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Register a new userExclusive electromagnetic production of strangeness on the nucleon : review of recent data in a Regge approach
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In view of the numerous experimental results recently released, we provide in this letter an update on the performance of our simple Regge model for strangeness electroproduction on the nucleon. Without refitting any parameters, a decent description of all measured observables and channels is achieved. We also give predictions for spin transfer observables, recently measured at Jefferson Lab which have high sensitivity to discriminate between different theoretical approaches.
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We present results on the Central Exclusive Production of charged particle pairs $h^{+}h^{-}$ ($h = pi, K, p$), $ppto p^prime+h^{+}h^{-}+p^prime$, obtained with the STAR experiment at RHIC in proton-proton collisions at a center-of-mass energy of $sqrt{s} = 200$ GeV. All final-state particles were reconstructed, including forward-scattered protons detected in the Roman Pot system. As a result, the Double Pomeron Exchange (DPE) events were selected and the non-exclusive backgrounds were efficiently rejected. Differential fiducial cross sections were measured as functions of observables related to the central hadronic final state and to the forward-scattered protons. The measured cross sections were compared to phenomenological model predictions based on the DPE. We also present preliminary results on the measurement of the same physics process at higher collision energy $sqrt{s} = 510$ GeV. The data demonstrate features similar to those observed at $sqrt{s} = 200$ GeV.
We review activities in the field of theoretical, phenomenological and experimental studies related to the production of the Higgs boson in central exclusive processes at LHC in models beyond Standard Model. Prospects in the context of the Higgs boson discovery at LHC in 2012 and of proposals to build forward proton detectors at ATLAS and CMS side are summarized.
We fitted the pi-pi mass distribution in the range 0.5 < mpipi < 1.1 GeV measured in hard exclusive positron-proton reactions at HERA by the form dictated by QCD at leading twist level. Extracted parameters are related to valence quark distribution in the pion, and to the pion and rho meson distribution amplitudes. We obtain, for the first time, a measurement of the second Gegenbauer coefficient of the rho meson distribution amplitude: $a_2^{(rho)}= -0.10pm 0.20 $ for a photon virtuality of <Q^2>=21.2 GeV^2.
Previous approaches to the photo- and electro-production of strangeness off the proton, based upon effective hadronic Lagrangians, are extended here to incorporate the so called off-shell effects inherent to the fermions with spin >= 3/2. A formalism for intermediate-state, spin 3/2, nucleonic and hyperonic resonances is presented and applied to the processes $gamma + p ---> K^{+} + Lambda$, for $E_{gamma}^{lab}$ <= 2.5 GeV, $e + p ---> e + K^+ + Lambda$, as well as the branching ratio for the crossed channel reaction $K^- + p ---> gamma + Lambda$, with stopped kaons. The sensitivity, from moderate to significant, of various observables to such effects are discussed.
We study the production of prompt diphotons in the central region of rapidity within the framework of the quasi-multi-Regge-kinematics approach applying the hypothesis of quark and gluon Reggeization. We describe accurately and without free parameters the experimental data which were obtained by the CDF Collaboration at the Tevatron Collider. It is shown that the main contribution to studied process is given by the direct fusion of two Reggeized gluons into a photon pair, which is described by the effective Reggeon-Reggeon to particle-particle vertex. The contribution from the annihilation of Reggeized quark-antiquark pair into a diphoton is also considered. At the stage of numerical calculations we use the Kimber-Martin-Ryskin prescription for unintegrated quark and gluon distribution functions, with the Martin-Roberts-Stirling-Thorne collinear parton densities for a proton as input.
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