3. Needs of 𝜋-production in T2K
11/18/15 NuINT 2015, Osaka
Needed for oscillation analysis
Main background around oscillation dip
Energy misreconstruction
𝜋-production itself: FSI model ( 𝜋 absorption,
scattering, charge exchange…)
Dominant background to charged-current
quasielastic scattering measurements
Pion absorption
Detector inefficiency
Also background to other cross-section
measurements
T2K shares same energy peak (0.6 GeV) as
MiniBooNE Compare results
3
PhysRevD.91.072010
PhysRevC.88.017601
νμ CC candidates
at T2K far detector
6.6x1020 POT
4. Needs of 𝜋-production in T2K (cont’d)
11/18/15 NuINT 2015, Osaka
Outstanding issues:
CC1𝜋+: inconsistency between MINERvA and
MiniBooNE in overall normalization and
pion kinematics
CC1𝜋 coherent: MINERvA observed this rare
interaction above 1.5 GeV, but prediction
overestimated at low E 𝜋
T2K important keys to these issues:
Fairly clean N-𝛥 coupling information
(narrow peak at 𝛥 resonance ); multiple
targets (12C, 16O,…) for FSI constraints
CC1𝜋 coherence below 1.5 GeV
(~0.8 GeV for off-axis, ~1.5 GeV for on-axis)
4
arXiv:1406.6415
PhysRevLett.113.261802
MINERvA
5. The T2K experiment
11/18/15 NuINT 2015, Osaka 5
High intensity, pure muon (anti) neutrino beam
The world’s first off-axis designed neutrino experiment
Far Detector (SK) is 2.50 off the beam’s axis
Narrow band beam, peaked at oscillation maximum (0.6 GeV)
5
10
5
0
30
60
90
120
150
180
Angle(degrees)
Data
Best fit
Background component
Momentum (MeV/c)
0 500 1000 1500
0
0.2
0.4
0.6
0.8
1
Data
Best fit
(km/GeV)Recon.L/E
2
10 3
10
0
0.5
1
1.5
Ratiotono
oscillations
Events/0.1GeV
0
20
40
60
DATA
Best-fit MC with Oscillations
MC without Oscillations
0
Events/100MeV
2
4
6
8
10
12
14 No oscillation
Best fit spectra
Data
Energy (GeV)mnReconstructed
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Ratio
0.5
1
1.5
PRL. 112, 181801 (2014)PRL 112, 061802 (2014) Paper preparation Paper preparation
Primary goal is to measure precisely neutrino oscillations
Stay tuned for:
Observe
CP phase
Unknowns…
T2K Preliminary
T2K Preliminary
6. T2K on-axis detector: INGRID
11/18/15 NuINT 2015, Osaka 6
Designed for measuring 𝜈 beam intensity,
direction and profile
16 scintillator-steel interleaved
“standard” modules formed a cross
shape (7.1 tons/each)
Fully active scintillator Proton Module to
detect protons and pions specifically for
cross-section studies.
Key features for cross-section:
o Broad flux spectrum, mean ~1.51 GeV
o Target materials: scintillator and iron
o Large number of interactions
Upstream view Top view
Display of MC event interacted in
Proton Module and μ tracked by INGRID
7. T2K off-axis detector: ND280
11/18/15 NuINT 2015, Osaka
Aim to understand unoscillated 𝜈 beam: constrains flux
and cross-section parameters
Tracker, composed of Fine-Grained Detector (FGD)
and Time Projection Chamber (TPC), is central part
o Two FGDs: active target w/ scintillator only
(FGD1) or scintillator-water interleaved (FGD2)
o Three TPCs: mainly Argon (95%) filled, for
momentum measurement and particle ID
𝜋0 detector (POD) for water-scintillator target and 𝜋0
tagging
Electromagnetic calorimeters (ECal) to detect gamma
rays and reconstruct 𝜋0
Side muon range detectors (SMRD) to tag entering
cosmic muons or side-exiting muons
Key features for cross-section:
o Narrow flux spectrum , mean ~ 0.85 GeV
o Multiple targets: scintillator, water, argon, lead
o High final state ID resolution, charge separation
7
0.2 T
8. T2K interaction topologies
11/18/15 NuINT 2015, Osaka 8
Final state topologies based on the true particles exiting the nucleus
(takes advantage of ND280 high final state ID resolution)
(MeV/c)m
p
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Numberofentries
0
50
100
150
200
250
Data
pCC-0
pCC-1
CC-Other
BKG
External
No truth
(MeV/c)m
p
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Numberofentries
0
50
100
150
200
250
Data
CCQE
RES
DIS
COH
NC
mnanti-
en
out FGD FV
other
no truth
(MeV/c)m
p
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Numberofentries
0
500
1000
1500
2000
2500
3000
3500
4000 Data
CCQE
RES
DIS
COH
NC
mnanti-
en
out FGD FV
other
no truth
(MeV/c)m
p
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Numberofentries
0
100
200
300
400
500 Data
pCC-0
pCC-1
CC-Other
BKG
External
No truth
(MeV/c)m
p
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Numberofentries
0
500
1000
1500
2000
2500
3000
3500
4000 Data
pCC-0
pCC-1
CC-Other
BKG
External
No truth
Topology
definition
Breakdown by
final state ID
Breakdown by ν
generator truth
T2K Preliminary T2K Preliminary T2K Preliminary
T2K Preliminary T2K Preliminary T2K Preliminary
63% CCQE 39% RES 68% DIS
72% CC0π 51% CC1π 70% CCother
9. T2K recent pion production
measurements
11/18/15 NuINT 2015, Osaka 9
Various activities on pion production are ongoing at T2K near detectors.
