J-PARC Seminar
28 10 20

Neutrino Interaction
Studies and Issues at T2K
Morgan O. Wascko
m.wascko@imperial.ac.uk

Imperial College London & KEK

Outline• Introduction:neutrino oscillation and CP violation• Key issues for modelling neutrino interactions• T2K experiment• T2K Neutrino Interaction Model• Some ideas on how to improve data publication• Conclusion

JPARC Seminar, 2016 10 20

Morgan O. Wascko

2

Neutrino Oscillation

JPARC Seminar, 2016 10 20

Morgan O. Wascko

3

Neutrino oscillationµeνPontecorvo
Sov.Phys.JETP
6:429,1957

W

W

SourceDetector

Maki,
Nakagawa,
SakataProg.Theor.Phys. 28,
870 (1962)

Sov.Phys.JETP
26:984-988,1968

Simple 2 neutrino exampleif weak eigenstates (νe, νμ) differ from mass eigenstates (ν1, ν2):

✓ ◆
✓
ne
cosq
=
nµ
sinq

ν1

ν2

◆✓ ◆
sinq
n1
cosq
n2

Poscillation (nµ ! ne ) = sin2 2qsin2✓

1.27 Dm2 (eV 2 ) L(km)En (GeV )JPARC Seminar, 2016 10 20

νμ

ϴ
νe

◆
Morgan O. Wascko

4

Current neutrino picture

Mass (eV)flavour
atmospheric
0
1 0
10
⌫e
1
0
0
@ ⌫µ A = @ 0 c23 s23 A @⌫⌧0s23 c23

0.05

0.009

<2

accelerator
c130
s13 ei0 s13 e
1
0
0
c13

solar
i

10

10

1
0
c12 s12 0↵
A @ s12 c12 0 A @ 0 ei 221
0
0 1
0
0

flavour key: νe νµ ντ

mass
10
1
0
⌫1
0 A @ ⌫2 A
↵
i 231
⌫3
e

VALUE

ν3

atmosphericsolar

Majorana

ν2
ν1|Δm232|2.35±0.12 E-03 (eV2)Δm2217.58±0.24 E-05 (eV2)sin2θ120.31±0.018

sin2θ230.42±0.08

sin2θ130.02±0.007

δCP

3𝜋/2?

Accelerator experiments measure: Δm232 (including sign), sin2θ23, sin2θ23 & δCP
JPARC Seminar, 2016 10 20

Morgan O. Wascko

5Breakthrough Prize Awards Ceremony

T2K founding spokesperson Ko Nishikawa and all T2K collaboration
members won the 2016 Breakthrough Prize for fundamental physics!
Kajita-san

Nishikawa-san

Breakthrough Prize Partygoers

T2K Spokespersons

Measuring CPV in T2K
2.5° Off-axis ν fluxµ

-3∆m232=2.5x10 eV2, sin2θ23=0.5

1Osc. Prob

Osc. Prob

νµ→νµ = νµ→νµ

0.1

νµ→νe, νµ→νe

2.5° Off-axis ν fluxµ

δcp=0°, NH, ν

0.08

δcp=270°, NH, νδcp=0°, NH, ν

0.06

δcp=270°, NH, ν

0.04

0.5

0.02
0

0.5

1

1.5

2

2.5
3
Eν (GeV)• Tests CPT symmetry• Leading order dependence on sin 2θ
• Can’t separate θ >45° from θ <45°
• Leading order dependence on |Δm |• Doesn’t depend on the sign of the
2

23

23

23
2

32

mass splitting (hierarchy)

0

0.5

1

1.5

2

2.5
3
Eν (GeV)• Tests CP symmetry• Leading order dependence on sin 2θ
• Leading order dependence on sin θ• Can separate θ >45° from θ <45°
• Sub-leading dependence on sin(δ )• Can detect CP violation• Sub-leading dependence on Δmthrough matter effect• Relatively small in T2K due to baseline
2

13

2

23

23

23

cp

2

32

JPARC Seminar, 2016 10 20

Morgan O. Wascko

7

How to measure CPV
Convenient to discuss CPV as an asymmetry between neutrino and antineutrino oscillation

To first order, can express this in terms of mixing angles as

rge
a
l
s
a
!
t
e
c
b
e
ff
C a n 2 5% e
as ~Coherent forward scattering of νes on electrons in matter changes
energy and path-length dependence
Must separate matter effects from true CP violation

Most robust strategy is to perform two CPV experiments✓ One with strong matter effects✓ One without strong matter effects
Current generation: NOvA & T2K
Next generation: DUNE & Hyper-Kamiokande
JPARC Seminar, 2016 10 20

Morgan O. Wascko

8δCP (radians)

MC

T2K 2016: δCP vs. θ13

3sensitivity•

T2K Run1-7c preliminary21
068.27%CL
90%CL
Best-fit-1Normal Hierarchy• T2K-only• T2K with reactor sin 2θ = 0.085±0.005
2

-3
0

CP

values and reactor θ13

Fixed Mass Hierarchy
0.02

0.04

0.06

13

• Below: δ with Feldman-Cousins critical

Inverted Hierarchy-2

Left: δCP vs. θ13 (fixed Δχ2, fixed hierarchy)

0.08

0.1
2

δCP (radians)

note change in horizontal scale3

sensitivity

2Best-fit

6

Inverted Hierarchy

8

sensitivity

T2K Run1-7c preliminary
Normal Hierarchy

5

Inverted Hierarchy

4
3

-1

Fixed Mass Hierarchy

2

-2

1

T2K Run1-7c preliminary
-3
0.015

9
7

Normal Hierarchy
01068.27%CL (-2ln L = 2.3)
crit90%CL (-2ln L = 4.61)
crit

1

-2lnL

sin θ13

0
0.02

0.025

0.03

0.035

-3

sin2 θ13
JPARC Seminar, 2016 10 20

-2

-1

0

1

2

3

δCP (radians)
Morgan O. Wascko

9δCP (radians)

