A. Blanchet’s research while affiliated with University of Geneva and other places

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Publications (52)


FIG. 1. The (sin 2 θ 23 , δ CP ) credible regions obtained with the SK, T2K, and combined datasets. The MO is marginalized over and a prior uniform in δ CP is used.
FIG. 2. Posterior density for the Jarlskog invariant with credible intervals overlaid, marginalized over both MOs, and assuming a uniform prior in either δ CP or sin δ CP . The left edges of the intervals are close to each other in the region −0.033 ≤ J CP ≤ −0.035.
FIG. 3. Distribution of the MO test statistic under true normal (NO) and inverted (IO) ordering hypotheses. The filled areas to the left (right) of the data result indicate the p values for the inverted (normal) hypotheses.
FIG. 4. Sensitivity to reject the CP-conserving hypothesis for different true values of δ CP assuming the normal MO. Other oscillation parameters are set to sin 2 θ 23 ¼ 0.528, sin 2 θ 13 ¼ 0.0218, and Δm 2 32 ¼ 2.509 × 10 −3 eV 2 .
First Joint Oscillation Analysis of Super-Kamiokande Atmospheric and T2K Accelerator Neutrino Data
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  • Full-text available

January 2025

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53 Reads

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3 Citations

Physical Review Letters

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S. Abe

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C. Bronner

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M. Zito

The Super-Kamiokande and T2K Collaborations present a joint measurement of neutrino oscillation parameters from their atmospheric and beam neutrino data. It uses a common interaction model for events overlapping in neutrino energy and correlated detector systematic uncertainties between the two datasets, which are found to be compatible. Using 3244.4 days of atmospheric data and a beam exposure of 19.7 ( 16.3 ) × 10 20 protons on target in (anti)neutrino mode, the analysis finds a 1.9 σ exclusion of C P conservation (defined as J C P = 0 ) and a 1.2 σ exclusion of the inverted mass ordering. Published by the American Physical Society 2025

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Role of deexcitation in the final-state interactions of protons in neutrino-nucleus interactions

December 2023

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37 Reads

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9 Citations

Physical Review D

Present and next generation of long-baseline accelerator experiments are bringing the measurement of neutrino oscillations into the precision era with ever-increasing statistics. One of the most challenging aspects of achieving such measurements is developing relevant systematic uncertainties in the modeling of nuclear effects in neutrino-nucleus interactions. To address this problem, state-of-the-art detectors are being developed to extract detailed information about all particles produced in neutrino interactions. To fully profit from these experimental advancements, it is essential to have reliable models of propagation of the outgoing hadrons through nuclear matter able to predict how the energy is distributed between all the final-state observed particles. In this article, we investigate the role of nuclear deexcitation in neutrino-nucleus scattering using two Monte Carlo cascade models: NuWro and INCL coupled with the deexcitation code ABLA. The ablation model ABLA is used here for the first time to model deexcitation in neutrino interactions. As input to ABLA, we develop a consistent simulation of nuclear excitation energy tuned to electron-scattering data. The paper includes the characterization of the leading proton kinematics and of the nuclear cluster production during cascade and deexcitation. The observability of nuclear clusters as vertex activity and their role in a precise neutrino energy reconstruction is quantified.


First measurement of muon neutrino charged-current interactions on hydrocarbon without pions in the final state using multiple detectors with correlated energy spectra at T2K

December 2023

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135 Reads

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5 Citations

Physical Review D

This paper reports the first measurement of muon neutrino charged-current interactions without pions in the final state using multiple detectors with correlated energy spectra at T2K. The data was collected on hydrocarbon targets using the off-axis T2K near detector (ND280) and the on-axis T2K near detector (INGRID) with neutrino energy spectra peaked at 0.6 GeV and 1.1 GeV, respectively. The correlated neutrino flux presents an opportunity to reduce the impact of the flux uncertainty and to study the energy dependence of neutrino interactions. The extracted double-differential cross sections are compared to several Monte Carlo neutrino-nucleus interaction event generators showing the agreement between both detectors individually and with the correlated result.


