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 $x$.
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Strange and multistrange baryon and antibaryon production has been studied in sulphur sulphur interactions at 200 GeV/ c per nucleon at central rapidity using the CERN Omega Spectrometer. Particle production ratios and transverse mass spectra are presented for Λ, Ξ − , Λ and Ξ − .
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We have searched for the decay D 0 → μ + μ − among 1.25 × 10 5 μ + μ − pairs produced by 350 GeV/ c π − particles interacting in copper and tungsten targets. Using a high-resolution silicon-microstrip detector followed by a large-acceptance magnetic spectrometer and a muon filter we are able to discriminate between prompt and non-prompt muons and to measure dimuon masses. No candidate compatible with a D 0 → μ + μ − decay has been found, allowing us to set an upper limit on the branching fraction B( D 0 → μ + μ − ) of 7.6 × 10 −6 at the 90% confidence level.
NUCLEUS OF TARGET=CU+WT.
Charged hadronic four-body decays of D 0 mesons have been studied in the E687 photoproduction experiment at Fermilab. Branching ratios relative to the D 0 → K − π + π + π − decay mode for the Cabibbo-suppressed decays D 0 → π − π + π − π + , D 0 → K − K + π − π + have been measured and the first evidence of the D 0 → K − K + K − π + decay mode is reported. An analysis of the D 0 → K − K + π − π + resonance structure is also presented.
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The C12(γ,p)11B differential cross section has been measured over proton angles ranging from 58° to 128°, using tagged photons of energy 80–157 MeV, for low-lying regions of residual excitation energy in B11. The data have been compared with four different types of calculation. It is shown that scaling of the cross section with momentum mismatch occurs for both the ground-state and excited-state data.
EX IN 0 MEV REGION (FROM 0 TO 1.5 MEV). ANGULAR BINS OF 5 DEG WIDTH.
EX = 7 (FROM 6.5 TO 8.0 MEV). ANGULAR BINS OF 5 DEG WIDTH.
EX = 13 (FROM 12.0 TO 13.5 MEV). ANGULAR BINS OF 5 DEG WIDTH.
The ratio of the number of W+1 jet to W+0 jet events is measured with the D0 detector using data from the 1992–93 Tevatron Collider run. For the W→eν channel with a minimum jet ET cutoff of 25 GeV, the experimental ratio is 0.065±0.003stat±0.007syst. Next-to-leading order QCD predictions for various parton distributions agree well with each other and are all over 1 standard deviation below the measurement. Varying the strong coupling constant αs in both the parton distributions and the partonic cross sections simultaneously does not remove this discrepancy.
Two values of ALPHA_S corresponds the two different parton distribution functions (pdf) used in extraction of ALPHA_S from the ratio. The dominant systematic error is from the jet energy scale uncertainty.
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.
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 $d\sigma / dQ~2$ 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.
Additional overall normalization error of 3.5 pct due to systematic errors of the luminosity measurement.
Additional overall normalization error of 1.8 pct due to systematic errors of the luminosity measurement.
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 $0.04\le x_\gamma \le 1$ at the average factorization scale $75$ GeV$~2$.
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Gluon density of the photon (alpha is the fine structure constant).
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