Neutral currents in elastic neutrino-nucleon scattering

We investigate elastic neutrino (antineutrino)-nucleon scattering in the case where some pieces of neutral currents are related to those which appear in electromagnetism and in weak charge-changing reactions. From Gargamelle preliminary results on elastic reactions we get numerical constraints on the parameters which connect the vector parts of neutral currents with the electromagnetic current. Using inclusive neutral current data we give predictions on elastic cross sections in the case of various models of neutral currents.     

Weak nucleon currents in beta decay and muon capture

We made extensive investigations on the weak charged nucleon currents and structure of complex nuclei in weak nuclear processes. Using our new formalism, which has almost no approximation as far as the lepton part is concerned, we have studied the beta-ray spectra and beta-ray angular distributions in the¹²B and¹²N beta decays. The weak magnetism predicted by CVC is in excellent agreement with the experimental data on beta-ray spectra given by the Columbia and Heidelberg groups. It is noticed here that the difference _– – ₊ of the coefficients in the beta-ray angular distributions in aligned¹²B and¹²N is free from ambiguity of the nuclear model. We found practically no second-class induced tensor current with the data given by the Osaka, Louvain and Zürich groups. On the other hand, the sum _– + ₊ of the coefficients represents the time component of the main axial vector current, and it is free from weak form factors. With this sum we studied the exchange-current and core-polarization effects. These two effects are large, and they are almost cancelled out by each other in this case. We also found the strength of the induced pseudoscalar form factor which is generally consistent with PCAC, from nuclear polarizations of¹²B in muon capture of¹²C performed by the Zürich and Tokyo groups. These nuclear polarizations are insensitive to the nuclear model, if the exchange-current and corepolarization effects are properly taken into account.This paper was partially delivered at the Annual Meeting of the Korean Physical Society, Seoul, 1983; the Asia Pacific Physics Conference, Singapore, 1983; and the International Symposium on Nuclear Spectroscopy and Nuclear Interactions, Osaka, 1984.The present paper is based on our recent theoretical investigations, which have been performed by the theory group, Department of Physics, Osaka Unicersity. The author would like to express his sincere thanks to Professors H. Ohtsubo, Y. Yokoo, Drs. T. Sato, K. Koshigiri, M. Nishimura, M. Kobayashi, and Mr. M. Fukui for their collaboration, to Professors C.W. Kim, Y.K. Lee and K. Kubodera for their stimulating discussions during his 1983 summer visit to Johns Hopkins University, to Professors K. Sugimoto, T. Minamisono, V.L. Telegdi, L. Grenacs, T. Yamazaki and K. Nagamine for sending him their experimental results before publication. Numerical calculations were performed with the aid of NEAC ACOS 1000, Computor Center, Osaka University. This work is partly supported by Grant-in-Aid for Scientific Research, The Ministry of Education, Science, and Culture.This paper is dedicated to Professor K. Sugimoto in commemoration of his sixtieth birthday.     

Single-photon production in neutrino-nucleon interactions

Some processes in which single photons are produced via charged and neutral currents in neutrino-nucleon interactions at energies not higher than 10 GeV are considered.     

Pion production by neutral currents in neutrino-nucleon collisions

It is argued that the apparent arbitrariness of the “anomaly” in Fujikawa's approach should be placed into the context of the regularization of the theory not just the regularization of the anomaly. When the theory is regularized at the level of the action the consistent anomaly arises. The converse also holds, namely that if the anomaly is not consistent then the regulator employed does not, by itself, regulate the theory at the level of the action. The criterion that the regularization presription be given at the outset is advocated, and a discussion of results of various two-dimensional models given.     

Charm dimuon production in neutrino-nucleon interactions in the NOMAD experiment

We present our new measurement of charm dimuon production in neutrino-iron interactions based upon the full statistics collected by the NOMAD experiment. After background subtraction we observe 15,340 charm dimuon events, providing the largest sample currently available. The analysis exploits the large inclusive charged current sample (about 9 million events after all analysis cuts) to constrain the total systematic uncertainty to ∼2%. The extraction of strange sea and charm production parameters is also discussed.     

