A complete set of polarization-transfer observables has been measured for quasifree (p→,n→) reactions on H2, C12, and Ca40 at a bombarding energy of 495 MeV and a laboratory scattering angle of 18°. The data span an energy-loss range from 0 to 160 MeV, with a corresponding momentum transfer range of qc.m.=1.7–1.9 fm−1. The laboratory observables are used to construct partial cross sections proportional to the nonspin response and three orthogonal spin responses. These results are compared to the transverse spin response measured in deep inelastic electron scattering and to nuclear responses based on the random phase approximation. The polarization observables for all three targets are remarkably similar and reveal no evidence for an enhancement of the spin-longitudinal nuclear response relative to the spin-transverse response. These results suggest the need for substantial modifications to the standard form assumed for the residual particle-hole interaction.
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In this paper Au+Au collisions at 11.6A GeV/c are characterized by two global observables: the energy measured near zero degrees (EZCAL) and the total event multiplicity. Particle spectra are measured for different event classes that are defined in a two-dimensional grid of both global observables. For moderately central events (σ/σint<12%) the proton dN/dy distributions do not depend on EZCAL but only on the event multiplicity. In contrast the shape of the proton transverse spectra shows little dependence on the event multiplicity. The change in the proton dN/dy distributions suggests that different conditions are formed in the collision for different event classes. These event classes are studied for signals of new physics by measuring pion and kaon spectra and yields. In the event classes doubly selected on EZCAL and multiplicity there is no indication of any unusual pion or kaon yields, spectra, or K/π ratio even in the events with extreme multiplicity.
Table for event classification (from CLASS1 to CLASS8) where ZCAL energy solely used for event selection. Number of Projectile Participants Npp=197*(1-E(P=3)/EKIN(P=1)).
CLASS1 (see Table for event classification).
CLASS1 (see Table for event classification).
A polarized internal atomic hydrogen target and a stored, polarized beam are used to measure the spin-dependent total cross section Delta_sigma_T/sigma_tot, as well as the polar integrals of the spin correlation coefficient combination A_xx-A_yy, and the analyzing power A_y for pp-> pp pi0 at four bombarding energies between 325 and 400 MeV. This experiment is made possible by the use of a cooled beam in a storage ring. The polarization observables are used to study the contribution from individual partial waves.
SIG(C=DEL_T) defined as the cross section with the spins of the colliding protons antiparallel, minus the cross section with spins parallel, using transversely polarized beam and target.
The results from the first kinematically complete measurement of the dd --> 4Hepipi reaction are reported. The aim was to investigate a long standing puzzle regarding the origin of the peculiar pipi-invariant mass distributions appearing in double pion production in light ion collisions, the so-called ABC effect. The measurements were performed at the incident deuteron energies of 712 MeV and 1029 MeV, with the WASA detector assembly at CELSIUS in Uppsala, Sweden. We report the observation of a characteristic enhancement at low pipi-invariant mass at 712 MeV, the lowest energy yet. At the higher energy, in addition to confirming previous experimental observations, our results reveal a strong angular dependence of the pions in the overall centre of mass system. The results are qualitatively reproduced by a theoretical model, according to which the ABC effect is described as resulting from a kinematical enhancement in the production of the pion pairs from two parallel and independent NN--> dpi sub-processes.
Total cross section for neutral and charged pion channels.
Invariant PI0 PI0 mass distribution at deuteron kinetic energy 1.029 GeV.
Invariant PI+ PI- mass distribution at deuteron kinetic energy 1.029 GeV.
Reaction cross sections and production cross sections for neutrons, hydrogen, and helium have been measured for 1.2, 1.8 GeV p+Fe, Ni, Ag, Ta, W, Au, Pb and U and are compared with different intra-nuclear-cascade- combined with evaporation-models. Agreement for neutrons and considerable differences for light charged particles are observed between experiment and calculation as well as between different models. The discrepancies are associated with specific deficiencies in the models. The exclusive data measured with two 4π-detectors for neutron and charged particle detection allowed furthermore a systematic comparison of observables characteristic of different stages of the temporal evolution of a spallation reaction: inelastic collision probability, excitation energy distribution, pre-equilibrium emission, and inclusive production cross sections.
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The results of intranuclear cascade calculations (ideal gas with two-body collisions and no mean field), complemented by a simple percolation procedure, are compared with experimental data on protons and light nuclear fragments (d, t, He3, and He4) measured in 400 and 800 MeV/nucleon Ne+Nb collisions using a large solid angle detector. The model reproduces quite well global experimental observables like nuclear fragment multiplicity distributions or production cross sections, and nuclear fragment to proton ratios. For rapidity distributions the best agreement occurs for peripheral reactions. Transverse momentum analysis confirms once again that the cascade, although being a microscopic approach, gives too small a collective flow, the best agreement being reached for Z=2 nuclear fragments. Nevertheless these comparisons are encouraging for further improvements of the model. Moreover, such an approach is easy to extend to any other models that could calculate the nucleon phase space distribution after the compression stage of the reaction, when light nuclear fragments emitted at large angles are constructed from percolation.
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First exclusive data for the $pp \to nn\pi^+\pi^+$ reaction have been obtained at CELSIUS with the WASA detector setup at a beam energy of $T_p$ = 1.1 GeV. Total and differential cross sections disagree with theoretical calculations, which predict the $\Delta\Delta$ excitation to be the dominant process at this beam energy. Instead the data require the excitation of a higher-lying $\Delta$ state, most likely the $\Delta(1600)$, to be the leading process.
Total cross section.
Distribution of the invariant mass of the PI+PI+ system.
Distribution of the cosine of the PI+_PI+ opening angle DELTA at an incident kinetic energy of 1.1 GeV.
The production of $J/\psi$ mesons with rapidity $1.5<y<4.0$ or $-5.0<y<-2.5$ and transverse momentum $p_\mathrm{T}<14 \mathrm{GeV}/c$ is studied with the LHCb detector in proton-lead collisions at a nucleon-nucleon centre-of-mass energy $\sqrt{s_{NN}}=5 \mathrm{TeV}$. The analysis is based on a data sample corresponding to an integrated luminosity of about $1.6 \mathrm{nb}^{-1}$. For the first time the nuclear modification factor and forward-backward production ratio are determined separately for prompt $J/\psi$ mesons and $J/\psi$ from $b$-hadron decays. Clear suppression of prompt $J/\psi$ production with respect to proton-proton collisions at large rapidity is observed, while the production of $J/\psi$ from $b$-hadron decays is less suppressed. These results show good agreement with available theoretical predictions. The measurement shows that cold nuclear matter effects are important for interpretations of the related quark-gluon plasma signatures in heavy-ion collisions.
Single differential production cross sections of prompt J/PSI mesons and of J/PSI from B decay as a function of transverse momentum in the FORWARD region. The errors shown are statistical and the uncorrelated and correlated components of the systematic uncertainties.
Single differential production cross sections of prompt J/PSI mesons and of J/PSI from B decay as a function of transverse momentum in the BACKWARD region. The errors shown are statistical and the uncorrelated and correlated components of the systematic uncertainties.
Double differential production cross sections of prompt J/PSI mesons as a function of transverse momentum and rapidity in the FORWARD region. The errors shown are statistical and the uncorrelated and correlated components of the systematic uncertainties.
We report on the production of inclusive $\Upsilon$(1S) and $\Upsilon$(2S) in p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV at the LHC. The measurement is performed with the ALICE detector at backward ($-4.46< y_{{\rm cms}}<-2.96$) and forward ($2.03< y_{{\rm cms}}<3.53$) rapidity down to zero transverse momentum. The production cross sections of the $\Upsilon$(1S) and $\Upsilon$(2S) are presented, as well as the nuclear modification factor and the ratio of the forward to backward yields of $\Upsilon$(1S). A suppression of the inclusive $\Upsilon$(1S) yield in p-Pb collisions with respect to the yield from pp collisions scaled by the number of binary nucleon-nucleon collisions is observed at forward rapidity but not at backward rapidity. The results are compared to theoretical model calculations including nuclear shadowing or partonic energy loss effects.
Inclusive UPSI(1S) production cross section as a function of rapidity in p-Pb collisions at sqrt(s_NN) = 5.02 TeV. The data was collected in 2013 with two beam configurations, p-Pb and Pb-p with integrated luminosities of 5.0 nb-1 and 5.8 nb-1, respectively.
Inclusive UPSI(1S) production cross section as a function of rapidity in p-Pb collisions at sqrt(s_NN) = 5.02 TeV. The data was collected in 2013 with two beam configurations, p-Pb and Pb-p with integrated luminosities of 5.0 nb-1 and 5.8 nb-1, respectively.
Inclusive UPSI(2S) production cross section as a function of rapidity in p-Pb collisions at sqrt(s_NN) = 5.02 TeV. The data was collected in 2013 with two beam configurations, p-Pb and Pb-p with integrated luminosities of 5.0 nb-1 and 5.8 nb-1, respectively.
The yields of the K*(892)$^{0}$ and $\Phi$(1020) resonances are measured in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV through their hadronic decays using the ALICE detector. The measurements are performed in multiple centrality intervals at mid-rapidity (|$y$|<0.5) in the transverse-momentum ranges 0.3 < $p_{\rm T}$ < 5 GeV/$c$ for the K*(892)$^{0}$ and 0.5 < $p_{\rm T}$ < 5 GeV/$c$ for the $\Phi$(1020). The yields of K*(892)$^{0}$ are suppressed in central Pb-Pb collisions with respect to pp and peripheral Pb-Pb collisions (perhaps due to rescattering of its decay products in the hadronic medium), while the longer lived $\Phi$(1020) meson is not suppressed. These particles are also used as probes to study the mechanisms of particle production. The shape of the $p_{\rm T}$ distribution of the $\Phi$(1020) meson, but not its yield, is reproduced fairly well by hydrodynamic models for central Pb-Pb collisions. In central Pb-Pb collisions at low and intermediate $p_{\rm T}$, the p/$\Phi$(1020) ratio is flat in $p_{\rm T}$, while the p/$\pi$ and $\Phi$(1020)/$\pi$ ratios show a pronounced increase and have similar shapes to each other. These results indicate that the shapes of the $p_{\rm T}$ distributions of these particles in central Pb-Pb collisions are determined predominantly by the particle masses and radial flow. Finally, $\Phi$(1020) production in Pb-Pb collisions is enhanced, with respect to the yield in pp collisions and the yield of charged pions, by an amount similar to the $\Lambda$ and $\Xi$.
Transverse-momentum distributions of (K*(892)0 + anti-K*(892)0)/2 in Pb-Pb collisions at sqrt(sNN)=2.76 TeV, centrality 0.0-20.0%.
Transverse-momentum distributions of (K*(892)0 + anti-K*(892)0)/2 in Pb-Pb collisions at sqrt(sNN)=2.76 TeV, centrality 20.0-40.0%.
Transverse-momentum distributions of (K*(892)0 + anti-K*(892)0)/2 in Pb-Pb collisions at sqrt(sNN)=2.76 TeV, centrality 40.0-60.0%.
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