Single particles and jets in deeply inelastic scattering at low x are measured with the H1 detector in the region away from the current jet and towards the proton remnant, known as the forward region. Hadronic final state measurements in this region are expected to be particularly sensitive to QCD evolution effects. Jet cross-sections are presented as a function of Bjorken-x for forward jets produced with a polar angle to the proton direction, theta, in the range 7 < theta < 20 degrees. Azimuthal correlations are studied between the forward jet and the scattered lepton. Charged and neutral single particle production in the forward region are measured as a function of Bjorken-x, in the range 5 < theta < 25 degrees, for particle transverse momenta larger than 1 GeV. QCD based Monte Carlo predictions and analytical calculations based on BFKL, CCFM and DGLAP evolution are compared to the data. Predictions based on the DGLAP approach fail to describe the data, except for those which allow for a resolved photon contribution.
Forward Jet cross section. Axis error includes +- 7/7 contribution (Dependence of the model used to correct the data).
Forward Di-jet cross section. Axis error includes +- 7/7 contribution (Dependence of the model used to correct the data).
We have measured the cross section of four charged pion production in photon-photon interactions in the invariant mass range 1.0≦Wγγ≦3.2 GeV and up toQ2=16 GeV2. For 1.2 GeV≦Wγγ≦1.7 GeV the process is dominated by ρ0ρ0 production with a rapid rise in cross section around 1.2 GeV, well below the nominal ρ0ρ0 threshold. The observed distributions in the two particle masses and in the production and decay angles are well described by an incoherent sum of the phase-space subprocesses γγ →ρ0ρ0, →ρ0π+π−, and →π+π−π+π−. A spin-parity analysis of the ρ0ρ0 system showsJP=2+ to dominate, although 0+ is also possible forWγγ≦1.4 GeV. Negative partity states are excluded.
Fractions of subprocesses from 2-parameter fit to the no-tag data in limited energy range. The Q=1R contribution is set equal to zero.
Fractions of subprocesses from 2-parameter fit to the single-tag data in limited energy range. The Q=1R contribution is set equal to zero.
Measurements of energy-energy correlations in hadronic final states produced in e + e − annihilation at c.m. energies between 7.7 and 31.6 GeV are presented. The data are compared to perturbative QCD predictions. Good qualitative agreement above 20 GeV c.m. energy is found. The importance of non-perturbative effects is discussed, as well as the detailed behaviour of the correlation near 180°.
OPPOSITE SIDE ENERGY-ENERGY CORRELATIONS NEAR 180 DEG.
ENERGY-ENERGY CORRELATION INTEGRATED IN THE REGION 60 TO 120 DEG.
FORWARD-BACKWARD ASYMMETRY IN THE ENERGY-ENERGY CORRELATION.
Measurements of the charged multiplicities for hadron production in e + e − annihilation in the center of mass energy range 9–32 GeV have been made. The average charged multiplicity has an energy dependence much stronger than ln s and similar to that reported for pp collisions. Quantitative differences are observed in the magnitude of both the average multiplicity 〈 n ch 〉 and the dispersion D ch for e + e − and pp interactions at the same center of mass energy. 〈 n ch 〉 and the ratio 〈 n ch / D ch in e + e − annihilations are significantly larger than in pp collisions and are found to be in overall agreement with QCD predictions. KNO scaling is seen to be satisfied.
THE FINAL TABLE ENTRY COMBINES THE DATA FROM THE THREE HIGHEST ENERGY BINS.
We present the first data on photon-photon annihilation into hadrons for CM energies > 1 GeV obtained with the detector PLUTO at the e + e − storage ring PETRA. Cross sections are extracted using an inelastic eγ scattering formalism. The results are compared to expectations from Regge-like models.
DEPENDENCE OF CROSS SECTION FOR ELECTRON-PHOTON SCATTERING (ANALOGOUS TO HAND'S FORMULA) ON VISIBLE HADRONIC ENERGY, CALCULATED BY TAKING PION MASSES FOR ALL CHARGED PARTICLES.
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 average charged multiplicity, and the peak and width of the fragmentation function (in LN(1/XP)) as a function of the mean Q, for the total hemisphere of the Breit frame without the energy flow selection discussed in the text of the paper.
The average charged multiplicity, and the peak and width of the fragmentation function (in LN(1/XP)) as a function of the mean Q, with the energy flow selection, obtained from the Total Current Hemisphere sample.
Invariant charged hadron energy spectrum in the current hemisphere for a mean Q of 5.5. Results are given for all the data and for the energy flow selecteddata.
First results from the magnetic detector PLUTO at the new e + e − storage ring PETRA are shown. The ratio R of the cross section for hadron production to that for μ-pair production has been measured to be R = 5.0 ± 0.5 at 13 GeV and 4.3 ±0.5 at 17 GeV. Both values have an additional systematic error of 20%. The events show a typical 2-jet structure. The mean transverse momentum approaches a constant value with increasing energy implying a shrinkage of the jet opening angle.
TAU HEAVY LEPTON PAIR CONTRIBUTIONS HAVE BEEN SUBTRACTED. R AT 13 AND 17 GEV, TOGETHER WITH SOME SELECTED LOWER ENERGY MEASUREMENTS FROM PLUTO AT DORIS.
