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H1 Collaboration

Publications and source records attributed to H1 Collaboration.

155 records · Page 9Linked to original sources
arXiv1996

A Measurement and QCD Analysis of the Proton Structure Function $F_2(x,Q^2)$ at HERA

A new measurement of the proton structure function $F_2(x,Q^2)$ is reported for momentum transfers squared $Q^2$ between 1.5 GeV$^2$ and 5000 GeV$^2$ 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.

hep-ex↗
arXiv1996

Elastic and Inelastic Photoproduction of \jpsi Mesons at HERA

Results on \jpsi production in $e p$ interactionsin the H1 experiment at HERA are presented. The \jpsi mesons are produced by almost real photons ($Q^2\approx 0$) and detected via their leptonic decays. The data have been taken in 1994 and correspond to an integrated luminosity of $2.7 {pb}^{-1}$. The $γp$ cross section for elastic \jpsi production is observed to increase strongly with the \cm energy. The cross section for diffractive $J/ψ$ production with proton dissociation is found to be of similar magnitude as the elastic cross section. Distributions of transverse momentum and decay angle are studied and found to be in accord with a diffractive production mechanism. For inelastic \jpsi production the total $γp$ cross section, the distribution of transverse momenta, and the elasticity of the \jpsi are compared to NLO QCD calculations in a colour singlet model and agreement is found. Diffractive \psiprime production has been observed and a first estimate of the ratio to \jpsi production in the HERA energy regime is given.

hep-ex↗
arXiv1995

A Search for Leptoquarks at HERA

A search for leptoquarks at HERA was performed in H1 using 1994 $e^+ p$ data corresponding to an integrated luminosity of about $3 \pb^{-1}$. Single leptoquarks were searched for in direct positron-quark fusion processes taking into account possible decays into lepton-quark pairs of either the first, the second, or the third generation. No significant deviation from the Standard Model predictions is found in the various final states studied and mass dependent exclusion limits are derived on the Yukawa couplings of the leptoquarks. Compared with earlier results from an analysis of $e^-p$ data, exclusion limits are considerably improved for leptoquarks which could be produced via $e^+$-{\it valence~quark} fusion. For leptoquarks with lepton flavour conserving couplings, masses up to $275 \GeV$ (depending on the leptoquark type) are excluded for coupling values larger than $\sqrt{ 4 πα_{em}}$. For leptoquarks with lepton flavour violating couplings, masses up to $225 \GeV$ are excluded for the first time in a direct search for couplings with leptons of the second or third generation larger than $\sqrt{ 4 πα_{em}}$. Fourteen possible combinations of couplings are studied and stringent exclusion limits comparable or better than any existing direct or indirect limits are obtained for each leptoquark type.

hep-ex↗
arXiv1995

Transverse Energy and Forward Jet Production in the Low $x$ Regime at HERA

The production of transverse energy in deep inelastic scattering is measured as a function of the kinematic variables $x$ and $Q^2$ using the H1 detector at the ep collider HERA. The results are compared to the different predictions based upon two alternative QCD evolution equations, namely the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) and the Balitsky-Fadin-Kuraev-Lipatov (BFKL) equations. In a pseudorapidity interval which is central in the hadronic centre of mass system between the current and the proton remnant fragmentation region the produced transverse energy increases with decreasing $x$ for constant $Q^2$. Such a behaviour can be explained with a QCD calculation based upon the BFKL ansatz. The rate of forward jets, proposed as a signature for BFKL dynamics, has been measured.

hep-ex↗
arXiv1995

The Gluon Density of the Proton at Low $x$ from a QCD Analysis of $F_2$

We present a QCD analysis of the proton structure function $F_2$ measured by the H1 experiment at HERA, combined with data from previous fixed target experiments. The gluon density is extracted from the scaling violations of $F_2$ in the range $2\cdot 10^{-4}<x<3\cdot 10^{-2}$ and compared with an approximate solution of the QCD evolution equations. The gluon density is found to rise steeply with decreasing $x$.

hep-ex↗
arXiv1995

A Direct Determination of the Gluon Density in the Proton at Low x

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.

hep-ex↗
arXiv1995

A Study of the Fragmentation of Quarks in $e^-p$ Collisions at HERA

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.

hep-ex↗
arXiv1995

Leptoquarks and Compositeness Scales from a Contact Interaction Analysis of Deep Inelastic $e^\pm \, p$ Scattering at HERA

A contact interaction analysis is presented to search for new phenomena beyond the Standard Model in deep inelastic $e^\pm p \rightarrow e^\pm \, hadrons$ scattering. The data are collected with the H1 detector at HERA and correspond to integrated luminosities of $0.909 \ {\rm pb}^{-1}$ and $2.947 \ {\rm pb}^{-1}$ for electron and positron beams, respectively. The differential cross sections $dσ/ dQ^2$ are measured in the $Q^2$ range bet\-ween $160 \ \GeV^2$ and $20,000 \ \GeV^2$. The absence of any significant deviation from the Standard Model prediction is used to constrain the couplings and masses of new leptoquarks and to set limits on electron--quark compositeness scales and on the radius of light quarks.

hep-ex↗
arXiv1995

Inclusive Parton Cross Sections in Photoproduction and Photon Structure

Photoproduction of 2-jet events is studied with the H1 detector at HERA. Parton cross sections are extracted from the data by an unfolding method using leading order parton-jet correlations of a QCD generator. The gluon distribution in the photon is derived in the fractional momentum range $0.04\le x_γ\le 1$ at the average factorization scale $75$ GeV$^2$.

hep-ex↗
arXiv1995

A Measurement of the Proton Structure Function $F_{\!2}(x,Q^2)$

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 $F_{\!2}$.

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