An analysis based on 124 000 selected $\tau$ pairs recorded by the ALEPH detector at LEP provides the vector $(V)$ and axial-v
Total vector spectral function. The error has been set to zero if it is smaller than the point size.
Invariant mass-squared distributions of the decay $\tau^- \to 2\pi^- \pi^+ \nu_\tau$. The error has been set to zero if it is smaller than the point size.
Invariant mass-squared distributions of the decay $\tau^- \to \pi^- 2\pi^0 \nu_\tau$. The error has been set to zero if it is smaller than the point size.
We have measured the xF and PT dependence of the polarization of Λ0 hyperons produced in exclusive final states pp→pΛ0K+π+π−, pp→pΛ0K+π+π−π+π−, pp→pΛ0K+π+π−π+π−π+π−, and pp→pΛ0K+π+π−π+π−π+π−π+π− at 27.5 GeV/ c. We present an empirical parametrization for Λ0 polarization as a function of xF and PT: P=(−0.443±0.037)xFPT for −1≤xF≤1 and 0≤PT≤1.8GeV/c. This parametrization is independent of the final state and provides a good description of the data. We note that the mechanism responsible for Λ0 polarization appears to be independent of the production mechanism.
Result of a linear fit to all the data in the XL and PT region.
We report results of inclusive measurements of anti-Lambda, produced in the forward direction at the SPS with sqrt(s) = 630 GeV, using the UA8 small angle Roman Pot spectrometers. These measurements cover the range in Feynman-x_f and transverse momentum, 0.6 < x_f < 1.0 and 0.4 < p_t < 0.7 GeV, respectively. Within a systematic uncertainty of +-20% on the absolute cross section measurements, the results are indistinguishable from those made by some of us in two earlier experiments at the CERN Intersecting Storage Rings, with energies, sqrt(s) = 53 and 62 GeV. In the x_f-range, 0.6-0.9, the absolute cross sections are lower by a factor of 2 to 3 than the predictions of the Lund model as embodied in the PYTHIA 5.6 and JETSET 7.3 Monte Carlo programs, indicating inadequacies in knowledge of the baryon fragmentation function. For the largest x_f-range, 0.9-1.0, the measurements agree with the Monte Carlo predictions. We have measured the average anti-Lambda polarization for our events and find (6 +- 12%), consistent with previous measurements at the ISR in the present region of x_f - p_t.
Invariant cross section for inclusive LAMBDABAR production, multiplied by a factor 2, from the UP spectrometer.
Invariant cross section for inclusive LAMBDABAR production, multiplied by a factor 2, from the DOWN spectrometer.
The measured LAMBDABAR polarization.
Elastic and proton-dissociative rho0 photoproduction (gamma p-->rho0 p,gamma p -->rho0 N,with rho0-->pi+pi-) has been studied in ep interactions at HERA for gamma-p centre-of-mass energies in the range 50
Integrated elastic rho0 photoproduction cross section.
Integrated elastic pi+ pi- photoproduction cross section.
Differential T distribution. Statistical errors only.
From a data sample of $9.98 {\mathrm{ pb^{-1}}}$ integrated luminosity, collected by DELPHI at a centre-of-mass energy of 172 GeV, 118 events were selected as W-pa
Overall total cross section.
Cross sections for different decay topologies.
The reaction e+e−→μ+μ− has been measured at s=57.77GeV, based on 289.6±2.6 pb−1 data collected with the VENUS detector at TRISTAN. The production cross section is measured in bins of the production angle within an angular acceptance of |cosθ|<~0.75, according to a model-independent definition. The result is consistent with the prediction of the standard electroweak theory. Although a trend in measurements at lower energies that the total cross section tends to be smaller than the prediction remains, the discrepancy is not significant. The model-independent result is converted to the differential cross section in the effective-Born scheme by unfolding photon-radiation effects. This result can be extrapolated to quantities for the full solid angle as σtotEB=30.05±0.59 pb and AFBEB=−0.350±0.017, by imposing an ordinary assumption on the production-angle dependence. The converted results are used to set constraints on extensions of the standard theory. S-matrix parametrization, and possible contributions from contact interactions and heavy neutral-scalar exchanges are examined.
Primary model-independant results.
Differential cross section in the effective-Born scheme.
Total cross section and forward backward asymmetry results in the effective-Born scheme.
Σ + p elastic scattering has been studied using a scintillating fiber block (SCIFI) which served as a target for the production of Σ + hyperons as well as for subsequent Σ + scattering on hydrogen. A new technique for the analysis of the hyperon-nucleon scattering in the SCIFI has been developed and established. In this paper, Σ + p elastic scattering events have been identified in the Σ + momentum range of 300–600 MeV/ c , and differential cross sections have been obtained at two angles. The results are compared with various theoretical baryon-baryon interaction models.
No description provided.
The transverse momentum and rapidity distributions of net protons and negatively charged hadrons have been measured for minimum bias proton-nucleus and deuteron-gold interactions, as well as central oxygen-gold and sulphur-nucleus collisions at 200 GeV per nucleon. The rapidity density of net protons at midrapidity in central nucleus-nucleus collisions increases both with target mass for sulphur projectiles and with the projectile mass for a gold target. The shape of the rapidity distributions of net protons forward of midrapidity for d+Au and central S+Au collisions is similar. The average rapidity loss is larger than 2 units of rapidity for reactions with the gold target. The transverse momentum spectra of net protons for all reactions can be described by a thermal distribution with `temperatures' between 145 +- 11 MeV (p+S interactions) and 244 +- 43 MeV (central S+Au collisions). The multiplicity of negatively charged hadrons increases with the mass of the colliding system. The shape of the transverse momentum spectra of negatively charged hadrons changes from minimum bias p+p and p+S interactions to p+Au and central nucleus-nucleus collisions. The mean transverse momentum is almost constant in the vicinity of midrapidity and shows little variation with the target and projectile masses. The average number of produced negatively charged hadrons per participant baryon increases slightly from p+p, p+A to central S+S,Ag collisions.
No description provided.
No description provided.
The value YRAP = 4PI is the extrapolation for 4PI acceptance.
Photon diffractive dissociation, $\gamma p \to Xp$, has been studied at HERA with the ZEUS detector using $ep$ interactions where the virtuality $Q^2$ of the exchanged photon is smaller than 0.02 GeV$^2$. The squared four-momentum $t$ exchanged at the proton vertex was determined in the range $0.073<|t|<0.40$ GeV$^2$ by measuring the scattered proton in the ZEUS Leading Proton Spectrometer. In the photon-proton centre-of-mass energy interval $176
T is the squared four momentum transfer at the proton vertex.
SLOPE of the DN/DT distribution.
A thrust analysis of Large-Rapidity-Gap events in deep-inelastic ep collisions is presented, using data taken with the H1 detector at HERA in 1994. The average thrust of the final states X, which emerge from the dissociation of virtual photons in the range 10 < Q2 < 100 GeV2, grows with hadronic mass M_X and implies a dominant 2-jet topology. Thrust is found to decrease with growing Pt, the thrust jet momentum transverse to the photon-proton collision axis. Distributions of Pt2 are consistent with being independent of MX. They show a strong alignment of the thrust axis with the photon-proton collision axis, and have a large high-Pt tail. The correlation of thrust with MX is similar to that in e+e- annihilation at sqrt(see)=MX, but with lower values of thrust in the ep data. The data cannot be described by interpreting the dissociated system X as a qqbar state but inclusion of a substantial fraction of qqbarg parton configurations leads naturally to the observed properties. The soft colour exchange interaction model does not describe the data.
PT distribution of the photon-originated jet relative to the to the GAMMA* P collision axis in the jet center-of-mass frame, divided by the total GAMMA* P cross section for the respective M_x bin. Jet momentum defined as vector sum of momenta in the positive(negative) thrust hemisphere (thrust jet momentum).
PT distribution of the photon-originated jet relative to the to the GAMMA* P collision axis in the jet center-of-mass frame, divided by the total GAMMA* P cross section for the respective M_x bin. Jet momentum defined as vector sum of momenta in the positive(negative) thrust hemisphere (thrust jet momentum).
PT distribution of the photon-originated jet relative to the to the GAMMA* P collision axis in the jet center-of-mass frame, divided by the total GAMMA* P cross section for the respective M_x bin. Jet momentum defined as vector sum of momenta in the positive(negative) thrust hemisphere (thrust jet momentum).
Forum