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Radiative B decays are sensitive probes for new physics. In particular, the measurement parameters sensitive to the photon polarisation could help constrain various models of new physics. We present three methods used by the LHCb collaboration to measure the photon polarisation using 3fb-1 of integrated luminosity.

A measurement of the phase difference between the short- and long-distance contributions to the [Formula: see text] decay is performed by analysing the dimuon mass distribution. The analysis is based on collision data corresponding to an integrated luminosity of 3[Formula: see text] collected by the LHCb experiment in 2011 and 2012. The long-distance contribution to the [Formula: see text] decay is modelled as a sum of relativistic Breit-Wigner amplitudes representing different vector meson resonances decaying to muon pairs, each with their own magnitude and phase. The measured phases of the [Formula: see text] and [Formula: see text] resonances are such that the interference with the short-distance component in dimuon mass regions far from their pole masses is small. In addition, constraints are placed on the Wilson coefficients, [Formula: see text] and [Formula: see text], and the branching fraction of the short-distance component is measured.

A method is proposed to measure the photon polarisation parameter \\[\\lambda _{\\gamma }\\] in \\[{{b}} \\!\\rightarrow {s} {\\gamma } \\] transitions using an amplitude analysis of \\[B\\!\\rightarrow K\\pi \\pi {\\gamma } \\] decays. Simplified models of the \\[{K} {\\pi } {\\pi } \\] system are used to simulate \\[{{{B} ^+}} \\!\\rightarrow {{K} ^+} {{\\pi } ^-} {{\\pi } ^+} {\\gamma } \\] and \\[{{B} ^0} \\!\\rightarrow {{K} ^+} {{\\pi } ^-} {{\\pi } ^0} {\\gamma } \\] decays, validate the amplitude analysis method, and demonstrate the feasibility of a measurement of the \\[\\lambda _{\\gamma }\\] parameter irrespective of the model parameters. Similar sensitivities to \\[\\lambda _{\\gamma }\\] are obtained with both the charged and neutral hadronic systems. In the absence of any background and distortion due to experimental effects, the statistical uncertainty expected from an analysis of \\[{{{B} ^+}} \\!\\rightarrow {{K} ^+} {{\\pi } ^-} {{\\pi } ^+} {\\gamma } \\] decays in an LHCb data set corresponding to an integrated luminosity of 9 \\[\\,\\hbox {fb}^{-1}\\] is estimated to be 0.009. A similar measurement using \\[{{B} ^0} \\!\\rightarrow {{K} ^+} {{\\pi } ^-} {{\\pi } ^0} {\\gamma } \\] decays in a Belle II data sample corresponding to an integrated luminosity of 5 \\[\\hbox {\\,ab}^{-1}\\] would lead to a statistical uncertainty of 0.018.

(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image).Measurements are presented of electroweak boson production using data from pp collisions at a centre-of-mass energy of ... TeV. The analysis is based on an integrated luminosity of 2.0 fb super(-1) recorded with the LHCb detector. The bosons are identified in the W arrow right mu nu and Z arrow right mu super(+) mu super(-) decay channels. The cross-sections are measured for muons in the pseudorapidity range 2.0 < eta < 4.5, with transverse momenta p sub(T) > 20 GeV/c and, in the case of the Z boson, a dimuon mass within ... GeV/c super(2). The results are ... ... ... ... ... ... ... ... where the first uncertainties are statistical, the second are systematic, the third are due to the knowledge of the LHC beam energy and the fourth are due to the luminosity determination. The evolution of the W and Z boson cross-sections with centre-of-mass energy is studied using previously reported measurements with 1.0 fb super(-1) of data at 7 TeV. Differential distributions are also presented. Results are in good agreement with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics. [Figure not available: see fulltext.]

A measurement of CP-violating observables is performed using the decays B $^{±}$→ DK $^{±}$and B $^{±}$→ Dπ $^{±}$ , where the D meson is reconstructed in one of the self-conjugate three-body final states$ {K}_{\\mathrm{S}}^0 $ π $^{+}$ π $^{−}$and$ {K}_{\\mathrm{S}}^0 $ K $^{+}$ K $^{−}$(commonly denoted$ {K}_{\\mathrm{S}}^0 $ h $^{+}$ h $^{−}$ ). The decays are analysed in bins of the D-decay phase space, leading to a measurement that is independent of the modelling of the D-decay amplitude. The observables are inter- preted in terms of the CKM angle γ. Using a data sample corresponding to an integrated luminosity of 9 fb $^{−1}$collected in proton-proton collisions at centre-of mass energies of 7, 8, and 13 TeV with the LHCb experiment, γ is measured to be$ \\left({68.7}_{-5.1}^{+5.2}\\right){}^{\\circ} $ . The hadronic parameters$ {r}_B^{D K},{r}_B^{D\\pi},{\\delta}_B^{D K},\\kern0.5em \\mathrm{and}\\kern0.5em {\\delta}_B^{D\\pi} $ , which are the ratios and strong-phase differences of the suppressed and favoured B $^{±}$decays, are also reported.[graphic not available: see fulltext]

