118031301
Muon pair production by muons and narrow muon bundles underground
We consider the process of muon pair production by high-energy muons and its consequences for the characteristics of muon flux underground. It is shown that the accounting of this process in the muon propagation through the rock results in an additional flux of narrow double- and triple-muon events which is comparable to the conventional flux of narrow muon bundles with low multiplicity.
121667127
The potential of liquid xenon for WIMP search: the ZEPLIN diagnostic array
Abstract A Liquid Xenon based WIMP detector diagnostic array is currently developed by the UKDMC with the help of international collaborators. After a brief reminder on the detection principle in Liquid Xenon, the individual detectors will be described. ZEPLIN I, a detector with a 4 kg fiducial mass with a background discrimination based on Pulse Shape Analysis, is already underground and starting operation. Two setups with improved background discrimination tools (as the ionisation is also recorded) are designed and scheduled to move underground in the second half of 2001. Both of them, ZEPLIN II and ZEPLIN III, are predicted to be sensitive to rate of 0.1–0.01 events/kg/day within 2 years of data taking. Furthermore, new ideas for lower background readout devices are studied, in order to avoid the use of PhotoMultiplier Tubes (PMTs).
119286983
Muon-induced background in the EDELWEISS dark matter search
Abstract A dedicated analysis of the muon-induced background in the EDELWEISS dark matter search has been performed on a data set acquired in 2009 and 2010. The total muon flux underground in the Laboratoire Souterrain de Modane (LSM) was measured to be Φ μ = ( 5.4 ± 0.2 - 0.9 + 0.5 )  muons/m 2 /d. The modular design of the μ -veto system allows the reconstruction of the muon trajectory and hence the determination of the angular dependent muon flux in LSM. The results are in good agreement with both MC simulations and earlier measurements. Synchronization of the μ -veto system with the phonon and ionization signals of the Ge detector array allowed identification of muon-induced events. Rates for all muon-induced events Γ μ = ( 0.172 ± 0.012 ) evts / ( kg d ) and of WIMP-like events Γ μ – n = 0.008 - 0.004 + 0.005 evts / ( kg d ) were extracted. After vetoing, the remaining rate of accepted muon-induced neutrons in the EDELWEISS-II dark matter search was determined to be Γ irred μ – n 6 · 10 - 4 evts / ( kg d ) at 90% C.L. Based on these results, the muon-induced background expectation for an anticipated exposure of 3000 kg d for EDELWEISS-III is N 3000 kg d μ – n 0.6 events.
12347950
The ZEPLIN-III dark matter detector: Performance study using an end-to-end simulation tool
We present results from a GEANT4-based Monte Carlo tool for end-to-end simulations of the ZEPLIN-III dark matter experiment. ZEPLIN-III is a two-phase detector which measures both the scintillation light and the ionisation charge generated in liquid xenon by interacting particles and radiation. The software models the instrument response to radioactive backgrounds and calibration sources, including the generation, ray-tracing and detection of the primary and secondary scintillations in liquid and gaseous xenon, and subsequent processing by data acquisition electronics. A flexible user interface allows easy modification of detector parameters at run time. Realistic datasets can be produced to help with data analysis, an example of which is the position reconstruction algorithm developed from simulated data. We present a range of simulation results confirming the original design sensitivity of a few times 10−8 pb to the WIMP-nucleon cross-section.
120314532
Progress report from the UK Dark Matter search at Boulby Mine
Abstract The UK Dark Matter Collaboration is currently running a series of scintillation devices at the Boulby mine in North Yorkshire to search for the neutralino, the hypothetical WIMP solution to the dark matter problem. Results of the current NaI(T1) detector array will be discussed, illustrating a population of events of unknown origin. Diagnostic tests performed to investigate the origin of these anomalous events will be outlined, including alpha, beta and neutron calibrations.
115887438
Particle polarization in inclusive reactions
118411779
Study of forward Z + jet production in pp collisions at $ \sqrt{s} $ = 7 TeV
A bstractA measurement of the Z(→ μ+μ−) + jet production cross-section in pp collisions at a centre-of-mass energy $ \sqrt{s} $ = 7 TeV is presented. The analysis is based on an integrated luminosity of 1.0 fb−1 recorded by the LHCb experiment. Results are shown with two jet transverse momentum thresholds, 10 and 20 GeV, for both the overall cross-section within the fiducial volume, and for six differential cross-section measurements. The fiducial volume requires that both the jet and the muons from the Z boson decay are produced in the forward direction (2.0 < η < 4.5). The results show good agreement with theoretical predictions at the second-order expansion in the coupling of the strong interaction.

