Protons On Target Research Articles

Measurements of neutrino oscillation parameters from the T2K experiment using 3.6times 10^{21} protons on target

The T2K experiment presents new measurements of neutrino oscillation parameters using 19.7(16.3)times 10^{20} protons on target (POT) in (anti-)neutrino mode at the far detector (FD). Compared to the previous analysis, an additional 4.7times 10^{20} POT neutrino data was collected at the FD. Significant improvements were made to the analysis methodology, with the near-detector analysis introducing new selections and using more than double the data. Additionally, this is the first T2K oscillation analysis to use NA61/SHINE data on a replica of the T2K target to tune the neutrino flux model, and the neutrino interaction model was improved to include new nuclear effects and calculations. Frequentist and Bayesian analyses are presented, including results on sin ^2theta _{13} and the impact of priors on the delta _{textrm{CP}} measurement. Both analyses prefer the normal mass ordering and upper octant of sin ^2theta _{23} with a nearly maximally CP-violating phase. Assuming the normal ordering and using the constraint on sin ^2theta _{13} from reactors, sin ^2theta _{23}=0.561^{+0.021}_{-0.032} using Feldman–Cousins corrected intervals, and varDelta {}m^2_{32}=2.494_{-0.058}^{+0.041}times 10^{-3}~text {eV}^2 using constant varDelta chi ^{2} intervals. The CP-violating phase is constrained to delta _{textrm{CP}}=-1.97_{-0.70}^{+0.97} using Feldman–Cousins corrected intervals, and delta _{textrm{CP}}=0,pi is excluded at more than 90% confidence level. A Jarlskog invariant of zero is excluded at more than 2sigma credible level using a flat prior in delta _{textrm{CP}}, and just below 2sigma using a flat prior in sin delta _{textrm{CP}}. When the external constraint on sin ^2theta _{13} is removed, sin ^2theta _{13}=28.0^{+2.8}_{-6.5}times 10^{-3}, in agreement with measurements from reactor experiments. These results are consistent with previous T2K analyses.

First Leptophobic Dark Matter Search from the Coherent-CAPTAIN-Mills Liquid Argon Detector.

We report the first results of a search for leptophobic dark matter (DM) from the Coherent-CAPTAIN-Mills (CCM) liquid argon (LAr) detector. An engineering run with 120 photomultiplier tubes (PMTs) and 17.9×10^{20} protons on target (POT) was performed in fall 2019 to study the characteristics of the CCM detector. The operation of this 10-ton detector was strictly light based with a threshold of 50keV and used coherent elastic scattering off argon nuclei to detect DM. Despite only 1.5months of accumulated luminosity, contaminated LAr, and nonoptimized shielding, CCM's first engineering run has already achieved sensitivity to previously unexplored parameter space of light dark matter models with a baryonic vector portal. With an expected background of 115 005 events, we observe 115 005+16.5 events which is compatible with background expectations. For a benchmark mediator-to-DM mass ratio of m_{V_{B}}/m_{χ}=2.1, DM masses within the range 9 MeV≲m_{χ}≲50 MeV are excluded at 90% C. L. in the leptophobic model after applying the Feldman-Cousins test statistic. CCM's upgraded run with 200 PMTs, filtered LAr, improved shielding, and 10 times more POT will be able to exclude the remaining thermal relic density parameter space of this model, as well as probe new parameter space of other leptophobic DM models.

T2K measurements of muon neutrino and antineutrino disappearance using 3.13×1021 protons on target

We report measurements by the T2K experiment of the parameters $\theta_{23}$ and $\Delta m^2_{32}$ which govern the disappearance of muon neutrinos and antineutrinos in the three-flavor PMNS neutrino oscillation model at T2K's neutrino energy and propagation distance. Utilizing the ability of the experiment to run with either a mainly neutrino or a mainly antineutrino beam, muon-like events from each beam mode are used to measure these parameters separately for neutrino and antineutrino oscillations. Data taken from $1.49 \times 10^{21}$ protons on target (POT) in neutrino mode and $1.64 \times 10^{21}$ POT in antineutrino mode are used. The best-fit values obtained by T2K were $\sin^2\left(\theta_{23}\right)=0.51^{+0.06}_{-0.07} \left(0.43^{+0.21}_{-0.05}\right)$ and $\Delta m^2_{32}=2.47^{+0.08}_{-0.09} \left(2.50^{+0.18}_{-0.13}\right)$\evmass for neutrinos (antineutrinos). No significant differences between the values of the parameters describing the disappearance of muon neutrinos and antineutrinos were observed. An analysis using an effective two-flavor neutrino oscillation model where the sine of the mixing angle is allowed to take non-physical values larger than 1 is also performed to check the consistency of our data with the three-flavor model. Our data were found to be consistent with a physical value for the mixing angle.

