The other oscillations: Atmospheric neutrinos

Transcription

1 The other oscillations: Atmospheric neutrinos Higher energy phenomenon Measurements dominated by SuperK SSI 2004 Experimental Neutrino Oscillations - Gratta 55

2 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 56

3 A composite data-set E.Kearns, Nu2004 SSI 2004 Experimental Neutrino Oscillations - Gratta 57

4 Δm 2 (ev 2 ) SSI 2004 Experimental Neutrino Oscillations - Gratta 58 E.Kearns, Nu2004

5 SSI 2004 e µ Experimental Neutrino Oscillations - Gratta 59 E.Kearns, Nu2004

6 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 60 E.Kearns, Nu2004

7 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 SSI 2004 Experimental Neutrino Oscillations - Gratta 61 E.Kearns, Nu2004

8 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 62

9 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 63

10 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 64

11 approximate 90% CL from global SK fit to atmospheric neutrinos Minos should soon substantially improve the accuracy of this measurement T.Nakaya, SSI 2004 Nu2004 Experimental Neutrino Oscillations - Gratta 65

12 What we have discovered: There is mixing involving ν e 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 66

13 For reactor energies a m 2 ~ 10-3 ev requires a baseline of ~1 km Statistical errors only SSI 2004 Experimental Neutrino Oscillations - Gratta 67

14 The neutrino oscillation experiment at the Palo Verde Nuclear Generating Station (AZ) ~750 m U. of Alabama, ASU, Caltech, Stanford Collaboration Plant of the Arizona Public Service Co. SSI 2004 Experimental Neutrino Oscillations - Gratta 68

15 Chooz and Palo Verde where optimized in rather different ways: At an existing deep site (300 mwe) Homogeneous detector: antineutrinos are double coincidences Smaller detector (5 ton) but high effic. (~100%) 2 reactors: 8.5 GW th New reactors: zero power data (but worry they would not come up) Baselines 1115 m and 998 m Expect ~25 evts/day (no osc) At an artificial shallow site (32 mwe) Segmented detector: antineutrinos are 4-fold coincidences Larger detector (12 ton) but lower efficiency (~10%) 3 reactors: 11.6 GW th Well established reactors: can only turn off one at the time for background studies Baselines 890m and 750 m Expect ~50 evts/day (no osc) SSI 2004 Experimental Neutrino Oscillations - Gratta 69

16 SSI 2004 Experimental Neutrino Oscillations - Gratta 70

17 SSI 2004 Experimental Neutrino Oscillations - Gratta 71

18 Both detectors used Gd-loaded scintillator (0.1% by mass) to reduce the n-capture time from 170µs (p) to 27µs (Gd) to increase the n-capture energy from 2.2MeV (p) to 8MeV (Gd) PMT response Cell 1: August 2000: AL eff =343 cm August 1999: AL eff =357 cm August 1998: AL eff =389 cm Distance from PMT (cm) All cells effective attenuation lengths: August 2000: µ=298 cm August 1999: µ=309 cm August 1998: µ=350 cm AL eff (cm) This is not trivial for a detector of large dimensions (large light attenuation length, stability) SSI 2004 Experimental Neutrino Oscillations - Gratta 72

19 Chooz managed to start data taking before the reactors were fully commissioned, this provided zero power measurements and the demonstration that the detected neutrino rate is proportional to the reactor s thermal power Daily ν Candidates Chooz all data Reactor Power (GW) SSI 2004 Experimental Neutrino Oscillations - Gratta 73

20 neutrinos detected neutrinos expected 1.01±0.04 Chooz 1.04±0.08 Palo Verde so this time we do not see oscillations SSI 2004 Experimental Neutrino Oscillations - Gratta 74

21 Conclusion: The mixing angle is smaller than the sensitivity of these experiments: θ < 90% CL (Chooz) SSI 2004 Experimental Neutrino Oscillations - Gratta 75

