The reaction pn → pp π − at 7.0 GeV/ c is studied in a pd experiment. Observations on isobar production and low-mass enhancement are reported. The I = 1 2 isobars and the low-mass enhancement produced at the neutron vertex are discussed in terms of the diffraction dissociation plus duality model.
PART OF THE DIFFERENCE BETWEEN DEL PRODUCTION AT THE NEUTRON AND AT THE PROTON VERTICES COULD ARISE FROM DEUTERON EFFECTS.
Cross sections for γd and γn interactions and photoproduction of ϱ 0 and ω are studied at 4.3 GeV, using a linearly polarized photon beam in a deuterium bubble chamber. We find that σ T (γ n ) ⋍ σ T (γ p ) within about 5% and that the γn average charge multiplicity is lower than γp by 0.42±0.09. About 4000 ϱ 0 events and 70 coherent ω events are observed. We present total and differential cross sections for both xoherent and incoherent ϱ 0 production on deuterium, as well as decay angular distributions and density-matrix elements. We find that the t -channel isospin-one exchange amplitude in γ N → ϱ 0 N (e.g. A 2 exchange) is at most 5–13% of the dominant isoscalar amplituds. The ϱ 0 production mechanism is dominantly s -channel helicity-conserving (SHC) on both neutrons and protons. We find that relative to the SHC amplitudes, the single and double helicity-flip amplitudes at the γϱ 0 vertex are of the order of 10–15% for | t | > 0.25 GeV 2 , and have the same sign on both nucleons. This shows that helicity-flip is mainly due to isoscalar exchanges. The ratio of ω to ϱ 0 coherent forward cross sections is found to be 0.16±0.04. The natural-parity exchange part of γ N → ω N is strongly dominated by isoscalar exchanges, and the magnitude of the isovector-exchange is consistent with zero.
The process pn → pp π − is studied in pd collisions at 11.6 GeV/ c . A broad low-mass enhancement of p π − is found in the diffractive reaction pn → p(p π − ) with a cross section slightly smaller than that of a similar analysis at 7.0 GeV/ c . The non-diffractive reaction pn → (p π − )p shows some evidence for resonance production and its cross-section dependence on energy is characteristic of meson exchange. Samples of mass, momentum transfer, and decay angular distributions are compared with the predictions of a double Regge model and a reggeized one-pion exchange model. Using in addition information from the reactions pp → pp π 0 , pp → pn π + at 12.0 GeV/ c , an isospin analysis of the single pion production reaction from nucleon-nucleon scattering, N 1 N 2 → N 3 (N 4 π ) is presented.
The non-strange four-prong events of π + p interactions at 3.5 GeV/ c are studied. Cross sections are calculated for all resonance productions in the channels π + p → p π + π + π − ( σ T = 3.18 ± 0.13 mb) and π + p → p π + π + π − π o ( σ T = 4.03 ± 0.16 mb). The dominant two body reactions Δ ++ ϱ o and Δ ++ ω o are investigated in detail, and production and decay distributions are presented as well as joint decay density matrix elements and joint correlation terms. The Δ ++ ϱ o reaction is compared to predictions of OPE with absorption and the Δ ++ ω o is compared to rho-exchange with sharp cutoff.
BREIT-WIGNER RESONANCE FITS, ALLOWING FOR PHASE SPACE AND RELEVANT REFLECTIONS, TO <P PI+ PI+ PI- PI0> FINAL STATE.
The ratio R of inclusive π + π − production at low transverse momenta is measured in π + n and pn interactions at 195 GeV/ c . R ( 1 R ) in the proton (neutron) fragmentation region increases with Feynman- x and is smaller than R from π + fragmentation. The results agree with a quark-quark scattering model originally proposed for “hard” processes and disagree with a modified version of the model which includes gluon scattering.
