Charged Current Antineutrino Interactions Research Articles

Neutron measurements from antineutrino hydrocarbon reactions

Charged-current anti-neutrino interactions on hydrocarbon scintillator in the MINERvA detector are used to study activity from their final-state neutrons. To ensure that most of the neutrons are from the primary interaction, rather than hadronic reinteractions in the detector, the sample is limited to momentum transfers below 0.8 GeV/c. From 16,129 interactions, 15,246 neutral particle candidates are observed. The reference simulation predicts 64\% of these candidates are due to neutrons from the anti-neutrino interaction directly, but also overpredicts the number of candidates by 15\% overall, which is beyond the standard uncertainty estimates for models of neutrino interactions and neutron propagation in the detector. Using the measured distributions for energy deposition, time of flight, position, and speed, we explore the sensitivity to the details those two aspects of the models. We also use multiplicity distributions to evaluate the presence of a two-nucleon knockout process. These results provide critical new information toward a complete description of the hadronic final state of neutrino interactions, which is vital to neutrino oscillation experiments.

Single neutral pion production by charged-current [formula omitted] interactions on hydrocarbon at [formula omitted

Single neutral pion production via muon antineutrino charged-current interactions in plastic scintillator (CH) is studied using the MINERvA detector exposed to the NuMI low-energy, wideband antineutrino beam at Fermilab. Measurement of this process constrains models of neutral pion production in nuclei, which is important because the neutral-current analog is a background for ν¯e appearance oscillation experiments. The differential cross sections for π0 momentum and production angle, for events with a single observed π0 and no charged pions, are presented and compared to model predictions. These results comprise the first measurement of the π0 kinematics for this process.

Measurement of charm production in antineutrino charged-current interactions

During the years 1994–1997, the emulsion target of the CHORUS detector was exposed to the wide-band neutrino beam of the CERN SPS collecting about 106 neutrino interactions. A measurement of ν¯μ-induced charm production is performed by using the presence of a 5% ν¯μ component in the νμ beam. The measurement takes advantage of the capability to observe the decay topology in the emulsion. The analysis is based on a sample of charged-current interactions with at least one identified muon. About 100 000 were located in the emulsion target and fully reconstructed. By requiring a positive muon charge as determined by the CHORUS muon spectrometer, 32ν¯μ-induced charm events were observed with an estimated background of 3.2 events. At an average antineutrino energy in the neutrino beam of 18 GeV, the charm production rate induced by antineutrinos is measured to be σ(ν¯μN→μ+c¯X)/σ(ν¯μN→μ+X)=(5.0−0.9+1.4(stat)±0.7(syst))%. The ratio between neutral and charged charm production rates in this process is (2.6−1.0+1.7(stat)±0.8(syst)). The charm production rate as a function of the antineutrino energy is found to be in good agreement with previous results derived from di-lepton data.

Spin alignment and parity violation effects inρ 0 production in neutrino and antineutrino charged-current interactions

Most of the measured events on hydrogen, deuterium and neon targets from BEBC at CERN and the 15-foot Bubble Chamber at Fermilab are combined to measure spin-density matrix elements for ρ0 production in the current-fragmentation region in neutrino and antineutrino charged-current interactions. The spin-alignment parameter η is found to be 0.08±0.11 for neutrino and 0.41±0.11 for antineutrino interactions. The parity-odd density matrix element Im(ρ10+ρ−10) is consistent with zero in both reactions. In the combined neutrino and antineutrino data an indication of parity violation is observed: Im ρ1−1=0.38±0.16 atxB>0.2,Q2>8 GeV2 andz>0.6.

Study ofD *+ and search forD **0 production by neutrinos in BEBC

Data from BEBC experiments are combined to provide large statistics for neutrino interactions. ChargedD * mesons are produced in (1.22±0.25)% of neutrino and (1.01±0.31)% of antineutrino charged current interactions. The mean fraction of the hadronic laboratory energy taken by theD *+ in these events is 0.59±0.03±0.08. Less than 18% of all chargedD * mesons from (anti)neutrino interactions are found to be daughters ofD **0 (at the 90% confidence level).

Determination of the ratior v =d v u v of the valence quark distributions in the proton from neutrino and antineutrino reactions on hydrogen and deuterium

Based on a QCD analysis of the parton momentum distributions in the proton, the ratior v =d v /u v of thed andu valence quark distributions is determined as function ofx in the range 0.01<x<0.7. The analysis uses data from neutrino and antineutrino charged current interactions on hydrogen and deuterium, obtained with BEBC in the (anti)neutrino wideband beam of the CERN SPS. Since v mainly depends on the deuterium/hydrogen ratios of the normalisedx-y-Q2-distributions many systematic effects cancel. It is found thatr v decreases with increasingx, and drops below the naiveSU(6) expectation of 0.5 forx≳0.3. An extrapolation ofr v tox=1 is consistent with the hypothesisr v (1)=0.

