The production of jets is studied in deep-inelastic e+p scattering at low negative four momentum transfer squared 5<Q^2<100 GeV^2 and at inelasticity 0.2<y<0.7 using data recorded by the H1 detector at HERA in the years 1999 and 2000, corresponding to an integrated luminosity of 43.5 pb^-1. Inclusive jet, 2-jet and 3-jet cross sections as well as the ratio of 3-jet to 2-jet cross sections are measured as a function of Q^2 and jet transverse momentum. The 2-jet cross section is also measured as a function of the proton momentum fraction xi. The measurements are well described by perturbative quantum chromodynamics at next-to-leading order corrected for hadronisation effects and are subsequently used to extract the strong coupling alpha_s.
Inclusive Jet Cross Section ${\rm\frac{d\sigma_{jet}}{dQ^2}}$.
2-Jet Cross Section ${\rm\frac{d\sigma_{2-jet}}{dQ^2}}$.
3-Jet Cross Section ${\rm\frac{d\sigma_{3-jet}}{dQ^2}}$.
A measurement of the proton structure function F 2 ( x , Q 2 ) is presented with about 1000 neutral current deep inelastic scattering events for Bjorken x in the range x ⋍ 10 −2 – 10 −4 and Q 2 > 5 GeV 2 . The measurement is based on an integrated luminosity of 22.5 nb −1 recorded by the H1 detector in the first year of HERA operation. The structure function F 2 ( x , Q 2 ) shows a significant rise with decreasing x .
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The inclusive jet cross section in photoproduction has been measured as a function of transverse energy and pseudorapidity using the H 1 detector at the HERA electron-proton collider. The results are compared with leading order QCD calculations.
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Deep inelastic e^+ scattering data, taken with the H1 detector at HERA, are used to study the event shape variables thrust, jet broadening and jet mass in the current hemisphere of the Breit frame over a large range of momentum transfers Q between 7 GeV and 100 GeV. The data are compared with results from e^+e^- experiments. Using second order QCD calculations and an approach to relate hadronisation effects to power corrections an analysis of the Q dependences of the means of the event shape parameters is presented, from which both the power corrections and the strong coupling constant are determined without any assumption on fragmentation models. The power corrections of all event shape variables investigated follow a 1/Q behaviour and can be described by a common parameter alpha_0.
Usual definition of Thrust.
The same as usual thrust definition but with the thrust axis replaced by the current hemisphere axis (0,0,-1), where positive Z direction coincide with theincoming proton beam direction.
No description provided.
High transverse momentum pi0-mesons have been measured with the H1 detector at HERA in deep-inelastic ep scattering events at low Bjorken-x, down to x <~ 4.10^{-5}. The measurement is performed in a region of small angles with respect to the proton remnant in the laboratory frame of reference, namely the forward region, and corresponds to central rapidity in the centre of mass system of the virtual photon and proton. This region is expected to be particularly sensitive to QCD effects in hadronic final states. Differential cross-sections for inclusive pi0-meson production are presented as a function of Bjorken-x and the four-momentum transfer Q^2, and as a function of transverse momentum and pseudorapidity. A recent numerical BFKL calculation and predictions from QCD models based on DGLAP parton evolution are compared with the data.
Axis error includes +- 5/5 contribution (Trigger efficiency).
Axis error includes +- 5/5 contribution (Trigger efficiency).
Axis error includes +- 5/5 contribution (Trigger efficiency).
The double-differential inclusive di-jet cross section in photoproduction processes is measured with the H1 detector at HERA. The cross section is determined as a function of the average transverse jet energy E_T^jets for ranges of the fractional energy x_gamma^jets of the parton from the photon side. An effective leading order parton distribution in the photon is determined at large parton fractional energies for scales between 80<p_T^2<1250 GeV^2. The measurement is compatible with the logarithmic scale dependence that is predicted by perturbative QCD.
