Neutrino oscillation experiments: Recent results and implications

Title transparency Neutrino oscillation experiments: Recent results and implications W. Hampel MPI Kernphysik Heidelberg

Motivation for talk On the way from the Standard Model to String Theory: appropriate to summarize the present status of Neutrino Oscillations since their experimental verification constitutes the first departure from the Standard Model of Particle Physics: Non-zero neutrino mass Violation of lepton flavor conservation

Outline Outline Neutrino oscillations Atmospheric neutrinos Long baseline experiment KK Solar neutrinos Running and stopped experiments Near future: Borexino Reactor anti-neutrino experiment KamLAND Conclusions Related topics which will not be covered: Future long baseline experiments Future solar ν experiments: LENS;,... Direct ν mass measurements (tritium) Neutrinoless β decay experiments LSND, Karmen experiments (sterile ν)

nu oscillations: formula Neutrino mixing ν ν P e µ = ν cosθ + ν 1 = ν sin Θ νe νe 1 ( x) = + ν 1 sin sin Θ cosθ Θ sin Disappearance experiment Pν e ν µ ( x) = sin Oscillation length m E ν =1 MeV E ν =1 GeV 1 ev.5 m.5 km 10-4 ev 5 km 5000 km 10-8 ev 50000 km 1.7 AU Θ sin Appearance experiment lv x π lv mν m Different propagation velocities x π lv 1 ν P νe ν e 1.0 0.5 0.0 (x) l v quantum mechanical interference oscillations [ m] = Definition: l v.48e v [ MeV ] m1 m [ ev ] 1 m ) ( m m sin Θ Θ = 45 Θ = 13 x

MSW effect: principle Mikheyev-Smirnov-Wolfenstein Effect Modification of vacuum neutrino oscillations when neutrinos propagate through matter: L. Wolfenstein, Phys.Rev. D17 (1978) 369. Reason: Coherent forward scattering of neutrinos from the electrons in matter results in an asymmetry between ν e and ν µ (ν τ ) ν e e - ν µ µ - ν e ν e W W Z 0 e - ν e µ ν µ e - e - ν µ ν µ e - Z0 e - This results in a transformation: θ v θ m ν 1 ν 1m ν ν m L v L m Transformation depends on: θ v, m, E ν, N e First application to solar neutrinos S.P Mikheyev + A.Yu. Smirnov, Sov. J. Nucl. Phys. 4 (1986) 913. Earth effect: partial regeneration of ν e in the earth possible: day/night modulation of ν signal

Prob. 3 nu formula Bilenky 3 neutrino oscillations A possible case: ν e ν µ maximal mixing (solar ν) ν µ ν τ maximal mixing (atmospheric ν) U e3 0.037 (CHOOZ experiment) ) cos (1 sin 1 1 ) ( 1 E L m P sun e e = θ ν ν U e3 0 for τ µ ν ν,, 3 1 e i U j j ij i = = = = 0.037 1 ~ 1 ~ 1 ~ 1 ~ 1 ~ 1 ~ 1 ~ 1 ~ U

Chooz+Paloverde -neutrino oscillation exclusion plots from the Chooz and Palo Verde reactor ν e experiments ν oscillation analysis of the Chooz data: U e3 0.037 If LMA solution for solar ν is valid and m > x10-4 ev then a 3ν oscillation analysis of the Chooz data is required: e.g. for m > 6x10-4 ev U e3 0.017 Bilenky et al. hep-ph/01116 sin θ 0.14

Atmospheric nu (principle) Flux ratio: ν µ + ν µ ν e + ν e = ~ Absolute flux uncertainty: ~0% Flux ratio uncertainty: ~5% Atmospheric neutrinos p,α π µ e ν µ ν µ Upper atmosphere ν e Earth Type of events: 1 Fully contained Partially contained 3 Upcoming throughgoing muon 4 Upcoming stopping muon Underground detector µ e µ µ 1 3 ν µ ν µ 4

Expected zenith angle distribution Expected zenith angle distribution of atmospheric neutrinos ~15 km Isotropic primary cosmic ray flux + spherically symmetric atmosphere E ν > a few GeV: up/down symmetry (at lower energies: geomagnetic effects) ~ 13000 km Up/down asymmetry at higher energies: clear indication of neutrino oscillations ~ 13000 km ~15 km

Table of atm nu experiments Summary of atmospheric neutrino experiments Experiment Status Detection technique Type of events Fiducial mass Total exposure Baksan running liquid scintillator UTG µ 10.6 y NUSEX finished Fe plates gas counter FC 0.13 kt 0.75 kt. y Fréjus finished Fe plates gas counter FC, PC 0.7 kt.0 kt. y Kamiokande finished HO Cherenkov FC, PC, UTG µ 1.04 kt 7.7 kt. y IMB finished HO Cherenkov FC, UTG µ US µ 3.3 kt 7.7 kt. y Macro finished liquid scintill. gas counter UTG µ 5.9 y Soudan- finished Fe plates gas counter FC 0.77 kt 5.9 kt. y Super- Kamiokande stopped HO Cherenkov FC, PC, UTG µ, US µ.5 kt 91 kt. y FC: fully contained event PC: partially contained event UTG µ : upward through-going muon, US µ : upward stopping muon

