ArcAdiA

A proposal for B-physics on current lattices

2010-04-11T22:00:00Z

A proposal for B-physics on current lattices Blossier, Benoit; Dimopoulos, Petros; Frezzotti, Roberto; Herdoiza, Gregorio; Jansen, Karl; Lubicz, Vittorio; Martinelli, Guido; Michael, Chris; Rossi, Giancarlo; Shindler, Andrea; Simula, Silvano; Tarantino, Cecilia; Urbach, Carsten 2010-04-12 JHEP 2010 1-25 A method to extract B-physics parameters (b-quark mass and fB, fBs decay constants) from currently available lattice data is presented and tested. The approach is based on the idea of constructing appropriate ratios of heavy-light meson masses and decay constants, respectively, possessing a precisely known static limit, and evaluating them at various pairs of heavy quark masses around the charm. Via a smooth interpolation in the heavy quark mass from the easily accessible charm region to the asymptotic point, B-physics parameters are computed with a few percent (statistical + systematic) error using recently produced Nf = 2 maximally twisted Wilson fermions data.

An improved Standard Model prediction of BR(B →τν) and its implicationsfor New Physics

2010-02-24T23:00:00Z

An improved Standard Model prediction of BR(B →τν) and its implicationsfor New Physics Bona, Marcella; Ciuchini, Marco; Franco, Enrico; Lubicz, Vittorio; Martinelli, Guido; Parodi, Fabrizio; Pierini, Maurizio; Schiavi, Carlo; Silvestrini, Luca; Sordini, Viola; Stocchi, Achille; Tarantino, Cecilia; Vagnoni, Vincenzo 2010-02-25 Physics Letters B 687 61-69 The recently measured B →τν branching ratio allows to test the Standard Model by probing virtual effects of new heavy particles, such as a charged Higgs boson. The accuracy of the test is currently limited by the experimental error on BR(B → τν) and by the uncertainty on the parameters f B and |Vub|. The redundancy of the Unitarity Triangle fit allows to reduce the error on these parameters and thus to perform a more precise test of the Standard Model. Using the current experimental inputs, we obtain BR(B →τν)SM = (0.84±0.11)×10−4, to be compared with BR(B →τν)exp = (1.73±0.34)×10−4. The Standard Model prediction can be modified by New Physics effects in the decay amplitude as well as in the Unitarity Triangle fit. We discuss how to disentangle the two possible contributions in the case of minimal flavour violation at large tan β and generic loop-mediated New Physics. We also consider two specific models with minimal flavour violation: the Type-II Two Higgs Doublet Model and the Minimal Supersymmetric Standard Model.

FCNC processes in the Littlest Higgs model with T-parity: an update

2010-02-28T23:00:00Z

FCNC processes in the Littlest Higgs model with T-parity: an update Blanke, Monika; Buras, Andrzej J.; Duling, Bjoern; Recksiegel, Stefan; Tarantino, Cecilia 2010-03 Acta Physica Polonica B 41 657-683 We update our 2006–2007 results for FCNC processes in the Littlest Higgs model with T-parity (LHT). The removal of the logarithmic UV cutoff dependence in our previous results through a new contribution to the Z0-penguin diagrams identified by Goto et al. and del Aguila et al., while making the deviations from the SM expectations in the quark sector less spectacular, still allows for sizable new physics effects in K ! and KL ! 0`+`􀀀 decays and in the CP-asymmetry S with the latter unaffected by the new contribution. We extend our analysis by a study of the fine-tuning required to fit the data on "K and by the inclusion of the decay KL ! + 􀀀. A number of correlations can distinguish this model from the custodially protected Randall–Sundrum model analysed recently. We also reconsider lepton flavour violating decays, including now a discussion of fine-tuning. While the `i ! `j decays are unaffected by the removal of the logarithmic cutoff dependence, the branching ratios for decays with three leptons in the final state, like ! 3e are lowered by almost an order of magnitude. In spite of this, the pattern of lepton flavour violation in the LHT model can still be distinguished from the one in supersymmetric models.

