Abstract The ratio of production cross-sections of ψ(2S) over J/ψ mesons as a function of charged-particle multiplicity in proton-proton collisions at a centre-of-mass energy s $$ \sqrt{s} $$ = 13 ...TeV is measured with a data sample collected by the LHCb detector, corresponding to an integrated luminosity of 658 pb −1. The ratio is measured for both prompt and non-prompt ψ(2S) and J/ψ mesons. When there is an overlap between the rapidity ranges over which multiplicity and charmonia production are measured, a multiplicity-dependent modification of the ratio is observed for prompt mesons. No significant multiplicity dependence is found when the ranges do not overlap. For non-prompt production, the ψ(2S)-to-J/ψ production ratio is roughly independent of multiplicity, irrespective of the rapidity range over which the multiplicity is measured. The results are compared to predictions of the co-mover model and agree well except in the low multiplicity region. The ratio of production cross-sections of ψ(2S) over J/ψ mesons are cross-checked with other measurements in di-lepton channels and found to be compatible.
Abstract The production of ψ(2S) mesons in proton-lead collisions at a centre-of-mass energy per nucleon pair of s NN $$ \sqrt{s_{\textrm{NN}}} $$ = 8.16 TeV is studied with the LHCb detector using ...data corresponding to an integrated luminosity of 34 nb −1. The prompt and nonprompt ψ(2S) production cross-sections and the ratio of the ψ(2S) to J/ψ cross-section are measured as a function of the meson transverse momentum and rapidity in the nucleon-nucleon centre-of-mass frame, together with forward-to-backward ratios and nuclear modification factors. The production of prompt ψ(2S) is observed to be more suppressed compared to pp collisions than the prompt J/ψ production, while the nonprompt productions have similar suppression factors.
Abstract The first observation of the B c + → J / ψ π + π 0 $$ {B}_c^{+}\to J/\psi {\pi}^{+}{\pi}^0 $$ decay is reported with high significance using proton-proton collision data, corresponding to an ...integrated luminosity of 9 fb −1, collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV. The ratio of its branching fraction relative to the B c + → J / ψ π + $$ {B}_c^{+}\to J/\psi {\pi}^{+} $$ channel is measured to be B B c + → J / ψ π + π 0 B B c + → J / ψ π + = 2.80 ± 0.15 ± 0.11 ± 0.16 , $$ \frac{{\mathcal{B}}_{B_c^{+}\to J/\psi {\pi}^{+}{\pi}^0}}{{\mathcal{B}}_{B_c^{+}\to J/\psi {\pi}^{+}}}=2.80\pm 0.15\pm 0.11\pm 0.16, $$ where the first uncertainty is statistical, the second systematic and the third related to imprecise knowledge of the branching fractions for B + → J/ψK *+ and B c + → J / ψ π + $$ {B}_c^{+}\to J/\psi {\pi}^{+} $$ decays, which are used to determine the π 0 detection efficiency. The π + π 0 mass spectrum is found to be consistent with the dominance of an intermediate ρ + contribution in accordance with a model based on QCD factorisation.
Abstract The production cross-section of J/ψ pairs in proton-proton collisions at a centre-of-mass energy of s $$ \sqrt{s} $$ = 13 TeV is measured using a data sample corresponding to an integrated ...luminosity of 4.2 fb −1 collected by the LHCb experiment. The measurement is performed with both J/ψ mesons in the transverse momentum range 0 < p T < 14 GeV/c and rapidity range 2.0 < y < 4.5. The cross-section of this process is measured to be 16.36 ± 0.28 (stat) ± 0.88 (syst) nb. The contributions from single-parton scattering and double-parton scattering are separated based on the dependence of the cross-section on the absolute rapidity difference ∆y between the two J/ψ mesons. The effective cross-section of double-parton scattering is measured to be σ eff = 13.1 ± 1.8 (stat) ± 2.3 (syst) mb. The distribution of the azimuthal angle ϕ CS of one of the J/ψ mesons in the Collins-Soper frame and the p T-spectrum of the J/ψ pairs are also measured for the study of the gluon transverse-momentum dependent distributions inside protons. The extracted values of ⟨cos 2ϕ CS⟩ and ⟨cos 4ϕ CS⟩ are consistent with zero, but the presence of azimuthal asymmetry at a few percent level is allowed.
Abstract A search for CP violation in D 0 → K S 0 K + π − $$ {D}^0\to {K}_S^0{K}^{+}{\pi}^{-} $$ and D 0 → K S 0 K − π + $$ {D}^0\to {K}_S^0{K}^{-}{\pi}^{+} $$ decays is reported. The search is ...performed using an unbinned model-independent method known as the energy test that probes local CP violation in the phase space of the decays. The data analysed correspond to an integrated luminosity of 5.4 fb −1 collected in proton-proton collisions by the LHCb experiment at a centre-of-mass energy of s $$ \sqrt{s} $$ = 13 TeV, amounting to approximately 950 thousand and 620 thousand signal candidates for the D 0 → K S 0 K − π + $$ {D}^0\to {K}_S^0{K}^{-}{\pi}^{+} $$ and D 0 → K S 0 K + π − $$ {D}^0\to {K}_S^0{K}^{+}{\pi}^{-} $$ modes, respectively. The method is validated using D 0 → K − π + π − π + and D 0 → K S 0 π + π − $$ {D}^0\to {K}_S^0{\pi}^{+}{\pi}^{-} $$ decays, where CP-violating effects are expected to be negligible, and using background-enhanced regions of the signal decays. The results are consistent with CP symmetry in both the D 0 → K S 0 K − π + $$ {D}^0\to {K}_S^0{K}^{-}{\pi}^{+} $$ and the D 0 → K S 0 K + π − $$ {D}^0\to {K}_S^0{K}^{+}{\pi}^{-} $$ decays, with p-values for the hypothesis of no CP violation of 70% and 66%, respectively.
