ABSTRACT The associated production of a $W$ boson with a jet originating from either a light part... more ABSTRACT The associated production of a $W$ boson with a jet originating from either a light parton or heavy-flavor quark is studied in the forward region using proton-proton collisions. The analysis uses data corresponding to integrated luminosities of 1.0 and $2.0\,{\rm fb}^{-1}$ collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, respectively. The $W$ bosons are reconstructed using the $W\to\mu\nu$ decay and muons with a transverse momentum, $p_{\rm T}$, larger than 20 GeV in the pseudorapidity range $2.0<\eta<4.5$. The partons are reconstructed as jets with $p_{\rm T} > 20$ GeV and $2.2 < \eta < 4.2$. The sum of the muon and jet momenta must satisfy $p_{\rm T} > 20$ GeV. The fraction of $W+$jet events that originate from beauty and charm quarks is measured, along with the charge asymmetries of the $W\!+\!b$ and $W\!+\!c$ production cross-sections. The ratio of the $W+$jet to $Z+$jet production cross-sections is also measured using the $Z\to\mu\mu$ decay. All results are in agreement with Standard Model predictions.
A search is presented for hidden-sector bosons, χ, produced in the decay B^{0}→K^{*}(892)^{0}χ, w... more A search is presented for hidden-sector bosons, χ, produced in the decay B^{0}→K^{*}(892)^{0}χ, with K^{*}(892)^{0}→K^{+}π^{-} and χ→μ^{+}μ^{-}. The search is performed using pp-collision data corresponding to 3.0 fb^{-1} collected with the LHCb detector. No significant signal is observed in the accessible mass range 214≤m(χ)≤4350 MeV, and upper limits are placed on the branching fraction product B(B^{0}→K^{*}(892)^{0}χ)×B(χ→μ^{+}μ^{-}) as a function of the mass and lifetime of the χ boson. These limits are of the order of 10^{-9} for χ lifetimes less than 100 ps over most of the m(χ) range, and place the most stringent constraints to date on many theories that predict the existence of additional low-mass bosons.
Top quark production in the forward region in proton-proton collisions is observed for the first ... more Top quark production in the forward region in proton-proton collisions is observed for the first time. The W +b final state with W → µν is reconstructed using muons with a transverse momentum, p T , larger than 25 GeV in the pseudorapidity range 2.0 < η < 4.5. The b jets are required to have 50 < p T < 100 GeV and 2.2 < η < 4.2, while the transverse component of the sum of the muon and b-jet momenta must satisfy p T > 20 GeV. The results are based on data corresponding to integrated luminosities of 1.0 and 2.0 fb −1 collected at center-of-mass energies of 7 and 8 TeV by LHCb. The inclusive top quark production cross-sections in the fiducial region are
Measurements are presented of the CP violation observables S and C in the decays of B^{0} and B[o... more Measurements are presented of the CP violation observables S and C in the decays of B^{0} and B[over ¯]^{0} mesons to the J/ψK_{S}^{0} final state. The data sample corresponds to an integrated luminosity of 3.0 fb^{-1} collected with the LHCb experiment in proton-proton collisions at center-of-mass energies of 7 and 8 TeV, and contains a total of 41 560 selected B^{0} and B[over ¯]^{0} decays. The analysis of the time evolution of these decays yields S=0.731±0.035(stat)±0.020(syst) and C=-0.038±0.032(stat)±0.005(syst). In the standard model, S equals sin(2β) to a good level of precision. The values are consistent with the current world averages and with the standard model expectations.
A measurement of the cross-section for Z-boson production in the forward region of pp collisions ... more A measurement of the cross-section for Z-boson production in the forward region of pp collisions at 8 TeV centre-of-mass energy is presented. The measurement is based on a sample of Z → e + e − decays reconstructed using the LHCb detector, corresponding to an integrated luminosity of 2.0 fb −1 . The acceptance is defined by the requirements 2.0 < η < 4.5 and p T > 20 GeV for the pseudorapidities and transverse momenta of the leptons. Their invariant mass is required to lie in the range 60-120 GeV. The cross-section is determined to be σ(pp → Z → e + e − ) = 93.81 ± 0.41(stat) ± 1.48(syst) ± 1.14(lumi) pb , where the first uncertainty is statistical and the second reflects all systematic effects apart from that arising from the luminosity, which is given as the third uncertainty. Differential cross-sections are presented as functions of the Z-boson rapidity and of the angular variable φ * , which is related to the Z-boson transverse momentum.
