arXiv subjects

N. Carrasco

Publications and source records attributed to N. Carrasco.

30 records · Page 2Linked to original sources

arXiv2014

D-Dbar Mixing in the Standard Model and Beyond from Nf=2 Twisted Mass QCD

We present the first unquenched lattice QCD results for the bag parameters controlling the short distance contribution to D meson oscillations in the Standard Model and beyond. We have used the gauge configurations produced by the European Twisted Mass Collaboration with Nf = 2 dynamical quarks, at four lattice spacings and light meson masses in the range 280-500 MeV. Renormalization is carried out non-perturbatively with the RI-MOM method. The bag-parameter results have been used to constrain New Physics effects in D-Dbar mixing, to put a lower bound to the generic New Physics scale and to constrain off-diagonal squark mass terms for TeV-scale Supersymmetry.

hep-lat↗

arXiv2014

B-physics from Nf=2 tmQCD: the Standard Model and beyond

We present a lattice QCD computation of the b-quark mass, the B and B_s decay constants, the B-mixing bag parameters for the full four-fermion operator basis as well as determinations for ξand f_{Bq}\sqrt{B_i^{(q)}} extrapolated to the continuum limit and to the physical pion mass. We used N_f = 2 twisted mass Wilson fermions at four values of the lattice spacing with pion masses ranging from 280 to 500 MeV. Extrapolation in the heavy quark mass from the charm to the bottom quark region has been carried out on ratios of physical quantities computed at nearby quark masses, exploiting the fact that they have an exactly known infinite mass limit. Our results are m_b(m_b, \overline{\rm{MS}})=4.29(12) GeV, f_{Bs}=228(8) MeV, f_{B}=189(8) MeV and f_{Bs}/f_B=1.206(24). Moreover with our results for the bag-parameters we find ξ=1.225(31), B_1^{(s)}/B_1^{(d)}=1.01(2), f_{Bd}\sqrt{\hat{B}_{1}^{(d)}} = 216(10) MeV and f_{Bs}\sqrt{\hat{B}_{1}^{(s)}} = 262(10) MeV. We also computed the bag parameters for the complete basis of the four-fermion operators which are required in beyond the SM theories. By using these results for the bag parameters we are able to provide a refined Unitarity Triangle analysis in the presence of New Physics, improving the bounds coming from B_{(s)}-\bar B_{(s)} mixing.

hep-lat↗

arXiv2013

A first look at maximally twisted mass lattice QCD calculations at the physical point

In this contribution, a first look at simulations using maximally twisted mass Wilson fermions at the physical point is presented. A lattice action including clover and twisted mass terms is presented and the Monte Carlo histories of one run with two mass-degenerate flavours at a single lattice spacing are shown. Measurements from the light and heavy-light pseudoscalar sectors are compared to previous $N_f = 2$ results and their phenomenological values. Finally, the strategy for extending simulations to $N_f = 2 + 1 + 1$ is outlined.

hep-lat↗

arXiv2013

A determination of the average up-down, strange and charm quark masses from $N_f=2+1+1$

We present a lattice QCD determination of the average up-down, strange and charm quark masses based on simulations performed by the European Twisted Mass Collaboration with $N_f = 2 + 1 + 1$ dynamical fermions. We simulated at three different values of the lattice spacing, the smallest being approximately $0.06fm$, and with pion masses as small as $210 \text{MeV}$. Our results are: $m_{ud}(2\text{GeV})=3.70(17)\text{MeV}$, $m_s(2\text{GeV})=99.2(3.9)\text{MeV}$, $m_c(m_c)=1.350(49)\text{GeV}$, $m_s/m_{ud}=26.64(30)$ and $m_c/m_s=11.65(12)$.

hep-lat↗

arXiv2013

A $N_f = 2 + 1 + 1$ "twisted" determination of the $b$-quark mass, $f_{B}$ and $f_{B_s}$

We present a lattice QCD determination of the $b$-quark mass and of the $f_{B_s}$ and $f_B$ decay constants performed with $N_f = 2 + 1 + 1$ twisted mass Wilson fermions. We have used simulations at three values of the lattice spacing generated by ETMC with pion masses ranging from 210 to 440 MeV. To obtain physical quantities we performed a combined chiral and continuum limit and an extrapolation in the heavy quark mass from the charm to the $b$-quark region using suitable ratios calculated at nearby heavy-quark masses having an exactly known static limit. Our results are: $m_b(m_b) = 4.29 (13)$ GeV, $f_B = 196 (9)$ MeV, $f_{B_s} = 235 (9)$ MeV, $f_{B_s} / f_B = 1.201 (25)$, $(f_{B_s}/f_B)/(f_K/f_π) = 1.007 (16)$ and $(f_{B_s}/f_B)/(f_{D_s}/f_D) = 1.008 (13)$.

hep-lat↗

arXiv2013

B-physics computations from Nf=2 tmQCD

We present an accurate lattice QCD computation of the b-quark mass, the B and Bs decay constants, the B-mixing bag-parameters for the full four-fermion operator basis, as well as estimates for ξand f_{Bq}\sqrt{B_q} extrapolated to the continuum limit and the physical pion mass. We have used Nf = 2 dynamical quark gauge configurations at four values of the lattice spacing generated by ETMC. Extrapolation in the heavy quark mass from the charm to the bottom quark region has been carried out using ratios of physical quantities computed at nearby quark masses, having an exactly known infinite mass limit.

