The ratio R = (d σ /d t )( γ d → ( π 0 n)p)/(d σ /d t )( γ d → ( π 0 p)n), was measured at the Deutsches Elektronen-Synchrotron DESY, Hamburg at a mean photon energy of 4.0 GeV in the four-momentum transfer range between t = − 0.2 (GeV/ c ) 2 and t = − 1.2 (GeV/ c ) 2 in steps of approximately 0.08 (GeV/ c ) 2 . The ratio R is less than 1 up to t = − 0.9 (GeV/ c ) 2 and shows a broad minimum around t = − 0.6 (GeV/ c ) 2 . Corrections for nuclear effects in the deuterium were not applied but are shown to be small.
No description provided.
The differential cross section of the reaction γ p → π 0 p has been measured at the Deutsches Elektronen Synchrotron DESY, Hamburg, at a mean photon energy of 4.0 GeV in the four-momentum transfer range between t = −0.2 (GeV/ c ) 2 and t = −1,2 (GeV/ c ) 2 in steps of approximately 0.08 (GeV/ c ) 2 . The experiment was carried out in connection with the measurements of the photoproduction of π 0 mesons on deuterium, which were described in the preceding article. In the present paper the contributions arising from background reactions are discussed in more detail.
No description provided.
An experiment has been performed to study the inclusive photoproduction of π 0 mesons. Photoproduced π 0 's were detected in a hodoscope consisting of 14 lead glass Cerenkov counters. To obtain the cross sections at a photon energy of 6 GeV we used the photon-difference method. Data are presented in terms of the Feynman variable x = q ‖ ∗ (√s/2) and the trnasverse momentum q⊥. We have measured four q ⊥ distributions at x = 0.2, 0.4, 0.6 and 0.8. The results dhow that the π 0 rate at small values of q ⊥ is smaller than the π± rate. The data can be fitted smoothly by a form A exp (− Bq ⊥ 2 ) with a value about 3.5 GeV −2 for the slope parameter B .
No description provided.
No description provided.
No description provided.
A narrow pentaquark state, $P_c(4312)^+$, decaying to $J/\psi p$ is discovered with a statistical significance of $7.3\sigma$ in a data sample of ${\Lambda_b^0\to J/\psi p K^-}$ decays which is an order of magnitude larger than that previously analyzed by the LHCb collaboration. The $P_c(4450)^+$ pentaquark structure formerly reported by LHCb is confirmed and observed to consist of two narrow overlapping peaks, $P_c(4440)^+$ and $P_c(4457)^+$, where the statistical significance of this two-peak interpretation is $5.4\sigma$. Proximity of the $\Sigma_c^+\bar{D}^{0}$ and $\Sigma_c^+\bar{D}^{*0}$ thresholds to the observed narrow peaks suggests that they play an important role in the dynamics of these states.
Distribution of $(J/\psi p)$ system invariant mass from the decay of $\Lambda_{b}^{0}$ candidates in the channel $\Lambda_{b}^{0} \to J/\psi p K^{-}$.
Distribution of $(J/\psi p)$ system invariant mass from the decay of $\Lambda_{b}^{0}$ candidates in the channel $\Lambda_{b}^{0} \to J/\psi p K^{-}$. $\Lambda_{b}^{0}$ candidates are selected after the suppression of the dominant $\Lambda^{*} \to p K^{-}$ contributions using the $m_{Kp} > 1.9$ GeV$/c^2$ requirement.
$\cos \theta_{P_c}$-weighted ditribution of $(J/\psi p)$ system invariant mass from the decay of $\Lambda_{b}^{0}$ candidates in the channel $\Lambda_{b}^{0} \to J/\psi p K^{-}$. Here $\theta_{P_c}$ is the helicity angle of the pentaquark exotic state (the angle between $K^-$ and $J/\psi$ in the pentaquark state rest frame).
Using a data sample corresponding to an integrated luminosity of $2.0\,fb^{-1}$, collected by the LHCb experiment, the production of the $\eta_c(1S)$ state in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=13 \text{ TeV}$ is studied in the rapidity range ${2.0 < y < 4.5}$ and in the transverse momentum range ${6.5 < p_{T} < 14.0\text{ GeV}}$. The cross-section for prompt production of $\eta_c(1S)$ mesons relative to that of the $J/\psi$ meson is measured using the ${p\bar{p}}$ decay mode and is found to be ${\sigma_{\eta_c(1S)}/\sigma_{J/\psi} = 1.69 \pm 0.15 \pm 0.10 \pm 0.18}$. The quoted uncertainties are, in order, statistical, systematic and due to uncertainties on the branching fractions of the ${J/\psi\to p \bar{p}}$ and ${\eta_c\to p \bar{p}}$ decays. The prompt $\eta_c(1S)$ production cross-section is determined to be ${\sigma_{\eta_c(1S)} = 1.26 \pm 0.11\pm 0.08 \pm 0.14 \,\mu b}$, where the last uncertainty includes that on the ${J/\psi}$ meson cross-section. The ratio of the branching fractions of $b$-hadron decays to the $\eta_c(1S)$ and ${J/\psi}$ states is measured to be ${\mathcal{B}_{b\to\eta_c X}/\mathcal{B}_{b\to J/\psi X} = 0.48 \pm 0.03 \pm 0.03 \pm 0.05}$, where the last uncertainty is due to those on the branching fractions of the ${J/\psi \to p \bar{p}}$ and ${\eta_c\to p \bar{p}}$ decays. The difference between the ${J/\psi}$ and $\eta_c(1S)$ masses is also determined to be ${113.0 \pm 0.7 \pm 0.1\text{ MeV}}$, which is the most precise single measurement of this quantity to date.