fB and fBs with maximally twisted Wilson fermions

2009-12-31T23:00:00Z

fB and fBs with maximally twisted Wilson fermions Blossier, Benoit; Dimopoulos, Petros; Frezzotti, Roberto; Herdoiza, Gregorio; Jansen, Karl; Lubicz, Vittorio; Martinelli, Guido; Michael, Chris; Rossi, Giancarlo; Sanfilippo, Francesco; Shindler, Andrea; Simula, Silvano; Tarantino, Cecilia; Urbach, Carsten; Wagner, Marc 2010 151-158 We present a lattice QCD calculation of the heavy-light decay constants fB and fBs performed with Nf = 2 maximally twisted Wilson fermions, at four values of the lattice spacing. The decay constants have been also computed in the static limit and the results are used to interpolate the observables between the charmand the infinite-mass sectors, thus obtaining the value of the decay constants at the physical b quark mass. Our preliminary results are fB = 191(14)MeV, fBs = 243(14)MeV, fBs/ fB = 1.27(5). They are in good agreement with those obtained with a novel approach, recently proposed by our Collaboration (ETMC), based on the use of suitable ratios having an exactly known static limit.

Status of the Unitarity Triangle Analysis

2008-12-31T23:00:00Z

Status of the Unitarity Triangle Analysis Bona, Marcella; Ciuchini, Marco; Franco, Enrico; Lubicz, Vittorio; Martinelli, Guido; Parodi, Fabrizio; Pierini, Maurizio; Schiavi, Carlo; Silvestrini, Luca; Sordini, Viola; Stocchi, Achille; Tarantino, Cecilia; Vagnoni, Vincenzo 2009 160-163 We present an update of the Unitarity Triangle (UT) analysis, within the Standard Model (SM) and beyond. Within the SM the main novelties are the inclusion in eK of the contributions of x and fe 6= p /4 pointed out by A. J. Buras and D. Guadagnoli, and an accurate prediction of BR(B→tn), by using the indirect determination of |Vub| from the UT fit, which can be compared to the present experimental result. In the generalization of the UT analysis to investigate New Physics (NP) effects, the estimate of x is more delicate and only the effect of fe 6= p /4 has been included. We confirm an hint of NP in the Bs-¯Bs mixing at the 2.9s level, which makes a comparison with new experimental data certainly desired.

Update of the Unitarity Triangle Analysis

2009-08-14T22:00:00Z

Update of the Unitarity Triangle Analysis Tarantino, Cecilia 2009-08-15 NUCLEAR PHYSICS A 827 439C-444C We present the update of the Unitarity Triangle (UT) analysis withinthe Standard Model (SM) and beyond. Within the SM, combining the directmeasurements on sides and angles, the UT turns out to beoverconstrained in a consistent way, showing that the CKM matrix is thedominant source of flavour mixing and CP-violation and that New Physics(NP) effects can appear at most as small corrections to the CKMpicture. Generalizing the UT analysis to investigate NP effects,constraints on b -> s transitions are also included and both CKM and NPparameters are fitted simultaneously. While no evidence of NP effectsis found in K-(K) over bar and B-d-(B) over bar (d) mixing, in theB-s-(B) over bar (s) mixing an hint of NP is found at the 2.9 sigma,level. The UT analysis beyond the SM also allows us to derive bounds onthe coefficients of the most general Delta F = 2 effective Hamiltonian,that can be translated into bounds on the NP scale.

FCNC Processes in the LHT Model: a 2009 Look

2008-12-31T23:00:00Z

FCNC Processes in the LHT Model: a 2009 Look Tarantino, Cecilia 2009 185-188 We present a summary of our recent analysis update of flavour changing neutral current (FCNC) processes in the Littlest Higgs model with T-parity (LHT). The essential novelties of our update are: the removal of the logarithmicUV cutoff dependence by the inclusion of the new contribution to the Z0-penguin diagrams identified by Goto et al. and by del Aguila et al., the study of the decay KL →m+m−, a discussion of fine-tuning in eK and Br(m →eg ).

