Three-jet production is studied for the first time in deep-inelastic positron-proton scattering. The measurement carried out with the H1 detector at HERA covers a large range of four-momentum transfer squared 5 < Q^2 < 5000 GeV^2 and invariant three-jet masses 25 < M_(3jet) < 140 GeV. Jets are defined by the inclusive k_T algorithm in the Breit frame. The size of the three-jet cross section and the ratio of the three-jet to the dijet cross section R_(3/2) are described over the whole phase space by the predictions of perturbative QCD in next-to-leading order. The shapes of angular jet distributions deviate significantly from a uniform population of the available phase space but are well described by the QCD calculation.
The inclusive 3-Jet cross section as a function of Q**2.
The ratio of 3 jets to 2 jets as a function of Q**2.
The inclusive 3-JET cross section as a function of Bjorken scaling variableX for the Q**2 range 5 to 100 GeV**2.
A measurement is presented of dijet and 3-jet cross sections in low-|t| diffractive deep-inelastic scattering interactions of the type ep -> eXY, where the system X is separated by a large rapidity gap from a low-mass baryonic system Y. Data taken with the H1 detector at HERA, corresponding to an integrated luminosity of 18.0 pb^(-1), are used to measure hadron level single and double differential cross sections for 4<Q^2<80 GeV^2, x_pom<0.05 and p_(T,jet)>4 GeV. The energy flow not attributed to jets is also investigated. The measurements are consistent with a factorising diffractive exchange with trajectory intercept close to 1.2 and tightly constrain the dominating diffractive gluon distribution. Viewed in terms of the diffractive scattering of partonic fluctuations of the photon, the data require the dominance of qqbarg over qqbar states. Soft colour neutralisation models in their present form cannot simultaneously reproduce the shapes and the normalisations of the differential cross sections. Models based on 2-gluon exchange are able to reproduce the shapes of the cross sections at low x_pom values.
Average values, over the specified interval, of the differential hadron level dijet cross section as a function of Q**2.
Average values, over the specified interval, of the differential hadron level dijet cross section as a function of the average transverse momentum of the two jets in the c.m.frame.
Average values, over the specified interval, of the differential hadron level dijet cross section as a function of the average pseudorapidity of the two jets in the lab frame.
A precise measurement of the inclusive deep-inelastic e^+p scattering cross section is reported in the kinematic range 1.5<= Q^2 <=150 GeV^2 and 3*10^(-5)<= x <=0.2. The data were recorded with the H1 detector at HERA in 1996 and 1997, and correspond to an integrated luminosity of 20 pb^(-1). The double differential cross section, from which the proton structure function F_2(x,Q^2) and the longitudinal structure function F_L(x,Q^2) are extracted, is measured with typically 1% statistical and 3% systematic uncertainties. The measured partial derivative (dF_2(x,Q^2)/dln Q^2)_x is observed to rise continuously towards small x for fixed Q^2. The cross section data are combined with published H1 measurements at high Q^2 for a next-to-leading order DGLAP QCD analysis.The H1 data determine the gluon momentum distribution in the range 3*10^(-4)<= x <=0.1 to within an experimental accuracy of about 3% for Q^2 =20 GeV^2. A fit of the H1 measurements and the mu p data of the BCDMS collaboration allows the strong coupling constant alpha_s and the gluon distribution to be simultaneously determined. A value of alpha _s(M_Z^2)=0.1150+-0.0017 (exp) +0.0009-0.0005 (model) is obtained in NLO, with an additional theoretical uncertainty of about +-0.005, mainly due to the uncertainty of the renormalisation scale.
The reduced deep inelastic cross section , and F2, with data taken in the dedicated low Q**2 trigger run of 1997. For y < 0.6, F2 is extracted using the quoted values of R, defined from a QCD fit to the H1 cross section data. The firstDSYS error is the uncorrelated systematic error, and the second is the correlat ed systematic error.
The reduced deep inelastic cross section , and F2, with data taken in 1996/97. For y < 0.6, F2 is extracted using the quoted values of R, defined from a QCD fit to the H1 cross section data. The first DSYS error is the uncorrelated systematic error, and the second is the correlated systematic error.