Relative $\eta_c$ to $J/\psi$ differential production cross-sections for prompt production. The uncertainties are statistical, systematic, and due to the ${\eta_c\to p\bar{p}}$ and ${J/\psi\to p\bar{p}}$ branching fractions, respectively.
Differential production cross-sections of $\eta_c$ for prompt production. The uncertainties are statistical, systematic, and due to the $\eta_c\to p \bar{p}$ and $J/\psi\to p \bar{p}$ branching fractions and $J/\psi$ production cross-section.
Relative $\eta_c$ to $J/\psi$ differential production cross-sections for production in $b$-hadron inclusive decays. The uncertainties are statistical, systematic, and due to the ${\eta_c\to p\bar{p}}$ and ${J/\psi\to p\bar{p}}$ branching fractions, respectively.
The inclusive $b \bar{b}$- and $c \bar{c}$-dijet production cross-sections in the forward region of $pp$ collisions are measured using a data sample collected with the LHCb detector at a centre-of-mass energy of 13 TeV in 2016. The data sample corresponds to an integrated luminosity of 1.6 fb$^{-1}$. Differential cross-sections are measured as a function of the transverse momentum and of the pseudorapidity of the leading jet, of the rapidity difference between the jets, and of the dijet invariant mass. A fiducial region for the measurement is defined by requiring that the two jets originating from the two $b$ or $c$ quarks are emitted with transverse momentum greater than 20 GeV$/c$, pseudorapidity in the range $2.2 < \eta < 4.2$, and with a difference in the azimuthal angle between the two jets greater than 1.5. The integrated $b \bar{b}$-dijet cross-section is measured to be $53.0 \pm 9.7$ nb, and the total $c \bar{c}$-dijet cross-section is measured to be $73 \pm 16$ nb. The ratio between $c \bar{c}$- and $b \bar{b}$-dijet cross-sections is also measured and found to be $1.37 \pm 0.27$. The results are in agreement with theoretical predictions at next-to-leading order.
The total $b \bar{b}$-dijet and $c \bar{c}$-dijet cross-sections and their ratio in the fiducial region, compared with the NLO predictions. The first uncertainty is the combined statistical and systematic uncertainty and the second is the uncertainty from the luminosity. For the predictions, the first uncertainty corresponds to the scale uncertainty, the second to the PDF uncertainty.
Numerical results of $b \bar{b}$- and $c \bar{c}$-dijet cross-sections, $c \bar{c}$/$b \bar{b}$ dijet cross-section ratios and their total uncertainties as a function of the leading jet $\eta$ (pseudorapidity).
Numerical results of $b \bar{b}$- and $c \bar{c}$-dijet cross-sections, $c \bar{c}$/$b \bar{b}$ dijet cross-section ratios and their total uncertainties as a function of $\Delta y^*$.
We present an angular analysis of the $B^{+}\rightarrow K^{\ast+}(\rightarrow K_{S}^{0}\pi^{+})\mu^{+}\mu^{-}$ decay using 9$\,\mbox{fb}^{-1}$ of $pp$ collision data collected with the LHCb experiment. For the first time, the full set of CP-averaged angular observables is measured in intervals of the dimuon invariant mass squared. Local deviations from Standard Model predictions are observed, similar to those in previous LHCb analyses of the isospin-partner $B^{0}\rightarrow K^{\ast0}\mu^{+}\mu^{-}$ decay. The global tension is dependent on which effective couplings are considered and on the choice of theory nuisance parameters.
Results for the CP-averaged observables Fl, Afb and S3–S9. The first uncertainties are statistical and the second systematic.
Results for the optimised observables FL and P1–P'8. The first uncertainties are statistical and the second systematic.
The CP-averaged observable Fl versus q2. The first (second) error bars represent the statistical (total) uncertainties.
The cross-section for prompt antiproton production in collisions of protons with an energy of $6.5$ TeV incident on helium nuclei at rest is measured with the LHCb experiment from a data set corresponding to an integrated luminosity of $0.5\,nb^{-1}$. The target is provided by injecting helium gas into the LHC beam line at the LHCb interaction point. The reported results, covering antiproton momenta between $12$ and $110\,\mathrm{GeV/}c$, represent the first direct determination of the antiproton production cross-section in ${\rm p He}$ collisions, and impact the interpretation of recent results on antiproton cosmic rays from space-borne experiments.
