1,968 research outputs found

    Distinct doping dependences of the pseudogap and superconducting gap La2x_{2-x}Srx_{x}CuO4_4 cuprate superconductors

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    We have performed a temperature-dependent angle-integrated photoemission study of lightly-doped to heavily-overdoped La2x_{2-x}Srx_{x}CuO4_4 and oxygen-doped La2_2CuO4.10_{4.10}. We found that both the magnitude Δ\Delta* of the (small) pseudogap and the temperature \textit{T}* at which the pseudogap is opened increases with decreasing hole concentration, consistent with previous studies. On the other hand, the superconducting gap Δsc\Delta_{sc} was found to remain small for decreasing hole concentration. The results can be explained if the superconducting gap opens only on the Fermi arc around the nodal (0,0)-(π,π\pi,\pi) direction while the pseudogap opens around \sim(π\pi, 0).Comment: 4 pages, 3 figure

    Coherent quasi-particles-to-incoherent hole-carriers crossover in underdoped cuprates

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    In underdoped cuprates, only a portion of the Fermi surface survives as Fermi arcs due to pseudogap opening. In hole-doped La2_{2}CuO4_4, we have deduced the "coherence temperature" TcohT_{coh} of quasi-particles on the Fermi arc above which the broadened leading edge position in angle-integrated photoemission spectra is shifted away from the Fermi level and the quasi-particle concept starts to lose its meaning. TcohT_{coh} is found to rapidly increase with hole doping, an opposite behavior to the pseudogap temperature TT^*. The superconducting dome is thus located below both TT^* and TcohT_{coh}, indicating that the superconductivity emerges out of the coherent Fermionic quasi-particles on the Fermi arc. TcohT_{coh} remains small in the underdoped region, indicating that incoherent charge carriers originating from the Fermi arc are responsible for the apparently metallic transport at high temperatures

    Measurement of the cross-section and forward-backward charge asymmetry for the b and c-quark in e+e- annihilation with inclusive muons at sqrt(s) = 58 GeV

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    We have studied inclusive muon events using all the data collected by the TOPAZ detector at sqrt(s)=58 GeV with an integrated luminosity of 273pb-1. From 1328 inclusive muon events, we measured the ratio R_qq of the cross section for qq-bar production to the total hadronic cross section and forward-backward asymmetry A^q_FB for b and c quarks. The obtained results are R_bb = 0.13+-0.02(stat)+-0.01(syst), R_cc = 0.36+-0.05(stat)+-0.05(syst), A^b_FB = -0.20+-0.16(stat)+-0.01(syst) and A^c_FB = -0.17+-0.14(stat)+-0.02(syst), in fair agreement with a prediction of the standard model.Comment: To be published in EPJ C. 24 pages, 12 figure

    Evolution with hole doping of the electronic excitation spectrum in the cuprate superconductors

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    The recent scanning tunnelling results of Alldredge et al on Bi-2212 and of Hanaguri et al on Na-CCOC are examined from the perspective of the BCS/BEC boson-fermion resonant crossover model for the mixed-valent HTSC cuprates. The model specifies the two energy scales controlling the development of HTSC behaviour and the dichotomy often now alluded to between nodal and antinodal phenomena in the HTSC cuprates. Indication is extracted from the data as to how the choice of the particular HTSC system sees these two basic energy scales (cursive-U, the local pair binding energy and, Delta-sc, the nodal BCS-like gap parameter) evolve with doping and change in degree of metallization of the structurally and electronically perturbed mixed-valent environment.Comment: 19 pages, 5 figure

    A Measurement of the D±D^{*\pm} Cross Section in Two-Photon Processes

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    We have measured the inclusive D±D^{*\pm} production cross section in a two-photon collision at the TRISTAN e+ee^+e^- collider. The mean s\sqrt{s} of the collider was 57.16 GeV and the integrated luminosity was 150 pb1pb^{-1}. The differential cross section (dσ(D±)/dPTd\sigma(D^{*\pm})/dP_T) was obtained in the PTP_T range between 1.6 and 6.6 GeV and compared with theoretical predictions, such as those involving direct and resolved photon processes.Comment: 8 pages, Latex format (article), figures corrected, published in Phys. Rev. D 50 (1994) 187

    K0(K0ˉ)K^0(\bar{K^0}) Production in Two-Photon Processes at TRISTAN

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    We have carried out an inclusive measurement of K0(K0ˉ)K^0(\bar{K^0}) production in two-photon processes at TRISTAN. The mean s\sqrt{s} was 58 GeV and the integrated luminosity was 199 pb1^{-1}. High-statistics KsK_s samples were obtained under such conditions as no-, anti-electron, and remnant-jet tags. The remnant-jet tag, in particular, allowed us, for the first time, to measure the cross sections separately for the resolved-photon and direct processes.Comment: 20 pages, Latex format, 4 figures and KEK-mark included. Table 1 revised. To be published in Phys. Lett.

