118589904
Form factors for rare B decays: strategy, methodology, and numerical study
llare presentlyaround 10 percent [1]. So far, measurements are consistent with Standard Model expectations[2, 3]. Future experiments like LHCb are going to reduce the experimental uncertainties further.Thus, we are entering an era of precision ﬂavour physics, req uiring experimentalists and theoriststo focus on reducing statistical errors and employing multiple cross-checks to further quantifysystematic uncertainties.Lattice QCD can contribute to this by providing ﬁrst-principles nonperturbative calculationsof hadronic matrix elements relevant for rare B decays. In this report, we present our currentprogress in doing these computations. We use a non-relativistic effective action for the b quarkcalled moving NRQCD (mNRQCD) [4], which helps reduce discretisation errors in the ﬁnal statemeson at large recoil. This is achieved by giving the B meson a signiﬁcant velocity in the latticeframe, so that at a given q
37916668
Renormalization of bilinear quark operators for overlap fermions
We present nonperturbative renormalization constants of fermionic bilinears on the lattice in the quenched approximation at {beta}=6.1 using an overlap [H. Neuberger, Phys. Lett. B 417, 141 (1998)] fermion action with hypercubic (HYP)-blocked links. We consider the effects of the exact zero modes of the Dirac operator and find they are important in calculating the renormalization constants of the scalar and pseudoscalar density. The results are given in the RI' and MS schemes and compared to perturbative calculations.
16381056
Lattice QCD calculation of form factors describing the rare decays $B \to K^* \ell^+ \ell^-$ and $B_s \to \phi \ell^+ \ell^-$
The rare decays $B^0 \to K^{*0} \mu^+ \mu^-$ and $B_s \to \phi \mu^+ \mu^-$ are now being observed with enough precision to test Standard Model predictions. A full understanding of these decays requires accurate determinations of the corresponding hadronic form factors. Here we present results of lattice QCD calculations of the $B \to K^*$ and $B_s \to \phi$ form factors; we also determine the form factors relevant for the tree-level decays $B_s \to K^* \ell \nu$. We use full-QCD configurations including 2+1 flavors of sea quarks using an improved staggered action, and we employ lattice non-relativistic QCD to describe the bottom quark.
18642908
Moments of meson distribution functions with dynamical twisted mass fermions
We present our preliminary results on the lowest moment hxi of quark distribution functions of the pion using two flavor dynamical simulations with Wilson twisted mass fermions at maximal twist. The calculation is done in a range of pion masses from 300 to 500 MeV. A stochastic source method is used to reduce inversions in calculating propagators. Finite volume effects at the lowest quark mass are examined by using two different lattice volumes. Our results show that we achieve statistical errors of only a few percent. We plan to compute renormalization constants non-perturbatively and extend the calculation to two more lattice spacings and to the nucleons.
118450238
Oscillatory behavior of the domain wall fermions revisited
In the generic domain wall fermion formulation of chiral fermions on the lattice, the zero modes of the four-dimensional Wilson fermion operator with the negative mass parameter -M-5 introduce unphysical massive modes propagating in the four-dimensional spacetime. In the free fermion case, the pole mass of this kind of unphysical modes is given by (E) over bar = ln(1-M-5), which acquires an imaginary part, i pi, when M-5 > 1 and results in an oscillatory behavior of the domain wall fermion propagator in time. The existence of the unphysical modes in the presence of gauge fields is investigated in the mean field approximation, and their physical consequences are discussed. In addition, we also give a semiquantitative criterion for tuning M-5 in the realistic numerical study.
118634793
Lattice study on $\eta_{c2}$ and X(3872)
Properties of 2(-+) charmonium eta(c2) are investigated in quenched lattice QCD. The mass of eta(c2) is determined to be 3.80(3) GeV, which is close to the mass of D-wave charmonium psi(3770) and in agreement with quark model predictions. The transition width of eta(c2) -> gamma J/psi is also obtained with a value of Gamma = 3.8(9) keV. Since the possible 2(-+) assignment to X(3872) has not been ruled out by experiments, our results help to clarify the nature of X(3872). DOI: 10.1103/PhysRevD.87.014501
125575431
Measurement of the branching ratios for J / psi --> gamma pi0, gamma eta, gamma eta' --> 3gamma on the BES
85538672
Study of kaon decay to two pions
The weak decay of the kaon to two pions is studied within the model of Nambu and Jona-Lasinio. Using the standard effectiveweak Hamiltonian, both the decay amplitude arising from an intermediate state σ meson and the direct decay amplitude are calculated. The effect of final state interactions is also included. When the matching scale is chosen such that the decay amplitude with isospin I ¼ 2 is close to its experimental value, our model including the σ meson contributes up to 80% of the total I ¼ 0 amplitude. This supports recent suggestions that the σ meson should play a vital role in explaining the ΔI ¼ 1=2 rule in this system.
7825870
Study of inclusive strange-baryon production and search for pentaquarks in two-photon collisions at LEP
Measurements of inclusive production of the Λ, Ξ- and Ξ*(1530) baryons in two-photon collisions with the L3 detector at LEP are presented. The inclusive differential cross sections for Λ and Ξ- are measured as a function of the baryon transverse momentum, pt, and pseudo-rapidity, η. The mean number of Λ, Ξ- and Ξ*(1530) baryons per hadronic two-photon event is determined in the kinematic range 0.4 GeV<pt<2.5 GeV, |η|<1.2. Overall agreement with the theoretical models and Monte Carlo predictions is observed. A search for inclusive production of the pentaquark θ+(1540) in two-photon collisions through the decay θ+→pK0S is also presented. No evidence for production of this state is found.
119534738
Measurement of the Photon Structure Function at High Q 2 at LEP
The structure functions of real and virtual photons are derivedfrom cross section measurements of the reaction$\rm e^+e^-\rightarrow e^+e^- + \hbox{hadrons}$ at LEP.The reaction is studied at $\sqrt{\rm {s}} \simeq 91$ GeV with the L3detector. One of the final state electrons is detected at a large angle relative to the beam direction, leading to $Q^2$ values between40 GeV$^2$ and 500 GeV$^2$.The other final state electron is either undetected or it is detected ata four-momentum transfer squared $P^2$ between 1 GeV$^2$ and 8 GeV$^2$.These measurements are compared with predictions of the Quark PartonModel and other QCD based models.
119254848
Low Mass Neutralino Dark Matter in the MSSM with Constraints from $B_s\to \mu^+\mu^-$ and Higgs Search Limits
An analysis of spin independent neutralino-proton cross sections ${\ensuremath{\sigma}}_{\mathrm{SI}}(\ensuremath{\chi}p)$ that includes this low mass region is given. The analysis is done in minimal supersymmetric standard model (MSSM) with radiative electroweak symmetry breaking (REWSB). It is found that cross sections as large as ${10}^{\ensuremath{-}40}\text{ }\text{ }{\mathrm{cm}}^{2}$ can be accommodated in MSSM within the REWSB framework. However, inclusion of sparticle mass limits from current experiments, as well as lower limits on the Higgs searches from the Tevatron, and the current experimental upper limit on ${B}_{s}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ significantly limit the allowed parameter space reducing ${\ensuremath{\sigma}}_{\mathrm{SI}}(\ensuremath{\chi}p)$ to lie below $\ensuremath{\sim}{10}^{\ensuremath{-}41}\text{ }\text{ }{\mathrm{cm}}^{2}$ or even lower for neutralino masses around 10 GeV. These cross sections are an order of magnitude lower than the cross sections needed to explain the reported data in the recent dark matter experiments in the low neutralino mass region.