Low-Mass Drell-Yan Cross-Section Measurements with the LHCb Experiment

The LHCb experiment is one of the four main experiments at CERN's flagship accelerator LHC. It is designed for the study of particles containing $b$ or $c$ quarks. However, due to its very forward angular coverage of approximately 30 to 250 mrad, the experiment is well suited to contribute to electroweak physics as well. Measurements of electroweak boson production at LHCb provide important insight into the parton distribution functions of the proton. In addition precision measurements can test the Standard Model where predictions are most precise. This thesis presents the measurements of the low-mass Drell-Yan production cross section with subsequent decay into two muons. For the main analysis, the full 1 fb$^{-1}$ collected by LHCb in 2011 at $\sqrt{s}$ = 7 $TeV$ is analysed. The cross section is measured differentially as a function of the di-muon mass and the di-muon rapidity. The results obtained are in agreement with the predictions calculated at next-to-next-to leading order in perturbative quantum chromodynamics. The previous measurement based on the data collected in 2010 is included in the appendix of this thesis

Measurement of the inclusive φ cross-section in pp collisions at √s = 7 TeV

The cross-section for inclusive phi meson production in pp collisions at a centre-of-mass energy of sqrt(s) = 7 TeV has been measured with the LHCb detector at the Large Hadron Collider. The differential cross-section is measured as a function of the phi transverse momentum p_T and rapidity y in the region 0.6 phi X) = 1758 pm 19(stat) ^{+43}_{-14}(syst) pm 182(scale) microbarn, where the first systematic uncertainty depends on the p_T and y region and the second is related to the overall scale. Predictions based on the Pythia 6.4 generator underestimate the cross-section

The LHCb Silicon Tracker: lessons learned (so far)

The LHCb Silicon Tracker is part of the main tracking system of the LHCb detector. It covers the full acceptance angle in front of the dipole magnet in the Tracker Turicensis (TT) station and the innermost part in the three Inner Tracker (IT) stations downstream of the magnet. We report on final elements of the production, the installation and commissioning process in the experiment. Focusing on electronic and hardware issues we describe the lessons learned and the pitfalls encountered. First experience of detector operation is presented

Measurement of the D+s - D-s production asymmetry in 7 TeV pp collisions

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 View the MathML source and View the MathML source 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 View the MathML source 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

Measurement of the Bs0→Ds(∗)+Ds(∗)−B_{s}^{0} \rightarrow D_{s}^{(*)+}D_{s}^{(*)-} branching fractions

The branching fraction of the decay $B_{s}^{0} \rightarrow D_{s}^{(*)+}D_{s}^{(*)-}$ is measured using $pp$ collision data corresponding to an integrated luminosity of $1.0fb^{-1}$, collected using the LHCb detector at a centre-of-mass energy of $7$TeV. It is found to be \begin{align*} {\mathcal{B}}(B_{s}^{0}\rightarrow~D_{s}^{(*)+}D_{s}^{(*)-}) = (3.05 \pm 0.10 \pm 0.20 \pm 0.34)\%, \end{align*} where the uncertainties are statistical, systematic, and due to the normalisation channel, respectively. The branching fractions of the individual decays corresponding to the presence of one or two $D^{*\pm}_{s}$ are also measured. The individual branching fractions are found to be \begin{align*} {\mathcal{B}}(B_{s}^{0}\rightarrow~D_{s}^{*\pm}D_{s}^{\mp}) = (1.35 \pm 0.06 \pm 0.09 \pm 0.15)\%, \newline{\mathcal{B}}(B_{s}^{0}\rightarrow~D_{s}^{*+}D_{s}^{*-}) = (1.27 \pm 0.08 \pm 0.10 \pm 0.14)\%. \end{align*} All three results are the most precise determinations to date.The branching fraction of the decay Bs0→Ds(*)+Ds(*)- is measured using pp collision data corresponding to an integrated luminosity of 1.0  fb-1, collected using the LHCb detector at a center-of-mass energy of 7 TeV. It is found to be B(Bs0→Ds(*)+Ds(*)-)=(3.05±0.10±0.20±0.34)%, where the uncertainties are statistical, systematic, and due to the normalization channel, respectively. The branching fractions of the individual decays corresponding to the presence of one or two Ds*± are also measured. The individual branching fractions are found to be B(Bs0→Ds*±Ds∓)=(1.35±0.06±0.09±0.15)%, B(Bs0→Ds*+Ds*-)=(1.27±0.08±0.10±0.14)%. All three results are the most precise determinations to date.The branching fraction of the decay $B_{s}^{0} \rightarrow D_{s}^{(*)+}D_{s}^{(*)-}$ is measured using $pp$ collision data corresponding to an integrated luminosity of $1.0fb^{-1}$, collected using the LHCb detector at a centre-of-mass energy of $7$TeV. It is found to be \begin{align*} {\mathcal{B}}(B_{s}^{0}\rightarrow~D_{s}^{(*)+}D_{s}^{(*)-}) = (3.05 \pm 0.10 \pm 0.20 \pm 0.34)\%, \end{align*} where the uncertainties are statistical, systematic, and due to the normalisation channel, respectively. The branching fractions of the individual decays corresponding to the presence of one or two $D^{*\pm}_{s}$ are also measured. The individual branching fractions are found to be \begin{align*} {\mathcal{B}}(B_{s}^{0}\rightarrow~D_{s}^{*\pm}D_{s}^{\mp}) = (1.35 \pm 0.06 \pm 0.09 \pm 0.15)\%, \newline{\mathcal{B}}(B_{s}^{0}\rightarrow~D_{s}^{*+}D_{s}^{*-}) = (1.27 \pm 0.08 \pm 0.10 \pm 0.14)\%. \end{align*} All three results are the most precise determinations to date

