arXiv subjects

Elvira Gamiz

Publications and source records attributed to Elvira Gamiz.

30 records · Page 2Linked to original sources

arXiv2005

Charged Kaon K^+ --> 3 pi CP Violating Asymmetries vs epsilon'_K / epsilon_K

We present the next-to-leading order full results in Chiral Perturbation Theory for the charged Kaon K --> 3 pi slope g CP violating asymmetries. We discuss the constraints that a measurement of these asymmetries would impose on the Standard Model results of epsilon_K' and search for new physics. We also study the kind of information that such measurement can provide on Im G_8, Im (e^2 G_E) and higher order weak couplings.

hep-ph↗

arXiv2005

One-loop matching of Delta S=2 four-quark operators with improved staggered fermions

We compute O(alpha_s) lattice-to-continuum perturbative matching coefficients for the Delta S=2 flavor changing four-quark operators for the Asqtad improved staggered action. In conjunction with lattice simulations with three flavors of light, dynamical quarks, our results yield an unquenched determination of B_K, the parameter that determines the amount of indirect CP violation in the neutral kaon system. Its value is an important input for the unitarity triangle analysis of weak decays.

hep-lat↗

arXiv2005

The B_K Kaon Parameter in the 1/N_c Expansion

We present work going on calculating the kaon B_K parameter in the 1/N_c expansion. The goal of this work is to analyze analytically in the presence of chiral corrections this phenomenologically very important parameter. We present the method used and preliminary results for the chiral limit value for which we get the invariant \hat B_K^χ=0.29 \pm 0.15. We also give some analytical indications of why the large N_c prediction of \hat B_K= 3/4 may have small 1/N_c corrections in the real case.

hep-ph↗

arXiv2004

Extraction of m_s and |V_us| from Hadronic Tau Decays

We review recent work to determine the strange quark mass m_s as well as the proposal to determine |V_{us}| using hadronic tau decay data. The recent update of the strange spectral function by OPAL and their moments of the invariant mass distribution are employed. Our results are |V_us|=0.2208 +- 0.0034 and m_s (2 GeV)=81 +- 22 MeV. Our result is already competitive to the standard extraction of |V_us| from K_e3 decays and to the new proposals to determine it. The error on V_us is dominated by experiment and will be eventually much improved by the B-factories hadronic tau data. Ultimately, a simultaneous fit of both m_s and |V_us| to a set of moments of the hadronic tau decays invariant mass distribution will provide one of the most accurate determinations of these Standard Model parameters.

hep-ph↗

arXiv2004

Charged Kaon K -> 3 pi CP Violating Asymmetries

First full next-to-leading order analytical results in Chiral Perturbation Theory for the charged Kaon K -> 3 pi slope g and decay rates CP-violating asymmetries are presented. We discuss the constraints that a measurement of these asymmetries would impose on the Standard Model calculations of epsilon_K' and the kind of information it can provide on Im G_8, Im (e^2 G_E) and higher order weak couplings.

hep-ph↗

arXiv2004

Kaon Physics: CP Violation and Hadronic Matrix Elements

In this Ph.D. Thesis we analyze some CP-violating observables in Kaon decays. In Chapters 1-3 we describe the framework in which this Thesis has been developed and establish the definitions and notation. In Chapter 4 we study CP-violating asymmetries in the decays of charged Kaons K\to 3π. The calculation of the ΔI=3/2 contribution to $ε_K'$ in the chiral limit, is reported in Chapter 6. In Chapter 7 we perform a calculation of the direct CP-violating parameter $ε_K'$ using some of the results obtained in the other chapters. We also develop a new approach that can be used to systematically determine hadronic matrix elements from the calculation of a set of Green's functions compatible with all the QCD and phenomenology constraints. This is described in Chapter 5. The first application of this approach -the calculation of the chiral corrections to \hat B_K- is also sketched in Chapter 5.

