Neutrino Oscillations: experimental triumphs, remaining puzzles. Giorgio Gratta Physics Department, Stanford

Size: px

Start display at page:

Download "Neutrino Oscillations: experimental triumphs, remaining puzzles. Giorgio Gratta Physics Department, Stanford"

Nicholas Stephens
6 years ago
Views:

1 Neutrino Oscillations: experimental triumphs, remaining puzzles Giorgio Gratta Physics Department, Stanford

2 What we do know: - Status of neutrino mixing How did we learn it: - Solar neutrino - Atmospheric neutrino - Reactor neutrinos - K2K Addressing remaining puzzles in neutrino mixing: - LNSD/miniBoone see Sam Zeller - θ 13 experiments - Hierarchy/CP violation: ν-fact/ fact/β-beams - Absolute m, Majorana/Dirac ν see Steve Elliott Impossible to be complete: I will just make an arbitrary -and hopefully interesting- selection SSI 2004 Experimental Neutrino Oscillations - Gratta 2

3 If m ν 0 0 then the 3 weak-interactions eigenstates can be represented as superposition of mass eigenstates ν j From LEP and SLC we know that there are 2.981±0.008 active, light ν flavors We also know that 3 ν flavors were active in Big Bang Nucleosynthesis ν = j U jl ν l j Neutrinos are produced and detected by weak interaction but propagate in vacuum as mass eigenstates 2 i( ml / 2E) L Ulje ν l l j l i( m / 2E) L SSI 2004 Experimental Neutrino Oscillations - Gratta 3 U Neutrino oscillations lj e 2 l U * j l ν j ν j

4 A possible representation of the Pontecorvo-Maki-Nakagawa-Sakata matrix U U = U U e1 µ 1 τ 1 U U U e2 µ 2 τ 2 U U U e3 µ 3 τ 3 = information on CP is here Neutrino factory? cosθ12 - sinθ 0 12 sinθ cosθ Solar ν KamLAND Future solar ν exp. 0 cosθ iδ CP 1 - e sinθ e CPsinθ 0 cosθ -iδ 13 Chooz/Palo Verde Off axis Future reactors cosθ 23 - sinθ 23 0 sinθ cosθ Atmospheric ν K2K Minos et al θ 12 ~32 θ 13 90%CL θ 23 ~ e 0 -iα / 2 0 e 0 0 -iα/2+ iβ Neutrinoless double beta decay SSI 2004 Experimental Neutrino Oscillations - Gratta 4

5 Oscillations give the proof that neutrino masses are non-zero, but we still do not know the absolute mass scale and the hierarchy ~20 ev 0.3 ev 2.8 ev From 0νββ if ν is Majorana From tritium endpoint (Maintz and Troitsk) solar~ ev 2 ~ ev 2 ~ ev 2 solar~ ev 2 ~1 ev From WMAP Time of flight from SN1987A (PDG 2002)? Sign of m 2 13 (Future accelerator experiments) SSI 2004 Experimental Neutrino Oscillations - Gratta 5

6 ν e are abundant by-products of nuclear fusion in the sun 2 + p + p H + e + ν e MeV pp 99.75% 2 p + e + p H + ν e MeV pep 0.25% 2 3 H + p He + γ MeV 3 86% 14% hep 2.4* He+ He α + 2p MeV 3 7 He+ α Be+ γ MeV 3 + He+ p α + e + ν e 7 7 Be 99.89% 7 Be + e Li + γ + ν e MeV 7 Li + p α + α MeV % 8 Be + p B + γ MeV 8 B 0.11% 8 + B Be + e + ν e MeV 8 Be α + α + 3MeV SSI 2004 Experimental Neutrino Oscillations - Gratta 6

the fusion reactions take place Matter effects play an

7 The detectors are located far away from the Sun L=10 8 km But neutrinos are produced deep inside the Sun, where most the fusion reactions take place Matter effects play an essential role SSI 2004 Experimental Neutrino Oscillations - Gratta 7

8 Several experiments detecting solar neutrinos Chlorine: 37 Cl+ν e 37 Ar+e - Homestake mine (US) Taking data from (!) The father of all solar neutrino experiments Gallium: 71 Ga+ν e 71 Ge+e - SAGE (Baksan( Baksan,, Russia), Gallex and GNO (Gran( Sasso,, Italy) Lowest threshold Calibrated with a neutrino source Cerenkov: e - +ν e e - +ν e Kamiokande and SuperKamiokande (Japan), SNO (Sudbury, Canada) Largest statistics See D.Casper s talk Cerenkov: : DνD scattering SNO (Sudbury, Canada) For the first time measure ν e and ν X separately See D.Waller s talk Radiochemical, no real-time information SSI 2004 Experimental Neutrino Oscillations - Gratta 8

