524 research outputs found

    A pet study of human skill learning: Changes in brain activity related to learning an orientation discrimination task

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    peer reviewedUsing 15O-water 3D positron emission tomography we investigated the effect of training in orientation discrimination upon cerebral activity in healthy human adults. When subjects are trained in this discrimination task, they learn the visuo-motor stimulus-response association required by the task and they increase their perceptual abilities in orientation discrimination. The present study was designed to investigate the rCBF modifications related to both these learning processes induced by training in orientation discrimination. PET data were acquired on two separate days (before and after training). Comparing the activation pattern related to orientation discrimination before and after the training period we observed activity decreases located in the left cerebellar cortex, in the right precentral gyrus and bilaterally in the fusiform gyri. The only region showing an activity increase was located in the body of the right caudate nucleus. These findings confirm the role of the neostriatum in skill learning and highlight the importance of mechanisms resulting in cortical and cerebellar neuronal activity decreases in this type of learning

    Measurement of the branching fraction and CPCP asymmetry in B+→J/ψρ+B^{+}\rightarrow J/\psi \rho^{+} decays

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    International audienceThe branching fraction and direct C ⁣PC\!P asymmetry of the decay B+ ⁣→J/ψρ+{{{B} ^+}} \!\rightarrow {{J /\psi }} {{\rho } ^+} are measured using proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV, corresponding to a total integrated luminosity of 3   fb −1\,\text{ fb }^{-1} . The following results are obtained: B(B+ ⁣→J/ψρ+)=(3.81+0.25−0.24±0.35)×10−5,AC ⁣P(B+ ⁣→J/ψρ+)=−0.045+0.056−0.057±0.008,\begin{aligned} \mathcal {B}({{B} ^+} \!\rightarrow {{J /\psi }} {{\rho } ^+} )&= (3.81^{+0.25-0.24} \pm 0.35) \times 10^{-5},\\ \mathcal {A}^{{C\!P}} ({{B} ^+} \!\rightarrow {{J /\psi }} {{\rho } ^+} )&= -0.045^{+0.056-0.057} \pm 0.008, \end{aligned} where the first uncertainties are statistical and the second systematic. Both measurements are the most precise to date

    Study of ΄\Upsilon production in ppPb collisions at sNN=8.16\sqrt{s_{NN}}=8.16 TeV

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    International audienceThe production of ϒ(nS) mesons (n = 1, 2, 3) in pPb and Pbp collisions at a centre-of-mass energy per nucleon pair sNN=8.16 \sqrt{s_{\mathrm{NN}}}=8.16 TeV is measured by the LHCb experiment, using a data sample corresponding to an integrated luminosity of 31.8 nb−1^{−1}. The ϒ(nS) mesons are reconstructed through their decays into two opposite-sign muons. The measurements comprise the differential production cross-sections of the ϒ(1S) and ϒ(2S) states, their forward-to-backward ratios and nuclear modification factors. The measurements are performed as a function of the transverse momentum pT_{T} and rapidity in the nucleon-nucleon centre-of-mass frame y∗^{*} of the ϒ(nS) states, in the kinematic range pT_{T} < 25 GeV/c and 1.5 < y∗^{*} < 4.0 (−5.0 < y∗^{*} < −2.5) for pPb (Pbp) collisions. In addition, production cross-sections for ϒ(3S) are measured integrated over phase space and the production ratios between all three ϒ(nS) states are determined. Suppression for bottomonium in proton-lead collisions is observed, which is particularly visible in the ratios. The results are compared to theoretical models

    Search for the rare decay B+→Ό+Ό−Ό+ΜΌB^{+} \rightarrow {\mu}^{+}{\mu}^{-}{\mu}^{+}{\nu}_{{\mu}}

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    International audienceA search for the rare leptonic decay {{{B} ^+}} \!\rightarrow {\mu ^+} {\mu ^-} {\mu ^+} {{\upnu } _\mu } is performed using proton-proton collision data corresponding to an integrated luminosity of 4.7 fb−14.7 \, {\hbox {fb}}^{-1} collected by the LHCb experiment. The search is carried out in the region where the lowest of the two ÎŒ+Ό−{\mu ^+\mu ^-} mass combinations is below 980 MeV ⁣/c2980 {\mathrm {\,MeV\!/}c^2} . The data are consistent with the background-only hypothesis and an upper limit of 1.6×10−81.6 \times 10^{-8} at 95% confidence level is set on the branching fraction in the stated kinematic region
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