Exclusive photoproduction of ρ0(770) mesons is studied using the H1 detector at the ep collider HERA. A sample of about 900,000 events is used to measure single- and double-differential cross ...sections for the reaction γp→π+π-Y. Reactions where the proton stays intact (mY=mp) are statistically separated from those where the proton dissociates to a low-mass hadronic system (mp<mY<10GeV). The double-differential cross sections are measured as a function of the invariant mass mππ of the decay pions and the squared 4-momentum transfer t at the proton vertex. The measurements are presented in various bins of the photon–proton collision energy Wγp. The phase space restrictions are 0.5≤mππ≤2.2GeV, |t|≤1.5GeV2, and 20≤Wγp≤80GeV. Cross section measurements are presented for both elastic and proton-dissociative scattering. The observed cross section dependencies are described by analytic functions. Parametrising the mππ dependence with resonant and non-resonant contributions added at the amplitude level leads to a measurement of the ρ0(770) meson mass and width at mρ=770.8-2.7+2.6(tot.)MeV and Γρ=151.3-3.6+2.7(tot.)MeV, respectively. The model is used to extract the ρ0(770) contribution to the π+π- cross sections and measure it as a function of t and Wγp. In a Regge asymptotic limit in which one Regge trajectory α(t) dominates, the intercept α(t=0)=1.0654-0.0067+0.0098(tot.) and the slope α′(t=0)=0.233-0.074+0.067(tot.)GeV-2 of the t dependence are extracted for the case mY=mp.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) A first measurement is presented of exclusive photoproduction of ... mesons associated with leading neutrons at HERA. The ...data were taken with the H1 detector in the years 2006 and 2007 at a centre-of-mass energy of ... GeV and correspond to an integrated luminosity of 1.16 pb... The ... mesons with transverse momenta ... GeV are reconstructed from their decays to charged pions, while leading neutrons carrying a large fraction of the incoming proton momentum, ..., are detected in the Forward Neutron Calorimeter. The phase space of the measurement is defined by the photon virtuality ... GeV..., the total energy of the photon-proton system ... GeV and the polar angle of the leading neutron ... mrad. The cross section of the reaction ... is measured as a function of several variables. The data are interpreted in terms of a double peripheral process, involving pion exchange at the proton vertex followed by elastic photoproduction of a ... meson on the virtual pion. In the framework of one-pion-exchange dominance the elastic cross section of photon-pion scattering, ..., is extracted. The value of this cross section indicates significant absorptive corrections for the exclusive reaction ...
Differential cross sections for the production of at least four jets have been measured in proton--proton collisions at $\sqrt{s} = 8$ TeV at the Large Hadron Collider using the ATLAS detector. The ...dataset corresponds to an integrated luminosity of 20.3 $fb^{-1}$. The cross sections, corrected for detector effects, are compared to leading-order and next-to-leading-order calculations as a function of the jet momenta, invariant masses, minimum and maximum opening angles and other kinematic variables.
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