Data

T2K 2016: δCP vs. θ13

3measurement

T2K Run1-7c preliminary•2
68.27%CL
90%CL
Best-fit
PDG 2015

1
0• T2K-only• T2K with reactor sin 2θ = 0.085±0.005
2

Normal Hierarchy-1CPvalues and reactor θ13

Fixed Mass Hierarchy
0.04

0.06

0.08

0.1
2

δCP (radians)

note change in horizontal scale3

sin θ13

measurement

T2K Run1-7c preliminary

2

0

25

measurement

T2K Run1-7c preliminary
20

Normal Hierarchy
Inverted Hierarchy

68.27%CL
90%CL
Best-fit1

δCP = [-3.13, -0.39] (NH), [-2.09, -0.74] (IH)@90% CL
-2lnL

0.02

13

• Below: δ with Feldman-Cousins critical

Inverted Hierarchy

-2
-3
0

Left: δCP vs. θ13 (fixed Δχ2, fixed hierarchy)

15
10

Normal Hierarchy-1

Inverted Hierarchy

5-2

Fixed Mass Hierarchy
-3
0.015

0
0.02

0.025

0.03

0.035

-3

sin2 θ13
JPARC Seminar, 2016 10 20

-2

-1

0

1

2

3

δCP (radians)
Morgan O. Wascko

10

T2K 2016: Discussion•The case of NH & δ

CP =−π/2

observed vs. expected number of νe and νe candidates
EXPECTED (NH, sin2Θ23=0.528)

that induces the largest
asymmetry•

For NH & δCP =−π/2 , T2K
Observes:•more ν candidates thanepredicted for•fewer ν̅ candidates thanepredicted

OBS.

δCP=-π/2

δCP=0

δCP=+π/2

δCP=π

νe

32

27.0

22.7

18.5

22.7

ν̅e

4

6.0

6.9

7.7

6.8

• Toy MC run to assess probability of outcome

given a set of “true” parameters• Below: fraction where δCP =0 excluded at 90%

or 2 σ CL for NH, δCP = -π/2, 0•Statistical fluctuations, or

TRUE PARAMETERS

physics effect?

•Need more data!

δCP=-π/2, NH

δCP=0, NH

90%

0.187

0.102

2σ

0.089

0.047

JPARC Seminar, 2016 10 20

Morgan O. Wascko

11

Interaction model issues for CPV• Signature of CPV is difference between measured

P(νµ→νe) and P(νµ̅ →νe̅ ), with important informationfrom energy distributions• Anything that creates artificial differences fromexpectations is a systematic errors for our CPV search• ν vs. ν• interaction backgrounds• ν vs. ν̅• energy reconstruction• nuclear targets, nucleon FF• additional interaction strength, modes,µ

ekinematics…

JPARC Seminar, 2016 10 20

Morgan O. Wascko

12

What do weneed?

K2K 1kt data

•Need to predict event rates andkinematics of final state particles•Need to accurately calculate inferred(physics) variables from our observed
variables•

For oscillations, need to reconstructneutrino energy
different ways to do thisAll methods need good xsecs!
all beams are relatively wideband

K2K SK prediction••••Need to accurately predict backgroundcontamination➡Need to understand neutrino-nucleus
cross-sections precisely➡Need good models

Phys.Rev.D 74 072003 (2006)
JPARC Seminar, 2016 10 20

Morgan O. Wascko

13

Xsecs and Oscillations•Cross section models used byexperiments cannot fully describe
observations by: K2K, MiniBooNE,
SciBooNE, MINERvA, T2K, …

•Leads to inflation of systematic
uncertainties•Model dependence often injected
into data analysis•Inferred variables•Energy, Q reconstruction•Background subtraction•Using these models will always

Systematic uncertainties reported by theworld’s most sensitive νe appearance
experiments vs. time

Experimentxsec err (%)

total err (%)

MiniBooNE(2007)

12.3

17.6

T2K (2012)

7.5

10.3

T2K (2016)

4%

6%

2

give such uncertainties.

•Need to improve models!

How are we improving the errors?
Using better models!
How are we improving models?
Tuning with better data!

JPARC Seminar, 2016 10 20

Morgan O. Wascko

14

T2K

Super Kamiokande

JPARC Seminar, 2016 10 20

Morgan O. Wascko

15

The T2K Collaboration
CanadaTRIUMFU. B. Columbia
U. Regina
U. Toronto
U. Victoria
U. Winnipeg
York U.
FranceCEA Saclay
IPN Lyon
LLR E. Poly.
LPNHE Paris
Germany
U. Aachen

Italy
INFN, U. Roma
INFN, U. Napoli
INFN, U. Padova
INFN, U. BariJapan
ICRR Kamioka
ICRR RCCN
Kavli IPMU
KEKKobe U.
Kyoto U.
Miyagi U. Edu.
Okayama U
Osaka City U.
Tokyo Metropolitan U.
U. Tokyo
Yokohama National U.

