Data are presented for the exclusive reaction pp → pp π+ π− at\(\sqrt s= 62GeV\) with two leading protons at large Feynman-x and a centrally produced π+;π− system. In this kinematical configuration one expects a substantial contribution from Double Pomeron Exchange, which is a potential source of glueballs. The experiment was performed at the CERN ISR using the Split Field Magnet spectrometer. In the mass range between 1,000 and 1,700 MeV/c2 the invariant mass distribution for the central π+;π− system exhibits a very significant signal for thef0(1270) and no other obvious resonant states.
The ratios of neutral-current to charged-current cross sections of v and v interactions, seperately, on proton and neutron targets have been measured. The Big European Bubble Chamber (BEBC), filled with deuterium and equipped with an external muon identifier (EMI) and an internal picket fence (IPF), was exposed to the CERN SPS (anti)neutrino wide-band beam. The measured ratios are R v p= = 0.405 ± 0.024 ± 0.021 , R v n = 0.243 ± 0.013 ± 0.016, R v p = 0.301 ± 0.027 ± 0.024 and R v n = 0.490 ± 0.050 ± 0.037 . (The first error is statistical and the second systematic). From combinations of these ratios the following neutral-current chiral coupling constants have been determined: u L 2 = 0.099 ± 0.018 ± 0.008, d L 2 = 0.202 ± 0.020 ± 0.019, u R 2 = 0.020 ± 0.016 ± 0.009 and d R 2 = 0.002 ± 0.017 ± 0.010. These results agree with the predictions of the SU(2) × U(1) standard electroweak model. Assuming ϱ = 1, the corresponding value of sin 2 θ w is found to be 0.247 ± 0.029, whereas a two-parameter fit to the data yields sin 2 θ w = 0.243 ± 0.046 and ϱ = 0.996 ± 0.041.
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Only statistical errors are given.
Ratios of inclusive cross sections σ(π+)/σ(π++K++p) and\(\sigma (\pi ^ -)/\sigma (\pi ^ -+ K^ -+ \bar p)\) were measured for proton-proton interactions with a highpT hadron in the final state around c.m.s. scattering angles θ≅20°, 20° and 45° at two ISR energies\(\sqrt s= 31\) Gev and 62 GeV. Results are shown as functions of transverse and longitudinal momentum and are compared with parton model predictions. The different dependences of positive and negative pion fractions atpT≅2–3 GeV/c on longitudinal momenta is similar to that observed in soft hadronic interactions at low values ofpT where the leading proton effect (diquark fragmentation) is known to contribute. The quantitative agreement of the data with diquark model predictions indicates the presence of diquark fragmentation also in highpT jets.
Events are analyzed in which a high transverse momentum proton was produced at polar angles of 10°, 20° and 45°. The experiment was performed with the Split Field Magnet detector at the CERN ISR at\(\sqrt s \)=62 GeV. A 4-jet structure of these events is found [1]. The measured charge structure of spectator jets is compatible with proton production from hard diquark scattering. This is supported by a study of baryon number compensation in the towards jets. The observed charge compensation in the towards jets suggests dominance of hard (ud) scattering. Evidence forΔ++ production at high transverse momentum indicates the presence of an additional (uu) scattering component. The properties of the recoiling away jets are compatible with the fragmentation of a valence quark and/or of a gluon as in the case of meson triggers.
We have studied single diffraction dissociation ( p p→ p X ) in proton-antiproton collisions at √ s =1.8TeV, covering the ranges 3⪅ M X ⪅200 GeV and 0.05⪅| t |⪅0.11 (GeV/ c ) 2 . Parameterizing the production to be of the form dσ ( d t d M 2 X ) = (M 2 X ) −α exp (bt) , we obtain α = 1.13±0.07 and b = 10.5±1.8(GeV/ c ) −2 . The total single diffraction dissociation cross section is 2 σ SD =8.1±1.7 mb. Comparisons are made to previous lower energy data, and to an earlier measurement by us at the same energy.
New measurements are reported of total cross sections for π ± , K ± , p and p on protons and deuterons at 11 momenta between 23 and 280 GeV/ c .
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Total cross sections of π ± , K ± , p and p on protons and deuterons have been measured at 6 momenta between 200 and 370 GeV/ c .
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A search for new long-lived particles decaying to leptons is presented using proton-proton collisions produced by the LHC at sqrt(s) = 8 TeV. Data used for the analysis were collected by the CMS detector and correspond to an integrated luminosity of 19.7 inverse femtobarns. Events are selected with an electron and a muon that have transverse impact parameter values between 0.02 cm and 2 cm. The search has been designed to be sensitive to a wide range of models with nonprompt e-mu final states. Limits are set on the "displaced supersymmetry" model, with pair production of top squarks decaying into an e-mu final state via R-parity-violating interactions. The results are the most restrictive to date on this model, with the most stringent limit being obtained for a top squark lifetime corresponding to c tau = 2 cm, excluding masses below 790 GeV at 95% confidence level.
Numbers of expected and observed events in the three search regions (see the text for the definitions of these regions). Background and signal expectations are quoted as $N_{\text{exp}} \pm 1\sigma$ stat $\pm 1\sigma$ syst. If the estimated background is zero in a particular search region, the estimate is instead taken from the preceding region. Since this should always overestimate the background, we denote this by a preceding "<".
Expected and observed 95% CL cross section exclusion contours for top squark pair production in the plane of top squark lifetime ($c\tau$) and top squark mass. These limits assume a branching fraction of 100\% through the RPV vertex $\tilde{t}$ $\to$ b l, where the branching fraction to any lepton flavor is equal to 1/3. As indicated in the plot, the region to the left of the contours is excluded by this search.
Electron reconstruction efficiency as function of its tranverse impact parameter, $d_0$.
Charmonium is a valuable probe in heavy-ion collisions to study the properties of the quark gluon plasma, and is also an interesting probe in small collision systems to study cold nuclear matter effects, which are also present in large collision systems. With the recent observations of collective behavior of produced particles in small system collisions, measurements of the modification of charmonium in small systems have become increasingly relevant. We present the results of J/ψ measurements at forward and backward rapidity in various small collision systems, p+p, p+Al, p+Au and 3He+Au, at √sNN =200 GeV. The results are presented in the form of the observable RAB, the nuclear modification factor, a measure of the ratio of the J/ψ invariant yield compared to the scaled yield in p+p collisions. We examine the rapidity, transverse momentum, and collision centrality dependence of nuclear effects on J/ψ production with different projectile sizes p and 3He, and different target sizes Al and Au. The modification is found to be strongly dependent on the target size, but to be very similar for p+Au and 3He+Au. However, for 0%–20% central collisions at backward rapidity, the modification for 3He+Au is found to be smaller than that for p+Au, with a mean fit to the ratio of 0.89±0.03(stat)±0.08(syst), possibly indicating final state effects due to the larger projectile size.
J/psi nuclear modification in p+Au collisions as a function of nuclear thickness (T_A). The statistical and systematic uncertainties vary point-to-point and are listed for each measured value. An additional global systematic uncertainty is provided in each column heading, which applies to all data points per column.
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