The measured value of the reduced cross section derivative D(SIG(C=REDUCED))/DLN(Y) calculated at fixed Q**2 bins. The data below 13.5 GeV come from the special low Q**2 run in 1997. The larger Q**2 come from the 1996/97 data.
The inclusive e^-p single and double differential cross sections for neutral and charged current processes are measured with the H1 detector at HERA, in the range of four-momentum transfer squared Q^2 between 150 and 30000 GeV^2, and Bjorken x between 0.002 and 0.65. The data were taken in 1998 and 1999 with a centre-of-mass energy of 320 GeV and correspond to an integrated luminosity of 16.4 pb^(-1). The data are compared with recent measurements of the inclusive neutral and charged current e^+p cross sections. For Q^2>1000 GeV^2 clear evidence is observed for an asymmetry between e^+p and e^-p neutral current scattering and the generalised structure function xF_3 is extracted for the first time at HERA. A fit to the charged current data is used to extract a value for the W boson propagator mass. The data are found to be in good agreement with Standard Model predictions.
The NC single differential cross section, as a function of X, for Y < 0.9 and Q**2 > 1000 GeV**2. The first DSYS error is the uncorrelated systematic errorand the second is the correlated systematic error.
The NC single differential cross section, as a function of X, for Y < 0.9 and Q**2 > 10000 GeV**2. The first DSYS error is the uncorrelated systematic error and the second is the correlated systematic error.
The CC single differential cross section, as a function of X, for measured for 0.03 < Y < 0.85 and Q**2 > 1000 GeV**2. and corrected by KCOR to Y < 0.9. The first DSYS error is the uncorrelated systematic error and the second is the correlated systematic error.
Jet production is studied in the Breit frame in deep-inelastic positron-proton scattering over a large range of four-momentum transfers 5 < Q^2 < 15000 GeV^2 and transverse jet energies 7 < E_T < 60 GeV. The analysis is based on data corresponding to an integrated luminosity of L_int \simeq 33 pb^(-1) taken in the years 1995-1997 with the H1 detector at HERA at a center-of-mass energy sqrt(s)=300 GeV. Dijet and inclusive jet cross sections are measured multi-differentially using k_perp and angular ordered jet algorithms. The results are compared to the predictions of perturbative QCD calculations in next-to-leading order in the strong coupling constant alphas.QCD fits are performed in which alphas and the gluon density in the proton are determined separately. The gluon density is found to be in good agreement with results obtained in other analyses using data from different processes. The strong coupling constant is determined to be alphas(MZ)=0.1186+-0.0059. In addition an analysis of the data in which both alphas and the gluon density are determined simultaneously is presented.
Inclusive single jet cross section as a function of ET and Q**2.. Data are analysed in the Breit frame using the inclusive kT alogrithm.
Inclusive dijet cross section as a function Q**2.. Data are analysed in the Breit frame using the inclusive kT alogrithm.
Inclusive di-jet cross section as a function of ET and Q**2.. Data are analysed in the Breit frame using the inclusive kT alogrithm.
Jet production in charged and neutral current events in the kinematic range of Q^2 from 640 to 35000 GeV^2 is studied in deep-inelastic positron-proton scattering at HERA. The measured rate of multi-jet events and distributions of jet polar angle, transverse energy, dijet mass, and other dijet variables are presented. Using parton densities derived from inclusive DIS cross sections, perturbative QCD calculations in NLO are found to give a consistent description of both the neutral and charged current dijet production. A direct, model independent comparison of the jet distributions in charged and neutral current events confirms that the QCD dynamics of the hadronic final state is independent of the underlying electroweak scattering process.
Rates of charged current events as a function of Q**2.
Rates of neutral current events as a function of Q**2.
Normalised distribution in Y2 for NC and CC dijet events. Y2 is the smallest scaled value of KT (KTJET**2/W**2) given by the combination of (2+1) jets. The +1 refers to the proton remnant jet.
