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<y<4.5. The production cross-section is measured to be 13.5±0.9±0.8nb. The first uncertainty is statistical, and the second is systematic. The differential cross-sections as functions of several kinematic variables of the J/ψ pair are measured and compared to theoretical predictions.
A search for the rare decays B0s→τ+τ− and B0→τ+τ− is performed using proton--proton collision data collected with the LHCb detector. The data sample corresponds to an integrated luminosity of 3fb−1 ...collected in 2011 and 2012. The τ leptons are reconstructed through the decay τ−→π−π+π−ντ. Assuming no contribution from B0→τ+τ− decays, an upper limit is set on the branching fraction B(B0s→τ+τ−)<6.8×10−3 at 95\% confidence level. If instead no contribution from B0s→τ+τ− decays is assumed, the limit is B(B0→τ+τ−)<2.1×10−3 at 95\% confidence level. These results correspond to the first direct limit on B(B0s→τ+τ−) and the world's best limit on B(B0→τ+τ−).
Search for the B0s→η′φ decay Aaij, R.; Beaucourt, L.; Chefdeville, M. ...
The journal of high energy physics,
05/2017, Letnik:
5
Journal Article
Recenzirano
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.
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.
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.
Using proton-proton collision data corresponding to an integrated luminosity of 3.0 fb-1, recorded by the LHCb detector at center-of-mass energies of 7 and 8 TeV, the Bc+→D0K+ decay is observed with ...a statistical significance of 5.1 standard deviations. By normalizing to B+→D¯ 0 π+ decays, a measurement of the branching fraction multiplied by the production rates for Bc+ relative to B+ mesons in the LHCb acceptance is obtained, RD0K=(fc/fu)×B (Bc+→D0K+)=(9. 3-2.5+2.8±0.6 )×10-7 , where the first uncertainty is statistical and the second is systematic. This decay is expected to proceed predominantly through weak annihilation and penguin amplitudes, and is the first Bc+ decay of this nature to be observed.
The first observation of the rare decayB0s→ϕπ+π− and evidence for B0→ϕπ+π− are reported, using pp collision data recorded by the LHCb detector at centre-of-mass energies s√=7 and 8~TeV, corresponding ...to an integrated luminosity of 3\,fb−1. The branching fractions in the π+π− invariant mass range 400<m(π+π−)<1600MeV/c2 are 3.48±0.23±0.17±0.35×10−6 and 1.82±0.25±0.41±0.14×10−7 for B0s→ϕπ+π− and B0→ϕπ+π− respectively, where the uncertainties are statistical, systematic and from the normalisation mode B0s→ϕϕ. A combined analysis of the π+π− mass spectrum and the decay angles of the final-state particles identifies the exclusive decays B0s→ϕf0(980), B0s→ϕf2(1430), and B0s→ϕρ with branching fractions of 1.12±0.16+0.09−0.08±0.11×10−6, 0.61±0.13+0.12−0.05±0.06×10−6 and 2.7±0.7±0.2±0.2×10−7, respectively.
A study of B+c→K+K−π+ decays is performed for the first time using data corresponding to an integrated luminosity of 3.0 fb−1 collected by the LHCb experiment in pp collisions at centre-of-mass ...energies of 7 and 8 TeV. Evidence for the decay B+c→χc0(→K+K−)π+ is reported with a significance of 4.0 standard deviations, resulting in the measurement of σ(B+c)σ(B+)×B(B+c→χc0π+) to be (9.8+3.4−3.0(stat)±0.8(syst))×10−6. Here B denotes a branching fraction while σ(B+c) and σ(B+) are the production cross-sections for B+c and B+ mesons. An indication of b¯c weak annihilation is found for the region m(K−π+)<1.834GeV/c2, with a significance of 2.4 standard deviations.
Using a data set corresponding to an integrated luminosity of 3fb−1, collected by the LHCb experiment in pp collisions at centre-of-mass energies of 7 and 8 TeV, the effective lifetime in the ...B0s→J/ψη decay mode, τeff, is measured to be τeff=1.479±0.034 (stat)±0.011 (syst) ps. Assuming CP conservation, τeff corresponds to the lifetime of the light B0s mass eigenstate. This is the first measurement of the effective lifetime in this decay mode.
Measurements of the differential branching fraction and angular moments of the decay B0→K+π−μ+μ− in the K∗0,2(1430)0 in the K+π− invariant mass range 1330<m(K+π−)<1530 MeV/c2 are presented. ...Proton-proton collision data are used, corresponding to an integrated luminosity of 3 fb−1 collected by the LHCb experiment. Differential branching fraction measurements are reported in five bins of the invariant mass squared of the dimuon system, q2, between 0.1 and 8.0 GeV2/c4. For the first time, an angular analysis sensitive to the S-, P- and D-wave contributions of this rare decay is performed. The set of 40 normalised angular moments describing the decay is presented for the q2 range 1.1--6.0 GeV2/c4.