119194940
Measurement of b-hadron branching fractions for two-body decays into charmless charged hadrons
A bstractBased on data corresponding to an integrated luminosity of 0.37 fb−1 collected by the LHCb experiment in 2011, the following ratios of branching fractions are measured:$ \begin{array}{*{20}{c}} {{{{\mathcal{B}\left( {B^0 \to {\pi^{+}}{\pi^{-}}} \right)}} \left/ {{\mathcal{B}\left( {B^0 \to {K^{+}}{\pi^{-}}} \right)}} \right.}=0.262\pm 0.009\pm 0.017,} \\ {\left( {{f_s \left/ {f_d } \right.}} \right)\cdot {{{\mathcal{B}\left( {B_s^0\to {K^{+}}{K^{-}}} \right)}} \left/ {{\mathcal{B}\left( {B^0 \to {K^{+}}{\pi^{-}}} \right)}} \right.}=0.316\pm 0.009\pm 0.019,} \\ {\left( {{f_s \left/ {f_d } \right.}} \right)\cdot {{{\mathcal{B}\left( {B_s^0\to {\pi^{+}}{K^{-}}} \right)}} \left/ {{\mathcal{B}\left( {B^0 \to {K^{+}}{\pi^{-}}} \right)}} \right.}=0.074\pm 0.006\pm 0.006,} \\ {\left( {{f_d \left/ {f_s } \right.}} \right)\cdot {{{\mathcal{B}\left( {B^0 \to {K^{+}}{K^{-}}} \right)}} \left/ {{\mathcal{B}\left( {B_s^0\to {K^{+}}{K^{-}}} \right)}} \right.}=0.018_{-0.007}^{+0.008}\pm 0.009,} \\ {\left( {{f_s \left/ {f_d } \right.}} \right)\cdot {{{\mathcal{B}\left( {B_s^0\to {\pi^{+}}{\pi^{-}}} \right)}} \left/ {{\mathcal{B}\left( {B^0 \to {\pi^{+}}{\pi^{-}}} \right)}} \right.}=0.050_{-0.009}^{+0.011}\pm 0.004,} \\ {{{{\mathcal{B}\left( {\Lambda_b^0\to p{\pi^{-}}} \right)}} \left/ {{\mathcal{B}\left( {\Lambda_b^0\to p{K^{-}}} \right)}} \right.}=0.86\pm 0.08\pm 0.05,} \\ \end{array} $where the first uncertainties are statistical and the second systematic. Using the current world average of $ \mathcal{B}\left( {B^0 \to {K^{+}}{\pi^{-}}} \right) $ and the ratio of the strange to light neutral B meson production fs/fd measured by LHCb, we obtain:$ \begin{array}{*{20}{c}} {\mathcal{B}\left( {B^0 \to {\pi^{+}}{\pi^{-}}} \right)=\left( {5.08\pm 0.17\pm 0.37} \right)\times {10^{-6 }},} \\ {\mathcal{B}\left( {B_s^0\to {K^{+}}{K^{-}}} \right)=\left( {23.0\pm 0.7\pm 2.3} \right)\times {10^{-6 }},} \\ {\mathcal{B}\left( {B_s^0\to {\pi^{+}}{K^{-}}} \right)=\left( {5.4\pm 0.4\pm 0.6} \right)\times {10^{-6 }},} \\ {\mathcal{B}\left( {B^0 \to {K^{+}}{K^{-}}} \right)=\left( {0.11_{-0.04}^{+0.05}\pm 0.06} \right)\times {10^{-6 }},} \\ {\mathcal{B}\left( {B_s^0\to {\pi^{+}}{\pi^{-}}} \right)=\left( {0.95_{-0.17}^{+0.21}\pm 0.13} \right)\times {10^{-6 }}.} \\ \end{array} $
 The measurements of $ \mathcal{B}\left( {B_s^0\to {K^{+}}{K^{-}}} \right) $, $ \mathcal{B}\left( {B_s^0\to {\pi^{+}}{K^{-}}} \right) $ and $ \mathcal{B}\left( {B^0 \to {K^{+}}{K^{-}}} \right) $ are the most precise to date. The decay mode $ B_s^0\to {\pi^{+}}{\pi^{-}} $ is observed for the first time with a significance of more than 5σ.
119255801
Measurement of the polarization amplitudes and triple product asymmetries in the B-s(0) -> phi phi decay
Using 1.0 fb^{-1} of pp collision data collected at a centre-of-mass energy of sqrt{s}=7 TeV with the LHCb detector, measurements of the polarization amplitudes, strong phase difference and triple product asymmetries in the B_s^0 -> phi phi decay mode are presented. The measured values are |A_0|^2 = 0.365 +- 0.022 (stat) +- 0.012 (syst), |A_perp|^2 = 0.291 +- 0.024 (stat) +- 0.010 (syst), cos(delta_parallel) = -0.844 +- 0.068 (stat) +- 0.029 (syst), A_U = -0.055 +- 0.036 (stat) +- 0.018 (syst), A_V = 0.010 +- 0.036 (stat) +- 0.018 (syst) .
44348987
Searches for violation of lepton flavour and baryon number in tau lepton decays at LHCb
Searches for the lepton flavour violating decay tau(-) -> mu(-)mu(+)mu(-) and the lepton flavour and baryon number violating decays tau(-) -> (p) over bar mu(+)mu(-) and tau(-) -> p mu(-)mu(-) have been carried out using proton-proton collision data, corresponding to an integrated luminosity of 1.0 fb(-1), taken by the LHCb experiment at root s = 7 TeV. No evidence has been found for any signal, and limits have been set at 90% confidence level on the branching fractions: B(tau(-) -> mu(-)mu(+)mu(-) mu(+)mu(-)) p mu(-)mu(-)) (p) over bar mu(+)mu(-) and tau(-) -> p mu(-)mu(-) decay modes represent the first direct experimental limits on these channels. (C) 2013 CERN. Published by Elsevier B.V. All rights reserved.