Measurements of the ν μ and ν ¯ μ -induced coherent charged pion production cross sections on C 12 by the T2K experiment

November 2023

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73 Reads

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1 Citation

Physical Review D

We report an updated measurement of the νμ-induced, and the first measurement of the ν¯μ-induced coherent charged pion production cross section on C12 nuclei in the Tokai-to-Kamioka experiment. This is measured in a restricted region of the final-state phase space for which pμ,π>0.2 GeV, cos(θμ)>0.8 and cos(θπ)>0.6, and at a mean (anti)neutrino energy of 0.85 GeV using the T2K near detector. The measured νμ charged current coherent pion production flux-averaged cross section on C12 is (2.98±0.37(stat)±0.31(syst)−0.00+0.49(Q2 model))×10−40 cm2. The new measurement of the ν¯μ-induced cross section on C12 is (3.05±0.71(stat)±0.39(syst)−0.00+0.74(Q2 model))×10−40 cm2. The results are compatible with both the NEUT 5.4.0 Berger-Sehgal (2009) and GENIE 2.8.0 Rein-Sehgal (2007) model predictions.


Updated T2K measurements of muon neutrino and antineutrino disappearance using 3.6 × 10 21 protons on target

October 2023

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76 Reads

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17 Citations

Physical Review D

Muon neutrino and antineutrino disappearance probabilities are identical in the standard three-flavor neutrino oscillation framework, but CPT violation and nonstandard interactions can violate this symmetry. In this work we report the measurements of sin2θ23 and Δm322 independently for neutrinos and antineutrinos. The aforementioned symmetry violation would manifest as an inconsistency in the neutrino and antineutrino oscillation parameters. The analysis discussed here uses a total of 1.97×1021 and 1.63×1021 protons on target taken with a neutrino and antineutrino beam respectively, and benefits from improved flux and cross section models, new near-detector samples and more than double the data reducing the overall uncertainty of the result. No significant deviation is observed, consistent with the standard neutrino oscillation picture.


FIG. 2: Missing energy profile extracted from the hole spectral function of Carbon [26]. The area under the "SF profile" distribution is normalized to one. The highlighted area, labelled "1p 3/2 ", represents the expected contribution of valence nucleons, as described in the text.
FIG. 5: Average number of particles produced per event for INCL, INCL coupled with ABLA and NuWro. NuWro produces only protons and neutrons.
The role of de-excitation in the final-state interactions of protons in neutrino-nucleus interactions

September 2023

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65 Reads

Present and next generation of long-baseline accelerator experiments are bringing the measurement of neutrino oscillations into the precision era with ever-increasing statistics. One of the most challenging aspects of achieving such measurements is developing relevant systematic uncertainties in the modeling of nuclear effects in neutrino-nucleus interactions. To address this problem, state-of-the-art detectors are being developed to extract detailed information about all particles produced in neutrino interactions. To fully profit from these experimental advancements, it is essential to have reliable models of propagation of the outgoing hadrons through nuclear matter able to predict how the energy is distributed between all the final-state observed particles. In this article, we investigate the role of nuclear de-excitation in neutrino-nucleus scattering using two Monte Carlo cascade models: NuWro and INCL coupled with the de-excitation code ABLA. The ablation model ABLA is used here for the first time to model de-excitation in neutrino interactions. As input to ABLA, we develop a consistent simulation of nuclear excitation energy tuned to electron-scattering data. The paper includes the characterization of the leading proton kinematics and of the nuclear cluster production during cascade and de-excitation. The observability of nuclear clusters as vertex activity and their role in a precise neutrino energy reconstruction is quantified.


Measurements of neutrino oscillation parameters from the T2K experiment using 3.6×10213.6\times 10^{21} protons on target

September 2023

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239 Reads

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110 Citations

The European Physical Journal C

The T2K experiment presents new measurements of neutrino oscillation parameters using 19.7(16.3)×1020 protons on target (POT) in (anti-)neutrino mode at the far detector (FD). Compared to the previous analysis, an additional 4.7×1020 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 sin2θ13 and the impact of priors on the δCP measurement. Both analyses prefer the normal mass ordering and upper octant of sin2θ23 with a nearly maximally CP-violating phase. Assuming the normal ordering and using the constraint on sin2θ13 from reactors, sin2θ23=0.561-0.032+0.021 using Feldman-Cousins corrected intervals, and Δm322=2.494-0.058+0.041×10-3eV2 using constant Δχ2 intervals. The CP-violating phase is constrained to δCP=-1.97-0.70+0.97 using Feldman-Cousins corrected intervals, and δCP=0,π is excluded at more than 90% confidence level. A Jarlskog invariant of zero is excluded at more than 2σ credible level using a flat prior in δCP, and just below 2σ using a flat prior in sinδCP. When the external constraint on sin2θ13 is removed, sin2θ13=28.0-6.5+2.8×10-3, in agreement with measurements from reactor experiments. These results are consistent with previous T2K analyses.