8388828
Observation of photon polarization in the b→sγ transition.
This Letter presents a study of the flavor-changing neutral current radiative B±→K±π∓π±γ decays performed using data collected in proton-proton collisions with the LHCb detector at 7 and 8 TeV center-of-mass energies. In this sample, corresponding to an integrated luminosity of 3  fb-1, nearly 14 000 signal events are reconstructed and selected, containing all possible intermediate resonances with a K±π∓π± final state in the [1.1,1.9]  GeV/c2 mass range. The distribution of the angle of the photon direction with respect to the plane defined by the final-state hadrons in their rest frame is studied in intervals of K±π∓π± mass and the asymmetry between the number of signal events found on each side of the plane is obtained. The first direct observation of the photon polarization in the b→sγ transition is reported with a significance of 5.2σ.
118560313
Observation of Z production in proton-lead collisions at LHCb
A bstractThe first observation of Z boson production in proton-lead collisions at a centre-of-mass energy per proton-nucleon pair of sNN$$ \sqrt{s_{N\;N}} $$ = 5 TeV is presented. The data sample corresponds to an integrated luminosity of 1.6 nb−1 collected with the LHCb detector. The Z candidates are reconstructed from pairs of oppositely charged muons with pseudorapidities between 2.0 and 4.5 and transverse momenta above 20 GeV/c. The invariant dimuon mass is restricted to the range 60 − 120 GeV/c. The Z production cross-section is measured to be
σZ→μ+μ−fwd=13.5−4.0+5.4stat.±1.2syst.nb$$ {\sigma_Z}_{\to {\mu}^{+}{\mu}^{-}}\left(\mathrm{fwd}\right)={13.5}_{-4.0}^{+5.4}\left(\mathrm{stat}.\right)\pm 1.2\left(\mathrm{syst}.\right)\mathrm{nb} $$
 in the direction of the proton beam and
σZ→μ+μ−bwd=10.7−5.1+8.4stat.±1.0syst.nb$$ {\sigma}_{Z\to {\mu}^{+}{\mu}^{-}}\left(\mathrm{bwd}\right)={10.7}_{-5.1}^{+8.4}\left(\mathrm{stat}.\right)\pm 1.0\left(\mathrm{syst}.\right)\mathrm{nb} $$
 in the direction of the lead beam, where the first uncertainty is statistical and the second systematic.

119182463
Measurement of B meson production cross-sections in proton-proton collisions at $ \sqrt{s}=7 $ TeV
A bstractThe production cross-sections of B mesons are measured in pp collisions at a centre-of-mass energy of 7 TeV, using data collected with the LHCb detector corresponding to a integrated luminosity of 0.36 fb−1. The B+, B0 and $ B_s^0 $ mesons are reconstructed in the exclusive decays B+ → J/ψK+, B0 → J/ψK*0 and $ B_s^0\to {J \left/ {{\psi \phi }} \right.} $, with J/ψ → μ+μ−, K*0 → K+π− and ϕ → K+K−. The differential cross-sections are measured as functions of B meson transverse momentum pT and rapidity y, in the range 0 < pT< 40 GeV/c and 2.0 < y < 4.5. The integrated cross-sections in the same pT and y ranges, including charge-conjugate states, are measured to be
$ \begin{array}{*{20}{c}} {\sigma \left( {pp\to {B^{+}}+X} \right)=38.9\pm 0.3\left( {\mathrm{stat}.} \right)\pm 2.5\left( {\mathrm{syst}.} \right)\pm 1.3\left( {\mathrm{norm}.} \right)\upmu \mathrm{b},} \hfill \\ {\sigma \left( {pp\to {B^0}+X} \right)=38.1\pm 0.6\left( {\mathrm{stat}.} \right)\pm 3.7\left( {\mathrm{syst}.} \right)\pm 4.7\left( {\mathrm{norm}.} \right)\upmu \mathrm{b},} \hfill \\ {\sigma \left( {pp\to B_s^0+X} \right)=10.5\pm 0.2\left( {\mathrm{stat}.} \right)\pm 0.8\left( {\mathrm{syst}.} \right)\pm 1.0\left( {\mathrm{norm}.} \right)\upmu \mathrm{b},} \hfill \\ \end{array} $where the third uncertainty arises from the pre-existing branching fraction measurements.

125101712
Measurement of CP asymmetry in $B^0_s \rightarrow D^{\mp}_s K^{\pm}$ decays
We report on measurements of the time-dependent CP violating observables in $B^0_s\rightarrow D^{\mp}_s K^{\pm}$ decays using a dataset corresponding to 1.0 fb$^{-1}$ of pp collisions recorded with the LHCb detector. We find the CP violating observables $C_f=0.53\pm0.25\pm0.04$, $A^{\Delta\Gamma}_f=0.37\pm0.42\pm0.20$, $A^{\Delta\Gamma}_{\bar{f}}=0.20\pm0.41\pm0.20$, $S_f=-1.09\pm0.33\pm0.08$, $S_{\bar{f}}=-0.36\pm0.34\pm0.08$, where the uncertainties are statistical and systematic, respectively. We use these observables to make the first measurement of the CKM angle $\gamma$ in $B^0_s\rightarrow D^{\mp}_s K^{\pm}$ decays, finding $\gamma$ = (115$_{-43}^{+28}$)$^\circ$ modulo 180$^\circ$ at 68% CL, where the error contains both statistical and systematic uncertainties.