3 research outputs found

    Exclusive photoproduction of pi degrees up to large values of Mandelstam variables s, t, and u with CLAS

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    Exclusive photoproduction cross sections have been measured for the process γppπ0(e+e(γ))\gamma p \rightarrow p\pi^0(e^+e^-(\gamma)) with the Dalitz decay final state using tagged photon energies in the range of Eγ=1.2755.425E_{\gamma} = 1.275-5.425 GeV. The complete angular distribution of the final state π0\pi^0, for the entire photon energy range up to large values of tt and uu, has been measured for the first time. The data obtained show that the cross section dσ/dtd\sigma/dt, at mid to large angles, decreases with energy as s6.89±0.26s^{-6.89\pm 0.26} . This is in agreement with the perturbative QCD quark counting rule prediction of s7s^{-7} . Paradoxically, the size of angular distribution of measured cross sections is greatly underestimated by the QCD based Generalized Parton Distribution mechanism at highest available invariant energy s=11s=11 GeV2^2. At the same time, the Regge exchange based models for π0\pi^0 photoproduction are more consistent with experimental data.Comment: 7 pages, 6 figure

    Observation of B-s(0) -> chi(c1)phi decay and study of B-0 -> chi K-c1,K-2*(0) decays

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    The first observation of the decay B-s(0) -> chi(c1)phi and a study of B-0 -> chi K-c1,K-2*(0) decays are presented. The analysis is performed using a dataset, corresponding to an integrated luminosity of 1.0 fb(-1), collected by the LHCb experiment in pp collisions at a centre-of-mass energy of 7 TeV. The following ratios of branching fractions are measured: B(B-s(0) -> chi(c1)phi)/B(B-s(0) -> J/psi phi) = (18.9 +/- 1.8 (stat) +/- 1.3 (syst) +/- 0.8(B)) x 10(-2), B(B-0 -> chi K-c1*(0))//B(B-0 -> J/psi K*(0)) = (19.8 +/- 1.1 (stat) +/- 1.2 (syst) +/- 0.9(B)) x 10(-2), B(B-0 -> chi K-c2*(0))//B(B-0 -> chi K-c1*(0)) = (17.1 +/- 5.0 (stat) +/- 1.7 (syst) +/- 1.1(B)) x 10(-2), where the third uncertainty is due to the limited knowledge of the branching fractions of chi(c) -> J/psi gamma modes

    Search for the rare decay D-0 -> mu(+) mu(-)

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    A search for the rare decay D-0 -> mu(+) mu(-) is performed using a data sample, corresponding to an integrated luminosity of 0.9 fb(-1), of pp collisions collected at a centre-of-mass energy of 7 TeV by the LHCb experiment. The observed number of events is consistent with the background expectations and corresponds to an upper limit of B(D-0 -> mu(+) mu(-)) < 6.2 (7.6) x 10(-9) at 90% (95%) confidence level. This result represents an improvement of more than a factor twenty with respect to previous measurements
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