Neutral kaon mixing beyond the standard model withnf=2+1chiral fermions

Abstract

General rightsCopyright for the publications made accessible via the Edinburgh Research Explorer is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights. Take down policyThe University of Edinburgh has made every reasonable effort to ensure that Edinburgh Research Explorer content complies with UK legislation. If you believe that the public display of this file breaches copyright please contact openaccess@ed.ac.uk providing details, and we will remove access to the work immediately and investigate your claim. We compute the hadronic matrix elements of the four-quark operators needed for the study of K 0 À " K 0 mixing beyond the Standard Model (SM). We use n f ¼ 2 þ 1 flavors of domain-wall fermion that exhibit good chiral-flavor symmetry. The renormalization is performed nonperturbatively through the RI-MOM scheme and our results are converted perturbatively to MS. The computation is performed on a single lattice spacing a $ 0:086 with a lightest unitary pion mass of 290 MeV. The various systematic errors, including the discretization effects, are estimated and discussed. Our results confirm a previous quenched study, where large ratios of non-SM to SM matrix elements were obtained.

Neutral Kaon mixing beyond the Standard Model

“…This prescription has good chiral symmetry properties and leading O(a 2 ) scaling. We extend our previous work [3] by adding a second lattice spacing to quantify discretisation effects and by using both exceptional and non-exceptional kinematics for our intermediate renormalisation schemes.…”

“…Their results are shown in Tab.1. There is some tension between these measurements; our previous work [3] used a single lattice spacing, n f = 2 + 1 flavours and renormalised the operators non-perturbatively using the intermediate, exceptional, RI-MOM scheme. The works [4,5] also used the RI-MOM scheme, have n f = 2 and n f = 2 + 1 + 1 flavours respectively and performed an a 2 → 0 extrapolation.…”

“…B 5 RBC-UKQCD [3] 0.53(2) 0.43(5) 0.75(9) 0.69(7) 0.47 (6) ETM [4] 0.51(2) 0.47(2) 0.78(4) 0.75(3) 0.60(3) ETM [5] 0.51(2) 0.46(3) 0.79(5) 0.78(5) 0.49(4) SWME [6] 0.52(2) 0.53(2) 0.77(6) 0.98(6) 0.75(8) Recently, several groups have measured a dimensionless prescription of these BSM operators (their bag parameters) in modern, dynamical fermion simulations. Their results are shown in Tab.1.…”

Calculation of BSM Kaon B-parameters using improved staggered quarks in N_f = 2+1 QCD.

“…In this talk we present an update on our previous results for the BSM B-parameters [1,2], and compare to those from other collaborations using different fermion discretizations [3,4].…”

Fierz transformations and renormalization schemes for fourquark operators

“…Beyond the quenched approximation, these quantities have been computed by RBC-UKQCD, [1,2], by ETM [3,4] and by SWME [5,6]. The renormalisation factors have also been studied by Alpha [7].…”