FIG. 1. Feynman diagram for coherent charged pion production from a neutrino off a nucleus. This is specific to the PCAC class of models. The square of the magnitude of the 4-momentum transfer to the nucleus is |pA| 2 = |q − pπ| 2 = |t|.
FIG. 3. νµ data, nominal Monte Carlo (MC) simulation (pre-fit), and post-fit Monte Carlo simulation comparisons in VA, |t|, Q 2 , pπ, and cos(θπ). The stacked histograms represent the true reaction types of the events. The smaller post-fit χ 2 stat.
FIG. 4. ¯ νµ data, nominal Monte Carlo (MC) simulation (pre-fit), and post-fit Monte Carlo simulation comparisons in VA, |t|, Q 2 , pπ, and cos(θπ). The stacked histograms represent the true reaction types of the events. The post-fit χ 2 stat. are not changed as much as in the νµ case due to lower statistics. As with the νµ case, only the VA distribution is statistically incompatible with the data. Note that the fit does not consider these distributions, but only sees a single bin for the signal sample.
Measurements of the νμ\nu_{\mu} and νˉμ\bar{\nu}_{\mu}-induced Coherent Charged Pion Production Cross Sections on 12C^{12}C by the T2K experiment

August 2023

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126 Reads

We report an updated measurement of the νμ\nu_{\mu}-induced, and the first measurement of the νˉμ\bar{\nu}_{\mu}-induced coherent charged pion production cross section on 12C^{12}C nuclei in the T2K experiment. This is measured in a restricted region of the final-state phase space for which pμ,π>0.2p_{\mu,\pi} > 0.2 GeV, cos(θμ)>0.8\cos(\theta_{\mu}) > 0.8 and cos(θπ)>0.6\cos(\theta_{\pi}) > 0.6, and at a mean (anti)neutrino energy of 0.85 GeV using the T2K near detector. The measured νμ\nu_{\mu} CC coherent pion production flux-averaged cross section on 12C^{12}C is (2.98±0.37(stat.)±0.31(syst.)+0.490.00(Q2model))×1040 cm2(2.98 \pm 0.37 (stat.) \pm 0.31 (syst.) \substack{ +0.49 \\ -0.00 } \mathrm{ (Q^2\,model)}) \times 10^{-40}~\mathrm{cm}^{2}. The new measurement of the νˉμ\bar{\nu}_{\mu}-induced cross section on 12C^{12}{C} is (3.05±0.71(stat.)±0.39(syst.)+0.740.00(Q2model))×1040 cm2(3.05 \pm 0.71 (stat.) \pm 0.39 (syst.) \substack{ +0.74 \\ -0.00 } \mathrm{(Q^2\,model)}) \times 10^{-40}~\mathrm{cm}^{2}. The results are compatible with both the NEUT 5.4.0 Berger-Sehgal (2009) and GENIE 2.8.0 Rein-Sehgal (2007) model predictions.



Updated T2K measurements of muon neutrino and antineutrino disappearance using 3.6 ×\times 1021^{21} protons on target

May 2023

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88 Reads

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2 Citations

Muon neutrino and antineutrino disappearance probabilities are identical in the standard three-flavor neutrino oscillation framework, but CPT violation and non-standard interactions can violate this symmetry. In this work we report the measurements of sin2θ23\sin^{2} \theta_{23} and Δm322\Delta m_{32}^2 independently for neutrinos and antineutrinos. The aforementioned symmetry violation would manifest as an inconsistency in the neutrino and antineutrino oscillation parameters. The analysis discussed here uses a total of 1.97×\times1021^{21} and 1.63×\times1021^{21} protons on target taken with a neutrino and antineutrino beam respectively, and benefits from improved flux and cross-section models, new near detector samples and more than double the data reducing the overall uncertainty of the result. No significant deviation is observed, consistent with the standard neutrino oscillation picture.


Citations (27)


... Various accelerator experiments [10], such as Minos [11] and T2K [12], produce beams of ν µ or ν µ by accelerating and colliding protons into a target. Likewise, cosmic rays (usually protons) interact with other nuclei in the atmosphere, mostly producing muonic (anti-)neutrinos [13], which are detected by experiments such as IceCube [14] and Super-Kamiokande [15,16]. In these contexts, the survival probability P µµ is useful and can be derived from Eq. (5): ...

Reference:

Analytical Expressions for Neutrino Oscillation
First Joint Oscillation Analysis of Super-Kamiokande Atmospheric and T2K Accelerator Neutrino Data

Physical Review Letters

... It is a nuclear shell model built largely from electron scattering data, and allows a detailed description of the initial nuclear state. Through its implementation in the NEUT neutrino-nucleus interaction event generator [9], the SF model is used in the T2K experiment's recent measurements of neutrino oscillations [10] and neutrino-nucleus cross sections [11][12][13][14]. It has also been used to study the sensitivity of T2K's neardetector upgrade [15]. ...

