Inclusive Reactions Research Articles

Antihyperon polarization in inclusive processes at high energies

We propose a model that we believe is the main source of the antihyperon polarization in high-energy protonnucleus inclusive reactions. The polarization is originated by the final-state interactions between the antihyperons and other produced particles in these collisions (predominantly pions). The model is based on two elements: the low-energy pion-hyperon interaction (described by chiral effective Lagrangians) and the statistical fluctuations plus expansion of the background matter.

Efficient Method for Lorentz Integral Transforms of Reaction Cross Sections

The Lorentz Integral Transform (LIT) method is reformulated via the Lanczos algorithm both for inclusive and exclusive reactions. The new technique is tested for the total photoabsorption cross section of 3H and 4He. Due to the rapid convergence of the algorithm one has a decrease in cpu time by two orders of magnitude, but at the same time an excellent agreement with the results of a conventional LIT calculation. The present work opens up the possibility of ab initio calculations for inclusive and exclusive processes for A greater equal 6 with inclusion of complete final state interactions.

Measurement of the Z/A dependence of neutrino charged-current total cross-sections

A relative measurement of total cross-sections is reported for polyethylene, marble, iron, and lead targets for the inclusive charged-current reaction νμ + N → μ- + X. The targets, passive blocks of ∼ 100 kg each, were exposed simultaneously to the CERN SPS wide-band muon-neutrino beam over a period of 18 weeks. Systematic effects due to differences in the neutrino flux and detector efficiency for the different target locations were minimised by changing the position of the four targets on their support about every two weeks. The relative neutrino fluxes on the targets were monitored within the same experiment using charged-current interactions in the calorimeter positioned directly downstream of the four targets. From a fit to the Z/A dependence of the total cross-sections a value is deduced for the effective neutron-to-proton cross-section ratio.

Positivity constraints on initial spin observables in inclusive reactions.

For any inclusive reaction of the type A1(spin 1/2)+A2(spin 1/2)-->B+X, we derive new positivity constraints on spin observables and study their implications for theoretical models in view, in particular, of accounting for future data from the polarized pp collider at Brookhaven RHIC. We find that the single transverse spin asymmetry A(N), in the central region for several processes, for example, jet production, direct photon production, and lepton-pair production, is expected to be such that |A(N)| < or approximately 1/2, rather than the usual bound |A(N)|< or =1.

Transverse single-spin asymmetries in gauge boson production

Transverse single-spin asymmetries (SSA) in inclusive reactions are now considered to be directly related to the transverse momentum kT of the fundamental partons involved in the process. Several possible leading-twist QCD mechanisms have been proposed to explain the available data, in particular the Sivers effect which was resurrected recently. We show that from the measurement of transverse SSA in inclusive production of gauge bosons, one can learn more about the Sivers functions and possibly to achieve a reliable flavor separation.

Inclusive spectra of(p,xp)and(p,xd)reactions on90,92Zrand92Monuclei atEp=30.3MeV

New experimental data for the inclusive reactions (p,xp) and (p,xd) on isotopes of the nuclei $^{90,92}$Zr and $^{92}$Mo, have been measured at E$_{p}$=30.3 MeV, which has not been investigated in detail so far. We show the extension of the pre-equilibrium reactions to this energy region and interpret the results of these experiments. Moreover, we display the mechanism of the reaction and the level of energy-dependence. The adequacy of the theoretical models in explaining the measured experimental data is also discussed. In our theoretical analysis, the contributions of multi-step direct and compound processes in the formation of cross-sections are determined and we assert that the traditional frameworks are valid for the description of the experimental data.

Extracting the Pomeron-Pomeron cross section from diffractive mass spectra

We have calculated the mass distribution ($d\sigma/dM_X$) as observed by UA8 Collaboration in the inclusive reaction $p \bar p \to p X \bar p$ at $\sqrt s = 630 GeV$, using the Interacting Gluon Model (IGM) with Double Pomeron Exchange included. The only new parameter is the $IP IP$ cross section, which we can extract from fitting experimental data. We compare our results with the values obtained in the UA8 study. Assuming a constant Pomeron-Pomeron total cross section ($\sigma_{IP IP} = 1 mb$), we make predictions for $d\sigma/dM_X$ at Tevatron and LHC energies.