A measurement of Z → τ ⁺ τ ⁻production cross-section is presented using data, corresponding to an integrated luminosity of 2 fb ⁻¹ , from pp collisions at √s̅=8 TeV collected by the LHCb experiment. The τ ⁺ τ ⁻candidates are reconstructed in final states with the first tau lepton decaying leptonically, and the second decaying either leptonically or to one or three charged hadrons. The production cross-section is measured 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. The cross-section is determined to be σ_(pp)_(→ Z→ τ⁺)_(τ⁻)=95.8 ± 2.1 ± 4.6 ± 0.2 ± 1.1 pb, where the first uncertainty is statistical, the second is systematic, the third is due to the LHC beam energy uncertainty, and the fourth to the integrated luminosity uncertainty. This result is compatible with NNLO Standard model predictions. The ratio of the cross-sections for Z → τ ⁺ τ ⁻to Z → μ ⁺ μ ⁻(Z → e ⁺ e ⁻ ), determined to be 1.01 ± 0.05 (1.02 ± 0.06), is consistent with the lepton-universality hypothesis in Z decays.

A study ofB⁰_(s) → η_(c) φandB⁰_(s) → η_(c) π⁺π⁻decays is performed usingppcollision data corresponding to an integrated luminosity of 3.0 \\rm fb⁻¹ , collected with the LHCb detector in Run 1 of the LHC. The observation of the decayB⁰_(s) → η_(c) φis reported, where theη_(c)meson is reconstructed in thepp̄ ,K⁺K⁻π⁺π⁻ ,π⁺π⁻π⁺π⁻andK⁺K⁻K⁺K⁻decay modes and theφ(1020)in theK⁺ K⁻decay mode. The decayB⁰_(s) → J/ψ φis used as a normalisation channel. Evidence is also reported for the decayB⁰_(s) → η_(c) π⁺π⁻ , where theη_(c)meson is reconstructed in thepp̄decay mode, using the decayB⁰_(s) → J/ψ π⁺ π⁻as a normalisation channel. The measured branching fractions are eqnarray* B (B⁰_(s) _(c) ) &=& (5.01 0.53 0.27 0.63 ) 10⁻4 , B (B⁰_(s) _(c) ⁺ ⁻) &=& (1.76 0.59 0.12 0.29 ) 10⁻4 , eqnarray* where in each case the first uncertainty is statistical, the second systematic and the third uncertainty is due to the limited knowledge of the external branching fractions.

A search for the rare two-body charmless baryonic decayB⁺ → p Λ̄is performed withppcollision data, corresponding to an integrated luminosity of3\\mbox{ fb}{⁻¹}{} , collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. An excess ofB⁺ → p Λ̄candidates with respect to background expectations is seen with a statistical significance of 4.1 standard deviations, and constitutes the first evidence for this decay. The branching fraction, measured using theB⁺ → K⁰_(\\mathrm S) π⁺decay for normalisation, is eqnarray B(B⁺ p ) & = & ( 2.4 ⁺1.0₋0.8 0.3 ) 10⁻7 , eqnarray where the first uncertainty is statistical and the second systematic.

A test of lepton universality, performed by measuring the ratio of the branching fractions of the B $^{0}$→ K $^{*0}$μ $^{+}$μ $^{−}$and B $^{0}$→ K $^{*0}$e $^{+}$e $^{−}$decays,$ {R}_{K^{*0}} $, is presented. The K $^{*0}$meson is reconstructed in the final state K $^{+}$π $^{−}$ , which is required to have an invariant mass within 100 MeV/c $^{2}$of the known K $^{*}$ (892) $^{0}$mass. The analysis is performed using proton-proton collision data, corresponding to an integrated luminosity of about 3 fb $^{−1}$ , collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The ratio is measured in two regions of the dilepton invariant mass squared, q $^{2}$ , to be$ {R}_{K^{*0}}=\\left\\{\\begin{array}{l}{0.66_{-}^{+}}_{0.07}^{0.11}\\left(\\mathrm{stat}\\right)\\pm 0.03\\left(\\mathrm{syst}\\right)\\kern1em \\mathrm{f}\\mathrm{o}\\mathrm{r}\\kern1em 0.045<{q}^2<1.1\\kern0.5em {\\mathrm{GeV}}^2/{c}^4,\\hfill \\\ {}{0.69_{-}^{+}}_{0.07}^{0.11}\\left(\\mathrm{stat}\\right)\\pm 0.05\\left(\\mathrm{syst}\\right)\\kern1em \\mathrm{f}\\mathrm{o}\\mathrm{r}\\kern1em 1.1<{q}^2<6.0\\kern0.5em {\\mathrm{GeV}}^2/{c}^4.\\hfill \\end{array}\\right. $

Bose-Einstein correlations of same-sign charged pions, produced in proton-proton collisions at a 7 TeV centre-of-mass energy, are studied using a data sample collected by the LHCb experiment. The signature for Bose-Einstein correlations is observed in the form of an enhancement of pairs of like-sign charged pions with small four-momentum difference squared. The charged-particle multiplicity dependence of the Bose-Einstein correlation parameters describing the correlation strength and the size of the emitting source is investigated, determining both the correlation radius and the chaoticity parameter. The measured correlation radius is found to increase as a function of increasing charged-particle multiplicity, while the chaoticity parameter is seen to decrease.