An experimental investigation of the structure of identified quark and gluon jets is presented. Observables related to both the global and internal structure of jets are measured; this allows for test
The measured jet broadening distributions (B) in quark and gluon jets seperately.
Measured distributions of -LN(Y2), where Y2 is the differential one-subjet rate, that is the value of the subjet scale parameter where 2 jets appear from the single jet.
The mean subjet multiplicity (-1) for gluon jets and quark jets for different values of the subject resolution parameter Y0.
Dijet cross sections as functions of several jet observables are measured in photoproduction using the H1 detector at HERA. The data sample comprises e^+p data with an integrated luminosity of 34.9 pb^(-1). Jets are selected using the inclusive k_T algorithm with a minimum transverse energy of 25 GeV for the leading jet. The phase space covers longitudinal proton momentum fraction x_p and photon longitudinal momentum fraction x_gamma in the ranges 0.05<x_p<0.6 and 0.1<x_gamma<1. The predictions of next-to-leading order perturbative QCD, including recent photon and proton parton densities, are found to be compatible with the data in a wide kinematical range.
Differential ep cross section for dijet production as a function of the invariant mass of the two jets.
Differential ep cross section for dijet production as a function of the average transverse energy the two jets.
Differential ep cross section for dijet production as a function of the maximum transverse energy the leading jet.
Inclusive D* production is measured in deep-inelastic ep scattering at HERA with the H1 detector. In addition, the production of dijets in events with a D* meson is investigated. The analysis covers values of photon virtuality 2< Q^2 <=100 GeV^2 and of inelasticity 0.05<= y <= 0.7. Differential cross sections are measured as a function of Q^2 and x and of various D* meson and jet observables. Within the experimental and theoretical uncertainties all measured cross sections are found to be adequately described by next-to-leading order (NLO) QCD calculations, based on the photon-gluon fusion process and DGLAP evolution, without the need for an additional resolved component of the photon beyond what is included at NLO. A reasonable description of the data is also achieved by a prediction based on the CCFM evolution of partons involving the k_T-unintegrated gluon distribution of the proton.
Visible cross section for inclusive D*+- production.
Visible cross section for inclusive D*+- production.
Visible cross section for inclusive D*+- production with two jets.
In this extended analysis using the ZEUS detector at HERA, the photoproduction of isolated photons together with a jet is measured for different ranges of the fractional photon energy, $x_\gamma^{\mathrm{meas}}$, contributing to the photon-jet final state. Cross sections are evaluated in the 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 $4 < E_T^{\rm jet} < 35$ GeV and $-1.5 < \eta^{\rm jet} < 1.8$, for an integrated luminosity of 374 $\mathrm{pb}^{-1}$. The kinematic observables studied comprise the transverse energy and pseudorapidity of the photon and the jet, the azimuthal difference between them, the fraction of proton energy taking part in the interaction, and the difference between the pseudorapidities of the photon and the jet. Higher-order theoretical calculations are compared to the results.
Differential cross-section D(SIG)/DET(GAMMA) for photons in the given X(GAMMA) range accompanied by a jet. The corresponding hadronisation corrections are also given.
Differential cross-section D(SIG)/DETARAP(GAMMA) for photons in the given X(GAMMA) range accompanied by a jet. The corresponding hadronisation corrections are also given.
Differential cross-section D(SIG)/DET(JET) for photons in the given X(GAMMA) range accompanied by a jet. The corresponding hadronisation corrections are also given.
We have studied hadronic events produced at LEP at centre-of-mass energies of 130 and 136 GeV. Distributions of event shape observables, jet rates, momentum spectra and multiplicities are presented and compared to the predictions of several Monte Carlo models and analytic QCD calculations. From fits of event shape and jet rate distributions to\({\mathcal{O}}(\alpha _s^2 ) + NLLA\) QCD calculations, we determineαs(133 GeV)=0.110±0.005(stat.)±0.009(syst.). We measure the mean charged particle multiplicity 〈nch〉=23.40±0.45(stat.) ±0.47(syst.) and the position ζ0 of the peak in the ζp = ln(1/xp) distribution ζ0=3.94±0.05(stat.)±0.11(syst.). These results are compared to lower energy data and to analytic QCD or Monte Carlo predictions for their energy evolution.
Determination of alpha_s.
Multiplicity and high moments.
Tmajor distribution.
The splitting processes in identified quark and gluon jets are investigated using longitudinal and transverse observables. The jets are selected from symmetric three-jet events measured in Z decays with the Delphi detector in 1991-1994. Gluon jets are identified using heavy quark anti-tagging. Scaling violations in identified gluon jets are observed for the first time. The scale energy dependence of the gluon fragmentation function is found to be about two times larger than for the corresponding quark jets, consistent with the QCD expectation CA/CF. The primary splitting of gluons and quarks into subjets agrees with fragmentation models and, for specific regions of the jet resolution y, with NLLA calculations. The maximum of the ratio of the primary subjet splittings in quark and gluon jets is 2.77±0.11±0.10. Due to non-perturbative effects, the data are below the expectation at small y. The transition from the perturbative to the non-perturbative domain appears at smaller y for quark jets than for gluon jets. Combined with the observed behaviour of the higher rank splittings, this explains the relatively small multiplicity ratio between gluon and quark jets.
Scaled energy distribution of charged hadrons produced in Quark jets in 'Y'topology 3-JET events.
Scaled energy distribution of charged hadrons produced in Gluon jets in 'Y'topology 3-JET events.
Scaled energy distribution of charged hadrons produced in Quark jets in 'Mercedes' topology 3-JET events.
