118437820
Meson Mass Decomposition
Center for High Energy Physics, Peking University, Beijing 100871, ChinaHadron masses can be decomposed as a sum of components which are deﬁned through hadronicmatrix elements of QCD operators. The components consist of the quark mass term, the quarkenergy term, the glue energy term and the trace anomaly term. We calculate these components ofmesons with lattice QCD for the ﬁrst time. The calculation is carried out with overlap fermionon 2+1 ﬂavor domain-wall fermion gauge conﬁgurations. We conﬁrm that ˘50% of the lightpion mass comes from the quark mass and ˘10% comes from the quark energy, whereas, thecontributions are found to be the other way around for the r mass. The combined glue compo-nents contribute ˘40 50% for both mesons. It is interesting to observe that the quark masscontribution to the mass of the vector meson is almost linear in quark mass over a large quarkmass region below the charm quark mass. For heavy mesons, the quark mass term dominates themasses, while the contribution from the glue components is about 400 ˘500 MeV for the heavypseudoscalar and vector mesons. The charmonium hyperﬁne splitting is found to be dominatedby the quark energy term which is consistent with the quark potential model.32st International Symposium on Lattice Field Theory - LATTICE 2014June 22 - June 29, 2014Columbia UniversityNew York, USA
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
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.
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.
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.
121114134
Measurement of the running of the electromagnetic coupling at large momentum-transfer at LEP
The evolution of the electromagnetic coupling, α, in the momentum-transfer range 1800 GeV2 < -Q2 < 21600 GeV2 is studied with about 40 000 Bhabha-scattering events collected with the L3 detector at LEP at centre-of-mass energies √s = 189-209 GeV. The running of α is parametrised as: α(Q2) = α0/1 - C Δα(Q2), where α ≡ α(Q2 = 0) is the fine-structure constant and C = 1 corresponds to the evolution expected in QED. A fit to the differential cross section of the e+e- → e+e- process for scattering angles in the range |cos θ| < 0.9 excludes the hypothesis of a constant value of α, C = 0, and validates the QED prediction with the result: C = 1.05±0.07±0.14, where the first uncertainty is statistical and the second systematic. © 2005 Elsevier B.V. All rights reserved.
120107147
Partial wave analysis of psi-prime ---> pi+ pi- pi0 at BESII
118457565
Pseudoscalar Meson and Decuplet Baryon Scattering Lengths
The excited states of the nucleon and their strong interactions with various hadrons play an important role in our understanding of non-perturbative QCD. Generally speaking, their coupling with the pseudoscalar pion, kaon and eta is governed by chiral dynamics. The first excited state of the nucleon, J = 3/2 ∆(1232), belongs to the lightest decuplet. It is degenerate with the nucleon in the large Nc limit [1, 2]. From the strong decay widths, one can extract the coupling constants of the pseudoscalar meson decuplet baryon interaction. Although it may be quite difficult to measure their scattering lengths experimentally, unlike in the pion-nucleon and kaon-nucleon cases [3–5], it is still interesting to study the scattering processes theoretically. As two well-known non-perturbative approaches of QCD at low energy, chiral perturbation theory and lattice QCD have been widely used in studying meson-baryon interactions [6–14]. With the explicitly consistent power counting scheme, the heavy baryon chiral perturbation theory (HBχPT) is a practical and useful tool in the study of the meson baryon scattering. The expansion is organized with p/Λχ, where p represents the momentum (mass) of the meson or the small residue momentum of the baryon in the non-relativistic limit, and Λχ = 4πfπ is the scale of chiral symmetry breaking. Numerically it is around the baryon mass in the chiral limit. Because of the large mass of the strange quark, the chiral corrections from the kaon and eta meson loops are significantly larger than that from the pion loop, which leads to the worse convergence of the chiral expansion in the SU(3) case. In HBχPT, the effects of excited baryons are encoded in the unknown low energy constants (LECs) in the Lagrangians. In the large Nc limit, one expects that the inclusion of the decuplet baryon contribution may partially cancel the octet contribution and be helpful to the chiral expansion. In order to investigate the contributions of the ∆, HBχPT with explicit spin-3/2 baryons and the small-scale expansion scheme have been developed in Refs. [15, 16]. Now the expansion is organized with ǫ, where ǫ means p in HBχPT or the mass difference δ between ∆ and the nucleon in the chiral limit, which is widely used in the exploration of the decuplet related processes [17–21]. There exists another power counting scheme “δ expansion” in the two-flavor case, where mπ scales as δ 2 [22–25]. In our previous work [21], we studied the decuplet contributions to the pseudoscalar meson octet baryon scattering lengths, which is an important observable reflecting their strong interaction near the threshold. The inclusion of the decuplet baryons does not improve the convergence significantly. In this paper, we will study the scattering lengths of the pseudoscalar mesons and the light decuplet baryons in the framework of the SU(3) heavy baryon chiral perturbation theory with explicit decuplet baryons. We will explore whether the small scale expansion works well in this case.
54637650
Low Mass Gluino within the Sparticle Landscape, Implications for Dark Matter, and Early Discovery Prospects at LHC-7
We analyze supergravity models that predict a low mass gluino within the landscape of sparticle mass hierarchies. The analysis includes a broad class of models that arise in minimal and in nonminimal supergravity unified frameworks and in extended models with additional U(1) n hidden sector gauge symmetries. Gluino masses in the range (350 − 700) GeV are investigated. Masses in this range are promising for early discovery at the LHC at √ s = 7 TeV (LHC-7). The models exhibit a wide dispersion in the gaugino-Higgsino eigencontent of their LSPs and in their associated sparticle mass spectra. A signature analysis is carried out and the prominent discovery channels for the models are identified with most models needing only ∼ 1 fb 1 for discovery at LHC-7. In addition, significant variations in the discovery capability of the low mass gluino models are observed for models in which the gluino masses are of comparable size due to the mass splittings in different models and the relative position of the light gluino within the various sparticle mass hierarchies. The models are consistent with the current stringent bounds from the Fermi-LAT, CDMS-II, XENON100, and EDELWEISS-2 experiments. A subclass of these models, which include a mixed-wino LSP and a Higgsino LSP, are also shown to accommodate the positron excess seen in the PAMELA satellite experiment.
119778744
Studies of hadronic event structure in E+ E- annihilation from 30-Gev to 209-Gev with the L3 detector
In this Report, QCD results obtained from a study of hadronic event structure in high energy e^+e^- interactions with the L3 detector are presented. The operation of the LEP collider at many different collision energies from 91 GeV to 209 GeV offers a unique opportunity to test QCD by measuring the energy dependence of different observables. The main results concern the measurement of the strong coupling constant, \alpha_s, from hadronic event shapes and the study of effects of soft gluon coherence through charged particle multiplicity and momentum distributions.