22 The full mixing matrix can be parameterized using three angles θ 12 θ 23 θ 13, one CP violating phase δ CP, and two Majorana phases α, β 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 = 0 0 cosθ iδ CP - e sinθ sinθ cosθ 12 - sinθ 0 sinθ iδ CP iα / 2 cosθ 23 sinθ cosθ 12 e - sinθ 23 cosθ e cosθ e 0 0 -iα/2+ iβ Conventionally we can take θ 12 to be associated with solar neutrino phenomena and hence m sol 2 = m 22 -m 1 2 having also found, from matter effects, that m 2 > m 1 SSI 2004 Experimental Neutrino Oscillations - Gratta 76

23 It then follows that m 3 must be separated from the m 1 m 2 pair by the larger m atm2 interval m 3 can be larger or smaller than m 1 and m 2 because matter effects play negligible role in atm neutrinos θ 23 is associated with the atm neutrino oscillations The expressions for the probabilities P(ν e ν e ), P(ν e ν µ ), P(ν µ ν µ ) and P(ν µ ν τ ) (from which all the others can be calculated using conservation of probability and CPT invariance) are in general quite complicated functions of the mixing angles, CP phases and m 2 (the Majorana phases are not relevant) [see for instance V.Barger et al hep-ph/ ] But for m 12 2 << m 23 2 and θ 13 0 P(ν µ ν τ ) [atm ν oscillation] and P(ν e ν e ) [solar/kl ν] are determined by independent parameters and 2-flavor approx. works well SSI 2004 Experimental Neutrino Oscillations - Gratta 77

24 So the neutrino sector is really strange! Log 10 mass [ev] d e c s u µ t b τ V CKM Adapted from PDG Upper limit on m ν U PMNS ( m 2 solar/kl )1/2 ( m 2 atm )1/ (0.0) 0.48(0.38) 0.53(0.60) (0.38) 0.67(0.60) 0.71 ( ) : value for θ 13 =0 δ=0 SSI 2004 Experimental Neutrino Oscillations - Gratta 78

25 What next? Precise meas. of θ (Borexino, KamLAND solar, future solar ν exp), 23 (Minos,, future accelerator exp), 2 12 (KamLAND reactor), 2 23 (Minos,, future accelerator exp) (Steve Elliott s talk) θ 23 m 12 m 23 Measure neutrino mass scale (Steve Elliott s talk) Make sure there are no surprises (miniboone Measure θ 13 Inverted or normal hierarchy (is m 3 > or < than m 1, m 2?) CP violation in the lepton sector (only possible if 13 turns out to be not too small) θ 13 miniboone,, Sam Zeller s talk) SSI 2004 Experimental Neutrino Oscillations - Gratta 79

26 What sensitivity we need to get to θ 13? No real information from theory ( U PNMS V CKM! ) If sin 2 2θ 13 <0.01 measuring CP and sign ( m 2 13) very hard From ~0.1 to ~0.01 is ~1 BJ unit It turns out that a sensitivity of 0.01 for θ 13 is (challenging but) possible for both accelerators and reactors SSI 2004 Experimental Neutrino Oscillations - Gratta 80

27 Method 1: Accelerator Appearance ν µ ν e µ e sin 2 2θ 13 sin 2 θ 23 sin 2 2 m 31L + 4E + α sin 2θ 12 cosθ 13 sin 2θ 12 sin 2θ 23 sinδ CP sin 3 2 m 31L cosδ 4E CP 2 m 31L cos sin 4E 2 2 m 31L + 4E 2 + O( α ) m α = m mp ~1GeV ν µ beam need km baseline for m 2 ~ ev Very large detector Use near detector to measure background ν e in the beam Find small excess over a large background θ 13 is mixed with other parameters overburden so that degeneracies occur In addition matter effects play a role SSI 2004 Experimental Neutrino Oscillations - Gratta 81

28 Off-axis beams trade intensity for narrow E ν spectrum Angle also tunes the neutrino energy E ν (GeV) Hayato Nu04 SSI 2004 Experimental Neutrino Oscillations - Gratta 82

