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Register a new userProbing Nuclear Effects at the T2K Near Detector Using Transverse Kinematic Imbalance
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Stephen Dolan
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In this work we utilise variables characterising kinematic imbalance in the plane transverse to an incoming neutrino, which have recently been shown to act as a direct probe of nuclear effects (such as final state interactions, Fermi motion and multi-nucleon processes) in $mathcal{O}$(GeV) neutrino scattering. We present a methodology to measure the charged current differential cross-section with no final state pions and at least one final state proton ($CC0pi+Np, N geq 1$) in these variables at the near detector of the T2K experiment (ND280), using the upstream Fine Grained Detector (FGD1) as a hydrocarbon target. Overall these measurements will allow us to better understand the impact of nuclear effects on the observables in neutrino scattering, providing valuable constraints on the systematic uncertainties associated with neutrino oscillation and scattering measurements for both T2K and other experiments with similar energy neutrino beams.
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Kinematic imbalance of the final-state particles in the plane transverse to the neutrino direction provides a sensitive probe of nuclear effects. In this contribution, we report the MINERvA measurement of the single-transverse kinematic imbalance in neutrino charged-current quasielastic-like events on CH targets. To improve the momentum measurements of the final-state particles, we develop a method to select elastically scattering contained (ESC) protons and a general procedure to correct the transverse momentum scales.
This paper reports the first T2K measurement of the transverse kinematic imbalance in the single-$pi^+$ production channel of neutrino interactions. We measure the differential cross sections in the muon-neutrino charged-current interaction on hydrocarbon with a single $pi^+$ and at least one proton in the final state, at the ND280 off-axis near detector of the T2K experiment. The extracted cross sections are compared to the predictions from different neutrino-nucleus interaction event generators. Overall, the results show a preference for models which have a more realistic treatment of nuclear medium effects including the initial nuclear state and final-state interactions.
This paper reports on the search for heavy neutrinos with masses in the range $140 < M_N < 493$ MeV/c$^2$ using the off-axis near detector ND280 of the T2K experiment. These particles can be produced from kaon decays in the standard neutrino beam and then subsequently decay in ND280. The decay modes under consideration are $N to ell^{pm}_{alpha} pi^{mp}$ and $N to ell^+_{alpha} ell^-_{beta} u (bar u)$ ($alpha,beta=e,mu$). A search for such events has been made using the Time Projection Chambers of ND280, where the background has been reduced to less than two events in the current dataset in all channels. No excess has been observed in the signal region. A combined Bayesian statistical approach has been applied to extract upper limits on the mixing elements of heavy neutrinos to electron-, muon- and tau- flavoured currents ($U_e^2$, $U_{mu}^2$, $U_{tau}^2$) as a function of the heavy neutrino mass, e.g. $U_e^2 < 10^{-9}$ at $90%$ C.L. for a mass of $390$ MeV/c$^2$. These constraints are competitive with previous experiments.
Neutrino neutral-current induced single photon production is a sub-leading order process for accelerator-based neutrino beam experiments including T2K. It is, however, an important process to understand because it is a background for electron (anti)neutrino appearance oscillation experiments. Here, we performed the first search of this process below 1 GeV using the fine-grained detector at the T2K ND280 off-axis near detector. By reconstructing single photon kinematics from electron-positron pairs, we achieved 95% pure gamma ray sample from 5.738$times 10^{20}$ protons-on-targets neutrino mode data. We do not find positive evidence of neutral current induced single photon production in this sample. We set the model-dependent upper limit on the cross-section for this process, at 0.114$times 10^{-38}$ cm$^2$ (90% C.L.) per nucleon, using the J-PARC off-axis neutrino beam with an average energy of $left<E_ uright>sim 0.6$ GeV. This is the first limit on this process below 1 GeV which is important for current and future oscillation experiments looking for electron neutrino appearance oscillation signals.
The T2K experiment has performed a search for $ u_e$ disappearance due to sterile neutrinos using $5.9 times 10^{20}$ protons on target for a baseline of $280 m$ in a neutrino beam peaked at about $500 MeV$. A sample of u_e CC interactions in the off-axis near detector has been selected with a purity of 63% and an efficiency of 26%. The p-value for the null hypothesis is 0.085 and the excluded region at 95% CL is approximately $sin^2 2 theta_{ee} > 0.3$ for $Delta m^2_{eff} > 7 eV^2 / c^4$.
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