Search results for "symmetry"
showing 10 items of 3576 documents
πB8B8andσB8B8couplings from a chiral quark potential model
2008
From an SU(2)$\ensuremath{\bigotimes}$SU(2) chiral quark potential model incorporating spontaneous chiral symmetry breaking the asymptotic $\ensuremath{\pi}$ and $\ensuremath{\sigma}$ exchange pieces of the $\mathit{NN}$ potential are generated. From them the $\ensuremath{\pi}\mathit{NN}$ and $\ensuremath{\sigma}\mathit{NN}$ coupling constants can be extracted. The generalization to SU(3)$\ensuremath{\bigotimes}$SU(3) allows for a determination of $\ensuremath{\pi}{B}_{8}{B}_{8}$ and $\ensuremath{\sigma}{B}_{8}{B}_{8}$ coupling constants according to exact SU(3) hadron symmetry. The implementation of the values of the couplings at ${Q}^{2}=0$ provided by QCD sum rules and/or phenomenology m…
QCD corrections to static heavy-quark form factors
2005
Interactions of heavy quarks, in particular of top quarks, with electroweak gauge bosons are expected to be very sensitive to new physics effects related to electroweak symmetry breaking. These interactions are described by the so-called static form factors, which include anomalous magnetic moments and the effective weak charges. We compute the second-order QCD corrections to these static form factors, which turn out to be sizeable and need to be taken into account in searches for new anomalous coupling effects.
Heavy quark spin symmetry and heavy baryons: electroweak decays
2010
Heavy quark spin symmetry is discussed in the context of single and doubly heavy baryons. A special attention is paid to the constraints/simplifications that this symmetry imposes on the non-relativistic constituent quark model wave functions and on the b->c semileptonic decays of these hadrons.
Exclusive c → s, d Semileptonic Decays of Spin-1/2 and Spin-3/2 cb Baryons
2013
We present results for exclusive semileptonic decay widths of ground state spin-$1/2$ and spin-$3/2$ $cb$ baryons corresponding to a $c\to s, d$ transition at the quark level. The relevance of hyperfine mixing in spin-1/2 $cb$ baryons is shown. Our form factors are compatible with heavy quark spin symmetry constraints obtained in the infinite heavy quark mass limit.
Hyperfine mixing in b -> c semileptonic decay of doubly heavy baryons
2010
We qualitatively corroborate the results of [W. Roberts, M. Pervin, Int. J. Mod. Phys. A 24 (2009) 2401] according to which hyperfine mixing greatly affects the decay widths of b -> c semileptonic decays involving doubly heavy bc baryons. However, our predictions for the decay widths of the unmixed states differ from those reported in the work of Roberts and Pervin by a factor of 2, and this discrepancy translates to the mixed case. We further show that the predictions of heavy quark spin symmetry, might be used in the future to experimentally extract information on the admixtures in the actual physical bc baryons, in a model independent manner.
Heavy Baryon Transitions in a Relativistic Three-Quark Model
1996
Exclusive semileptonic decays of bottom and charm baryons are considered within a relativistic three-quark model with a Gaussian shape for the baryon-three-quark vertex and standard quark propagators. We calculate the baryonic Isgur-Wise functions, decay rates and asymmetry parameters.
Heavy quark symmetry constraints on semileptonic form factors and decay widths of doubly heavy baryons
2007
We show how heavy quark symmetry constraints on doubly heavy baryon semileptonic decay widths can be used to test the validity of different quark model calculations. The large discrepancies in the results observed between different quark model approaches can be understood in terms of a severe violation of heavy quark spin symmetry constraints by some of those models.
Perturbative generation of a strange-quark asymmetry in the nucleon
2004
We point out that perturbative evolution in QCD at three loops generates a strange-antistrange asymmetry s(x)-sbar(x) in the nucleon's sea just from the fact that the nucleon has non-vanishing up and down quark valence densities. The recently computed three-loop splitting functions allow for an estimate of this effect. We find that a fairly sizable asymmetry may be generated. Results for analogous asymmetries in the heavy-quark sector are also presented.
Effective Field Theories for heavy probes in a hot QCD plasma and in the early universe
2016
International audience; There are many interesting problems in heavy-ion collisions and in cosmology that involve the interaction of a heavy particle with a medium. An example is the dissociation of heavy quarkonium seen in heavy-ion collisions. This was believed to be due to the screening of chromoelectric fields that prevents the heavy quarks from binding, however in the last years several perturbative and lattice computations have pointed out to the possibility that dissociation is due to the finite lifetime of a quarkonium state inside the medium. Regarding cosmology, the study of the behavior of heavy Majorana neutrinos in a hot medium is important to understand if this model can expla…
A new measurement of the Collins and Sivers asymmetries on a transversely polarised deuteron target
2007
New high precision measurements of the Collins and Sivers asymmetries of charged hadrons produced in deep-inelastic scattering of muons on a transversely polarised 6LiD target are presented. The data were taken in 2003 and 2004 with the COMPASS spectrometer using the muon beam of the CERN SPS at 160 GeV/c. Both the Collins and Sivers asymmetries turn out to be compatible with zero, within the present statistical errors, which are more than a factor of 2 smaller than those of the published COMPASS results from the 2002 data. The final results from the 2002, 2003 and 2004 runs are compared with naive expectations and with existing model calculations.