Search results for " phenomenology"
showing 10 items of 3693 documents
Pion radiative weak decays in nonlocal chiral quark models
2010
We analyze the radiative pion decay pi+ -> e+ nu_e gamma within nonlocal chiral quark models that include wave function renormalization. In this framework we calculate the vector and axial-vector form factors FV and FA at q^2=0 --where q^2 is the (e+ ��_e) squared invariant mass-- and the slope a of FV(q^2) at q^2 -> 0. The calculations are carried out considering different nonlocal form factors, in particular those taken from lattice QCD evaluations, showing a reasonable agreement with the corresponding experimental data. The comparison of our results with those obtained in the (local) NJL model and the relation of FV and a with the form factor in pi^0 -> gamma* gamma decays are d…
Stable heavy pentaquarks in constituent models
2017
It is shown that standard constituent quark models produce $(\bar c c qqq)$ hidden-charm pentaquarks, where $c$ denotes the charmed quark and $q$ a light quark, which lie below the lowest threshold for spontaneous dissociation and thus are stable in the limit where the internal $\bar c c$ annihilation is neglected. The binding is a cooperative effect of the chromoelectric and chromomagnetic components of the interaction, and it disappears in the static limit with a pure chromoelectric potential. Their wave function contains color sextet and color octet configurations for the subsystems and can hardly be reduced to a molecular state made of two interacting hadrons. These pentaquark states co…
A non-relativistic model for the $[cc][\bar{c}\bar{c}]$ tetraquark
2017
We use a non-relativistic model to study the spectroscopy of a tetraquark composed of $[cc][\bar{c}\bar{c}]$ in a diquark-antidiquark configuration. By numerically solving the Schr\"{o}dinger equation with a Cornell-inspired potential, we separate the four-body problem into three two-body problems. Spin-dependent terms (spin-spin, spin-orbit and tensor) are used to describe the splitting structure of the $c\bar{c}$ spectrum and are also extended to the interaction between diquarks. Recent experimental data on charmonium states are used to fix the parameters of the model and a satisfactory description of the spectrum is obtained. We find that the spin-dependent interaction is sizable in the …
On the Origin of Model Relations among Transverse-Momentum Dependent Parton Distributions
2011
Transverse-momentum dependent parton distributions (TMDs) are studied in the framework of quark models. In particular, quark-model relations among TMDs are reviewed, elucidating their physical origin in terms of the quark-spin structure in the nucleon. The formal aspects of the derivation of these relations are complemented with explicit examples, emphasizing how and to which extent the conditions which lead to relations among TMDs are implemented in different classes of quark models.
A$_{FB}$ in the SMEFT: precision Z physics at the LHC
2021
We study the forward-backward asymmetry $A_{FB}$ in $pp \to \ell^+\ell^-$ at the Z peak within the Standard Model Effective Field Theory (SMEFT). We find that this observable provides per mille level constraints on the vertex corrections of the Z boson to quarks,which close a flat direction in the electroweak precision SMEFT fit. Moreover, we show that current $A_{FB}$ data is precise enough so that its inclusion in the fit improves significantly LEP bounds even in simple New Physics setups. This demonstrates that the LHC can compete with and complement LEP when it comes to precision measurements of the Z boson properties
Parton distributions and lattice QCD calculations: A community white paper
2018
Progress in particle and nuclear physics 100, 107 - 160 (2018). doi:10.1016/j.ppnp.2018.01.007
Light- and strange-quark mass dependence of the ρ(770) meson revisited
2020
Recent lattice data on $\pi\pi$-scattering phase shifts in the vector-isovector channel, pseudoscalar meson masses and decay constants for strange-quark masses smaller or equal to the physical value allow us to study the strangeness dependence of these observables for the first time. We perform a global analysis on two kind of lattice trajectories depending on whether the sum of quark masses or the strange-quark mass is kept fixed to the physical point. The quark mass dependence of these observables is extracted from unitarized coupled-channel one-loop Chiral Perturbation Theory. This analysis guides new predictions on the $\rho(770)$ meson properties over trajectories where the strange-qua…
String breaking by light and strange quarks in QCD
2019
The energy spectrum of a system containing a static quark anti-quark pair is computed for a wide range of source separations using lattice QCD with $N_\mathrm{f}=2+1$ dynamical flavours. By employing a variational method with a basis including operators resembling both the gluon string and systems of two separated static mesons, the first three energy levels are determined up to and beyond the distance where it is energetically favourable for the vacuum to screen the static sources through light- or strange-quark pair creation, enabling both these screening phenomena to be observed. The separation dependence of the energy spectrum is reliably parameterised over this saturation region with a…
Form factors of radiative pion decays in nonlocal chiral quark models
2012
We study the radiative pion decay π +→e +ν eγ within nonlocal chiral quark models that include wave function renormalization. In this framework we analyze the momentum dependence of the vector form factor F V(q2) and the slope of the axial-vector form factor F A(q2) at threshold. Our results are compared with available experimental information and with the predictions given by the Nambu-Jona-Lasinio model. In addition we calculate the low energy constants δ 5 and δ 6, comparing our results with the values obtained in chiral perturbation theory.
D mesic nuclei
2010
The energies and widths of several D-0 meson bound states for different nuclei are obtained using a D-meson selfenergy in the nuclear medium, which is evaluated in a selfconsistent manner using techniques of unitarized coupled-channel theory. The kernel of the meson-baryon interaction is based on a model that treats heavy pseudoscalar and heavy vector mesons on equal footing, as required by heavy quark symmetry. We find D-0 bound states in all studied nuclei, from C-12 up to Pb-208. The inclusion of vector mesons is the keystone for obtaining an attractive D-nucleus interaction that leads to the existence of D-0-nucleus bound states, as compared to previous studies based on SU(4) flavor sym…