Brazilian Journal of Physics ISSN: 0103-9733 [email protected] Sociedade Brasileira de Física Brasil Nakahata, Masayuki Neutrino Physics (Rapporteur talk) Brazilian Journal of Physics, vol. 44, núm. 5, 2014, pp. 465-482 Sociedade Brasileira de Física Sâo Paulo, Brasil Available in: http://www.redalyc.org/articulo.oa?id=46432476005 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative Braz J Phys (2014) 44:465–482 DOI 10.1007/s13538-014-0228-4 PARTICLES AND FIELDS Neutrino Physics (Rapporteur talk) Masayuki Nakahata Received: 28 April 2014 / Published online: 31 May 2014 © Sociedade Brasileira de F´ısica 2014 Abstract Papers related to neutrino physics, submitted in in this short rapporteur report, only papers that have notable the categories NU-EX (experimental results), NU-IN (meth- results have been selected. ods, techniques, and instrumentation) and NU-TH (theory, model, and simulations) are reviewed with a brief introduc- tion on the current understanding of neutrino masses and 2 Neutrino Masses and Mixings mixings. Before discussing the contributed papers at ICRC2013, our Keywords Neutrino current understanding of neutrino masses and mixings will be described. The relation between the mass eigenstates (ν1, ν2,andν3) and the weak interaction (flavor) eigenstates (νe, 1 Introduction νμ,andντ ) can be written: ⎛ ⎞ ⎛ ⎞ ⎛ ⎞ The categories NU-EX, NU-IN, and NU-TH at ICRC2013 νe Ue1 Ue2 Ue3 ν1 ⎝ ⎠ = ⎝ ⎠ ⎝ ⎠ cover neutrino physics over a wide energy range. As shown νμ Uμ1 Uμ2 Uμ3 ν2 . in Fig. 1, neutrino sources include solar neutrinos with ener- ντ Uτ1 Uτ2 Uτ3 ν3 gies of several megaelectronvolt, supernova burst neutrinos The unitary matrix U, which is referred to as the with energies of a few tens of MeV, atmospheric neutri- Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix, can nos with energies from a few hundred megaelectronvolt to be decomposed into three mixing angles (θ , θ , θ )and a petaelectronvolt, and high-energy astrophysical neutrinos 12 23 13 one Charge conjugation Parity (CP) phase (δ) as follows: with energies of several teraelectronvolt or more. ⎛ ⎞ ⎛ ⎞ ⎛ ⎞ iδ The number of papers submitted to the various cate- 10 0 c13 0 s13e c21 s12 0 ⎝ ⎠ ⎝ ⎠ ⎝ ⎠ gories are 1 for solar neutrinos, 5 for supernova neutrinos, 0 c23 s23 010 −s12 c12 0 −iδ 13 for atmospheric neutrinos, 64 for high-energy astrophys- 0 −s23 c23 −s13e 0 c13 001 ical neutrinos, and 5 for other topics. So, a total of 88 papers were submitted, and all of them are impressive in one way where cij ≡ cos θij and sij ≡ sin θij . The general expres- or another. But, since it is impossible to cover all of them sion for the neutrino oscillation probability in a vacuum, P(να → νβ ; L),is m2 L − ∗ ∗ 2 jk M. Nakahata () δαβ 4 Re Uαj Uβj UαkUβk sin Kamioka Observatory, Institute for Cosmic Ray Research, 4E j<k University of Tokyo, Tokyo, Japan 2 e-mail: [email protected] ∗ ∗ mjkL +2 Im Uαj U U Uβk sin , βj αk 2E M. Nakahata j<k Kavli Institute for the Physics and Mathematics 2 ≡ 2 − 2 of the Universe (WPI), University of Tokyo, Tokyo, Japan where mjk mj mk. 466 Braz J Phys (2014) 44:465–482 Fig. 1 Energy range covered by Solar neutrinos Atmospheric neutrinos neutrino physics High energy neutrino astronomy Supernova burst SN1987A 6 9 12 15 18 21 10 10 10 10 10 10 Energy (eV) 2 2 The value of sin (2θ23) and the absolute value of m32 3 Solar Neutrinos have been measured using atmospheric and accelerator neutrinos, and the resulting contours are shown in Fig. 2. Solar neutrinos have been measured in the Homestake, 2 | 2 | The value of sin (2θ23) is close to unity and m32 is Kamiokande, SAGE, GALLEX/GNO, Super-Kamiokande, × −3 2 2 about 2.4 10 eV . The sign of m32 is not yet known; a SNO, KamLAND, and Borexino experiments. Figure 6 positive sign is referred to as normal and a negative sign is shows the νe survival probability (P(νe → νe)) as a func- 2 2 referred to as inverted.sin (2θ12) and m21 were measured tion of neutrino energy, determined by combining the results using solar neutrinos and in a long baseline reactor experi- of these experiments [2]. ment (KamLAND), and the resulting contours are shown in The expected probability for neutrino oscillations, tak- Fig. 3. ing into account the Mikehev-Smirnov-Wolfenstein (MSW) 2 ± 2 +0.20 × sin (θ12) is 0.304 0.013 and m21 is 7.45−0.19 effect, is