arXiv subjects

V. Lubicz

Publications and source records attributed to V. Lubicz.

At least 73 records · Page 4Linked to original sources

arXiv2015

QED Corrections to Hadronic Processes in Lattice QCD

In this paper, for the first time a method is proposed to compute electromagnetic effects in hadronic processes using lattice simulations. The method can be applied, for example, to the leptonic and semileptonic decays of light or heavy pseudoscalar mesons. For these quantities the presence of infrared divergences in intermediate stages of the calculation makes the procedure much more complicated than is the case for the hadronic spectrum, for which calculations already exist. In order to compute the physical widths, diagrams with virtual photons must be combined with those corresponding to the emission of real photons. Only in this way do the infrared divergences cancel as first understood by Bloch and Nordsieck in 1937. We present a detailed analysis of the method for the leptonic decays of a pseudoscalar meson. The implementation of our method, although challenging, is within reach of the present lattice technology.

hep-lat↗

arXiv2014

Perturbative and non-perturbative renormalization results of the Chromomagnetic Operator on the Lattice

The Chromomagnetic operator (CMO) mixes with a large number of operators under renormalization. We identify which operators can mix with the CMO, at the quantum level. Even in dimensional regularization (DR), which has the simplest mixing pattern, the CMO mixes with a total of 9 other operators, forming a basis of dimension-five, Lorentz scalar operators with the same flavor content as the CMO. Among them, there are also gauge noninvariant operators; these are BRST invariant and vanish by the equations of motion, as required by renormalization theory. On the other hand using a lattice regularization further operators with $d \leq 5$ will mix; choosing the lattice action in a manner as to preserve certain discrete symmetries, a minimul set of 3 additional operators (all with $d<5$) will appear. In order to compute all relevant mixing coefficients, we calculate the quark-antiquark (2-pt) and the quark-antiquark-gluon (3-pt) Green's functions of the CMO at nonzero quark masses. These calculations were performed in the continuum (dimensional regularization) and on the lattice using the maximally twisted mass fermion action and the Symanzik improved gluon action. In parallel, non-perturbative measurements of the $K-π$ matrix element are being performed in simulations with 4 dynamical ($N_f = 2+1+1$) twisted mass fermions and the Iwasaki improved gluon action.

hep-lat↗

arXiv2014

K -> pi matrix elements of the chromagnetic operator on the lattice

We present preliminary results of the first lattice QCD calculation of the K -> pi matrix elements of the chromomagnetic operator O_{CM}=g sbar sigma_{munu} G_{munu} d, which appears in the effective Hamiltonian describing Delta S=1 transitions in and beyond the Standard Model. Having dimension 5, the chromomagnetic operator is characterized by a rich pattern of mixing with operators of equal and lower dimensionality. The multiplicative renormalization factor as well as the mixing coefficients with the operators of equal dimension have been computed at one-loop in perturbation theory. The power divergent coefficients controlling the mixing with operators of lower dimension have been computed non-perturbatively, by imposing suitable subtraction conditions. The numerical simulations have been carried out using the gauge field configurations produced by the European Twisted Mass Collaboration with N_f=2+1+1 dynamical quarks at three values of the lattice spacing. Our preliminary result for the B-parameter of the chromomagnetic operator is B_{CMO}=0.29(11), which can be compared with the estimate B_{CMO}~1-4 currently used in phenomenological analyses.

hep-lat↗

arXiv2014

Lattice QCD Study of $B$-meson Decay Constants from ETMC

We discuss a lattice QCD computation of the $B$-meson decay constants by the ETM collaboration where suitable ratios allow to reach the bottom quark sector by combining simulations around the charm-quark mass with an exactly known static limit. The different steps involved in this ratio method are discussed together with an account of the assessment of various systematic effects. A comparison of results from simulations with two and four flavour dynamical quarks is presented.

hep-lat↗

arXiv2014

Heavy flavour precision physics from Nf = 2 + 1 + 1 lattice simulations

We present precision lattice calculations of the pseudoscalar decay constants of the charmed sector as well as determinations of the bottom quark mass and its ratio to the charm quark mass. We employ Nf=2+1+1 dynamical quark gauge configurations generated by the European Twisted Mass Collaboration, using data at three values of the lattice spacing and pion masses as low as 210 MeV. Strange and charm sea quark masses are close to their physical values.

hep-lat↗

arXiv2014

Up, down, strange and charm quark masses with Nf = 2+1+1 twisted mass lattice QCD

