Saturation of gluon density and soft pp collisions at LHC

We find the relation of the unintegrated gluon distribution at low intrinsic transverse momenta to the inclusive spectrum of the hadrons produced in pp collision at LHC energies in the mid-rapidity region and low hadron transverse momenta. It allows us to study the saturation of the gluon density at low Q ² more carefully and find the saturation scale that does not contradict to both the LHC and HERA data.     

Study of the40Ca(π−, 2n)38K reaction at rest

The (π ^?,2n) reaction on⁴⁰Ca has been investigated via the determination of the momenta for the two neutrons emitted simultaneously following the absorption ofπ ^?. The³⁸K excitation spectrum, opening-angle distributions, and recoil momentum distribution are determined. The direct mechanism is established for transitions to the lower part of the³⁸K excitation spectrum.     

The inclusive proton spectrum for\bar pd \to 3\pi p at rest re-examined

We re-analyze the spectator proton distribution for ¯pd→π ⁺ π^? π^? p. For this channel previous calculations underestimated the cross section for proton momenta of 300 to 600 MeV/c by about a factor 7 while the channels with higher pion multiplicities and the ¯pd→K¯ Kmπp reactions were well explained. By using detailed experimental information on ¯pn and ¯pp annihilation, meson rescattering can in fact explain the cross section also for the 3π case. The¯ pp annihilation followed by charge exchange pion rescattering is much larger than in the 5π case. Vector meson exchange is small but not negligible at high spectator momenta.     

General relativistic Boltzmann equation, II: Manifestly covariant treatment

In a preceding article we presented a general relativistic treatment of the derivation of the Boltzmann equation. The four-momenta occurring in this formalism were all on-shell four-momenta, verifying the mass-shell restriction p²=m²c². Due to this restriction, the resulting Boltzmann equation, although covariant, turned out to be not manifestly covariant. In the present article we switch from mass-shell momenta to off-shell momenta, and thereby arrive at a Boltzmann equation that is manifestly covariant.     

Study of the mechanism of the reaction 2H(π−, π−p)n at relatively high neutron momenta

The ²H(π^?, π^? p)n reaction is experimentally studied at 1 GeV/c for spectator neutron momenta up to 200 MeV/c. The spectator momentum and polar angle distributions and the Treiman-Yang angle distribution are in good agreement with theoretical calculations allowing for the diagrams in which the initial pion rescatters on the nucleons inside the deuteron not more than twice. We conclude that our understanding of the mechanism of the nucleon knock-out from a deuteron is correct. The simple example of the reaction on a deuteron confirms the possibility of describing direct processes with a small number of Feynman diagrams.     

Azimuthal correlations and Bose Einstein effects in the reaction K+p → K+p2π+2π− AT 16 GeV/c

Azimuthal distributions between all possible particle pairs are studied in the reaction K⁺p → K⁺p2(π⁺π^?) at 16 GeV/c. It is shown that the hypothesis of uncorrelated transverse momenta at fixed rapidities of the final-state particles, is sufficient to describe the main features of the data. An interesting exception occurs for identical particle pairs where a genuine short-range correlation, attributed to Bose-Einstein symmetrization, is observed. The correlation length of this effect is shown to be related to the impact parameter distribution of the produced pions.     

Dielectron Production in Pion-Nucleon Reactions at Intermediate Energies

Dielectron production in the πN interaction at not large energies is studied assuming that the electron- positron pair is produced from splitting of the virtual time-like photon. It allows us to get the interesting information on a nucleon form factor in the time-like region of four momentum transfer squared. The dominant contribution of the Δ-isobar creation in the intermediate state at incident pion momenta of about 0.3–0.4 GeV/c is shown. The experimental distributions over the angle and effective mass \({M_{{e^ + }{e^ - }}}\) of the e⁺e^? pair are described satisfactorily. This stimulated us to present theoretical predictions for the \({M_{{e^ + }{e^ - }}}\) distribution in the process π^?p → ne⁺e^? at different incident momenta, which could be verified, for example, by the HADES experiments.     

