6,766 research outputs found
Relativistic effects in two-particle emission for electron and neutrino reactions
Two-particle two-hole contributions to electroweak response functions are
computed in a fully relativistic Fermi gas, assuming that the electroweak
current matrix elements are independent of the kinematics. We analyze the
genuine kinematical and relativistic effects before including a realistic
meson-exchange current (MEC) operator. This allows one to study the
mathematical properties of the non-trivial seven-dimensional integrals
appearing in the calculation and to design an optimal numerical procedure to
reduce the computation time. This is required for practical applications to CC
neutrino scattering experiments, where an additional integral over the neutrino
flux is performed. Finally we examine the viability of this model to compute
the electroweak 2p-2h response functions.Comment: Major revision (shortened). 22 pages, 18 figure
2p-2h excitations in neutrino scattering: angular distribution and frozen approximation
We study the phase-space dependence of 2p-2h excitations in neutrino
scattering using the relativistic Fermi gas model. We follow a similar approach
to other authors, but focusing in the phase-space properties, comparing with
the non-relativistic model. A careful mathematical analysis of the angular
distribution function for the outgoing nucleons is performed. Our goals are to
optimize the CPU time of the 7D integral to compute the hadron tensor in
neutrino scattering, and to conciliate the different relativistic and non
relativistic models by describing general properties independently of the
two-body current. For some emission angles the angular distribution becomes
infinite in the Lab system, and we derive a method to integrate analytically
around the divergence. Our results show that the frozen approximation, obtained
by neglecting the momenta of the two initial nucleons inside the integral of
the hadron tensor, reproduces fairly the exact response functions for constant
current matrix elements.Comment: 8 pages, 4 figures. Contribution to 16th International Workshop on
Neutrino Factories and Future Neutrino Beam Facilities, 25-30 August, 2014.
Held at University of Glasgow, United Kingdo
The frozen nucleon approximation in two-particle two-hole response functions
We present a fast and efficient method to compute the inclusive two-particle
two-hole (2p-2h) electroweak responses in the neutrino and electron
quasielastic inclusive cross sections. The method is based on two
approximations. The first neglects the motion of the two initial nucleons below
the Fermi momentum, which are considered to be at rest. This approximation,
which is reasonable for high values of the momentum transfer, turns out also to
be quite good for moderate values of the momentum transfer . The
second approximation involves using in the "frozen" meson-exchange currents
(MEC) an effective -propagator averaged over the Fermi sea. Within the
resulting "frozen nucleon approximation", the inclusive 2p-2h responses are
accurately calculated with only a one-dimensional integral over the emission
angle of one of the final nucleons, thus drastically simplifying the
calculation and reducing the computational time. The latter makes this method
especially well-suited for implementation in Monte Carlo neutrino event
generators.Comment: 8 pages, 5 figures and 1 tabl
Two-nucleon emission in neutrino and electron scattering from nuclei: the modified convolution approximation
The theoretical formalism of inclusive lepton-nucleus scattering in the
two-nucleon emission channel is discussed in the context of a simplified
approach, the modified convolution approximation. This allows one to write the
2p2h responses of the relativistic Fermi gas as a folding integral of two 1p1h
responses with the energies and momenta transferred to each nucleon. The idea
behind this method is to introduce different average momenta for the two
initial nucleons in the matrix elements of the two-body current, with the
innovation that they depend on the transferred energies and momenta. This
method treats exactly the two-body phase space kinematics, and reduces the
formulae of the response functions from seven-dimensional integrals over
momenta to much simpler three-dimensional ones. The applicability of the method
is checked by comparing with the full results within a model of electroweak
meson-exchange currents. The predictions are accurate enough, especially in the
low-energy threshold region where the average momentum approximation works the
best.Comment: 35 pages, 13 figure
Neutrino-Oxygen CC0 scattering in the SuSAv2-MEC model
We present the predictions of the SuSAv2-MEC model for the double
differential charged-current muonic neutrino (antineutrino) cross section on
water for the T2K neutrino (antineutrino) beam. We validate our model by
comparing with the available inclusive electron scattering data on oxygen and
compare our predictions with the recent T2K -O data, finding
good agreement at all kinematics. We show that the results are very similar to
those obtained for C scattering, except at low energies, and we
comment on the origin of this difference. A factorized spectral function model
of O is also included for purposes of comparison.Comment: 28 pages, 10 figures, JLAB-THY-17-2586. Version 2 accepted for
publication in Journal of Physics G: Nucl. Part. Phy
Nuclear dependence of the 2p2h electroweak response in the Relativistic Fermi Gas model
We present the results of a recent study of meson-exchange two-body currents