First measurement of muon neutrino charged-current interactions on hydrocarbon without pions in the final state using multiple detectors with correlated energy spectra at T2K

Physical Review D

... Given the significant physics potential of TKI measurements, a wealth of literature has emerged on the combined analysis of T2K and MINERvA CC0π TKI data [11,[31][32][33][34][35][36][37]. However, model studies incorporating TKI data with pion production have been notably absent. ...

Role of deexcitation in the final-state interactions of protons in neutrino-nucleus interactions

Physical Review D

... Cross section measurements of the ν µ CC-Cohπ process demonstrate the feasibility of requirement 3 (e.g., Ref. [17][18][19][20][21]). The DUNE ND will be a pixelated liquid argon time projection chamber (LArTPC) [1], which projects to have a particularly strong ability to isolate this process. ...

Measurements of the ν μ and ν ¯ μ -induced coherent charged pion production cross sections on C 12 by the T2K experiment

Physical Review D

... Nevertheless, the use of matter effects in neutrino oscillations has been guiding most of the experimental efforts. The long-baseline accelerator neutrino experiments NOvA [20] and T2K [21] as well as the atmospheric neutrinos experiments Super-Kamiokande [22], Ice-Cube [23], and KM3NeT/ORCA [24], operate in a regime where neutrino oscillations are mostly driven by the higher mass-squared splitting and matter effects are significant in the ν μ → ν e (and antineutrino) appearance probabilities. They are responsible for the current status of our understanding of the MO question. ...

Updated T2K measurements of muon neutrino and antineutrino disappearance using 3.6 × 10 21 protons on target

Physical Review D

... Providing those answers, with the determination of the neutrino mass ordering by clarifying the sign of ∆m 2 31 and the precise measurement of the δ CP -phase to investigate the presence of CP violation in the leptonic sector, would open a way to explore new physics. While the quark mixing matrix has been extensively tested with robust precision, the unitarity of the PMNS matrix, assumed in many oscillation analyses [4,5], still has to be experimentally proven. Under the PMNS matrix unitarity hypothesis, solar [6,7], reactor [8][9][10][11], and atmospheric [1,12,13] neutrino experiments mostly exploited the ν e ,ν e , and ν µ ,ν µ disappearance channels, whereas the high-statistics in ν e andν e appearance channels have been investigated in long-baseline accelerator experiments [4,5]. ...

Measurements of neutrino oscillation parameters from the T2K experiment using 3.6×10213.6\times 10^{21} protons on target

The European Physical Journal C

... To fully read a single ERAM module, two FECs are required, which are directly mounted onto the detector PCB. When the AFTER chip is fed with a Dirac current pulse ( ) = ( ), its response, prior to late discretization stage is proportional to the function [4]: ...

Characterization of charge spreading and gain of encapsulated resistive Micromegas detectors for the upgrade of the T2K Near Detector Time Projection Chambers
  • Citing Article
  • August 2023

Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment

... The T2K Near Detector Upgrade Stefan Roth Figure 1: The measurement of the Bragg peak of stopping protons (left) and the result of the dE/dx analysis for tracks of different particle types (right) [5] All Micromegas modules were characterized on a X-ray test bench measuring for each individual readout pad the mean charge and the charge dispersion to adjacent pads [6]. The performances of TPC prototypes have been determined at the DESY test beam facility [7,8]. For all track angles relative to the pad geometry of the Micromegas modules and for all drift distances a spatial resolution of better than 800 m was achieved, as shown in Figure 2. Furthermore, a dE/dx resolution of better than 10 % was demonstrated. ...

Analysis of test beam data taken with a prototype of TPC with resistive Micromegas for the T2K Near Detector upgrade
  • Citing Article
  • April 2023

Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment

... To date, no data from hadron decays or meson mixing seems to require CP violation beyond the SM [6]. Conversely, CP violation in the lepton sector has not been discovered yet, although there are hints for it both in neutrino oscillation measurements by Nova [20] and T2K [21], and in global fits [6]. If confirmed, it would remain to be seen if it can be explained by the single CP violating phase that appears in the lepton analogue of the CKM matrix, the Pontecorvo-Maki-Nakagawa-Sakata matrix [22][23][24], or new physics is called for. ...

Measurements of neutrino oscillation parameters from the T2K experiment using 3.6×10213.6\times10^{21} protons on target