Measurement of the ratio of total and differential cross sections on neutrons and protons for charged-current neutrino events

Charged-current neutrino interactions have been analysed in a sample of pictures from BEBC equipped with a TST. Using a method independent of both the neutrino flux and nuclear interaction corrections, the ratio R= σ_n/σ_p has been measured. The result is R=1.98±0.19 for the ratio of total cross sections. Bjorken x distributions for proton and neutron targets and for u and d quarks are compared.     

First observation of the production and decay of the Σc+

An event with the decay chain Σ_c⁺ → Λ_c⁺ + π⁰, Λ_c⁺ → K^? + p + π⁺, has been observed in an exposure of BEBC, equipped with a track sensitive target, to the wide band neutrino beam from the SPS at CERN. The event has a unique three constraint kinematic fit to the ΔS = ?ΔQ reaction v + p → μ^? + p + K^? + π⁺ + π⁺ + π⁰ with both gammas from the π⁰ decay detected. The proton and other final state particles are identified. The masses are M(Λ_c⁺) = 2290 ± 3 MeV/c², M(Σ_c⁺) = 2457 ± 4 MeV/c² and M(Σ_c⁺) ? M(Λ_c⁺) = 168 ± 3 MeV/c². Including other data one obtains M (Σ_c⁺⁺) ? M(Σ_c⁺) = 0 ± 4 MeV/c².     

Observation of trimuon events produced in neutrino and antineutrino interactions

We report two trimuon events producedin v interactions. Of these, one is of the charge type ?++, not previously reported. In an antineutrino exposure, one candidate of the charge type +?? has been observed. This type of event has also not been reported previously. The combined π → μ and K → μ background for the three events are calculated to be ～ 0.7 events. The rate relative to charged current events corresponding to these three events is of the order of 4 × 10^?5.     

Experimental study of structure functions and sum rules in charge-changing interactions of neutrinos and antineutrinos on nucleons

High-energy exclusive and inclusive cross sections are discussed in terms of their dependence on the transverse-position variables (impact parameters) of incident and outgoing particles. The objective is to clarify the points of conflict and agreement of various models with each other and with intuitive ideas based on macroscopic collisions. First the impact parameter representation of states and amplitudes is reviewed. New impact parameter conservation laws and sum rules are derived from Lorentz invariance. The generalized optical theorem of Mueller is extended to give the impact parameter distribution of produced particles. Mueller-Regge behaviour is shown to imply three-dimensional limiting fragmentation in (impact parameter, rapidity)- space and a specific linear structure of the final-state particle density in the central region of this space. The predictions of weak- and strong-coupling multiperipheral models, the φ³ ladder eikonal model and the dual resonance model are presented, with emphasis on the dependence of average multiplicity on impact parameter and the dependence of mean square impact parameter on multiplicity. Special techniques for strong-coupling multiperipheral models are used to study the breakdown of the random-walk impact-parameter structure of the weak-coupling case, and to show explicitly that the average multiplicity is a decreasing function of impact parameter in the strongly coupled ABFST model.     

Observation of charmed baryon production in νp interactions in BEBC

Two examples of charmed baryon production by neutrinos have been observed in BEBC filled with hydrogen. Both events fit uniquely the reaction νp → μ^?pK^?π⁺π⁺ and thus apparently violate the ΔS = ΔQ rule. None of the appropriate mass combinations is consistent with the mass values of the D⁰ and D⁺ mesons. However, for the mass combinations of the pK^?π⁺ systems, values of (2.285 ± 0.005) GeV and (2.280 ± 0.003) GeV are found for event 1 and 2, respectively. These values agree with the mass of (2.285 ± 0.006) GeV for the Λ_c⁺ charmed baryon determined recently in e⁺e^? collisions at SLAC.     