hep-ph↗

arXiv2003

Charged Kaon K \to 3 pi CP Violating Asymmetries at NLO in CHPT

We give the first full next-to-leading order analytical results in Chiral Perturbation Theory for the charged Kaon K \to 3 pi slope g and decay rates CP-violating asymmetries. We have included the dominant Final State Interactions at NLO analytically and discussed the importance of the unknown counterterms. We find that the uncertainty due to them is reasonable just for Δg_C, i.e. the asymmetry in the K^+ \to pi^+ pi^+ pi^- slope g; we get Δg_C = -(2.4 +- 1.2) 10^{-5}. The rest of the asymmetries are very sensitive to the unknown counterterms. In particular, the decay rate asymmetries can change even sign. One can use this large sentivity to get valuable information on those counterterms and on Im(G_8) coupling --very important for the CP-violating parameter epsilon'_K-- from the eventual measurement of these asymmetries. We also provide the one-loop O(e^2 p^2) electroweak octet contributions for the neutral and charged Kaon K \to 3 pi decays.

hep-ph↗

arXiv2003

Hadronic Matrix Elements for Kaons

We review some work done by us calculating matrix elements for Kaons. Emphasis is put on the matrix elements which are relevant to predict non-leptonic Kaon CP violating observables. In particular, we recall our results for the \hat B_K parameter which governs the \bar{K^0}-K^0 mixing and update our results for epsilon'_K including estimated all-higher-order CHPT corrections and the new results from recent analytical calculations of the ΔI=3/2 component. Some comments on future prospects on calculating matrix elements for Kaons are also added.

hep-ph↗

arXiv2003

CP-Violating Asymmetries in K^+ -> 3 pi in the Standard Model

We update the CP-violating asymmetries in K^+ -> 3 pi. In particular we study Delta g_C and Delta g_N -the asymmetries in the slope g. We emphasize its complementarity to the direct CP-violation parameter epsilon_K' and the large sensitivity to the size of the imaginary part of the octet coupling Im G_8 at lowest order in CHPT. We also give the prospects of a full calculation at next-to-leading order of this and other CP-violating asymmetries which will be presented elsewhere.

hep-ph↗

arXiv2003

QCD Short-distance Constraints and Hadronic Approximations

This paper discusses a general class of ladder resummation inspired hadronic approximations. It is found that this approach naturally reproduces many successes of single meson per channel saturation models (e.g. VMD) and NJL based models. In particular the existence of a constituent quark mass and a gap equation follows naturally. We construct an approximation that satisfies a large set of QCD short-distance and large $N_c$ constraints and reproduces many hadronic observables. We show how there exists in general a problem between QCD short-distance constraints for Green Functions and those for form factors and cross-sections following from the quark-counting rule. This problem while expected for Green functions that do not vanish in purely perturbative QCD also persists for many Green functions that are order parameters.

hep-ph↗

arXiv2002

Matching the Electroweak Penquins Q_7 and Q_8

We report on recent advances on the computation of the matrix elements of the electroweak penguins Q_7 and Q_8 which are relevant for the Delta I=3/2 contribution to epsilon'_K in the chiral limit. The matching of scale and scheme dependences between Wilson coefficients and these matrix elements is done analytically at NLO in alpha_S.

hep-ph↗

arXiv2001

Matching the Electroweak Penguins $Q_7$, $Q_8$ and Spectral Correlators

Exact analytical expressions for the $ΔS=1$ coupling $\im G_E$ in terms of observable spectral functions are given. This coupling determines the size of the $ΔI=3/2$ contribution to $ε'$. We show analytically how the scheme-dependence and scale dependences vanish to all orders in $1/N_c$ and NLO in $α_S$ explicitly both for $Q_7$ and $Q_8$. Numerical results are derived for both $Q_7$ and $Q_8$ from the $τ$-data and known results on the scalar spectral functions. In particular we study the effect of all higher dimension operators. The coefficients of the leading operators in the OPE of the needed correlators are derived to NLO in $α_S$.

hep-ph↗