Oscillating Neutrinos and T2K

Transcription

1 Oscillating Neutrinos and T2K UVic Physics/Astronomy Colloquium Dean Karlen / University of Victoria & TRIUMF

2 Brief history of neutrinos Neutrinos were postulated by W. Pauli in 1930 to explain the apparent energy non-conservation in nuclear beta decay suggested that neutrinos only rarely interact with matter able to carry away energy undetected In the 1950s, Reines and Cowan (at Los Alamos) worked to develop an experiment that could detect neutrinos: first idea: detonate a 20 kton fission bomb! approved, but not attempted next idea: use a nuclear reactor as a steady high intensity source 2

3 Discovery of neutrinos Reines and Cowan succeeded in detecting neutrinos at the Savannah River nuclear reactor in 1956 reaction: inverse beta decay: prompt + delayed coincidence ν e e + e p n <10 µs Cd two 200 L tanks with water and cadmium salt to reduce n capture time to < 10 µs sandwiched by three scintillator tanks to detect the gammas (cf. T2K near detector tracker!) 3

4 Results: Reines and Cowan experiment signal/background: 3:1 predicted cross section (1956): (6.3 ± 1.5) cm 2 observed cross section: cm 2 (uncertainty ~ 5%) Agreement with theory too good? 1957 discovery of parity non-conservation in weak interactions: revised IBD cross section: (10.0 ± 1.7) cm 2 subsequent reanalysis of the original data: cm 2 4

5 More than one kind of neutrino In 1962, the existence of a second kind of neutrino, ν µ, was established by an experiment that directed high energy protons from the BNL AGS onto a target neutrinos produced by the decay of secondary hadrons tended to produce penetrating muons in the downstream detectors: 34 muon like, at most 5 electron like 5

6 Neutrino interactions Neutrinos only interact via the weak force weak because interaction involves a heavy mediator (W or Z) eg: neutrino from beta decay W n p e ν e eg: neutrino interactions in matter ν e e ν µ µ W W n p 6 n p

7 Neutrinos change their identity In the 1980s and 90s, experiments were performed to measure the rate of ν e and ν µ interactions from natural neutrino sources: neutrinos produced in the nuclear reactions in sun neutrinos produced in cosmic ray interactions with the atmosphere The results did not agree with Standard Model predictions The prevailing theory of neutrino properties had to be modified to explain the results when produced, a neutrino has a definite type (flavour) electron, muon, or tau (depending on the charged lepton involved) when the neutrino interacts at some later time, it may produce a different type of charged lepton as if it changed its identity lepton flavour not conserved: the neutrino oscillated 7

8 PMNS explanation In the 1960s, Pontecorvo, Maki, Nakagawa, and Sakata postulated that neutrinos might behave that way U = states of definite flavour = linear combination of states of definite mass if the masses differ, they get out of phase, leading to neutrino oscillation c 23 s 23 0 s 23 c 23 Solar and cosmic experiments: θ 12 = 34 ± 2, θ 23 = 45 ± 7 ν α = U αα ν i Δm 2 21 = 8.0 ± ev 2 2, Δm 32 = 2.4 ± ev 2 Reactor experiments: θ 13 < 95% CL : Is it zero? 3 i=1 c 13 0 s 13 e iδ s 13 e iδ 0 c 13 α = e, μ, τ i = 1,2,3 c 12 s 12 0 s 12 c s 23 = sin θ 23 c 23 = cos θ 23 8

9 θ 13 oscillation experiments Experiments that measure neutrino oscillation involving ν e over a suitable baseline can be sensitive to θ 13 Nuclear reactors produce a high flux of ν e with E ~ 1 MeV 2 L 1 P ν e ν e sin 2 2θ 13 sin 2 Δm 31 4E ν 2 L + cos 4 θ 13 sin 2 2θ 12 sin 2 Δm 21 4E ν Δm 2 31 L = 1.27 Δm 2 31 L GeV 4E ν ev 2 π km E ν 2 L 0.5 km E ν MeV Accelerators can produce high flux of ν µ with E ~ 1 GeV baselines of several 100 km required 9

10 Reactor measurements Three new experiments are just getting underway: Double Chooz (France), Reno (Korea), Daya Bay (China) larger detectors: more events + more shielding: less background include an identical near detector to reduce sensitivity to modelling the neutrino flux and cross section and the detector properties 2 L 1 P ν e ν e sin 2 2θ 13 sin 2 Δm 31 4E ν + cos 4 θ 13 sin 2 2θ 12 sin 2 Δm 21 2 L 4E ν sin 2 2θ 13 = 0.1 near far 10