Vector and scalar form factors for K- and D-mesonsemileptonic decays from twisted mass fermionswith Nf = 2

2008-12-31T23:00:00Z

Vector and scalar form factors for K- and D-mesonsemileptonic decays from twisted mass fermionswith Nf = 2 Di Vita, Stefano; Haas, Benjamin; Lubicz, Vittorio; Mescia, Federico; Simula, Silvano; Tarantino, Cecilia 2009 257-264 We present lattice results for the formfactors relevant in the K→p ℓnℓ and D→p ℓnℓ semileptonic decays, obtained from simulations with two flavors of dynamical twisted-mass fermions and pion masses as light as 260 MeV. For K →p ℓn decays we discuss the estimates of the main sources of systematic uncertainties, including the quenching of the strange quark, leading to our final result f+(0) = 0.9560(57)stat.(62)syst.. Combined with the latest experimental data, our value of f+(0) implies for the CKMmatrix element |Vus| the value 0.2267(5)exp.(20) f+(0) consistent with the first-row CKM unitarity. For D →p ℓnℓ decays the application of Heavy Meson Chiral Perturbation Theory allows to extrapolate our results for both the scalar and the vector form factors at the physical point with quite good accuracy, obtaining a nice agreement with the experimental data. In particular at zero-momentumtransfer we obtain f+(0) = 0.64(5). A preliminary analysis of the discretization effects is presented and discussed.

K ->pi l nu semileptonic form factors from two-flavor lattice QCD

2009-11-30T23:00:00Z

K ->pi l nu semileptonic form factors from two-flavor lattice QCD Lubicz, Vittorio; Mescia, Federico; Simula, Silvano; Tarantino, Cecilia 2009-12 Physical review D 80 111502 We present new lattice results of the K ->pi l nu semileptonic formfactors obtained from simulations with two flavors of dynamicaltwisted-mass fermions, using pion masses as light as 260 MeV. Our mainresult is f(+)(0)=0.9560(84), which, combined with the latestexperimental data for K-l3 decays, leads to|V-us|=0.2267(5)(exp)(20)(f+)(0). Using the PDG(2008) determinations of|V-ud| and |V-ub| our result implies for the unitarity relation|V-ud|(2)+|V-us|(2)+|V-ub|(2)=1.0004(15). For the O(p(6)) term of thechiral expansion of f(+)(0) we get Delta f equivalent tof(+)(0)-1-f(2)=-0.0214(84).

K ->pi l nu semileptonic form factors from two-flavor lattice QCD

2009-12-29T23:00:00Z

K ->pi l nu semileptonic form factors from two-flavor lattice QCD Lubicz, Vittorio; Mescia, Federico; Simula, Silvano; Tarantino, Cecilia 2009-12-30 Physical Review D 80 111502 We present new lattice results of the K ->pi l nu semileptonic form factors obtained from simulations with two flavors of dynamicaltwisted-mass fermions, using pion masses as light as 260 MeV. Our main result is f(+)(0)=0.9560(84), which, combined with the latest experimental data for Kl3 decays, leads to |Vus|=0.2267(5)(exp)(20)(f+(0)). Using the PDG(2008) determinations of|Vud| and |Vub| our result implies for the unitarity relation |Vud|^2+|Vus|^2+|Vub|^2=1.0004(15). For the O(p^6) term of the chiral expansion of f+(0) we get Delta f = f+(0)-1-f2=-0.0214(84).

Pseudoscalar decay constants of kaon and D-mesons from Nf=2 twisted mass Lattice QCD