Momentum dependence measurements of the np → pn charge - exchange peak between 1 and 2 GeV/c

21 differential cross section measurements of the np → pn charge-exchange reaction have been carried out at the synchrotron Saturne (Saclay), for incident neutron momenta between 1 and 2 GeV/c and in the squared four-momentum transfer range 0 ? ?t ? 0.4 (GeV/c)². The π exchange peak is seen at all the incident momenta. The s dependence of the very forward slope of this peak shows weak structures near the threshold of inelastic channels.     

Perturbative fragmentation of a vector color particle into bound states involving a heavy antiquark

Vector-particle fragmentation into possible S-wave bound states involving a heavy antiquark is considered for high-energy processes at high transverse momenta, and the relevant fragmentation function is calculated in the leading order of perturbative QCD for various patterns of the anomalous magnetic moment. One-loop equations describing the q ² evolution of the fragmentation-function moments that is caused by hard-gluon emission from the vector particle are derived. The integrated probabilities of fragmentation are obtained. The distribution of the bound state in the transverse momentum defined with respect to the fragmentation axis is calculated in the scaling limit.     

K0 production by K+ on platinum at 3 GeV/c

We have measured the momenta of about 2600 K⁰'s produced by 2.93 GeV/c K⁺'s in the reaction K⁺Pt (or scintillator)→K⁰+anything. We present the yields in a form available for designing high-energy K⁰ sources. A simple model treats the kaon-nucleon interactions in the nucleus as though the nucleons were free except for the effects of the Fermi distribution and exclusion of final momenta. Single inelastic and double elastic-inelastic elementary particle interactions are all that need be considered to give a good fit to the data over the limited (0° to about 30°) range of production angles observed. This requires an extensive calculation of the probabilities for forming the various final states, and for observing the K⁰'s with the target and veto used.     

A measurement of π+p backward elastic differential cross sections from 1.282 to 2.472 GeV/c

New high-statistics measurements of π⁺p elastic scattering differential cross sections are presented at 30 momentum points between 1.282 and 2.472 GeV/c, covering most of the angular distribution outside the forward diffractive peak. These data show significant disagreements at some momenta with previous high-statistics experiments and with current partial wave analyses.     

Neutron-proton charge-exchange scattering from 8 to 29 GeV/c

The differential cross sections for neutron-proton charge-exchange scattering have been measured for incident neutron momenta between 8 and 29 GeV/c and for four-momentum transfers |t| between 0.002 and 1.0 (GeV/c)². A neutron beam with a broad momentum spectrum was scattered from a liquid hydrogen target. The momenta and scattering angles of the forward-scattered protons were measured by a spark-chamber magnet spectrometer. The flight times and scattering angles of the recoil neutrons were measured by a bank of thick scintillation counters. The efficiencies of the neutron counters were determined in a separate measurement. Absolute normalization of the data was obtained from a measurement of the diffraction dissociation of neutrons from carbon nuclei. Differential cross sections, based on ～ 23 000 events, are presented for 9 different momenta. The shape of the differential cross sections and the momentum dependence are examined in detail.     

Experimental study of the selection rule ΔS = ΔQ in Ke3 and Kμ3 decays

We have studied the time distribution of semi-leptonic decays of the neutral K meson produced in a hydrogen bubble chamber in the reaction K⁺p → K^opπ⁺ with K⁺ momenta between 1.2 and 1.7 GeV/c. We have identified 306 πev decays and 74 πμv decays of known lepton charge with proper times between 0.04 and 20 K_S lifetimes.     

Perturbative expansions in QCD and analytic properties of α s

It is shown that analytic properties of standard QCD perturbation theory contradict known spectral properties and contain, in particular, infrared-generated Landau ghost poles and cuts. As an outcome, a rigorous background perturbation theory is developed and its analytic properties are shown to be in agreement with general requirements. In the limiting case of large N _c, where QCD amplitudes contain only pole singularities, the strong coupling constant α _s(Q ²) is shown to be a meromorphic function of external momenta as well. Some simple models and examples are given where nonperturbative β function and α _s(Q ²) can be written explicitly. The general form of amplitudes at large N _c is given in the framework of background perturbation theory, and its correspondence with standard perturbation theory at highmomenta is demonstrated in the example of e ⁺ e ^? annihilation. For timelike momenta, the background coupling constant differs drastically from the standard one, but the background series averaged over energy intervals has the same (AF) behavior at high momenta in the Euclidean and in the Minkowskian region.     