This talk highlights measurements which are official only.
① CC1𝜋+
CC1𝜋+ in water (ND280-FGD2)
② CC1𝜋+ coherent
CC1𝜋+ coherence in carbon (ND280-FGD1)
CC1𝜋+ coherence in carbon (INGRID)
10. 11/18/15 NuINT 2015, Osaka 10
① CC1𝜋+
Signal definition
Main contribution from resonance
Simulation: Rein-Sehgal model
NEUT (“official” ν generator)
GENIE (alternative ν generator)
11. CC1𝜋+ in Water (ND280-FGD2)
11/18/15 NuINT 2015, Osaka
Signal: CC w/ 1 𝜋+ in water layer of FGD2
Event selection:
Negative muon-like track (TPC)
Positive pion-like track (TPC ID)
Reject events w/ 𝜋0 (ECal)
Muon-like track starts in x-scintillator layer
Phase-space restriction applied to remove
areas of low detector acceptance
Dominant backgrounds:
CC 1𝜋+ in scintillator layers (XY)
CC non-1𝜋+ (dominated by DIS)
11
x y
True signal
Intrinsic bkg.
for sideband
/ GeVp
p
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Numberofevents/0.05GeV
0
20
40
60
80
100
120
140
Data
XYpCC1
waterpCC1
otherpCC1
XYpCC non-1
waterpCC non-1
otherpCC non-1
CCmnnon
Out of FV
Data
XYpCC1
waterpCC1
otherpCC1
XYpCC non-1
waterpCC non-1
otherpCC non-1
CCmnnon
Out of FV
50.6% CC1pi
(30.9% from water)
T2K Preliminary
pqcos
0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Numberofevents/0.01
0
20
40
60
80
100
120
140
160
Data
XYpCC1
waterpCC1
otherpCC1
XYpCC non-1
waterpCC non-1
otherpCC non-1
CCmnnon
Out of FV
Data
XYpCC1
waterpCC1
otherpCC1
XYpCC non-1
waterpCC non-1
otherpCC non-1
CCmnnon
Out of FV
P 𝜋,μ > 200 MeV,
cosθ 𝜋,μ> 0.3
T2K Preliminary
Phase-space restriction
scintillator
water
scintillator
12. CC1𝜋+ in Water (ND280-FGD2)(cont’d)
11/18/15 NuINT 2015, Osaka
Two control samples to constrain background
12
CC-other water-enhancedCC1𝜋+ scintillator
/ GeVp
p
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Numberofevents/0.05GeV
0
10
20
30
40
50
60
70
80 Data
XYpCC1
waterpCC1
otherpCC1
XYpCC non-1
waterpCC non-1
otherpCC non-1
CCmnnon
Out of FV
Data
XYpCC1
waterpCC1
otherpCC1
XYpCC non-1
waterpCC non-1
otherpCC non-1
CCmnnon
Out of FV
/ GeVp
p
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Numberofevents/0.05GeV
0
10
20
30
40
50
Data
XYpCC1
waterpCC1
otherpCC1
XYpCC non-1
waterpCC non-1
otherpCC non-1
CCmnnon
Out of FV
Data
XYpCC1
waterpCC1
otherpCC1
XYpCC non-1
waterpCC non-1
otherpCC non-1
CCmnnon
Out of FV
Flux-integrated differential cross section based on Bayesian
unfolding method
In muon kinematics
In pion kinematics
In muon-pion angle
In neutrino reconstructed energy
T2K Preliminary T2K Preliminary
38% 1𝜋+ XY
6% 1𝜋+ water
38% non-1𝜋+ water
6% 1𝜋+ water
13. 11/18/15 NuINT 2015, Osaka 13
CC1 𝜋+ in Water (ND280-FGD2)(cont’d)
T2K PreliminaryT2K Preliminary
14. CC1 𝜋+ in Water (ND280-FGD2)(cont’d)
11/18/15 NuINT 2015, Osaka 14
(GeV)nTrue E
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
/Nucleon)2cm-38
)(10n
(Es
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
POT)21
/50MeV/102
flux(/cmmnT2K
0
200
400
600
800
1000
1200
1400
1600
1800
9
10´
fluxmnT2K
NEUT prediction
GENIE prediction
NEUT average
GENIE average
T2K Run II-IV data
T2K Preliminary
T2K Preliminary
T2K Preliminary
Data lower than GENIE prediction
