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CP Violation and Mass Hierarchy with a Combined Sensitivity of T2K-II

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CP Violation and Mass Hierarchy with a Combined Sensitivity of T2K-II CP violation and mass hierarchy with a combined sensitivity of T2K-II, NOνA and JUNO Nath Ankur1, Cao Son2, Ngoc Tran Van3, Van Nguyen Th4, Quyen Phan To3, Francis Ng K1 1Tezpur University, Assam, India; 2High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki, Japan; 3Institute For Interdisciplinary Research in Science and Education, Quy Nhon, Vietnam; 4Institute of Physics (IOP), VAST, Hanoi, Vietnam Abstract Result Recent T2K data indicates a CP violation in the neutrino oscillations and mildly favours the normal neutrino mass hierarchy. This work explores Unless mentioned, the following values (mostly from global analysis [6]) ues, δCP = 0; π, is calculated assuming either the MH is known or not the physics potentials with a combined sensitivity of T2K-II, NOνA, and JUNO experiments. T2K-II, a proposed run extension up to 2026 by are taken as the truth for sensitivity studies: known. Although the result below is tagged as with \unknown" MH, it T2K collaboration, is sensitive to CP violation at a level of 3σ or higher if δCP ∼ −π=2. NOνA, proposed to run until 2024, provides a significant should be closely equivalent to \known" MH when all experiments are 2 2 2 sensitivity to both mass hierarchy and CP violation. JUNO, expected to take data for six years starting from 2021, has 3σ or higher sensitivity sin θ12; sin θ13; sin θ23; δCP = (0:310; 0:02241; 0:5; −π=2) combined since MH is solved definitely in this case. to the mass hierarchy and 1% or better precision measurement of solar parameters and atmospheric mass splitting. It is shown that the joint 2 2 −5 2 −3 2 ∆m21; ∆m31 = 7:39 × 10 eV ; 2:523 × 10 eV analysis can determine definitely the neutrino mass hierarchy. Also it provides > 4σ to exclude CP conserving values if δCP ∼ −π=2 and > 50% Preliminary fractional region of δCP can be explored at ≥ 3σ significance. 9 Mass Hierarchy (MH) Sensitivity Assume neutrino MH is nor- True: NH, sinθ2 =0.5 2 23 mal, statistical significance χ to exclude the inverted MH is calculated 8 T2K-2 only Objectives at each possible true value of δ . =0 CP CP 7 + short-baseline reactor δ Neutrino oscillations establish that neutrinos have mass and the leptons are mixed. Lepton mixing matrix, which connects the mass 6 + NOvA (extend to 2024) eigenstates and flavor eigenstates of neutrinos, is presumed to be unitary 3 × 3 matrix, which are commonly parameterized by three mixing Preliminary 5 + JUNO a 10 angles θ12; θ13; θ23, one Dirac CP-violation phase δCP . The probability for a α-flavor to oscillate into β-flavor,P(να!νβ ), depends on these four 2 2 9 4 parameters, two mass square splitting ∆m ; ∆m , its energy, Eν , propagation distance L, and amount of matter it passing through, ρ: 21 31 8 3 2 2 7 2 P(να!νβ ) = f θ12; θ13; θ23; δCP ; ∆m21; ∆m31; Eν ; L; ρ (1) 6 Sigma to exclude sin 1 • Experiments basically measures the oscillation probabilities to extract parameters, e.g T2K, NOvA measure P ( ν disappearance), (νµ!νµ) µ 5 0 −3 −2 −1 0 1 2 3 P(νµ!νe) ( νe appearance), and corresponding processes with νµ; JUNO will measure P(νe!νe) (IH assumed) 2 4 δ NOvA only True values of CP [rad] χ 3 2 ∆ JUNO only π • Each experiment is sensitive to a specific set of parameters, e.g T2K, NOvA are sensitive to θ13; θ23; δCP ; ∆m31 ; JUNO (a) For θ23 = 4 , MH is not known 2 2 2 NOvA + JUNO θ12; θ13; ∆m21; ∆m31 . Also there are degeneracy among parameters, challenging the precision measurements from single experiment. Preliminary 1 Joint analysis 9 Joint analysis It is essential to combine data from multiple experiments to attain a precision measurement. Main objectives of T2K-2, NOvA 0 0 1 2 3 4 5 6 8 2θ sin 23 = 0.50 and JUNO joint analysis are to (i) determine the neutrino mass hierarchy (MH), (ii) enhance sensitivity to CP violation, (iii) δ =0 CP [rad.] (True, MH) 2 CP 7 θ sin 23 = 0.60 precision measurement of other oscillation parameters, and (iv) to test the unitary of the lepton mixing matrix. 