PolandIFJ PAN, Cracow
NCBJ, Warsaw
U. Silesia, Katowice
U. Warsaw
Warsaw U.T.
U. Wroclaw
RussiaINR
Spain
IFAE(Bacelona)
IFIC, Valencia
U.A. Madrid
Switzerland
ETH Zurich
U. Bern
U. Geneva

United Kingdom
Imperial C. London
Lancaster U.
Liverpool U.
Oxford U
Queen Mary U. L.
Royal Holloway U.L.
Sheffield U.
Warwick U.
STFC/RAL
STFC/Daresbury
USA
Boston U.
Colorado S. U.
Duke U.
Louisiana S. U.
Michigan State U.
Stony Brook U.
U. C. Irvine
U. Colorado
U. Pittsburgh
U. Rochester
U. Washington~500 members, 62 Institutes, 11 countries
JPARC Seminar, 2016 10 20

Morgan O. Wascko

16

T2K strategy
Search for δCP by comparing νµ→νe and νμ̅ →νe̅ .

Intense beam
protons

oscillation

π, π, π, π, ΚΦν(E)Gigantic detector

ν, ν, ν, ν

σ

σ

νµ

µ

νe

p

e

p

Φνnear(E)⋅σnear(E)⋅εnear(E) ⇔ Φνfar(E,𝜃,𝛥m2,𝛿)⋅σfar(E)⋅εfar(E)µνprotonJPARC Seminar, 2016 10 20πMorgan O. Wascko

17Off-Axis BeamSK

ND Off-axis

J-PARC∠2.5°

ND On-axis•Use kinematics of pion decay
to tune the neutrino energy•Flux peak at target energy fordesired value of L/E•Eν well matched to Super-K

JPARC Seminar, 2016 10 20

Morgan O. Wascko

18

LinacNeutrino Beam to Kamioka

1200yearold 30
G eV
templeMa
i
J-PARC Facility(KEK/JAEA）
View to North

ean
ic Oc
Pacif

Near
Detector

3 GeV
Synchrotron

Design Intensity
750kW

n ri

ng

Photo:20
January 2008

Construction
2001~2009

J-PARC neutrino beamline overview
Near Detectorμ+Target

π+

×

νμ
109m

Beam dump
Decay volume (He gas filled)π+μ+Target installed in 1st horn.

νμMuon monitor

π+

×

p

Pions are focused by
3 electromagnetic Horns.
JPARC Seminar, 2016 10 20

Morgan O. Wascko

20

Neutrino flux predictions
neutrino beam

antineutrino beam

• <1% impurity from ν (ν̅ ) at energy peak; importanteebackground for νe(νe̅ )appearance• “wrong sign” component: neutrinos contaminating
antineutrino beam, vice versa.

JPARC Seminar, 2016 10 20

Morgan O. Wascko

21

NA61 pion data
Shown √stat2 + syst2 errors
Not shown 2.3% norm. error

NA61 experiment measures particle
production from C at T2K beamenergy (30 GeV)
Phase-space of pions contributing to
the SK νμ flux with NA61 coverage

N. Abgrall et al. (NA61/SHINE Collaboration),
Phys. Rev. C 84, 034604 (2011)

Covers almost all of the relevant pion
phase-space for νμ production at T2K
Similar for K production and negative
particles
No analogous measurement forneutrino interactions!

JPARC Seminar, 2016 10 20

Morgan O. Wascko

22

37 m

The Near Detector pit
houses both theoff-axis (ND280) andon-axis (INGRID)
detectors
2.5 deg

0 deg

19 m
JPARC Seminar, 2016 10 20

Morgan O. Wascko

23

Beam delivery & stability•Beam delivery• 1.51e21 POT TOTAL•7.57e20 POT nu•7.53e20 POT nubar~7.5e20 POT in next
•Expect
data run
operated stably above•Beam
400 kW in 2016!

2011

2012

27 May 2016
POT total: 1.510×1021

2013

2014

2015

2016

!-mode POT: 7.57×1020 (50.14%)!-mode POT: 7.53×1020 (49.86%)

Ring power supply•Main
upgrade approved by
MEXT•Will allow operation up toand beyond 750 kW in 2018
JPARC Seminar, 2016 10 20

Morgan O. Wascko

24Off-Axis Detector (ND280) Elements
SMRD in Magnet
Yoke air gaps

2x2 m

7m

JPARC Seminar, 2016 10 20

Morgan O. Wascko

25

ND280 event displays: ! candidates

ND280 neutrino events

!µ%

µ-

!µ
7

sand muon + DIS candidate

quasi-elastic candidate

µ&T

!µ
.

.

.
single pion candidate
JPARC Seminar, 2016 10 20

DIS candidate
Morgan O. Wascko

26

Super-K(far)detector
Super-Kamiokande•

50 kton (22.5 kton
http://www-sk.icrr.u-tokyo.ac.jp/sk/

LINAC

Electronics hut

Water and air
purification system

fiducial volume) water 50kton water
Cherenkov detector

32kt ID viewed by
Atotsu~11,000
20''
PMT forControl room
20-inchPMTs
entrance
detector(ID) inner~2m ODviewed(40%
photoPMTs
coverage)by 8-inch
 ~2,000
22.5kt fid.
vol. facing
outward
(2m
from
8''
PMT
forwall)outer detector
Etotal=~4.5MeV(OD): vetoenergy thresholdcosmics,
radioactivity,
Ikeno-yama
1km
SK-I: April
1996~
eventsKamioka-cho, Gifu (2700mwe) exiting
Japan
3km
2km  SK-IV is running


•

ID

41.4m

OD

39.3m

•

Mozumi•Good reconstructionSK

Atotsufor T2K energy range•Threshold 4 MeV

Inner Detector (ID) PMT: ~11100 (SK-I,III,IV), ~5200 (SK-II)
Seminar, 2016 10 20
Outer Detector (OD) PMT: JPARC
1885

Far

Morgan O. Wascko

27

Muon Ring

Electron Ring

T2K phase 2•T2K data favours maximal CPV•CPV may be observable in thenear future!