29 First approved off-axis SuperBeam SuperBeam Jaeri to Kamioka ( J2K ) Phase MW beam θ 13, θ 23, m 23 Phase 2 201X ~4MW beam CP violation? JAERI Dec 2003 SSI 2004 Experimental Neutrino Oscillations - Gratta 83

30 J2K SSI 2004 Experimental Neutrino Oscillations - Gratta 84

31 Target & Horn Decay tunnel Front detector: ν intensity, direction, E spectrum Muon monitors: fast beam intensity and direction Intermediate detector: almost same E-spectrumE as far detector. Main source of systematics in K2K (not yet approved) SSI 2004 Experimental Neutrino Oscillations - Gratta 85

32 J2K sensitivity 0.5 sin 2 2θ 13 sensitivity sin 2 2θ 13 ~0.018 (3σ) sin 2 2θ 13 ~0.006 (90%) Also: θ 23, m 232 precision ~10 times present SSI 2004 Experimental Neutrino Oscillations - Gratta 86

33 Summary of super-beam experiments E p (GeV) Power (MW) Beam E ν (GeV) L (km) M det (kt) ν µ CC (/yr) ν K2K WB ~50 ~1% MINOS(LE) WB ~2, % CNGS WB ~2 ~5, % T2K-I OA ~3, % NOνA OA ~2 810? 50 ~4, % C2GT OA 0.8 ~1200 1,000? ~5, % T2K-II 50 4 OA ~500 ~360, % NOνA+PD OA ~2 810? 50? ~23, % BNL-Hs 28 1 WB/OA ~ ~500 ~13,000 SPL-Frejus WB ~500 ~18, % FeHo 8/120 4 WB/OA 1~ ~500 ~50,000 Running, constructing or approved experiments SSI 2004 Experimental Neutrino Oscillations - Gratta 87

34 Method 2: Reactor Disappearance ν e ν e m31l 2 e sin 2θ 13 sin + O( α ) 4E P e Use a near detector to measure reactor flux, spectrum and detector efficiency to cancel all systematics Look for small deviation from 1/r 2 with plenty of reactor signal Possibly more limited in sensitivity but maybe good enough Cheaper than superbeam but limited in scope Very clean θ 13 measurement (no degeneracy, no matter effects) First explicit discussion of a θ 13 measurement using reactors: L.A. Mikaelyan, V.V. Sinev, Phys. Atom. Nucl. 63 No.6 (2000) 1002 SSI 2004 Experimental Neutrino Oscillations - Gratta 88

35 ~100m ~1000m The use of multiple baselines can reduce most of the systematics. Multi-baselines reactor measurements have been done in the past, more as a cross-check than as a method to increase the precision. 3 baselines baselines (with ONE detector) detector) at Goesgen Goesgen SSI 2004 Experimental Neutrino Oscillations - Gratta 89

36 Can one substantially improve on the Chooz errors? Best to-date systematics from Chooz Get zero statistical error large detector large reactor (maybe more than one?) Reduce reactor and x-section systematics 2 baseline measurement Reduce systematics from detector efficiency build identical near and far detectors, alternate their role during running (only time variations of efficiency matter) Keep backgrounds low and measure them well Do it overkill, this is a tricky measurement and better be right SSI 2004 Experimental Neutrino Oscillations - Gratta 90

37 Need underground detectors location (shielding) possibly with a tunnel that allows the placement and movement of detectors SSI 2004 Experimental Neutrino Oscillations - Gratta 91

38 Zheleznogorsk SSI 2004 Experimental Neutrino Oscillations - Gratta 92

39 Baseline optimization (Huber et al.) Reactor spectrum peaks at ~3.5 MeV: Oscillation Max. for m 2 = ev 2 at L ~ 1.7 km but L optimization relatively forgiving Exposure (t GW th yr) Signal (no oscillations) Reactor-I k 3GW 3yr 45ton Reactor-II k 6GW 6yr 200ton Note: baseline could be conceivably tuned after some running if there is a tunnel Huber et al. hep-ph/ SSI 2004 Experimental Neutrino Oscillations - Gratta 93