11 Reno (Korea) 11

12 Located near Hong Kong Daya Bay (China) Multiple identical detectors at three sites: 4 detectors at far site, 2 detectors at the 2 near locations compare detectors at same site to confirm systematic errors tunnels between detector locations allow them to be exchanged if the systematic errors dictate Daya Bay near detector started data taking August 15, 2011 Ling Ao near detector to start later this year Far detector to start summer

13 Daya Bay detectors standard 4 concentric volumes outermost volume: water pool detectors performing well 13

14 Comparison of reactor experiments Specifications: Experiment Power (GW) L near/far (m) Depth n/f (mwe) Target mass (tons) sin 2 2θ 13 sensitivity* Double Chooz / / / RENO / /450 16/ Daya Bay /910 40,40/ * 90% CL upper limit if θ 13 = 0 (after 3 years running) Start of physics data collection: Experiment Near detector(s) Far detector Double Chooz end/2012 4/2011 RENO 8/2011 8/2011 Daya Bay 8/ fall/2011 summer/2012 Significant competition between similar detectors over the coming years 14

15 Accelerator experiments An accelerator neutrino experiment can estimate θ 13 by measuring the ν e appearance probability: start with a nearly pure beam of ν µ several 100 km away, detect and distinguish ν e and ν µ P ν μ ν e sin 2 θ 23 sin 2 2θ 13 sin 2 Δm 23 2 L 4E ν 15

16 T2K The T2K project, approved in December 2003, arose from a fortunate coincidence of two major facilities needed for neutrino oscillation experiment separated by an appropriate distance: The Japan Proton Accelerator Research Center (JPARC): the world s highest intensity proton beam Super Kamiokande: the world s largest water Cherenkov detector Super Kamiokande JPARC and neutrino beamline 16

17 T2K an off axis experiment The beam axis is directed 2.5 away from SK to: increase the flux of ~ 0.6 GeV neutrinos at SK those most sensitive to oscillation parameters for a 295 km baseline decrease the flux of higher energy neutrinos at SK which can be mis-reconstructed as lower energy neutrinos (background) relation between E ν and p π at fixed angles observed E ν spectrum at SK Interaction rate (arb units) E ν (GeV) 17

18 Neutrino detection Charged Current interactions identify the flavour of the neutrino For neutrinos with E ~ 0.6 GeV, the dominant cross section is CC quasi- elastic (CCQE) ν l l W n p The neutrino energy is estimated by measuring the momentum of the charged lepton and using momentum conservation 18

19 T2K - overview 30 GeV proton beam from J-PARC MR π +,K + μ-mon Near detectors off-axis ν SK ν 0m 120m 280m 295 km Several detector systems in place to monitor beam properties and stability: beamline monitors: proton beam position and direction at target muon monitor: direction of µ from hadron decays on-axis near detector: ν direction and rate off-axis near detector: ν spectrum, rate, purity, ν interaction studies 19

20 T2K - beamline superconducting magnets To SuperK muon monitor near detectors target beam dump horn 20

21 T2K near detectors On-Axis: INGRID 14 identical modules iron/scintillator sandwich 7 tons each ND280 INGRID

22 Off-Axis: ND280 T2K near detectors a multipurpose magnetic spectrometer (former UA1 magnet) pi-zero detector (P0D) tracker: scintillator (+ water) modules (FGDs) sandwiched by 3 TPCs electromagnetic calorimeters side muon range detectors UVic / TRIUMF / UBC groups led the tracker project design, construction, installation, operation 22

23 T2K near detector tracker Neutrinos interact in one of the 2 fine-grain detectors and the reaction products are detected in the Time Projection Chambers 2.5 m 23

24 UVic connections The electronics connections for the fine-grained detector were designed and constructed at UVic (thanks to electronics shop) 24

25 UVic connections Our group led the TPC project from inception Still at UVic: TPC prototype built at TRIUMF/UVic in 2005 proof of concept full funding for the 3 TPCs followed 25