Measurement of the CP-violating phase ϕs\phi_s in Bˉs0→Ds+Ds−\bar{B}^{0}_{s}\to D_{s}^{+}D_{s}^{-} decays

We present a measurement of the $CP$-violating weak mixing phase $\phi_s$ using the decay $\bar{B}^{0}_{s}\to D_{s}^{+}D_{s}^{-}$ in a data sample corresponding to $3.0$ fb$^{-1}$ of integrated luminosity collected with the LHCb detector in $pp$ collisions at centre-of-mass energies of 7 and 8 TeV. An analysis of the time evolution of the system, which does not constrain $|\lambda|=1$ to allow for the presence of $CP$ violation in decay, yields $\phi_s = 0.02 \pm 0.17$ (stat) $\pm 0.02$ (syst) rad, $|\lambda| = 0.91^{+0.18}_{-0.15}$ (stat) $\pm0.02$ (syst). This result is consistent with the Standard Model expectation.We present a measurement of the CP-violating weak mixing phase ϕs using the decay B¯s0→Ds+Ds- in a data sample corresponding to 3.0 fb-1 of integrated luminosity collected with the LHCb detector in pp collisions at center-of-mass energies of 7 and 8 TeV. An analysis of the time evolution of the system, which does not use the constraint |λ|=1 to allow for the presence of CP violation in decay, yields ϕs=0.02±0.17(stat)±0.02(syst)  rad, |λ|=0.91-0.15+0.18(stat)±0.02(syst). This result is consistent with the standard model expectation.We present a measurement of the $CP$-violating weak mixing phase $\phi_s$ using the decay $\bar{B}^{0}_{s}\to D_{s}^{+}D_{s}^{-}$ in a data sample corresponding to $3.0$ fb$^{-1}$ of integrated luminosity collected with the LHCb detector in $pp$ collisions at centre-of-mass energies of 7 and 8 TeV. An analysis of the time evolution of the system, which does not constrain $|\lambda|=1$ to allow for the presence of $CP$ violation in decay, yields $\phi_s = 0.02 \pm 0.17$ (stat) $\pm 0.02$ (syst) rad, $|\lambda| = 0.91^{+0.18}_{-0.15}$ (stat) $\pm0.02$ (syst). This result is consistent with the Standard Model expectation

Searches for Λb0\Lambda^0_{b} and Ξb0\Xi^{0}_{b} decays to KS0pπ−K^0_{\rm S} p \pi^{-} and KS0pK−K^0_{\rm S}p K^{-} final states with first observation of the Λb0→KS0pπ−\Lambda^0_{b} \rightarrow K^0_{\rm S}p \pi^{-} decay