•T2K will reach full stats in ~2021•Next gen experiments start in
2025, or later•Let’s extend T2K until ~2026•With MR power upgrade, canachieve ~20E21 POT•>3 𝜎 CPV sensitivity•Smoothly transition to next gen
experiments with useful data

•Can expand collaboration as
well•T2K phase 2 given Stage 1 Status
by KEK/J-PARC directorate

JPARC Seminar, 2016 10 20

Morgan O. Wascko

30

T2K phase 2•Expect up to 500 ν events, depending onevalue of 𝛅CP•Sensitivity to excluding sin𝛅 =0 for:•known true NH•true sin𝛅 =−𝛑/2•effective statistical improvement fromCP

effect ofoctantCP

increased horn current, SK FV, SK data
samples

effect ofsystematics•Two panels show:•effect of the true octant (value of θ )•effects of systematics•Significant sensitivity enhancements
23

possible if systematics can be
improved!

JPARC Seminar, 2016 10 20

Morgan O. Wascko

31

K. Mahn, Neutrino 2016

Processes in Neutrino Scattering!
merely players

Modeling ν-nucleus
Energy transfer!
interactions
figure from Ref 1•

Charged Current Quasi Elastic (CCQE) and multinucleon processes (2p2h)
Observable

CCQE
µ"
"

νµ"
W"
N"

neutrino (anti)
•

2p2h
νµ"
W"

muon or electron (+)
N,"N"

N’"
•

proton (neutron)

JPARC Seminar, 2016 10 20µ""

N’,N’"
3

Morgan O. Wascko

32Ingredients for Interaction Model•A “Base” physics model•Llewellyn Smith RFG w/ dipole vector

FFs, Nieves 2p2h, R-S resonance region,
duality (B-Y) DIS•Can use different base models for tests•Empirical fit parameters•E.g., M , κ, normalisation(Eν)•FSI Model tune
•Constrained by low energy hadroneffAmeasurements•External and (future) Internal Measurements•Must understand uncertainties•Measurements relevant to our physics
model

JPARC Seminar, 2016 10 20

Morgan O. Wascko

33

•Assume interactions near 1GeV
involve only one nucleon•

Nucleonlower Q2.

Borrowed from M. Dorman

Impulseapproximation

higher Q2.

Nucleus“Fermi Motion”

λ>1 fm for Q2<1(GeV/c)2•Neutrino experiments assume
quasi-free interactions•Are nucleons actually quasifree? If not, could we tell?

•

Can low Q2 region be describedby impulse approximation?
Science Vol.320. no.5882, pp.1476
JPARC Seminar, 2016 10 20

Morgan O. Wascko

34

µ-

νµ

Quasi-Elastic
Scattering

q

n

W+

CCQE

p

• Experiments use Llewellyn Smith
formalism (1971)• Form-factors parameterise nucleon
weak charge distributions••

FV measured by electron scattering,
FP negligible due to kinematics,
FA assumed to be dipole

Important for accelerator ν beams• Dominant process near 1 GeV• Simple energy reconstructiond(σ × Φν)/dQ2 (× 10-38 cm2/nucleon)(where Q2 = −q2)

JPARC Seminar, 2016 10 20

NEUT

1.2

CC-inclusive
CCQE-like

1

CC 1π

0.8

CC other
CC coherent

0.6
0.4
0.2
0
0

0.2

0.4

0.6

0.8

1

1.2

Q2 (GeV)Morgan O. Wascko

35

Nuclear Models

Ankowski, NuInt09•Most experiments use RFG•Smith & Moniz (1971)
US Secretary of energy
does not need citations
anymore!
Prouse (Imperial College London)•Most theorists preferνµ CCQE on 12C
RFG
Spectral funtion•Affects neutrino energy(Eν = 0.68 GeV)

something elsereconstruction!

➡Impacts oscillation
experiment!

JPARC Seminar, 2016 10 20

Eµ (GeV)Morgan O. Wascko
36

#Final State Interactions
##

W. Ma, Neutrino 2016

#
L!0#

P. de Perio,#
NuInt11#

9BJ&*M#G#•Neutrino interaction

products are created in
the nuclear environment.1#.1#@D"M!"#9N#•Need to simulate how
they get out•Tune with external

P#H#@D"MK0QR#

hadron data

D#

•Crucial piece of any
analysis

JPARC Seminar, 2016 10 20

Morgan O. Wascko

37

A “new” process?
•Problem with impulse
approximation?

•np-nh events, a.k.a. Meson
Exchange Currents

M. Martini•Neutrino interacts with correlated
nucleons within the nucleus

total cross sections•Evidence for such processes seen•Multiple theoretical approaches
being developed•σ [10-38 cm2]

via enhancements in transverse
cross sections in e-A scattering

6

T2K studying Nieves & Martinimodels, but would like to expand

CCQE SF
Nieves5
TEM
Marteau
4

numu on C

J. Zmuda

3
2
1
0
200

JPARC Seminar, 2016 10 20

400

600
800
Eν [MeV]

1000

1200

Morgan O. Wascko38

2p2h: ν vs ν●

S. Bolognesi, Neutrino 2016

Important systematics on oscillation analysis (δCP measurement) :2p2h xsec in ν

2p2h xsec in ν

Martini et al
Nieves et al

Martini et al
Nieves et al

Eν (GeV)Eν (GeV)

2p2h only

5
JPARC Seminar, 2016 10 20

Morgan O. Wascko

39

Single Pion
Productionµ-, νµ

νµ
W,Z

π
N’

N

nucleon weak charge distributions•• Model is tuned on data from 1970s
18 resonances• 2nd largest xsec near 1 GeV• Major background to CCQE
• Now being developed as a signal
sample!