Exchange currents and nucleon magnetic moments

We investigate the effect of gluon and pion exchange currents on the magnetic moments of the nucleon using the constituent quark model. We also study the effect of scalar exchange currents connected with the confinement and sigma exchange potentials. We conclude that although individual exchange currents are quite large, the total exchange current contribution is relatively small, due to a cancellation of gluon, pion, and scalar exchange currents.Lecture presented at the Indian-Summer School on Interaction in Hadronic Systems, Praha (The Czech Republic), 25–31 August 1993.I would like to thank my colleagues Dr. E. Hernandez and Prof. K. Yazaki, for their collaboration in this field.     

On the origin of like-sign dimuons in neutrino-nucleon and antineutrino-nucleon interactions

The so-called quasi-parton mechanism is considered taking into account nonperturbative effects in QCD and enabling one to explain like-sign dimuon production inv _μ( \(\bar v_\mu\) )N interactions. The rates of production cross sections of like-sign dimuons and trimuons of nonelectromagnetic origin to inclusive cross sections, as well as the average kinematical characteristics of the fast muon are obtained. The contribution of quasi-parton mechanism in γN, μN, π^± p,pp channels is considered. The energy distribution for slow muon inv _μ N interaction is received.     

Axial exchange currents and nucleon spin

We calculate the axial couplings g_A⁸(0) and g_A⁰(0) related to the spin of the nucleon in a constituent quark model. In addition to the standard one-body axial currents, the model includes two-body axial exchange currents. The latter are necessary to satisfy the Partial Conservation of Axial Current (PCAC) condition. For both axial couplings we find significant corrections to the standard quark model prediction. Exchange currents reduce the valence quark contribution to the nucleon spin and afford an interpretation of the missing nucleon spin as orbital angular momentum carried by nonvalence quark degrees of freedom.     

Primary cosmic-ray nucleon spectrum from the atmospheric gamma-ray and muon data

Summary The available experimental inclusive cross-sections for single-pion and kaon production in proton-proton collisions between 0.01 and 2 TeV incident-proton laboratory energy have been used to determine a phenomenological form for the inclusive cross-sections. This has been used together with the recent high-precision measurements of atmospheric gamma-ray and single-muon spectra between 0.002 to 50 TeV to derive the primary nucleon spectrum in the formI(E)=I ₀E-γ up to the primary energy ≥100 TeV. The parametersI ₀ and γ, vary in the range 1.75┌2.7 and 2.63┌2.78, respectively.

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Riassunto Sono state usate le sezioni d'urto inclusive sperimentali disponibili per la produzione di pioni singoli e kaoni negli urti protone-protone ad una energia del protone incidente nel laboratorio compresa tra 0.01 e 2 TeV per determinare una forma fenomenologica per la sezione d'urto inclusiva. Questa è stata usata assieme a recenti misure ad alta precisione dei raggi gamma e degli spettri di muoni singoli tra 0.002 e 50 TeV per derivare lo spettro primario dei nucleoni nella formaI(E)=I ₀E-γ fino a un'energia primaria ≥100 TeV. I parametriI ₀ e γ variano nell'intervallo 1.75┌2.7 e 2.63┌2.78 rispettivamente.

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Резуме Имеущиеся экспериментальные инклюзивные поперечные сечения для рождения отельных пионов и каонов в протон-протонных соударениях при энергиях падающих протонов в лабораторной системе коорлинат от 0.01 до 2 ГэВ используются для определения феноменологической формы для инклюзивного поперечного сечения. Эти результаты вместе с недавними измерениями спектров атмосферных гамма-лучей и отдельных мюонов в области от 0.002 до 50 ТэВ используются затем для получения спектра первичных нуклонов в видеI(E)=I ₀E-γ вплоть до первичной энергии ≥100 ТэВ. ПараметрыI ₀ и γ нзменяются соответственно в областях 1.75┌2.7 и 2.63┌2.78.

