Double spectator poles and quasi-free inelastic scattering in the 6Li + 6Li → 2α + 2d reaction

We have searched for double spectator pole events in the reaction ${}^6\text{Li}\text{+}{}^6\text{Li}\text{→ 2α + 2}\text{d}$, such that the deuteron from the projectile goes forward with the beam velocity while α or d from the target remains at rest. Triple coincidence studies of the reaction show such events, but with the 0° deuteron energy spectrum peaked at slightly higher velocities. Similar effects are seen in d-⁶Li double coincidence spectra from the single breakup reaction ${}^6\text{Li}\text{→}{}^6\text{Li}\text{+ α +}\text{d}$. Quasi-free inelastic scattering, where the d from the projectile receives no momentum transfer while the α excites the target to its first excited state, is also shown to be an important mechanism.     

Mass yield distributions for the reactions Ca+Ca,Nb+Nb at EA = 400 MeV and Ca+Ca at EA = 800 MeV in the molecular-dynamical model

Mass yield distributions obtained on the basis of the molecular-dynamical model are presented for the reactions Ca+Ca, Nb+Nb at $\text{E}\text{A}\text{= 400}\text{MeV}$ and Ca+Ca at $\text{E}\text{A}\text{= 800}\text{MeV}$. For the fragments with masses up to a quarter of the mass of the initial nucleus the model predicts a power law for mass spectra with almost the same value of the exponent. Such behaviour is roughly a result of the superposition of the fireball break-up and the disintegration of spectator regions.     

Antiproton-neutron interactions at 100 GeV/c

From an exposure of the 30-inch deuterium filled bubble chamber to a 100 GeV/c antiproton-enriched beam at FNAL, we have calculated the topological cross sections for antiproton-neutron interactions with three or more charged particles in the final state. A comparison of our data with pn data at the same momentum allows us to estimate the annihilation contribution to each multiplicity, and hence calculate the average value, and width, of the annihilation multiplicity distribution. Our results are consistent with those from $\text{p}\text{p}$ data at 100 GeV/c, but depart from the trend of lower-energy $\text{p}\text{p}$ data.     

Antiproton annihilations in deuterium at rest into two pions: Evidence for pN bound states near threshold

The charged pion spectra in $\text{p}$d→π⁻π⁰p_s, π⁻π⁺n_s have been measured. The Doppler broadening of the pion mom entum due to the spectator neutron recoil is at least a factor of two larger than that due to the proton and in disagreement with that expected from the deuteron wave function. This effect and earlier observations on spectators are well described by assuming narrow $\text{N}$N bound states near threshold.     

Soft gluons in semi-inclusive deep inelastic experiments

The longitudinal and transverse properties of the QCD contribution to semi-inclusive deep inelastic scattering is worked out within the soft gluon resummation procedure. The Λ parameter needed to reproduce the data is in agreement with the value extracted from scaling violations. The intrinsic transverse momentum squared of a quark inside a proton is around 0.45 GeV². Predictions for the transverse correlations $\text{〈}\text{p}{}_{\mathrm{1\perp }}\text{·}\text{p}{}_{\mathrm{2\perp }}\text{〉}$ of two outgoing pions are guven.     

Comparison of the reaction pp → K0K0 at rest in hydrogen and deuterium. A test of S-state annihilation dominance

From the comparison of the frequency of antiproton annihilation at rest in two mesons in H₂ and D₂, the dominance of S-wave in $\text{p}\text{p}$ annihilation at rest is confirmed, the P-wave contribution being less than 6% at the 95% confidence level. The apparent discrepancy between the channels $\text{p}\text{p}\text{→}\text{K}{}^0\text{K}{}^0$ and $\text{p}\text{p}\text{→ππ}$ is due to the strong dependence of the annihilation dynamics from the angular momentum.     

Mueller-Regge analysis in the central region

Mueller-Regge analysis of inclusive spectra in the central region for fixed p⊥ is carried out from 12 GeV/c to ISR energies. An analysis of the difference between π⁺ and π^? single- particle spectra reveals that both Mueller-Regge energy dependence and factorization are in accord with experiments only in a limited region of moderate value of $\text{p?}$, i.e. $\text{p? ? 0.7}\text{GeV/c}$. This suggests that double Regge exchange is a good approximation only for 0;t∥ and ∥u∥ ? 4 GeV². The K/π ratio calculated on the basis of an additive quark-counting picture is also consistent with experiments inside this region. The P? central vertex determined from ISR data turns out to be much smaller than one would obtain from low energy (12–24 GeV/c) data. The P-M-P exchange contribution to ππ correlations in rapidity thus estimated can explain only a part of observed correlations, which indicates that there should be a large positive contribution from some other effects, such as long range effects and/or Q exchange. The transverse momentum dependence of the P? central vertex also determined from ISR data predicts that the P-?-P exchange contribution to normalized ππ correlations increases as $\text{p}{}_1\text{?}$ and $\text{p}{}_{\mathrm{2?}}$ increase.     

