344 research outputs found

    QCD Chiral restoration at finite TT under the Magnetic field: Studies based on the instanton vacuum model

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    We investigate the chiral restoration at finite temperature (T)(T) under the strong external magnetic field B‚Éó=B0z^\vec{B}=B_{0}\hat{z} of the SU(2) light-flavor QCD matter. We employ the instanton-liquid QCD vacuum configuration accompanied with the linear Schwinger method for inducing the magnetic field. The Harrington-Shepard caloron solution is used to modify the instanton parameters, i.e. the average instanton size (ŌĀňČ)(\bar{\rho}) and inter-instanton distance (RňČ)(\bar{R}), as functions of TT. In addition, we include the meson-loop corrections (MLC) as the large-NcN_{c} corrections because they are critical for reproducing the universal chiral restoration pattern. We present the numerical results for the constituent-quark mass as well as chiral condensate which signal the spontaneous breakdown of chiral-symmetry (SBŌá\chiS), as functions of TT and BB. Besides we find that the changes for the FŌÄF_\pi and mŌÄm_\pi due to the magnetic field is relatively small, in comparison to those caused by the finite TT effect.Comment: 4 pages, 1 table, 6figs. arXiv admin note: significant text overlap with arXiv:1103.605

    Extended nonlocal chiral-quark model for the heavy-light quark systems

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    In this talk, we report the recent progress on constructing a phenomenological effective model for the heavy-light quark systems, which consist of (u,d,s,c,b) quarks, i.e. extended nonlocal chiral-quark model (ExNLChQM). We compute the heavy-meson weak-decay constants to verify the validity of the model. From the numerical results, it turns out that (f_D, f_B, f_{D_s}, f_{B_s})=(207.54,208.13,262.56,262.39) MeV. These values are in relatively good agreement with experimental data and various theoretical estimations.Comment: 3 pages, 4 figures, Talk given at the 20th International IUPAP Conference on Few-Body Problems in Physics (FB20), 20~25 August 2012, Fukuoka, Japa

    Unpolarized fragmentation function for the pion and kaon via the nonlocal chiral-quark model

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    In this talk we present our recent studies for the unpolarized fragmentation functions for the pion and kaon, employing the nonlocal chiral quark model, which manifests the nonlocal interaction between the quarks and pseudoscalar mesons, in the light-cone frame. It turns out that the nonlocal interaction produces considerable differences in comparison to typical local-interaction models.Comment: 4 pages, 2 figures, Talk given at the international conference The Fifth Asia-Pacific Conference on Few-Body Systems in Physics 2011 (APFB2011), Seoul, Republic of Korea, 22-26 August 201

    Determination of the parity of the pentaquark baryons : Theta^+ and Xi_5

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    We study determination of the parity of the pentaquark baryons in two different processes. First, we investigate the Theta^+ production via the vec{p} vec{p} -> Sigma^+ Theta^+ reaction process which was proposed to determine unambiguously the parity of Theta^+. We observe the clear differences in the total cross sections and the spin observable A_{xx}. As for the Xi_5 in the bar{K} N -> K Xi_5 reaction process, the total cross section for the positive parity presents about one hundred times lager than that of the negative one due to the huge destructive interference.Comment: 5 pages, 8 figures, Talk given at International Workshop on BARYONS04, Ecole polytechnique, Paris, France, 25-29 Oct 200

    Photoproduction of Theta baryon from the neutron

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    We study photoproduction reactions for Theta^+, which was recently observed as a candidate of an exotic five quark state uudd(bar s). We employ effective lagrangian interactions in the linear and non-linear formalism of chiral symmetry and investigate two cases of spin and parity of Theta^+, J^P = 1/2^+ and 1/2^-. We calculate cross sections and discuss possibilities to discriminate one from the other.Comment: 14 pages, 19 figure

    Z^* Resonances: Phenomenology and Models

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    We explore the phenomenology of, and models for, the Z^* resonances, the lowest of which is now well established, and called the Theta. We provide an overview of three models which have been proposed to explain its existence and/or its small width, and point out other relevant predictions, and potential problems, for each. The relation to what is known about KN scattering, including possible resonance signals in other channels, is also discussed.Comment: 29 pages, uses RevTeX4; expanded version (published form

    Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV

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    Results are presented from a search for a W' boson using a dataset corresponding to 5.0 inverse femtobarns of integrated luminosity collected during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV. The W' boson is modeled as a heavy W boson, but different scenarios for the couplings to fermions are considered, involving both left-handed and right-handed chiral projections of the fermions, as well as an arbitrary mixture of the two. The search is performed in the decay channel W' to t b, leading to a final state signature with a single lepton (e, mu), missing transverse energy, and jets, at least one of which is tagged as a b-jet. A W' boson that couples to fermions with the same coupling constant as the W, but to the right-handed rather than left-handed chiral projections, is excluded for masses below 1.85 TeV at the 95% confidence level. For the first time using LHC data, constraints on the W' gauge coupling for a set of left- and right-handed coupling combinations have been placed. These results represent a significant improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe

    Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV