Using the CLEO detector at the Cornell $e~+e~-$ storage ring, CESR, we study the two-photon production of $\Lambda \overline{\Lambda}$, making the first observation of $\gamma \gamma \to \Lambda \overline{\Lambda}$. We present the cross-section for $ \gamma \gamma \to \Lambda \overline{\Lambda}$ as a function of the $\gamma \gamma$ center of mass energy and compare it to that predicted by the quark-diquark model.
No description provided.
No description provided.
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Using data collected with the CLEO II detector at the Cornell Electron Storage Ring, we determine the ratio R(chrg) for the mean charged multiplicity observed in Upsilon(1S)->gggamma events, to the mean charged multiplicity observed in e+e- -> qqbar gamma events. We find R(chrg)=1.04+/-0.02+/-0.05 for jet-jet masses less than 7 GeV.
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.
Using data taken with the CLEO II detector at the Cornell Electron Storage Ring, we have determined the ratio of branching fractions: $R_{\gamma} \equiv \Gamma(\Upsilon(1S) \rightarrow \gamma gg)/\Gamma(\Upsilon(1S) \rightarrow ggg) = (2.75 \pm 0.04(stat.) \pm 0.15(syst.))%$. From this ratio, we have determined the QCD scale parameter $\Lambda_{\overline{MS}}$ (defined in the modified minimal subtraction scheme) to be $\Lambda_{\overline{MS}}= 233 \pm 11 \pm 59$ MeV, from which we determine a value for the strong coupling constant $\alpha_{s}(M_{\Upsilon(1S)}) = 0.163 \pm 0.002 \pm 0.014$, or $\alpha_{s}(M_{Z}) = 0.110 \pm 0.001 \pm 0.007$.
The ALPHAS at MZ is extrapolation from M(UPSI).
The scale dependence of the evolution of photoproduction cross sections with the photon-proton centre of mass energy W is studied using low Q~2 < 0.01 GeV~2 e~+p interactions collected by the H1 experiment at HERA. The value of the largest transverse momentum of a charged particle in the photon fragmentation region is used to define the hard scale. The slope of the $W$ dependence of the cross section is observed to increase steeply with increasing transverse momentum. The result is compared to measurements of the Q~2 evolution of the W dependence of the virtual photon-proton cross section. Interpretations in terms of QCD and in terms of Regge phenomenology are discussed.
The gamma p cross section is parameterized as CONST*(W**2)**POWER.
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.
Using data recorded by the CLEO-II detector at CESR, we report evidence of a pair of excited charmed baryons, one decaying into Λc+π+ and the other into Λc+π−. The doubly charged state has a measured mass difference M(Λc+π+)−M(Λc+) of 234.5±1.1±0.8 MeV/c2 and a width of 17.9−3.2+3.8±4.0MeV/c2, and the neutral state has a measured mass difference M(Λc+π−)−M(Λc+) of 232.6±1.0±0.8 MeV/c2 and a width of 13.0−3.0+3.7±4.0MeV/c2. We interpret these data as evidence of the Σc*++ and Σc*0, the spin 32+ excitations of the Σc baryons.
CONST(NAME=EPS) is the parameter of the Peterson fragmentation function (C.Peterson et al., PR D27, 105 (1983)) D(N)/D(Z) = FD(Z) = const * (1/Z)*1/(1- (1/Z)-CONST(NAME=EPS)/(1-Z))**2.
The energy loss spectrum of 150 GeV muons has been measured with a prototype of the ATLAS hadron calorimeter in the H8 beam of the CERN SPS. The differential probability dP/dv per radiation length of a fractional energy loss v = ΔEμ/Eμ has been measured in the range v = 0.01 ÷ 0.95; it is compared with the theoretical predictions for energy losses due to bremsstrahlung and production of electron—positron pairs or of energetic knock-on electrons. The integrated probability \(\int_{0.01}^{0.95}({\rm d}P/{\rm d}v){\rm d}v\) is (1.610 ± 0.015stat ± 0.105syst) · 10−3 in agreement with the theoretical predictions 1.556 · 10−3 and 1.619 · 10−3. Agreement with theory is also found in two intervals of v where production of electron-positron pairs and knock-on electrons dominates. In the region of bremsstrahlung dominance (v = 0.12 ÷ 0.95) the measured integrated probability (1.160 ± 0.040stat ± 0.075syst) · 10−4 is in agreement with the theoretical value of 1.185 · 10−4, obtained using the Petrukhin and Shestakov description of the bremsstrahlung process. The same result is about 3.6 standard deviations (defined as the quadratic sum of statistical and systematic errors) lower than the theoretical prediction of 1.472 · 10−4, obtained using Tsai’s description of bremsstrahlung.
Measured differential probability values DPROB/DNU for fractional energy loss. Only statistical errors are given.
Integrated probability (DELTA(PROB)) per radiation length.
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.
First results on inclusive D0 and D* production in deep inelastic $ep$ scattering are reported using data collected by the H1 experiment at HERA in 1994. Differential cross sections are presented for both channels and are found to agree well with QCD predictions based on the boson gluon fusion process. A charm production cross section for 10GeV$~2\le Q~2\le100$GeV$~2$ and $0.01\le y\le0.7$ of $\sigma\left(ep\rightarrow c\overlinecX\right) = (17.4 \pm 1.6 \pm 1.7 \pm 1.4)$nb is derived. A first measurement of the charm contribution F2_charm(x,Q~2) to the proton structure function for Bjorken $x$ between $8\cdot10~{-4}$ and $8\cdot10~{-3}$ is presented. In this kinematic range a ratio F2_charm/F2= 0.237\pm0.021{+0.043\atop-0.039}$ is observed.
Inclusive D meson production cross sections. The second systematc error represents the model uncertainty.
Inclusive charm meson cross section averaged for the two processes. The second systematc error represents the model uncertainty.
Ratio of cross sections of D0 and D* production.
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