     

Average inelasticity and average Q2 in deep-inelastic neutrino-nucleon interactions

We show that under the assumptions of scaling and the Callan-Gross relation, the average inelasticity of neutrino as well as antineutrino scattering from an isoscalar nucleon target is completely determined by the ratio of the total cross sections for these reactions. Bounds are obtained on the average (momentum-transfer)² in terms of this ratio. Constraints applicable to scattering from proton or neutron targets are derived.     

Search for right-handed currents in muon decay

We report new limits on right-handed currents, based on precise measurements of the endpoint of the e⁺ spectrum from ⁺ decay. Highly polarized ⁺ from the TRIUMF surface beam were stopped in pure metal foils within either an 1.1-T spin-holding logitudinal field, or a 70-gauss spin-precessing transverse field. Decay e⁺ emitted within 200 mrad of the beam direction were momentum-analyzed to ±0.2%. For the spin-held data, decay via (V-A) currents requires the e⁺ rate to approach zero in the beam direction at the endpoint. Measurement of this rate sets the 90%-confidence limits P />0.9959 and M(W_R)>380 GeV, where W_R is the possible right-handed gauge boson. For the spin-precessed data we independently determine a 90% confidence limit P />0.9918.We are indebted to the entire TRIUMF management and staff for their splendid support of this experiment. In its early stages we benefited from discussion with J. Brewer, R. Cahn, K. Crowe, and W. Wenzel. Rapid commissioning of the polarimeter was made possible by the superb efforts of the LBL support staff. This research was supported in part by the U.S. Department of Energy, Division of Basic Energy Sciences, Office of Energy Research under contracts W-7405-ENG-48 and AC02-ER02289.     

Electroweak interactions probing the nucleon structure

The possibility is studied of isolating single electroweak structure functions in deep inelastic lepton-nucleon scattering atQ ² aroundM _Z ² . Utilizing the cross-section dependence on the lepton charge and longitudinal polarization λ it is shown that the most-conclusive results follow from measurements of σ⁺(?λ)±σ^?(+λ). Considerable simplifications of the problem are possible if λ can be tuned to sin² θ dependent values of about 0.2. New quark-parton model relations are derived.     

Creation of the nuclear alignment and theG-parity conservation law in weak nucleon currents

-ray angular distributions from nuclear spin aligned¹²B and¹²N were detected and the correlation coefficients were determined. From the comparison of these with the experimental weak magnetism term, it was concluded that the parity of the weak nucleon currents in the iso-spin space was strictly conserved.     

Shell-model approach to the nucleon elastic scattering by nuclei

On the basis of the shell-model approach to nuclear reactions the averaged scattering matrix is parametrized. The method is applied to the calculation of s-neutron strength functions. It is shown that in contrast to the optical model predictions the isotopic dependence of the strength function in its minimum (A ≈ 100?140) is mainly determined by the 3s-state spectroscopic factor.     

Photon-hadron interactions revisited in deep inelastic muon scattering

New results for deep inelastic muon scattering are reviewed. These include shadowing results tox _bj ∼10⁻⁵, nucleon structure functions measurements, the Gottfried sum rule and the use of deep inelastic scattering to obtain information on gluon distributions. The future of muon scattering in the HERA era is discussed.     

Search for emission of nucleons and nucleon pairs following muon capture in selected light nuclei

Preliminary results of measurements of proton energy spectra and search for coincidentp, n pair emission following negative muon capture in¹²C,¹⁶O,²⁷Al are given. A very clear signal for proton emission is found, which can be exploited in future detailed studies.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.This work was supported in part by the U.S. National Science Foundation, grant 83-10044-A 2, the German Bundesministerium für Forschung und Technologie, the International Buero Julich, and the Swiss National Science Foundation.