in lepton-nucleus inclusive scattering at various kinematics and for different
nuclei within the Relativistic Fermi Gas model. We show that the associated
nuclear response functions at their peaks scale as , for Fermi
momentum going from 200 to 300 MeV/c and momentum transfer from
to 2 GeV/c. This behavior is different from what is found for the
quasielastic response, which scales as . This result can be valuable in
the analyses of long-baseline neutrino oscillation experiments, which need to
implement these nuclear effects in Monte Carlo simulations for different
kinematics and nuclear targets.Comment: 11 pages, 6 figures, Proccedings of the Workshop "Advanced Aspects in
Nuclear Structure and Reactions at Different Energy Scales", 25-28 April
2017, Arbanasi, Bulgari
Emission of neutron-proton and proton-proton pairs in electron scattering induced by meson-exchange currents
We use a relativistic model of meson-exchange currents to compute the
proton-neutron and proton-proton yields in scattering from C in
the 2p-2h channel. We compute the response functions and cross section with the
relativistic Fermi gas model for a range of kinematics from intermediate to
high momentum transfers. We find a large contribution of neutron-proton
configurations in the initial state, as compared to proton-proton pairs. The
different emission probabilities of distinct species of nucleon pairs are
produced in our model only by meson-exchange currents, mainly by the
isobar current. We also analyze the effect of the exchange contribution and
show that the direct/exchange interference strongly affects the determination
of the np/pp ratio.Comment: 5 pages, 6 figure
Influence of Zn excess on compositional, structural and vibrational properties of Cu2ZnSn0.5Ge0.5Se4 thin films and their effect on solar cell efficiency
This Accepted Manuscript will be available for reuse under a CC BY-NC-ND licence after 24 months of embargo periodThe effect of Zn content on compositional, structural and vibrational properties of Cu2ZnSn1-xGexSe4 (CZTGSe, x ~ 0.5) thin films is studied. Kesterite layer is deposited by co-evaporation onto 5 × 5 cm2 Mo/SLG substrate followed by a thermal treatment at maximum temperature of 480 °C, obtaining areas with different composition and morphology which are due to the sample position in the co-evaporation system and to the non-uniform temperature distribution across the substrate. Kesterite layers with higher Zn amounts are characterized by lower Cu and Ge contents; however, a uniform Ge distribution through the absorber layer is detected in all cases. The excess Zn concentration leads to the formation of ZnSe secondary phase on the surface and in the bulk of the absorber as determined by Raman spectroscopy. When higher Ge content and no ZnSe are present in the absorber layer, a compact structure is formed with larger grain size of kesterite. This effect could explain the higher Voc of the solar cell. The Zn content does not affect the bandgap energy significantly (Eg near 1.3 eV), although the observed effect of Zn excess in CZTGSe results in a decreased device performance from 6.4 to 4.2%. This investigation reveals the importance of the control of the off-stoichiometric CZTGSe composition during the deposition process to enhance solar cells propertiesThis work was supported by Spanish Ministry of Science, Innovation and Universities Project WINCOST (ENE2016-80788-C5-2-R) and European Project INFINITE CELL (H2020-MSCA-RISE-2017-777968). ARP also acknowledges financial support from Community of Madrid within Youth Employment Program (PEJD-2017-PRE/IND-4062). MG acknowledges the financial support from ACCIÓ-Generalitat de Catalunya within the TECNIOspring Plus fellowship (TECSPR18-1-0048
Density dependence of 2p-2h meson-exchange currents
We analyze the density dependence of the contribution of meson-exchange
currents to the lepton-nucleus inclusive cross section in the two-particle
two-hole channel. The model is based on the Relativistic Fermi Gas, where each
nucleus is characterized by its Fermi momentum . We find that the 2p-2h
nuclear response functions at their peaks scale as for Fermi momentum
going from 200 to 300 MeV/c and momentum transfer from to 2 GeV/c.
This behavior is different from what is found for the quasielastic response,
which scales as . Additionally, the deep scaling region is also
discussed and there the usual scaling behavior is found to be preferable.Comment: 9 pages, 8 figure
Emission of neutron-proton and proton-proton pairs in neutrino scattering
We use a recently developed model of relativistic meson-exchange currents to
compute the neutron-proton and proton-proton yields in
scattering from C in the 2p-2h channel. We compute the response
functions and cross sections with the relativistic Fermi gas model for
different kinematics from intermediate to high momentum transfers. We find a
large contribution of neutron-proton configurations in the initial state, as
compared to proton-proton pairs. In the case of charge-changing neutrino
scattering the 2p-2h cross section of proton-proton emission ({\it i.e.,} np in
the initial state) is much larger than for neutron-proton emission ({\it i.e.,}
two neutrons in the initial state) by a -dependent factor. The
different emission probabilities of distinct species of nucleon pairs are
produced in our model only by meson-exchange currents, mainly by the
isobar current. We also analyze other effects including exchange contributions
and the effect of the axial and vector currents.Comment: 9 pages and 8 figure
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