Normalization Studies on the 2016-2018 Data for the KOTO Experiment

The KOTO experiment is searching for the rare decay of the neutral kaon, . KOTO collected data from 2016 to 2018 and accumulated 3.1 × 1019 Protons on Target (POT). Results on the normalization analysis of this dataset are described. Three normalization modes, , , and , are used to calculate the flux and the number of kaons at the beam exit. The data is well reproduced by the Monte Carlo and the total number of kaons is (7.14 ± 0.05) × 1012. This gives a Single Event Sensitivity (SES) of 6.9 × 10−10.

Study of Charged-Current neutrino interactions on water with nuclear emulsion in the NINJA experiment

Neutrino-nucleus interaction is one of the major sources of the uncertainty for neutrino oscillation experiments. The NINJA experiment aims to measure neutrino-water interactions containing low-momentum secondary particles using a nuclear emulsion detector. Since the nuclear emulsion has sub-micron position resolution, it allows us to observe the interaction vertices clearly. Short proton tracks down to 200 MeV/c momentum are expected to be observed, which are hardly reconstructed in plastic scintillator based detectors. A series of test experiments has been carried out with prototype detectors at J-PARC. In a test run in 2017-2018, a 3 kg water target detector was exposed to anti-neutrino beam corresponding to 0.7 × 1021 POT (protons on target). We have successfully detected low momentum protons above 200 MeV/c threshold from neutrino-water interactions.

Design of a high power production target for the beam dump facility at CERN

The Beam Dump Facility (BDF) project is a proposed general-purpose facility at CERN, dedicated to beam dump and fixed target experiments. In its initial phase, the facility is foreseen to be exploited by the Search for Hidden Particles (SHiP) experiment. Physics requirements call for a pulsed 400 GeV/c proton beam as well as the highest possible number of protons on target (POT) each year of operation, in order to search for feebly interacting particles. The target/dump assembly lies at the heart of the facility, with the aim of safely absorbing the full high intensity Super Proton Synchrotron (SPS) beam, while maximizing the production of charmed and beauty mesons. High-Z materials are required for the target/dump, in order to have the shortest possible absorber and reduce muon background for the downstream experiment. The high average power deposited on target (305 kW) creates a challenge for heat removal. During the BDF facility Comprehensive Design Study (CDS), launched by CERN in 2016, extensive studies have been carried out in order to define and assess the target assembly design. These studies are described in the present contribution, which details the proposed design of the BDF production target, as well as the material selection process and the optimization of the target configuration and beam dilution. One of the specific challenges and novelty of this work is the need to consider new target materials, such as a molybdenum alloy (TZM) as core absorbing material and Ta2.5W as cladding. Thermo-structural and fluid dynamics calculations have been performed to evaluate the reliability of the target and its cooling system under beam operation. In the framework of the target comprehensive design, a preliminary mechanical design of the full target assembly has also been carried out, assessing the feasibility of the whole target system.

Implementation of Feldman-Cousins corrections and oscillation calculations in the HPC environment for the NOvA Experiment

Analysis of neutrino oscillation data involves a combination of complex fitting procedures and statistical correction techniques that are used to determine the full three-flavor PMNS parameters and constraint contours. These techniques rely on computationally intensive “multi-universe” stochastic modeling. The process of calculating these contours and corrections can dominate final stages of the data analysis and become a bottleneck for examining the ef-fect of systematic variations on the final results. As part of the DOE SciDAC-4 sponsored research program, we present a new implementation of a neutrino oscillation fitting and framework to carry out calculations of Feldman-Cousins corrections. This implementation is specifically designed and optimized to operate on modern High-Performance Computing (HPC) facilities. We present the performance of the system in calculating allowed regions for the NOvA experiment based on 8.9 x 1020 and 6.9 x 1020 protons-on-target (POT) neutrino and antineutrino datasets, and compare the performance of this new implementation run at the NERSC supercomputing facility with that from methods used previously by the NOvA collaboration running on grid computing facilities.

