A search for associated production of a $Z$ boson with an open charm meson is presented using a data sample, corresponding to an integrated luminosity of $1.0\,\mathrm{fb}^{-`}$ of proton--proton collisions at a centre-of-mass energy of 7\,TeV, collected by the LHCb experiment. %% Seven candidate events for associated production of a $Z$ boson with a $D^0$ meson and four candidate events for a $Z$ boson with a $D^+$ meson are observed with a combined significance of 5.1standard deviations. The production cross-sections in the forward region are measured to be $$\sigma_{Z\rightarrow\mu^+\mu^-\!,D^0} = 2.50\pm1.12\pm0.22pb$$ $$\sigma_{Z\rightarrow\mu^+\mu^-\!,D^+} = 0.44\pm0.23\pm0.03pb,$$ where the first uncertainty is statistical and the second systematic.
Cross-sections in the fiducial region for associated production of a Z boson and a D meson.
The differential cross-section as a function of rapidity has been measured for the exclusive production of $J/\psi$ and $\psi(2S)$ mesons in proton-proton collisions at $\sqrt{s}=7$ TeV, using data collected by the LHCb experiment, corresponding to an integrated luminosity of 930 pb$^{-1}$. The cross-sections times branching fractions to two muons having pseudorapidities between 2.0 and 4.5 are measured to be $$\begin{array}{rl} \sigma_{pp\rightarrow J/\psi\rightarrow{\mu^+}{\mu^-}}(2.0<\eta_{\mu^\pm }<4.5)=&291\pm 7\pm19 {\rm \ pb},\\ \sigma_{pp\rightarrow\psi(2S)\rightarrow{\mu^+}{\mu^-}}(2.0<\eta_{\mu^\pm}<4.5)=&6.5\pm 0.9\pm 0.4 {\rm \ pb},\end{array}$$ where the first uncertainty is statistical and the second is systematic. The measurements agree with next-to-leading order QCD predictions as well as with models that include saturation effects.
Cross section times branching ratio to two muons with pseudorapidities between 2.0 and 4.5.
Cross-section measurements for $J/\psi$ and $\psi(2s)$ decaying into two muons (pb) as a function of rapidity. The tabulated errors are the uncorrelated statistical uncertainties.
The neutral current e+/-p cross section has been measured up to values of Bjorken x of approximately 1 with the ZEUS detector at HERA using an integrated luminosity of 187 inv. pb of e-p and 142 inv. pb of e+p collisions at sqrt(s) = 318GeV. Differential cross sections in x and Q2, the exchanged boson virtuality, are presented for Q2 geq 725GeV2. An improved reconstruction method and greatly increased amount of data allows a finer binning in the high-x region of the neutral current cross section and leads to a measurement with much improved precision compared to a similar earlier analysis. The measurements are compared to Standard Model expectations based on a variety of recent parton distribution functions.
Double differential cross section for Q^2=725 GeV^2.
Double differential cross section for Q^2=875 GeV^2.
Double differential cross section for Q^2=1025 GeV^2.
The photoproduction of isolated photons, both inclusive and together with a jet, has been measured with the ZEUS detector at HERA using an integrated luminosity of $374\, \mathrm{pb}^{-1}$. Differential cross sections are presented in the isolated-photon transverse-energy and pseudorapidity ranges $6 < E_T^\gamma < 15$ GeV and $-0.7 < \eta^\gamma < 0.9,$ and for jet transverse-energy and pseudorapidity ranges $4 < E_T^{jet} < 35$ GeV and $-1.5 < \eta^{jet} < 1.8,$ for exchanged-photon virtualities $Q^2 < 1$ GeV$^2$. Differential cross sections are also presented for inclusive isolated-photon production as functions of the transverse energy and pseudorapidity of the photon. Higher-order theoretical calculations are compared to the results.
The measured differential photoproduction cross section DSIG/DET(gamma) for isolated inclusive photons.
The measured differential photoproduction cross section DSIG/DETARAP(gamma) for isolated inclusive photons.
The measured differential photoproduction cross section DSIG/DET(gamma) for isolated photons accompanied by a jet.