HADRON SPIN DYNAMICS

Spin effects in exclusive and inclusive reactions provide an essential new dimension for testing QCD and unraveling hadron structure. Remarkable new experiments from SLAC, HERMES (DESY), and Jefferson Lab present many challenges to theory, including measurements at HERMES and SMC of the single spin asymmetries in ep → e′ π X where the proton is polarized normal to the scattering plane. This type of single spin asymmetry may be due to the effects of rescattering of the outgoing quark on the spectators of the target proton, an effect usually neglected in conventional QCD analyses. Many aspects of spin, such as single-spin asymmetries and baryon magnetic moments are sensitive to the dynamics of hadrons at the amplitude level, rather than probability distributions. I will illustrate the novel features of spin dynamics for relativistic systems by examining the explicit form of the light-front wavefunctions for the two-particle Fock state of the electron in QED, thus connecting the Schwinger anomalous magnetic moment to the spin and orbital momentum carried by its Fock state constituents and providing a transparent basis for understanding the structure of relativistic composite systems and their matrix elements in hadronic physics. I also present a survey of outstanding spin puzzles in QCD, particularly ANN in elastic pp scattering, the J/ψ → ρπ puzzle, and J/ψ polarization at the Tevatron.

Estimation of Sea Level Muon Energy Spectrum at High Latitude from the Latest Primary Nucleon Spectra Near the Top of the Atmosphere

The vertical muon energy spectra at sea level have been estimated from directly measured primary cosmic-ray nucleon spectrum. The hadronic energy moments have been calculated from the CERN LEBC EHS data on the Lorentz invariant cross-section results on pp → π±X and pp → K±X inclusive reactions and are duly corrected for A–A collisions. Finally, the sea level muon energy spectra have been calculated from the decay of conventional mesons, using standard formulation. The estimated muon spectra are found to be in good agreement with the directly measured muon spectra obtained from the different experiments.

Nuclear correlation effects in neutrino-nucleus interactions

We present a model of neutrino-nucleus cross-sections computations taking into account nuclear effects such as short range correlations — through the ring approximation of the RPA, Delta resonance excitation with a medium modified decay width and ( np-nh) excitations ( n=2,3) relevant in the region between the quasi-elastic peak and the Delta peak. The inclusive reaction cross-section is split into exclusive channels classified according to the number of final state pions. This model was originally developped for the water Čerenkov experiments in which the pions in the final state often lead to Čerenkov ring(s) and are therefore crucial for the analysis.

A study of inclusive Double- ${\cal P}$ omeron-Exchange in $p \bar{p} \to p X \bar{p}$ at $\sqrt{s} = 630$ GeV

We report measurements of the inclusive reaction, p pbar -> p X pbar, in events where either or both the beam-like final-state baryons were detected in Roman-pot spectrometers and the central system was detected in the UA2 calorimeter. A Double-Pomeron-Exchange (DPE) analysis of these data and single diffractive data from the same experiment demonstrates that, for central masses of a few GeV, the extracted Pomeron-Pomeron total cross section exhibits an enhancement which exceeds factorization expectations by an order-of-magnitude. This may be a signature for glueball production. The enhancement is shown to be independent of uncertainties connected with possible non-universality of the Pomeron flux factor. Based on our analysis, we present DPE cross section predictions, for unit (1 mb) Pomeron-Pomeron total cross section, at the Tevatron, LHC and the 920 GeV fixed-target experiment, HERA-B.

