hence acquires small couplings to quarks and leptons which can be calculated in the FSM apart from the mixing parameter [Formula: see text]. The exchange of this mixed state [Formula: see text] will contribute to [Formula: see text] and to the Lamb shift. By adjusting [Formula: see text] alone, it is found that the FSM can satisfy all present experimental bounds on the [Formula: see text] and Lamb shift anomalies for [Formula: see text] and [Formula: see text], and for the latter for both hydrogen and …
Towards a unified picture of constituent and current quarks
1997
Using a simple picture of the constituent quark as a composite system of point-like partons, we construct the parton distributions by a convolution between constituent quark momentum distributions and constituent quark structure functions. We evaluate the latter at a low hadronic scale with updated phenomenological information, and we build the momentum distributions using well-known quark models. The resulting parton distributions and structure functions are evolved to the experimental scale and good agreement with the available DIS data is achieved. When compared with a similar calculation using non-composite constituent quarks, the accord with experiment of the present calculation become…