The first observation of the decays Λb0→χc 1p K- and Λb0→χc 2p K- is reported using a data sample corresponding to an integrated luminosity of 3.0 fb-1, collected by the LHCb experiment in p p ...collisions at center-of-mass energies of 7 and 8 TeV. The following ratios of branching fractions are measured: B/(Λb0→χc 1p K-) B (Λb0→J /ψ p K-) =0.242 ±0.014 ±0.013 ±0.009 ,B/(Λb0→χc 2p K-) B (Λb0→J /ψ p K-) =0.248 ±0.020 ±0.014 ±0.009 ,B/(Λb0→χc 2p K-) B (Λb0→χc 1p K-) =1.02 ±0.10 ±0.02 ±0.05 , where the first uncertainty is statistical, the second systematic, and the third due to the uncertainty on the branching fractions of the χc 1→J /ψ γ and χc 2→J /ψ γ decays. Using both decay modes, the mass of the Λb0 baryon is also measured to be mΛb0=5619.44 ±0.28 ±0.26 MeV /c2 , where the first and second uncertainties are statistical and systematic, respectively.
The SoLid experiment aims to measure neutrino oscillation at a baseline of 6.4 m from the BR2 nuclear reactor in Belgium. Anti-neutrinos interact via inverse beta decay (IBD), resulting in a positron ...and neutron signal that are correlated in time and space. The detector operates in a surface building, with modest shielding, and relies on extremely efficient online rejection of backgrounds in order to identify these interactions. A novel detector design has been developed using 12800 5 cm cubes for high segmentation. Each cube is formed of a sandwich of two scintillators, PVT and 6LiF:ZnS(Ag), allowing the detection and identification of positrons and neutrons respectively. The active volume of the detector is an array of cubes measuring 80x80x250 cm (corresponding to a fiducial mass of 1.6 T), which is read out in layers using two dimensional arrays of wavelength shifting fibres and silicon photomultipliers, for a total of 3200 readout channels. Signals are recorded with 14 bit resolution, and at 40 MHz sampling frequency, for a total raw data rate of over 2 Tbit/s. In this paper, we describe a novel readout and trigger system built for the experiment, that satisfies requirements on: compactness, low power, high performance, and very low cost per channel. The system uses a combination of high price-performance FPGAs with a gigabit Ethernet based readout system, and its total power consumption is under 1 kW. The use of zero suppression techniques, combined with pulse shape discrimination trigger algorithms to detect neutrons, results in an online data reduction factor of around 10000. The neutron trigger is combined with a large per-channel history time buffer, allowing for unbiased positron detection. The system was commissioned in late 2017, with successful physics data taking established in early 2018.
The CP asymmetry in the mixing of B0s and B̅0s mesons is measured in proton-proton collision data corresponding to an integrated luminosity of 3.0 fb−1, recorded by the LHCb experiment at ...centre-of-mass energies of 7 and 8 TeV. Semileptonic B0s and B̅0s decays are studied in the inclusive mode D∓sμ±νμX with the D∓s mesons reconstructed in the K+K−π∓ final state. Correcting the observed charge asymmetry for detection and background effects, the CP asymmetry is found to be assl=(0.39±0.26±0.20)%, where the first uncertainty is statistical and the second systematic. This is the most precise measurement of assl to date, and is consistent with the prediction from the Standard Model of particle physics.
The polarization of photons produced in radiative B-s(0) decays is studied for the first time. The data are recorded by the LHCb experiment in pp collisions corresponding to an integrated luminosity ...of 3 fb(-1) at center-of-mass energies of 7 and 8 TeV. A time-dependent analysis of the B-s(0) ->phi gamma decay rate is conducted to determine the parameter A(Delta), which is related to the ratio of right-over left-handed photon polarization amplitudes in b -> s gamma transitions. A value of A(Delta) = -0.98(-0.52)(-0.20)(+0.46)(+0.23) is measured. This result is consistent with the standard model prediction within 2 standard deviations.
A time-dependent angular analysis of B0s→ψ(2S)ϕ decays is performed using data recorded by the LHCb experiment. The data set corresponds to an integrated luminosity of 3.0\invfb collected during Run ...1 of the LHC. The CP-violating phase and decay-width difference of the B0s system are measured to be ϕs=0.23+0.29−0.28±0.02 rad and ΔΓs=0.066+0.041−0.044±0.007 ps−1, respectively, where the first uncertainty is statistical and the second systematic. This is the first time that ϕs and ΔΓs have been measured in a decay containing the ψ(2S) resonance.
The SoLid experiment has been designed to search for an oscillation pattern induced by a light sterile neutrino state, utilising the BR2 reactor of SCK\(\bullet\)CEN, in Belgium. The detector ...leverages a new hybrid technology, utilising two distinct scintillators in a cubic array, creating a highly segmented detector volume. A combination of 5 cm cubic polyvinyltoluene cells, with \(^6\)LiF:ZnS(Ag) sheets on two faces of each cube, facilitate reconstruction of the neutrino signals. % The polyvinyltoluene scintillator is used as an \(\overline{\nu}_e\) target for the inverse beta decay of (\(\overline{\nu}_e + p \rightarrow e^{+}+n\)), with the \(^6\)LiF:ZnS(Ag) sheets used for associated neutron detection. Scintillation signals are read out by a network of wavelength shifting fibres connected to multipixel photon counters. Whilst the high granularity provides a powerful toolset to discriminate backgrounds; by itself the segmentation also represents a challenge in terms of homogeneity and calibration, for a consistent detector response. The search for this light sterile neutrino implies a sensitivity to distortions of around \(\mathcal{O}\)(10)\% in the energy spectrum of reactor \(\overline{\nu}_e\). Hence, a very good neutron detection efficiency, light yield and homogeneous detector response are critical for data validation. The minimal requirements for the SoLid physics program are a light yield and a neutron detection efficiency larger than 40 PA/MeV/cube and 50 \% respectively. In order to guarantee these minimal requirements, the collaboration developed a rigorous quality assurance process for all 12800 cubic cells of the detector. To carry out the quality assurance process, an automated calibration system called CALIPSO was designed and constructed.
Production cross-sections of prompt charm mesons are measured with the first data from $pp$ collisions at the LHC at a centre-of-mass energy of $13\,\mathrm{TeV}$. The data sample corresponds to an ...integrated luminosity of $4.98 \pm 0.19\,\mathrm{pb}^{-1}$ collected by the LHCb experiment. The production cross-sections of $D^{0}$, $D^{+}$, $D_{s}^{+}$, and $D^{*+}$ mesons are measured in bins of charm meson transverse momentum, $p_{\mathrm{T}}$, and rapidity, $y$, and cover the range $0 < p_{\mathrm{T}} < 15\,\mathrm{GeV}/c$ and $2.0 < y < 4.5$. The ratios of the integrated cross-sections between charm mesons agree with previously measured fragmentation fractions. The inclusive $c\overline{c}$ cross-section within the range of $0 < p_{\mathrm{T}} < 8\,\mathrm{GeV}/c$ is found to be \ \sigma(pp \to c\overline{c}X) = 2940 \pm 3 \pm 180 \pm 160\,\mu\mathrm{b} \ where the uncertainties are due to statistical, systematic and fragmentation fraction uncertainties, respectively.
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