9 Neutrino energy spectrum includes lines and continua SSI 2004 Experimental Neutrino Oscillations - Gratta 9

10 Homestake Mine, Lead SD 1400 m underground 615 tons of perchloroethilene (C 2 Cl 4 ) 2.2*10 30 atoms of 37 Cl 36 Ar or 38 Ar added to the fluid as carrier gas SSI 2004 Experimental Neutrino Oscillations - Gratta 10

11 30 years of solar neutrinos with the Chlorine detector Expected from SSM SSI 2004 Experimental Neutrino Oscillations - Gratta 11

12 1 SNU = 1 1 SNU = 1 ν interaction/sec per 10 interaction/sec per target atoms target atoms SSI 2004 Experimental Neutrino Oscillations - Gratta 12

Ga has lower threshold: to date, only technique sensitive to pp neutrinos! 71 Ga has lower threshold: In Gallex/GNO 30.3 ton of Ga in aqueous solution of GaCl 4.

13 Ga has lower threshold: to date, only technique sensitive to pp neutrinos! 71 Ga has lower threshold: In Gallex/GNO 30.3 ton of Ga in aqueous solution of GaCl GeCl 4 is volatile and is purged/counted ton of metallic Ga kept liquid (>29.8 C) Extraction by HCl etch and GeCl4 and Ar purge SAGE, Baksan SSI 2004 Experimental Neutrino Oscillations - Gratta 13

14 Both Ga experiments have been calibrated with a 51 Cr source of about 1 MCi SNU 51 Cr source measurements SAGE data Expected from SSM SSI 2004 Experimental Neutrino Oscillations - Gratta 14

Sun, all flavors together The SNO detector: 1 kton of heavy

15 In order to better understand the situation it would be nice to also measure the total number of neutrinos from the Sun, all flavors together The SNO detector: 1 kton of heavy water SSI 2004 Experimental Neutrino Oscillations - Gratta 15

16 Neutrino interactions in D 2 O Charged Current (CC): ν e +d p+p+e - Electron neutrinos only ν e d p p e - ν x e - e - ν x Elastic Scattering (ES): ν x + e - ν x +e σ(ν e )=σ(ν µ )=σ(ν τ ) this is all SuperK sees Neutral Current (NC): ν x +d p+n+ p+n+ν x Same for all neutrino flavors! νx d n p ν x SSI 2004 Experimental Neutrino Oscillations - Gratta 16

17 Remarkably the SNO measurement gives Φ NC >Φ CC Phys. Rev.Lett. 89 (2002) Energy Unconstrained For up-to to-date results see Waller s talk So ν e are missing, but the total number of neutrinos is right! SSI 2004 Experimental Neutrino Oscillations - Gratta 17

18 1 SNU = 1 ν interaction/sec per target atoms 66.9 ± ± 5.5 SSI 2004 Experimental Neutrino Oscillations - Gratta 18

19 Clearly all this smells of flavor mixing Global fit to all solar neutrino exps eliminates most of the solutions except for the MSW-LMA solution (The solar neutrino anomaly is a sort of neutrino-birefringence of dense matter occurring because neutrinos have finite masses -- see Boris Kayser talk) SSI 2004 Experimental Neutrino Oscillations - Gratta 19

20 All of this is very interesting but wouldn t it be great if we could reproduce it with artificial means? SSI 2004 Experimental Neutrino Oscillations - Gratta 20

21 Nuclear reactors are very intense sources of ν e deriving from beta-decay of the neutron-rich rich fission fragments n N n N2 N 1 n n N 2 N 1 e - ν e ν e ν e ν e ν e nuclear nuclear reactor reactor ν e ν e ν e ν e Look for a deficit of ν e and spectral distortions at a distance L L ν e ν x? ν e detector SSI 2004 Experimental Neutrino Oscillations - Gratta 21

22 U + n X + X 2n stable nuclei with A most likely from fission Zr 58 Ce together these have 98 protons and 136 neutrons Example: 235 U fission so, on average 6 n have to decay to 6 p to reach stable matter SSI 2004 Experimental Neutrino Oscillations - Gratta 22

23 Power/commercial reactors are generally used since only requirement is to have large power 200MeV / fission 6 ν fission e / A typical large power reactor produces 3 GW thermal and antineutrinos/s the Chooz plant in France SSI 2004 Experimental Neutrino Oscillations - Gratta 23

24 >99.9% of ν- are produced by fissions in 235U, 238 U, 239 Pu, 241 Pu 235 U, 238 U, 239 Pu, 241 Pu contribution <10-3 not taken into account for neutrino flux calculations { SSI 2004 Experimental Neutrino Oscillations - Gratta 24

25 A specific signature is provided by the inverse-β reaction + ν e + p e + n τ 200 µs p + n d + γ ( 2.2 MeV ) Event tagging by coincidence in time, space and energy of the neutron capture E ν measurement Threshold: E ν >1.8MeV E T ) ν e + + T + ( M M + n { kev n p m { 1.8 MeV only ~1.5 antineutrinos/fission can be detected e + SSI 2004 Experimental Neutrino Oscillations - Gratta 25

26 The ν e energy spectrum Reactor ν e spectrum (a.u( a.u.).) Observed spectrum (a.u( a.u.).) ν e +p n+e + cross section (10-43 cm 2 ) E ν (MeV) SSI 2004 Experimental Neutrino Oscillations - Gratta 26

27 An experiment relevant for solar ν will have ~100 km baseline and hence will need a huge detector and a huge source Statistical errors only SSI 2004 Experimental Neutrino Oscillations - Gratta 27

28 ~1 km high Mt Ikenoyama SSI 2004 Experimental Neutrino Oscillations - Gratta 28

29 Many reactors contribute to the antineutrino flux at KamLAND Site Dist (km) Cores (#) P therm (GW) Flux (cm -2 s - 1 ) Rate noosc * (yr - 1 kt - 1 ) * E ν >3.4MeV (E prompt >2.6MeV) Japan South Korea Kashiwazaki Ohi Takahama Tsuruga Hamaoka Mihama Sika Fukushima1 Fukushima2 Tokai2 Onagawa Simane Ikata Genkai Sendai Tomari Ulchin Yonggwang Kori Wolsong Detailed power and fuel Composition calculation used From electrical power Japanese average fuel used Total Nominal SSI 2004 Experimental Neutrino Oscillations - Gratta 29

30 The total electric power produced as a by-product of the νs s is: ~60 GW or... ~4% of the world s manmade power or ~20% of the world s nuclear power SSI 2004 Experimental Neutrino Oscillations - Gratta 30

31 A limited range of baselines contribute to the flux of reactor antineutrinos at Kamioka Over the data period Reported here Korean reactors 3.4±0.3% Rest of the world +JP research reactors 1.1±0.5% Japanese spent fuel 0.04±0.02% 0.02% SSI 2004 Experimental Neutrino Oscillations - Gratta 31

32 KamLAND: Kamioka Liquid scintillator AntiNeutrino Detector 1 kton liq. Scint.. Detector in the Kamiokande cavern fast PMTs large area PMTs 34% photocathode coverage H 2 O Cerenkov veto counter SSI 2004 Experimental Neutrino Oscillations - Gratta 32

33 The completed detector, looking up SSI 2004 Experimental Neutrino Oscillations - Gratta 33

Scintillator is a blend of 20% pseudocumene and 80% dodecane Different density paraffines are used to tune the density of buffer to 4

34 Scintillator is a blend of 20% pseudocumene and 80% dodecane Different density paraffines are used to tune the density of buffer to of that of the scintillator PPO concentration is 1.52 g/l in scintillator SSI 2004 Experimental Neutrino Oscillations - Gratta 34

35 Autoradiography of KamLAND Top flange and chimney region Central thermometer Balloon Bottom flange and plumbing 238 U = (3.5±0.5)x10-18 g/g In this region measure SSI 2004 Experimental Neutrino Oscillations - Gratta 35

36 A brief history of KamLAND Start data taking Run A (data-set of 1 st paper) Dates Jan 2002 Mar 9 Oct Live time (days) * * Was with old analysis Electronics upgrade & 20 PMT commissioning Jan/Feb Run B Oct - Jan Data-set presented here Mar 9, 2002 Jan 11, T.Araki et al, arxiv:hep-ex/ ex/ Jun 13, 04 submitted to Phys Rev Lett SSI 2004 Experimental Neutrino Oscillations - Gratta 36

37 Vertexing is performed using timing from the 17 PMTs Am/Be(~8MeV) -60 (2.6MeV) -65 (1.1MeV) -68 (1.0MeV) z SSI 2004 Experimental Neutrino Oscillations - Gratta 37

38 Tagged cosmogenics can be used for calibration 12 B τ=29.1ms Q=13.4MeV 12 N τ=15.9ms Q=17.3MeV µ Fit to data shows that 12 B: 12 N ~ 100:1 SSI 2004 Experimental Neutrino Oscillations - Gratta 38

