Search results for "current"
showing 10 items of 2224 documents
Improved determination of the electroweak penguin contribution to ϵ′/ϵ in the chiral limit
2003
We perform a finite energy sum rule analysis of the flavor ud two-point V-A current correlator, Delta Pi (Q^2). The analysis, which is performed using both the ALEPH and OPAL databases for the V-A spectral function, Delta rho, allows us to extract the dimension six V-A OPE coefficient, a_6, which is related to the matrix element of the electroweak penguin operator, Q_8, by chiral symmetry. The result for a_6 leads directly to the improved (chiral limit) determination epsilon'/epsilon = (- 15.0 +- 2.7) 10^{-4}. Determination of higher dimension OPE contributions also allows us to perform an independent test using a low-scale constrained dispersive analysis, which provides a highly nontrivial…
Non-perturbative improvement of the vector current in Wilson lattice QCD
2015
Many observables of interest in lattice QCD are extracted from correlation functions involving the vector current. If Wilson fermions are used, it is therefore of practical importance that, besides the action, the current be O($a$) improved in order to remove the leading discretization errors from the observables. Here we introduce and apply a new method to determine the improvement coefficient for the two most widely used discretizations of the current.
Z physics constraints on vector leptoquarks
1996
We analyze the constraints on vector leptoquarks coming from radiative corrections to $Z$ physics. We perform a global fitting to the LEP data including the oblique and non-universal contributions of the most general effective Lagrangian for vector leptoquarks, which exhibits the $SU(2)_L \times U(1)_Y$ gauge invariance. We show that the $Z$ physics leads to stronger bounds on second and third generation vectors leptoquarks than the ones obtained from low energy and the current collider experiments.
Nuclear PDFs at NLO - status report and review of the EPS09 results
2011
We review the current status of the global DGLAP analysis of nuclear parton distribution functions, nPDFs, focusing on the recent EPS09 analysis, whose output, EPS09NLO, is the best-constrained NLO nPDF set on the market. Collinear factorization is found to work very well in the kinematical region studied. With the error sets released in the EPS09 package one can compute how the nPDF-related uncertainties propagate into factorizable nuclear hard-process cross sections. A comparison with the other existing NLO nPDF sets is shown, and the BRAHMS forward-$\eta$ hadron data from d+Au collisions are discussed in the light of the EPS09 nPDFs and their error sets.
Why a scalar explanation of the L3 events is implausible
1993
We investigate the question of whether an additional light neutral scalar can explain the $l^+ l^- \gamma \gamma$ events with high invariant mass photon pairs recently observed by the L3 collaboration. We parameterize the low energy effects of the unknown dynamics in terms of higher dimensional effective operators. We show that operators which allow for the scalar to be produced and decay into photon pairs will allow other observable processes that should have been seen in current experiments.
Status of four-neutrino mass schemes: a global and unified approach to current neutrino oscillation data
2001
We present a unified global analysis of neutrino oscillation data within the framework of the four-neutrino mass schemes (3+1) and (2+2). We include all data from solar and atmospheric neutrino experiments, as well as information from short-baseline experiments including LSND. If we combine only solar and atmospheric neutrino data, (3+1) schemes are clearly preferred, whereas short-baseline data in combination with atmospheric data prefers (2+2) models. When combining all data in a global analysis the (3+1) mass scheme gives a slightly better fit than the (2+2) case, though all four-neutrino schemes are presently acceptable. The LSND result disfavors the three-active neutrino scenario with …
Muon capture by a proton in heavy baryon chiral perturbation theory
1997
The matrix element for muon capture by a proton is calculated to O(p^3) within heavy baryon chiral perturbation theory using the new O(p^3) Lagrangian of Ecker and Mojzis. External nucleon fields are renormalized using the appropriate definition of the wave function renormalization factor Z_N. Our expression for Z_N differs somewhat from that found in existing literature, but is the one which is consistent with the Lagrangian we use and the one which ensures, within our approach, the nonrenormalization of the vector coupling as required by the conserved vector current. Expressions for the standard muon capture form factors are derived and compared to experimental data and we determine three…
νd→μ−Δ++nreaction and axial vectorN−Δcoupling
1999
The reaction $\ensuremath{\nu}\stackrel{\ensuremath{\rightarrow}}{d}{\ensuremath{\mu}}^{\ensuremath{-}}{\ensuremath{\Delta}}^{++}n$ is studied in the region of low ${q}^{2}$ to investigate the effect of deuteron structure and width of the $\ensuremath{\Delta}$ resonance on the differential cross section. The results are used to extract the axial vector $N\ensuremath{-}\ensuremath{\Delta}$ coupling ${C}_{5}^{A}$ from the experimental data on this reaction. The possibility to determine this coupling from electroweak interaction experiments with high intensity electron accelerators is discussed.
New ways to search for right-handed current inB→ρℓν¯decay
2014
An interesting possibility to ease the tension between various determinations of $|{V}_{ub}|$ is to allow a small right-handed contribution to the standard model weak current. The present bounds on such a contribution are fairly weak. We propose new ways to search for such a beyond standard model contribution in semileptonic $B\ensuremath{\rightarrow}\ensuremath{\rho}\ensuremath{\ell}\overline{\ensuremath{\nu}}$ decay. Generalized asymmetries in one, two, or three angular variables are introduced as discriminators, which do not require an unbinned analysis of the fully differential distribution, and a detailed study of the corresponding theoretical uncertainties is performed. A discussion o…
CP properties of the leptonic sector for majorana neutrinos
1983
Abstract The leptonic sector of the electroweak theory is analyzed for massive Majorana neutrinos. For n generations, the Majorana mass lagrangian is diagonalized using the polar reduction to guarantee physical positive masses independently of the CP properties or the choice of the phases of the fields. When CP invariance holds, the CP eigenvalues of the definite mass neutrino fields are determined without commitment to a particular phase choice. For charged current interactions, we find that the observable CP violating phases can be parametrized a la Kobayashi-Maskawa for the vertec. Extra ( n − 1) relative phases of the massive neutrino fields are significant. The extra phases are observa…