40 Are backgrounds a problem? How deep does one have to go? Experiment Chooz Palo Verde Depth (mwe) Signal (ν day -1 ton -1 ) Bkgd (day -1 ton -1 ) S/N Depth helps! Large is good KamLAND *10-3 (no osc.) 1.7* Reduction of uncorrelated background requires low activity materials and shielding, generally not a big problem, it can be measured with good accuracy. Gd loading helps, but it also makes the scintillator less clean, there must be a tradeoff Correlated background from fast n and β-n n activity, both triggered by µ-spallation.. This is why the detector has to go underground. SSI 2004 Experimental Neutrino Oscillations - Gratta 94

41 Fast n background Example of a β-n n emitter SSI 2004 Experimental Neutrino Oscillations - Gratta 95

42 n-production from µ quite well studied at Palo Verde, high energy spectrum and vetoed events can be used to predict background in the interesting region Measurement of bkgnd to 20% appears possible 25mwe Bezrukov 20mwe SUF 32mwe Palo Verde 316mwe Bezrukov FLUKA 750mwe Enikeev Y-F.Wang, L.Miller, GG; Phys. Rev. D 62, (2000) F.Boehm et al., Phys. Rev. D 62, (2000) 3650mwe LVD FLUKA is quite accurate for most variables Y-F.Wang et al., Phys. Rev. D 64, (2001) 5200mwe Mont Blanc Parametrization based on FLUKA SSI 2004 Experimental Neutrino Oscillations - Gratta 96

43 Sensitivity achievable a function of exposure Assume bkgnd negligible; σ cal relative near/far energy calibration σ norm relative near/far flux normalization sin 2 2θ 13 sensitivity 90%CL at m 2 = ev 2 Fit uses spectral shape only Statistical error only Exposure (ton GW th yr) Huber et al hep-ph/ SSI 2004 Experimental Neutrino Oscillations - Gratta 97

44 Sensitivity achievable a function of exposure Of course bin-to-bin mis-calibration will degrade the ultimate sensitivity level. sin 2 2θ 13 sensitivity 90%CL at m 2 = ev 2 Exposure (ton GW th yr) Huber et al hep-ph/ SSI 2004 Experimental Neutrino Oscillations - Gratta 98

45 A number of sites is under investigation in Russia, Japan, US, Europe and other exotic locations Reactor Location Detector L (km) Power Overburden Det Mass (t) Chooz France GW (2) 300 mwe 5 Palo Verde US GW (3) 32 mwe 11.3 KamLAND Japan ~200 km 200 GW(69) 2700 mwe 1000 Krasnoyarsk Russia 0.11/1 ~1 GW? 600 mwe 46 Diablo Canyon US (CA) 0.5-1/ GW (2) 800 mwe 100 Braidwood US (IL) 0.2/ GW (2) 450 mwe Kashiwasaki Japan 2 near 0.3/ GW (7) 140/600 mwe 8.5 Daya Bay PR China 2 near 0.3/ GW (4) 200/1000 mwe (near 25) 50 Double-Chooz France 0.45/ GW(2) 60/300 mwe 13 Texono Taiwan (~2?) 4.1 GW Angra Brazil? ~ 4 GW Reactor Location Detector L Power Overburden Detector M SSI 2004 Experimental Neutrino Oscillations - Gratta 99

46 Kashiwazaki (Japan) The largest nuclear power plant in the world! far near near SSI 2004 Experimental Neutrino Oscillations - Gratta 100

47 Diablo Canyon (PG&E) The prettiest reactor location in the world! other possibilities in this area 2 1 Locus of points that have same ratio of distances between the two reactors under the mountain ridge SSI 2004 Experimental Neutrino Oscillations - Gratta 101

48 Double-Chooz (funding from France approved) SSI 2004 Experimental Neutrino Oscillations - Gratta 102

49 Double Chooz has a less ambitious sin 2 2θ 13 =0.03 sensitivity goal but is the only experiment already on the way Errors are quite different for reactor and accelerator experiments stat only all errors P. Huber et al. hep-ph/ SSI 2004 Experimental Neutrino Oscillations - Gratta 103

