ترغب بنشر مسار تعليمي؟ اضغط هنا

Linear Sigma Model predictions for V->Sgamma and S->Vgamma decays

280   0   0.0 ( 0 )
 نشر من قبل Rafel Escribano
 تاريخ النشر 2008
  مجال البحث
والبحث باللغة English




اسأل ChatGPT حول البحث

The radiative decays $Vto Sgamma$ and $Sto Vgamma$ with $V=rho, omega, phi$ and $S=a_0, sigma, f_0$ are calculated within the framework of the Linear Sigma Model. Current experimental data on the $phito f_0gamma$ and $rhotosigmagamma$ branching ratios and the ratio $Gamma(phito f_0gamma)/Gamma(phito a_0gamma)$ are satisfactorily accommodated in our approach. We also estimate the decay widths of the $f_0,a_0torhogamma,omegagamma$ transitions. All the processes considered are of interest for ongoing experimental programs in Frascati, Julich and Novosibirsk.



قيم البحث

اقرأ أيضاً

High-energy jets recoiling against missing transverse energy (MET) are powerful probes of dark matter at the LHC. Searches based on large MET signatures require a precise control of the $Z( ubar u)+$jet background in the signal region. This can be ac hieved by taking accurate data in control regions dominated by $Z(ell^+ell^-)+$jet, $W(ell u)+$jet and $gamma+$jet production, and extrapolating to the $Z( ubar u)+$jet background by means of precise theoretical predictions. In this context, recent advances in perturbative calculations open the door to significant sensitivity improvements in dark matter searches. In this spirit, we present a combination of state-of-the art calculations for all relevant $V+$jets processes, including throughout NNLO QCD corrections and NLO electroweak corrections supplemented by Sudakov logarithms at two loops. Predictions at parton level are provided together with detailed recommendations for their usage in experimental analyses based on the reweighting of Monte Carlo samples. Particular attention is devoted to the estimate of theoretical uncertainties in the framework of dark matter searches, where subtle aspects such as correlations across different $V+$jet processes play a key role. The anticipated theoretical uncertainty in the $Z( ubar u)+$jet background is at the few percent level up to the TeV range.
The structure of the scalar mesons has been a subject of debate for many decades. In this work we look for $bar{q}q$ states among the physical resonances using an extended Linear Sigma Model that contains scalar, pseudoscalar, vector, and axial-vecto r mesons both in the non-strange and strange sectors. We perform global fits of meson masses, decay widths and amplitudes in order to ascertain whether the scalar $bar{q}q$ states are below or above 1 GeV. We find the scalar states above 1 GeV to be preferred as $bar{q}q$ states.
Extensions of the Standard Model that include vector-like quarks commonly also include additional particles that may mediate new production or decay modes. Using as example the minimal linear $sigma$ model, that reduces to the minimal $SO(5)/SO(4)$ c omposite Higgs model in a specific limit, we consider the phenomenology of vector-like quarks when a scalar singlet $sigma$ is present. This new particle may be produced in the decays $T to t sigma$, $B to b sigma$, where $T$ and $B$ are vector-like quarks of charges $2/3$ and $-1/3$, respectively, with subsequent decay $sigma to W^+ W^-, ZZ, hh$. By scanning over the allowed parameter space we find that these decays may be dominant. In addition, we find that the presence of several new particles allows for single $T$ production cross sections larger than those expected in minimal models. We discuss the observability of these new signatures in existing searches.
125 - G. Ramalho , K. Tsushima 2013
We study the effect of the meson cloud dressing in the octet baryon to decuplet baryon electromagnetic transitions. Combining the valence quark contributions from the covariant spectator quark model with those of the meson cloud estimated based on th e flavor SU(3) cloudy bag model, we calculate the transition magnetic form factors at $Q^2=0$ ($Q^2=-q^2$ and $q$ the four-momentum transfer), and also the decuplet baryon electromagnetic decay widths. The result for the $gamma^ast Lambda to Sigma^{ast 0}$ decay width is in complete agreement with the data, while that for the $gamma^ast Sigma^+ to Sigma^{ast +}$ is underestimated the data by 1.4 standard deviations. This achievement may be regarded as a significant advance in the present theoretical situation.
The photon polarization in $D_{(s)} to K_1 (to Kpipi) gamma$ decays can be extracted from an up-down asymmetry in the $K pi pi$ system, along the lines of the method known to $B to K_1 (to Kpipi) gamma$ decays. Charm physics is advantageous as partne r decays exist: $D^+ to K_1^+ (to Kpipi) gamma$, which is standard model-like, and $D_s to K_1^+ (to Kpipi) gamma$, which is sensitive to physics beyond the standard model in $|Delta c| =|Delta u|=1$ transitions. The standard model predicts their photon polarizations to be equal up to U-spin breaking corrections, while new physics in the dipole operators can split them apart at order one level. We estimate the proportionality factor in the asymmetry multiplying the polarization parameter from axial vectors $K_1(1270)$ and $K_1(1400)$ to be sizable, up to the few ${cal{O}}(10)%$ range. The actual value of the hadronic factor matters for the experimental sensitivity, but is not needed as an input to perform the null test.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا