Study of fermion pair production in \mathrm{e^+ e^-} collisions at 130–183 GeV

The cross sections and forward-backward asymmetries of hadronic and leptonic events produced in collisions at centre-of-mass energies from 130 to 183 GeV are presented. Results for , , , , and production show no significant deviation from the Standard Model predictions. This enables constraints to be set upon physics beyond the Standard Model such as four-fermion contact interactions, leptoquarks, bosons and R-parity violating squarks and sneutrinos. Limits on the energy scale of contact interactions are typically in the range from 2 to 10 TeV. Limits on R-parity violating sneutrinos reach masses of a few hundred GeV/ for large values of their Yukawa couplings. Received: 8 March 1999 / Published online: 8 December 1999     

Inclusive production of charged hadrons and {\rm K}^0_{\rm S} mesons in photon–photon collisions

The production of charged hadrons and mesons in the collisions of quasi-real photons has been measured using the OPAL detector at LEP. The data were taken at centre-of-mass energies of 161 and 172 GeV. The differential cross-sections as a function of the transverse momentum and the pseudorapidity of the charged hadrons and mesons have been compared to the leading order Monte Carlo simulations of PHOJET and PYTHIA and to perturbative next-to-leading order (NLO) QCD calculations. The distributions have been measured in the range GeV of the hadronic invariant mass W. By comparing the transverse momentum distribution of charged hadrons measured in interactions with -proton and meson-proton data we find evidence for hard photon interactions in addition to the purely hadronic photon interactions. Received: 4 June 1998 / Published online: 6 November 1998     

Higher order bose-einstein correlations in π+p and K+p collisions at 250 GeV/c

Bose-Einstein correlations up to fourth order are presented at $\sqrt s = 22GeV$ . Genuine third-order correlations are observed. The experimental data are compared with predictions from a quantum statistical approach of radiation from a partially coherent source and with the FRITIOF model.     

Measurements of forward jet production in polarized pp collisions at √s = 500 GeV

The A _N DY project at RHIC was proposed to measure the analyzing power for Drell-Yan production. Test runs took place during polarized proton operations of RHIC in 2011 and 2012 with a model of the A _N DY apparatus in place. In total, an integrated luminosity of 9 pb^?1 with beam polarization of 50% was sampled. The primary detector components were a hadron calorimeter (HCal) that spanned the pseudorapidity interval 2.4 < η < 4.0 and a small electromagnetic calorimeter (ECal). Basic goals for A _N DY test running were to establish the impact of a third interaction region on RHIC performance and to demonstrate HCal calibration. Energy scale of HCal was established using neutral pion reconstruction and checked with hadronic response. In addition, data with a trigger based on HCal energy sum were taken to study jet events. First measurements of analyzing power in the forward jet production are reported.     

Phase space dependence of the multiplicity distribution in π+ andpp collisions at 250 GeV/c

The charged particle multiplicity distribution has been studied for non-single-diffractive π⁺ p andpp collisions at \(\sqrt s = 22\) GeV, for full phase space as well as for intervals in rapidity, azimuthal angle and transverse momentum. In general, the multiplicity distribution is well described by a negative binomial. From comparison of the distribution for negative or positive particles to that of all charged particles, cascading is favoured as an interpretation over stimulated emission. Interesting consequences follow from a comparison of our results to those at collider energies and toe ⁺ e ^? data at comparable energy. Furthermore, evidence is given that the multiplicity distribution is not exactly of negative binomial type in every (connected or disconnected) phase space region.     

Search for charged Higgs bosons in e+e− collisions at s=189 GeV

A search for pair-produced charged Higgs bosons is performed with the L3 detector at LEP using data collected at a centre-of-mass energy of 188.6 GeV, corresponding to an integrated luminosity of 176.4 pb⁻¹. Higgs decays into a charm and a strange quark or into a tau lepton and its associated neutrino are considered. The observed events are consistent with the expectations from Standard Model background processes. A lower limit of 65.5 GeV on the charged Higgs mass is derived at 95% confidence level, independent of the decay branching ratio Br(H^±→τν).     

Measurements of higher order flow harmonics in Au+Au collisions at √s(NN)=200 GeV

Flow coefficients ν(n) for n=2, 3, 4, characterizing the anisotropic collective flow in Au+Au collisions at √s(NN)=200 GeV, are measured relative to event planes Ψ(n), determined at large rapidity. We report ν(n) as a function of transverse momentum and collision centrality, and study the correlations among the event planes of different order n. The ν(n) are well described by hydrodynamic models which employ a Glauber Monte Carlo initial state geometry with fluctuations, providing additional constraining power on the interplay between initial conditions and the effects of viscosity as the system evolves. This new constraint can serve to improve the precision of the extracted shear viscosity to entropy density ratio η/s.     

Study of the process e^＋e^- →π^＋π^-π^0π^0 at energies √s 〈 1 GeV

In an experiment with the Spherical Neutral Detector at VEPP-2M collider the cross section of the process e^＋e^- →π^＋π^-π^0π^0 was measured. At energies √s 〈 920 MeV this cross section was measured for the first time. The energy dependence of the cross section is well discribed by the vector dominance model with contributions from p, p＇, p＂ mesons. The decay probability ρ→π^＋π^-π^0π^0 was found to be Bρ = （1.60±0.74±0.18） × 10^-5. The upper limit for the decay ω→π^＋π^-π^0π^0 was improved by two orders of magnitude compared to the previous measurements and is Bω 〈 2 × 10^-4 at 90% confidence level.     

Partonic interactions and two particle transverse momentum correlations in Au + Au collisions at √sNN=130GeV

Partonic effects on two-particle transverse momentum correlations are studied for Au+Au collisions at \sqrt{s_{_{\rm NN}}}=130GeV in the Monte Carlo model, AMPT. This study demonstrates that in these collisions partonic interactions contribute significantly to the correlations. Additionally, model calculations are compared with data of the two-particle transverse momentum correlations measured by the STAR Collaboration at RHIC, and it is found that AMPT with string melting can well reproduce the measured centrality dependence of the two-particle transverse momentum correlations in Au+Au collisions at \sqrt{s_{_{\rm NN}}}=130GeV.     

Measurements of dihadron correlations relative to the event plane in Au+Au collisions at √sNN=200 GeV

Dihadron azimuthal correlations containing a high transverse momentum (PT) trigger particle are sensitive to the properties of the nuclear medium created at RHI...     

Search for heavy isosinglet neutrinos in e+e− annihilation at 130

《Physics letters. [Part B]》1999,461(4):397-404

Forward-backward multiplicity correlations in σ+ p,K + p andpp collisions at 250 GeV/c

Forward-backward multiplicity correlations in σ⁺,K ⁺ p andpp collisions at 250 GeV/c ( \(\sqrt s \) =22 GeV) are given for all charges and for the different charge combinations. The correlations are found to be caused predominantly by centrally produced particles. It is demonstrated that this result is an agreement with observations at the ISR and the CERNp \(\bar p\) -Collider. The results are compared to expectations from LUND, DPM and FRITIOF Monte Carlo models and a geometrical picture relating correlations in hadron-hadron collisions toe ⁺ e ^? data in terms of impact parameters is tested.     

Neutral strange particle production inK + andπ + collisions with Al and Au nuclei at 250 GeV/c

Data are presented on inclusiveK _s ⁰ and production inK ⁺ and ⁺ collisions with Al and Au nuclei at 250 GeV/c. Results are given on total inclusive cross sections and theA dependence, as well as on distributions in Feynman-x _F , rapidityy and transverse momentum. Ratios ofK _S ⁰ and of to ⁺ production are presented. The data are compared with predictions of the quark-parton model FRITIOF.     

Role of the Λ(1600) in the ${K}^{-}p \rightarrow {\rm{\Lambda }}{\pi }^{0}{\pi }^{0}$ reaction

Role of the Λ(1600) is studied in the ${K}^{-}p\to {\rm{\Lambda }}{\pi }^{0}{\pi }^{0}$ reaction by using the effective Lagrangian approach near the threshold. We perform a calculation for the total and differential cross sections by considering the contributions from the Λ(1600) and Λ(1670) intermediate resonances decaying into ${\pi }^{0}{{\rm{\Sigma }}}^{* 0}(1385)$ with ${{\rm{\Sigma }}}^{* 0}(1385)$ decaying into ${\pi }^{0}{\rm{\Lambda }}$. Additionally, the non-resonance process from u-channel nucleon pole is also taken into account. With our model parameters, the current experimental data on the total cross sections of the ${K}^{-}p\to {\rm{\Lambda }}{\pi }^{0}{\pi }^{0}$ reaction can be well reproduced. It is shown that we really need the contribution from the Λ(1600) with spin-parity ${J}^{P}=1/{2}^{+}$, and that these measurements can be used to determine some of the properties of the Λ(1600) resonance. Furthermore, we also plot the π⁰Λ invariant mass distributions which could be tested by the future experimental measurements.     

Inclusive production of protons, anti-protons and neutrons in p+p collisions at 158 GeV/c beam momentum

New data on the production of protons, anti-protons and neutrons in p+p interactions are presented. The data come from a sample of 4.8 million inelastic events obtained with the NA49 detector at the CERN SPS at 158 GeV/c beam momentum. The charged baryons are identified by energy loss measurement in a large TPC tracking system. Neutrons are detected in a forward hadronic calorimeter. Inclusive invariant cross sections are obtained in intervals from 0 to 1.9 GeV/c (0 to 1.5 GeV/c) in transverse momentum and from ?0.05 to 0.95 (?0.05 to 0.4) in Feynman x for protons (anti-protons), respectively. p _T integrated neutron cross sections are given in the interval from 0.1 to 0.9 in Feynman x. The data are compared to a wide sample of existing results in the SPS and ISR energy ranges as well as to proton and neutron measurements from HERA and RHIC.