Abstract A Dalitz plot analysis of $${{B} ^0} \!\rightarrow \eta _c(1S) {{K} ^+} {{\pi } ^-} $$ B0→ηc(1S)K+π- decays is performed using data samples of pp collisions collected with the $$\text{ LHCb ...} $$ LHCb detector at centre-of-mass energies of $${\sqrt{s}} =7,~8$$ s=7,8 and $$13{\,\mathrm {Te}\mathrm {V}} $$ 13TeV , corresponding to a total integrated luminosity of $$4.7 \,\text{ fb }^{-1} $$ 4.7fb-1 . A satisfactory description of the data is obtained when including a contribution representing an exotic $$\eta _c(1S) \pi ^-$$ ηc(1S)π- resonant state. The significance of this exotic resonance is more than three standard deviations, while its mass and width are $$4096 \pm 20~^{+18}_{-22} \,\mathrm {Me}\mathrm {V} $$ 4096±20-22+18MeV and $$152 \pm 58~^{+60}_{-35} \,\mathrm {Me}\mathrm {V} $$ 152±58-35+60MeV , respectively. The spin-parity assignments $$J^P=0^+$$ JP=0+ and $$J^{P}=1^-$$ JP=1- are both consistent with the data. In addition, the first measurement of the $${{B} ^0} \!\rightarrow \eta _c(1S) {{K} ^+} {{\pi } ^-} $$ B0→ηc(1S)K+π- branching fraction is performed and gives $$\begin{aligned} \displaystyle \mathcal {B}({{B} ^0} \!\rightarrow \eta _c(1S) {{K} ^+} {{\pi } ^-} ) = (5.73 \pm 0.24 \pm 0.13 \pm 0.66) \times 10^{-4}, \end{aligned}$$ B(B0→ηc(1S)K+π-)=(5.73±0.24±0.13±0.66)×10-4, where the first uncertainty is statistical, the second systematic, and the third is due to limited knowledge of external branching fractions.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract A measurement of CP-violating observables in B ± → D * K ± and B ± → D *π± decays is made where the photon or neutral pion from the D * → Dγ or D * → Dπ0 decay is not reconstructed. The D ...meson is reconstructed in the self-conjugate decay modes, D → K S 0 $$ {K}_S^0 $$ π+π− or D → K S 0 $$ {K}_S^0 $$ K + K −. The distribution of signal yields in the D decay phase space is analysed in a model-independent way. The measurement uses a data sample collected in proton-proton collisions at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of approximately 9 fb −1. The B ± → D * K ± and B ± → D *π± CP-violating observables are interpreted in terms of hadronic parameters and the CKM angle γ, resulting in a measurement of γ = ( 92 − 17 + 21 $$ {92}_{-17}^{+21} $$ ) ° . The total uncertainty includes the statistical and systematic uncertainties, and the uncertainty due to external strong-phase inputs.
Abstract A study of B c + → χ c π + $$ {B}_c^{+}\to {\chi}_c{\pi}^{+} $$ decays is reported using proton-proton collision data, collected with the LHCb detector at centre-of-mass energies of 7, 8, ...and 13 TeV, corresponding to an integrated luminosity of 9 fb −1. The decay B c + → χ c 2 π + $$ {B}_c^{+}\to {\chi}_{c2}{\pi}^{+} $$ is observed for the first time, with a significance exceeding seven standard deviations. The relative branching fraction with respect to the B c + → J / ψ π + $$ {B}_c^{+}\to J/\psi {\pi}^{+} $$ decay is measured to be B B c + → χ c 2 π + B B c + → J / ψ π + = 0.37 ± 0.06 ± 0.02 ± 0.01 , $$ \frac{{\mathcal{B}}_{B_c^{+}\to {\chi}_{c2}{\pi}^{+}}}{{\mathcal{B}}_{B_c^{+}\to J/\psi {\pi}^{+}}}=0.37\pm 0.06\pm 0.02\pm 0.01, $$ where the first uncertainty is statistical, the second is systematic, and the third is due to the knowledge of the χ c2 → J/ψγ branching fraction. No significant B c + → χ c 1 π + $$ {B}_c^{+}\to {\chi}_{c1}{\pi}^{+} $$ signal is observed and an upper limit for the relative branching fraction for the B c + → χ c 1 π + $$ {B}_c^{+}\to {\chi}_{c1}{\pi}^{+} $$ and B c + → χ c 2 π + $$ {B}_c^{+}\to {\chi}_{c2}{\pi}^{+} $$ decays of B B c + → χ c 1 π + B B c + → χ c 2 π + = < 0.49 $$ \frac{{\mathcal{B}}_{B_c^{+}\to {\chi}_{c1}{\pi}^{+}}}{{\mathcal{B}}_{B_c^{+}\to {\chi}_{c2}{\pi}^{+}}}=<0.49 $$ is set at the 90% confidence level.
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