Measurement of the front-end dead-time of the LHCb muon detector and evaluation of its contribution to the muon detection inefficiency

A method is described which allows to deduce the dead-time of the front-end electronics of the LHCb muon detector from a series of measurements performed at different luminosities at a bunch-crossing rate of 20 MHz. The measured values of the dead-time range from 70 ns to 100 ns. These results allow to estimate the performance of the muon detector at the future bunch-crossing rate of 40 MHz and at higher luminosity

First observation of Bs -> D_{s2}^{*+} X mu nu decays

Using data collected with the LHCb detector in proton-proton collisions at a centre-of-mass energy of 7 TeV, the semileptonic decays Bs -> Ds+ X mu nu and Bs -> D0 K+ X mu nu are detected. Two structures are observed in the D0 K+ mass spectrum at masses consistent with the known D^+_{s1}(2536) and $D^{*+}_{s2}(2573) mesons. The measured branching fractions relative to the total Bs semileptonic rate are B(Bs -> D_{s2}^{*+} X mu nu)/B(Bs -> X mu nu)= (3.3\pm 1.0\pm 0.4)%, and B(Bs -> D_{s1}^+ X munu)/B(Bs -> X mu nu)= (5.4\pm 1.2\pm 0.5)%, where the first uncertainty is statistical and the second is systematic. This is the first observation of the D_{s2}^{*+} state in Bs decays; we also measure its mass and width.Comment: 8 pages 2 figures. Published in Physics Letters

Prompt K_short production in pp collisions at sqrt(s)=0.9 TeV

The production of K_short mesons in pp collisions at a centre-of-mass energy of 0.9 TeV is studied with the LHCb detector at the Large Hadron Collider. The luminosity of the analysed sample is determined using a novel technique, involving measurements of the beam currents, sizes and positions, and is found to be 6.8 +/- 1.0 microbarn^-1. The differential prompt K_short production cross-section is measured as a function of the K_short transverse momentum and rapidity in the region 0 < pT < 1.6 GeV/c and 2.5 < y < 4.0. The data are found to be in reasonable agreement with previous measurements and generator expectations.Comment: 6+18 pages, 6 figures, updated author lis

The LHCb upgrade I

The LHCb upgrade represents a major change of the experiment. The detectors have been almost completely renewed to allow running at an instantaneous luminosity five times larger than that of the previous running periods. Readout of all detectors into an all-software trigger is central to the new design, facilitating the reconstruction of events at the maximum LHC interaction rate, and their selection in real time. The experiment's tracking system has been completely upgraded with a new pixel vertex detector, a silicon tracker upstream of the dipole magnet and three scintillating fibre tracking stations downstream of the magnet. The whole photon detection system of the RICH detectors has been renewed and the readout electronics of the calorimeter and muon systems have been fully overhauled. The first stage of the all-software trigger is implemented on a GPU farm. The output of the trigger provides a combination of totally reconstructed physics objects, such as tracks and vertices, ready for final analysis, and of entire events which need further offline reprocessing. This scheme required a complete revision of the computing model and rewriting of the experiment's software

Test results of a full size prototype of the muon chambers for region M2/R4 of the LHCb muon system

A full size prototype M2R4-01 of the Wire Pad Chambers for region M2/R4 of the LHCb Muon System hs been constructed at PNPI and tested in the T11 beam at CERN. The prototype contained two double-gap chambers with the sensitive area of 25x120 cm2. Each double-gap chamber contained 24 wire pads of 5x25 cm2 size. The prototype was fully instrumented with the FE electronics based on SONY chips with active adapters at the input allowing to optimize the parameters of the read out channels. The chamber was tested with four different concentrations of the gas components in the Ar/CO2/CF4 gas mixture. The beam tests showed quite satisfactory performance of the M2R4-01 prototype : a wide efficiency plateau uniform over the whole sensitive area of the chamber, low noise rates and cross-talks. It was demonstrated that the gas mixtures Ar(40%)+CO2(40%,30%)+CF4(20%,30%) provide higher stability against the HV-trips thus extending essentially the operational plateau of the chamber

Beam tests of WPC-7 prototype of iwire pad chambers for the LHCb muon system

A new prototype of the Wire Pad Chamber for the LHCb Muon System, WPC-7, has been constructed at PNPI and tested in the T11 beam at CERN. This prototype proved to be more stable against the electrical discharges at high voltages thus extending the operational plateau of the chamber by 200V. This made it possible to operate with larger wire pad sizes up to 12x16cm2. This report presents the results from the beam tests of the WPC-7 prototype : time resolution and efficiency, cross-talk, noise counting rates, streamer probability measured at various high voltages and discriminator thresholds

Beam tests of WPC-8 and WPC-9 prototypes of the wire pad chambers for the LHCb muon system

Two new prototypes, WPC-8 and WPC-9, of the Wire Pad Chambers have been constructed at PNPI. The design of these double-gap wire chambers was similar to the previously tested WPC-7 prototype with one important difference: the anode wire planes were electrically independent, which allows to operate the new prototypes either in the double-gap or in the single-gap modes. The prototypes have been tested in the T11 beam at CERN, and this report presents the results of the tests. As in the previous tests, the PNPI front-end electronics based on the discrete elements was used in the read out channels. In addition, a new option of the FE electronics based on the SONY chip has been developed (SONY++) with an active adapter at the input of the chip allowing to reduce the input impedance and the width of the shaped signals. The SONY++ option was tested with the WPC-9 prototype with very satisfactory results. The performance proved to be identical to that with the PNPI FE electronics

Measurement of sigma (pp -> bbX) at √s=7 TeV in the forward region

Decays of b hadrons into final states containing a D-0 meson and a muon are used to measure the bb; production cross-section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC. In the pseudorapidity interval 2 < eta < 6 and integrated over all transverse momenta we find that the average cross-section to produce b-flavoured or b-flavoured hadrons is (75.3 +/- 5.4 +/- 13.0) mu b