(same as MiniBooNE result)
Suppression observed specifically
P 𝜋+ > 0.3 GeV & P 𝜋+ < 0.8 GeV
cosθ 𝜋+ > 0.9 (coherent channel
contribution is significant)
(5.56x1020 POT)
(5.56x1020 POT)
(5.56x1020 POT)
15. 11/18/15 NuINT 2015, Osaka 15
① CC1𝜋+
CC1𝜋+ in water (ND280-FDG2)
CC1𝜋+ in carbon (ND280-FGD1) (under review -MC only)
CC1𝜋+ in water (ND280-P0D) (under review -MC only)
② CC1𝜋+ coherent
CC1𝜋+ coherence in carbon (ND280-FGD1), ~ 0.8 GeV
CC1𝜋+ coherence in carbon (INGRID), ~1.5 GeV
Interesting features
Pion created from off-shell W boson despite small
nucleus binding energy (~10s MeV)
Very small four-momentum transfer, |t|~ ℏ2/R2 to
leave nucleus in its ground state
Small angle scattering of produced lepton
Puzzle: K2K and SciBooNE found no evidence of
CC coherent below 1.5 GeV but NC coherent
signal was clearly observed at same energy
(GeV)nE
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
/nucleus)2
(cmC
pCCcoh.
s
0
1
2
3
4
5
6
7
39-
10´
POT)21
/50MeV/102
flux(/cmmn
0
200
400
600
800
1000
1200
1400
1600
1800
2000
9
10´
SciBooNE
K2K SciBar
AnMINER
fluxmnOn-axis
NEUT
GENIE
NEUT flux average
GENIE flux average
W+
17. 11/18/15 NuINT 2015, Osaka
Sidebands to constrain expected N0 of
backgrounds in the signal box
Background estimate method
Split sidebands into bins of reconstructed
invariant hadronic mass, W
Normalization parameters to fit pion
momentum template for each W bin
Background in signal box is retuned based
on fitted normalization parameters.
17
Coherent in Carbon (ND280-FGD1)
T2K Preliminary T2K Preliminary
T2K Preliminary
18. 11/18/15 NuINT 2015, Osaka
An excess of 45±18, with 2.2σ significance
Two models used to estimate signal efficiency
Rein-Seghal: PCAC model; relate with pion-nucleus elastic scattering, use “officially”
in event generators, valid for high energy neutrino, less reliable at < 2 GeV
Alvarez-Ruso: Microscopic model; excitation of Δ resonance, full quantum mechanical
treatment, valid up to 5 GeV
18
Coherent in Carbon (ND280-FGD1) (cont’d)
T2K PreliminaryT2K Preliminary
New result
Rein-Seghal:
Alvarez-Ruso:
Statistical power limited to distinguish between two models
Data: 5.54x1020 POT
Data: 5.54x1020 POT
19. CC coherent in Carbon (INGRID)
11/18/15 NuINT 2015, Osaka
Challenging:
Pion momentum is not well-reconstructed
impossible to reconstruct |t|-transfer
Unavoidable model-dependence
Coherent interaction enhanced:
Muon angle scattering (<150)
Energy deposit around vertex (<37 MeV)
19
T2K PreliminaryT2K Preliminary
(NEUT 5.1.4.2)(NEUT 5.1.4.2)
21. CC coherent in Carbon (INGRID) (cont’d)
11/18/15 NuINT 2015, Osaka
On-going efforts to improve analysis:
Increase signal significance (multi-variate
approach to select candidate event)
Use sidebands to control the dominant
background (CC resonance and CC deep-
inelastic scattering )
More than 2.5σ excess can be achieved if data
agrees with GENIE prediction
21
True Neutrino Energy (GeV)
0 2 4 6 8 10
Signalefficiency(%)
0
20
40
60
80
100
MVA method
Nominal method
) binsqReconstructed p-cos(
0 2 4 6 8 10
Uncertaintyonsignal(%)
0
10
20
30
40
50
Signal Only
Signal + Sidebands
) binsqReconstructed p-cos(