Double-differential cross-section in antiproton momentum and transverse momentum for antiproton production in collisions of 6.5 TeV protons on He nuclei at rest. The antiproton momentum is defined in the laboratory frame. Results are averaged over the given kinematic range of each bin. The uncertainty is split into an uncertainty delta_uncorr, uncorrelated among the kinematic bins, and an uncertainty delta_corr, fully correlated among the kinematic bins. For both uncertainties, the systematic uncertainty, dominant for most bins, and the statistical uncertainty, are added in quadrature. The average value within each bin is also reported for the antiproton momentum, the transverse momentum, and x-Feynman xF=2 p_Z*/SQRT(S), where p_Z* is the longitudinal antiproton momentum in the center-of-mass system and SQRT(S) the nucleon-nucleon center-of-mass energy. These average values are obtained from simulation (based on EPOS LHC), to avoid biases from reconstruction effects and given the good agreement with data observed for the simulated kinematic spectra.
Double-differential cross-section in antiproton momentum and transverse momentum for antiproton production in collisions of 6.5 TeV protons on He nuclei at rest. The antiproton momentum is defined in the laboratory frame. Results are averaged over the given kinematic range of each bin. The uncertainty is split into an uncertainty delta_uncorr, uncorrelated among the kinematic bins, and an uncertainty delta_corr, fully correlated among the kinematic bins. For both uncertainties, the systematic uncertainty, dominant for most bins, and the statistical uncertainty, are added in quadrature. The average value within each bin is also reported for the antiproton momentum, the transverse momentum, and x-Feynman xF=2 p_Z*/SQRT(S), where p_Z* is the longitudinal antiproton momentum in the center-of-mass system and SQRT(S) the nucleon-nucleon center-of-mass energy. These average values are obtained from simulation (based on EPOS LHC), to avoid biases from reconstruction effects and given the good agreement with data observed for the simulated kinematic spectra.
The differential cross-section of prompt inclusive production of long-lived charged particles in proton-proton collisions is measured using a data sample recorded by the LHCb experiment at a centre-of-mass energy of ${\sqrt{s} = 13\,\mathrm{TeV}}$. The data sample, collected with an unbiased trigger, corresponds to an integrated luminosity of ${5.4\,\mathrm{nb}^{-1}}$. The differential cross-section is measured as a function of transverse momentum and pseudorapidity in the ranges ${p_\mathrm{T} \in [0.08, 10)\,\mathrm{GeV}\,c^{-1}}$ and ${\eta \in [2.0, 4.8)}$ and is determined separately for positively and negatively charged particles. The results are compared with predictions from various hadronic-interaction models.
Double differential cross-sections of prompt inclusive production of long-lived negatively charged particles as a function of transverse momentum and pseudorapidity.
Double differential cross-sections of prompt inclusive production of long-lived positively charged particles as a function of transverse momentum and pseudorapidity.
Correlation for the uncertainties of the differential cross-section of prompt inclusive production of long-lived charged particles.
A study of multiplicity and pseudorapidity distributions of inclusive photons measured in pp and p$-$Pb collisions at a center-of-mass energy per nucleon$-$nucleon collision of $\sqrt{s_{\rm NN}} = 5.02$ TeV using the ALICE detector in the forward pseudorapidity region $2.3 < \eta_{\rm lab} < 3.9$ is presented. Measurements in p$-$Pb collisions are reported for two beam configurations in which the directions of the proton and lead ion beam were reversed. The pseudorapidity distributions in p$-$Pb collisions are obtained for seven centrality classes which are defined based on different event activity estimators, i.e., the charged-particle multiplicity measured at midrapidity as well as the energy deposited in a calorimeter at beam rapidity. The inclusive photon multiplicity distributions for both pp and p$-$Pb collisions are described by double negative binomial distributions. The pseudorapidity distributions of inclusive photons are compared to those of charged particles at midrapidity in \pp collisions and for different centrality classes in p$-$Pb collisions. The results are compared to predictions from various Monte Carlo event generators. None of the generators considered in this paper reproduces the inclusive photon multiplicity distributions in the reported multiplicity range. The pseudorapidity distributions are, however, better described by the same generators.
Inclusive photon multiplicity distribution measured within $2.3<\eta_{\rm lab}<3.9$ in pp collisions at $\sqrt{s} = 5020~\mathrm{GeV}$.
Inclusive photon multiplicity distribution measured within $2.3<\eta_{\rm lab}<3.9$ in p-Pb collisions at $\sqrt{s_\mathrm{NN}} = 5020~\mathrm{GeV}$.
Inclusive photon multiplicity distribution measured within $2.3<\eta_{\rm lab}<3.9$ in Pb-p collisions at $\sqrt{s_\mathrm{NN}} = 5020~\mathrm{GeV}$.
Forum