• Previous measurements disagree!
• Disagreement reconciled byd(σ × Φν)/dQ2 (× 10-38 cm2/nucleon)• Described by Rein-Sehgal model (1983)• Again, form-factors parameterise
0.8

NEUT

0.7
0.6

CC-0π

CC-1π

0.5
CC-Nπ

0.4
0.3
0.2
0.1
0
0

0.2

0.4

0.6

0.8

1

1.2

Q2 (GeV)Wilkinson et al.

JPARC Seminar, 2016 10 20

Morgan O. Wascko

40

T2K ν-nucleus interaction model•

T2K’s primary neutrino generator MC is NEUT

•
•
•
•

•

•

•

Simulates neutrino-nucleus interactions
Used by SK, SciBooNE, K2K
Tuned with fits to external data sets
2012: mainly MiniBooNE CCQE, CC1π+, CC1π0, NC1π0•

Fits used to tune model parameters for prior inputs tooscillation analysis•

Constrained and cross-checked with SciBooNE and K2K
data

2014: MiniBooNE and MINERvA ν and ν̅ data sets•

Fits used to down select default interaction model and tune
parameters for prior inputs to oscillation analysis•

Published CCQE fits in early 2016

2016: Expanding fits to include bubble chamber and other data

Also use GENIE and NuWro for cross-check analyses, systematic
errors studies, and deeper inquiries into neutrino interactions
JPARC Seminar, 2016 10 20

Morgan O. Wascko

41

NEUT interaction model
QE

2••CC resonant 𝜋: Rein-Sehgal, M

CCQE: Llewellyn Smith, MA =1.0 GeV/c
RES
=1.2
A

GeV/c

2

•
•Nuclear model: Smith-Moniz RFG•Also have 2D spectral function
2p2h: Nieves model

implemented•RPA effects included•Coherent pion: Rein-Sehgal•DIS with Bodek-Yang corrections•Neutrino and antineutrino interactions
simulated•ν and ν simulated•Only differ at low energy•Radiative corrections•Second class currents
𝜇eσ/Eν (× 10-38 cm2/nucleon/GeV)σ/Eν (× 10-38 cm2/nucleon/GeV)2014 model & parameters (NEUT v5.3.3)
1.2
1
0.8

CC-inclusive

CCQE-likeCC other

CC coherent

⌫µ

CC 1π

0.6
0.4
0.2

0
0
0.45

0.4

0.35
0.3
0.25

0.5

1

CC-inclusive
CC other

1.5

2

CCQE-likeCC coherent

⌫µ

2.5

CC 1π

3

Eν (GeV)

0.2

0.15
0.1
0.05
0
0

0.5

1

1.5

2

2.5

3

Eν (GeV)
JPARC Seminar, 2016 10 20

Morgan O. Wascko

42

T2K/NIWG External data fits
Simultaneously fit MINERvA and MiniBooNE CCQE
data sets in neutrino and antineutrino modes
MINERvA

MiniBooNE

Neutrino

Antineutrino

arXiv:1601.05592 [hep-ex]
JPARC Seminar, 2016 10 20

Morgan O. Wascko

43

T2K ν-nucleus measurements

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44

Discussion

JPARC Seminar, 2016 10 20

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45

Growing Consensus
T2K

measurements at manyenergies, nuclei•Differentiate between process
coh π)•...and final state particle crosssections

2•σ(CCQE), σ(CC res π), σ(CC (cm )

cross-sections...

×10

16
(a)
14
pµ
12
10
8
6
4
2
0
0.4 0.6

MicroBooNE
MINERvAcosθp2

 (cm )

-39

cosθπ

cosθµ

•We need broad coverage•Model independent

MiniBooNE data with total error
pπ data with preliminary error
SciBooNE
RFG model with Meff
A =1.03 GeV,  =1.000
RFG model with Meff
A =1.35 GeV,  =1.007

0.8

1

1.2

1.4

pp 2
1.6
1.8(GeV)
EQE,RFG

×10-39

16
(b)
14
12
10
8
6
4
2
0
10-1

NOMAD data with total error
SciBooNE data with preliminary error

MiniBooNE data with total error
RFG model with Meff
A =1.03 GeV,  =1.000
RFG model with Meff
A =1.35 GeV,  =1.007
Free nucleon with MA =1.03 GeV

1

10

EQE,RFG(GeV)•σ(CC), σ(µ), σ(µ+p), σ(µ+π)
Must succeed to achieve low errors for CPV discovery!
JPARC Seminar, 2016 10 20

Morgan O. Wascko

46

What does model dependence mean?

•Distinguish between σ model anddetector model

Absolute flux-averaged
differential cross section formula
Uij :unsmearing matrix•Any MC-derived quantity is, ofNjobs : data

course, model-dependent•Restricting corrections(unsmearing, BGs, efficiencies) todetector MC quantities—not crosssection processes—is probably
the best we can do•This is why we should publish final

state particle cross sections, inaddition to process measurements,
etc.

•

Can we move to generator-lessmeasurements??

N̂i =

P

obs
U
(N
j
j ij

εi :efficiency

Bj )

✏i
bj : background

d
1 N̂i
=
dxi
T ⌫ xiT :integrated
target number

JPARC Seminar, 2016 10 20

Φ :integrated ν-flux
Morgan O. Wascko

47

protons

Is it so bad?
Φνnear(E)⋅σnear(E)⋅εnear(E) ⇔ Φνfar(E,𝜃,𝛥m2,𝛿)⋅σfar(E)⋅εfar(E)• Interaction models are useful:• Relate final state particles to neutrino energy, estimate systematic errors.
• Cannot do oscillation analysis without a model, but error cancellation only
works if the model matches Nature!