A search for previously unobserved decays of beauty baryons to the final states $K^0_{\rm\scriptscriptstyle S} p \pi^{-}$ and $K^0_{\rm\scriptscriptstyle S}p K^{-}$ is reported. The analysis is based on a data sample corresponding to an integrated luminosity of $1.0\,$fb$^{-1}$ of $pp$ collisions. The $\Lambda^0_{b} \rightarrow \overline{\kern -0.2em K}^0_{\rm\scriptscriptstyle S}p \pi^{-}$ decay is observed with a significance of $8.6\,\sigma$, with branching fraction \begin{eqnarray*} {\cal{B}}(\Lambda^0_{b} \rightarrow \overline{\kern -0.2em K}^0 p \pi^{-}) & = & \left( 1.26 \pm 0.19 \pm 0.09 \pm 0.34 \pm 0.05 \right) \times 10^{-5} \,, \end{eqnarray*} where the uncertainties are statistical, systematic, from the ratio of fragmentation fractions $f_{\Lambda}/f_{d}$, and from the branching fraction of the $B^0 \rightarrow K^0_{\rm\scriptscriptstyle S}\pi^{+}\pi^{-}$ normalisation channel, respectively. A first measurement is made of the $CP$ asymmetry, giving \begin{eqnarray*} A_{C\!P} (\Lambda^0_{b} \rightarrow \overline{\kern -0.2em K}^0 p \pi^{-}) & = & 0.22 \pm 0.13\mathrm{\,(stat)} \pm 0.03\mathrm{\,(syst)} \, . \end{eqnarray*} No significant signals are seen for $\Lambda^0_{b} \rightarrow K^0_{\rm\scriptscriptstyle S}p K^{-}$ decays, $\Xi^{0}_{b}$ decays to both the $K^0_{\rm\scriptscriptstyle S}p \pi^{-}$ and $K^0_{\rm\scriptscriptstyle S}p K^{-}$ final states, and the $\Lambda^0_{b} \rightarrow D^{-}_{s} (\rightarrow K^0_{\rm\scriptscriptstyle S} K^{-}) p$ decay, and upper limits on their branching fractions are reported.A search for previously unobserved decays of beauty baryons to the final states $K^0_{\rm\scriptscriptstyle S} p \pi^{-}$ and $K^0_{\rm\scriptscriptstyle S}p K^{-}$ is reported. The analysis is based on a data sample corresponding to an integrated luminosity of $1.0\,$fb$^{-1}$ of $pp$ collisions. The $\Lambda^0_{b} \rightarrow \overline{\kern -0.2em K}^0_{\rm\scriptscriptstyle S}p \pi^{-}$ decay is observed with a significance of $8.6\,\sigma$, with branching fraction \begin{eqnarray*} {\cal{B}}(\Lambda^0_{b} \rightarrow \overline{\kern -0.2em K}^0 p \pi^{-}) & = & \left(1.26 \pm 0.19 \pm 0.09 \pm 0.34 \pm 0.05 \right) \times 10^{-5} \,, \end{eqnarray*} where the uncertainties are statistical, systematic, from the ratio of fragmentation fractions $f_{\Lambda}/f_{d}$, and from the branching fraction of the $B^0 \rightarrow K^0_{\rm\scriptscriptstyle S}\pi^{+}\pi^{-}$ normalisation channel, respectively. A first measurement is made of the $CP$ asymmetry, giving \begin{eqnarray*} A_{C/!P} (\Lambda^0_{b} \rightarrow \overline{\kern -0.2em K}^0 p \pi^{-}) & = & 0.22 \pm 0.13\mathrm{\,(stat)} \pm 0.03\mathrm{\,(syst)} \, . \end{eqnarray*} No significant signals are seen for $\Lambda^0_{b} \rightarrow K^0_{\rm\scriptscriptstyle S}p K^{-}$ decays, $\Xi^{0}_{b}$ decays to both the $K^0_{\rm\scriptscriptstyle S}p \pi^{-}$ and $K^0_{\rm\scriptscriptstyle S}p K^{-}$ final states, and the $\Lambda^0_{b} \rightarrow D^{-}_{s} (\rightarrow K^0_{\rm\scriptscriptstyle S} K^{-}) p$ decay, and upper limits on their branching fractions are reported

Measurement of CPCP violation in B0→J/ψKS0B^0 \rightarrow J/\psi K^0_S decays

Measurements are presented of the $CP$ violation observables $S$ and $C$ in the decays of $B^0$ and $\overline{B}{}^0$ mesons to the $J/\psi K^0_S$ final state. The data sample corresponds to an integrated luminosity of $3.0\,\text{fb}^{-1}$ collected with the LHCb experiment in proton-proton collisions at center-of-mass energies of $7$ and $8\,\text{TeV}$. The analysis of the time evolution of $41500$ $B^0$ and $\overline{B}{}^0$ decays yields $S = 0.731 \pm 0.035 \, \text{(stat)} \pm 0.020 \,\text{(syst)}$ and $C = -0.038 \pm 0.032 \, \text{(stat)} \pm 0.005\,\text{(syst)}$. In the Standard Model, $S$ equals $\sin(2\beta)$ to a good level of precision. The values are consistent with the current world averages and with the Standard Model expectations.Measurements are presented of the CP violation observables S and C in the decays of B0 and B¯0 mesons to the J/ψKS0 final state. The data sample corresponds to an integrated luminosity of 3.0  fb-1 collected with the LHCb experiment in proton-proton collisions at center-of-mass energies of 7 and 8 TeV, and contains a total of 41 560 selected B0 and B¯0 decays. The analysis of the time evolution of these decays yields S=0.731±0.035(stat)±0.020(syst) and C=-0.038±0.032(stat)±0.005(syst). In the standard model, S equals sin(2β) to a good level of precision. The values are consistent with the current world averages and with the standard model expectations.Measurements are presented of the $CP$ violation observables $S$ and $C$ in the decays of $B^0$ and $\overline{B}{}^0$ mesons to the $J/\psi K^0_S$ final state. The data sample corresponds to an integrated luminosity of $3.0\,\text{fb}^{-1}$ collected with the LHCb experiment in proton-proton collisions at center-of-mass energies of $7$ and $8\,\text{TeV}$. The analysis of the time evolution of $41500$ $B^0$ and $\overline{B}{}^0$ decays yields $S = 0.731 \pm 0.035 \, \text{(stat)} \pm 0.020 \,\text{(syst)}$ and $C = -0.038 \pm 0.032 \, \text{(stat)} \pm 0.005\,\text{(syst)}$. In the Standard Model, $S$ equals $\sin(2\beta)$ to a good level of precision. The values are consistent with the current world averages and with the Standard Model expectations

