Neutrino mixing II. Can ν e ν µ ν τ? If this happens:

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1 Can ν e ν µ ν τ? If this happens: Neutrino mixing II neutrinos have mass (though there are some subtleties involving the MSW mechanism) physics beyond the (perturbative) Standard Model participates Outline: quick reminder about mixing phenomenology experimental signatures and a review of some of the results present/planned experiments 2/27/01 HEP lunch talk: George Gollin 1

2 Mixing phenomenology We produce flavor eigenstates ν e,µ,τ... u µ + π + W + d ν µ weak interaction produces a ν µ but the mass eigenstates ν 1, ν 2, ν 3 are what propagate sensibly : ( ) = ( 0) ν τ ν imc 1 τ i i e 2 ħ ν i ( ) = ν ( ) i 2 3 i 0 im c x ( 2E ħ) x e ν proper time τ flight path x ν 1, ν 2, ν 3 phases rotate relative to each other if masses are unequal. change basis using the MNS (Maki-Nakagawa-Sakata) matrix: νe ν1 ν = U ν µ 2 ν τ ν 3

3 Mixing phenomenology iδ c13 0 s13e c12 s12 0 U = 0 c23 s s12 c iδ 0 s23 c 23 s13e 0 c ν µ ντ νe ν ν τ e νµ t = 0 ( ) ν ν 0 = 1 µ ν ν sec ( ) µ n e n m n t P = P = 1. P = n e n m n t P = P = P = n 1 n 2 n 3 m 1 = 0.1 ev m 2 = 0.3 ev m 3 = 0.4 ev q 12 =10. deg q 13=20. deg q 23 =30. deg t = 0. sec n 1 n 2 n 3 m 1 = 0.1 ev m 2 = 0.3 ev m 3 = 0.4 ev q 12 =10. deg q 13=20. deg q 23 =30. deg t = sec ν 1, ν 2, ν 3 phases have changed: heavier species phase-rotate more rapidly.

4 Two-flavor mixing phenomenology ( ν ) µ νe ( θ ) P ; L sin 2 12 sin 1.27 m21 E Green curve is contour of fixed probability to observe oscillation ev 2 L km GeV Large m 2 : uncertainty in L/E corresponds to several oscillations. Medium m 2 : uncertainty in L/E is a fraction of an oscillation; 1.27 m 2 L/E ~ π/2 for some events Small m 2 : sin 2 (1.27 m 2 L/E) < 1 since L/E is always small; P corresponds to larger and larger sin 2 (2θ) as m 2 L/E shrinks.

5 Places to look for signs of ν oscillation Atmospheric neutrinos from cosmic ray interactions pions, muons decay in flight, yielding twice as many ν µ as ν e. + + π µν µ e + νν e µ Solar neutrinos, in particular from the p-p reaction which produces most of the sun s energy Standard Solar Model (SSM) predictions for ν e flux and spectrum seem fairly robust. Accelerator- (or reactor-) based experiments produce ν beam of known ν e /ν µ /ν τ content and energy spectrum. Any surprises concerning detected ν flux or species mixture might indicate ν e and/or ν µ oscillations. 2/27/01 HEP lunch talk: George Gollin 5

6 Atmospheric neutrinos Cosmic ray interactions in the atmosphere produce ν s through decays of π, µ. Expect ~twice as many ν µ as ν e detect neutrinos, compare ν e and ν µ rates. 4 d Nν dadωde dt ν Also expect upwards-going and downwards-going rates and ν µ /ν e mix to be equal (same as argument for zero electric field inside a charged sphere) ( ) 9 2 ~10 ν m ster 100 MeV year Earth + + π µν µ e + νν e µ at 1 GeV 50/year/kT target which produces downwards-going ν s ν detector Earth s atmosphere Largest detector is 50kT Super-Kamiokande... target which produces upwards-going ν s

7 50 kt water Cerenkov detector: 22.5 kt fiducial; 11,412 pmt s Super-Kamiokande 1000 meters underground (2.2 Hz rate from cosmic rays) ν µ µx: fairly sharp Cerenkov ring ν e ex : diffuse ring ν µ interactions in the rock below Super-K create upward-going muons Use upward-going events to unfold downward-going ν-induced from µ- induced events. UIUC Assembly Hall Super-Kamiokande