39 Energy calibration uses discrete γ and B/ 12 N 68 Ge 60 Co n-p n- 12 C 65 Zn Carefully include Birks law, Cherenkov and light absorption/optics to obtain constants for γ and e type depositions σ/e ~ 6.2% at 1MeV SSI 2004 Experimental Neutrino Oscillations - Gratta 39

40 Estimate of total volume and fiducial fraction SSI 2004 Experimental Neutrino Oscillations - Gratta 40

41 Fraction of volume inside the fiducial radius verified using µ-produced 12 B/ 12 N and n (assumed uniform) 12 B/ 12 N neutrons SSI 2004 Experimental Neutrino Oscillations - Gratta 41

Selecting antineutrinos, E prompt >2.6MeV - R prompt, delayed - R e-n < 2 m, delayed < 5.5 m - 0.5 µs s < T e-n < 1 ms - 1.8 MeV < E delayed < 2.6 MeV - 2.6 MeV < E prompt < 8.

42 Selecting antineutrinos, E prompt >2.6MeV - R prompt, delayed - R e-n < 2 m, delayed < 5.5 m µs s < T e-n < 1 ms MeV < E delayed < 2.6 MeV MeV < E prompt < 8.5 MeV Tagging efficiency 89.8% ton 5.5 m fiducial cut Balloon edge In addition: - 2s veto for showering/bad µ - 2s veto in a R = 3m tube along track Dead-time 9.7% SSI 2004 Experimental Neutrino Oscillations - Gratta 42

43 Systematic % Scintillator volume Fiducial fraction Energy threshold Cuts efficiency Live time 0.06 Reactor P thermal 2.1 Fuel composition 1.0 Time lag 0.01 Antineutrino spectrum 2.5 Antineutrino x-sectionx 0.2 Total 6.5 SSI 2004 Experimental Neutrino Oscillations - Gratta 43

44 Results ton yr Observed events 258 No osc. expected 365±24(syst) Background 7.5±1.3 Inconsistent with simple 1/R 2 propagation at % CL (Observed-Background)/Expected = 0.686±0.044(stat) 0.044(stat)±0.045(syst) 0.045(syst) Caveat: this specific number does not have an absolute meaning in i KamLAND, since, with oscillations, it depends on which reactors are on/off SSI 2004 Experimental Neutrino Oscillations - Gratta 44

45 2003 saw a substantial dip in reactor antineutrino flux SSI 2004 Experimental Neutrino Oscillations - Gratta 45

Good correlation with reactor flux 90% CL Expected Expected for for no no oscillations oscillations Fit constrained through known background χ 2 =2.1/4 ~0.

46 Good correlation with reactor flux 90% CL Expected Expected for for no no oscillations oscillations Fit constrained through known background χ 2 =2.1/4 ~0.03 for 3TW hypothetical Earth core reactor (But a horizontal line still gives a decent fit with χ 2 =5.4/4) SSI 2004 Experimental Neutrino Oscillations - Gratta 46

47 Energy spectrum now adds substantial information Best fit to oscillations: m 2 = ev 2 sin 2 2θ=0.83 Straightforward χ 2 on the histo is 19.6/11 A fit to a simple rescaled reactor spectrum is excluded at 99.89% CL (χ( 2 =43.4/19) Using equal probability bins χ 2 /dof=18.3/18 (goodness of fit is 42%) SSI 2004 Experimental Neutrino Oscillations - Gratta 47

48 Un-binned likelihood fit to 2-flavor 2 oscillations All solar ν experiments LMA2 excluded at 99.6% CL m 2 = ev 2 sin 2 2θ=0.83 LMA0 disfavored at 94% CL SSI 2004 Experimental Neutrino Oscillations - Gratta 48

49 A shape-only fit gives similar results m 2 = ev 2 sin 2 2θ=0.98 SSI 2004 Experimental Neutrino Oscillations - Gratta 49

50 KamLAND uses a range of L and it cannot assign a specific L to each event Nevertheless the ratio of detected/expected for L 0 /E (or( 1/E) ) is an interesting quantity, as it decouples the oscillation pattern from the reactor energy spectrum no oscillation expectation Hypothetical single 180km baseline experiment SSI 2004 Experimental Neutrino Oscillations - Gratta 50

51 More exotic, non-oscillations oscillations models for the antineutrino channel start being less favored by data Decay * excluded at 95% CL Decoherence excluded at 94% CL * V.Barger et al. Phys. Rev. Lett. 82 (1999) 2640 E.Lisi et al., Phys. Rev. Lett. 85 (2000) 1166 SSI 2004 Experimental Neutrino Oscillations - Gratta 51

