Oscillating Neutrinos and T2K

UVic Physics/Astronomy Colloquium

Dean Karlen / University of Victoria & TRIUMF

Oscillating Neutrinos and T2K

Brief history of neutrinos

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 2

• 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

Discovery of neutrinos

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 3

• Reines and Cowan succeeded in detecting neutrinos at the Savannah River nuclear reactor in 1956 • reaction: inverse beta decay: prompt + delayed coincidence

• 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!)

p n

Cd

νe e+

e−

<10 µs

Reines and Cowan experiment

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 4

• Results: • signal/background: 3:1

• predicted cross section (1956):

(6.3 ± 1.5) × 10-44 cm2

• observed cross section:

6 × 10-44 cm2 (uncertainty ~ 5%)

• Agreement with theory too good? • 1957 discovery of parity non-conservation in weak interactions:

• revised IBD cross section: (10.0 ± 1.7) × 10-44 cm2

• subsequent reanalysis of the original data: 12−4+7 × 10−44 cm2

More than one kind of neutrino

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 5

• In 1962, the existence of a second kind of neutrino, νµ, 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

Neutrino interactions

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 6

• Neutrinos only interact via the “weak” force • weak because interaction involves a heavy mediator (W or Z)

• eg: neutrino from beta decay

• eg: neutrino interactions in matter νe e−

n p

W

νµ µ−

n p

W

νe

e−

n p

W

Neutrinos change their identity

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 7

• In the 1980s and 90s, experiments were performed to measure the rate of νe and νµ 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”

PMNS explanation

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 8

• In the 1960s, Pontecorvo, Maki, Nakagawa, and Sakata postulated that neutrinos might behave that way…

• states of definite flavour = linear combination of states of definite mass

• if the masses differ, they get out of phase, leading to neutrino oscillation

• Solar and cosmic experiments: • 𝜃12 = 34 ± 2° , 𝜃23 = 45 ± 7°

• Δ𝑚212 = 8.0 ± 0.5 × 10−5 eV2 , Δ𝑚32

2 = 2.4 ± 0.1 × 10−3 eV2

• Reactor experiments: 𝜃13 < 11° @ 95% CL : Is it zero?

|𝜈𝛼⟩ = �𝑈𝛼𝛼∗ |𝜈𝛼⟩3

𝛼=1

𝛼 = 𝑒, 𝜇, 𝜏 𝑖 = 1,2,3

𝑈 =1 0 00 𝑐23 𝑠230 −𝑠23 𝑐23

×𝑐13 0 𝑠13𝑒−𝛼𝛿0 1 0

−𝑠13𝑒−𝛼𝛿 0 𝑐13×

𝑐12 𝑠12 0−𝑠12 𝑐12 0

0 0 1

𝑠23 = sin𝜃23 𝑐23 = cos𝜃23

θ13 oscillation experiments

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 9

• Experiments that measure neutrino oscillation involving νe over a suitable baseline can be sensitive to θ13 • Nuclear reactors produce a high flux of 𝜈𝑒 with E ~ 1 MeV

• Accelerators can produce high flux of νµ with E ~ 1 GeV

• baselines of several 100 km required

1 − 𝑃 𝜈𝑒� → 𝜈𝑒� ≈ sin2 2𝜃13 sin2Δ𝑚31

2 𝐿4𝐸𝜈

+ cos4 𝜃13 sin2 2𝜃12 sin2Δ𝑚21

2 𝐿4𝐸𝜈

Δ𝑚312 𝐿

4𝐸𝜈= 1.27

Δ𝑚312

eV2𝐿

kmGeV𝐸𝜈

∼𝜋2

⇒ 𝐿 ∼ 0.5 km 𝐸𝜈

MeV

Reactor measurements

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 10

• 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

1 − 𝑃 𝜈𝑒� → 𝜈𝑒� ≈ sin2 2𝜃13 sin2Δ𝑚31

2 𝐿4𝐸𝜈

+ cos4 𝜃13 sin2 2𝜃12 sin2Δ𝑚21

2 𝐿4𝐸𝜈

sin2 2𝜃13 = 0.1

near far

Reno (Korea)

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 11

Daya Bay (China)

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 12

• Located near Hong Kong

• 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 2012

Daya Bay detectors

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 13

• “standard” 4 concentric volumes • outermost volume: water pool

• detectors performing well

Comparison of reactor experiments

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 14

• Specifications:

• Start of physics data collection:

Experiment Power (GW)

L near/far (m)

Depth n/f (mwe)

Target mass (tons)

sin22θ13 sensitivity*

Double Chooz 8.7 400/1050 110/300 8.3/8.3 0.03 RENO 16.4 290/1380 120/450 16/16 0.02 Daya Bay 17.7 360-1980 270/910 40,40/80 0.01

* 90% CL upper limit if θ13 = 0 (after 3 years running)

Experiment Near detector(s) Far detector Double Chooz end/2012 4/2011 RENO 8/2011 8/2011 Daya Bay 8/2011 + fall/2011 summer/2012

Significant competition between similar detectors over the coming years

Accelerator experiments

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 15

• An accelerator neutrino experiment can estimate θ13 by measuring the νe appearance probability: • start with a nearly pure beam of νµ