We present a lattice QCD calculation of the up, down, strange and charm quark masses performed using the gauge configurations produced by the European Twisted Mass Collaboration with Nf = 2 + 1 + 1 dynamical quarks, which include in the sea, besides two light mass degenerate quarks, also the strange and charm quarks with masses close to their physical values. The simulations are based on a unitary setup for the two light quarks and on a mixed action approach for the strange and charm quarks. The analysis uses data at three values of the lattice spacing and pion masses in the range 210 - 450 MeV, allowing for accurate continuum limit and controlled chiral extrapolation. The quark mass renormalization is carried out non-perturbatively using the RI-MOM method. The results for the quark masses converted to the bar{MS} scheme are: mud(2 GeV) = 3.70(17) MeV, ms(2 GeV) = 99.6(4.3) MeV and mc(mc) = 1.348(46) GeV. We obtain also the quark mass ratios ms/mud = 26.66(32) and mc/ms = 11.62(16). By studying the mass splitting between the neutral and charged kaons and using available lattice results for the electromagnetic contributions, we evaluate mu/md = 0.470(56), leading to mu = 2.36(24) MeV and md = 5.03(26) MeV.

hep-lat↗

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↗

arXiv2014

The UTfit Collaboration Average of $D$ meson mixing data: Winter 2014

We update the analysis of $D$ meson mixing including the latest experimental results as of January 2014. We derive constraints on the parameters $M_{12}$, $Γ_{12}$ and $Φ_{12}$ that describe $D$ meson mixing using all available data, allowing for CP violation. We also provide posterior distributions for observable parameters appearing in $D$ physics.

hep-ph↗

arXiv2013

The chromomagnetic operator on the lattice

We study matrix elements of the "chromomagnetic" operator on the lattice. This operator is contained in the strangeness-changing effective Hamiltonian which describes electroweak effects in the Standard Model and beyond. Having dimension 5, the chromomagnetic operator is characterized by a rich pattern of mixing with other operators of equal and lower dimensionality, including also non gauge invariant quantities; it is thus quite a challenge to extract from lattice simulations a clear signal for the hadronic matrix elements of this operator. We compute all relevant mixing coefficients to one loop in lattice perturbation theory; this necessitates calculating both 2-point (quark-antiquark) and 3-point (gluon-quark-antiquark) Green's functions at nonzero quark masses. We use the twisted mass lattice formulation, with Symanzik improved gluon action. For a comprehensive presentation of our results, along with detailed explanations and a more complete list of references, we refer to our forthcoming publication [1].

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

Pseudoscalar decay constants $f_K/f_π$, $f_D$ and $f_{D_s}$ with $N_f = 2 + 1 + 1$ ETMC configurations

We present a lattice QCD calculation of the pseudoscalar decay constants $f_K$, $f_D$ and $f_{D_s}$ 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 $210$MeV. Our main results are: $f_{K^+}/f_{π^+}=1.183(17)$, $f_{K^+}=154.4(2.1)$MeV, $f_{D_s}=242.1(8.3)$MeV, $f_D=201.9(8.0)$MeV, $f_{D_s}/f_D=1.199(25)$ and $(f_{D_s}/f_D) / (f_K/f_π) = 1.005(15)$.

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↗

arXiv2013

Leading isospin breaking effects on the lattice

We present a method to evaluate on the lattice the leading isospin breaking effects due to both the small mass difference between the up and down quarks and the QED interaction. Our proposal is applicable in principle to any QCD+QED gauge invariant hadronic observable which can be computed on the lattice. It is based on the expansion of the path-integral in powers of the small parameters (m_d - m_u)/Lambda_{QCD} and alpha_{em}, where m_f is the renormalized quark mass and alpha_{em} the renormalized fine structure constant. In this paper we discuss in detail the general strategy of the method and the conventional, although arbitrary, separation of QCD from QED isospin breaking corrections. We obtain results for the pion mass splitting, M_{pi+}^2-M_{pi0}^2= 1.44(13)(16) x 10^3 MeV^2, for the Dashen's theorem breaking parameter epsilon_{gamma}= 0.79(18)(18), for the light quark masses, [m_d - m_u](MSbar,2 GeV)= 2.39(8)(17) MeV, [m_u / m_d](MSbar,2 GeV)= 0.50(2)(3) and for the flavour symmetry breaking parameters R and Q. We also update our previous results for the QCD isospin breaking corrections to the Kl2 decay rate and for the QCD contribution to the neutron-proton mass splitting.

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↗