Remark on baryonic decays of B mesons

We point out that B mesons might possess significant baryonic decay modes like B → Λ_c$\text{N}$. Invoking a simple-minded spectator ansatz for B decays we estimate BR(B → Λ_c$\text{N}$+X) ≈ 2–13% while exclusive two-body channels might reach values of a few percent. Observation of such transitions could yield valuable information on the dynamics of weak decays and maybe even on charm baryons. The search for bottom baryons would, however, be made more difficult by a sizeable baryonic branching ratio of bottom mesons.     

Magnetic field effects on positron annihilation in metals

It is shown that the positron annihilation rate from a state with momentum k parallel to the magnetic field is periodic in $\text{1}\text{B}$, and that the periodicity is determined by the area of the section of the fermi surface whose z component of momentum is k.     

Polarization transfer in the deuteron break-up reaction at 56 MeV

The polarization transfer coefficients K^yy′ of the break-up spectra in the reactions ¹²C, ⁵⁸Ni, ²⁰⁹Bi($\text{d}$, $\text{p}$X) were measured at 56 MeV. In the forwardd angles (13.5° and 20.0°), the K_y^y′ data at the break-up peak are nearly equal to $\text{2}\text{3}$ (the spectator model prediction) and they decrease at both sides of the peak. The deviation due to the deuteron D-state is estimated, using PWBA and DWBA.     

Features of diffractive scattering and the nature of the N1(1400) observed in NN→N(Nπ) reactions at 5.7 GeV/c

The results for the diffractive scattering contribution ($\text{F}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}^0$) obtained in a cross channel isospin analysis of the $\text{N}\text{N}\text{→}\text{N}\text{(}\text{N}\text{π)}$ reactions at 5.7 GeV/c are compared with those obtained for other ZN → Z′(Nπ) reactions where Z stands for N, π and the carbon nucleus. The dependence of the diffractive scattering on the mass M_πN and the momentum transfer t seems very weakly related to the nature of Z and the incident momentum.A comparison between amplitudes of the isospin exchange I_ex = 0 and I_ex = 1 leading to $\text{N}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ production shows that $\text{N}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(1492)}$ and $\text{N}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(1670)}$ are produced essentialy through I_ex = 1.     

Quantum number effects in events with a charged particle of large transverse momentum: (I). Leading particles in single and diquark jets

In an experiment performed with the SFM facility at the CERN ISR, we have studied events with a large-p_T particle (π⁺, π^-, K^-, p) produced at polar angle settings of 20° and 45°. The longitudinal momentum distributions of leading fragments in the spectator jet of the same rapidity hemisphere as the trigger are strongly correlated to the nature of the trigger particle involved. These distributions are compared with predictions from dimensional counting rules, if parton scattering via vector gluon exchange is assumed for the large-p_T process. Given slight modifications of the original counting rules, we observe a fair agreement. As to the fastest particle (jet leader) in the “away” jet, its average charge is about $\text{1}\text{3}$ independent of the charge of the trigger; this value is expected for the case of three valence quarks participating in the hard scattering process. From the analysis of the trigger jet we find ?⁰/π⁺ and ?⁰/π^- production ratios near unity at a value of the transverse momentum of about 2 GeV/c.     

On the QCD perturbative predictions for the signal ofW± production in hadronic collisions

Evidence for the intermediate bosons in high energy pp and p?p collisions as signal in the cross section of large p_T charged lepton pp, $\text{p}\text{p}\text{→}\text{W}{}^{\mathrm{\pm }}\text{+}\text{X}$, W^±→?^±ν_? is considered for CM energy range $\text{s}\text{=100?800}\text{GeV}$. Besides the usual Drell-Yan term which gives a very sharp peak in the lepton p_T distribution, the first order QCD contribution is included thus producing the intermediate boson with transverse momentum and smearing the lepton distribution. Scaling violation of the structure functions is incorporated and compared with the case when it is absent.     

Hadronic production of charm via flavour excitation

We present a calculation of the contribution of flavour excitation diagrams to the hadronic production of open charm. The main new ingredients in the calculation are: (i) a proper treatment of the QCD evolution of the input charm sea distribution, with constraints from the existing charm structure function data; (ii) use of the available charm transverse momentum data to fix the $\text{t}\text{?}{}_{\mathrm{<mtext>min</mtext>}}$ cutoff which regulates the $\text{t}\text{?}\text{? 0}$ divergence in the diagrams. We are then able to make a stable calculation of the resulting charm cross section. The flavour excitation contribution turns out to be an order of magnitude larger than for fusion. As a result the observed magnitudes of the charm cross section at accelerator and ISR energies are satisfactorily reproduced, thus eliminating a long standing difficulty of the perturbative QCD approach to open charm production. Furthermore, we calculate the longitudinal and transverse spectra of charmed hadrons using a simple recombination model. We show that the existing ISR data on the production of fast Λ_c are well, and naturally, reproduced by this approach. Qualitative predictions for bottom production are also discussed.     