• several 100 km away, detect and distinguish νe and νµ

𝑃 𝜈𝜇 → 𝜈𝑒 ≈ sin2 𝜃23 sin2 2𝜃13 sin2Δ𝑚23

2 𝐿4𝐸𝜈

T2K

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 16

• 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

JPARC and neutrino beamline Super Kamiokande

T2K – an off axis experiment

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 17

• 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)

Inte

ract

ion

rate

(arb

uni

ts)

𝐸𝜈 (GeV)

relation between Eν and pπ at fixed angles observed Eν spectrum at SK

Neutrino detection

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 18

• 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)

• The neutrino energy is estimated by measuring the momentum of the charged lepton and using momentum conservation

νl l−

n p

W

T2K - overview

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 19

• 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

30 GeV proton beam from J-PARC MR

π+,K+

ν

120m 0m 280m 295 km

off-axis μ-mon

ν

Near detectors SK

T2K - beamline

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 20

beam dump

muon monitor

horn

target

superconducting magnets

near detectors

To SuperK

T2K – near detectors

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 21

• On-Axis: INGRID • 14 identical modules

• iron/scintillator sandwich

• 7 tons each

INGRID

ND280

0°

2.5°

T2K – near detectors

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 22

• Off-Axis: ND280 • 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

T2K – near detector tracker

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 23

• Neutrinos interact in one of the 2 fine-grain detectors and the reaction products are detected in the Time Projection Chambers

2.5 m

UVic connections

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 24

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

UVic connections

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 25

• 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

UVic connections

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 26

• 3 TPCs installed in Japan in 2009

TPCs distinguish electrons from muons with dE/dx

T2K – far detector (Super K)

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 27

• Operated since April 1996

• Fiducial volume: 22.5 kton

39 m

42 m

T2K – SK particle identification

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 28

SK atmospheric ν data compared with simulation:

T2K - analysis

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 29

• Evaluate this by counting the number of νe events at SK:

• 𝑁𝜈𝑒 background: νe contamination of T2K beam, π0 production

• 𝑁𝜈𝜇 no−oscillation: number of νµ 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

• Nνµ interactions in the off-axis near detector

𝑃 𝜈𝜇 → 𝜈𝑒 ≈ sin2 𝜃23 sin2 2𝜃13 sin2Δ𝑚23

2 𝐿4𝐸𝜈

𝑃 𝜈𝜇 → 𝜈𝑒 = 𝑁𝜈𝑒 candidates − 𝑁𝜈𝑒 background𝜀 𝜈𝑒 selection 𝜎 𝜈𝑒

𝑁𝜈𝜇 no−oscillation𝜎 𝜈𝜇

�

T2K dataset

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 30

• Physics data collection from March 2010 – March 2011

• Proton intensity reached 145 kW

• Collected a few percent of the total expected dataset …

shutdown

March 11, 2011

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 31

• 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

• No damage to SK

JPARC

Structural damage

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 32

• Severe road damage on site

• Little building damage

• Accelerator not severely damaged • Returning to operation by end 2011

T2K On-Axis ND (INGRID)

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 33

• νµ interaction rate per POT stable

• direction stable and correctly centred

T2K Off-Axis ND (ND280): example events

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 34

T2K Off-Axis ND νµ CCQE selection

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 35

• Data compared to simulation (not tuned)

𝑅𝑁𝑁𝜇, Data 𝑅𝑁𝑁

𝜇, MC� = 1.036 ± 0.028 (stat) −0.037+0.044 (det. sys) ± 0.038 (phys. model)

T2K-SK event selection

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 36

• Fully contained events (start and stop inside fiducial volume) • in time with neutrino beam from J-PARC

T2K-SK event selection

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 37

• SK was well understood and well calibrated prior to T2K • All νe candidate selection criteria set prior to data collection:

• in time, fully contained events consistent with a single ring, plus:

T2K-SK event selection

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 38

• A total of 6 candidates selected • expected number if θ13 = 0 is 1.5 ± 0.3

• probability to see 6 or more events if θ13 = 0 is 0.007 (p-value) → 2.5σ

T2K-SK candidate event #1

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 39

• View from inside water tank • grey dots: unhit PMTs

• color: arrival time

• size: light collected

T2K-SK event distributions

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 40

• expect a uniform distribution in R2: K-S test p-value = 0.03 • do not see excess events outside fiducial volume

fiducial volume

T2K confidence intervals

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 41

• 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

• T2K publication: • Phys. Rev. Lett. 107, 041801 (2011)

(released June 15, 2011)

sin2 2𝜃23 = 1 Δ𝑚23

2 = 2.4 × 10−3eV2

Global neutrino analysis

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 42

• Fogli et al, recently updated their analysis of all oscillation data • Find the significance for θ13 > 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:1106.6028v1

Summary

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 43

• Significant advances in measuring θ13 have come about in the past few years • precision reactor experiments are coming on-line

• T2K has given first strong indication that 𝜃13 ≠ 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 θ13 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

Acknowledgements

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 44

• T2K – International: • 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

MINOS result

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 45

• 62 events selected

• Fit energy and PID discriminant (LEM):

MINOS - T2K comparison

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 46

L. Whitehead BNL / MINOS

Prediction with T2K’s best fit point: Overlay of MINOS and T2K contours:

NOvA

September 14, 2011 Oscillating Neutrinos and T2K Dean Karlen / University of Victoria and TRIUMF 47

• 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