3,342 research outputs found

    Trimer classical spin liquid from interacting fractional charges

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    We study a problem of interacting fractional charges with the J(1)-J(2)-J(3) Ising model on a checkerboard lattice under magnetic field. As a result of the interplay between repulsive interactions and particle density tuning by a magnetic field, the fractional charges form a classical spin liquid (CSL) phase. The CSL phase is composed of degenerate spin configurations, which can be mapped to the trimer covering of dual square lattice. The CSL state shows macroscopic ground-state entropy, implying the emergence of a novel quantum spin liquid phase when quantum fluctuations are turned on. In addition to the CSL phase, the system exhibits multiple magnetization plateaus, reflecting the fertile screening processes of dimer-monomer mixtures

    The ZEUS Forward Plug Calorimeter with Lead-Scintillator Plates and WLS Fiber Readout

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    A Forward Plug Calorimeter (FPC) for the ZEUS detector at HERA has been built as a shashlik lead-scintillator calorimeter with wave length shifter fiber readout. Before installation it was tested and calibrated using the X5 test beam facility of the SPS accelerator at CERN. Electron, muon and pion beams in the momentum range of 10 to 100 GeV/c were used. Results of these measurements are presented as well as a calibration monitoring system based on a 60^{60}Co source.Comment: 38 pages (Latex); 26 figures (ps

    Combined QCD and electroweak analysis of HERA data

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    A simultaneous fit of parton distribution functions (PDFs) and electroweak parameters to HERA data on deep inelastic scattering is presented. The input data are the neutral current and charged current inclusive cross sections which were previously used in the QCD analysis leading to the HERAPDF2.0 PDFs. In addition, the polarisation of the electron beam was taken into account for the ZEUS data recorded between 2004 and 2007. Results on the vector and axial-vector couplings of the Z boson to u- and d-type quarks, on the value of the electroweak mixing angle and the mass of the W boson are presented. The values obtained for the electroweak parameters are in agreement with Standard Model predictions.Comment: 32 pages, 10 figures, accepted by Phys. Rev. D. Small corrections from proofing process and small change to Fig. 12 and Table

    Measurement of the cross-section ratio sigma_{psi(2S)}/sigma_{J/psi(1S)} in deep inelastic exclusive ep scattering at HERA

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    The exclusive deep inelastic electroproduction of Ōą(2S)\psi(2S) and J/Ōą(1S)J/\psi(1S) at an epep centre-of-mass energy of 317 GeV has been studied with the ZEUS detector at HERA in the kinematic range 2<Q2<802 < Q^2 < 80 GeV2^2, 30<W<21030 < W < 210 GeV and ‚ą£t‚ą£<1|t| < 1 GeV2^2, where Q2Q^2 is the photon virtuality, WW is the photon-proton centre-of-mass energy and tt is the squared four-momentum transfer at the proton vertex. The data for 2<Q2<52 < Q^2 < 5 GeV2^2 were taken in the HERA I running period and correspond to an integrated luminosity of 114 pb‚ąí1^{-1}. The data for 5<Q2<805 < Q^2 < 80 GeV2^2 are from both HERA I and HERA II periods and correspond to an integrated luminosity of 468 pb‚ąí1^{-1}. The decay modes analysed were őľ+őľ‚ąí\mu^+\mu^- and J/Ōą(1S)‚ÄČŌÄ+ŌÄ‚ąíJ/\psi(1S) \,\pi^+\pi^- for the Ōą(2S)\psi(2S) and őľ+őľ‚ąí\mu^+\mu^- for the J/Ōą(1S)J/\psi(1S). The cross-section ratio ŌÉŌą(2S)/ŌÉJ/Ōą(1S)\sigma_{\psi(2S)}/\sigma_{J/\psi(1S)} has been measured as a function of Q2,WQ^2, W and tt. The results are compared to predictions of QCD-inspired models of exclusive vector-meson production.Comment: 24 pages, 8 figure

    Limits on the effective quark radius from inclusive epep scattering at HERA

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    The high-precision HERA data allows searches up to TeV scales for Beyond the Standard Model contributions to electron-quark scattering. Combined measurements of the inclusive deep inelastic cross sections in neutral and charged current epep scattering corresponding to a luminosity of around 1 fb‚ąí1^{-1} have been used in this analysis. A new approach to the beyond the Standard Model analysis of the inclusive epep data is presented; simultaneous fits of parton distribution functions together with contributions of "new physics" processes were performed. Results are presented considering a finite radius of quarks within the quark form-factor model. The resulting 95% C.L. upper limit on the effective quark radius is 0.43‚čÖ10‚ąí160.43\cdot 10^{-16} cm.Comment: 10 pages, 4 figures, accepted by Phys. Lett.

