Sanjib Kumar Agarwalla

Invited review: Physics potential of the ICAL detector at the India-based Neutrino Observatory (INO)

The upcoming 50 kt magnetized iron calorimeter (ICAL) detector at the India-based Neutrino Observatory (INO) is designed to study the atmospheric neutrinos and antineutrinos separately over a wide range of energies and path lengths. The primary focus of this experiment is to explore the Earth matter effects by observing the energy and zenith angle dependence of the atmospheric neutrinos in the multi-GeV range. This study will be crucial to address some of the outstanding issues in neutrino oscillation physics, including the fundamental issue of neutrino mass hierarchy. In this document, we present the physics potential of the detector as obtained from realistic detector simulations. We describe the simulation framework, the neutrino interactions in the detector, and the expected response of the detector to particles traversing it. The ICAL detector can determine the energy and direction of the muons to a high precision, and in addition, its sensitivity to multi-GeV hadrons increases its physics reach substantially. Its charge identification capability, and hence its ability to distinguish neutrinos from antineutrinos, makes it an efficient detector for determining the neutrino mass hierarchy. In this report, we outline the analyses carried out for the determination of neutrino mass hierarchy and precision measurements of atmospheric neutrino mixing parameters at ICAL, and give the expected physics reach of the detector with 10 years of runtime. We also explore the potential of ICAL for probing new physics scenarios like CPT violation and the presence of magnetic monopoles.

Resolving the octant of theta23 with T2K and NOvA

A bstractPreliminary results of MINOS experiment indicate that θ23 is not maximal. Global fits to world neutrino data suggest two nearly degenerate solutions for θ23: one in the lower octant (LO: θ23 < 45◦) and the other in the higher octant (HO: θ23 > 45◦). νμ→ νe oscillations in superbeam experiments are sensitive to the octant and are capable of resolving this degeneracy. We study the prospects of this resolution by the current T2K and upcoming NOνA experiments. Because of the hierarchy-δCP degeneracy and the octant-δCP degeneracy, the impact of hierarchy on octant resolution has to be taken into account. As in the case of hierarchy determination, there exist favorable (unfavorable) values of δCP for which octant resolution is easy (challenging). However, for octant resolution the unfavorable δCP values of the neutrino data are favorable for the anti-neutrino data and vice-verse. This is in contrast to the case of hierarchy determination. In this paper, we compute the combined sensitivity of T2K and NOνA to resolve the octant ambiguity. If sin2θ23 = 0.41, then NOνA can rule out all the values of θ23 in HO at 2σ C.L., irrespective of the hierarchy and δCP. Addition of T2K data improves the octant sensitivity. If T2K were to have equal neutrino and anti-neutrino runs of 2.5 years each, a 2σ resolution of the octant becomes possible provided sin2θ23 ≤ 0.43 or ≥ 0.58 for any value of δCP.

Degeneracy between θ23 octant and neutrino non-standard interactions at DUNE

Abstract We expound in detail the degeneracy between the octant of θ 23 and flavor-changing neutral-current non-standard interactions (NSIs) in neutrino propagation, considering the Deep Underground Neutrino Experiment (DUNE) as a case study. In the presence of such NSI parameters involving the e − μ ( e e μ ) and e − τ ( e e τ ) flavors, the ν μ → ν e and ν ¯ μ → ν ¯ e appearance probabilities in long-baseline experiments acquire an additional interference term, which depends on one new dynamical CP-phase ϕ e μ / e τ . This term sums up with the well-known interference term related to the standard CP-phase δ creating a source of confusion in the determination of the octant of θ 23 . We show that for values of the NSI coupling (taken one at-a-time) as small as few % (relative to the Fermi coupling constant G F ), and for unfavorable combinations of the two CP-phases δ and ϕ e μ / e τ , the discovery potential of the octant of θ 23 gets completely lost.

Optimization of the Neutrino Factory, revisited

We perform the baseline and energy optimization of the Neutrino Factory including the latest simulation results on the magnetized iron detector (MIND). We also consider the impact of τ decays, generated by νμ → ντ or νe → ντ appearance, on the mass hierarchy, CP violation, and θ13 discovery reaches, which we find to be negligible for the considered detector. For the baseline-energy optimization for small sin2 2θ13, we qualitatively recover the results with earlier simulations of the MIND detector. We find optimal baselines of about 2500km to 5000km for the CP violation measurement, where now values of Eμ as low as about 12 GeV may be possible. However, for large sin2 2θ13, we demonstrate that the lower threshold and the backgrounds reconstructed at lower energies allow in fact for muon energies as low as 5 GeV at considerably shorter baselines, such as FNAL-Homestake. This implies that with the latest MIND analysis, low-and high-energy versions of the Neutrino Factory are just two different versions of the same experiment optimized for different parts of the parameter space. Apart from a green-field study of the updated detector performance, we discuss specific implementations for the two-baseline Neutrino Factory, where the considered detector sites are taken to be currently discussed underground laboratories. We find that reasonable setups can be found for the Neutrino Factory source in Asia, Europe, and North America, and that a triangular-shaped storage ring is possible in all cases based on geometrical arguments only.

