1,550 research outputs found
Study of η â ηâČ mixing from measurement of B (s)0 â J/Ïη(âČ) decay rates
A study of B and B0 s meson decays into J/Ïη and J/Ïη0 final states is performed using a data set of proton-proton collisions at centre-of-mass energies of 7 and 8 TeV, collected by the LCHb experiment and corresponding to 3.0 fbâ1 of integrated luminosity. The decay B0 â J/Ïη0 is observed for the first time. The following ratios of branching fractions are measured: B(B0 â J/Ïη0 ) B(B0 s â J/Ïη0) = (2.28 ± 0.65 (stat) ± 0.10 (syst) ± 0.13 (fs/fd)) Ă 10â2 , B(B0 â J/Ïη) B(B0 s â J/Ïη) = (1.85 ± 0.61 (stat) ± 0.09 (syst) ± 0.11 (fs/fd)) Ă 10â2 , where the third uncertainty is related to the present knowledge of fs/fd, the ratio between the probabilities for a b quark to form a B0 s or a B0 meson. The branching fraction ratios are used to determine the parameters of ηâη 0 meson mixing. In addition, the first evidence for the decay B0 s â Ï(2S)η 0 is reported, and the relative branching fraction is measured, B(B0 s â Ï(2S)η 0 ) B(B0 s â J/Ïη0) = (38.7 ± 9.0 (stat) ± 1.3 (syst) ± 0.9(B)) Ă 10â2 , where the third uncertainty is due to the limited knowledge of the branching fractions of J/Ï and Ï(2S) mesons
Search for the rare decay Îc+ âpÎŒ+ÎŒ-
The flavor-changing neutral-current (FCNC) decay ÎĂŸ c â pÎŒĂŸÎŒâ (inclusion of the charge-conjugate processes is implied throughout) is expected to be heavily suppressed in the Standard Model (SM) by the Glashow-IliopoulosMaiani mechanism [1]. The branching fractions for shortdistance c â ulĂŸlâ contributions to the transition are expected to be of OĂ°10â9Ă in the SM but can be enhanced by effects beyond the SM. However, long-distance contributions proceeding via a tree-level amplitude, with an intermediate meson resonance decaying into a dimuon pair [2,3], can increase the branching fraction up to OĂ°10â6Ă [4]. The short-distance and hadronic contributions can be separated by splitting the data set into relevant regions of dimuon mass. The ÎĂŸ c â pÎŒĂŸÎŒâ decay has been previously searched for by the BABAR Collaboration [5], yielding 11.1 5.0 2.5 events and an upper limit on the branching fraction of 4.4 Ă 10â5 at 90% C.L. Similar FCNC transitions for the b-quark system (b â slĂŸlâ) exhibit a pattern of consistent deviations from the current SM predictions both in branching fractions [6] and angular observables [7], with the combined significance reaching 4 to 5 standard deviations [8,9]. Processes involving c â ulĂŸlâ transitions are far less explored at both the experimental and theoretical levels, which makes such measurements desirable. Similar analyses of the D system have reported evidence for the longdistance contribution [10]; however, the short-distance contributions have not been established [11]
Observation of the B0 âÏ0Ï0 decay from an amplitude analysis of B0 â (Ï+Ï-) (Ï+Ï-) decays
Proton-proton collision data recorded in 2011 and 2012 by the LHCb experiment, corresponding to an integrated luminosity of 3.0 fbâ1 , are analysed to search for the charmless B0 â Ï 0Ï 0 decay. More than 600 B0 â (Ï +Ï â)(Ï +Ï â) signal decays are selected and used to perform an amplitude analysis, under the assumption of no CP violation in the decay, from which the B0 â Ï 0Ï 0 decay is observed for the first time with 7.1 standard deviations significance. The fraction of B0 â Ï 0Ï 0 decays yielding a longitudinally polarised final state is measured to be fL = 0.745+0.048 â0.058(stat) ± 0.034(syst). The B0 â Ï 0Ï 0 branching fraction, using the B0 â ÏKâ (892)0 decay as reference, is also reported as B(B0 â Ï 0Ï 0 ) = (0.94 ± 0.17(stat) ± 0.09(syst) ± 0.06(BF)) Ă 10â6
Searches for Î0b and Î0b decays to K0SpÏâ and K0SpKâ final states with first observation of the Î0bâK0SpÏâ decay
A search for previously unobserved decays of beauty baryons to the final states K0 S pÏâ and K0 S pKâ is reported. The analysis is based on a data sample corresponding to an integrated luminosity of 1.0 fbâ1 of pp collisions. The Î 0 b â K0pÏâ decay is observed with a significance of 8.6 Ï, with branching fraction B(Î 0 b â K0 pÏâ) = (1.26 ± 0.19 ± 0.09 ± 0.34 ± 0.05) Ă 10â5 , where the uncertainties are statistical, systematic, from the ratio of fragmentation fractions fÎ0 b /fd, and from the branching fraction of the B0â K0Ï +Ï â normalisation channel, respectively. A first measurement is made of the CP asymmetry, giving ACP (Î 0 b â K0 pÏâ) = 0.22 ± 0.13 (stat) ± 0.03 (syst). No significant signals are seen for Î 0 b â K0 S pKâ decays, Î0 b decays to both the K0 S pÏâ and K0 S pKâ final states, and the Î 0 b â Dâ s (â K0 SKâ)p decay, and upper limits on their branching fractions are reported
