The transition between photoproduction and deep-inelastic scattering is investigated in jet production at the HERA ep collider, using data collected by the H1 experiment. Measurements of the differential inclusive jet cross-sections dsigep/dEt* and dsigmep/deta*, where Et* and eta* are the transverse energy and the pseudorapidity of the jets in the virtual photon-proton centre of mass frame, are presented for 0 < Q2 < 49 GeV2 and 0.3 < y < 0.6. The interpretation of the results in terms of the structure of the virtual photon is discussed. The data are best described by QCD calculations which include a partonic structure of the virtual photon that evolves with Q2.
The ET differential jet cross section in the virtual-photon CM frame.
The ET differential jet cross section in the virtual-photon CM frame.
The ET differential jet cross section in the virtual-photon CM frame.
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.
The data on the differential event shape distrubutions are shown only as a illustration to show the agreement with the Lepto and pQCD calculations and contain only statistical errors. The authors are preparing another paper which details these differential distributions including full point-to-point systematics.
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.
Low x deep-inelastic ep scattering data, taken in 1994 at the H1 detector at HERA, are analysed in the Breit frame of reference. The evolution of the peak and width of the current hemisphere fragmentation function is presented as a function of Q and compared with e+e- results at equivalent centre of mass energies. Differences between the average charged multiplicity and the multiplicity of e+e- annihilations at low energies are analysed. Invariant energy spectra are compared with MLLA predictions. Distributions of multiplicity are presented as functions of Bjorken-x and Q^2, and KNO scaling is discussed.
The current hemisphere fragmentation as a function of XP in the Breit frame.
The current hemisphere fragmentation as a function of LN(1/XP) in the Breitframe.
Current hemisphere fragmentation as a function of Q for the XP range 0.02 to 0.05, to show scaling violations.
We have measured the neutron structure function g$_{2}^{n}$ and the virtual photon-nucleon asymmetry A$_{2}^{n}$ over the kinematic range $0.014\leq x \leq 0.7$ and $1.0 \leq Q^{2} \leq 17.0$ by scattering 48.3 GeV longitudinally polarized electrons from polarized $^{3}$He. Results for A$_{2}^{n}$ are significantly smaller than the $\sqrt{R}$ positivity limit over most of the measured range and data for g$_2^{n}$ are generally consistent with the twist-2 Wandzura-Wilczek prediction. Using our measured g$_{2}^{n}$ we obtain results for the twist-3 reduced matrix element $d_{2}^{n}$, and the integral $\int$g$_{2}^{n}(x)dx$ in the range $0.014\leq x \leq 1.0$. Data from this experiment are combined with existing data for g$_{2}^{n}$ to obtain an average for $d_{2}^{n}$ and the integral $\int$g$_{2}^{n}(x)dx$.
Data measured using the 2.75 degree spectrometer.
Data measured using the 5.5 degree spectrometer.
Measured value of the twist-3 reduced matrix element D2.
We present a Next-to-Leading order perturbative QCD analysis of world data on the spin dependent structure functions $g_1^p, g_1^n$, and $g_1^d$, including the new experimental information on the $Q^2$ dependence of $g_1^n$. Careful attention is paid to the experimental and theoretical uncertainties. The data constrain the first moments of the polarized valence quark distributions, but only qualitatively constrain the polarized sea quark and gluon distributions. The NLO results are used to determine the $Q^2$ dependence of the ratio $g_1/F_1$ and evolve the experimental data to a constant $Q^2 = 5 GeV^2$. We determine the first moments of the polarized structure functions of the proton and neutron and find agreement with the Bjorken sum rule.
Data from the 2.75 degree spectrometer.
Data from the 2.75 degree spectrometer evolved to a mean Q**2 of 5 GeV**2 using the MSBAR parameterization. The second systematic error is due to the evolution.
Data from the 5.5 degree spectrometer.
We report on a precision measurement of the neutron spin structure function $g^n_1$ using deep inelastic scattering of polarized electrons by polarized ^3He. For the kinematic range 0.014<x<0.7 and 1 (GeV/c)^2< Q^2< 17 (GeV/c)^2, we obtain $\int^{0.7}_{0.014} g^n_1(x)dx = -0.036 \pm 0.004 (stat) \pm 0.005 (syst)$ at an average $Q^2=5 (GeV/c)^2$. We find relatively large negative values for $g^n_1$ at low $x$. The results call into question the usual Regge theory method for extrapolating to x=0 to find the full neutron integral $\int^1_0 g^n_1(x)dx$, needed for testing quark-parton model and QCD sum rules.
No description provided.
No description provided.
No description provided.
Inclusive $K^0$ and $\Lambda$ photoproduction has been investigated at HERA with the H1 detector at an average photon-proton center of mass energy of 200 GeV in the transverse momentum range 0.5 <p_t <5 GeV. The production rates as a function of $p_t$ and center of mass rapidity are compared to those obtained in deep inelastic scattering at $\av{Q^2}=23 GeV^2$. A similar comparison is made of the rapidity spectra of charged particles. The rate of strangeness photoproduction is compared with $p\bar p$ measurements. The observations are also compared with next-to-leading order QCD calculations and the predictions of a Monte Carlo model.
Additional systematic uncertainty given above.
Additional systematic uncertainty given above.
Additional systematic uncertainty given above.
The results of a measurement of the proton structure function F_2(x,Q~2)and the virtual photon-proton cross section are reported for momentum transfers squared Q~2 between 0.35 GeV~2 and 3.5 GeV~2 and for Bjorken-x values down to 6 10~{-6} using data collected by the HERA experiment H1 in 1995. The data represent an increase in kinematic reach to lower x and Q~2 values of about a factor of 5 compared to previous H1 measurements. Including measurements from fixed target experiments the rise of F_2 with decreasing x is found to be less steep for the lowest Q~2 values measured. Phenomenological models at low Q~2 are compared with the data.
No description provided.
No description provided.
No description provided.
A measurement of the inclusive cross section for the deep-inelastic scattering of positrons off protons at HERA is presented at momentum transfers $8.5 \leq Q~2 \leq 35 GeV~2$ and large inelasticity $y = 0.7$, i.e. for the Bjorken-x range $0.00013 \leq x \leq 0.00055$. Using a next-to-leading order QCD fit to the structure function F_2 at lower y values, the contribution of F_2 to the measured cross section at high y is calculated and, by subtraction, the longitudinal structure function F_{L} is determined for the first time with an average value of $F_L=0.52 \pm 0.03 (stat)$~ {+0.25}_{-0.22}$ (syst) at $Q~2=15.4 GeV~2$ and $x=0.000243$.
Inclusive cross section scaled by the kinematic factor K given by:. X*Q**4/((2*PI*ALPHA**2)*Y+). Y+=2(1-Y)+Y**2.
F2 values corresponding to the cross section measurements. X*Q**4/((2*PI*ALPHA**2)*Y+). Y+=2(1-Y)+Y**2.
Longitudinal structure function measurements.
Transverse momentum spectra of charged particles produced in deep inelastic scattering are measured as a function of the kinematic variables x_B and Q2 using the H1 detector at the ep collider HERA. The data are compared to different parton emission models, either with or without ordering of the emissions in transverse momentum. The data provide evidence for a relatively large amount of parton radiation between the current and the remnant systems.
Charged particle PT distribution in the pseudorapidity interval 1.5 to 2.5.
Charged particle PT distribution in the pseudorapidity interval 1.5 to 2.5.
Charged particle PT distribution in the pseudorapidity interval 1.5 to 2.5.
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