The inclusive single and double differential cross-sections for neutral and charged current processes with four-momentum transfer squared Q^2 between 150 and 30,000 GeV2 and with Bjorken x between 0.0032 and 0.65 are measured in e^+ p collisions. The data were taken with the H1 detector at HERA between 1994 and 1997, and they correspond to an integrated luminosity of 35.6 pb^-1. The Q^2 evolution of the parton densities of the proton is tested, yielding no significant deviation from the prediction of perturbative QCD. The proton structure function F_2(x,Q^2) is determined. An extraction of the u and d quark distributions at high x is presented. At high Q^2 electroweak effects of the heavy bosons Z0 and W are observed and found to be consistent with Standard Model expectation.
The NC single differential cross section, as a function of Q**2 in the range from 200 to 30000 Gev**2, measured for y < 0.9 and final state electron energy> 11 Gev, and also with the same y cut but after correction for the electron en ergy cut. Also tabulated are the QED corrections to the data, which have alreadybeen applied. The first DSYS error is the uncorrelated systematic error and the second is the correlated systematic error.
The various sources of error (in percent) to the individual NC reduced cross section given in table 4 - see text of paper for more details. DTOT - TOTAL error. DSTA - STATISTICAL error. DUNC - UNCORRELATED SYSTEMATIC error. DUNC(E) - UNCORRELATED SYSTEMATIC error from the positron energy. DUNC(T) - UNCORRELATED SYSTEMATIC error from the polar positron angle. DUNC(H) - UNCORRELATED SYSTEMATIC error from the hadronic energy. DCOR - CORRELATED SYSTEMATIC error. DCOR(E+) - CORRELATED SYSTEMATIC from one sig variation in the positron energy. DCOR(T+) - CORRELATED SYSTEMATIC from one sig variation in the positron polar angle. DCOR(H+) - CORRELATED SYSTEMATIC from one sig variation in the hadron energy. DCOR(N+) - CORRELATED SYSTEMATIC from one sig variation in the noise subtraction. DCOR(B+) - CORRELATED SYSTEMATIC from one sig variation in the background subtraction.
The various sources of error (in percent) to the individual CC double differential cross sections given in table 5 - see text of paper for more details. DTOT - TOTAL error. DSTA - STATISTICAL error. DUNC - UNCORRELATED SYSTEMATIC error. DUNC(H) - UNCORRELATED SYSTEMATIC error from the hadronic energy. DCOR - CORRELATED SYSTEMATIC error. DCOR(V+) - CORRELATED SYSTEMATIC from one sig variationin the cut on the Vap/Vp ratio. DCOR(H+) - CORRELATED SYSTEMATIC from one sig variation in the hadron energy. DCOR(N+) - CORRELATED SYSTEMATIC from one sig variation in the noise subtraction. DCOR(B+) - CORRELATED SYSTEMATIC from one sig variation in the background subtraction.
Measurements of transverse energy flow are presented for neutral current deep-inelastic scattering events produced in positron-proton collisions at HERA. The kinematic range covers squared momentum transfers Q^2 from 3.2 to 2,200 GeV^2, the Bjorken scaling variable x from 8.10^{-5} to 0.11 and the hadronic mass W from 66 to 233 GeV. The transverse energy flow is measured in the hadronic centre of mass frame and is studied as a function of Q^2, x, W and pseudorapidity. A comparison is made with QCD based models. The behaviour of the mean transverse energy in the central pseudorapidity region and an interval corresponding to the photon fragmentation region are analysed as a function of Q^2 and W.
The inclusive transverse energy flow at a mean X of 0.00008 and mean Q**2 of 3.2 GeV**2 for the low Q**2 sample.
The inclusive transverse energy flow at a mean X of 0.00014 and mean Q**2 of 3.8 GeV**2 for the low Q**2 sample.
The inclusive transverse energy flow at a mean X of 0.00026 and mean Q**2 of 3.9 GeV**2 for the low Q**2 sample.
Di-jet event rates have been measured for deep-inelastic scattering in the kinematic domain ~5 < Q^2 < ~100 GeV^2 and ~10^(-4) < x_Bj < ~10^(-2), and for jet transverse momenta squared p_t^2 > ~Q^2. The analysis is based on data collected with the H1 detector at HERA in 1994 corresponding to an integrated luminosity of about 2 pb^(-1). Jets are defined using a cone algorithm in the photon-proton centre of mass system requiring jet transverse momenta of at least 5 GeV. The di-jet event rates are shown as a function of Q^2 and x_Bj. Leading order models of point-like interacting photons fail to describe the data. Models which add resolved interacting photons or which implement the colour dipole model give a good description of the di-jet event rate. This is also the case for next-to-leading order calculations including contributions from direct and resolved photons.
Di-jet rates for 'Symmetric' and 'Asymmetric' scenarios for jet energy cuts.
Di-jet rates for 'Sum' scenario for jet energy cuts.
Di-jet rates for 'Symmetric' and 'Asymmetric' scenarios for jet energy cuts.
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