    Measurement of the forward-backward asymmetries for charm- and bottom-quark pair productions at <s><\sqrt{s}>=58GeV with electron tagging

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    We have measured, with electron tagging, the forward-backward asymmetries of charm- and bottom-quark pair productions at =58.01GeV, based on 23,783 hadronic events selected from a data sample of 197pb1^{-1} taken with the TOPAZ detector at TRISTAN. The measured forward-backward asymmetries are AFBc=0.49±0.20(stat.)±0.08(sys.)A_{FB}^c = -0.49 \pm 0.20(stat.) \pm 0.08 (sys.) and AFBb=0.64±0.35(stat.)±0.13(sys.)A_{FB}^b = -0.64 \pm 0.35(stat.) \pm 0.13 (sys.), which are consistent with the standard model predictions.Comment: 19 pages, Latex format (article), 5 figures included. to be published in Phys. Lett.

    Leading order analysis of neutrino induced dimuon events in the CHORUS experiment

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    We present a leading order QCD analysis of a sample of neutrino induced charged-current events with two muons in the final state originating in the lead-scintillating fibre calorimeter of the CHORUS detector. The results are based on a sample of 8910 neutrino and 430 antineutrino induced opposite-sign dimuon events collected during the exposure of the detector to the CERN Wide Band Neutrino Beam between 1995 and 1998. % with Eμ1,Eμ2>5E_{\mu 1},E_{\mu 2} > 5 GeV and Q2>3Q^2 > 3 GeV2^2 collected %between 1995 and 1998. The analysis yields a value of the charm quark mass of \mc = (1.26\pm 0.16 \pm 0.09) \GeVcc and a value of the ratio of the strange to non-strange sea in the nucleon of κ=0.33±0.05±0.05\kappa = 0.33 \pm 0.05 \pm 0.05, improving the results obtained in similar analyses by previous experiments.Comment: Submitted to Nuclear Physics

    Measurement of inclusive electron cross section in γγ\gamma \gamma collisions at TRISTAN

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    We have studied open charm production in γγ\gamma \gamma collisions with the TOPAZ detector at the TRISTAN e+ee^{+}e^{-} collider. In this study, charm quarks were identified by electrons (and positrons) from semi-leptonic decays of charmed hadrons. The data corresponded to an integrated luminosity of 95.3 pb1^{-1} at a center-of-mass energy of 58 GeV. The results are presented as the cross sections of inclusive electron production in γγ\gamma \gamma collisions with an anti-tag condition, as well as the subprocess cross sections, which correspond to resolved-photon processes. The latter were measured by using a sub-sample with remnant jets. A comparison with various theoretical predictions based on direct and resolved-photon processes showed that our data prefer that with relatively large gluon contents in a photon at small x(x0.1)x (x \le 0.1), with the next-to-leading order correction, and with a charm-quark mass of 1.3 GeV.Comment: 26 pages, Latex format (article), 5 figures included, to be published in Phys. Lett.

    Search for short baseline nu(e) disappearance with the T2K near detector

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    8 pages, 6 figures, submitted to PRD rapid communication8 pages, 6 figures, submitted to PRD rapid communicationWe thank the J-PARC staff for superb accelerator performance and the CERN NA61 collaboration for providing valuable particle production data. We acknowledge the support of MEXT, Japan; NSERC, NRC and CFI, Canada; Commissariat `a l’Energie Atomique and Centre National de la Recherche Scientifique–Institut National de Physique Nucle´aire et de Physique des Particules, France; DFG, Germany; INFN, Italy; National Science Centre (NCN), Poland; Russian Science Foundation, RFBR and Ministry of Education and Science, Russia; MINECO and European Regional Development Fund, Spain; Swiss National Science Foundation and State Secretariat for Education, Research and Innovation, Switzerland; STFC, UK; and DOE, USA. We also thank CERN for the UA1/NOMAD magnet, DESY for the HERA-B magnet mover system, NII for SINET4, the WestGrid and SciNet consortia in Compute Canada, GridPP, UK. In addition participation of individual researchers and institutions has been further supported by funds from ERC (FP7), EU; JSPS, Japan; Royal Society, UK; DOE Early Career program, USA
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