42582723
Measurement of the Ds+ - Ds- production asymmetry in 7 TeV pp collisions
Article history: Received 4 May 2012 Received in revised form 30 May 2012 Accepted 1 June 2012 Available online 6 June 2012 Editor: W.-D. Schlatter Heavy quark production in 7 TeV centre-of-mass energy pp collisions at the LHC is not necessarily flavour symmetric. The production asymmetry, AP, between D+s and D−s mesons is studied using the φπ± decay mode in a data sample of 1.0 fb−1 collected with the LHCb detector. The difference between π+ and π− detection efficiencies is determined using the ratios of fully reconstructed to partially reconstructed D∗± decays. The overall production asymmetry in the D±s rapidity region 2.0 to 4.5 with transverse momentum larger than 2 GeV is measured to be AP = (−0.33 ± 0.22 ± 0.10)%. This result can constrain models of heavy flavour production. © 2012 CERN. Published by Elsevier B.V. All rights reserved.
119185671
Observation of associated production of a Z boson with a D meson in the forward region
A bstractA search for associated production of a Z boson with an open charm meson is presented using a data sample, corresponding to an integrated luminosity of 1.0 fb−1 of proton-proton collisions at a centre-of-mass energy of 7TeV, collected by the LHCb experiment. Seven candidate events for associated production of a Z boson with a D0 meson and four candidate events for a Z boson with a D+ meson are observed with a combined significance of 5.1 standard deviations. The production cross-sections in the forward region are measured to be
$ \begin{array}{*{20}{c}} {{\upsigma_{{\mathrm{Z}\to {\upmu^{+}}}}}{{{_{{{\upmu^{-}}}}}}_{{,{{\mathrm{D}}^0}}}}=2.50\pm 1.12\pm 0.22\ \mathrm{pb}} \\ {{\upsigma_{{\mathrm{Z}\to {\upmu^{+}}}}}{{{_{{{\upmu^{-}}}}}}_{{,{{\mathrm{D}}^{+}}}}}=0.44\pm 0.23\pm 0.03\ \mathrm{pb},} \\ \end{array} $
where the first uncertainty is statistical and the second systematic.

119113679
Search for CP violation in the decay $D^+ \to \pi^-\pi^+\pi^+$
A search for CP violation in the phase space of the decay $D^+\to\pi^-\pi^+\pi^+$ is reported using $pp$ collision data, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected by the LHCb experiment at a centre-of-mass energy of 7 TeV. The Dalitz plot distributions for $3.1\times 10^6$ $D^+$ and $D^-$ candidates are compared with binned and unbinned model-independent techniques. No evidence for CP violation is found.
1877144
Measurement of the neutron flux produced by cosmic ray muons with LVD at Gran Sasso
The flux of muon-produced neutrons far away from the muon track may constitute a background for the underground detectors searching for rare events. The muon events collected by the first LVD tower from March, 1996, to February, 1998, (1.56 years of live time) were used to estimate the neutron flux at various distances from the muon track or muon-produced cascade.
118965700
Measurements and simulations of muon-induced neutrons
The first measurements of the muon-induced neutron flux at the Boulby Underground Laboratory are presented. The experiment was carried out with an 0.73 tonne liquid scintillation detector that also served as an anticoincidence system for the ZEPLIN-II direct dark matter search. The experimental method exploited the delayed coincidences between high-energy muon signals and gamma-rays from radiative neutron capture on hydrogen or other elements. The muon-induced neutron rate, defined as the average number of detected neutr ons per detected muon, was measured as 0.079± 0.003 (stat.) neutrons/muon using neutron-capture signals above 0.55 MeV in a time window of 40-190 μs after the muon trigger. Accurate Monte Carlo simulations of the neutron production, transport and detection in a precisely modeled laboratory and experimental setup using the GEANT4 toolkit gave a result 1.8 times higher than the measured value. The difference greatly exceeds all statistical and systematic uncertainties. As the vast majority of neutrons detected in the current setup were produced in lead we evaluated from our measurements the neutron yield in lead as (1.31± 0.06)× 10 3 neutrons/muon/(g/cm 2 ) for a mean muon energy of about 260 GeV.
115887438
Particle polarization in inclusive reactions
16753165
Measurements of neutrons produced by high-energy muons at the Boulby Underground Laboratory
We present the first measurements of the muon-induced neutron flux at the Boulby Underground Laboratory. The experiment was carried out with an 0.73 tonne liquid scintillator that also served as an anticoincidence system for the ZEPLIN-II direct dark matter search. The experimental method exploited the delayed coincidences between high-energy muon signals and gamma-rays from radiative neutron capture on hydrogen or other elements. The muon-induced neutron rate, defined as the average number of detected neutrons per detected muon, was measured as 0.079±0.003 (stat.) neutrons/muon using neutron-capture signals above 0.55 MeV in a time window of 40–190 μs after the muon trigger. Accurate Monte Carlo simulations of the neutron production, transport and detection in a precisely modeled laboratory and experimental setup using the GEANT4 toolkit gave a result 1.8 times higher than the measured value. The difference greatly exceeds all statistical and systematic uncertainties. As the vast majority of neutrons detected in the current setup were produced in lead we evaluated from our measurements the neutron yield in lead as (1.31±0.06)×10-3 neutrons/muon/(g/cm2) for a mean muon energy of about 260 GeV.
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.