A measurement of the $Z(\rightarrow\mu^+\mu^-)$+jet production cross-section in $pp$ collisions at a centre-of-mass energy $\sqrt{s} = 7$ TeV is presented. The analysis is based on an integrated luminosity of $1.0\,\text{fb}^{-1}$ recorded by the LHCb experiment. Results are shown with two jet transverse momentum thresholds, 10 and 20 GeV, for both the overall cross-section within the fiducial volume, and for six differential cross-section measurements. The fiducial volume requires that both the jet and the muons from the Z boson decay are produced in the forward direction ($2.0<\eta<4.5$). The results show good agreement with theoretical predictions at the second-order expansion in the coupling of the strong interaction.
The $Z$+jet cross-section at Born level in $pp$ collisions at $\sqrt{s}=7$ TeV. The first uncertainty is statistical, the second is systematic and the third is the uncertainty due to the luminosity determination.
The cross-section ratio $\sigma(Z+\mathrm{jet})/\sigma(Z)$ at Born level in $pp$ collisions at $\sqrt{s}=7$ TeV. The first uncertainty is statistical, the second is systematic and the third is the uncertainty due to the luminosity determination.
Differential cross-section for $Z$+jet in the leading jet $p_T$, for $p_{T}^{\mathrm{jet}} > 10$ GeV/$c$. These results are not corrected for FSR from the final state muons from the $Z$ boson decay.
The production of $J/\psi$ mesons with rapidity $1.5<y<4.0$ or $-5.0<y<-2.5$ and transverse momentum $p_\mathrm{T}<14 \mathrm{GeV}/c$ is studied with the LHCb detector in proton-lead collisions at a nucleon-nucleon centre-of-mass energy $\sqrt{s_{NN}}=5 \mathrm{TeV}$. The analysis is based on a data sample corresponding to an integrated luminosity of about $1.6 \mathrm{nb}^{-1}$. For the first time the nuclear modification factor and forward-backward production ratio are determined separately for prompt $J/\psi$ mesons and $J/\psi$ from $b$-hadron decays. Clear suppression of prompt $J/\psi$ production with respect to proton-proton collisions at large rapidity is observed, while the production of $J/\psi$ from $b$-hadron decays is less suppressed. These results show good agreement with available theoretical predictions. The measurement shows that cold nuclear matter effects are important for interpretations of the related quark-gluon plasma signatures in heavy-ion collisions.
Single differential production cross sections of prompt J/PSI mesons and of J/PSI from B decay as a function of transverse momentum in the FORWARD region. The errors shown are statistical and the uncorrelated and correlated components of the systematic uncertainties.
Single differential production cross sections of prompt J/PSI mesons and of J/PSI from B decay as a function of transverse momentum in the BACKWARD region. The errors shown are statistical and the uncorrelated and correlated components of the systematic uncertainties.
Single differential production cross sections of prompt J/PSI mesons and of J/PSI from B decay as a function of rapidity in the FORWARD region. The errors shown are statistical and the uncorrelated and correlated components of the systematic uncertainties.
An angular analysis of the decay $J/\psi \rightarrow \mu^{+} \mu^{-}$ is performed to measure the polarization of prompt $J/\psi$ mesons produced in $pp$ collisions at $\sqrt{s}=7\; \mathrm{TeV}$. The dataset corresponds to an integrated luminosity of 0.37 fb$^{-1}$ collected with the LHCb detector. The measurement is presented as a function of transverse momentum, $p_\mathrm{T}$, and rapidity, $y$, of the $J/\psi$ meson, in the kinematic region $2 < p_\mathrm{T} < 15\; \mathrm{GeV}/c$ and $2.0<y<4.5$.
Measured $J/\psi$ polarization parameters in bins of $p_T$ and $y$ in the helicity frame. The first uncertainty is statistical (from the fit and the background subtraction) while the second is the systematic uncertainty.
Measured $J/\psi$ polarization parameters in bins of $p_T$ and $y$ in Collins-Soper frame. The first uncertainty is statistical (from the fit and the background subtraction) while the second is the systematic uncertainty.
Integrated cross sections for prompt $J/\psi$ production in the polarization analysis range and extrapolate to $p_T$ = 0.