Measurement of the (B)over-bar(0)-B-0 and (B)over-bars(0)-B-s(0) production asymmetries in pp collisions at root s=7 TeV

The $\bar{B}^0-B^0$ and $\bar{B}^0_s-B^0_s$ production asymmetries, $A_\mathrm{P}(B^0)$ and $A_\mathrm{P}(B^0_s)$, are measured by means of a time-dependent analysis of $B^0 \to J/\psi K^{*0}$, $B^0 \to D^- \pi^+$ and $B^0_s \to D_s^- \pi^+$ decays, using a data sample corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected by LHCb in $pp$ collisions at a centre-of-mass energy of 7 TeV. The measurements are performed as a function of transverse momentum and pseudorapidity of the $B^0$ and $B^0_s$ mesons within the LHCb acceptance. The production asymmetries, integrated over $p_\mathrm{T}$ and $\eta$ in the range $4 < p_\mathrm{T} < 30$ GeV/c and $2.5<\eta<4.5$, are determined to be $A_\mathrm{P}(B^0) = (-0.35 \pm 0.76 \pm 0.28)\%$ and $A_\mathrm{P}(B^0_s) = (1.09 \pm 2.61 \pm 0.66)\%$, where the first uncertainties are statistical and the second systematic

Search for the rare decays B0→J/ψγB^{0}\to J/\psi \gamma and Bs0→J/ψγB^{0}_{s} \to J/\psi \gamma

A search for the rare decay of a $B^{0}$ or $B^{0}_{s}$ meson into the final state $J/\psi\gamma$ is performed, using data collected by the LHCb experiment in $pp$ collisions at $\sqrt{s}=7$ and $8$ TeV, corresponding to an integrated luminosity of 3 fb$^{-1}$. The observed number of signal candidates is consistent with a background-only hypothesis. Branching fraction values larger than $1.7\times 10^{-6}$ for the $B^{0}\to J/\psi\gamma$ decay mode are excluded at 90% confidence level. For the $B^{0}_{s}\to J/\psi\gamma$ decay mode, branching fraction values larger than $7.4\times 10^{-6}$ are excluded at 90% confidence level; this is the first branching fraction limit for this decay.A search for the rare decay of a B0 or Bs0 meson into the final state J/ψγ is performed, using data collected by the LHCb experiment in pp collisions at s=7 and 8 TeV, corresponding to an integrated luminosity of 3  fb-1. The observed number of signal candidates is consistent with a background-only hypothesis. Branching fraction values larger than 1.5×10-6 for the B0→J/ψγ decay mode are excluded at 90% confidence level. For the Bs0→J/ψγ decay mode, branching fraction values larger than 7.3×10-6 are excluded at 90% confidence level; this is the first branching fraction limit for this decay.A search for the rare decay of a $B^{0}$ or $B^{0}_{s}$ meson into the final state $J/\psi\gamma$ is performed, using data collected by the LHCb experiment in $pp$ collisions at $\sqrt{s}=7$ and $8$ TeV, corresponding to an integrated luminosity of 3 fb$^{-1}$. The observed number of signal candidates is consistent with a background-only hypothesis. Branching fraction values larger than $1.7\times 10^{-6}$ for the $B^{0}\to J/\psi\gamma$ decay mode are excluded at 90% confidence level. For the $B^{0}_{s}\to J/\psi\gamma$ decay mode, branching fraction values larger than $7.4\times 10^{-6}$ are excluded at 90% confidence level, this is the first branching fraction limit for this decay