The European physical journal. C, Particles and fields
A search is presented for long-lived particles with a mass between 25 and 50 [Formula: see text] ... more A search is presented for long-lived particles with a mass between 25 and 50 [Formula: see text] and a lifetime between 1 and 200[Formula: see text] in a sample of proton-proton collisions at a centre-of-mass energy of [Formula: see text] TeV, corresponding to an integrated luminosity of 0.62 [Formula: see text], collected by the LHCb detector. The particles are assumed to be pair-produced by the decay of a standard model-like Higgs boson. The experimental signature of the long-lived particle is a displaced vertex with two associated jets. No excess above the background is observed and limits are set on the production cross-section as a function of the long-lived particle mass and lifetime.
The semileptonic CP asymmetry in B^{0}-B[over ¯]^{0} mixing, a_{sl}^{d}, is measured in proton-pr... more The semileptonic CP asymmetry in B^{0}-B[over ¯]^{0} mixing, a_{sl}^{d}, is measured in proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb^{-1}, recorded by the LHCb experiment. Semileptonic B^{0} decays are reconstructed in the inclusive final states D^{-}μ^{+} and D^{*-}μ^{+}, where the D^{-} meson decays into the K^{+}π^{-}π^{-} final state and the D^{*-} meson into the D[over ¯]^{0}(→K^{+}π^{-})π^{-} final state. The asymmetry between the numbers of D^{(*)-}μ^{+} and D^{(*)+}μ^{-} decays is measured as a function of the decay time of the B^{0} mesons. The CP asymmetry is measured to be a_{sl}^{d}=(-0.02±0.19±0.30)%, where the first uncertainty is statistical and the second systematic. This is the most precise measurement of a_{sl}^{d} to date and is consistent with the prediction from the standard model.
Decays of the form B 0 (s) → J/ψ K 0 S h + h ( )− (h ( ) = K, π) are searched for in protonproton... more Decays of the form B 0 (s) → J/ψ K 0 S h + h ( )− (h ( ) = K, π) are searched for in protonproton collision data corresponding to an integrated luminosity of 1.0 fb −1 recorded with the LHCb detector. The first observation of the B 0 s → J/ψ K 0 S K ± π ∓ decay is reported, with significance in excess of 10 standard deviations. The B 0 → J/ψ K 0 S K + K − decay is also observed for the first time. The branching fraction of B 0 → J/ψ K 0 S π + π − is determined, to significantly better precision than previous measurements, using B 0 → J/ψ K 0 S as a normalisation channel. Branching fractions and upper limits of the other B 0
Study of the kinematic dependences of Λ 0 b production in pp collisions and a measurement of the ... more Study of the kinematic dependences of Λ 0 b production in pp collisions and a measurement of the Λ 0 b → Λ + c π − branching fraction
A binned Dalitz plot analysis of B ± → DK ± decays, with D → K 0 S π + π − and D → K 0 S K + K − ... more A binned Dalitz plot analysis of B ± → DK ± decays, with D → K 0 S π + π − and D → K 0 S K + K − , is performed to measure the CP -violating observables x ± and y ± , which are sensitive to the Cabibbo-Kobayashi-Maskawa angle γ. The analysis exploits a sample of proton-proton collision data corresponding to 3.0 fb −1 collected by the LHCb experiment. Measurements from CLEO-c of the variation of the strong-interaction phase of the D decay over the Dalitz plot are used as inputs. The values of the parameters are found to be x + = (−7.7 ± 2.4 ± 1.0 ± 0.4) × 10 −2 , x − = (2.5 ± 2.5 ± 1.0 ± 0.5) × 10 −2 , y + = (−2.2 ± 2.5 ± 0.4 ± 1.0) × 10 −2 , and y − = (7.5 ± 2.9 ± 0.5 ± 1.4) × 10 −2 . The first, second, and third uncertainties are the statistical, the experimental systematic, and that associated with the precision of the strong-phase parameters. These are the most precise measurements of these observables and correspond to γ = (62 +15 −14 ) • , with a second solution at γ → γ + 180 • , and r B = 0.080 +0.019 −0.021 , where r B is the ratio between the suppressed and favoured B decay amplitudes.