    Search for a narrow baryonic state decaying to pKS0{pK^0_S} and pňČKS0{\bar{p}K^0_S} in deep inelastic scattering at HERA

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    A search for a narrow baryonic state in the pKS0pK^0_S and pňČKS0\bar{p}K^0_S system has been performed in epep collisions at HERA with the ZEUS detector using an integrated luminosity of 358 pb‚ąí1^{-1} taken in 2003-2007. The search was performed with deep inelastic scattering events at an epep centre-of-mass energy of 318 GeV for exchanged photon virtuality, Q2Q^2, between 20 and 100 GeV2\rm{} GeV^{2}. Contrary to evidence presented for such a state around 1.52 GeV in a previous ZEUS analysis using a sample of 121 pb‚ąí1^{-1} taken in 1996-2000, no resonance peak was found in the p(pňČ)KS0p(\bar{p})K^0_S invariant-mass distribution in the range 1.45-1.7 GeV. Upper limits on the production cross section are set.Comment: 16 pages, 4 figures, accepted by Phys. Lett. B. Minor changes from journal reviewing process, including a small correction to figure

    Measurement of neutral current e+/-p cross sections at high Bjorken x with the ZEUS detector

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    The neutral current e+/-p cross section has been measured up to values of Bjorken x of approximately 1 with the ZEUS detector at HERA using an integrated luminosity of 187 inv. pb of e-p and 142 inv. pb of e+p collisions at sqrt(s) = 318GeV. Differential cross sections in x and Q2, the exchanged boson virtuality, are presented for Q2 geq 725GeV2. An improved reconstruction method and greatly increased amount of data allows a finer binning in the high-x region of the neutral current cross section and leads to a measurement with much improved precision compared to a similar earlier analysis. The measurements are compared to Standard Model expectations based on a variety of recent parton distribution functions.Comment: 39 pages, 9 figure

    Measurement of inclusive D*+- and associated dijet cross sections in photoproduction at HERA

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    Inclusive photoproduction of D*+- mesons has been measured for photon-proton centre-of-mass energies in the range 130 < W < 280 GeV and a photon virtuality Q^2 < 1 GeV^2. The data sample used corresponds to an integrated luminosity of 37 pb^-1. Total and differential cross sections as functions of the D* transverse momentum and pseudorapidity are presented in restricted kinematical regions and the data are compared with next-to-leading order (NLO) perturbative QCD calculations using the "massive charm" and "massless charm" schemes. The measured cross sections are generally above the NLO calculations, in particular in the forward (proton) direction. The large data sample also allows the study of dijet production associated with charm. A significant resolved as well as a direct photon component contribute to the cross section. Leading order QCD Monte Carlo calculations indicate that the resolved contribution arises from a significant charm component in the photon. A massive charm NLO parton level calculation yields lower cross sections compared to the measured results in a kinematic region where the resolved photon contribution is significant.Comment: 32 pages including 6 figure

    Measurement of the diffractive structure function in deep inelastic scattering at HERA

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    This paper presents an analysis of the inclusive properties of diffractive deep inelastic scattering events produced in epep interactions at HERA. The events are characterised by a rapidity gap between the outgoing proton system and the remaining hadronic system. Inclusive distributions are presented and compared with Monte Carlo models for diffractive processes. The data are consistent with models where the pomeron structure function has a hard and a soft contribution. The diffractive structure function is measured as a function of \xpom, the momentum fraction lost by the proton, of ő≤\beta, the momentum fraction of the struck quark with respect to \xpom, and of Q2Q^2. The \xpom dependence is consistent with the form \xpoma where a¬†=¬†1.30¬†¬Ī¬†0.08¬†(stat)¬†‚ąí¬†0.14+¬†0.08¬†(sys)a~=~1.30~\pm~0.08~(stat)~^{+~0.08}_{-~0.14}~(sys) in all bins of ő≤\beta and Q2Q^2. In the measured Q2Q^2 range, the diffractive structure function approximately scales with Q2Q^2 at fixed ő≤\beta. In an Ingelman-Schlein type model, where commonly used pomeron flux factor normalisations are assumed, it is found that the quarks within the pomeron do not saturate the momentum sum rule.Comment: 36 pages, latex, 11 figures appended as uuencoded fil
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