hep-lat↗

arXiv2013

Kaon Mixing Beyond the SM from Nf=2 tmQCD and model independent constraints from the UTA

We present the first unquenched, continuum limit, lattice QCD results for the matrix elements of the operators describing neutral kaon oscillations in extensions of the Standard Model. Owing to the accuracy of our calculation on ΔS=2 weak Hamiltonian matrix elements, we are able to provide a refined Unitarity Triangle analysis improving the bounds coming from model independent constraints on New Physics. In our non-perturbative computation we use a combination of Nf=2 maximally twisted sea quarks and Osterwalder-Seiler valence quarks in order to achieve both O(a)-improvement and continuum-like renormalization properties for the relevant four-fermion operators. The calculation of the renormalization constants has been performed non-perturbatively in the RI-MOM scheme. Based on simulations at four values of the lattice spacing and a number of quark masses we have extrapolated/interpolated our results to the continuum limit and physical light/strange quark masses.

hep-lat↗

arXiv2012

B-physics from lattice QCD...with a twist

We present a precise lattice QCD determination of the b-quark mass, of the B and Bs decay constants and first results for the B-meson bag parameters. For our computation we employ the so-called ratio method and our results benefit from the use of improved interpolating operators for the B-mesons. QCD calculations are performed with Nf = 2 dynamical light-quarks at four values of the lattice spacing and the results are extrapolated to the continuum limit. The preliminary results are mb(mb) = 4.35(12) GeV for the MSbar b-quark mass, fBs = 234(6) MeV and fB = 197(10) MeV for the B-meson decay constants, BBs(mb) = 0.90(5) and BB(mb) = 0.87(5) for the B-meson bag parameters.

hep-ph↗

arXiv2012

Neutral meson oscillations in the Standard Model and beyond from Nf=2 Twisted Mass Lattice QCD

We present the ETMC results for the bag parameters describing the neutral kaon mixing in the Standard Model and beyond and preliminary results for the bag parameters controlling the short distance contributions in the D^0-\bar{D}^0 oscillations. We also present preliminary results for the B_{Bd}, B_{Bs}, B_{Bs}/B_{Bd} and ξ-parameter controlling B^0_-\bar{B}^0 oscillations in the Standard Model employing the so-called ratio method. Using Nf=2 maximally twisted sea quarks and Osterwalder-Seiler valence quarks we achieve both O(a)-improvement and continuum like renormalization pattern. Simulations are performed at three-values of the lattice spacing and several values of quark masses in the light, strange, charm region and above charm up to ~2.5m_c. Our results are extrapolated to the continuum limit and extrapolated/interpolated to the physical quark masses.

hep-lat↗

arXiv2012

B-physics from the ratio method with Wilson twisted mass fermions

We present a precise lattice QCD determination of the b-quark mass, of the B and Bs decay constants and first preliminary results for the B-mesons bag parameter. Simulations are performed with Nf = 2 Wilson twisted mass fermions at four values of the lattice spacing and the results are extrapolated to the continuum limit. Our calculation benefits from the use of improved interpolating operators for the B-mesons and employs the so-called ratio method. The latter allows a controlled interpolation at the b-quark mass between the relativistic data around and above the charm quark mass and the exactly known static limit.

hep-lat↗

arXiv2011

Renormalisation constants of quark bilinears in lattice QCD with four dynamical Wilson quarks

We present preliminary results of the non-perturbative computation of the RI-MOM renormalisation constants in a mass-independent scheme for the action with Iwasaki glue and four dynamical Wilson quarks employed by ETMC. Our project requires dedicated gauge ensembles with four degenerate sea quark flavours at three lattice spacings and at several values of the standard and twisted quark mass parameters. The RI-MOM renormalisation constants are obtained from appropriate O(a) improved estimators extrapolated to the chiral limit.

hep-lat↗

arXiv2011

K^0-\bar{K}^0 mixing in the Standard Model from Nf=2+1+1 Twisted Mass Lattice QCD

We present preliminary results at β = 1.95 (a = 0.077 fm) on the first unquenched N_f=2+1+1 lattice computation of the B_K parameter which controls the neutral kaon oscillations in the Standard Model. Using N_f=2+1+1 maximally twisted sea quarks and Osterwalder-Seiler valence quarks we achieve O(a) improvement and a continuum-like renormalization pattern for the four-fermion operator. Our results are extrapolated/interpolated to the physical light/strange quark mass but not yet to the continuum limit. The computation of the relevant renormalization constants is performed non perturbatively in the RI'-MOM scheme using dedicated simulations with N_f=4 degenerate sea quark flavours produced by the ETM collaboration. We get B_K^{RGI} (a = 0.077) = 0.747(18), which when compared to our previous unquenched N_f=2 determination and most of the existing results, suggests a rather weak B_K^{RGI} dependence on the number of dynamical flavours. We are at the moment analysing lattice data at two additional β values which will allow us to perform an extrapolation to the continuum limit.

hep-lat↗