8 Super-Kamiokande Parent ν µ energy spectra for stopping and through-going upward muons (hep-ex/ v3, 12/1/99) ( νµ νe ) ( θ ) P ; L sin 2 12 sin 1.27 m21 E L ~ 10 4 km, E ~ 10 2 GeV m 2 sensitivity ~ few 10-3 ev 2 L µ energy spectra, stopping upward muons (hep-ex/ v3, 12/1/99)

9 Other detectors MACRO in Gran Sasso tunnel 5.3 kt tracking: streamer tubes calorimetry: liquid scintillator Soudan 2 in Minnesota 0.9 kt tracking and calorimetry combined: TPC drift tubes in corrugations of steel sheets

10 Atmospheric results: upward-going ν µ / ν e ratios Plotted: ( µ e) ( µ e) data Monte Carlo (= 1 if no oscillations) (hep-ex/ v2) Monte Carlo calculations are important, but well-verified by a variety of means (e.g. confirmation of geomagnetic effects)

11 Atmospheric results: up-down asymmetry upwards-downwards asymmetry as a function of µ, e energy (from Super-K, in hep-ex/ v2) (hep-ex/ v2) FC: track starts, stops inside detector PC: track starts in detector then exits Super-K result (not limit!) ν µ flux is up-down asymmetric, ν e is not!

12 Role of MSW effect in ν results Recall perturbation theory in quantum mechanics: unperturbed eigenstates are, ν, ν e µ including perturbation V yields eigenstates ν, ν, ντ a b νc νb ν + ν ν V ν ρ µ µ ρ ρ= e, τ Eµ Eρ neutrinos propagating through matter to arrive at a detector have been interacting while in flight (that s the perturbation V): ν e ν e e ν e A ν e e Z Z W ν e ν e e ν e A e ν e ν µ ν µ e ν µ A + + Z Z ν µ ν µ e ν µ A ν τ ν τ ν sterile ν sterile ν τ e ν τ A + Z + Z ν τ e ν τ A

13 Role of MSW effect in ν results ν e interactions include a W-exchange diagram which shifts ν e energy (relative to ν µ, ν τ ) by 2G. (solar N e ~ 1026 /cm 3 ; terrestrial N e ~ /cm 3 F N e.) νρ V νµ νb νµ + νρ E E ρ= e, τ µ ρ ( ) m Eµ E p + m p + m + G N GN 2 p e F e 2 F e 2 m21 2 2pGFNe would enhance ν µ ν e mixing considerably since E µ - E e denominator is small. Also, differences in ν µ and ν sterile interactions can enhance ν µ ν sterile mixing. Atmospheric ν µ ν sterile : p ~ 15 GeV/c, m 2 ~ ev 2. Solar ν e ν µ : p ~ 1 MeV/c, m 2 ~ 10-5 ev 2.

14 Atmospheric results commentary Super-K data reported in hep-ex/ (9/1/00), 70.5 kt year: 9178 FC events: 3107 e-like, 2988 µ-like, 3083 multiple-c-ring 665 PC events (all muons??) 1269 upward-going through muons ν e flux is up-down symmetric so it seems that ν µ ν e ν µ upwards-going rate < ν µ downwards-going rate so νµ ντ or νsterile Super-K analysis selects an enriched NC signal to investigate ν ν ν : up/down symmetry in NC rate means ν τ, not ν sterile. µ τ vs. sterile Conclusion: νµ ντ 2/27/01 HEP lunch talk: George Gollin 14

15 Solar neutrinos (most of the sun s energy from pp) 2/27/01 HEP lunch talk: George Gollin 15

16 Solar neutrinos Standard Solar Model neutrino fluxes accurate to a few per cent... 2/27/01 HEP lunch talk: George Gollin 16

17 Solar neutrinos Three different kinds of experiments, covering different energy ranges: SAGE, Gallex: ν e + Ga31 Ge32 + e (E ν > 232 kev) Homestake mine: ν e + Cl17 Ar18 + e (E ν > 814 kev) Water Cerenkov: νe + e νe+ e elastic scattering (E ν > ~ 6 MeV) Target Experiment observed/expected ν source 37 Cl Homestake 71 Ga SAGE 71 Ga Gallex ± B, 7 Be ± pp, pep, 7 Be ± pp, pep, 7 Be Water C Water C Super-K Kamiokande ± B 0.56 ± B 2/27/01 HEP lunch talk: George Gollin 17

18 So what gives? How good is the SSM? probably pretty good. It gets the helioseismology right. ( ν ν ) ( θ) P e x ; L sin 2 sin 1.27 m E L L ~ km, E ~ 10-3 GeV m 2 sensitivity ~ 10-5 ev 2 for large mixing angle. 2/27/01 HEP lunch talk: George Gollin 18

