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Observations of Λb0 → ΛK+π− and Λb0 → ΛK+ K− decays and searches for other Λb0 and Ξb0 decays to Λh+ h′− final states

  • Garrido Beltrán, Lluís
  • Gascón Fora, David
  • Graciani Díaz, Ricardo
  • Graugés Pous, Eugeni
  • Marin Benito, Carla
  • Picatoste Olloqui, Eduardo
  • Rives Molina, Vicente José
  • Calvo Gómez, Míriam
  • LHCb Collaboration
A search is performed for the charmless three-body decays of the Λ b 0 and Ξ b 0 baryons to the final states Λh + h′−, where h (′) = π or K. The analysis is based on a data sample, corresponding to an integrated luminosity of 3 fb−1 of pp collisions, collected by the LHCb experiment. The Λ b 0  → ΛK +π− and Λ b 0  → ΛK + K − decays are observed for the first time and their branching fractions and CP asymmetry parameters are measured. Evidence is seen for the Λ b 0  → Λπ+π− decay and limits are set on the branching fractions of Ξ b 0 baryon decays to the Λh + h′− final states.
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Study of ψ(2S) production and cold nuclear matter effects in pPb collisions at √ sNN = 5 TeV

  • Garrido Beltrán, Lluís
  • Gascón Fora, David
  • Graciani Díaz, Ricardo
  • Graugés Pous, Eugeni
  • Marin Benito, Carla
  • Picatoste Olloqui, Eduardo
  • Rives Molina, Vicente José
  • Vilasis-Cardona, Xavier
  • Calvo Gómez, Míriam
  • LHCb Collaboration
The production of ψ(2S) mesons is studied in dimuon final states using proton-lead (pPb) collision data collected by the LHCb detector. The data sample corresponds to an integrated luminosity of 1.6 nb−1. The nucleon-nucleon centre-of-mass energy of the pPb collisions is sNN−−−−√=5 TeV. The measurement is performed using ψ(2S) mesons with transverse momentum less than 14 GeV/c and rapidity y in the ranges 1.5 < y < 4.0 and −5.0 < y < −2.5 in the nucleon-nucleon centre-of-mass system. The forward-backward production ratio and the nuclear modification factor are determined for ψ(2S) mesons. Using the production cross-section results of ψ(2S) and J/ψ mesons from b-hadron decays, the bb¯¯ cross-section in pPb collisions at sNN−−−−√=5 TeV is obtained.
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Measurement of the Bc-meson production fraction and asymmetry in 7 and 13 TeV pp collisions

  • LHCb Collaboration
  • Calvo Gómez, Míriam
  • Camboni, Alessandro
  • Coquereau, Samuel
  • Garrido Beltrán, Lluís
  • Gascón Fora, David
  • Gironella Gironell, P.
  • Graciani Díaz, Ricardo
  • Graugés Pous, Eugeni
  • Manera Escalero, R.
  • Vázquez Gómez, Ricard
  • Vilasis-Cardona, Xavier
The production fraction of the Bc-meson with respect to the sum of B- A nd B0 mesons is measured in both 7 and 13 TeV center-of-mass (c.m.) energy pp collisions produced by the Large Hadron Collider (LHC), using the LHCb detector. The rate, approximately 3.7 per mille, does not change with energy, but shows a transverse momentum dependence. The Bc-Bc+ production asymmetry is also measured and is consistent with zero within the determined statistical and systematic uncertainties of a few percent.
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Amplitude analysis of B± → π±K+K− decays

  • LHCb Collaboration
  • Calvo Gómez, Míriam
  • Camboni, Alessandro
  • Coquereau, Samuel
  • Garrido Beltrán, Lluís
  • Gascón Fora, David
  • Gironella Gironell, Pere
  • Graciani Díaz, Ricardo
  • Graugés Pous, Eugeni
  • Vilasis-Cardona, Xavier
The first amplitude analysis of the B± → π ±K+K− decay is reported based on a data sample corresponding to an integrated luminosity of 3.0 fb−1 of pp collisions recorded in 2011 and 2012 with the LHCb detector. The data are found to be best described by a coherent sum of five resonant structures plus a nonresonant component and a contribution from ππ ↔ KK S-wave rescattering. The dominant contributions in the π ±K∓ and K+K− systems are the nonresonant and the B± → ρ(1450)0π ± amplitudes, respectively, with fit fractions around 30%. For the rescattering contribution, a sizeable fit fraction is observed. This component has the largest CP asymmetry reported to date for a single amplitude of (−66 ± 4 ± 2)%, where the first uncertainty is statistical and the second systematic. No significant CP violation is observed in the other contributions.
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Measurement of CP violation in the Bs0→ϕϕ decay and search for the B 0 → ϕϕ decay