A search for CP violation in Cabibbo-suppressed D ± → K 0 S K ± and D ± s → K 0 S π ± decays is p... more A search for CP violation in Cabibbo-suppressed D ± → K 0 S K ± and D ± s → K 0 S π ± decays is performed using pp collision data, corresponding to an integrated luminosity of 3 fb −1 , recorded by the LHCb experiment. The individual CP -violating asymmetries are measured to be A D ± →K 0 S K ± CP = (+0.03 ± 0.17 ± 0.14)% A Submitted to JHEP c CERN on behalf of the LHCb collaboration, license CC-BY-3.0. † Authors are listed on the following pages.
Time-integrated CP asymmetries in D 0 decays to the final states K − K + and π − π + are measured... more Time-integrated CP asymmetries in D 0 decays to the final states K − K + and π − π + are measured using proton-proton collisions corresponding to 3 fb −1 of integrated luminosity collected at centre-of-mass energies of 7 TeV and 8 TeV. The D 0 mesons are produced in semileptonic b-hadron decays, where the charge of the accompanying muon is used to determine the initial flavour of the charm meson. The difference in CP asymmetries between the two final states is measured to be ∆A CP = A CP (K − K + ) − A CP (π − π + ) = (+0.14 ± 0.16 (stat) ± 0.08 (syst))% .
are reported using data corresponding to an integrated luminosity of 3 fb −1 collected at 7 and 8... more are reported using data corresponding to an integrated luminosity of 3 fb −1 collected at 7 and 8 TeV center-of-mass energies in proton-proton collisions with the LHCb detector. In addition, the most precise measurement of the branching fraction BðB 0
An angular analysis of the decay B 0 → φK * (892) 0 is reported based on a pp collision data samp... more An angular analysis of the decay B 0 → φK * (892) 0 is reported based on a pp collision data sample, corresponding to an integrated luminosity of 1.0 fb −1 , collected at a centre-of-mass energy of √ s = 7 TeV with the LHCb detector. The P-wave amplitudes and phases are measured with a greater precision than by previous experiments, and confirm about equal amounts of longitudinal and transverse polarization. The S-wave K + π − and K + K − contributions are taken into account and found to be significant. A comparison of the B 0 → φK * (892) 0 and B 0 → φK * (892) 0 results shows no evidence for direct CP violation in the rate asymmetry, in the triple-product asymmetries or in the polarization amplitudes and phases.
ABSTRACT The associated production of a $W$ boson with a jet originating from either a light part... more ABSTRACT The associated production of a $W$ boson with a jet originating from either a light parton or heavy-flavor quark is studied in the forward region using proton-proton collisions. The analysis uses data corresponding to integrated luminosities of 1.0 and $2.0\,{\rm fb}^{-1}$ collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, respectively. The $W$ bosons are reconstructed using the $W\to\mu\nu$ decay and muons with a transverse momentum, $p_{\rm T}$, larger than 20 GeV in the pseudorapidity range $2.0&lt;\eta&lt;4.5$. The partons are reconstructed as jets with $p_{\rm T} &gt; 20$ GeV and $2.2 &lt; \eta &lt; 4.2$. The sum of the muon and jet momenta must satisfy $p_{\rm T} &gt; 20$ GeV. The fraction of $W+$jet events that originate from beauty and charm quarks is measured, along with the charge asymmetries of the $W\!+\!b$ and $W\!+\!c$ production cross-sections. The ratio of the $W+$jet to $Z+$jet production cross-sections is also measured using the $Z\to\mu\mu$ decay. All results are in agreement with Standard Model predictions.
A search is presented for hidden-sector bosons, χ, produced in the decay B^{0}→K^{*}(892)^{0}χ, w... more A search is presented for hidden-sector bosons, χ, produced in the decay B^{0}→K^{*}(892)^{0}χ, with K^{*}(892)^{0}→K^{+}π^{-} and χ→μ^{+}μ^{-}. The search is performed using pp-collision data corresponding to 3.0 fb^{-1} collected with the LHCb detector. No significant signal is observed in the accessible mass range 214≤m(χ)≤4350 MeV, and upper limits are placed on the branching fraction product B(B^{0}→K^{*}(892)^{0}χ)×B(χ→μ^{+}μ^{-}) as a function of the mass and lifetime of the χ boson. These limits are of the order of 10^{-9} for χ lifetimes less than 100 ps over most of the m(χ) range, and place the most stringent constraints to date on many theories that predict the existence of additional low-mass bosons.