Scaling violation favouring high multiplicity events at 540 GeV CMS energy

New data are presented on the charged multiplicity distribution for non single-diffractive events produced in pp? interactions at a CM energy $\text{s}\text{= 540}\text{GeV}$. The distribution in the full pseudorapidity range is compared with data from the ISR. Using the scaling variable $\text{z =}\text{n}\text{〈n〉}$ a change of shape is observed. The effect is manifested as an increase from 2% to 6% in the proportion of high multiplicity (z > 2) events. For the central pseudorapidity range, |η| ? 1.5, scaling is approximately valid up to $\text{s}\text{= 540}\text{GeV}$.     

Six-prong events produced in 5 GeV/cπ−p interactions

Results are presented from a study of 3184 six-prong π^?p interactions at 5 GeV/c in the Dubna 1 m hydrogen bubble chamber. Cross sections for the various reaction channels are given and their energy dependence is discussed. The emphasis of this paper is on exhibiting the semi-inclusive particle spectra is sufficient detail so that it will be possible to use it for testing models and developing new concepts. In particular, invariant distributions are plotted against the scaled longitudinal momentum x, the rapidity y and the longitudinal momentum p_L in the lab system. The net charge per x as well as y interval is also presented. It is found that the isotropic pion component is inconsistent with the Bose-Einstein formula. Comparison with data at other energies is made whenever possible.     

Transverse momentum of hadrons produced in ν and ν interactions on an isoscalar target in BEBC

The average transverse momentum squared, 〈p_⊥²〉, of hadrons is studied as a function of W² and of Q² for ν and $\text{ν}$ interactions on an isoscalar target. An increase of 〈p_⊥²〉 with W² is observed for the hadrons emitted forward in the hadronic c.m.s. The p_⊥ dependence of the fragmentation function is found to factorise from the structure function at fixed W, but does not factorise at fixed Q². Unlike the case of forward-going particles, the 〈p_⊥²〉 of hadrons going backward in the c.m.s. shows no strong dependence on W².     

Like-sign dimuon events produced in narrow-band neutrino and antineutrino beams

Forty seven events of the type v + Fe → μ^? + μ^? + X and nine events of the type $\text{v}\text{+}\text{Fe}\text{→ μ}{}^{\mathrm{+}}\text{+ μ}{}^{\mathrm{+}}\text{+}\text{X}$ have been observed, and zero events with like-sign muons of the opposite sign. Most of the observed events can be attributed to the background of normal charged current events, in which one of the pions or kaons of the hadron shower decays, and so produces a second muon. The remaining events correspond to rates of the order of (3 ± 2) × 10^?4 of those for charged current events. They may very well be due to the hadronic production of a charm-anticharm pair, with subsequent decay of one member of the pair. The observed rates correspond to charm-anticharm pair production in 0.5–1% of the hadron showers. No evidence can be found for a lepton-cascade origin of the observed events.     

Experimental study of opposite-sign dimuons produced in neutrino and antineutrino interactions

A large sample of opposite-sign dimuons, produced by the interaction of neutrinos and antineutrinos in iron, is analysed. The data agree very well with the hypothesis that the extra muon is the product of charm decay. They yield information on the strength and space-time structure of the charmproducing weak current. The strange-sea structure functionxs(x) is determined. The difference between neutrino and antineutrino dimuon production is analysed to provide a value of the Kobayashi-Maskawa weak mixing angleθ ₂.     

Opposite sign dimuon events produced in narrow band neutrino and antineutrino beams

On the basis of 315 dimuon events of opposite sign for which the nature (and energy) of the incident neutrino is known, and the momenta and hadronic shower energy are measured, we find a) very similar production by neutrinos and antineutrinos, and therefore confirmation of the GIM model for semileptonic weak interactions, b) energy spectra, excitation functions, angular correlations and transverse momentum distributions which are in remarkable agreement with the hypothesis of charm production and decay, c) evidence against models for which the second muon has a heavy lepton as origin, d) evidence against “bottom” quark production by antineutrinos, e) the amount and the structure function for the strange quark-antiquark sea, and f) an approximate branching ratio, of 0.15 for the muonic decay of the semistable charmed meson.     

