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187
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"Aslanides, E"
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Measurement of the phase difference between short- and long-distance amplitudes in the Formula: see text decay
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.
Journal Article
Measurement of forward W and Z boson production in pp collisions at ... TeV
(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.]
Journal Article
Measurement of the CKM angleγinB^(±)→ D K^(±)andB^(±) → D π^(±)decays withD → K_(\\mathrm) S⁰ h⁺ h
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]
Journal Article
Measurement of the J/ψ pair production cross-section in pp collisions at s√=13TeV
The production cross-section of J/ψ pairs is measured using a data sample of pp collisions collected by the LHCb experiment at a centre-of-mass energy of s√=13TeV, corresponding to an integrated luminosity of 279±11pb−1. The measurement is performed for J/ψ mesons with a transverse momentum of less than 10GeV/c in the rapidity range 2.0
Journal Article
Search for the B0s→η′φ decay
A search for the charmless B0s→η′ϕ decay is performed using pp collision data collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb−1. No signal is observed and upper limits on the B0s→η′ϕ branching fraction are set to 0.82×10−6 at 90% and 1.01×10−6 at 95% confidence level.
Journal Article
Study of the D0p amplitude in Λ0b→D0pπ− decays
An amplitude analysis of the decay Λ0b→D0pπ− is performed in the part of the phase space containing resonances in the D0p channel. The study is based on a data sample corresponding to an integrated luminosity of 3.0 fb−1 of pp collisions recorded by the LHCb experiment. The spectrum of excited Λ+c states that decay into D0p is studied. The masses, widths and quantum numbers of the Λc(2880)+ and Λc(2940)+ resonances are measured. The constraints on the spin and parity for the Λc(2940)+ state are obtained for the first time. A near-threshold enhancement in the D0p amplitude is investigated and found to be consistent with a new resonance, denoted the Λc(2860)+, of spin 3/2 and positive parity.
Journal Article
Observation of the suppressed decay Λ0b→pπ−μ+μ
The suppressed decay Λ0b→pπ−μ+μ−, excluding the J/ψ and ψ(2S)→μ+μ− resonances, is observed for the first time with a significance of 5.5 standard deviations. The analysis is performed with proton-proton collision data corresponding to an integrated luminosity of 3fb−1 collected with the LHCb experiment. The Λ0b→pπ−μ+μ− branching fraction is measured relative to the Λ0b→J/ψ(→μ+μ−)pπ− branching fraction givingB(Λ0b→pπ−μ+μ−)B(Λ0b→J/ψ(→μ+μ−)pπ−)=0.044±0.012±0.007,where the first uncertainty is statistical and the second is systematic. This is the first observation of a b→d transition in a baryonic decay.
Journal Article
Search for the Λb→Λη′ and Λb→Λη decays with the LHCb detector
A search is performed for the as yet unobserved baryonic Λb→Λη′ and Λb→Λη decays with 3fb−1 of proton-proton collision data recorded by the LHCb experiment. The B0→K0Sη′ decay is used as a normalisation channel. No significant signal is observed for the Λb→Λη′ decay. An upper limit is found on the branching fraction of B(Λb→Λη′)<3.1×10−6 at 90% confidence level. Evidence is seen for the presence of the Λb→Λη decay at the level of 3σ significance, with a branching fraction B(Λb→Λη)=(9.3+7.3−5.3)×10−6.
Journal Article
Measurement ofZ→τ⁺τ⁻production in proton-proton collisions at√s̅ = 8TeV
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.
Journal Article
Measurement of forward W→eν production in pp collisions at s√=8TeV
A measurement of the cross-section for W→eν production in pp collisions is presented using data corresponding to an integrated luminosity of 2fb−1 collected by the LHCb experiment at a centre-of-mass energy of s√=8TeV. The electrons are required to have more than 20GeV of transverse momentum and to lie between 2.00 and 4.25 in pseudorapidity. The inclusive W production cross-sections, where the W decays to eν, are measured to be _(W)⁺ e⁺ₑ&=1124.4 2.1 21.5 11.2 13.0 pb, _(W)⁻ e⁻ₑ&= 809.0 1.9 18.1 7.0 09.4 pb, 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. Differential cross-sections as a function of the electron pseudorapidity are measured. The W+/W− cross-section ratio and production charge asymmetry are also reported. Results are compared with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics. Finally, in a precise test of lepton universality, the ratio of W boson branching fractions is determined to be B(W e)/B(W )=1.020 0.002 0.019, where the first uncertainty is statistical and the second is systematic.
Journal Article