Top quark production in the forward region in proton-proton collisions is observed for the first ... more Top quark production in the forward region in proton-proton collisions is observed for the first time. The W +b final state with W → µν is reconstructed using muons with a transverse momentum, p T , larger than 25 GeV in the pseudorapidity range 2.0 < η < 4.5. The b jets are required to have 50 < p T < 100 GeV and 2.2 < η < 4.2, while the transverse component of the sum of the muon and b-jet momenta must satisfy p T > 20 GeV. The results are based on data corresponding to integrated luminosities of 1.0 and 2.0 fb −1 collected at center-of-mass energies of 7 and 8 TeV by LHCb. The inclusive top quark production cross-sections in the fiducial region are
Measurements are presented of the CP violation observables S and C in the decays of B^{0} and B[o... more Measurements are presented of the CP violation observables S and C in the decays of B^{0} and B[over ¯]^{0} mesons to the J/ψK_{S}^{0} final state. The data sample corresponds to an integrated luminosity of 3.0 fb^{-1} collected with the LHCb experiment in proton-proton collisions at center-of-mass energies of 7 and 8 TeV, and contains a total of 41 560 selected B^{0} and B[over ¯]^{0} decays. The analysis of the time evolution of these decays yields S=0.731±0.035(stat)±0.020(syst) and C=-0.038±0.032(stat)±0.005(syst). In the standard model, S equals sin(2β) to a good level of precision. The values are consistent with the current world averages and with the standard model expectations.
A measurement of the cross-section for Z-boson production in the forward region of pp collisions ... more A measurement of the cross-section for Z-boson production in the forward region of pp collisions at 8 TeV centre-of-mass energy is presented. The measurement is based on a sample of Z → e + e − decays reconstructed using the LHCb detector, corresponding to an integrated luminosity of 2.0 fb −1 . The acceptance is defined by the requirements 2.0 < η < 4.5 and p T > 20 GeV for the pseudorapidities and transverse momenta of the leptons. Their invariant mass is required to lie in the range 60-120 GeV. The cross-section is determined to be σ(pp → Z → e + e − ) = 93.81 ± 0.41(stat) ± 1.48(syst) ± 1.14(lumi) pb , where the first uncertainty is statistical and the second reflects all systematic effects apart from that arising from the luminosity, which is given as the third uncertainty. Differential cross-sections are presented as functions of the Z-boson rapidity and of the angular variable φ * , which is related to the Z-boson transverse momentum.
The European physical journal. C, Particles and fields
A search is presented for long-lived particles with a mass between 25 and 50 [Formula: see text] ... more A search is presented for long-lived particles with a mass between 25 and 50 [Formula: see text] and a lifetime between 1 and 200[Formula: see text] in a sample of proton-proton collisions at a centre-of-mass energy of [Formula: see text] TeV, corresponding to an integrated luminosity of 0.62 [Formula: see text], collected by the LHCb detector. The particles are assumed to be pair-produced by the decay of a standard model-like Higgs boson. The experimental signature of the long-lived particle is a displaced vertex with two associated jets. No excess above the background is observed and limits are set on the production cross-section as a function of the long-lived particle mass and lifetime.
The semileptonic CP asymmetry in B^{0}-B[over ¯]^{0} mixing, a_{sl}^{d}, is measured in proton-pr... more The semileptonic CP asymmetry in B^{0}-B[over ¯]^{0} mixing, a_{sl}^{d}, is measured in proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb^{-1}, recorded by the LHCb experiment. Semileptonic B^{0} decays are reconstructed in the inclusive final states D^{-}μ^{+} and D^{*-}μ^{+}, where the D^{-} meson decays into the K^{+}π^{-}π^{-} final state and the D^{*-} meson into the D[over ¯]^{0}(→K^{+}π^{-})π^{-} final state. The asymmetry between the numbers of D^{(*)-}μ^{+} and D^{(*)+}μ^{-} decays is measured as a function of the decay time of the B^{0} mesons. The CP asymmetry is measured to be a_{sl}^{d}=(-0.02±0.19±0.30)%, where the first uncertainty is statistical and the second systematic. This is the most precise measurement of a_{sl}^{d} to date and is consistent with the prediction from the standard model.
