Search results for "Fermion"

Nonperturbative renormalization of quark bilinears

1998

We compute non-perturbatively the renormalization constants of quark bilinears on the lattice in the quenched approximation at three values of the coupling beta=6/g_0^2=6.0,6.2,6.4 using both the Wilson and the tree-level improved SW-Clover fermion action. We perform a Renormalization Group analysis at the next-to-next-to-leading order and compute Renormalization Group invariant values for the constants. The results are applied to obtain a fully non-perturbative estimate of the vector and pseudoscalar decay constants.

Chiral quark cluster model approach to the baryon spectra and the NN interaction

2000

Azimuthal correlations of electrons from heavy-flavor decay with hadrons inp+pand Au+Au collisions atsNN=200GeV

2011

Measurements of electrons from the decay of open-heavy-flavor mesons have shown that the yields are suppressed in Au+Au collisions compared to expectations from binary-scaled p+p collisions. These measurements indicate that charm and bottom quarks interact with the hot dense matter produced in heavy-ion collisions much more than expected. Here we extend these studies to two-particle correlations where one particle is an electron from the decay of a heavy-flavor meson and the other is a charged hadron from either the decay of the heavy meson or from jet fragmentation. These measurements provide more detailed information about the interactions between heavy quarks and the matter, such as whet…

Search for New Bottomlike Quark Pair DecaysQQ¯→(tW∓)(t¯W±)in Same-Charge Dilepton Events

2010

We report the most restrictive direct limits on masses of fourth-generation down-type quarks b{sup '}, and quarklike composite fermions (B or T{sub 5/3}), decaying promptly to tW{sup +}-. We search for a significant excess of events with two same-charge leptons (e, mu), several hadronic jets, and missing transverse energy. An analysis of data from pp collisions with an integrated luminosity of 2.7 fb{sup -1} collected with the CDF II detector at Fermilab yields no evidence for such a signal, setting mass limits m{sub b}{sup '}, m{sub B}>338 GeV/c{sup 2} and m{sub T{sub 5{sub /{sub 3}}}}>365 GeV/c{sup 2} at 95% confidence level.

Predictions from warped flavor dynamics based on the T′ family group

2020

We propose a realistic theory of fermion masses and mixings using a five-dimensional warped scenario where all fermions propagate in the bulk and the Higgs field is localized on the IR brane. The assumed $T'$ flavor symmetry is broken on the branes by flavon fields, providing a consistent scenario where fermion mass hierarchies arise from adequate choices of the bulk mass parameters, while quark and lepton mixing angles are restricted by the family symmetry. Neutrino mass splittings, mixing parameters and the Dirac CP phase all arise from the type-I seesaw mechanism and are tightly correlated, leading to predictions for the neutrino oscillation parameters, as well as expected \znbb decay ra…

Cross Section and Parity-Violating Spin Asymmetries ofW±Boson Production in Polarizedp+pCollisions ats=500  GeV

2011

Large parity-violating longitudinal single-spin asymmetries A(L)(e+) = 0.86(-0.14)(+0.30) and Ae(L)(e-) = 0.88(-0.71)(+0.12) are observed for inclusive high transverse momentum electrons and positrons in polarized p + p collisions at a center-of-mass energy of root s = 500 GeV with the PHENIX detector at RHIC. These e(+/-) come mainly from the decay of W-+/- and Z(0) bosons, and their asymmetries directly demonstrate parity violation in the couplings of the W-+/- to the light quarks. The observed electron and positron yields were used to estimate W-+/- boson production cross sections for the e(+/-) channels of sigma(pp -> W+X) X BR(W+ -> e(+) nu(e)) = 144.1 +/- 21.2(stat)(-10.3)(+3.4)(syst)…

LHC diphoton resonance from gauge symmetry

2015

Motivated by what is possibly the first sign of new physics seen at the LHC, the diphoton excess at $750$ GeV in ATLAS and CMS, we present a model that provides naturally the necessary ingredients to explain the resonance. The simplest phenomenological explanation for the diphoton excess requires a new scalar state, $X(750)$, as well as additional vector-like (VL) fermions introduced in an ad-hoc way in order to enhance its decays into a pair of photons and/or increase its production cross-section. We show that the requiered VL quarks and their couplings can emerge naturally from a complete framework based on the $SU(3)_L \otimes U(1)_\mathcal{X}$ gauge symmetry.

The effect of hyperfine mixing in electromagnetic and semileptonic decays of doubly heavy baryons

2010

We consider the role played by hyperfine mixing in electromagnetic and semileptonic decays of doubly heavy baryons, which give rise to large corrections to the decay widths in both cases.

Sensitivity to charged scalars in B → D(*)τν and B → τν decays

2013

We analyze the recent experimental evidence for an excess of $\tau$-lepton production in several exclusive semileptonic $B$-meson decays in the context of two-Higgs-doublet models. These decay modes are sensitive to the exchange of charged scalars and constrain strongly their Yukawa interactions. While the usual Type-II scenario cannot accommodate the recent BaBar data, this is possible within more general models in which the charged-scalar couplings to up-type quarks are not as suppressed. Both the $B\to D^{(*)}\tau\nu_\tau$ and the $B\to\tau\nu_\tau$ data can be fitted within the framework of the Aligned Two-Higgs-Doublet Model, but the resulting parameter ranges are in conflict with the …

Flavour geometry and effective Yukawa couplings in the MSSM

2010

We present a new geometric approach to the flavour decomposition of an arbitrary soft supersymmetry-breaking sector in the MSSM. Our approach is based on the geometry that results from the quark and lepton Yukawa couplings, and enables us to derive the necessary and sufficient conditions for a linearly-independent basis of matrices related to the completeness of the internal [SU(3) circle times U(1)](5) flavour space. In a second step, we calculate the effective Yukawa couplings that are enhanced at large values of tan beta for general soft supersymmetry-breaking mass parameters. We highlight the contributions due to non-universal terms in the flavour decompositions of the sfermion mass mat…