also shown in the figure for the best-fit parame- −5 2 10 eV . Recently, θ13 was measured in accelerator exper- ters from solar global and solar+KamLAND analyses. At iments (T2K and MINOS) and short baseline reactor exper- ICRC2013, the latest results from the Super-Kamiokande iments (Daya Bay, RENO, and Double Chooz). A summary were presented [2]. Because of the matter effect on neu- of the measured values is shown in Fig. 4. trinos passing through the Earth, the flux at night is Combining the results of the reactor experiments, expected to be higher than that during the day. The results 2 sin (2θ13) is 0.093 ± 0.009. So, we know now all three of the Super-Kamiokande observations indicated that the 2 = − 1 + mixing angles and two independent values of m . As yet, day/night asymmetry (ADN ( day night)/ 2 ( day unknown properties are the mass hierarchy, the CP phase night))is−3.2 ± 1.1 ± 0.5 %, and it is 2.7σ away δ, and the absolute value of neutrino masses. A graphical from zero. Figure 7 shows the observed ADN as a func- 2 summary of known masses and mixings is shown in Fig. 5. tion of m21 together with the expected ADN. The obtained ) 4 ν θ ≤ π /c T2K 3 ( /4) 90% CL 2 0.004 23 T2K 3ν (θ ≥ π/4) 90% CL 23 ν | (eV T2K 2011 2 90% CL 32 2 0.0035 MINOS 2013 2ν 90% CL m Δ ν | SK zenith 2012 3 90% CL SK L/E 2012 2ν 90% CL 0.003 0.0025 T2K 3ν (θ ≤ π/4) best fit 23 0.002 T2K 3ν (θ ≥ π/4) best fit 23 0.82 0.84 0.86 0.88 0.9 0.92 0.94 0.96 0.98 1 2 θ sin (2 23) 2 2 Fig. 2 Contours for sin (2θ23) and the absolute value of m (from 32 2 2 [1]) Fig. 3 Contours for sin (θ12) and the absolute value of m21 from [2] Braz J Phys (2014) 44:465–482 467 ± 1rangeσ Pee all solar BORE-- BOREXINO XINO MSW (solar&KL) MSW (solar) SK & SNO Cl 2 sin 2 13 BORE-- Fig. 4 Measured values of θ13 XINO ADN is statistically consistent with the expectations for the 2 m21 values obtained from the KamLAND and solar global analyses. Fig. 6 νe survival probability determined by solar neutrino experi- ments [2]. Also shown are the expected probability curves considering the MSW effect for the best fit parameters obtained from solar global 4 Supernova Neutrinos and solar+KamLAND analyses Core collapse supernovae are the most energetic stellar phe- nomena in the universe. The total energy released by a core The second longest running is the LVD experiment, which collapse is estimated to be ∼ 3 × 1053erg, and 99 % of this is a 1,000-ton liquid scintillator detector. LVD also found energy is carried by neutrinos. no supernova candidate and established an upper limit of Figure 8 shows the history of underground detectors that <0.12/year at a 90 % CL [4]. Table 1 shows the list of are sensitive to galactic supernova bursts. The one with currently operating supernova detectors and their sensitivity. the longest operational history is the Baksan experiment, The Super-Kamiokande detector is able to detect several which is a 330 ton liquid scintillator detector located in thousand supernova events for a galactic supernova, and it the Baksan laboratory. Since no galactic supernova candi- is possible to get directional information using neutrino- date has been found during the 28-year period from 1980 to electron scattering events. The IceCube detector is capable 2013, this places an upper limit on the galactic supernova of measuring the precise time profile of bursts containing rate of <0.082/year at a 90 % confidence level (CL) [3]. many neutrino interaction events in ice. As a result of an Fig. 5 Graphical summary of Normal hierarchy? Inverted hierarchy? Degenerate? neutrino masses and mixings 2 m 2 m3 2 Δ 2 -5 2 m21 =~7.4x10 eV 2 m1 Δ 2 -3 2 m32 =~2.4x10 eV ν e ν μ Δ 2 -3 2 m32 =~ー2.4x10 eV ντ 2 m2 Δ 2 -5 2 m21 =~7.4x10 eV 2 2 m1 m3 468 Braz J Phys (2014) 44:465–482 Fig. 7 Day/night flux asymmetry measured by SK-I,II,III,IV Combine Day/Night Asymmetry Super-Kamiokande (gray band). 1 Also shown are the expected asymmetry (red)and±1σ 2 ranges of m21 from the solar 0 global (green) and KamLAND (blue) analyses (from [2]) -1 Day/Night Asymmetry (%) -2 -3 -4 -5 2 4 6 8 10 12 14 16 18 20 22 Δ 2 -5 2 m21 (10 eV ) IceCube collaboration, an offline burst search of the data expected SRN spectrums assuming some effective temper- from April 2008 to May 2011 was reported in [5], and atures of the supernova burst are shown in Fig.