Prompt production of charmonium $\chi_{c0}$, $\chi_{c1}$ and $\chi_{c2}$ mesons is studied using proton-proton collisions at the LHC at a centre-of-mass energy of $\sqrt{s}=7$TeV. The $\chi_{c}$ mesons are identified through their decay to $J/\psi\gamma$, with $J/\psi\to\mu^+\mu^-$ using photons that converted in the detector. A data sample, corresponding to an integrated luminosity of $1.0\mathrm{fb}^{-1}$ collected by the LHCb detector, is used to measure the relative prompt production rate of $\chi_{c1}$ and $\chi_{c2}$ in the rapidity range $2.0
Measurements of the ratio of $\chi_{c2}$ to $\chi_{c1}$ production cross-sections for the given $J/\psi$ $p_T$ range assuming unpolarized $\chi_c$ production. The first uncertainty is statistical, the second is systematic, the third is from the branching fractions used and the last gives the maximum correction due to the unknown polarization.
Ratio of $\chi_{c0}$ to $\chi_{c2}$ in the observed $J/\psi$\ $p_T$ range from 4-20 GeV. Also given is the $\chi_{c2}$ to $\chi_{c1}$ ratio in the same PT range for comparison. The first systematic error is dominated by the photon efficiency,the $\chi_{c1}$ tail parameters and background modelling, the third from the choiceof $p_T$ spectrum and the fourth from the branching fraction uncertainty.
The production cross-sections of B mesons are measured in pp collisions at a centre-of-mass energy of 7 TeV, using data collected with the LHCb detector corresponding to a integrated luminosity of 0.36 fb-1. The B+, B0 and Bs0 mesons are reconstructed in the exclusive decays B+ -> J/psi K+, B0 -> J/psi K*0 and Bs0 -> J/psi phi, with J/psi -> mu+ mu-, K*0 -> K+ pi- and phi -> K+ K-. The differential cross-sections are measured as functions of B meson transverse momentum pT and rapidity y, in the range 0 < pT < 40 GeV/c and 2.0 < y < 4.5. The integrated cross-sections in the same pT and y ranges, including charge-conjugate states, are measured to be sigma(pp -> B+ + X) = 38.9 +- 0.3 (stat.) +- 2.5 (syst.) +- 1.3 (norm.) mub, sigma(pp -> B0 + X) = 38.1 +- 0.6 (stat.) +- 3.7 (syst.) +- 4.7 (norm.) mub, sigma(pp -> Bs0 + X) = 10.5 +- 0.2 (stat.) +- 0.8 (syst.) +- 1.0 (norm.) mub, where the third uncertainty arises from the pre-existing branching fraction measurements.
Integrated cross sections for B mesons in the defined kinematic range. The second (sys) uncertainty is the normalisation uncertainty arising from the pre-existing branching fraction measurements.
Double Differential distributions for B0 production.
Double differential distributions for B+ production.
The production of J/psi and Upsilon mesons in pp collisions at sqrt(s) = 8 TeV is studied with the LHCb detector. The J/psi and Upsilon mesons are reconstructed in the mu+mu- decay mode and the signal yields are determined with a fit to the mu+mu- invariant mass distributions. The analysis is performed in the rapidity range 2.0<y<4.5 and transverse momentum range 0<p_T<14(15) GeV/c of the J/psi(Upsilon) mesons. The J/psi and Upsilon production cross-sections and the fraction of J/psi mesons from b-hadron decays are measured as a function of the meson p_T and y.
The total integrated cross sections for prompt J/PSI production, assuming no polarisation, and J/PSI production from b-hadron decays in the rapidity range 2.0-4.5 and transverse momentum 0-14 GeV/c;.
Differential production cross section in rapidity for prompt J/PSI mesons (assuming no polarisation) and from J/PSI from b-hadron decays.;.
The double-differential cross sections for prompt J/PSI production (assuming no polarisation) and production of J/PSI from b-hadron decays as a function of transverse momentum for the rapidity range 2.0-2.5. Also shown in the final column is the fraction (in %) of J/PSIs from the latter.
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