400 research outputs found

    Inclusive Jet Cross Sections in pˉp\bar{p}p Collisions at s\sqrt{s}= 630 and 1800 GeV

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    We have made a precise measurement of the inclusive jet cross section at s\sqrt{s}=1800 GeV. The result is based on an integrated luminosity of 92 pb^{-1} collected at the Fermilab Tevatron pˉp\bar{p}p Collider with the D\O detector. The measurement is reported as a function of jet transverse energy (60 GeV <= E_{T} < 550 GeV), and in the pseudorapidity intervals |\eta| <= 0.5 and 0.1 <= |\eta| <= 0.7. A preliminary measurement of the pseudorapidity dependence of inclusive jet production (|\eta| <= 1.5) is also discussed. The results are in good agreement with predictions from next-to-leading order (NLO) quantum chromodynamics (QCD). D\O has also determined the ratio of jet cross sections at s\sqrt{s}=630 GeV and s\sqrt{s}=1800 GeV (|\eta| <= 0.5). This preliminary measurement differs from NLO QCD predictions.Comment: Submitted to the International Europhysics Conference on High Energy Physics, EPS-HEP99, 15-21 July, 1999, Tampere, Finlan

    Reconciling the LEP and Slac Measurements of Sin^2(\Theta_W)

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    We consider whether a discrepancy between the SLAC and LEP measurements of \Sw can be explained by new physics. We find that only the contribution of a new neutral gauge boson, Zâ€ČZ^\prime, nearly degenerate with the Z can affect the SLAC measurement while leaving the LEP observables almost unaffected. We briefly discuss possible signals for this new gauge boson, including changes in the ZZ lineshape when measured with polarised electrons, small changes in RbR_b, AFBeA^e_{FB}, and larger changes in two jet and ttˉt\bar{t} production at hadron colliders.Comment: 8 pages , CERN-TH.7474/94, OUTP9424

    Dijet resonance from leptophobic Z' and light baryonic cold dark matter

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    In light of the recent CDF report on the excess in the Wjj channel, we analyze (non)supersymmetric U(1)_B x U(1)_L model, interpreting the dijet peak as a leptophobic U(1)_B gauge boson. If this excess is confirmed, it has an interesting implication for the baryonic cold dark matter (CDM) in the model: there should be light CDM with a few GeV mass, and direct detection cross section at the level of a few x 10^{-2} pb.Comment: 5 pages, 3 figures, version published in Phys. Lett.

    A Resolution of the Flavor Problem of Two Higgs Doublet Models with an Extra U(1)_H Symmetry for Higgs Flavor

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    We propose to implement the Natural Flavor Conservation criterion in the two Higgs doublet model (2HDM) to an extra U(1)_H gauge symmetry for Higgs flavor, assuming two Higgs doublets carry different U(1)_H charges. Then one can easily avoid the tree level FCNC from neutral Higgs mediations using local gauge symmetries, instead of softly broken ad hoc Z_2 symmetry, and the pseudoscalar boson could be eaten by extra Z_H boson. Imposing the anomaly cancellation, we find that the U(1)_H in the Type-II and Type-IV 2HDM's become leptophobic and leptophilic, respectively. For the Type-I case, U(1)_H depends on two parameters, and some simple cases include U(1)_H = U(1)_{B-L}, U(1)_R, or U(1)_Y. We sketch qualitative phenomenology of these models.Comment: 7 pages, version published in Phys. Lett.

    A device to characterize optical fibres

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    ATLAS is a general purpose experiment approved for the LHC collider at CERN. An important component of the detector is the central hadronic calorimeter; for its construction more than 600,000 Wave Length Shifting (WLS) fibres (corresponding to a total length of 1,120 Km) have been used. We have built and put into operation a dedicated instrument for the measurement of light yield and attenuation length over groups of 20 fibres at a time. The overall accuracy achieved in the measurement of light yield (attenuation length) is 1.5% (3%). We also report the results obtained using this method in the quality control of a large sample of fibres.Comment: 17 pages 20 figeres submitted to NIM journa

    Measuring Double Parton Distributions in Nucleons at Proton-Nucleus Colliders

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    We predict a strong enhancement of multijet production in proton-nucleus collisions at collider energies, as compared to a naive expectation of a cross section ∝A\propto A. The study of the process would allow to measure, for the first time, the double parton distribution functions in a nucleon in a model independent way and hence to study both the longitudinal and the transverse correlations of partons.Comment: 12 pages, 2 figure

    Squarks Below the Z

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    We investigate the possibility that the difference between the measurements of α3(MZ)\alpha_3(M_Z) from the hadronic branching ratio of the Z0Z^0 and the world average of other measurements is due to the decay of the Z0Z^0 into quark, anti-squark, and gluino. Consequences for supersymmetry breaking models are discussed.Comment: 9 pages, 4 figures not include

    A Mellin Space Program for W^{+/-} and Z^0 Production at NNLO

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    We present a program for the evaluation of full unpolarized cross sections for the W^{+/-} and Z^0 production in the narrow width approximation at NNLO in perturbative QCD using Mellin space techniques.Comment: 4 pages, 1 figure. Proceedings of the 10th Hellenic School on Elementary Particle Physics and Gravity, Corfu 2010, to be published in Fortschritte der Physi

    Stringy origin of Tevatron Wjj anomaly

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    The invariant mass distribution of dijets produced in association with W bosons, recently observed by the CDF Collaboration at Tevatron, reveals an excess in the dijet mass range 120-160 GeV/c^2, 3\sigma beyond Standard Model expectations. We show that such an excess is a generic feature of low mass string theory, due to the production and decay of a leptophobic Z', a singlet partner of SU(3) gluons coupled primarily to the U(1) baryon number. In this framework, U(1) and SU(3) appear as subgroups of U(3) associated with open strings ending on a stack of 3 D-branes. In addition, a minimal model contains two other stacks to accommodate the electro-weak SU(2) \in U(2) and the hypercharge U(1). Of the three U(1) gauge bosons, the two heavy Z' and Z" receive masses through the Green-Schwarz mechanism. For a given Z' mass, the model is quite constrained. Fine tuning three of its free parameters is just sufficient to simultaneously ensure: a small Z-Z' mixing in accord with the stringent LEP data on the ZZ mass; very small (less than 1%) branching ratio into leptons; and a large hierarchy between Z" and Z' masses. The heavier neutral gauge boson Z" is within the reach of LHC.Comment: v1 8 pages revtex; v2 better fit to the data (Z" within LHC reach), references added; v3 to appear in PL
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