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Quasi-elastic (z >0.95) photo-production of psi' mesons has been observed at HERA for photon-proton centre-of-mass energies in the range 40 to 160 GeV. The psi' mesons were identified through their decays to l+l- and to J/psi pi+ pi-, where the J/psi subsequently decays to l+l-, the lepton l being either a muon or an electron. The cross-section for quasi-elastic photoproduction was measured to be [18.0 +- 2.8 (stat) +- 3.0(syst)] nb at a photon-proton centre-of-mass energy of 80 GeV. The ratio of the psi' to J/psi quasi-elastic cross-sections is 0.150 +- 0.027 (stat) +- 0.022 (syst).
Overall value for photoproduction cross section combining the different decay modes and data sample.. 1994 and 1995 data.. The second systematic error is from the branching ratio uncertainties.
Combined cross section from PSI(3685) --> J/PSI(1S) < E+ E- > PI+ PI- and PSI(3685) --> J/PSI(1S) < MU+ MU- > PI+ PI- modes using both the 1994 and 1995 data.. The second systematic error is from the branching ratio uncertainties.
Cross section from PSI(3685) --> J/PSI(1S) < E+ E- > PI+ PI- mode.
A measurement is made of the cross section for the process ep --> eXY in deep-inelastic scattering with the H1 detector at HERA. The cross section is presented in terms of a differential structure function F_2^D(3)(x_P,beta,Q^2) of the proton over the kinematic range 4.5 < Q^2 < 75 GeV^2. The dependence of F_2^D(3) on x_P is found to vary with beta, demonstrating that a factorisation of F_2^D(3) with a single diffractive flux independent of beta and Q^2 is not tenable. An interpretation in which a leading diffractive exchange and a subleading reggeon contribute to F_2^D(3) reproduces well the x_P dependence of F_2^D(3) with values for the pomeron and subleading reggeon intercepts of alpha_P(0)=1.203 \pm 0.020(stat.)\pm 0.013(sys.) ^{+0.030}_{-0.035}(model} and alpha_reg(0)=0.50\pm 0.11(stat.)\pm 0.11 (sys.}^{+0.09}_{-0.10} (model), respectively. A fit is performed of the data using a QCD motivated model, in which parton distributions are assigned to the leading and subleading exchanges. In this model, the majority of the momentum of the pomeron must be carried by gluons in order for the data to be well described.
No description provided.
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The first measurement of diffractive scattering of quasi-real photons with large momentum transfer gamma p -> gamma Y, where Y is the proton dissociative system, is made using the H1 detector at HERA. The measurement is performed for initial photon virtualities Q^2 < 0.01 GeV^2. Cross sections are measured as a function of W, the incident photon-proton entre of mass energy, and t, the square of the four-momentum transferred at the proton vertex, in the range 175 < W < 247 GeV and 4<|t|<36 GeV^2. The W dependence is well described by a model based on perturbative QCD using a leading logarithmic approximation of the BFKL evolution. The measured |t| dependence is harder than that predicted by the model and those observed in exclusive vector meson production.
Cross section for the process E+ P --> E+ GAMMA DD as a function of W.
Cross section for the process GAMMA P --> GAMMA DD as a function of W.
Cross section for the process E+ P --> E+ GAMMA DD as a function of T.
A first measurement is reported of the longitudinal proton structure function F_L(x,Q^2) at the ep collider HERA. It is based on inclusive deep inelastic e^+p scattering cross section measurements with a positron beam energy of 27.5 GeV and proton beam energies of 920, 575 and 460 GeV. Employing the energy dependence of the cross section, F_L is measured in a range of squared four-momentum transfers 12 < Q^2 < 90 GeV^2 and low Bjorken x 0.00024 < x < 0.0036. The F_L values agree with higher order QCD calculations based on parton densities obtained using cross section data previously measured at HERA.
The measured longitudinal proton structure function FL at Q**2 = 12 GeV**2 extracted from the combined 920,575 and 450 GeV proton energy data.
The measured longitudinal proton structure function FL at Q**2 = 15 GeV**2 extracted from the combined 920,575 and 450 GeV proton energy data.
The measured longitudinal proton structure function FL at Q**2 = 20 GeV**2 extracted from the combined 920,575 and 450 GeV proton energy data.
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