52 Combined solar ν KamLAND 2-flavor analysis m tan θ = = ev 2 Includes (small) matter effects SSI 2004 Experimental Neutrino Oscillations - Gratta 52

53 it took 35 years but we have: 1) detected neutrinos from the sun 2) found that part of the neutrino flux is missing 3) found that only ν e are missing 4) found that matter effects in the sun (MSW effect) are responsible for the deficit 5) found that neutrinos have finite masses (required for MSW) 6) identified mixing parameters m 122, θ 12 7) found that we can reproduce this effect artificially with vacuum oscillations with the same m 122, θ 12 8) found that ν and anti-ν behave the same way 9) found that flavor mixing works better than other scenarios (e.g. decay) 10) found that our model for the sun (SSM) works very well SSI 2004 Experimental Neutrino Oscillations - Gratta 53

54 The other oscillations: Atmospheric neutrinos Higher energy phenomenon Measurements dominated by SuperK SSI 2004 Experimental Neutrino Oscillations - Gratta 54

SuperKamiokande: the largest artificial water Cerenkov detector ever built (50 kton) SK1 1996-2001 >11146 50cm PMTs 40% photocathode 22.

55 SuperKamiokande: the largest artificial water Cerenkov detector ever built (50 kton) SK > cm PMTs 40% photocathode 22.5kton fiducial mass PMTs recovered 19% photocathode K2K beam Original PMT coverage T2K beam SSI 2004 Experimental Neutrino Oscillations - Gratta 55

56 A composite data-set E.Kearns, Nu2004 SSI 2004 Experimental Neutrino Oscillations - Gratta 56

57 SSI 2004 Experimental Neutrino Oscillations - Gratta 57 E.Kearns, Nu2004

58 SSI 2004 e µ Experimental Neutrino Oscillations - Gratta 58 E.Kearns, Nu2004

59 The oscillatory pattern is now also visible with atmospheric neutrinos And flavor oscillation is favored over other models for disappearance SSI 2004 Experimental Neutrino Oscillations - Gratta 59 E.Kearns, Nu2004

60 Parameter regions fit by different channels nicely overlap A 3 flavor analysis favors ν µ -ν τ oscillation as responsible for the atmospheric neutrino anomaly (more on this later ) SSI 2004 Experimental Neutrino Oscillations - Gratta 60 E.Kearns, Nu2004

(100m) 10 11 ν µ every 2.2s Super-K at 250km 10 6 ν µ every 2.

61 Again, the quest is open to observe the oscillation phenomenon with artificial neutrinos 12 GeV KEK protons Mini-K (1kton water + other detectors) near detector (100m) ν µ every 2.2s Super-K at 250km 10 6 ν µ every 2.2s (detect ~1event/2days) p.o.t. collected in ~3.5 yrs SSI 2004 Experimental Neutrino Oscillations - Gratta 61

62 Although rate is low background greatly reduced by beam spill timing (0.83 ms delay, synchronized offline using GPS) In the 3.5 yrs of data the atm nu background in the KEK beam spill window is 10-2 events T diff (µs) T.Nakaya, SSI 2004 Nu2004 Experimental Neutrino Oscillations - Gratta 62

63 Expected no oscillation rate: K2K establishes: no oscill, floating normalization ν µ disappearance at 2.9σ (standard physics has 0.33% CL) E ν spectral distortion at 2.5σ (standard physics has 1.1% CL) Combined we have a 3.9σ effect (standard physics has 0.011% CL) T.Nakaya, SSI 2004 Nu2004 Experimental Neutrino Oscillations - Gratta 63

64 approximate 90% CL from global SK fit to atmospheric neutrinos T.Nakaya, SSI 2004 Nu2004 Experimental Neutrino Oscillations - Gratta 64

65 What we have discovered: There is mixing involving νe with best fit at m 2 = ev 2 and θ=32 (solar/kamland) There is also mixing involving ν µ with best fit at m 2 = ev 2 and θ=45 (atmospheric/k2k) If there are only 3 neutrino families, since the two mass differences are of different order of magnitude, we expect to find a third m 2 similar to the larger of the two above SSI 2004 Experimental Neutrino Oscillations - Gratta 65

Neutrino Experiments with Reactors

Neutrino Experiments with Reactors 1 Ed Blucher, Chicago Reactors as antineutrino sources Antineutrino detection Reines-Cowan experiment Oscillation Experiments Solar Δm 2 (KAMLAND) Atmospheric Δm 2 --