16533811
Two-dimensional lattice Gross-Neveu model with Wilson twisted mass fermions
Abstract We study the two-dimensional lattice Gross–Neveu model with Wilson twisted mass fermions in order to explore the phase structure in this setup. In particular, we investigate the behaviour of the phase transitions found earlier with standard Wilson fermions as a function of the twisted mass parameter μ . We find that qualitatively the dependence of the phase transitions on μ is very similar to the case of lattice QCD.
119398261
Light hadron spectrum and quark masses from quenched lattice QCD
We present the details of simulations for the light hadron spectrum in quenched QCD carried out on the CP-PACS parallel computer. Simulations are made with the Wilson quark action and the plaquette gauge action on lattices of size ${32}^{3}\ifmmode\times\else\texttimes\fi{}56\char21{}{64}^{3}\ifmmode\times\else\texttimes\fi{}112$ at four values of lattice spacings in the range $a\ensuremath{\approx}0.1\char21{}0.05\mathrm{fm}$ and spatial extent ${L}_{s}a\ensuremath{\approx}3\mathrm{fm}.$ Hadronic observables are calculated at five quark masses corresponding to ${m}_{\mathrm{PS}}{/m}_{V}\ensuremath{\approx}0.75\char21{}0.4,$ assuming the u and d quarks are degenerate, but treating the s quark separately. We find that the presence of quenched chiral singularities is supported from an analysis of the pseudoscalar meson data. The physical values of hadron masses are determined using ${m}_{\ensuremath{\pi}},$ ${m}_{\ensuremath{\rho}},$ and ${m}_{K}$ (or ${m}_{\ensuremath{\varphi}})$ as input to fix the physical scale of lattice spacing and the u, d, and s quark masses. After chiral and continuum extrapolations, the agreement of the calculated mass spectrum with experiment is at a 10% level. In comparison with the statistical accuracy of 1%\char21{}3% and systematic errors of at most 1.7% we have achieved, this demonstrates a failure of the quenched approximation for the hadron spectrum: the hyperfine splitting in the meson sector is too small, and in the baryon sector the octet masses and mass splitting of the decuplet are both smaller than experiment. Light quark masses are calculated using two definitions: the conventional one and the one based on the axial-vector Ward identity. The two results converge toward the continuum limit, yielding ${m}_{\mathrm{ud}}{=4.29(14)}_{\ensuremath{-}0.79}^{+0.51}\mathrm{MeV}$ where the first error is statistical and the second one is systematic due to chiral extrapolation. The s quark mass depends on the strange hadron mass chosen for input: ${m}_{s}{=113.8(2.3)}_{\ensuremath{-}2.9}^{+5.8}\mathrm{MeV}$ from ${m}_{K}$ and ${m}_{s}{=142.3(5.8)}_{\ensuremath{-}0}^{+22.0}\mathrm{MeV}$ from ${m}_{\ensuremath{\varphi}},$ indicating again a failure of the quenched approximation. We obtain the scale of QCD, ${\ensuremath{\Lambda}}_{\overline{\mathrm{MS}}}^{(0)}=219.5(5.4)\mathrm{MeV}$ with ${m}_{\ensuremath{\rho}}$ used as input. An $O(10%)$ deviation from experiment is observed in the pseudoscalar meson decay constants.
15136419
Going chiral: Overlap versus twisted mass fermions
We compare the behavior of overlap fermions, which are chirally invariant, and of Wilson twisted mass fermions at full twist in the approach to the chiral limit. Our quenched simulations reveal that with both formulations of lattice fermions pion masses of (250 MeV) can be reached in practical applications. Our comparison is done at a fixed value of the lattice spacing a 0.123 fm. A number of quantities are measured such as hadron masses, pseudoscalar decay constants and quark masses obtained from Ward identities. We also determine the axial vector renormalization constants in the case of overlap fermions.
3243998
Testing topology conserving gauge actions for Lattice QCD
We explore gauge actions for lattice QCD, which are constructed such that the occurrence of small plaquette values is strongly suppressed. Such actions orig inate from the admissibility condition in order to conserve the topological charge. The suppression of small plaquette values is expected to be advantageous for numerical studies in the e-regime and also for simulations with dynamical quarks. Performing simulations at a lattice spacing of about 0.1 fm, we present numerical results for the static potential, the physical scale r0, the stability of the topological charge history, the condition number of the kernel of the overlap operator and the acceptance rate against the step size in the local HMC algorithm.
56188967
Light hadron spectrum and quark masses in QCD with two flavors of dynamical quarks
Abstract We present updated results of the CP-PACS calculation of the light hadron spectrum in N f = 2 full QCD. Simulations are made with an RG-improved gauge action and a tadpole-improved clover quark action for sea quark masses corresponding to m PS / m V ≈ 0.8-0.6 and the lattice spacing a = 0.22-0.09 fm. A comparison of the N f = 2 QCD spectrum with new quenched results, obtained with the same improved action, shows clearly the existence of sea quark effects in vector meson masses. Results for light quark masses are also presented.
119104951
B meson decay constants from two-flavor lattice QCD with nonrelativistic heavy quarks
We present a study of leptonic $B$ meson decay constants in lattice QCD with two flavors ($N_f=2$) of light dynamical quarks using NRQCD for the heavy quark. Gauge configurations are generated with a renormalization-group improved gauge action and a meanfield-improved clover light quark action. Measurements are carried out at two values of $\beta=6/g^2$, each for four sea quark masses, corresponding to the inverse lattice spacing $a^{-1}\approx 1.3$ and 1.8 GeV in the chiral limit of sea quark. The continuum values of the decay constants are derived by evaluating the discretization errors at each finite lattice spacing. We find $f_B^{N_f=2}=204(8)(29)(+44) $ MeV, $f_{B_s}^{N_f=2} = 242(9)(34)(+38)$ MeV, and $f_{B_s}^{N_f=2}/f_B^{N_f=2} = 1.179(18)(23)$, where the errors listed are statistical, systematic and uncertainty due to choice of the physical quantity used to fix the scale. Comparison is made to quenched results ($N_f=0$) obtained with the same action combination and matching lattice spacings. We find $f_B^{N_f=2}/f_B^{N_f=0}=1.07(5)$, $f_{B_s}^{N_f=2}/f_{B_s}^{N_f=0}=1.10(5)$ and $(f_{B_s}/f_B)^{N_f=2}/(f_{B_s}/f_B)^{N_f=0}=1.03(2)$, which indicates a 5--10% increase in the values of the decay constants, but no appreciable change in the ratio $f_{B_s}/f_B$, due to sea quarks.
14502654
Beam test of novel n-in-p strip sensors for high radiation environment
Abstract Highly radiation tolerant n-in-p strip sensors have been developed for the high-luminosity LHC (HL-LHC). This paper reports the results of measurements with 392 MeV kinetic energy proton beam at RCNP in December 2011. The data was taken with a new DAQ system consisting of an universal read-out board ‘SEABAS’ and beam tracking telescopes whose spacial resolution is better than 5 μ m . The aim of this beam test is to evaluate the new 1 cm×1 cm n-in-p miniature sensors before and after 10 15  n eq  cm −2 irradiation. The median charge of un-irradiated sensor is 6.2 fC at full depletion voltage, while the median charge after 10 15  n eq  cm −2 irradiation of the sensor is 4.2 fC. The novel Punch-Through-Protection (PTP) has been implemented in these sensors. The length of active region of the sensor around PTP is observed to be decreased by 12 μ m in the irradiated sensors at 10 15  n eq  cm −2 .