2,486 research outputs found

    Results on Diffraction at HERA and Tevatron

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    Recent results on diffraction at HERA, from the H1 and ZEUS Collaborations, and at Tevatron, from the CDF and D0 Collaborations, are reviewed. The measurement of the diffractive structure function at HERA is presented, and the pomeron structure function is extracted from QCD fits. Diffractive dijet production is given as an example analysis of the diffractive final state. These analysis are consistent with a leading gluon partonic structure for the pomeron. Hard single diffraction, double diffraction and double pomeron exchange processes are studied at the Tevatron and complement the studies performed at HERA. Finally, HERA results on the diffractive (exclusive) production of a vector particle, either a vector meson or a photon, are presented and compared to models based on perturbative QCD.Comment: Results presented at "La Thuile" conference, feb/mar 2000, Italy. To appear in the proceedings. 12 pages, 10 figure

    Elastic production of Vector Mesons at HERA: study of the scale of the interaction and measurement of the helicity amplitudes

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    A compilation of H1 and ZEUS cross section measurements for elastic vector meson production is presented as a function of the scale K2=(Q2+MV2)/4K^2 = (Q^2+M_V^2)/4, where Q^2 is the exchanged photon virtuality and M_V is the mass of the vector meson. The ratio of longitudinal to transverse cross sections R = σL/σT\sigma_L/\sigma_T is presented as a function of Q^2/M^2_V. The cross sections are separated in a transverse and a longitudinal component, and are presented as a function of K^2. The intercept α(0)\alpha(0) -- 1 governing the energy dependence of the vector meson cross sections is compared with the λ\lambda parameter measured in inclusive F_2 analysis. For ρ\rho meson production, the helicity amplitude ratios Tij/T00|T_{ij}|/|T_{00}|, extracted from the H1 and ZEUS measurements of the spin density matrix elements are presented as a function of Q^2 and W and are compared to recent predictions.Comment: The note includes plots presented in the vector meson discussion session of the Workshop of Low-x Physics (june 1999), Tel-Aviv, Israel. 12 pages, 7 figures, 1 table. New version with new model predictio

    Search with the CMS detector for heavy resonances decaying into an electron pair

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    This note presents the CMS experiment potential to discover heavy resonances decaying into an electron-positron pair, such as Kaluza-Klein excitations of a Z or graviton boson predicted in extra dimension models (the TeV^-1 model and the Randall-Sundrum model), or as neutral heavy Z' boson predicted by Grand Unified Theories. Full and fast simulation and reconstruction are used to investigate these productions, with the pileup condition corresponding to a luminosity equal to 2 times 10^ 33; mathrm cm ^ -2 mathrm s ^ -1 . For an integrated luminosity of 60 fbinv, a 5 sigma discovery limit has been obtained for a mass of 5.9 tevct in the case of Kaluza-Klein excitation Z boson production. For the Randall-Sundrum graviton production, the limit is found for graviton masses of 1.8 tevct with a coupling parameter constant c=0.01 and 4.1 tevct for c=0.1 . For the six Z' models considered here, the 5 sigma discovery limit ranges for masses from 3.6 tevct (rm Z_psi) to 4.6 tevct (rm Z_ALRM)

    Model-independent constraints on the CKM matrix elements Vtb|V_{tb}|, Vts|V_{ts}| and Vtd|V_{td}|

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    Single top quark production cross sections at hadron colliders are traditionally used to extract the modulus of the VtbV_{tb} element of the Cabibbo-Kobayashi-Maskawa matrix under the following assumption: VtbVtd,Vts|V_{tb}| \gg |V_{td}|, |V_{ts}|. For the first time, direct limits on Vtd|V_{td}| and Vts|V_{ts}| are obtained using experimental data without the assumption of the unitarity of the CKM matrix. Limits on the Vtd|V_{td}|, Vts|V_{ts}| and Vtb|V_{tb}| are extracted from differential measurements of single top quark cross sections in tt-channel as a function of the rapidity and transverse momentum of the top quark and the light jet recoiling against the top quark. We have shown that the pseudorapidity of the forward jet in the single top production is one of the most powerful observables for discriminating between the Vtd|V_{td}| and Vtb|V_{tb}| events. We perform a global fit of top quark related CKM elements to experimental data from the LHC Runs I and II and Tevatron. Experimental data include inclusive and differential single top cross sections in tt-channel, inclusive tW production cross section, and top quark branching ratio to b quark and W boson. We present bounds on Vtb|V_{tb}|, Vts|V_{ts}| and Vtd|V_{td}| using current data and project the results for future LHC data sets corresponding to luminosities of 300 and 3000 \fb