The nuclear Coulomb sum rule in a relativistic model

The nuclear Coulomb sum rule is investigated in a relativistic quantum field theory of the nucleus based on baryons and mesons. First an effective, local, covariant, conserved electromagnetic current operator is constructed for the many-baryon system. It describes the electromagnetic structure of an isolated nucleon; the lowest-mass two-pion contribution to the spectral weight functions of the form factors is contained in it. The sum rule is then evaluated in a model based on baryons and neutral scalar and vector mesons. In the mean-field approximation (MFT) this model correctly describes the saturation properties of nuclear matter. The “one-body” term in the sum rule can be evaluated exactly through the use of the canonical anticommutation relations for the baryon field and the identification of conserved quantities. The remaining relativistic two-body contribution is evaluated in the MFT. Meson contributions to the sum rule at large momentum transfers $\text{q}\text{2k}{}_{\mathrm{<mtext>F</mtext>}}\text{? 1}$ completely dominate anticipated static, short-range, two-nucleon correlation contributions to the non-relativistic Coulomb sum rule. One possible implication is that the nucleus must (at least) be considered as a dynamic system of mesons and baryons.     

On some effective mechanism for charmed particle production in neutrino and antineutrino beams

The paper describes an effective mechanism for charmed particle production in neutrino and antineutrino reactions, which consists in production of charmed virtual vector F1-meson in a weak vertex νF1μ (without suppression by the Cabibbo angle) with further strong rescattering of F1-meson on nucleon. This “quasidiffractive” mechanism should make the basic contribution to the production of charmed particles in neutrino experiments basic energies up to some hundreds of GeV. The charmed particles are mainly produced at limited momentum transfers $\text{|q}{}^2\text{| ≈ M}{}^2{}_{\mathrm{<mtext>F</mtext>}}\text{1}$ and with equal cross sections in the neutrino and antineutrino beams.     

Diffraction dissociation of neutrons in the reaction dp → pppπ− at 25 GeV/c

We observe the reaction dp → p_spec (pπ^?)p in a bubble chamber exposure at 25 GeV/c incident deuteron momentum. The (pπ^?) system with invariant mass below 2.0 GeV is interpreted as neutron diffraction dissociation. The (pπ^?) mass spectra show little if any direct evidence of N¹ production. The decay angular distributions and the momentum transfer distributions of the (pπ^?) system suggest a smooth increase in contributions from higher partial waves $\text{(J ?}\text{3}\text{2}\text{)}$ with increased mass or momentum transfer. A simple partial-wave analysis shows a P₁₁ contribution below 1.3 GeV for small ?t′ and a dominant D₁₃ contribution elsewhere. Both the P₁₁ and D₁₃ amplitudes peak far below the N¹(1470) and N¹(1520) resonances. We also find evidence for the charge-exchange reaction np → p(pπ^?). In this process the (pπ^?) system shows evidence for Δ^o(1236) and N¹(1520) production.     

Transverse momentum distribution of partons in QCD

The renormalization group approach is applied to the study of transverse momentum distribution of partons in QCD. We generalize the method of Altarelli and Parisi to obtain a formula for the mean squared average transverse momentum as a function of Q² and x, the virtual photon mass squared and the longitudinal momentum fraction of the parton. For large Q², it decreases with x in addition to the expected increase with Q². This x-dependence reduces substantially the transverse momentum of massive μ-pairs produced by hadronic collisions from its linear dependence on $\text{(}\text{Q}{}^2\text{ln}\text{Q}{}^2\text{)}\text{1}\text{2}$.     

Kinematical scale breaking in high pT interactions

Assuming scaling in the longitudinal reduced momentum in the overall c.m. for the parton fragmentation function, there are, in any hard scattering model, at least three possible sources of a lack of scaling in $\text{(}\text{1}\text{σ}\text{)}\text{d}\text{σ}\text{d}\text{x}{}_{\mathrm{<mtext>e</mtext>}}$. In this paper we analyse these causes emphasising one of them, “the skew mechanism”, which occurs because the axes of the partons are not the x-axis used to express the reduced momenta of the hadrons and because, simultaneously, the transverse momentum of hadrons inside partons is not negligible. A particular result of our study is that the lack of scaling in $\text{(}\text{1}\text{σ}\text{)}\text{d}\text{σ}\text{d}\text{x}{}_{\mathrm{<mtext>e</mtext>}}$ observed by CCHK and BFS collaborations is not necessarily in contradiction with the scaling in the longitudinal reduced momentum of the jet.