First observation of the decay Bs -> D0bar phi 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 significance of the signal is 6.2 st
andard deviations. The branching fraction is measured relative to that of the decay Bs -> D0bar K*0bar to be 0.069 +/- 0.013 (stat) +/- 0.007 (syst). The first measurement of the ratio of branching fractions for the decays Bs -> D0bar K*0bar and Bd->D0bar K*0 is found to be 7.8 +/- 0.7 (stat) +/- 0.3 (syst) +/- 0.6 (f_s/f_d), where the last uncertainty is due to the ratio of the Bs and Bd fragmentation fractions.
A first flavour-tagged measurement of the time-dependent CP-violating asymmetry in $B_s^0 to phiphi$ decays is presented. In this decay channel, the CP-violating weak phase arises due to CP violation in the interference between $B_s^0$-$bar{B}_s^0$ m
ixing and the $b to s bar{s} s $ gluonic penguin decay amplitude. Using a sample of $pp$ collision data corresponding to an integrated luminosity of $1.0; fb^{-1}$ and collected at a centre-of-mass energy of $7 rm TeV$ with the LHCb detector, $880 B_s^0 to phiphi$ signal decays are obtained. The CP-violating phase is measured to be in the interval [-2.46, -0.76] rm rad$ at 68% confidence level. The p-value of the Standard Model prediction is 16%.
A measurement of the inclusive $Z to tautau$ cross-section in $pp$ collisions at $sqrt{s} = 7$ TeV is presented based on a dataset of 1.0 fb$^{-1}$ collected by the LHCb detector. Candidates for $Z to tautau$ decays are identified through reconstruct
ed final states with two muons, a muon and an electron, a muon and a hadron, or an electron and a hadron. The production cross-section for $Z$ bosons, with invariant mass between 60 and 120 GeV/$c^2$, which decay to $tau$ leptons with transverse momenta greater than 20 GeV/$c$ and pseudorapidities between 2.0 and 4.5, is measured to be $sigma_{pp to Z to tautau} = 71.4 pm 3.5 pm 2.8 pm 2.5$ pb; the first uncertainty is statistical, the second uncertainty is systematic, and the third is due to the uncertainty on the integrated luminosity. The ratio of the cross-sections for $Z to tautau$ to $Z to mumu$ is determined to be $0.93 pm 0.09$, where the uncertainty is the combination of statistical, systematic, and luminosity uncertainties of the two measurements.
The decay Bs->J/psipi+pi- can be exploited to study CP violation. A detailed understanding of its structure is imperative in order to optimize its usefulness. An analysis of this three-body final state is performed using a 1.0/fb sample of data produ
ced in 7 TeV pp collisions at the LHC and collected by the LHCb experiment. A modified Dalitz plot analysis of the final state is performed using both the invariant mass spectra and the decay angular distributions. The pi+pi- system is shown to be dominantly in an S-wave state, and the CP-odd fraction in this Bs decay is shown to be greater than 0.977 at 95% confidence level. In addition, we report the first measurement of the J/psipi+pi- branching fraction relative to J/psiphi of (19.79 +/- 0.47 +/- 0.52)%.
The decay mode $B^{0}_{s} to D^{mp}_{s} K^{pm} $ allows for one of the theoretically cleanest measurements of the CKM angle $gamma$ through the study of time-dependent $ensuremath{CP}xspace$ violation. This paper reports a measurement of its branchin
g fraction relative to the Cabibbo-favoured mode $B^{0}_{s} to D^{-}_{s} pi^{+}$ based on a data sample of 0.37 fb$^{-1}$ proton-proton collisions at $sqrt{s} = 7$ TeV collected in 2011 with the LHCb detector. In addition, the ratio of $ensuremath{mathrm{B}}xspace$ meson production fractions $ensuremath{f_s/f_d}$, determined from semileptonic decays, together with the known branching fraction of the control channel $B^{0} to D^{-} pi^{+}$, is used to perform an absolute measurement of the branching fractions: $B (B^0_s to D^-_s pi^+) ;= (2.95 pm 0.05 pm 0.17^{,+,0.18}_{,-,0.22}) times 10^{-3}$, $B (B^0_s to D^mp_s K^pm) = (1.90 pm 0.12 pm 0.13^{,+,0.12}_{,-,0.14}) times 10^{-4},$, where the first uncertainty is statistical, the second the experimental systematic uncertainty, and the third the uncertainty due to $f_s/f_d$.