Observation of Z production in proton-lead collisions at LHCb
The first observation of Z boson production in proton-lead collisions at a centreof-mass energy per proton-nucleon pair of â sNN = 5 TeV is presented. The data sample corresponds to an integrated luminosity of 1.6 nbâ1 collected with the LHCb detector. The Z candidates are reconstructed from pairs of oppositely charged muons with pseudorapidities between 2.0 and 4.5 and transverse momenta above 20 GeV/c. The invariant dimuon mass is restricted to the range 60 â 120 GeV/c2 . The Z production cross-section is measured to be ÏZâ”+”â (fwd) = 13.5 +5.4 â4.0 (stat.) ± 1.2(syst.) nb in the direction of the proton beam and ÏZâ”+”â (bwd) = 10.7 +8.4 â5.1 (stat.) ± 1.0(syst.) nb in the direction of the lead beam, where the first uncertainty is statistical and the second systematic
Quantum numbers of the X (3872 ) state and orbital angular momentum in its Ï0J /Ï decay
Angular correlations in B+ â X(3872)K+ decays, with X(3872) â Ï 0J/Ï, Ï 0 â Ï +Ï â and J/Ï â ” +” â, are used to measure orbital angular momentum contributions and to determine the J P C value of the X(3872) meson. The data correspond to an integrated luminosity of 3.0 fbâ1 of proton-proton collisions collected with the LHCb detector. This determination, for the first time performed without assuming a value for the orbital angular momentum, confirms the quantum numbers to be J P C = 1++. The X(3872) is found to decay predominantly through S wave and an upper limit of 4% at 95% C.L. is set on the D-wave contribution
Measurement of CP observables in B ± â DK ± and B ± â DÏ Â± with D â KS0K±Ïâ decays
Measurements of CP observables in B± â DK± and B± â Dϱ decays are presented, where D represents a superposition of D0 and DÂŻÂŻÂŻÂŻ0 states. The D meson is reconstructed in the three-body final states K0SK±Ïâ and K0SKâϱ. The analysis uses samples of B mesons produced in proton-proton collisions, corresponding to an integrated luminosity of 1.0, 2.0, and 6.0 fbâ1 collected with the LHCb detector at centre-of-mass energies of sâ = 7, 8, and 13 TeV, respectively. These measurements are the most precise to date, and provide important input for the determination of the CKM angle Îł
Observation of a new baryon state in the Îb0Ï+Ïâ mass spectrum
A new baryon state is observed in the Î0bÏ+Ïâ mass spectrum with high significance using a data sample of pp collisions, collected with the LHCb detector at centre-of-mass energies sâ = 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fbâ1. The mass and natural width of the new state are measured to be m=6072.3±2.9±0.6±0.2 MeV,Î=72±11±2 MeV, where the first uncertainty is statistical and the second systematic. The third uncertainty for the mass is due to imprecise knowledge of the Î0b baryon mass. The new state is consistent with the first radial excitation of the Î0b baryon, the Îb(2S)0 resonance. Updated measurements of the masses and the upper limits on the natural widths of the previously observed Îb(5912)0 and Îb(5920)0 states are also reported
Measurement of the shape of the Bs0âDsââÎŒ+ΜΌ differential decay rate
The shape of the B0sâDââsÎŒ+ΜΌ differential decay rate is obtained as a function of the hadron recoil parameter using proton-proton collision data at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.7 fbâ1 collected by the LHCb detector. The B0sâDââsÎŒ+ΜΌ decay is reconstructed through the decays DââsâDâsÎł and DâsâKâK+Ïâ. The differential decay rate is fitted with the Caprini-Lellouch-Neubert (CLN) and Boyd-Grinstein-Lebed (BGL) parametrisations of the form factors, and the relevant quantities for both are extracted
Observation of the semileptonic decay B+â ppÂŻ ÎŒ+ΜΌ
The Cabibbo-suppressed semileptonic decay B+âppÂŻÂŻÂŻÎŒ+ΜΌ is observed for the first time using a sample of pp collisions corresponding to an integrated luminosity of 1.0, 2.0 and 1.7 fbâ1 at centre-of-mass energies of 7, 8 and 13 TeV, respectively. The differential branching fraction is measured as a function of the ppÂŻÂŻÂŻ invariant mass using the decay mode B+ â J/ÏK+ for normalisation. The total branching fraction is measured to be B(B+âppÂŻÂŻÂŻÎŒ+ΜΌ)= (5.27+0.23â0.24±0.21±0.15)Ă10â6, where the first uncertainty is statistical, the second systematic and the third is from the uncertainty on the branching fraction of the normalisation channel
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