A leading order determination of the gluon density in the proton has been performed in the fractional momentum range $1.9 \cdot 10~{-3} < x_{g/p} < 0.18$ by measuring multi-jet events from boson-gluon fusion in deep-inelastic scattering with the H1 detector at the electron-proton collider HERA. This direct determination of the gluon density was performed in a kinematic region previously not accessible. The data show a considerable increase of the gluon density with decreasing fractional momenta of the gluons.
FG is gluon structure function. XPARTON here means the X of the gluon. For the experimental definitions of the XPARTON see paper.
A new measurement of the proton structure function $F_2(x,Q~2)$ is reported for momentum transfers squared $Q~2$ between 1.5GeV$~2$ and 5000GeV$~2$ and for Bjorken $x$ between $3\cdot 10~{-5}$ and $0.32$ using data collected by the HERA experiment H1 in 1994. The data represent an increase in statistics by a factor of ten with respect to the analysis of the 1993 data. Substantial extension of the kinematic range towards low $Q~2$ and $x$ has been achieved using dedicated data samples and events with initial state photon radiation. The structure function is found to increase significantly with decreasing $x$, even in the lowest accessible $Q~2$ region. The data are well described by a Next to Leading Order QCD fit and the gluon density is extracted.
Data from shifted vertex sample.
Data from shifted vertex sample.
Data from shifted vertex sample.
A measurement of the proton structure function $F_{\!2}(x,Q~2)$ is reported for momentum transfer squared $Q~2$ between 4.5 $GeV~2$ and 1600 $GeV~2$ and for Bjorken $x$ between $1.8\cdot10~{-4}$ and 0.13 using data collected by the HERA experiment H1 in 1993. It is observed that $F_{\!2}$ increases significantly with decreasing $x$, confirming our previous measurement made with one tenth of the data available in this analysis. The $Q~2$ dependence is approximately logarithmic over the full kinematic range covered. The subsample of deep inelastic events with a large pseudo-rapidity gap in the hadronic energy flow close to the proton remnant is used to measure the "diffractive" contribution to $F_{\!2}$.
No description provided.
No description provided.
No description provided.
A measurement of the inclusive deep-inelastic neutral current e+p scattering cross section is reported in the region of four-momentum transfer squared, 12<=Q^2<=150 GeV^2, and Bjorken x, 2x10^-4<=x<=0.1. The results are based on data collected by the H1 Collaboration at the ep collider HERA at positron and proton beam energies of E_e=27.6 GeV and E_p=920 GeV, respectively. The data are combined with previously published data, taken at E_p=820 GeV. The accuracy of the combined measurement is typically in the range of 1.3-2%. A QCD analysis at next-to-leading order is performed to determine the parton distributions in the proton based on H1 data.
Data from the 2000 running period at Q**2 There is an additional 1.2 PCT overall normalisation uncertainty not included.
Data from the 2000 running period at Q**2 There is an additional 1.2 PCT overall normalisation uncertainty not included.
Data from the 2000 running period at Q**2 There is an additional 1.2 PCT overall normalisation uncertainty not included.
Deep inelastic scattering (DIS) events, selected from 1993 data taken by the H1 experiment at HERA, are studied in the Breit frame of reference. The fragmentation function of the quark is compared with those of \ee data. It is shown that certain aspects of the quarks emerging from within the proton in \ep interactions are essentially the same as those of quarks pair-created from the vacuum in \ee annihilation. The measured area, peak position and widthof the fragmentation function show that the kinematic evolution variable, equivalent to the \ee squared centre of mass energy, is in the Breit frame the invariant square of the four-momentum transfer. We comment on the extent to which we have evidence for coherence effects in parton showers.
Distribution of the cosine of the Breit frame polar angle for data with the Breit frame energy flow selection. Statistical errors only.
Distribution of the cosine of the Breit frame polar angle for data before the Breit frame energy flow selection. Statistical errors only.
