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We present a new design study of the neutrino Super Beam based on the Superconducting Proton Linac at CERN. This beam is aimed at megaton mass physics, a large water Cherenkov detector, proposed for the Laboratoire Souterrain de Modane in France, with a baseline of 130 km. The aim of this proposed facility is to study CP violation in the neutrino sector. In the study reported here, we have developed the conceptual design of the neutrino beam, especially the target and the magnetic focusing device. Indeed, this beam presents several unprecedented challenges, related to the high primary proton beam power (4 MW), the high repetition rate (50 Hz), and the low kinetic energy of the protons (4.5 GeV). The design is completed by a study of all the main components of the system, starting from the transport system to guide the beam to the target up to the beam dump. This is the first complete study of a neutrino beam based on a pebble-bed target capable of standing the large heat deposition of MW class proton beams.

In the framework of the EUROnu design study, a new design for the CERN to Fréjus neutrino beam based on the SPL is under development by the WP2 group. The main challenge of this project lies with the design of a multi-MW neutrino beam facility. The horn and the decay tunnel parameters have been optimized to maximize any potential discovery. The target design, thermo-mechanical analysis, and power supply design of the horn system as well as any safety issues are being studied to meet the MW power requirements for the proton-beam.

Neutrino oscillation experiments provide a unique window in exploring several new physics scenarios beyond the standard three flavour. One such scenario is quantum decoherence in neutrino oscillation which tends to destroy the interference pattern of neutrinos reaching the far detector from the source. In this work, we study the decoherence in neutrino oscillation in the context of the ESSnuSB experiment. We consider the energy-independent decoherence parameter and derive the analytical expressions for P\\(_ e\\) and P\\(_ \\) probabilities in vacuum. We have computed the capability of ESSnuSB to put bounds on the decoherence parameters namely, \\(_21\\) and \\(_32\\) and found that the constraints on \\(_21\\) are competitive compared to the DUNE bounds and better than the most stringent LBL ones from MINOS/MINOS+. We have also investigated the impact of decoherence on the ESSnuSB measurement of the Dirac CP phase \\(_ CP\\) and concluded that it remains robust in the presence of new physics.

The ESSnuSB experiment aims to measure the leptonic CP phase \\(\\delta_{CP}\\) with an unprecedented resolution by probing neutrino oscillations at the second oscillation maximum. In the present work, the complementarity between the long-baseline neutrino program and atmospheric neutrinos is investigated for ESSnuSB. By simulating atmospheric neutrino events equivalent of 5.4 Mt\\(\\cdot\\)year exposure, the resolution for \\(\\delta_{\\rm CP}^{}\\) is found to improve from \\(7.5^\\circ\\) (\\(6.7^\\circ\\)) to \\(7.1^\\circ\\) (\\(6.5^\\circ\\)) at \\(1\\sigma\\)~CL for \\(\\delta_{\\rm CP}^{} = -90^\\circ\\) (\\(+90^\\circ\\)) with respect to super-beam neutrinos, resolving also the degeneracies arising from neutrino mass ordering. These findings highlight the synergies that exist between super-beam neutrinos and atmospheric neutrinos in ESSnuSB.

Atmospheric neutrinos provide a unique avenue to study neutrino interactions in matter. In this work, the prospects of constraining non-standard neutrino interactions with atmospheric neutrino oscillations are investigated for the proposed ESSnuSB far detector. By analyzing atmospheric neutrino samples equivalent to 5.4 Mt\\(\\cdot\\)year exposure, it is found that ESSnuSB could be able to set the upper bounds \\(|\\epsilon_{e\\mu}^m| < 0.053, |\\epsilon_{e\\tau}^m| < 0.057, |\\epsilon_{\\mu\\tau}^m| < 0.021, \\epsilon_{ee}^m - \\epsilon_{\\mu\\mu}^m < 0.075\\) and \\(|\\epsilon_{\\tau\\tau}^m - \\epsilon_{\\mu\\mu}^m| < 0.031\\) at \\(90\\%\\) CL, when the results are minimized for \\(\\phi_{e\\mu}^m, \\phi_{e\\tau}^m\\) and \\(\\phi_{\\mu\\tau}^m\\) and normal ordering is assumed for neutrino masses. It is also shown that the presence of non-standard interactions could affect the sensitivities to neutrino mass ordering and \\(\\theta_{23}^{}\\) octant in comparison to the standard interaction scheme. The results of this work highlight the complementarity between atmospheric and accelerator neutrino programs in ESSnuSB.