• Ulrich Mosel’s observation, NuInt11:• Theorist’s paradigm: “A good generator MC does not have to fit the data,
provided its model is correct”• Experimentalist’s paradigm: “A good generator MC does not have to becorrect, provided it fits the data”• We really do need model independent measurements!
• Provide enough info for later physicists to cleanly use data with a new model.
• Confront each model with multiple data sets
JPARC Seminar, 2016 10 20

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8
6
4
2
0
0.4

MiniBooNE data with total error
SciBooNE data with preliminary error
RFG model with Meff
A =1.03 GeV,  =1.000
RFG model with Meff
A =1.35 GeV,  =1.007

Utility of models: 2p2h events
0.6

0.8

1

1.2

1.4

2

 (cm )

-39

T. Katori

×10

16
(b)
14
12
10
8
6
4
2
0
10-1

1.6
1.8(GeV)2
EQE,RFGNOMAD data with total error
SciBooNE data with preliminary error

Significant
discrepancies
between BooNEs(~1 GeV) and
NOMAD (~10 GeV).

MiniBooNE data with total error
RFG model with Meff
A =1.03 GeV,  =1.000
RFG model with Meff
A =1.35 GeV,  =1.007
Free nucleon with MA =1.03 GeV

1

10

EQE,RFG(GeV)D. Schmitz

MINERvA data show
clues in recoil hadronenergy deposits

M. Martini
JPARC Seminar, 2016 10 20

Morgan O. Wascko

49Unique challenges of ν expts•••

Neutrino beams are relatively wideband in energy•

cannot control Eν/Q2 like measurements like e-A expts

All neutrino data samples are rife with backgrounds.

••

CCQE ↔ CC1π+ ↔ CC1π0 →? NC1π0
but really: µ ↔ µ+p ↔ µ+π+ ↔ µ+π0 →? π0

Knowing what we do (e.g. about 2p2h from e-Aexperiments), we cannot have confidence in one sample
without seeing all the others.

•

We’ve already learned that seeing each of them isn’t
enough!

• For example, to extract M from neutrino data:• Requires nuclear model & background predictions matchA

nature.

➡ Need predictions for all modes to measure any mode.
JPARC Seminar, 2016 10 20

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50

Best way to publish data?
• Measured quantities vs inferred quantities:• Lots of ongoing discussion on• How to interpret unfolded data?
• Generator dependencies?
• Can we evolve our data publication methods to makeour data easier for the community to use?

• Other fields publish data in different (and creative)
ways—we are studying some of these.

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INTERACTIONSDATA SAMPLES

NEUTRINOS@DETECTORJPARC Seminar, 2016 10 20

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CC0π

CC1π

CCOther

NEUTRINOS@DETECTOR
CC0π

CC1π

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Do we need to unfold?
• T2K data analysts use uncorrected data to performparameters fits.

• We use detector MC to naturally handle
efficiencies and smearing,• by comparing smeared MC samples after cuts
to data after cuts.

• We use MC samples/reweighting techniques toadjust MC until it matches data.

• Why not publish uncorrected data along withappropriate smearing and efficiency functions?

•“Should unfolded histograms be used to test hypotheses?” by
Cousins, May, Sun. arXiv:1607.07038 [physics.data-an]
JPARC Seminar, 2016 10 20

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MODEL A
DATA SAMPLESACCEPTANCE/
SMEARING TOOL

CC0π

MODEL B
CC1π…
CCOther

MODEL TJPARC Seminar, 2016 10 20

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55

This is various waysof describing Nature
MODEL AThis is our best
guess at describing
our apparatus

This is something uniquethat occurred in nature!

ACCEPTANCE/
SMEARING TOOL

CC0π

MODEL BDATA SAMPLES

CC1π

MODEL T

Goal: quantitatively
comparison to data

Previous experiments have done this:DLS @ BEVALAC
HADES @ GSI
DELPHES for colliders

JPARC Seminar, 2016 10 20

CCOtherMorgan O. Wascko

56

Can we implement new ideas later?
• What can we do if a new variable or analysis method
is developed after publication?

• Publish an ntuple of events: reconstructed final
state particles.

• Apply efficiency/smearing corrections to individual
events.

• Each event comes with a cross-section weight

derived with POT numbers, flux & detector MC.

• Allows one to make a plot giving cross sections
instead of number of events.

➡ Gives unprecedented knowledge to future analysers
since it would allow analysis of new variables
JPARC Seminar, 2016 10 20

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INTERACTIONSDATAVertex(x,y,z)mu–(px,py,pz) MeV/c

Vertex(x,y,z)mu–(px,py,pz) MeV/c
pi+(px,py,pz) MeV/c

NEUTRINOS@DETECTORJPARC Seminar, 2016 10 20…

…

Could include
experts-only info too,like PID info

Vertex(x,y,z)mu–(px,py,pz) MeV/cp+(px,py,pz) MeV/c
pi0(px,py,pz) MeV/cMorgan O. Wascko

58

NASA releases data to the public

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Conclusions• T2K’s sensitivity to CPV can be enhanced with better
understanding of neutrino-nucleus interactions• T2K has made many competitive neutrino-nucleus
interaction measurements• We are exploring new and better ways to publish data
• Participation in PhyStat-nu workshops, which could
complement NuInt for our community• Let’s communicate more and find the best way to
study neutrino-nucleus interactions!

