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Add small final changes. Hopefully the last
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absolution1 committed Feb 17, 2016
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4 changes: 2 additions & 2 deletions chap2.tex
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Expand Up @@ -9,7 +9,7 @@ \section{Neutrino interactions at the GeV-scale}
\nu_\mu n \rightarrow \mu^- p.
\label{eq:CCQEInteraction}
\end{equation}
For Neutral Current Elastic (NCE) interactions, the incident neutrino remains after the interaction has occurred and no nucleon conversion takes place. Because of this fact, the target nucleon in a NCE interaction need not be a neutron. So, for $\nu_\mu$ NCE interactions, there are two channels available
For \DomTC{Neutral Current Elastic (NCE) interactions}, the incident neutrino remains after the interaction has occurred and no nucleon conversion takes place. Because of this fact, the target nucleon in a NCE interaction need not be a neutron. So, for $\nu_\mu$ NCE interactions, there are two channels available
\begin{equation}
\nu_\mu n \rightarrow \nu_\mu n,
\label{eq:NCEInteractionNeutronTarget}
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%As introduced above, consideration of nuclear effects in cross-section measurements is important. This is especially true for neutrino interactions on heavy target nuclei. As one can imagine, the presence of a nucleus can dramatically effect the interactions that are observed in a detector. A popular model for the nucleus is the Relativistic Fermi-Gas (RFG) model~\cite{Smith:1972xh}. The RFG model treats the nucleus as a collection of non-interacting nucleons sitting in a potential well. The nucleons are stacked in the potential well according to the Pauli exclusion principle. This leads to a uniform momentum distribution of the nucleons up to the Fermi momentum $p_F$. Importantly, the Pauli exclusion principle has a further effect. Because the final state nucleon is forbidden from occupying a state taken by another nucleon in the potential well, the energy transfer of the neutrino to the nucleon must result in a final state nucleon with a momentum above $p_F$, resulting in a reduction of the cross-section.
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The RFG can only model the effect of the nucleus on the initial neutrino interaction which creates the final states. However, these final states are created within the nucleus and so additional interactions of the final states with the nucleus can occur. The Final-State Interactions (FSI) can significantly alter the momentum and direction of the final-state particles. As the final-state particles are used to infer neutrino properties, the FSI effects can alter the interpretation of the reconstructed events. In simulation, variations of the cascade model are typically used. This involves pushing the final-state particles through the nucleus in discreet steps and, at each step, probabilistically updating the particle properties. If at any point a final-state particles knocks out another nucleon, the additional nucleon is also pushed through the nucleus in parallel. The discreet stepping occurs until all relevant particles have escaped the nucleus.
The RFG can only model the effect of the nucleus on the initial neutrino interaction which creates the final states. However, these final states are created within the nucleus and so additional interactions of the final states with the nucleus can occur. The Final-State Interactions (FSI) can significantly alter the momentum and direction of the final-state particles. As the final-state particles are used to infer neutrino properties, the FSI effects can alter the interpretation of the reconstructed events. In simulation, variations of the cascade model are typically used. This involves pushing the final-state particles through the nucleus in discrete steps and, at each step, probabilistically updating the particle properties. If at any point a final-state particles knocks out another nucleon, the additional nucleon is also pushed through the nucleus in parallel. The discreet stepping occurs until all relevant particles have escaped the nucleus.
\newline
\newline
To test such cross-section models, including nuclear effects, it is necessary to compare prediction with collected data. However, collected cross-section data for heavy nuclei is relatively sparse. In the case of lead, only two experiments have performed cross-section measurements. The first measurement was performed by the CHORUS~\cite{CHORUS_XSEC} experiment in 2003. The CHORUS detector, exposed to the CERN SPS beam with a wide-band $\nu_\mu$ beam of 27~GeV average energy, measured a cross-section for lead, iron, marble and polyethylene. However, because the absolute flux was not measured in the experiment, all of the cross-section measurements were normalised to a common constant. Their results are summarised in Fig.~\ref{fig:CHORUSXSec}\Yoshi{}{ADDRESSED - ``data/prediction'' is confusing because it looks like the ratio of the two. Say which experiment is, and when the data was taken, in the caption, not just the body text}.
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2 changes: 1 addition & 1 deletion chap4.tex
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Expand Up @@ -26,7 +26,7 @@ \subsection{Neutrino interaction simulation}
The main interactions modes at T2K energies are quasi-elastic scattering (CCQE), single pion production (CC1$\pi$) and Deep Inelastic Scattering (DIS) all of which have models in NEUT~\cite{LlewellynSmith1972261,Rein198179,1126-6708-2006-05-026}.
\newline
\newline
After the initial interactions, the final step is to simulate the final state interactions within the nucleus. Each particle involved in the interaction is pushed through the nucleus in discreet steps with the probability of a final state interaction being calculated at each step. If an interaction occurs, the final states of that interaction are also included in the subsequent steps. This interactive procedure models the particle cascade until all the final states have reached the nucleus boundary. At this point, all final state particles are recorded along with all of the information that created those particles. This information is stored in a vector file and passed on to the ND280 detector MC package which handles the detector's response to these final state particles.
After the initial interactions, the final step is to simulate the final state interactions within the nucleus. Each particle involved in the interaction is pushed through the nucleus in discrete steps with the probability of a final state interaction being calculated at each step. If an interaction occurs, the final states of that interaction are also included in the subsequent steps. This interactive procedure models the particle cascade until all the final states have reached the nucleus boundary. At this point, all final state particles are recorded along with all of the information that created those particles. This information is stored in a vector file and passed on to the ND280 detector MC package which handles the detector's response to these final state particles.
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\newline
While the above description provides a general overview of the NEUT-based simulation of neutrino interactions, the above only describes simulation of NEUT events within the ND280 detector itself. In reality, many interactions occur in the pit which surrounds the near detector, some of which have final state muons which enter ND280. So, a separate NEUT-based simulation of neutrino interactions from the T2K beam in the ND280 pit and the surrounding substrate are also generated. This kind simulation will be referred to as sand MC (because the interaction target is largely sand in the surrounding pit) from now on.
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