Neutral strange particle production in neutrino and antineutrino charged-current interactions on neon.

The production of the neutral strange particlesK0, Λ and\(\bar \Lambda \) invp and\(\bar vp\) charged current interactions is studied in an experiment with the Big European Bubble Chamber. Mean multiplicities are measured as a function of the event variablesEv,W2 andQ2 and of the hadron variablesxF,z andp T 2 .K*± (892) and∑*± (1385) signals are observed, whereas there is no evidence for∑*- (1385) production invp scattering. Forward, backward and total mean multiplicities are found to compare well with the predictions of an empirical model for deep-inelastic reactions in the case of the strange mesonsK0 andK*± (892) but less so for the strange baryons Λ,\(\bar \Lambda \) and∑*± (1385). The strange baryon multiplicities are used to obtain the decuplet to octet baryon production ratio and to assess the probabilities of auu orud system to break up.

Neutral strange particle production in neutrino and antineutrino charged current interactions on protons

The production of the neutral strange particlesK 0, Λ and $$\bar \Lambda $$ invp and $$\bar vp$$ charged current interactions is studied in an experiment with the Big European Bubble Chamber. Mean multiplicities are measured as a function of the event variablesE v,W 2 andQ 2 and of the hadron variablesx F,z andp T 2 .K *± (892) and∑ *± (1385) signals are observed, whereas there is no evidence for∑ *- (1385) production invp scattering. Forward, backward and total mean multiplicities are found to compare well with the predictions of an empirical model for deep-inelastic reactions in the case of the strange mesonsK 0 andK *± (892) but less so for the strange baryons Λ, $$\bar \Lambda $$ and∑ *± (1385). The strange baryon multiplicities are used to obtain the decuplet to octet baryon production ratio and to assess the probabilities of auu orud system to break up.

Coherent production ofa 1 ? mesons and (??)? systems by antineutrinos on neon

The coherent production of 3π systems by charged current antineutrino interactions on neon nuclei is studied in the bubble chamber BEBC exposed to the CERN SPS wide band beam. The coherent signal is attributed mainly to (ρπ) production, where the (ρπ) system is either non-resonant or comes from the decay ofa1 mesons. The kinematical variables and the total cross section are compared with the predictions of the meson dominance model.

Cross-section measurements of single pion production in charged current neutrino and antineutrino interactions

All six exclusive single pion production processes from neutrino and antineutrino charged current interactions are studied in the energy range between 3 and 30 GeV. Using a quark model for single pion production from Rein and Sehgal we fitted the aximal mass parameter from total cross sections and compare the results with values from other experiments and the world-averages.

Coherent production ofρ − mesons in charged current antineutrino-neon interactions in BEBC

Coherent production ofρ − mesons in charged current antineutrino interactions on neon nuclei is studied in the BEBC bubble chamber exposed to the CERN SPS wide band beam. The cross section is measured to be (95±25)·10−40 cm2 per neon nucleus, averaged over the beam energy spectrum. The distributions of kinematical variables and the absolute value of the cross section are in agreement with theoretical predictions based on the CVC hypothesis and the vector meson dominance model.

Coherent single pion production by antineutrino charged current interactions and test of PCAC

The cross section for coherent production of a single π− meson in charged current antineutrino interactions on neon nuclei has been measured in BEBC to be (175±25) 10−40 cm2/neon nucleus, averaged over the energy spectrum of the antineutrino wide band beam at the CERN SPS; this corresponds to (0.9±0.1) % of the total charged current\(\bar v_\mu \) cross section. The distributions of kinematical variables are in agreement with theoretical predictions based on the PCAC hypothesis and the meson dominance model; in particular, theQ 2 dependence is well described by a propagator containing a massm=(1.35±0.18) GeV. The absolute value of the cross section is also in agreement with the model. This analysis thus provides a test of the PCAC hypothesis in the antineutrino energy range 5–150 GeV.