Atmospheric nu: measured ratios Results of atmospheric neutrino experiments 1.4 1. Water Cerenkov detector Iron calorimeter 1.0 0.8 0.6 0.4 NUSEX Fréjus IMB 3 (sub-gev) Kamiokande (Multi-GeV) (sub-gev) Super-K (Multi-GeV) Soudan Double ratio R 0. 0.0

MACRO results MACRO results on upward through-going muons µ θ MACRO data Bartol flux m = 0.005 ev, sin θ=1 (best fit) upward horizontal

SK detector +accident from Shiozawa (ν00)

SK zenith angle distribution Super-Kamiokande results: Zenith angle distributions Total exposure time: 1144.4 days (70.4 kt. y ) No oscillations Best fit ( m =3.x10-3 ev, sin θ = 1.00) Sub-GeV: E vis < 1.33 GeV Multi-GeV: E vis >1.33 GeV 13000 km 500 km 15 km

4Allowed regions 4 atm exp. Comparison of allowed regions for ν µ ν τ oscillations of atmospheric neutrinos A Kamiokande B Soudan C MACRO D Super-Kamiokande Why ν µ ν τ? SK data: ν e data: unaffected ν τ appearance? no indication for ν s : NC π o production Earth MSW effect m (ev ) ν µ ν τ (90% c.l.) B C A D sin θ

KK map and priciples KEK to Kamioka Neutrino Oscillation Experiment (KK) from Nishikava (ν00)

KK expectation Expectations for the KK long baseline experiment m = 0.003 ev sin θ = 1.0 without oscillations with oscillations

KK actual results Recent results of the KK long baseline experiment published June 1, 00 Data taking from April 1999 to June 001 (~ 50% of the beam time originally allocated to KK) Measured number of events: 56 Expected number of events with no oscillations: 80.1 + 6. -5.4 Probability that observed deficit is due to a statistical fluctuation: < 1%

KK Dm sinth plot Comparison of the allowed m -sin θ regions: Super-K atmospheric neutrinos versus KK long baseline neutrinos KK from Nishikava (ν00) Super-K

pp cycle branching Solar hydrogen burning via the pp cycle p + p d + e + + ν p + e - + p d + ν p + d 3 He + γ 85% 15% 3 He + 3 He 4 He + p 3 He + 4 He 7 Be + γ pp I 99.9% 0.1% 7 Be + e - 7 Li + ν 7 Be + p 8 B + γ 7 Li + p 4 He pp II 8 B 4 He + e + + ν pp III

features of all solar detectors Spectral sensitivity and other features of the solar neutrino experiments performed so far Homestake since 1970 37 Cl(ν e,e - ) 37 Ar >0.81 MeV 610 t C Cl 4, radiochemical, Kamiokande 1987 1995 e - (ν e,ν e ) e - >7.5 MeV 840 t H O Cerenkov SAGE since 1990 71 Ga(ν e,e - ) 71 Ge >0.3 MeV 57 t Ga, radiochemical GALLEX/GNO since 1991 71 Ga(ν e,e - ) 71 Ge >0.3 MeV 30 t GaCl 3, radiochemical Super-K since 1996 e - (ν e,ν e ) e - >5.0 MeV.5 kt H O Cerenkov SNO since 1999 d (ν e,e - ) p+p d (ν x, ν x ) n+p e - (ν e,ν e ) e - >5.0 MeV 1.0 kt D O Cerenkov ν e + e - : σ(nc) = 0.14 x σ(cc)

NSSM plot for Cl and Kamiokande 1990: Comparison of the CC signal from the Homestake Cl detector with the CC + NC signal from the Kamiokande detector: first evidence for a ν µ or ν τ component in the solar neutriono signal Evidence is growing that the solar neutrino problem is actually not due to problems with the solar model but stems from our ignorance of the basic properties of neutrinos from WH, Physics World 9 (1990) 0.

GNO/SAGE propaganda plot Results of the Gallium Solar Neutrino Experiments CNO 8 B 7 Be pp + pep

Helioseism.: model + measurement Sound speed in the sun: comparison of helioseismological measurements with solar model calculations C ~ T/µ C model -C sun C sun 7 Be flux lowered (Ga rate 79 SNU)

SK cos(th) plot Super-Kamiokande solar neutrino result ν e + e - ν e + e - from M. Smy (ν00)

SNO nu reactions Sudbury Neutrino Observatory Reactions used for the detection of 8 B solar neutrinos from A. McDonald (ν000)

SNO results Results of the Sudbury Neutrino Observatory SNO Collaboration (nucl-ex/004008 v 9 May 00) Measurement of the solar 8 Bneutrino flux (in units of 10 6 cm - s -1 ) with the CC, ES and NC reactions (E kin > 5 MeV): +1.03 SSM = 5.15-0.8 Bahcall et al. (001) ν µ or ν τ appearance!!!