A study of trimuon events in 280 GeV muon interactions

In 280 GeV μ⁺ iron interactions the inelastic production of muon pairs has been observed in excess of QED processes. For energies greater than 20 GeV deposited in the target calorimeter the interactions are found to be mainly hadronic. Cross sections are presented for this process in the mass range 1?2.5 GeV/c² and in the kinematic regions covered by the apparatus acceptance. The data are in good agreement with a photon-gluon fusion model for charmed particle production.     

Observation of wrong-sign tri-muon events in 250 GeV muon-nucleon interactions

Two trimuon events of the type μ⁺N→μ⁺μ⁺μ⁺X and one μ⁺N→μ⁺μ^?μ^?X have been observed in 250 GeV μ⁺ -iron interactions. The expected rate from the decay of hadrons (charm, π, K) is about one event. Other processes that may contribute are both beauty production and charm production with $\text{D}{}^0\text{?}\text{D}{}^0$ mixing. The data give upper limits of 12×10^?36 cm² for the cross section of beauty pair production by muons, and 20% for $\text{D}{}^0\text{?}\text{D}{}^0$ transitions due to mixing, both at 90% confidence level.     

Measurement of the polarization of positive muons produced in high-energy antineutrino interactions

The question whether scalar-type interactions contribute to weak interactions at large momentum transfer has been investigated by a measurement of the longitudinal polarization of positive muons produced in charged-current interactions of high-energy antineutrinos with iron. At an average momentum transfer <Q ²>=4 GeV² the muon spin is found to be oriented forward with respect to the muon momentum vector, with an average polarization of 1.10±0.24, consistent with positive helicity. A limit on scalar contributions of σ_{s, p}/σ_tot <7% at the 95% confidence level can be deduced. A search for violation of time reversal invariance which could manifest itself by a polarization component perpendicular to the muon production plane gave a limit of σ_tv/σ_tot <16% (95% c.l.). It is concluded that the weak leptonic charged current retains its dominant vector and axial vector structure at large momentum transfers.     

Current and target jets produced in high energy neutrino-deuterium interactions

In an analysis of ≈ 7000 charged current events produced in high energy neutrino-deuterium interactions, we observe that the struck quark jet has a wider spread in P_t than that from the recoiling diquark jet for events with hadronic energy W > 9 GeV. This suggests that the effect signals the onset of gluon emission from the single quark.     

A study of second-order interference for pions produced in various hadronic interactions

Second-order interference of pion pairs of equal charge is observed in good statistics samples of 16 GeV/cπ⁺p and K^?p interactions (2 × 10⁶ and 10⁶ pion pair combinations, respectively) and in a smaller sample of $\text{p}\text{p}$ annihilations at rest. The effective radius R of the pion source is found to be approximately 1.4 fm for all three types of interaction. The interference does not appear to be “total”, about 60–80% of the like pairs interfering. It is shown that the numerical results for the radius R, for the depth cτ of the source “photosphere” and for the fraction λ of the interfering pairs are sensitive to any dynamical correlation in the background, and hence depend on the background chosen. It is argued that further refinements in the theoretical formulation of the phenomenon and in the experimental approach are needed for truly quantitative results.     

Correlations associated with small angle protons produced in proton-proton collisions at 31 GeV total energy

High energy inelastic protons with $\text{x = 2 p}{}_{\mathrm{<mtext>L</mtext>}}\text{/s}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{> 0.99}$ observed in 15.3/15.3 GeV proton-proton collisions at the CERN ISR are accompanied by particles whose angular distribution is confined to a narrow cone in the opposite direction. In constrast, lower energy protons (0.72 < x < 0.84) are accompanied in addition, by particles emitted at larger angles. The ratio of the associated charged multiplicities is approximately 0.4.     

Hadron production from photon-photon interactions in the CM energy range from 1 to 5 GeV

We present the first data on photon-photon annihilation into hadrons for CM energies > 1 GeV obtained with the detector PLUTO at the e⁺e^? storage ring PETRA. Cross sections are extracted using an inelastic eγ scattering formalism. The results are compared to expectations from Regge-like models.     

Recent developments in high energy physics

Recent results from experiments with solar, atmospheric and accelerator neutrinos are presented. Some of the important results from the LEP and TEVATRON colliders are summarised.