Comparison between Analyzing Powers from the Inclusive Reactions (→p, α) and (→p, 3He) on 59Co at an Incident Energy of 100 MeV

Analyzing power emission-energy distributions for the inclusive (→p, α) reaction on 59CO at an incident energy of 100 MeV are investigated The results of a simple a-cluster knockout model, evaluated in the distorted wave impulse approximation, are compared with the experimental distributions. It is found that the analyzing power distributions are consistent with a single-step knockout interpretation at high a-emission energies. Clear indications of the need to include multistep mechanisms are found only for emission energies close to the lowest value which was investigated. The results for the (→p, α) reaction are compared with existing information on the behaviour of analyzing distributions for the (→p, 3He) reaction.

Semiclassical Distorted Wave Model Analysis of Inclusive (N, N’x) Reactions for Incident Energies up to 400 MeV

The semiclassical distorted wave (SCDW) model with the Wigner transform of a one-body density matrix is applied to analyses of multistep direct processes in (p, p’x) reactions on 12C, 90Zr, and 197Au at incident energies near 150 MeV, and 392 MeV (p, p’x) and 346 MeV (p, nx) reactions on 40Ca. The calculations show good agreement with experimental double-differential cross sections over a wide mass range of target nuclei, except at backward angles.

Inclusive (d, x d’) Reactions on Nuclei in the Mass range 9 to 208 at an Incident Energy of 100 MeV

The inclusive (d, xd’) reaction on 9Be, 12C, 27Al, 58Ni, 93Nb, 181Ta, and 208Pb were investigated at an incident energy of 100 MeV for scattering angles between 10° and 120°. The measured spectra are rather smooth and featureless and reveal very similar qualitative features of the continuum compared to existing (p, xp’) and (α, xα’) data. The continuum angular distributions at various emission energies are described reasonably well with parameterized systematics which indicates a multistep mechanism as the underlying process of pre-equilibrium emission.

On the kinematics of (e, e′p) reactions

The problem of interpreting experimental data on quasielastic electron scattering on nuclei in A(e, e′p)(A−1) reactions is considered. It is shown that the existing discrepancies in experimental data on the reaction 4He(e, e′p)T are associated with the fact that the residual-nucleus momentum pm as determined from the law of energy-momentum conservation cannot be treated as that which is equal to the momentum p of the primary intranuclear nucleon. Under the assumption that the momentum transferred from the electron to the intranuclear nucleon is redistributed during the divergence of the products of the (e, e′p) reaction in question, the method for extracting p is modified by introducing a kinematical correction, whereby the situation is considerably improved. For a first approximation, the correction can be evaluated on the basis of data on A(e, e′) inclusive reactions. The argument behind this evaluation is illustrated by considering the example of the reaction 4He(e, e′p)T.

Single-neutron knockout from34,35Siand37S

Results of single-neutron knockout experiments from ${}^{34,35}\mathrm{Si}$ at $73A \mathrm{MeV}$ and from ${}^{37}\mathrm{S}$ at $69A \mathrm{MeV}$ on a Be target are reported. The final states in the reaction residues have been identified by measuring $\ensuremath{\gamma}$ rays in coincidence with the $(A\ensuremath{-}1)$ fragments. The results are compared with predictions based on the many-body shell model combined with eikonal and transfer-to-the-continuum reaction models. For the ${}^{9}\mathrm{Be}{(}^{34}\mathrm{Si}{,}^{33}\mathrm{Si}+\ensuremath{\gamma})X$ reaction, the measured parallel-momentum distributions of the reaction residues demonstrate the orbital-angular-momentum assignments l=2, 0, 2 to levels at 0, 1.010, and 4.32 MeV (adopted values). The measured absolute spectroscopic factors exhaust a large fraction of the sum rules for a full $(N=20) \mathrm{sd}$ shell. We also give results for the absolute and relative positions of the parallel-momentum distributions and present experimental and theoretical results for the complex spectra of the ${}^{9}\mathrm{Be}{(}^{35}\mathrm{Si}{,}^{34}\mathrm{Si}+\ensuremath{\gamma})X$ reaction. The measured inclusive cross section of 106(19) mb agrees well with the theoretical value of 98 mb, but more detailed conclusions are not possible. For the inclusive reaction ${}^{9}\mathrm{Be}{(}^{37}\mathrm{S}{,}^{36}\mathrm{S})X$ a cross section of 99(12) mb is found compared to the theoretical prediction of 85 mb where only final states with spectroscopic factors greater than 0.03 have been included.