50 A few words on applied neutrino physics Neutrino energy spectrum is a bit different for each of the 4 leading isotopes The antineutrino count rate varies in a known way as Pu is produced even at constant power Deviations from the expected trajectory with known power may reveal improper reactor use ν rate is directly related to power with known U/Pu ratio Example: ν counts 20 kg of fuel containing Pu are replaced with fresh U and then the reactor is restarted at the same power level A.Bernstein et al. J. Appl. Phys. 91 (2002) days in the fuel cycle SSI 2004 Experimental Neutrino Oscillations - Gratta 104

51 Technology demonstration detector (by LLNL & Sandia) ) being prepared at the San Onofre Nuclear Generating Station (CA) Set 1m 3 detector in the tendon gallery, 24.5 m from the core Heavy reactor building provides some shielding from cosmic rays Only good for inspections of cooperating reactors Continuous, real-time, quantitative information about core isotopics and/or power Non intrusive to reactor operation Reduction of manpower needed for inspections, cost effective Robust to many countermeasures SSI 2004 Experimental Neutrino Oscillations - Gratta 105

52 Daily Antineutrino Rate from SANDS 250 Reactor to 15% Start ramp to 100% Reactor trips Start ramp to 100% "antineutrinos" per day = reported thermal power 0 4/2/2004 4/4/2004 4/6/2004 4/8/2004 4/10/2004 4/12/2004 4/14/2004 Day SSI 2004 Experimental Neutrino Oscillations - Gratta 106

53 Limitations of conventional accelerator-based ν sources In a conventional accelerator-driven neutrino source neutrinos are produced by the decay of secondary particles (mainly π,, K) π and K are short lived, so focusing/momentum selection are very challenging µ are stopped to try limiting the ν produced in their decay SSI 2004 Experimental Neutrino Oscillations - Gratta 107

54 How about boosting a reactor, i.e. using neutrinos produced by whatever is stored in the accelerator can store µ: neutrino factory or unstable nuclei: β-beams no background neutrino species to worry about sharp energy (essentially from the boost) well understood divergence (again from the boost) (conceptually) easy to switch polarity The ideal neutrino mixing Lab! Unfortunately µ and unstable nuclei are by definition unstable particles, so their production and acceleration with large intensity is challenging SSI 2004 Experimental Neutrino Oscillations - Gratta 108

55 10 16 p/s µ/s = µ/yr µ/yr _ µ + e + ν e ν µ ν e /yr ν µ /yr oscillates ν e ν µ interacts giving µ WRONG SIGN MUON interacts giving µ + A.Blondel Nu04 SSI 2004 Experimental Neutrino Oscillations - Gratta 109

56 With a 40 kton detector able to distinguish charge 1yr data taking sin 2 2θ 13 =0.01 Baseline ν µ CC ν ecc CC ν µ (osc signal) 732 km 3500 km at J2K ~40 events! SSI 2004 Experimental Neutrino Oscillations - Gratta 110

57 CP violation: compare ν e ν µ to ν e ν µ (easy to switch sign) P( ν P( ν µ µ ν ) e ν ) + e P( ν P( ν ν e) ν ) in vacuum, at leading order in m 2 µ µ e sin 2θ 12 sin 2θ 2 2sin θ m12l sin 2Eν sin 2θ 13 sinδ CP Matter effects complicate things, but they also allow one to distinguish normal vs inverted hierarchy SSI 2004 Experimental Neutrino Oscillations - Gratta 111

58 Bueno, Campanelli, Rubbia hep-ph/ SSI 2004 Experimental Neutrino Oscillations - Gratta 112

59 Conclusions I have covered a small fraction of the different ideas and experiments connected to neutrino mixing (apologize for the many items that I left out) This is a fantastic field in rapid development It is a very broad field where fantasy is rewarded and surprises are common You should formulate and resolve the next puzzle!! SSI 2004 Experimental Neutrino Oscillations - Gratta 113