Measurement of total cross sections for neutrino and antineutrino charged-current interactions in hydrogen and neon

BEBC filled in turn with hydrogen, and with a neon-hydrogen mixture, was exposed to the CERN SPS wide band neutrino and antineutrino beams. The ratios of the charged-current cross sections per nucleon, σ(νH 2) σ(ν Ne) and σ( ν H 2) σ( ν Ne) , between 20 and 300 GeV were found to be 0.656 ± 0.020 and 1.425 ± 0.052, respectively. Multiplying these ratios by the revised cross sections in neon, σ(ν Ne) E = (0.723 ± 0.038) × 10 −38 cm 2/ GeV per nucleon and σ( ν Ne) E = (0.351 ± 0.019) × 10 −38 cm 2/ GeV per nucleon, and their ratio, σ( ν Ne) σ(ν Ne) = 0.485 ± 0.020 ,, yields values for the total charged-current cross sections on protons, σ(νp)/ E and σ( ν p) E , of (0.474 ± 0.029) × 10 −38 cm 2/GeV and (0.500 ± 0.032) × 10 −38 cm 2/GeV. respectively, and a value for the ratio σ( ν p) σ(ν p) of 1.053 ± 0.066.

A study of single-meson production in neutrino and antineutrino charged-current interactions on protons

We present results on exclusive single-charged pion and kaon production in neutrino and antineutrino interactions on protons in the energy range from 5 to 120 GeV. The data were obtained from exposures of BEBC to wide band beams at the CERN SPS. For invariant masses of the (pπ) system below 2 GeV, the pions originate predominantly from decays of baryon resonances excited by the weak charged current. Similarly, we observe the production of Λ(1520) decaying into p and K −. For invariant masses above 2 GeV pion production becomes peripheral by interaction of the weak current with a virtual π 0. We establish a contribution of longitudinally polarised intermediate vector bosons to this process.

Dilepton and trilepton production by antineutrinos and neutrinos in neon

A sample of over 25,000 fully measured neutrino and antineutrino charged current interactions in BEBC includes 192 dilepton candidates. The prompt signal after subtraction of background is 41 ±7µ+ e -, 35±7µ+µ- events from\(\bar v\) interactions, and 32±7µ-µ+ events from ν interactions. There are 2 trileptons, µ-µ- e + and µ-µ-µ+. Results are compared with other experimental data and with the standard model. Limits to prompt like sign µ+ e +, µ+µ+ and µ-µ- signals are given and compared with other experiments and with theoretical calculations.

Observation of coherent diffractive charged current interactions of antineutrinos on neon nuclei

First observation is reported of semi-inclusive coherent diffractive charged current interactions of antineutrinos on neon nuclei. A sharp peaking towards zero is observed in the | t| distribution of interactions for which the final state charge is 0 and from which only one negative hadron is emitted, unaccompanied by any evidence of nuclear fragmentation or reinteraction. This peak is correlated with high momentum of the outgoing charged hadron and with small values of Q 2 and x.

Fragmentation in neutrino and antineutrino charged current interactions on proton and neutron

Some experimental properties of the charged hadronic fragments are compared for νp, νn,\(\bar vp\) and\(\bar vn\) interactions: multiplicities of forward and backward going particles,xF distributions for pions, fragmentation functions and theirQ2 andW2 dependence. The results are compared with the predictions of the Lund fragmentation model.

Experimental study of the nucleon structure functions and of the gluon distribution from charged-current neutrino and antineutrino interactions

Inclusive neutrino and antineutrino charged current interactions were studied in the CHARM detector exposed to neutrino and antineutrino Wide Band Beams of the CERN 400 GeV SPS. The x and Q 2 dependence of the structure functions F 2 and xF 3 and of the antiquark momentum distribution q were determined. The data have been interpreted in terms of QCD theory using the Furmanski-Petronzio method. In this way we have determined Λ LO = [190 −40 +70 ( stat) ± 70 ( syst.)] MeV and the structure functions of quarks and gluons without specific assumptions on their analytic dependence. The results agree with previous experiments which relied on model assumptions in the analysis. We conclude that the model independent simultaneous analysis of the xF 3, F 2, q structure functions gives a more reliable determination of the gluon distribution in the nucleon.

Experimental study of differential cross sections in charged-current neutrino and antineutrino interactions

Inclusive neutrino and antineutrino charged-current interactions were studied using the electronic detector of the CHARM Collaboration exposed to the narrow-band beam of the CERN SPS. The relative contributions of quarks and antiquarks to the neutrino cross sections were deduced from the differential cross sectionsdσ/d y. The x and Q 2 dependence of the structure functions F 2 and F 3 were measured. Scaling violations were observed, in qualitative agreement with QCD. A value of the mass scale parameter of QCD,Λ = [0.29 ± 0.12 (stat.) ± 0.10 (syst.)] GeV, was deduced in a leading-order approximation, following the method of Buras and Gaemers.

A test of quark fragmentation in the quark-parton model framework

The hadronic system produced in charged-current antineutrino interactions is used to study fragmentation of the d-quark. Some problems encountered in defining the current quark fragments are discussed. The properties of the fragmentation function are in good agreement with the expectations of the naive quark-parton model and, in particular, at the present level of statistics we find no need for either a Q 2-or an x BJ-dependence.