2009-06-30T22:00:00Z

Pseudoscalar decay constants of kaon and D-mesons from Nf=2 twisted mass Lattice QCD ETM, Collaboration; Blossier, Benoit; Dimopoulos, Petros; Frezzotti, Roberto; Haas, Benjamin; Herdoiza, Gregorio; Jansen, Karl; Lubicz, Vittorio; Mescia, Federico; Palao, David; Shindler, Andrea; Simula, Silvano; Tarantino, Cecilia; Urbach, Carsten 2009-07 Journal of High Energy Physics 07 043 We present the results of a lattice QCD calculation of the pseudoscalar meson decay constants fπ, fK, fD and fDs, performed with Nf=2 dynamical fermions. The simulation is carried out with the tree-level improved Symanzik gauge action and with the twisted mass fermionic action at maximal twist. We have considered for the final analysis three values of the lattice spacing, a = 0.10 fm, 0.09 fm and 0.07 fm, with pion masses down to mπ = 270 MeV. Our results for the light meson decay constants are fK = 158.1(2.4) MeV and fK/fπ = 1.210(18). From the latter ratio, by using the experimental determination of Γ(K → μbar nuμ(γ))/Γ(π → μbar nuμ(γ)) and the average value of |Vud| from nuclear beta decays, we obtain |Vus| = 0.2222(34), in good agreement with the determination from semileptonic Kl3 decays and the unitarity constraint. For the D and Ds meson decay constants we obtain fD = 197(9) MeV, fDs = 244(8) MeV and fDs/fD = 1.24(3). Our result for fD is in good agreement with the CLEO experimental measurement. For fDs our determination is smaller than the PDG 2008 experimental average but in agreement with a recent improved measurement by CLEO at the 1.4 σ level.

f_B and f_Bs with maximally twisted Wilson fermions

2008-12-31T23:00:00Z

f_B and f_Bs with maximally twisted Wilson fermions ETM Collaboration; Blossier, Benoit; Dimopoulos, Petros; Frezzotti, Roberto; Herdoiza, Gregorio; Jansen, Karl; Lubicz, Vittorio; Martinelli, Guido; Michael, Chris; Rossi, Giancarlo; Sanfilippo, Francesco; Shindler, Andrea; Simula, Silvano; Tarantino, Cecilia; Urbach, Carsten; Wagner, Marc 2009 151 We present a lattice QCD calculation of the heavy-light decay constants f_B and f_Bs performed with Nf=2 maximally twisted Wilson fermions, at four values of the lattice spacing. The decay constants have been also computed in the static limit and the results are used to interpolate the observables between the charm and the infinite-mass sectors, thus obtaining the value of the decay constants at the physical b quark mass. Our preliminary results are f_B=191(14) MeV, f_Bs=243(14) MeV, f_Bs/f_B=1.27(5). They are in good agreement with those obtained with a novel approach, recently proposed by our Collaboration (ETMC), based on the use of suitable ratios having an exactly known static limit.

Pseudoscalar decay constants of kaon and D-mesons from N-f=2 twisted mass Lattice QCD

2009-06-30T22:00:00Z

Pseudoscalar decay constants of kaon and D-mesons from N-f=2 twisted mass Lattice QCD Blossier, Benoît; Dimopoulos, Pedro; Frezzotti, Roberto; Haas, Benjamin; Herdoiza, Gregorio; Jansen, Karl; Lubicz, Vittorio; Mescia, Federico; Palao, David; Shindler, Andrea; Simula, Silvano; Tarantino, Cecilia; Urbach, Carsten; Wenger, Urs 2009-07 Journal of high energy physics 2009 043 We present the results of a lattice QCD calculation of the pseudoscalar meson decay constants f(pi), f(K), f(D) and f(Ds), performed with N-f =2 dynamical fermions. The simulation is carried out with the tree-level improved Symanzik gauge action and with the twisted mass fermionic action at maximal twist. We have considered for the final analysis three values of the lattice spacing, a similar or equal to 0.10 fm, 0.09 fm and 0.07 fm, with pion masses down to m(pi) similar or equal to 270 MeV. Our results for the light meson decay constants are f(K) =158.1(2.4) MeV and f(K)/f(pi) = 1.210(18). From the latter ratio, by using the experimental determination of Gamma(K -> munu(mu)(gamma))/Gamma(pi -> mu nu(mu)(gamma)) and the average value of vertical bar V-ud vertical bar from nuclear beta decays, we obtain vertical bar V-us vertical bar = 0.2222(34), in good agreement with the determination from semileptonic K-13 decays and the unitarity constraint. For the D and D-s meson decay constants we obtain f(D) =197(9) MeV, f(Ds) = 244(8) MeV and f(Ds)/f(D) = 1.24(3). Our result for f(D) is in good agreement with the CLEO experimental measurement. For f(Ds) our determination is smaller than the PDG 2008 experimental average but in agreement with a recent improved measurement by CLEO at the 1.4 sigma level.