Search for muon antineutrino disappearance due to sterile antineutrino oscillations with the MINOS experiment

Three-flavour neutrino mixing has successfully explained a wide range of neutrino oscillation data. However, results such as the electron antineutrino appearance excesses seen by LSND and MiniBooNE can be explained in terms of neutrino oscillations adding a sterile neutrino at a larger mass scale than the existing three flavour mass states. MINOS is a two-detector, long-baseline neutrino oscillation experiment that uses magnetized tracker-calorimeter detectors to measure the energy and composition of the NuMI neutrino beam. These magnetized detectors give MINOS a unique ability to be able to separate muon neutrino and antineutrino interactions. Using data taken with the NuMI beam configured in antineutrino mode, MINOS is able to search for sterile antineutrinos by looking for the disappearance of muon antineutrinos over its 734 km baseline. The sterile antineutrino signature would be seen as modulations at high energy in the charged-current muon antineutrino spectrum. We present the first MINOS results constraining 3+1 sterile antineutrino oscillations, using a combination of 3.36×1020 protons-on-target (POT) of antineutrino-enhanced beam data, and 10.56×1020 protons-on-target (POT) of neutrino-dominated beam data. These results are compared with existing constraints and future improvements to the searches are discussed.

First oscillation analysis using neutrino and antineutrino data at T2K

We present details of the first T2K neutrino and antineutrino oscillation results, in which data collected using both a muon neutrino-enhanced neutrino beam and a muon antineutrino-enhanced neutrino beam are analysed, equating to 7.002×1020 protons on target (POT) and 7.471×1020 POT respectively. Both disappearance and appearance data are analysed using a Bayesian Markov Chain Monte Carlo method, providing the first ever sensitivity to the CP-violating phase δCP from T2K data alone. The T2K data favour near-maximal mixing, with sin2 θ23 and consistent with previous T2K measurements, a value of sin2 θ13 consistent with measurements by reactor experiments, and δCP close to -π/2. When fitting with T2K data alone, the 90% credible interval for δCP disfavours values around π/2: δCP ∉ [0.38, 2.60] rad. When using a prior on sin2 2θ13 from reactor measurements, the 90% credible interval contains δCP ∉ [−3.10, −0.17] rad, disfavouring the CP-conserving values 0 and ±π. The effect on this result of the δCP prior is also investigated and presented.

Physics sensitivity of a possible extended T2K run – T2K Phase 2

With recent suggestive physics results, compelling future physics opportunities, and the continued improvement of the J-PARC proton beam power, the T2K collaboration is proposing an extension of the T2K run from the currently approved full statistics of 7.8 × 1021 Protons-on-Target (POT) (expected by 2021) to 20 × 1021 POT (expected by 2027). The T2K collaboration also plans to increase the “effective” T2K Phase 2 statistics by improved analysis techniques and neutrino beamline hardware upgrades. The physics sensitivity of this extended run are shown, including the possibility of excluding sin δCP = 0 to 3σ or better in the case of maximal CP violation in the lepton sector. Improvements on the atmospheric neutrino oscillation parameter constraints will also be made by T2K Phase 2, where the final sensitivities depend on the true values of the oscillation parameters.

Reason for T2K to run in dominant neutrino mode for detectingCPviolation

The long-baseline experiment T2K in Japan has collected data in the neutrino mode corresponding to an exposure of $6.57 \times 10^{20}$ POT (Protons on Target) and currently it is running in the antineutrino mode. The main aim of the antineutrino run is to measure the leptonic phase $\delta_{CP}$ which may help to understand the matter-antimatter asymmetry of the universe. In this work we show that in T2K, antineutrinos are required only for removing the wrong octant solutions which in turn improves the CP sensitivity. If however the octant is known then pure neutrino run is capable of giving the maximum CP sensitivity. If we divide the total true parameter space into eight sets, then we find that T2K antineutrino run helps in improving the CP sensitivity for only two sets while for the remaining six combinations pure neutrino run gives the best CP sensitivity. Thus if the neutrino run is replaced by the antineutrino run then it causes a reduction in the CP sensitivity in 75$\%$ of the true parameter space due to lesser statistics. Thus it is worthwhile to study if the T2K antineutrino run can be reduced by the antineutrino runs of the other experiments, so that T2K can run in dominant neutrino mode to extract the best CP sensitivity. In this work we explore the possibility of the antineutrino component of NO$\nu$A and the atmospheric neutrino experiment ICAL@INO for compensating the antineutrino run of T2K.