Observation of QCD effects in transverse momenta of e+e− jets

Probability distributions of the total transverse momenta (K⊥) of charged particles produced in hadronic jets in e⁺e^? annihilations have been measured for center of mass energies in the range from 9.2 to 31.6 GeV. A linear increase of the average K_⊥² with Q² is observed. The data are successfully compared with high order QCD predictions (according to a simple q$\text{q}$ picture supplemented by multiple emission of soft gluons). Deviations from this picture at the highest energies and large K_⊥ are then analyzed in terms of hard gluon bremsstrahlung and qualitative agreement is found with first order QCD predictions. Scaling “in the mean” is found to be valid both for jet and single particle transverse momenta.     

Jets in inclusive e+e− and leptoproduction

The assumption of jets with bounded p_T leads to the following consequences: (a) In e⁺e^? annihilation the coefficient of the cos²θ term (a) of single-particle inclusive distributions] exhibits a unique dependence on the observed particle momentum. This dependence provides a measure of 〈p_T²〉 in a jet. (b) In two-particle inclusive annihilation the average of the squared relative p_T is determined by the same parameter and by the momenta of the two particles. (c) The observation that in the current fragmentation region of leptoproduction the p_T distribution of fast hadrons is broader than that of show ones is explained.     

Effect of the optical orientation of spin angular momenta of sodium atoms in the 32 S 1/2 state and metastable helium atoms in the 23 S 1 state on the Na-He gas-discharge plasma conduction

The observation of the effect of mutual orientation of spin angular momenta of sodium atoms in the 3² S _1/2 state and helium atoms in the 2³ S ₁ state on the electrical conduction of a Na-He gas-discharge plasma is reported. In the experiments, a simultaneous optical orientation of atoms by the optical emission of sodium and helium lamps was carried out. The influence of the mutual orientation on the conduction was observed as a change in the high-frequency voltage across electrodes of a gas-discharge camera caused by the destruction of orientation of sodium atoms. The effect is explained by the dependence of Penning ionization in the interaction of sodium and helium atoms on the mutual orientation of spin angular momenta of partners.     

The reaction π−p→K0Λ0 up to 2375 MeV/c: New results and analysis

New data are presented on the reaction π^?p→K⁰Λ⁰ at 13 incident momenta between 1395 and 2375 MeV/c. A partial-wave analysis has been performed using these data and previous data at lower momenta. The resulting resonance parameters are in broad agreement with recent πN analyses and with the predictions of SU(6)_W × O(3) for the couplings.     

Neutron-proton elastic scattering from 10 to 70 GeV/c

The neutron-proton elastic differential cross section has been measured for incident momenta between 10 and 70 GeV/c and for values of the momentum transfer squared between 0.1 and 2.8 (GeV/c)². The forward peak and the break at about ∣t∣ = 1 (GeV/c)² are very similar to corresponding pp data.     

Influence of fission fragment nuclear structure on scission configuration in252Cf (S.F.)

With the aim of investigating the influence of fragment nuclear structure e.g. shell closure configuration and odd-even nature on the scission configuration, fragment angular momenta have been deduced from the radiochemically determined independent isomeric yield ratios of the fission products¹¹¹Pd,¹³¹Te,¹³³Te,¹³⁴I and¹³⁸Cs in²⁵²Cf spontaneous fission. The fragments' angular momenta deduced are 8.8± 1.5, 5.8 ±1.0, 6.1±1.1, 11.5±1.1 and 9.8±1.2 ? respectively. The angular momenta data from this work and literature have been analysed to arrive at fragments' deformations at the scission bringing out the influence of the spherical 82n and deformed 66n and 88n shells. The fragment angular momenta were also seen to be inversely correlated to their elemental yields exhibiting odd-even fluctuations. This has been explained in terms of equilibration of the collective degrees of freedom in low energy fission.