The production of Upsilon(1S), Upsilon(2S) and Upsilon(3S) mesons in proton-proton collisions at the centre-of-mass energy of sqrt(s)=7 TeV is studied with the LHCb detector. The analysis is based on a data sample of 25 pb-1 collected at the Large Ha
dron Collider. The Upsilon mesons are reconstructed in the decay mode Upsilon -> mu+ mu- and the signal yields are extracted from a fit to the mu+ mu- invariant mass distributions. The differential production cross-sections times dimuon branching fractions are measured as a function of the Upsilon transverse momentum pT and rapidity y, over the range pT < 15 GeV/c and 2.0 < y < 4.5. The cross-sections times branching fractions, integrated over these kinematic ranges, are measured to be sigma(pp -> Upsilon(1S) X) x B(Upsilon(1S)->mu+ mu-) = 2.29 {pm} 0.01 {pm} 0.10 -0.37 +0.19 nb, sigma(pp -> Upsilon(2S) X) x B(Upsilon(2S)->mu+ mu-) = 0.562 {pm} 0.007 {pm} 0.023 -0.092 +0.048 nb, sigma(pp -> Upsilon(3S) X) x B(Upsilon(3S)->mu+ mu-) = 0.283 {pm} 0.005 {pm} 0.012 -0.048 +0.025 nb, where the first uncertainty is statistical, the second systematic and the third is due to the unknown polarisation of the three Upsilon states.
The production of B+- mesons in proton-proton collisions at sqrt(s)=7 TeV is studied using 35 pb-1 of data collected by the LHCb detector. The B+- mesons are reconstructed exclusively in the B+- -> J/psi K+- mode, with J/psi -> mu+ mu-. The different
ial production cross-section is measured as a function of the B+- transverse momentum in the fiducial region 0 < pT < 40 GeV/c and with rapidity 2.0 < y < 4.5. The total cross-section, summing up B+ and B-, is measured to be sigma(pp -> B+- X, 0 < pT < 40 GeV/c, 2.0 < y < 4.5) = 41.4 +- 1.5 (stat.) +- 3.1 (syst.) mub.
Measurements of $b$ hadron production ratios in proton-proton collisions at a centre-of-mass energy of 7 TeV with an integrated luminosity of 3 pb$^{-1}$ are presented. We study the ratios of strange $B$ meson to light $B$ meson production $f_s/(f_u+
f_d)$ and $Lambda_b^0$ baryon to light $B$ meson production $f_{Lambda_b}/(f_u+f_d)$ as a function of the charmed hadron-muon pair transverse momentum $p_T$ and the $b$ hadron pseudorapidity $eta$, for $p_T$ between 0 and 14 GeV and $eta$ between 2 and 5. We find that $f_s/(f_u+f_d)$ is consistent with being independent of $p_{rm T}$ and $eta$, and we determine $f_s/(f_u+f_d)$ = 0.134$pm$ 0.004 $^{+0.011}_{-0.010}$, where the first error is statistical and the second systematic. The corresponding ratio $f_{Lambda_b}/(f_u+f_d)$ is found to be dependent upon the transverse momentum of the charmed hadron-muon pair, $f_{Lambda_b}/(f_u+f_d)=(0.404pm 0.017 (stat) pm 0.027 (syst) pm 0.105 (Br))times[1 -(0.031 pm 0.004 (stat) pm 0.003 (syst))times p_T(GeV)]$, where Br reflects an absolute scale uncertainty due to the poorly known branching fraction Br(Lambda_c^+ to pK^-pi^+)$. We extract the ratio of strange $B$ meson to light neutral $B$ meson production $f_s/f_d$ by averaging the result reported here with two previous measurements derived from the relative abundances of $bar{B}_s to D_S^+ pi ^-$ to $bar{B}^0 to D^+K^-$ and $bar{B}^0 to D^+pi^-$. We obtain $f_s/f_d=0.267^{+0.021}_{-0.020}$.
Absolute luminosity measurements are of general interest for colliding-beam experiments at storage rings. These measurements are necessary to determine the absolute cross-sections of reaction processes and are valuable to quantify the performance of
the accelerator. Using data taken in 2010, LHCb has applied two methods to determine the absolute scale of its luminosity measurements for proton-proton collisions at the LHC with a centre-of-mass energy of 7 TeV. In addition to the classic van der Meer scan method a novel technique has been developed which makes use of direct imaging of the individual beams using beam-gas and beam-beam interactions. This beam imaging method is made possible by the high resolution of the LHCb vertex detector and the close proximity of the detector to the beams, and allows beam parameters such as positions, angles and widths to be determined. The results of the two methods have comparable precision and are in good agreement. Combining the two methods, an overall precision of 3.5% in the absolute luminosity determination is reached. The techniques used to transport the absolute luminosity calibration to the full 2010 data-taking period are presented.
A search is performed for the lepton number violating decay $B^{+}to h^- mu^+ mu^+$, where $h^-$ represents a $K^-$ or a $pi^-$, using data from the LHCb detector corresponding to an integrated luminosity of $36pb^{-1}$. The decay is forbidden in the
Standard Model but allowed in models with a Majorana neutrino. No signal is observed in either channel and limits of $B(B^{+} to K^- mu^+ mu^+) < 5.4times 10^{-8}$ and $B(B^{+} to pi^- mu^+ mu^+) < 5.8times 10^{-8}$ are set at the 95% confidence level. These improve the previous best limits by factors of 40 and 30, respectively.