The inclusive cross section for the photoproduction of neutral pions has been measured as a function of the transverse momentum, rapidity, and Feynman x of the pizero mesons at an average photon--proton centre-of-mass energy of 208 GeV and for photon virtualities below Q^2=0.01 GeV^2. The pizero measurement extends the range covered by previous charged particle measurements at HERA by two units of rapidity in the photon direction down to a value of -5.5 in the gamma p centre-of-mass frame. The pizero transverse momentum distribution is well described over the whole measured range by a power law ansatz, while an exponential fit falls below the data at transverse momentum values above 1.5 GeV/c. Good agreement with the predictions of the Monte Carlo models PYTHIA and PHOJET is found. In the context of the PYTHIA model the data are inconsistent with large intrinsic transverse momentum values in the photon.
The inclusive PI0 photoproduction cross section in bias of rapidity and PT.Bin centre corrections have been applied and the errors are the quadratic sum o f the statistics and systematics (which dominate).
The inclusive PI0 photoproduction cross section as a function of PT for therapidity range -3.5 to -1.5. Bin centres are given in addition to limits. Error s are the quadratic sum of statistics and systematics.
The inclusive PI0 photoproduction cross section as a function of XL (the Feyman X variable) for the rapidity range -3.5 to -1.5. Bin centres are given as well as limits. Errors are the quadratic sum of statistics and systematics.
The elastic electroproduction of phi mesons is studied at HERA with the H1 detector for photon virtualities 1 < Q^2 < 15 GeV^2 and hadronic centre of mass energies 40 < W < 130 GeV. The Q^2 and t dependences of the cross section are extracted (t being the square of the four-momentum transfer to the target proton). When plotted as function of (Q^2 + M_V^2) and scaled by the appropriate SU(5) quark charge factor, the phi meson cross section agrees within errors with the cross sections of the vector mesons V = rho, omega and J/psi. A detailed analysis is performed of the phi meson polarisation state and the ratio of the production cross sections for longitudinally and transversely polarised phi mesons is determined. A small but significant violation of s-channel helicity conservation (SCHC) is observed.
The measured ratio of PHI to RHO0 production.
The cross section for elastic PHI meson electro-production calculated by multiplying the PHI/RHO0 cross section ratio by the RHO0 cross section accurately measured in the earlier H1 publication (EPJ C13,371).
The corrected T distribution of elastic PHI meson production for W around 75 GeV and Q2 in the range 2.5 to 15 GeV**2 (mean = 4.8 GeV**2). Statistical error only.
Cross sections for elastic photoproduction of J/Psi and Upsilon mesons are presented. For J/Psi mesons the dependence on the photon-proton centre-of-mass energy W_gammap is analysed in an extended range with respect to previous measurements of 26<=W_gammap<= 285 GeV. The measured energy dependence is parameterized as sigma_gammap proportional W_gammap^delta with delta=0.83+-0.07. The differential cross section dsigma/dt for J/Psi mesons is derived, its dependence on W_gammap and on t is analysed and the effective trajectory (in terms of Regge theory) is determined to be alpha(t)=(1.27+-0.05)+(0.08+-0.17)*t/GeV^2. Models based on perturbative QCD and on pomeron exchange are compared to the data.
The cross sections for the elastic photoproduction of J/PSI particles.
Differential cross section, DSIG/DT, for the elastic photoproduction of J/PSI particles.
The slope of the DSIG/DT distribution.
The production of hard di-jet events in photoproduction at HERA is dominated by resolved photon processes in which a parton in the photon with momentum fraction x_gamma is scattered from a parton in the proton. These processes are sensitive to the quark and gluon content of the photon. The differential di-jet cross-section dsigma/dlog(x_gamma) is presented here, measured in tagged photoproduction at HERA using data taken with the H1 detector, corresponding to an integrated luminosity of 7.2 pb^(-1). Using a restricted data sample at high transverse jet energy, E_(T,jet)>6 GeV, the effective parton density f_gamma,eff(x_gamma) = [q(x_gamma) + bar(q)(x_gamma) +9/4g(x_gamma)] in the photon in leading order QCD is measured down to x_gamma=0.05 from which the gluon density in the photon is derived.
The di-jet photoproduction cross section for ET > 4 GeV.
The di-jet photoproduction cross section for ET > 6 GeV after pedestal energy subtraction.
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