2 δ (a) Individual and combined sensitivity to MH at sin θ23 = 0:5 2θ 6 sin 23 = 0.43 aIf neutrino is Majorana particle, two additional Majorana-CP-violation phases are included but these are irrelevant for neutrino oscillation Preliminary 10 5 9 4 Experimental and Simulation Details 8 3 GLoBES [1] is used for simulating the experiments and calculating the Parameters T2K-II NOνA JUNO 7 2 statistical significance. We describe the experiments closely as Exposure (POT) 20 × 1021 7:2 × 1021 6 yrs. @ 36 GW-th 6 Sigma to exclude sin 1 much as possible by using the updated information of flux, sig- Baseline (km) 295 810 52.5 5 0 −3 −2 −1 0 1 2 3 (IH assumed) nal/background efficiency, and systematic error. Each experi- 2 4 δ Energy peak/range ∼0.6 GeV ∼2.0 GeV 1-8 MeV Joint analysis True values of CP [rad] χ 3 2θ mental setup is validated at the event rate level and sensitivity (Far) Det. Type WC LS LS ∆ sin = 0.50 23 (b) For different values of θ23, MH is not known level. An overview of experimental specification is shown in Table 1 and 2θ (Far) Det. Mass 50 kt 14kt 20kt 2 sin 23 = 0.60 details are described below: 2θ 1 sin 23 = 0.43 Figure 3: Sensitivity to CP violation Table 1: Experimental Specifications 0 0 1 2 3 4 5 6 21 δ T2K-II An exposure of 20 × 10 proton-on-target (POT) equally di- CP [rad.] (True, MH) Appearance ν mode Disappearance ν mode Fig. 3(a) shows the sensitivity to the leptonic CP violation for 9 2 π vided among ν and ν running modes. The signal/background efficiency 22 (b) Combined sensitivity for three values of sin θ ν →ν 23 the case when θ23 = and the MH is assumed to be \not µ e ν ν 4 20 ν →ν 8 µ + µ µ e and spectral information for T2K-II is obtained by scaling the 2017 anal- ν 18 µ CC 7 NC + Cosmic known" by adding up experiments starting from T2K-2. Fig. 3(b) ν CC 16 µ Figure 2: Mass hierarchy resolving as a function of true δ ysis [2] to same exposure as T2K proposal [3]. Four data samples are NC + Cosmic 6 SIG, 2019 CP 14 ν ν shows the combined sensitivity to CP violation at different val- Beam e+ e 5 12 SIG, 2019 2 used: νµ disappearance, νe appearance in both ν-mode and ν-mode. A Beam BKG, 2019 ues of sin θ . Table 2 shows the fractional region of δ in 10 4 23 CP 3% systematic error for all samples and 3% energy resolution are used. 8 3 Fig.2(a) shows sensitivity to mass hierarchy from different experiment which CP violation can be explored with 3σ or higher significance. Number of events/0.5GeV 6 Number of events/0.1GeV 2 2 2 4 and combination at sin θ23 = 0:5. The combined sensitivity for different sin θ23 0.43 0.50 0.60 1 2 2 21 0 0 values of sin θ is shown in Fig.2(b). 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 23 Fraction of δ 61.6% 54.6% 53.3% NOνA w/ run extension A total exposure of 7:2×10 POT equally rec rec CP Reconstructed Neutrino Energy, Eν (GeV) Reconstructed Neutrino Energy, Eν (GeV) divided among ν and ν modes; We closely followed [4] to obtain the flux (a) Appearance (neutrino) (b) Disappearance (neutrino) 2 Table 2: Fractional region of δCP , depending on sin θ23, can be explored information and [5] to obtain the signal, background efficiency and spec- Appearance ν mode Disappearance ν mode CP Violation Sensitivity Considering δCP can be varied between 6 with 3σ or higher significance 9 ν →ν (−π; +π), the statistical significance of excluding the CP-conserving val- tral information. A 5% systematic error for all samples and energy reso- µ e ν ν ν →ν µ + µ µ e 5 8 ν lution from 8 − 10% are assigned. Fig. 1 shows an example of comparing µ CC NC + Cosmic 7 νµ CC NC + Cosmic 4 SIG, 2019 6 Beam ν +ν event rate obtained by our setup and real NOvA simulation. e e Summary and Discussion 5 SIG, 2019 Beam BKG, 2019 3 4 3 2 • Mass hierarchy will be determined with this joint analysis provement in solving the θ23 octant degeneracy, more precise 235 238 Number of events/0.5GeV Number of events/0.1GeV JUNO Neutrinos flux is simulated with four isotopes of U, U, 2 1 measurements on other oscillation parameters and provide a great 239 241 P u and P u with an efficiency of 73%, predicting 60 IBD events 1 • CP violation can be explored > 4σ if δCP ∼ −π=2 (T2K data 0 0 test to the standard neutrino oscillation paradigm. 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Reconstructed Anti-Neutrino Energy, Erec (GeV) Reconstructed AntiNeutrino Energy, Erec (GeV) per day. Detector setup is simplified with a single reactor core of 36 ν ν indication) and > 50% fractional region of δCP with ≥ 3σ signifi- cance.
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