The cross section for dijet production in pp collisions at sqrt(s) = 7 TeV is presented as a function of xi, a variable that approximates the fractional momentum loss of the scattered proton in single-diffractive events. The analysis is based on an integrated luminosity of 2.7 inverse nanobarns collected with the CMS detector at the LHC at low instantaneous luminosities, and uses events with jet transverse momentum of at least 20 GeV. The dijet cross section results are compared to the predictions of diffractive and nondiffractive models. The low-xi data show a significant contribution from diffractive dijet production, observed for the first time at the LHC. The associated rapidity gap survival probability is estimated.
$\sqrt{s}=7$ TeV, $pp \to \text{jet}_{1}\text{jet}_{2}$, $|\eta^{j_1,j_2}|<4.4$, $p_{T}^{j_1,j_2} > 20$ GeV.
The cross section of the diffractive process e^+p -> e^+Xp is measured at a centre-of-mass energy of 318 GeV, where the system X contains at least two jets and the leading final state proton p is detected in the H1 Very Forward Proton Spectrometer. The measurement is performed in photoproduction with photon virtualities Q^2 <2 GeV^2 and in deep-inelastic scattering with 4 GeV^2<Q^2<80 GeV^2. The results are compared to next-to-leading order QCD calculations based on diffractive parton distribution functions as extracted from measurements of inclusive cross sections in diffractive deep-inelastic scattering.
Integrated $e^{+}p$ diffractive dijet cross sections in $\gamma p$. The hadronisation correction factor ($1+\delta_{\text{hadr}}$) applied to the NLO calculation is also listed. The overall normalisation uncertainty of $6\%$ is not included in the table.
Integrated $e^{+}p$ diffractive dijet cross sections in DIS. The hadronisation correction factor ($1+\delta_{\text{hadr}}$) applied to the NLO calculation and the radiative correction ($1+\delta_{\text{rad}}$) are also listed. The overall normalisation uncertainty of $6\%$ is not included in the table.
Ratio of integrated $e^{+}p$ diffractive dijet cross sections for $Q^2<2\,\text{GeV}^2$ (photoproduction) to $Q^2>4\,\text{GeV}^2$ (DIS).
A measurement is presented of single- and double-differential dijet cross sections in diffractive deep-inelastic $ep$ scattering at HERA using data collected by the H1 experiment corresponding to an integrated luminosity of 290 pb^{-1}. The investigated phase space is spanned by the photon virtuality in the range of 4<Q^{2}<100 GeV^{2} and by the fractional proton longitudinal momentum loss x_pom<0.03. The resulting cross sections are compared with next-to-leading order QCD predictions based on diffractive parton distribution functions and the value of the strong coupling constant is extracted.
Integrated cross section in the measurement phase space.
Diffractive DIS dijet cross section measured differentially as a function of $Q^2$. The global normalisation uncertainty of $7.8\%$ is not listed explicitly but is included in the total systematic uncertainty. The last two columns show the correction factors for hadronisation and QED radiation, respectively.
Diffractive DIS dijet cross section measured differentially as a function of $y$. The global normalisation uncertainty of $7.8\%$ is not listed explicitly but is included in the total systematic uncertainty. The last two column show the correction factors for hadronisation and QED radiation, respectively.
A first measurement is presented of exclusive photoproduction of $\rho^0$ mesons associated with leading neutrons at HERA. The data were taken with the H1 detector in the years $2006$ and $2007$ at a centre-of-mass energy of $\sqrt{s}=319$ GeV and correspond to an integrated luminosity of $1.16$ pb$^{-1}$. The $\rho^0$ mesons with transverse momenta $p_T<1$ GeV are reconstructed from their decays to charged pions, while leading neutrons carrying a large fraction of the incoming proton momentum, $x_L>0.35$, are detected in the Forward Neutron Calorimeter. The phase space of the measurement is defined by the photon virtuality $Q^2 < 2$ GeV$^2$, the total energy of the photon-proton system $20 < W_{\gamma p} < 100$ GeV and the polar angle of the leading neutron $\theta_n < 0.75$ mrad. The cross section of the reaction $\gamma p \to \rho^0 n \pi^+$ is measured as a function of several variables. The data are interpreted in terms of a double peripheral process, involving pion exchange at the proton vertex followed by elastic photoproduction of a $\rho^0$ meson on the virtual pion. In the framework of one-pion-exchange dominance the elastic cross section of photon-pion scattering, $\sigma^{\rm el}(\gamma\pi^+ \to \rho^0\pi^+)$, is extracted. The value of this cross section indicates significant absorptive corrections for the exclusive reaction $\gamma p\to\rho^0 n \pi^+$.
The $\gamma p$ cross section integrated in the domain $0.35 < x_L < 0.95$ and $-t^\prime < 1$~GeV$^2$ and averaged over the energy range $20 < W_{\gamma p} < 100$ GeV for two intervals of leading neutron transverse momentum.
Differential photoproduction cross sections ${\rm d}\sigma_{\gamma p}/{\rm d}x_L$ for the exclusive process $\gamma p \to \rho^0 n \pi^+$ in two regions of neutron transverse momentum and $20 < W_{\gamma p} < 100$ GeV. The statistical, uncorrelated and correlated systematic uncertainties, $\delta_{stat}$, $\delta_{sys}^{unc}$ and $\delta_{sys}^{cor}$ respectively, are given, which does not include the global normalisation error of $4.4\%$.
Double differential photoproduction cross sections ${\rm d^2}\sigma_{\gamma p}/{\rm d}x_L{\rm d}p_{T,n}^2$ in the range $20 < W_{\gamma p} < 100$ GeV. The statistical, uncorrelated and correlated systematic uncertainties, $\delta_{stat}$, $\delta_{sys}^{unc}$ and $\delta_{sys}^{cor}$ respectively, are given, which does not include the global normalisation error of $4.4\%$.
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