0 2 4 6 8 10
Uncertaintyonbackground(%)
0
20
40
60
Signal Only
Signal + Sidebands
Work in progress
Work in progressWork in progress
22. Up-coming results & Prospects
11/18/15 NuINT 2015, Osaka
Up-coming results:
CC1𝜋+ in Carbon (ND280-FGD1) Under review
CC1𝜋+ in water (ND280-P0D) under review
CC1𝜋+ with proton identification (ND280-FGD1)
CC1𝜋+ coherent in water (ND280-FGD2)
Prospects:
CC1𝜋0 in water (ND280-P0D)
CC1𝜋+ in carbon (INGRID)
22
T2K has near detectors in two different neutrino fluxes simultaneously
unique capacity to make comparisons, joint fit
23. Summary
11/18/15 NuINT 2015, Osaka
Various cross-section measurements with fine final-state
resolution, thank to ND280 structures
First exclusive CC1𝜋+ in water indicated suppression at
low momentum (P 𝜋+ > 0.3 GeV & P 𝜋+ < 0.8 GeV)
small pion scattering (cosθ 𝜋+ > 0.9)
First experimental evidence of CC1𝜋+ coherent below 1.5 GeV
Stay tuned for more interesting results!!!
23
28. CC1𝜋+ in Water: Event migration
11/18/15 NuINT 2015, Osaka 28
Migration (both forward and backward)
Study
Going-through sample
Mask some FGD layer
Rerun reconstruction to verify that vertex
reconstructed at first non-masked layer
29. CC1 𝜋+ in Water (ND280-FGD2)(cont’d)
11/18/15 NuINT 2015, Osaka 29
T2K Preliminary
T2K Preliminary
Effort to reweight NEUT with
MINERvA coherent measurement
Suppression is smaller, but still
visible
P 𝜋+ > 0.5 GeV & P 𝜋+ < 0.7 GeV
cosθ 𝜋+ > 0.9
PhysRevLett.113.261802
MINERvA
30. CC1𝜋+ in Carbon (ND280-FGD1)
11/18/15 NuINT 2015, Osaka
Phase space restriction
0.18 GeV < P 𝜋< 1.6 GeV, θ 𝜋,μ<700
Event selections
Negative muon-like track
𝜋+-like track
No 𝜋- in TPC, no e± in TPC or ECAL
Backgrounds
Dominated by CC-other (22%)
Detailed in table
Three control samples are used
CC0𝜋1P: to control CC0𝜋 bkg
CCother1𝜋+: to control CCN𝜋 bkg
CCother1e±: to control CCX𝜋0 bkg
30
CC1𝜋+ 61% CCres 46%
Work in progress Work in progress
31. CC1𝜋+ in Carbon (ND280-FGD1)
11/18/15 NuINT 2015, Osaka 31
~2300 candidates (MC), results w/
respect to several variables:
Reconstructed ν energy
Muon kinematics (double
differential, Q2,Q3)
Pion kinematics
Muon-pion angles
Hadron invariant mass
Angles in Adler system, to
compare to ANL data
Analysis is under review.
Work in progress Work in progress
Work in progress Work in progress
Work in progress Work in progress
34. 11/18/15 NuINT 2015, Osaka
Dominated systematics: Background model
and vertex activity model
Vertex activity model:
Single particle-gun protons are generated
isotropically [0-250 MeV]
Vertex activity for protons formed
Extra vertex activity is added randomly
25% of MC events scattering off a neutron
target
34
Wo/ vertex activity added W/ vertex activity added
T2K Preliminary T2K Preliminary
Coherent in Carbon (ND280-FGD1) (cont’d)
37. Backup: Vertex activity
11/18/15 NuINT 2015, Osaka 37
Use sand muons enhanced
Data-MC vertex activity
difference is 2.7%
Vary PE as function of track angle,
simultaneously vary PE in vertex region
re-estimate cross-section. 13.6%
differences used as systematics
Add up quenching effect based on Birk’s
law 7.17%, and sum in quadrature
15.37%