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60

Thank you for yourattention!

Many thanks to: Sara Bolognesi, Mark Hartz, Kendall Mahn, Kevin
McFarland, Hiro Tanaka, Callum Wilkinson
for help with plots andslides(whether
JPARC
Seminar,2016 10 20 they knew it or not)Morgan O. Wascko

61

Accelerator Neutrinos
first accelerator neutrino beam•Accelerator neutrino

experiments were born inthe 1960s and came of age
in the 1970s•1960s - First pion decay

beam, first focussing horns•1970s - Development of big
bubble chambers•Discovery of 2nd generationof neutrinos and neutral
currents

first neutrino horn
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0.3
0.25
0.2

G.P.Zeller

Aachen, PL 125B, 230 (1983), Al
ANL, PL 92B, 363 (1980), D
2
GGM, NP B135, 45 (1978), C H8 CF3Br

i µp A i µp/0
i µp A i µp/0

3iµ n A i µ n/0

NUANCE ( i )NUANCE ( i )i µp A i µ n/+

i µn A i µp/-

From discovery to(precision) measurements...
Gargamelle

0.15
0.1
0.05
0

1

10

BNL

1

1

10

10

ANL

FNAL

BEBC

1

10

mCC, 1/ (10-38 cm2 / nucleon)

mNC, 1/ (10-38 cm2 / nucleon)

Early neutrino data

102
Ei (GeV)

2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0

G.P.Zeller
BEBC, NP B343, 285 (1990), D
2
BNL, PRD 34, 2554 (1986), D2
FNAL, PRL 41, 1008 (1978)
SKAT, ZP C41, 527 (1989), CF Br
3
NUANCE

ANL, PRL 30, 335 (1973), H
2
ANL, PRD 19, 2521 (1979), H , D2
2
ANL, PRD 25, 1161 (1982), H , D22

BEBC, NP B264, 221 (1986), H2

iµ n A µ-n/+iµn A µ-p/0

iµp A µ-p/+
1

10

102

1

10

102

1

10

102
Ei (GeV)

JPARC Seminar, 2016 10 20

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Morgan O. Wascko

63

mass (eV)10

12 A de Gouvea

10

11

10

10

Neutrino Mass
TeV
t

10

9

τ

10

8

µ

10

7

10

6

10

5

10

4

10

3

10

2

•Why are neutrino masses sosmall?

bc•Can neutrino mass come from the

GeV

s
d

same source as other Fermion
masses?

u
MeVe•If neutrinos are Majorana

particles, See-Saw mechanism
may explain it

keV•Exceedingly heavy right-

10

10
10
10
10

handed neutrinos pair withlight left-handed neutrinos

eV

1
10

•Most theorists think not!

-1

ν2

-3

meV

ν1

-4

from weak interaction•Also explains violation of
lepton number-50•Helicity on νs comes entirely

ν3

-2

1

2

3

4
fermion
JPARC Seminar, 2016 10 20

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64

2
2
T2K 2016: sin θ23 and Δm 32
IH

0.532+0.044
0.060

0.534+0.041
0.059+0.084|Δm232| (/10-3eV2) 2.545 0.082

2.510+0.082
0.083|∆ m232| (10-3 eV2/c4)

sin2θ23

3
Normal Hierarchy
2.8

Inverted Hierarchy|∆ m232| (10-3 eV2/c4)

NH

T2K Run1-7c preliminary

Fixed Mass Hierarchy

2.6
2.4

68%CL
90%CL
T2K best-fit

3.4
3.2

Normal Hierarchy

3
2.8
2.6
2.4

2.2

68.27%CL (-2ln L = 2.3)
crit90%CL (-2ln L = 4.61)

2.2

Best-fit

1.8

2

crit

2
0.3

3.6

0.35

0.4

0.45

0.5

0.55

0.6

0.65

0.7

0.3

sin2 θ23

JPARC Seminar, 2016 10 20

IceCube NOvA (2016) MINOS+
T2K Run1-7c preliminary Super-K
0.35

0.4

0.45

0.5

0.55

0.6

0.65

0.7

sin2 θ23

Morgan O. Wascko

65

Getting at δCP
In vacuum,22P (⇤µ (⇤ µ ) ⇤ ⇤e (⇤ e )) ⇥ sin 2⇥13 sin ⇥23 sin

231+ sin 2⇥13 cos ⇥13 sin 2⇥23 sin 2⇥12sin
2

31 sin21 cos(

2

2

32 ±

+ sin 2⇥12 cos ⇥23 cos ⇥13 sin
where

2

)
21

atmosphericinterference
solar

1.27 m2ij [eV2 ]L[km]ij =E[GeV]P (⇤µ ! ⇤e ) P (⇤ µ ! ⇤ e )1.27 m221 L sin 2⇥12
ACP =
⇡
⇥
⇥ sin
P (⇤µ ! ⇤e ) + P (⇤ µ ! ⇤ e )E
sin ⇥13~0.18
JPARC Seminar, 2016 10 20

Morgan O. Wascko

66Error budget for CPV••

Statistics - reduce with high event rates••

Need high beam power and large far detectors
Nevt ~ 𝚽𝛎 × Ntarget × 𝛆 × p

Systematics•

Neutrino flux - need good hadron production
experiments•

Detector - need good detector design and calibration
systems•

Cross section - need broad coverage of neutrino nucleus
interaction measurements•

Single near detector not sufficient!