The fragmentation function for the current hemisphere of the Breit frame. Data are Breit frame energy flow selected only. Statistical errors only.
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.
The helicity structure of the diffractive electroproduction of rho mesons, e + p -> e + rho + Y, is studied in a previously unexplored region of large four-momentum transfer squared at the proton vertex, t: 0 < t' < 3 GeV^2, where t' = |t| - |t|_min. The data used are collected with the H1 detector at HERA in the kinematic domain 2.5 < Q^2 < 60 GeV^2, 40 < W < 120 GeV. No t dependence of the r^04_00 spin density matrix element is found. A significant t dependent helicity non-conservation from the virtual photon to the rho meson is observed for the spin density matrix element combinations r^5_00+2r^5_11 and r^1_00+2r^1_11. These t dependences are consistently described by a perturbative QCD model based on the exchange of two gluons.
Measurements of the combinations of spin density matrices as a function of TP = |T| - |Tmin|, where |Tmin| is the minimal values of |T| kinematically required for the vector meson and the system X to aquire their effective mass through longitudinal momentum transfer.
The average charged track multiplicity and the normalised distribution of the scaled momentum, $\xp$, of charged final state hadrons are measured in deep-inelastic $\ep$ scattering at high $Q^2$ in the Breit frame of reference. The analysis covers the range of photon virtuality $100 < Q^2 < 20 000 \GeV^{2}$. Compared with previous results presented by HERA experiments this analysis has a significantly higher statistical precision and extends the phase space to higher $Q^{2}$ and to the full range of $\xp$. The results are compared with $e^+e^-$ annihilation data and with various calculations based on perturbative QCD using different models of the hadronisation process.
Average values of Q and X (plus errors) for the different Q**2 ranges.
Average charged hadron multiplicity as a function of Q**2.
Normalised distribution of the scaled momentum as a function of Q**2 in the X range 0 to 0.02.
Photoproduction data collected with the H1 detector at HERA in 1994 are used to study the cross-sections for inclusive charged particle production and the structure of the photon. The differential cross-sections dsigma/dpT2, for |eta| < 1 in the HERA laboratory frame, and dsigma/deta for pT > 2 GeV/c and pT > 3 GeV/c have been measured. Model calculations of these cross-sections, based on perturbative QCD, indicate that the results are sensitive to the parton densities of the photon as well as to higher order effects, which are phenomenologically treated by multiple interactions. This sensitivity is exploited to determine the leading order x_gamma distribution of partons in the photon using a new method based on high pT charged particles. The gluon content of the photon is extracted and found to rise with decreasing x_gamma.
Inclusive gamma-p cross section for charged particles in the photoproduction data.
The measured differential pseudorapidity distribution for inclusive chargedparticle production.
Using the H1 detector at HERA, charged particle multiplicity distributions in deep inelastic ep scattering have been measured over a large kinematical region. The evolution with $W$ and $Q~2$ of the multiplicity distribution and of the multiplicity moments in pseudorapidity domains of varying size is studied in the current fragmentation region of the hadronic centre-of-mass frame. The results are compared with data from fixed target lepton-nucleon interactions, $e~+e~-$ annihilations and hadron-hadron collisions as well as with expectations from QCD based parton models. Fits to the Negative Binomial and Lognormal distributions are presented.
Fully corrected multiplicity distributions. Note that the value of P0 in the 1 to 5 pseudorapidity region is not measured but taken from the reweighted DJANGO 6.0 Monte Carlo generator.
Fully corrected multiplicity distributions. Note that the value of P0 in the 1 to 5 pseudorapidity region is not measured but taken from the reweighted DJANGO 6.0 Monte Carlo generator.
Fully corrected multiplicity distributions. Note that the value of P0 in the 1 to 5 pseudorapidity region is not measured but taken from the reweighted DJANGO 6.0 Monte Carlo generator.
Forum