Backward emitted high-energy neutrons in hard reactions ofpandπ+on carbon

Beams of protons and pions of 5.9 GeV/c were incident on a C target. Neutrons emitted into the back hemisphere, in the laboratory system, were detected in (triple) coincidence with two emerging $p_t>$0.6 GeV/c particles. We present the momentum spectra of the backward going neutrons, which have the same universal shape observed in earlier (inclusive) reactions induced by hadrons, $\gamma$, $\nu$, and $\bar{\nu}$ beams. We also integrated the spectra and determined the fraction of the hard scattering events which are in coincidence with at least one neutron emitted into the back hemisphere, with momenta above 0.32 GeV/c. Contrary to the earlier measurements which found that only a small fraction (of the order of 10%) of the total inelastic cross section for light nuclei was associated with backward going nucleons, we find that about half of the events are of this nature. We speculate that the reason for the large difference is the strong total center of mass (s) dependence of the hard reaction and short range nucleon correlations in nuclei.

Λ0 POLARIZATION IN EXCLUSIVE AND INCLUSIVE p-NUCLEUS REACTIONS

Both Λ0 polarization from inclusive and exclusive p-Nucleus reactions follow the same trend as function of xF and [Formula: see text]. It is valid for -1.0&lt;xF&lt;+1.0 and 0.0&lt;PT&lt;2.0 GeV/c and for Nucleus=p, Be, Cu, W and Pb. The value of a depends on the target nature: it is -(0.443 ± 0.037), in exclusive pp reactions; -(0.376 ± 0.024), in inclusive pp reactions; -(0.232 ± 0.012), in inclusive p Be reactions; -(0.124 ± 0.015), in inclusive p Cu reactions; -(0.274 ± 0.023), in inclusive p W reactions; -(0.147 ± 0.023), in inclusive p Pb reactions. It is independent of the beam energy. And this equation is the most simple bilinear form that describes Λ0 polarization in -1.0&lt;xF&lt;+1.0 and 0.0&lt;PT&lt;2.0 GeV/c .

Neutrino anomaly and ν-nucleus interactions

A review of various calculations of the inclusive quasi-elastic reactions and pion production processes in neutrino reactions for various nuclei at intermediate energies relevant to solar, atmospheric and accelerator neutrinos is presented

Light-front-quantized QCD in the light-cone gauge: The doubly transverse gauge propagator

The light-front (LF) quantization of QCD in light-cone gauge has a number of remarkable advantages, including explicit unitarity, a physical Fock expansion, the absence of ghost degrees of freedom, and the decoupling properties needed to prove factorization theorems in high momentum transfer inclusive and exclusive reactions. We present a systematic study of LF-quantized gauge theory following the Dirac method and construct the Dyson-Wick S-matrix expansion based on LF-time-ordered products. The free theory gauge field is shown to satisfy the Lorentz condition as an operator equation as well as the light-cone gauge condition. Its propagator is found to be transverse with respect to both its four-momentum and the gauge direction. The interaction Hamiltonian of QCD can be expressed in a form resembling that of covariant theory, except for additional instantaneous interactions which can be treated systematically. The renormalization constants in YM theory are shown to satisfy the identity $Z_1=Z_3$ at one loop order. The QCD $\beta$ function computed in the noncovariant light-cone gauge agrees with that known in the conventional framework. Some comments on the relationship of our LF framework, with the doubly transverse gauge propagator, to the analytic effective charge and renormalization scheme defined by the pinch technique, the unitarity relations and the spectral representation are also made. LF quantization thus provides a consistent formulation of gauge theory, despite the fact that the hyperplanes $x^{\pm}=0$ used to impose boundary conditions constitute characteristic surfaces of a hyperbolic partial differential equation.