➡ Physics goals of future programme requires large improvement
in systematics of current generation of experiments
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•
•
•

•Need to accurately predict backgroundcontamination➡

- NC and 𝜈𝜏 CC background rate
(100% each)- Multiple calibration and light-level systematics(Hit energy, fiber attenuation, threshold effects)- Oscillation parameter uncertainties(current world knowledge)- Hadronic energy(21%, ~equiv. to 6% on E𝜈 )- Neutrino flux
(NA49 + beam transport model)- Absolute, relative normalization(1%, 2%)- Neutrino interactions(GENIE / Intranuke model)

30

Ryan Patterson, Caltech

Fermilab JETP, August 6, 2015

See Poster P1.035 by
K. Bays for more detailMuon Neutrino ND data
15¨

P. Vahle, Neutrino 2016

Addition of MEC events substantially
improves simulated hadronic energy
distribution¤

hadronic energy scale uncertainty reduced(14% to 5%)

NOvA Preliminary
300

Simulated selected events
Simulated background
Data
Shape-only 1-σ syst. range
ND area norm., 3.72 × 1020 POT

200

100

¨

Reconstructed neutrino energy unfolded,
true Far/Near ratio used to extrapolate
ND data for a FD prediction

0
0

1

2

3

NOvA Preliminary

Need to understand neutrino-nucleus
cross-sections precisely

80

Simulated selected events
Simulated background
Data
Shape-only 1-σ syst. range
ND area norm., 3.72 × 1020 POT

300

60

40

5

NOvA Preliminary

Simulated selected events
Simulated background
Data
Shape-only 1-σ syst. range
ND area norm., 3.72 × 1020 POT

100

4Reconstructed neutrino energy (GeV)

103 Events•(before tuning)

Uncertainties assessed•Need to accurately calculate inferred

For oscillations, need to reconstructneutrino energy
different ways to do thisAll methods need good xsecs!
all beams are relatively wideband

Take the full size of thistuning as a syst. uncertainty(impact reduced by ND-to-FD
prediction procedure)

Need to predict event rates andkinematics of final state particles(physics) variables from our observed
variables

Tune hadronic energy in ND
simulation to achieve better
agreement in E𝜈 and Ehad.

Hadronic energy syst. is
one with a noticeable effect

103 Events•

Most of our systematic
uncertainties have relatively
little influence on the result

103 Events

What do we
need?

Systematics

200

100

➡Need good models

20

0
0

1

2

3

4

Reconstructed muon energy (GeV)JPARC Seminar, 2016 10 20

5

0
0

0.5

1

1.5

2

2.5

3

Hadronic energy (GeV)

Morgan O. Wascko

68

Prospects

Mid-term plan of MRFXÌThe high repetition rate scheme is adopted to achieve the design beam intensity, 750 kW. Rep. rate will be
increased from ~ 0.4 Hz to ~1 Hz by replacing magnet PS’s, RF cavities and some injection and extraction devices.SXÌ Parts of stainless steel ducts are replaced with titanium ducts to reduce residual radiation dose. The beam
power will be gradually increased toward 100 kW watching the residual activity. •

1st stage of J-PARC MR power
supply upgrades approved•reduce cycle from 2.48 s to
1.3 s: 420 kW (current) →~800 kW

JFY

•

2016

2017

2018

2019 2020

800

New PSbuildings

FX power [kW] (study/trial)

320

> 360

400

450

700

SX power [kW] (study/trial)

-

33 - 40

50

50-70

50-70 ~100 ~100

2.48 s} R&D

Large scale
1st PS

Cycle time of main magnet PS
New magnet PS
High gradient rf system
2nd harmonic rf system
VHF cavity

Injection system
FX system

Mass production
installation/test

1.3 s


1.3 s


900

1.2 s


Manufacture, installation/test
R&D, manufacture, installation/test
R&D
Add.collimators (2 kW)Add.collimators (3.5kW)


ajgkhpVcdVjlopnthlhmrXVdhorfVlfmsifgrsphVYrhqr
ajgkhpVcdVjlopnthlhmrXVb_VqhorslXV`_VqhorfVlfmsifgrsphVYrhqr

Local shields

SX collimator / Local shields
Ti ducts and SX devices with
Ti chamber•“T2K-II”•extension of T2K run to2015

Li. current
upgrade

Ring collimators

Now aiming for > 1 MW
capability

2014

Beam ducts ESS

20x1021 POT on the timescale of 2026
currently approved for7.8x1021 POT (~2021)••accelerator and beam line

upgrades to reach 1.3 MW
JPARC Seminar, 2016 10 20

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69

T2K phase 2•Expect up to 500 ν events,eunknown MH(true NH)

depending on value of 𝛅CP•Sensitivity to exclude sin𝛅 =0 for:•known true NH•effective statistical improvement
CPfrom increased horn current,
SK FV, SK data samples

known MH(true NH)

•Two panels show:•effect of the mass hierarchy•bottom panel shows the
improvement from knowing
the hierarchy

JPARC Seminar, 2016 10 20

Morgan O. Wascko

70Upgrading T2K: far detector•SK-Gd project(GADZOOKS)•UCI-led initiative to add
Gd to SK water•enhance neutron
detection capability•improves low energy
antineutrino detection•provides WS BG
constraint in T2K ν
data•Three step timeline•T0: repairs to SK tank
•T1: load 0.02%
Gd2(SO4)3JPARC Seminar, 2016 10 20

Morgan O. Wascko

71Upgrading T2K: near detector
WAGASCI•High stats of T2K-II motivate
reduction of systematics•Improve/replace existing ND280
detector•Active water detector elements•Expand phase space (highModified
ND280 tracker

angle tracks)•Lower momentum thresholds•New intermediate distance water
Cherenkov detector•Merger of TITUS and NuPRISM•Farther future: HPTPC

JPARC Seminar, 2016 10 20

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72