Solar nu results: Table Summary of results from all 7 solar neutrino detectors Detector Homestake (CC) Kamiokande (ν+e - ) Super-Kam. (ν+e - ) GALLEX/GNO (CC) SAGE (CC) SNO (CC) (ν+e - ) (NC) Sensitivity for solar neutrinos 8 B, 7 Be 8 B pp, 7 Be, 8 B 8 B Result (relative to the SSM prediction) 0.33 ± 0.03 0.54 ± 0.08 0.46 ± 0.0 0.55 ± 0.05 0.55 ± 0.05 0.34 ± 0.0 0.46 ± 0.05 0.99 ± 0.1

MSW Gallium m versus tan θ plot for the GALLEX/GNO solar neutrino experiment SSM prediction (Bahcall et al. 001) 19 +9 SNU -7 Measured value (GALLEX/GNO collaboration): 70.8 ± 5.9 SNU +σ +1σ -1σ -σ

SNO Dm plot Only SNO data SNO + Cl + Ga data Ahmad et al. (SNO Collaboration), 00 (nucl-ex/004009)

Bahcall Dm plot Bahcall et al., 00 (hep-ph/004314) 10-3 10-4 10-5 Solar model: Bahcall et al. (001) free 8 Bflux m [ev ] 10-6 10-7 10-8 10-9 Active neutrinos Ga + Cl + SK (Sp, zenith) + SNO (CC, A DN, NC) 10-10 10-11 10-1 10-4 10-3 10-10 -1 1 10 tan δ

MSW Gallium with LMA + Low Sensitivy of the global oscillation solutions to the error of the GALLEX/GNO experiment LMA solution Low solution

Borexino detector/status Borexino solar neutrino detector Measurement of the 7 Be neutrino line via neutrino-electron elastic scattering in 300 t liquid scintillator (fiducial volume 100 t) Status: start detector filling: end of 00, begin measurements in summer 003 Simulated electron recoil spectrum 7 Be-ν (SSM) background

Borex MSW plot with LMA + Low Expected reduction of the CC+NC Borexino signal through neutrino oscillations 1E-3 1E-4 Borexino CC+NC signal E ν = 0.86 MeV Average over day and night and over the year 0.9 0.7 1E-5 m [ev ] 1E-6 1E-7 0.9 0.5 0.7 0.35 0.35 0.5 1E-8 1E-9 1E-4 1E-3 0.01 0.1 1 sin θ

Borexino rates (modulation) Expected BOREXINO event rates 60 40 No oscillations (only 1/R ) sin θ = 0.8 m = 9.0 x 10-11 ev sin θ = 0.93 m = 4. x 10-10 ev sin θ = 0.8 m = 1.1 x 10-10 ev events/d 0 SSM Rate [d -1 ] in 100 t (50 800 kev) 58 Expected time dependence 1/R² Summer 0 0 100 00 300 Time in the year [d] Low 3 10 % day/night modulation; small annual modulation LMA 33 None SMA 13 None VO Strong annual modulation (see graph)

KamLAND detector + principle KamLAND detector reactor neutrino disappearance experiment in the Kamioka mine (Japan) ν e ν e + p n + e + source: 0 nuclear power plants at distances between 81 and 940 km (85% of the signal results from baselines between 140 344 km) Balloon Mineral oil based liquid scintillator (1000 t) Status of the experiment: Start data taking January 00 First results to be published at the end of September (PANIC Conf.)

Kamland expectation for 3 values Expectation for KamLAND No oscillation versus three LMA solutions

Conclusions Conclusions Large underground experiments have detected neutrino oscillations and thus a non-zero neutrino mass Atmospheric neutrinos Atmospheric neutrino data are consistent with ν µ ν τ oscillations ( m ~.5 x 10-3 ev and sin θ = 1.0) confirmed by KK (presently at ~3σ) Solar neutrinos Standard Solar Model confirmed by helioseismology SNO NC data: consistent with SSM 8 B ν flux Neutrino deficit measured by all 6 experiments well described by ν e ν µ oscillations with large mixing and m either ~10-4 ev (LMA) or ~10-7 ev (Low) decided by KamLAND, Borexino, LENS,...

absolute nu masses Absolute neutrino masses Two extrem cases: quasi-degenerate (close to upper limit from T experiments) hierarchical ( m << m << m ) Normal hierarchy Inverted hierarchy (ν 3 heaviest) (ν 3 lightest) i j k m atm m sun m sun m atm

NY times SK atmospheric nu The New York Times on June 5, 1998 after the Super-Kamiokande Collaboration published the results on atmospheric neutrinos at the Neutrino 1998 Conference in Japan