Searches for heavy Majorana neutrinos in B− decays with final states containing hadrons plus a μ−μ− pair are performed using 0.41 fb−1 of data collected with the LHCb detector in proton-proton ...collisions at a center-of-mass energy of 7 TeV. No signals are found and upper limits are set on Majorana neutrino production and B− decay branching fractions as a function of the Majorana neutrino mass. A search is also made for the lepton flavour violating decay τ → μ+μ−μ− using 1.0 fb−1 of data collected by LHCb in 2011. The observed number of events is consistent with the background expectation, and an upper limit on the branching ratio is set. Using a similar procedure, the lepton flavour violating and baryon number violating decays τ− → μ+μ− and τ− → pμ−μ− are searched for, and upper limits provided at 95% confidence level.
Flavour physics at LHCb Adeva, B.
EPJ Web of Conferences,
01/2016, Letnik:
126
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
Some selected results of the LHCb experiment, running at the LHC with ppcollisions at 7 TeV and 8 TeV, are reported here, after operation with a total integratedluminosity of 3.0 fb−1 (Run 1). We ...focus on the most recent analyses on flavour physics,that include measurements of the CKM invariant phases γ and β, precision determination of the quark coupling strength Vub, observation of the very rare decays B0(s)→μ+μ−, search for new physics in the anomalous branching ratio of B→D*τv̄, and precision angular analysis of the rare decays B0→K*0μ+μ− and B0s→ϕμ+μ−. Detailed comparisons are performed in all cases with the predictions of the Standard Model, and a fewinteresting tensions are observed.
LHCb has recently reported the observation of exotic structures in the J/ψp channel, in Λb → J/ψK−p decay, which we discuss here and refer to as charmoniumpentaquarkstates. The data sample ...corresponds to an integrated luminosity of 3.0 fb−1acquired with the LHCb detector from 7 and 8 TeV pp collisions. An amplitude analysisof the three-body final state reproduces the two-body mass and angular distributions. Toobtain a satisfactory fit of the structures seen in the J/ψp mass spectrum, it is necessaryto include two Breit-Wigner amplitudes that each describe a resonant state. Details aregiven on the significance, and prefered quantum numbers, of these two resonances.
After observing and investigating the double-exotic (a double-exotic atom is a bound system, in which both oppositely charged components are unstable particles like μ,π,K,…) π+π− atom with the ground ...state lifetime τ of about 3×10−15 s, the upgraded DIRAC experiment at the CERN PS accelerator observes for the first time long-lived states of the same atom with lifetimes of about 10−11 s and more. The number of characteristic pion pairs resulting from the breakup (ionisation) of long-lived π+π− atoms amounts to 436±61, corresponding to a signal-to-error ratio of better than 7 standard deviations. This observation opens a new possibility to measure energy differences between p and s atomic states and so to determine ππ scattering lengths.
The adapted DIRAC experiment at the CERN PS accelerator observed for the first time long-lived hydrogenlike π^{+}π^{-} atoms, produced by protons hitting a beryllium target. A part of these atoms ...crossed the gap of 96 mm between the target and a 2.1 μm thick platinum foil, in which most of them dissociated. Analyzing the observed number of atomic pairs, n_{A}^{L}=436_{-61}^{+157}|_{tot}, the lifetime of the 2p state is found to be τ_{2p}=(0.45_{-0.30}^{+1.08}|_{tot})×10^{-11} s, not contradicting the corresponding QED 2p state lifetime τ_{2p}^{QED}=1.17×10^{-11} s. This lifetime value is three orders of magnitude larger than our previously measured value of the π^{+}π^{-} atom ground state lifetime τ=(3.15_{-0.26}^{+0.28}|_{tot})×10^{-15} s. Further studies of long-lived π^{+}π^{-} atoms will allow us to measure energy differences between p and s atomic states and so to discriminate between the isoscalar and isotensor ππ scattering lengths with the aim to check QCD predictions.
The goal of the DIRAC experiment at CERN (PS212) is to measure the π+π− atom lifetime with 10% precision. Such a measurement would yield a precision of 5% on the value of the S-wave ππ scattering ...lengths combination |a0−a2|. Based on part of the collected data we present a first result on the lifetime, τ=2.91−0.62+0.49×10−15 s, and discuss the major systematic errors. This lifetime corresponds to |a0−a2|=0.264−0.020+0.033mπ−1.
The measurement of charmonium states produced in proton-neon ( Formula omitted) collisions by the LHCb experiment in its fixed-target configuration is presented. The production of Formula omitted and ...Formula omitted mesons is studied with a beam of 2.5 Formula omitted protons colliding on gaseous neon targets at rest, corresponding to a nucleon-nucleon centre-of-mass energy Formula omitted. The data sample corresponds to an integrated luminosity of Formula omitted nb Formula omitted. The Formula omitted and Formula omitted hadrons are reconstructed in Formula omitted Formula omitted final states. The Formula omitted production cross-section per target nucleon in the centre-of-mass rapidity range Formula omitted is found to be Formula omitted. The ratio of Formula omitted and Formula omitted cross-sections is evaluated to Formula omitted. The Formula omitted to Formula omitted relative production rate is found to be Formula omitted in good agreement with other measurements involving beam and target nuclei of similar sizes.
Using a proton-proton collision data sample collected by the LHCb detector and corresponding to an integrated luminosity of Formula omitted, the lifetime of the light Formula omitted mass eigenstate, ...Formula omitted, is measured using the Formula omitted decay mode to be tauL=1.445±0.016(stat)±0.008(syst)ps.A combination of this result with a previous LHCb analysis using an independent dataset corresponding to 3 fb Formula omitted of integrated luminosity gives tauL=1.452±0.014±0.007±0.002ps,where the first uncertainty is statistical, the second due to the uncorrelated part of the systematic uncertainty and the third due to the correlated part of the systematic uncertainty.
The very rare Formula omitted decay is searched for by analysing Formula omitted decays. The analysis uses a sample of beauty mesons produced in proton-proton collisions collected with the LHCb ...detector between 2011 and 2018, corresponding to an integrated luminosity of 9 Formula omitted. The signal signature corresponds to simultaneous peaks in the Formula omitted and Formula omitted invariant masses. No evidence for an excess of events over background is observed and an upper limit is set on the branching fraction of the decay at Formula omitted at Formula omitted confidence level. This is the first limit on the branching fraction of Formula omitted decays and the most stringent limit on Formula omitted decays to leptonic final states. The analysis is the first search for a rare charm-meson decay exploiting production via beauty decays.
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