19 Solar neutrinos Simultaneous fit to the three different kinds of experiments yields four possible sets of parameters... Type Large angle Small angle m 2 = ev 2 m 2 = ev 2 MSW ν e ν active sin 2 2θ = 0.76 sin 2 2θ = m 2 = ev 2 MSW ν e ν sterile sin 2 2θ = Vacuum oscillation m2 = ev 2 sin 2 2θ = /27/01 HEP lunch talk: George Gollin 19

20 Solar neutrinos 4 sets of parameters: 3 for MSW oscillations, 1 for vacuum oscillations. Important for sorting this out: measure NC / CC ratio to see if there really are ν e ν µ, ν τ oscillations (ν µ, ν τ will only interact through NC at this energy.) SNO will do this fairly soon...

21 Solar neutrinos: SNO Sudbury Neutrino Observatory (SNO): 1kT D 2 O surrounded by water C veto. will observe ν e + d p + p + e - (CC) ν x + d p + n + ν x (NC) CC measures solar ν e flux; NC measures total (active) ν flux. Expect 5.5 NC events/day, 12.7 CC events/day (assuming 50% oscillation probability for solar neutrinos). 2/27/01 HEP lunch talk: George Gollin 21

22 Solar neutrinos: SNO SNO is only sensitive to 8 B neutrinos. 1 kt D 2 O 7.8 kt H 2 O (veto) ν e + d p + p + e - (CC: observe Cerenkov light from e - ) ν x + d p + n + ν x (NC: after thermalization, n + p d + γ 2.2 MeV )

23 Accelerator-based experiments L target decay volume proton beam π µ focusing horn δl n m near detector far detector ( ν ) µ νe ( θ ) P ; L sin 2 12 sin 1.27 m21 E L Produce ν beam of known ν e /ν µ /ν τ content and energy spectrum Look for change in ν e /ν µ /ν τ content as a function of L/E 2/27/01 HEP lunch talk: George Gollin 23

24 Accelerator-based experiments The only positive appearance result comes from the accelerator experiment LSND. (Super-K and solar neutrino results involve neutrino disappearance.) 1 ma 800 MeV proton beam water target copper beamstop neutrinos shielding veto steel detector water plug 24

25 LSND Liquid Scintillator Neutrino Detector: 1 ma 800 MeV (kinetic) energy proton beam produces π, µ most π -, µ - stop in shielding; signal: + + π µν µ + νµ νe then νep en then np dγ µ νν + + e e µ 2.2 MeV scintillation light from e + (delayed) scintillation light from 2.2 MeV γ Cerenkov cone from e + 25

26 LSND 167 T mineral oil with.031 g/l scintillator Detect both Cerenkov and scintillation light PMT s Typical e + energy: few dozen MeV νe νµ HEP lunch talk: George Gollin 26

27 ν µ ν e LSND result ± 23.4 candidates 17.3 ± 4 background 82.8 ± 23.7 events BNL E776 Karmen Bugey Oscillation probability: (0.32 ± 0.09 ± 0.05)% LSND 90% LSND 95%

28 LSND result Weaker evidence for ν µ ν e oscillations: signal is ν ν then ν C ex (60 MeV < E < 200 MeV) µ e e e 27.7 ± 6.4 candidates 9.6 ± 1.9 background 18.1 ± 6.6 ± 3.5 events Oscillation probability: (0.26 ± 0.10 ± 0.05)% 2/27/01 HEP lunch talk: George Gollin 28

29 Testing LSND BooNE (Booster Neutrino Experiment) at Fermilab Same idea as LSND, but higher energy: E ν ~ 1 GeV. Lightly doped mineral oil.

30 MiniBooNE: checking LSND Single detector, 40 foot diameter sphere. Uses LSND PMT s and electronics. 445 T fiducial target mass. If LSND is right: ~1000 ev/year.

31 Future accelerator experiments MINOS: long baseline. near detector at Fermilab 5.4 kt far detector in Soundan mine, Minnesota (730 km) both detectors are ironscintillator sandwiches.

32 K2K: long baseline too. Future accelerator experiments

33 Conclusions Are we having fun yet? You bet! Are we seeing neutrino oscillations? Maybe-- the Super-K results are very compelling 2/27/01 HEP lunch talk: George Gollin 33