Two particle–hole excitations in charged current quasielastic antineutrino-nucleus scattering

Abstract

We evaluate the quasielastic and multinucleon contributions to the antineutrino nucleus scattering cross section and compare our results with the recent MiniBooNE data. We use a local Fermi gas model that includes RPA correlations and gets the multinucleon part from a systematic many body expansion of the W boson selfenergy in the nuclear medium. The same model had been quite successful for the neutrino cross section and contains no new parameters. We have also analysed the relevance of 2p2h events for the antineutrino energy reconstruction. PACS numbers: 25.30.Pt,13.15.+g, 24.10.Cn,21.60.Jz Neutrino (antineutrino) charged-current (CC) scattering on nuclei without emitted pions is a crucial detection channel for many neutrino experiments [1-3] and has been extensively studied by several theoretical groups [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. It has been customary to take for granted that most of those events 1 could be attributed to the quasielastic (QE) scattering of the weak probe on a nucleon. Hence, the initial neutrino(antineutrino) energy could be approximately determined from the energy and angle of the final lepton assuming QE kinematics.This assumption soon led to some puzzling results. In particular, neutrino MiniBooNE data [3] were quite challenging showing substantially larger cross sections than the theoretical predictions [22,23]. A simple way out was to modify in the calculations some standard hadronic parameters, such as the nucleon axial mass M A [3,11,17], to fit data. However, the large obtained values (e.g. M A = 1.35 ± 0.17 GeV in [3]) were in clear conflict with other electron and even neutrino experiments which result in a value very close to one (M A = 1.014 ± 0.014 GeV in [24]).A more natural solution came from the incorporation of some standard nuclear effects such as RPA and multinucleon mechanisms. The importance of these effects in the non mesonic neutrino nucleus scattering was first explored in Refs. [8,9] and later in Refs. [12,18,19]. Some of these more complete models were found to describe well even the MiniBooNE double differential cross section while using standard values for all parameters of the calculations [19]. In these models, a substantial part of the cross section measured in Ref.[3] corresponds to events in which at least two nucleons are emitted.The relevance of the multinucleon mechanisms has some unwanted consequences. Obviously, the neutrino energy reconstruction, based on the QE kinematics is not so reliable [20,[25][26][27] and that implies larger systematic uncertainties in the experiments analysis. Furthermore, a clear separation of quasielastic and multinucleon events is not straightforward from the experimental point of view, even if final nucleons were detected, due to the energy thresholds and to the strong final state interaction of the nucleons in their way out of the nucleus. It is evident the need for comprehensive and theoretically well founded models that provide a good description for single and multinucleon process...

Quasielastic and multinucleon excitations in antineutrino-nucleus interactions

“…The consequence is that the multinucleon piece should weigh less on the cross section for antineutrinos than for neutrinos. This is not the case in other approaches [16][17][18][19][20][21]. The model closest in spirit to our treatment is the one of Bodek et al [22] characterized by a modification of the magnetic form factor so as to account for the observed excess in the dip region of the magnetic response.…”

Cross sections forνμandν¯μinduced pion production on hydrocarbon in the few-GeV region using MINERvA

“…At the lowest Q 2 , it is possible that nucleon-nucleon correlations and Pauli blocking may contribute. These effects have been studied theoretically and experimentally in quasielastic neutrino scattering [46,47]. Other effects can modify the cross section in Q 2 bins below 0.20 GeV 2 .…”

“…12b, 13b, and 14b (where coherent pion production cannot contribute) suggest a stronger turnover near Q 2 0.0 than is predicted by the generators. This could be due to longrange nucleon-nucleon correlations, usually treated via the Random Phase Approximation (RPA) [46,47], or to Pauli blocking. Pauli blocking should be applied for nonresonant pion production.…”

Measurement of Muon Antineutrino Quasielastic Scattering on a Hydrocarbon Target atEν∼3.5 GeV

“…Transverse enhancement is included as a parametrization affecting the Q 2 QE dependence in our analysis but is thought to be due to underlying multinucleon dynamical processes [51][52][53][54][55][56][57]. Such processes could have an effect on the vertex and recoil energy distributions that we do not simulate.…”