Neutrino oscillations with MINOS and MINOS+

The MINOS experiment ran from 2003 until 2012 and collected a data sample including 10.71×1020 protons-on-target (POT) of beam neutrinos, 3.36×1020 POT of beam antineutrinos and an atmospheric neutrino exposure of 37.88 kt yrs. The final measurement of the atmospheric neutrino oscillation parameters, Δm322 and θ23, came from a full three flavour oscillation analysis of the combined CC νμ and CC ν‾μ beam and atmospheric samples and the CC νe and CC ν‾e appearance samples. This analysis yielded the most precise measurement of the atmospheric mass splitting Δm322 performed to date. The results are |Δm322|=[2.28–2.46]×10−3 eV2 (68%) and sin2⁡θ23=0.35–0.65 (90%) in the normal hierarchy, and |Δm322|=[2.32–2.53]×10−3 eV2 (68%) and sin2⁡θ23=0.34–0.67 (90%) in the inverted hierarchy. The successor to MINOS in the NOνA era at FNAL, MINOS+, is now collecting data mostly in the 3–10 GeV region, and an analysis of νμ disappearance using the first 2.99×1020 POT of data produced results very consistent with those from MINOS. Future data will further test the standard neutrino oscillation paradigm and allow for improved searches for exotic phenomena including sterile neutrinos, large extra dimensions and non-standard interactions.

Physics potential of neutrino oscillation experiment with a far detector in Oki Island along the T2K baseline

Oki Island is located between Japan and Korea along the Tokai-To-Kamioka (T2K) baseline. The distance from J-PARC to Oki Island is about 653km, which is twice that of the T2K experiment (L=295km). When the off-axis angle of the neutrino beam from J-PARC is 3.0^\circ (2.0^\circ) at Super-Kamiokande (SK), the off-axis beam (OAB) with 1.4^\circ (0.6^\circ) reaches at Oki Island. We examine physics case of placing a far detector in Oki Island during the T2K experimental period. We estimate the matter density profile along the Tokai-to-Oki baseline by using recent seismological measurements. For a detector of 100kton fiducial volume and 2.5x10^21 POT (protons on target) exposure for both \nu_\mu and \bar{\nu}_\mu beams, we find that the mass hierarchy pattern can be distinguished at 3\sigma level if sin^22theta_rct \equiv 4|U_{e3}|^2(1-|U_{e3}|^2) \gsim 0.09, by observing the electron-like CCQE (Charged-Current Quasi Elastic) events. The CP phase in the Maki-Nakagawa-Sakata lepton flavor mixing matrix, \delta_mns, can be constrained with \pm 20^\circ. As a reference, we repeat the same analysis by placing the same detector in Korea at L=1000km and OAB=0.5^\circ (T2KK) and also by placing it at the SK site (T2K_122). The Tokai-to-Kamioka-OKI (T2KO) sensitivity to the mass hierarchy is about 1/3 (in \Delta \chi^2_min) of T2KK, while the sensitivity to the phase \delta_mns is similar between T2KO and T2KK. The T2K_122 option has almost no sensitivity to the mass hierarchy, and cannot measure the CP phase except when \delta_mns \sim -90^\circ (90^\circ) for the normal (inverted) hierarchy.

Improved statistics in the search for [formula omitted] oscillations in MiniBooNE

A search for ν¯μ→ν¯e oscillations in the MiniBooNE experiment at Fermilab has been completed using 11.27×1020 protons on target (POT), roughly doubling the statistics over prior published results. An excess of 78±30.8 events is observed in the signal region. The results from the fit to a simple two-neutrino mixing hypothesis are reported for the full antineutrino data sample and compared to prior results acquired with a neutrino beam. A simultaneous fit to both samples is performed fully accounting for systematic correlations, resulting in a 3.8σ overall excess of 240.3±34.5(stat)±52.6(syst) events.

Improved statistics in the search for [formula omitted] appearing in an [formula omitted] beam in the MiniBooNE detector

The MiniBooNE experiment at Fermi National Accelerator Laboratory recently updated a search for ν ¯ e appearing in an ν ¯ μ beam to include higher statistics. Previous results were published with a total of 3.39 × 10 20 protons on target (POT) [A.A. Aguilar-Arevalo, et al., Phys. Rev. Lett. 103 (2009) 111801, arXiv:0904.1958 ], while these results have been expanded to include a total of 5.66 × 10 20 POT [A.A. Aguilar-Arevalo, et al., Phys. Rev. Lett. 105 (2010) 181801, arXiv:1007.1150 ]. An excess of 20.9 ± 14.0 events is observed in the energy range from 475 E ν Q E cance of the excess peaking at 25.7 ± 7.2 in the lowest two energy bins 475 − 675 MeV . The consistency with the background-only hypothesis in the 475 − 1250 MeV region is 0.5%, after constraints from the measured ν ¯ μ spectrum have been applied. A fit to a 2ν-mixing hypothesis yields a best-fit point at ( Δ m 2 , s i n 2 2 θ ) = ( 0.064 eV 2 , 0.96 ) , although the 1σ allowed region encompasses a range of Δ m 2 values up to 1 eV 2 at reduced values of s i n 2 2 θ . After Feldman-Cousins corrections [G. Feldman, R. Cousins, Phys. Rev. D 57 (1998) 3873–3889, arXiv:physics/9711021 ], it is found that the best-fit is preferred at a 99.4% C.L. over a background-only hypothesis, with an absolute goodness-of-fit of 8.7%