  • LHCb Collaboration
  • Calvo Gómez, Míriam
  • Camboni, Alessandro
  • Coquereau, Samuel
  • Garrido Beltrán, Lluís
  • Gascón Fora, David
  • Gironella Gironell, Pere
  • Graciani Díaz, Ricardo
  • Graugés Pous, Eugeni
  • Vilasis-Cardona, Xavier
A measurement of the time-dependent CP-violating asymmetry in B0s → φφ decays is presented. Using a sample of proton-proton collision data corresponding to an integrated luminosity of 5.0 fb−1 collected by the LHCb experiment at centre-of-mass energies √ s = 7 TeV in 2011, 8 TeV in 2012 and 13 TeV in 2015 and 2016, a signal yield of around 9000 B0 s → φφ decays is obtained. The CP-violating phase φ sss¯ s is measured to be −0.073 ± 0.115(stat) ± 0.027(syst) rad, under the assumption it is independent of the helicity of the φφ decay. In addition, the CP-violating phases of the transverse polarisations under the assumption of CP conservation of the longitudinal phase are measured. The helicity-independent direct CP-violation parameter is also measured, and is found to be |λ| = 0.99 ± 0.05(stat) ± 0.01(syst). In addition, T-odd triple-product asymmetries are measured. The results obtained are consistent with the hypothesis of CP conservation in ¯b → ss¯ ss¯ transitions. Finally, a limit on the branching fraction of the B0 → φφ decay is determined to be B(B0 → φφ) < 2.7 × 10−8 at 90 % confidence level.
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Measurement of the CP-violating phase ϕs from Bs0→J/ψπ+π− decays in 13 TeV pp collisions

  • LHCb Collaboration
  • Alfonso Albero, Alejandro
  • Calvo Gómez, Míriam
  • Camboni, Alessandro
  • Coquereau, Samuel
  • Garrido Beltrán, Lluís
  • Gascón Fora, David
  • Gironella Gironell, Pere
  • Graciani Díaz, Ricardo
  • Graugés Pous, Eugeni
  • Vilasis-Cardona, Xavier
Decays of B0s and B0s mesons into J/ψ π+π− final states are studied in a data sample corresponding to 1.9 fb−1 of integrated luminosity collected with the LHCb detector in 13 TeV pp collisions. A time-dependent amplitude analysis is used to determine the final-state resonance contributions, the CP-violating phase φs = −0.057 ± 0.060 ± 0.011 rad, the decay-width difference between the heavier mass B0 s eigenstate and the B0 meson of −0.050 ± 0.004 ± 0.004 ps−1, and the CP-violating parameter |λ| = 1.01+0.08 −0.06 ± 0.03, where the first uncertainty is statistical and the second systematic. These results are combined with previous LHCb measurements in the same decay channel using 7 TeV and 8 TeV pp collisions obtaining φs = 0.002 ± 0.044 ± 0.012 rad, and |λ| = 0.949 ± 0.036 ± 0.019.
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Measurement of charged hadron production in Z-tagged jets in proton-proton collisions at s√=8 TeV

  • LHCb Collaboration
  • Calvo Gómez, Míriam
  • Camboni, Alessandro
  • Coquereau, Samuel
  • Garrido Beltrán, Lluís
  • Gascón Fora, David
  • Gironella Gironell, Pere
  • Graciani Díaz, Ricardo
  • Graugés Pous, Eugeni
  • Vilasis-Cardona, Xavier
The production of charged hadrons within jets recoiling against a Z boson is measured in proton-proton collision data at ffiffi s p ¼ 8 TeV recorded by the LHCb experiment. The charged-hadron structure of the jet is studied longitudinally and transverse to the jet axis for jets with transverse momentum pT > 20 GeV and in the pseudorapidity range 2.5 < η < 4. These are the first measurements of jet hadronization at these forward rapidities and also the first where the jet is produced in association with a Z boson. In contrast to previous hadronization measurements at the Large Hadron Collider, which are dominated by gluon jets, these measurements probe predominantly light-quark jets which are found to be more longitudinally and transversely collimated with respect to the jet axis when compared to the previous gluon dominated measurements. Therefore, these results provide valuable information on differences between quarks and gluons regarding nonperturbative hadronization dynamics.
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Search for the Lepton-Flavor-Violating Decays Bs0 →τ±μâ' and B0 →τ±μâ'