26 UVic connections 3 TPCs installed in Japan in 2009 TPCs distinguish electrons from muons with de/dx 26

27 T2K far detector (Super K) Operated since April 1996 Fiducial volume: 22.5 kton 42 m 39 m 27

28 T2K SK particle identification SK atmospheric ν data compared with simulation: 28

29 T2K - analysis P ν μ ν e sin 2 θ 23 sin 2 2θ 13 sin 2 Δm 23 2 L 4E ν Evaluate this by counting the number of ν e events at SK: P ν μ ν e = Nν e candidates Nν e background ε ν e selection σ ν e Nν μ no oscillation σ ν μ Nν e background: ν e contamination of T2K beam, π 0 production Nν μ no oscillation: number of ν µ events expected with no oscillation A complete simulation of the beamline and detectors, with internal and external data, is used to calculate these quantities such as: hadron production from target: NA61 experiment and others Nν µ interactions in the off-axis near detector 29

30 T2K dataset shutdown Physics data collection from March 2010 March 2011 Proton intensity reached 145 kw Collected a few percent of the total expected dataset 30

31 March 11, 2011 The first results from T2K were to be announced at a special seminar scheduled for 3:00 PM at the Japanese laboratory, KEK At 2:46 PM magnitude 9 earthquake struck, followed by devastating tsunami waves No injuries or tsunami damage at the JPARC lab JPARC No damage to SK 31

32 Structural damage Severe road damage on site Little building damage Accelerator not severely damaged Returning to operation by end

33 ν µ interaction rate per POT stable direction stable and correctly centred T2K On-Axis ND (INGRID) 33

34 T2K Off-Axis ND (ND280): example events 34

35 T2K Off-Axis ND ν µ CCQE selection Data compared to simulation (not tuned) μ, Data μ, MC RNN = ± (stat) (det. sys) ± (phys. model) R NN 35

36 T2K-SK event selection Fully contained events (start and stop inside fiducial volume) in time with neutrino beam from J-PARC 36

37 T2K-SK event selection SK was well understood and well calibrated prior to T2K All ν e candidate selection criteria set prior to data collection: in time, fully contained events consistent with a single ring, plus: 37

38 T2K-SK event selection A total of 6 candidates selected expected number if θ 13 = 0 is 1.5 ± 0.3 probability to see 6 or more events if θ 13 = 0 is (p-value) 2.5σ 38

39 View from inside water tank grey dots: unhit PMTs color: arrival time size: light collected T2K-SK candidate event #1 39

40 T2K-SK event distributions fiducial volume expect a uniform distribution in R 2 : K-S test p-value = 0.03 do not see excess events outside fiducial volume 40

41 T2K confidence intervals Additional factors that affect the oscillation probability CP violation parameter δ mass hierarchy (normal or inverted) Chooz upper limit shown (in red) independent of δ and mass hierarchy Δm 23 sin 2 2θ 23 = 1 2 = ev 2 T2K publication: Phys. Rev. Lett. 107, (2011) (released June 15, 2011) 41

42 Global neutrino analysis Fogli et al, recently updated their analysis of all oscillation data Find the significance for θ 13 > 0 is more than 3σ Incorporating new models for reactor flux increases significance the near detectors at the new reactor experiments will check flux models G.L. Fogli, E. Lisi, A. Marrone, A. Palazzo, and A.M. Rotunno arxiv: v1 42

43 Summary Significant advances in measuring θ 13 have come about in the past few years precision reactor experiments are coming on-line T2K has given first strong indication that θ 13 0 In the coming years watch to see how the different oscillation measurements compare with each other, and whether the PMNS description continues to hold Provided θ 13 is large enough, new projects may move ahead to definitively measure the amount of CP violation in the lepton sector important input to understanding the origin of the matter/anti-matter asymmetry in the Universe 43

44 T2K International: Acknowledgements Canada, France, Germany, Italy, Japan, Korea, Poland, Russia, Spain, Switzerland, UK, USA T2K Canada: UVic, UBC, TRIUMF, U Alberta, U Regina, York U, U Toronto T2K UVic: For TPC/FGD construction: P. Birney, C. Bojechko, N. Braam, K. Fransham, A. Gaudin, C. Hansen, R. Hasanen, N. Honkanen, DK, R. Langstaff, M. Lenckowski, J. Myslik, M. Pfleger, P. Poffenberger, M. Roney, V. Tvaskis Continuing with T2K Operation and Physics Analyses: C. Bojechko, A. Gaudin, A. Hillairet, DK, J. Myslik 44

45 MINOS result 62 events selected Fit energy and PID discriminant (LEM): 45

46 MINOS - T2K comparison Prediction with T2K s best fit point: Overlay of MINOS and T2K contours: L. Whitehead BNL / MINOS 46

47 NOvA The next generation long baseline experiment at Fermilab is expected to start taking data in 2014 When combined with T2K data, sensitive to δ and mass ordering G. Feldman 47