Re-evaluation of the T2KK physics potential with simulations including backgrounds

The Tokai-to-Kamioka-and-Korea (T2KK) neutrino oscillation experiment under examination can have a high sensitivity to determine the neutrino mass hierarchy for a combination of relatively large ( ∼ 3.0°) off-axis angle beam at Super-Kamiokande (SK) and small ( ∼ 0.5°) off-axis angle at L ∼ 1,000 km in Korea. We elaborate previous studies by taking into account smearing of reconstructed neutrino energy due to finite resolution of electron or muon energies, nuclear Fermi motion and resonance production, as well as the neutral current π0 production background to the νμ → νe oscillation signal. It is found that the mass hierarchy pattern can still be determined at 3σ level if sin22θRCT ≡ 4|Ue3|2(1 − |Ue3|2) ≳ 0.08(0.09) when the hierarchy is normal (inverted) with 5 × 1021} POT (protons on target) exposure, or 5 years of the T2K experiment, if a 100 kton water Čerenkov detector is placed in Korea. The π0 backgrounds deteriorate the capability of the mass hierarchy determination, whereas the events from CC nuclear resonance productions contribute positively to the hierarchy discrimination power. We also find that the π0 backgrounds seriously affect the CP phase measurement. Although δMNS can still be constrained with an accuracy of ∼ ±45° (±60°) at 1σ level for the normal (inverted) hierarchy with the above exposure if sin22θRCT ≳ 0.04, CP violation can no longer be established at 3σ level even for δMNS = ±90° and sin22θRCT = 0.1. About four times higher exposure will be needed to measure δMNS with ±30° accuracy.

The SciBooNE Experiment at FNAL

The SciBooNE experiment is designed to measure neutrino cross sections on carbon around 1 GeV region. This article introduces the SciBooNE experiment and reports on the current status of a cross section measurement of the neutral current neutral pion production. We used 0.99 × 10 20 protons on target (POT) for this measurement. After event selections, about 450 signal events are estimated in the Monte Carlo(MC) simulation.

Status of the FNAL SciBooNE experiment

SciBooNE is a new experiment at FNAL which will make precision neutrino-nucleus cross section measurements in the one GeV region. These measurements are essential for the future neutrino oscillation experiments. We started data taking in the antineutrino mode on June 8, 2007, and collected 5.19 × 1019 protons on target (POT) before the accelerator shutdown in August. The first data from SciBooNE are reported in this article.

K2K far detector analysis

The far detector analysis for ν μ disappearance in the KEK to Kamioka (K2K) long-baseline neutrino oscillation experiment is presented. The data used for this analysis is 8.9 × 10 19 protons on target (POT). A total of 107 events are observed in the far detector, Super-Kamiokande (SK), while 151 −10 +12 are expected without ν μ oscillation. Spectral distortion of the reconstructed neutrino energy (E ν ) is also observed, and it is consistent with ν μ − ν τ oscillation. The two-flavor ν μ − ν τ oscillation analysis is evaluated. We obtain an allowed region which is consistent with SK atmospheric neutrino oscillation analysis results. The probability to observe our results from a statistical fluctuation is 0.005% (4.0 σ ) in the case of no oscillation.

Recent results from K2K

The result for ν μ oscillation analysis in the KEK to Kamioka (K2K) long-baseline neutrino oscillation experiment are presented. The data used for this analysis is 8.9 × 1019 protons on target (POT). A total of 107 events are observed in the far detector, Super-Kamiokande (SK), while 151 −10 +12 expected if ν μ oscillation is not assumed. The spectrum distortion of the reconstructed neutrino energy (Eν) is also observed, and it is consistent with the ν μ − ν τ oscillation. The two-flavor ν μ - ν τ oscillation analysis is evaluated. We obtained the allowed region which is consistent with SK atmospheric neutrino oscillation analysis results. The probability to get these results without neutrino oscillation is 0.005% (4.0σ).