Neutrino oscillations constitute an excellent tool to probe physics beyond the Standard Model. In this paper, we investigate the potential of the ESSnuSB experiment to constrain the effects of flavour-dependent long-range forces (LRFs) in neutrino oscillations, which may arise due to the extension of the Standard Model gauge group by introducing new \\(U(1)\\) symmetries. Focusing on three specific \\(U(1)\\) symmetries -- \\(L_e - L_\\), \\(L_e - L_\\), and \\(L_ - L_\\), we demonstrate that ESSnuSB offers a favourable environment to search for LRF effects. Our analyses reveal that ESSnuSB can set \\(90\\%\\) confidence level bounds of \\(V_e < 2.99 10^-14 \\, eV\\), \\(V_e < 2.05 10^-14 \\, eV\\), and \\(V_ < 1.81 10^-14 \\, eV\\), which are competitive to the upcoming Deep Underground Neutrino Experiment (DUNE). It is also observed that reducing the systematic uncertainties from \\(5\\%\\) to \\(2\\%\\) improves the ESSnuSB limits on \\(V_\\). Interestingly, we find limited correlations between LRF parameters and the less constrained lepton mixing parameters \\(_23\\) and \\(_CP\\), preserving the robustness of ESSnuSB's sensitivity to CP violation. Even under extreme LRF potentials (\\(V_ 10^-13 \\, eV\\)), the CP-violation sensitivity and \\(_CP\\) precision remain largely unaffected. These results establish ESSnuSB as a competitive experimental setup for probing LRF effects, complementing constraints from other neutrino sources and offering critical insights into the physics of long-range forces.

In the effort to obtain a precise measurement of leptonic CP-violation with the ESS\\(\\nu\\)SB experiment, accurate and fast reconstruction of detector events plays a pivotal role. In this work, we examine the possibility of replacing the currently proposed likelihood-based reconstruction method with an approach based on Graph Neural Networks (GNNs). As the likelihood-based reconstruction method is reasonably accurate but computationally expensive, one of the benefits of a Machine Learning (ML) based method is enabling fast event reconstruction in the detector development phase, allowing for easier investigation of the effects of changes to the detector design. Focusing on classification of flavour and interaction type in muon and electron events and muon- and electron neutrino interaction events, we demonstrate that the GNN reconstructs events with greater accuracy than the likelihood method for events with greater complexity, and with increased speed for all events. Additionally, we investigate the key factors impacting reconstruction performance, and demonstrate how separation of events by pion production using another GNN classifier can benefit flavour classification.

This study provides an analysis of atmospheric neutrino oscillations at the ESSnuSB far detector facility. The prospects of the two cylindrical Water Cherenkov detectors with a total fiducial mass of 540 kt are investigated over 10 years of data taking in the standard three-flavor oscillation scenario. We present the confidence intervals for the determination of mass ordering, \\(\\theta_{23}\\) octant as well as for the precisions on \\(\\sin^2\\theta_{23}\\) and \\(|\\Delta m_{31}^2|\\). It is shown that mass ordering can be resolved by \\(3\\sigma\\) CL (\\(5\\sigma\\) CL) after 4 years (10 years) regardless of the true neutrino mass ordering. Correspondingly, the wrong \\(\\theta_{23}\\) octant could be excluded by \\(3\\sigma\\) CL after 4 years (8 years) in the case where the true neutrino mass ordering is normal ordering (inverted ordering). The results presented in this work are complementary to the accelerator neutrino program in the ESSnuSB project.

In this paper we study non-standard interactions mediated by a scalar field (SNSI) in the context of ESSnuSB experiment. In particular we study the capability of ESSnuSB to put bounds on the SNSI parameters and also study the impact of SNSI in the measurement of the leptonic CP phase \\(\\delta_{\\rm CP}\\). Existence of SNSI modifies the neutrino mass matrix and this modification can be expressed in terms of three diagonal real parameters (\\(\\eta_{ee}\\), \\(\\eta_{\\mu\\mu}\\) and \\(\\eta_{\\tau\\tau}\\)) and three off-diagonal complex parameters (\\(\\eta_{e \\mu}\\), \\(\\eta_{e\\tau}\\) and \\(\\eta_{\\mu\\tau}\\)). Our study shows that the upper bounds on the parameters \\(\\eta_{\\mu\\mu}\\), \\(\\eta_{\\tau\\tau}\\) and \\(\\eta_{\\mu\\tau}\\) depend upon how \\(\\Delta m^2_{31}\\) is minimized in the theory. However, this is not the case when one tries to measure the impact of SNSI on \\(\\delta_{\\rm CP}\\). Further, we show that the CP sensitivity of ESSnuSB can be completely lost for certain values of \\(\\eta_{ee}\\) and \\(\\eta_{\\mu\\tau}\\) for which the appearance channel probability becomes independent of \\(\\delta_{\\rm CP}\\).

The power supply studies for the four-horn system for the CERN to Fréjus neutrino Super Beam oscillation experiment are discussed here. The power supply is being studied to meet the physics potential and the mega-watt (MW) power requirements of the proton driver of the Super Beam. A one-half sinusoid current waveform with a 350 kA maximum current and pulse length of 100 \\mu s at 50 Hz frequency is generated and distributed to four-horns. In order to provide the necessary current needed to focus the charged mesons producing the neutrino beam, a bench of capacitors is charged at 50 Hz frequency to a +12 kV reference voltage and then discharged through a large switch to each horn via a set of strip-lines at the same rate. A current recovery stage allows to invert rapidly the negative voltage of the capacitor after the discharging stage in order to recuperate large part of the injected energy and thus to limit the power consuption. The energy recovery efficiency of that system is very high at 97%. For feasibility reasons, a modular architecture has been adopted with 8 modules connected in parallel to deliver 44 kA peak currents into the four-horn system.