Decays of the form B 0 (s) → J/ψ K 0 S h + h ( )− (h ( ) = K, π) are searched for in protonproton... more Decays of the form B 0 (s) → J/ψ K 0 S h + h ( )− (h ( ) = K, π) are searched for in protonproton collision data corresponding to an integrated luminosity of 1.0 fb −1 recorded with the LHCb detector. The first observation of the B 0 s → J/ψ K 0 S K ± π ∓ decay is reported, with significance in excess of 10 standard deviations. The B 0 → J/ψ K 0 S K + K − decay is also observed for the first time. The branching fraction of B 0 → J/ψ K 0 S π + π − is determined, to significantly better precision than previous measurements, using B 0 → J/ψ K 0 S as a normalisation channel. Branching fractions and upper limits of the other B 0
Study of the kinematic dependences of Λ 0 b production in pp collisions and a measurement of the ... more Study of the kinematic dependences of Λ 0 b production in pp collisions and a measurement of the Λ 0 b → Λ + c π − branching fraction
A binned Dalitz plot analysis of B ± → DK ± decays, with D → K 0 S π + π − and D → K 0 S K + K − ... more A binned Dalitz plot analysis of B ± → DK ± decays, with D → K 0 S π + π − and D → K 0 S K + K − , is performed to measure the CP -violating observables x ± and y ± , which are sensitive to the Cabibbo-Kobayashi-Maskawa angle γ. The analysis exploits a sample of proton-proton collision data corresponding to 3.0 fb −1 collected by the LHCb experiment. Measurements from CLEO-c of the variation of the strong-interaction phase of the D decay over the Dalitz plot are used as inputs. The values of the parameters are found to be x + = (−7.7 ± 2.4 ± 1.0 ± 0.4) × 10 −2 , x − = (2.5 ± 2.5 ± 1.0 ± 0.5) × 10 −2 , y + = (−2.2 ± 2.5 ± 0.4 ± 1.0) × 10 −2 , and y − = (7.5 ± 2.9 ± 0.5 ± 1.4) × 10 −2 . The first, second, and third uncertainties are the statistical, the experimental systematic, and that associated with the precision of the strong-phase parameters. These are the most precise measurements of these observables and correspond to γ = (62 +15 −14 ) • , with a second solution at γ → γ + 180 • , and r B = 0.080 +0.019 −0.021 , where r B is the ratio between the suppressed and favoured B decay amplitudes.
A search for CP violation in Cabibbo-suppressed D ± → K 0 S K ± and D ± s → K 0 S π ± decays is p... more A search for CP violation in Cabibbo-suppressed D ± → K 0 S K ± and D ± s → K 0 S π ± decays is performed using pp collision data, corresponding to an integrated luminosity of 3 fb −1 , recorded by the LHCb experiment. The individual CP -violating asymmetries are measured to be A D ± →K 0 S K ± CP = (+0.03 ± 0.17 ± 0.14)% A Submitted to JHEP c CERN on behalf of the LHCb collaboration, license CC-BY-3.0. † Authors are listed on the following pages.
Time-integrated CP asymmetries in D 0 decays to the final states K − K + and π − π + are measured... more Time-integrated CP asymmetries in D 0 decays to the final states K − K + and π − π + are measured using proton-proton collisions corresponding to 3 fb −1 of integrated luminosity collected at centre-of-mass energies of 7 TeV and 8 TeV. The D 0 mesons are produced in semileptonic b-hadron decays, where the charge of the accompanying muon is used to determine the initial flavour of the charm meson. The difference in CP asymmetries between the two final states is measured to be ∆A CP = A CP (K − K + ) − A CP (π − π + ) = (+0.14 ± 0.16 (stat) ± 0.08 (syst))% .
are reported using data corresponding to an integrated luminosity of 3 fb −1 collected at 7 and 8... more are reported using data corresponding to an integrated luminosity of 3 fb −1 collected at 7 and 8 TeV center-of-mass energies in proton-proton collisions with the LHCb detector. In addition, the most precise measurement of the branching fraction BðB 0
An angular analysis of the decay B 0 → φK * (892) 0 is reported based on a pp collision data samp... more An angular analysis of the decay B 0 → φK * (892) 0 is reported based on a pp collision data sample, corresponding to an integrated luminosity of 1.0 fb −1 , collected at a centre-of-mass energy of √ s = 7 TeV with the LHCb detector. The P-wave amplitudes and phases are measured with a greater precision than by previous experiments, and confirm about equal amounts of longitudinal and transverse polarization. The S-wave K + π − and K + K − contributions are taken into account and found to be significant. A comparison of the B 0 → φK * (892) 0 and B 0 → φK * (892) 0 results shows no evidence for direct CP violation in the rate asymmetry, in the triple-product asymmetries or in the polarization amplitudes and phases.
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Papers by O. Grünberg