Sixty-two charm events have been observed in an exposure of the SLAC Hybrid Facility toa backward sacttered laser beam. Based on 22 neutral and 21 charged decays we have measured the charmed-meson lifetimes to be τD0=(6.8−1.8+2.3)×10−13 sec, τD±=(7.4−2.0+2.3)×10−13 sec and their ratio τD±τD0=1.1−0.3+0.6. The inclusive charm cross section at a photon energy of 20 GeV has been measured to be 56−23+24 nb. Evidence is presented for a non-DD¯ component to charm production, consistent with (35±20)% Λc+ production and some D*± production. We have found no unambiguous F decays.
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.
Heavy quarkonia are observed to be suppressed in relativistic heavy ion collisions relative to their production in p+p collisions scaled by the number of binary collisions. In order to determine if this suppression is related to color screening of these states in the produced medium, one needs to account for other nuclear modifications including those in cold nuclear matter. In this paper, we present new measurements from the PHENIX 2007 data set of J/psi yields at forward rapidity (1.2<|y|<2.2) in Au+Au collisions at sqrt(s_NN)=200 GeV. The data confirm the earlier finding that the suppression of J/psi at forward rapidity is stronger than at midrapidity, while also extending the measurement to finer bins in collision centrality and higher transverse momentum (pT). We compare the experimental data to the most recent theoretical calculations that incorporate a variety of physics mechanisms including gluon saturation, gluon shadowing, initial-state parton energy loss, cold nuclear matter breakup, color screening, and charm recombination. We find J/psi suppression beyond cold-nuclear-matter effects. However, the current level of disagreement between models and d+Au data precludes using these models to quantify the hot-nuclear-matter suppression.
J/psi invariant yield in Au+Au collisions as a function of $N_{part}$ at forward rapidity ($p_{T}$ integrated). 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.
J/psi nuclear modification $R_{AA}$ in Au+Au collisions as a function of $N_{part}$ at forward rapidity ($p_T$ integrated). 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.
J/psi invariant yield in Au+Au collisions as a function of transverse momentum for the 0-20% centrality class at forward rapidity. 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.
Yields for J/psi production in Cu+Cu collisions at sqrt (s_NN)= 200 GeV have been measured by the PHENIX experiment over the rapidity range |y| < 2.2 at transverse momenta from 0 to beyond 5 GeV/c. The invariant yield is obtained as a function of rapidity, transverse momentum and collision centrality, and compared with results in p+p and Au+Au collisions at the same energy. The Cu+Cu data provide greatly improved precision over existing Au+Au data for J/psi production in collisions with small to intermediate numbers of participants, providing a key constraint that is needed for disentangling cold and hot nuclear matter effects.
J/psi-->e+e- invariant yield in Cu+Cu collisions as a function of p_T at mid-rapidity for the 0-20 centrality range. 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.
J/psi-->e+e- invariant yield in Cu+Cu collisions as a function of p_T at mid-rapidity for the 20-40 centrality range. 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.
J/psi-->e+e- invariant yield in Cu+Cu collisions as a function of p_T at mid-rapidity for the 40-60 centrality range. 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.
A search for the flavor-changing neutral-current decay $B^{+}\to K^{+}\nu\bar{\nu}$ is performed at the Belle II experiment at the SuperKEKB asymmetric energy electron-positron collider. The results are based on a data sample corresponding to an integrated luminosity of $63\,\mbox{fb}^{-1}$ collected at the $\Upsilon{(4S)}$ resonance and a sample of $9\,\mbox{fb}^{-1}$ collected at an energy $60\mathrm{\,Me\kern -0.1em V}$ below the resonance. A novel measurement method is employed, which exploits topological properties of the $B^{+}\to K^{+}\nu\bar{\nu}$ decay that differ from both generic bottom-meson decays and light-quark pair production. This inclusive tagging approach offers a higher signal efficiency compared to previous searches. No significant signal is observed. An upper limit on the branching fraction of $B^{+}\to K^{+}\nu\bar{\nu}$ of $4.1 \times 10^{-5}$ is set at the 90% confidence level.
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