Enhancing sensitivity to neutrino parameters at INO combining muon and hadron information

A bstractThe proposed ICAL experiment at INO aims to identify the neutrino mass hierarchy from observations of atmospheric neutrinos, and help improve the precision on the atmospheric neutrino mixing parameters. While the design of ICAL is primarily optimized to measure muon momentum, it is also capable of measuring the hadron energy in each event. Although the hadron energy is measured with relatively lower resolution, it nevertheless contains crucial information on the event, which may be extracted when taken concomitant with the muon data. We demonstrate that by adding the hadron energy information to the muon energy and muon direction in each event, the sensitivity of ICAL to the neutrino parameters can be improved significantly. Using the realistic detector response for ICAL, we present its enhanced reach for determining the neutrino mass hierarchy, the atmospheric mass squared difference and the mixing angle θ23, including its octant. In particular, we show that the analysis that uses hadron energy information can distinguish the normal and inverted mass hierarchies with Δχ2 ≈9 with 10 years exposure at the 50 kt ICAL, which corresponds to about 40% improvement over the muon-only analysis.

Physics reach of DUNE with a light sterile neutrino

A bstractWe investigate the implications of one light eV scale sterile neutrino on the physics potential of the proposed long-baseline experiment DUNE. If the future short-baseline experiments confirm the existence of sterile neutrinos, then it can affect the mass hierarchy (MH) and CP-violation (CPV) searches at DUNE. The MH sensitivity still remains above 5σ if the three new mixing angles (θ14, θ24, θ34) are all close to θ13. In contrast, it can decrease to 4σ if the least constrained mixing angle θ34 is close to its upper limit ∼ 300. We also assess the sensitivity to the CPV induced both by the standard CP-phase δ13 ≡ δ, and the new CP-phases δ14 and δ34. In the 3+1 scheme, the discovery potential of CPV induced by δ13 gets deteriorated compared to the 3ν case. In particular, the maximal sensitivity (reached around δ13 ∼ ± 900) decreases from 5σ to 4σ if all the three new mixing angles are close to θ13. It can further diminish to almost 3σ if θ34 is large (∼ 300). The sensitivity to the CPV due to δ14 can reach 3σ for an appreciable fraction of its true values. Interestingly, θ34 and its associated phase δ34 can influence both the νe appearance and νμ disappearance channels via matter effects, which in DUNE are pronounced. Hence, DUNE can also probe CPV induced by δ34 provided θ34 is large. We also reconstruct the two phases δ13 and δ14. The typical 1σ uncertainty on δ13 (δ14) is ∼ 200 (300) if θ34 = 0. The reconstruction of δ14 (but not that of δ13) degrades if θ34 is large.

Exploring the three flavor effects with future superbeams using liquid argon detectors

A bstractRecent measurement of a moderately large value of θ13 signifies an important breakthrough in establishing the standard three flavor oscillation picture of neutrinos. It has provided an opportunity to explore the sub-dominant three flavor effects in present and future long-baseline experiments. In this paper, we perform a comparative study of the physics reach of two future superbeam facilities, LBNE and LBNO in their first phases of run, to resolve the issues of neutrino mass hierarchy, octant of θ23, and leptonic CP violation. We also find that the sensitivity of these future facilities can be improved significantly by adding the projected data from T2K and NOνA. Stand-alone LBNO setup with a 10 kt detector has a mass hierarchy discovery reach of more than 7σ, for the lowest allowed value of sin2θ23(true) = 0.34. This result is valid for any choice of true δCP and hierarchy. LBNE10, in combination with T2K and NOνA, can achieve 3σ hierarchy discrimination for any choice of δCP, sin2θ23, and hierarchy. The same combination can provide a 3σ octant resolution for sin2θ23(true) ≤ 0.44 or for sin2θ23(true) ≥ 0.58 for all values of δCP(true). LBNO can give similar results with 10 kt detector mass. In their first phases, both LBNE10 and LBNO with 20 kt detector can establish leptonic CP violation for around 50% values of true δCP at 2σ confidence level. In case of LBNE10, CP coverage at 3σ can be enhanced from 3% to 43% by combining T2K and NOνA data, assuming sin2θ23(true) = 0.5. For LBNO setup, CP violation discovery at 3σ is possible for 46% values of true δCP if we add the data from T2K and NOνA.

Neutrino Mixings and Leptonic CP Violation from CKM Matrix and Majorana Phases

The high scale mixing unification hypothesis recently proposed by three of us (R. N. M., M. K. P. and G. R.) states that if at the seesaw scale the quark and lepton mixing matrices are equal, then for quasidegenerate neutrinos radiative corrections can lead to large solar and atmospheric mixings and small reactor angle at the weak scale in agreement with data. Evidence for quasidegenerate neutrinos could, within this framework, be interpreted as being consistent with quark-lepton unification at high scale. In the current work, we extend this model to show that the hypothesis works quite successfully in the presence of

Octant of

CP

\theta_{23}

-violating phases (which were set to zero in the first paper). In the case where the Pontecorvo-Maki-Nakagawa-Sakata matrix is identical to the Cabibbo-Kobayashi-Maskawa quark-mixing matrix at the seesaw scale, with a Dirac phase but no Majorana phase, the low energy Dirac phase is predicted to be (