  • LHCb Collaboration
  • Calvo Gómez, Míriam
  • Camboni, Alessandro
  • Coquereau, Samuel
  • Garrido Beltrán, Lluís
  • Gascón Fora, David
  • Gironella Gironell, Pere
  • Graciani Díaz, Ricardo
  • Graugés Pous, Eugeni
  • Vilasis-Cardona, Xavier
Results are reported from a search for the rare decays Bs0→τ±μâ' and B0→τ±μâ', where the τ lepton is reconstructed in the channel τ-→π-π+π-ντ. These processes are effectively forbidden in the standard model, but they can potentially occur at detectable rates in models of new physics that can induce lepton-flavor-violating decays. The search is based on a data sample corresponding to 3 fb-1 of proton-proton collisions recorded by the LHCb experiment in 2011 and 2012. The event yields observed in the signal regions for both processes are consistent with the expected standard model backgrounds. Because of the limited mass resolution arising from the undetected τ neutrino, the Bs0 and B0 signal regions are highly overlapping. Assuming no contribution from B0→τ±μâ', the upper limit B(Bs0→τ±μâ')<4.2×10-5 is obtained at 95% confidence level. If no contribution from Bs0→τ±μâ' is assumed, a limit of B(B0→τ±μâ')<1.4×10-5 is obtained at 95% confidence level. These results represent the first limit on B(Bs0→τ±μâ') and the most stringent limit on B(B0→τ±μâ').
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Observation of New Resonances in the Λb0 π+π- System

  • LHCb Collaboration
  • Calvo Gómez, Míriam
  • Camboni, Alessandro
  • Coquereau, Samuel
  • Garrido Beltrán, Lluís
  • Gascón Fora, David
  • Gironella Gironell, Pere
  • Graciani Díaz, Ricardo
  • Graugés Pous, Eugeni
  • Manera Escalero, R.
  • Vilasis-Cardona, Xavier
We report the observation of a new structure in the Λ0 bπþπ− spectrum using the full LHCb data set of pp collisions, corresponding to an integrated luminosity of 9 fb−1, collected at ffiffi s p ¼ 7, 8, and 13 TeV. A study of the structure suggests its interpretation as a superposition of two almost degenerate narrow states. The masses and widths of these states are measured to be mΛbð6146Þ0 ¼ 6146.17 0.33 0.22 0.16 MeV; mΛbð6152Þ0 ¼ 6152.51 0.26 0.22 0.16 MeV; ΓΛbð6146Þ0 ¼ 2.9 1.3 0.3 MeV; ΓΛbð6152Þ0 ¼ 2.1 0.8 0.3 MeV;with a mass splitting of Δm ¼ 6.34 0.32 0.02 MeV, where the first uncertainty is statistical, the second systematic. The third uncertainty for the mass measurements derives from the knowledge of the mass of the Λ0 b baryon. The measured masses and widths of these new excited states suggest their possible interpretation as a doublet of Λbð1DÞ0 states.
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A search for Ξcc++ → D+pK− π + decays

  • LHCb Collaboration
  • Alfonso Albero, Alejandro
  • Calvo Gómez, Míriam
  • Camboni, Alessandro
  • Coquereau, Samuel
  • Garrido Beltrán, Lluís
  • Gascón Fora, David
  • Gironella Gironell, Pere
  • Graciani Díaz, Ricardo
  • Graugés Pous, Eugeni
  • Vilasis-Cardona, Xavier
A search for the Ξ++cc baryon through the Ξ++cc→ D+pK−π+ decay is performed with a data sample corresponding to an integrated luminosity of 1.7 fb−1 recorded by the LHCb experiment in pp collisions at a centre-of-mass energy of 13 TeV. No significant signal is observed in the mass range from the kinematic threshold of the decay to 3800 MeV/c2. An upper limit is set on the ratio of branching fractions R=B(Ξ++cc→D+pK−π+)B(Ξ++cc→Λ+cK−π+π+) with ℛ < 1.7 (2.1) × 10−2 at the 90% (95%) confidence level at the known mass of the Ξ++cc state.
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