an intermediate water cherenkov detector for t2k & hk · 2016-11-21 · detector conﬁguration...

An Intermediate Water Cherenkov Detector for

T2K & HKMike Wilking

Stony Brook University The First Workshop on the Second

Hyper-Kamiokande Detector in Korea November 21st, 2016

Detector Configuration• Two groups have been working on near detector design

for Hyper-K: NuPRISM & TITUS

• These groups are in the process of merging:

• NuPRISM's vertical detector configuration spanning many off-axis angles will be preserved

• Goal is to load with Gd (pending safety approval)

• Plan to operate the detector in the T2K era

• Stage-1 approval has already been granted

• A TDR for Stage-2 approval will be submitted in 2017

10 m 14m

6 m or 8 m

10m

NuPRISM

Near/Intermediate Detectors Upgrade of ND280, New intermediate detectors

•  Upgrade of ND280 is discussed towards T2K-II. •  Further measurement of neutrino interaction and cross-sections.

•  New water-based detectors at 1-2km from beam target. •  Two designs are proposed. -> They will be unified soon.

•  Reduction of the systematic errors •  νe/νμ cross-sections, near/intermediate water targets.

��

Proposed intermediate detectors�

TITUS�nuPRISM�

ND280 upgrade�New TPCs�

New target detectors�Under optimization�

11 m

22 m

TITUS

Goals of an Intermediate Water Detector1. Constrain relationship between

Erec & Etrue

• Erec formula assumes single-nucleon knockout

• ~20-30% of interactions eject multiple nucleons

• Produces an energy bias that is highly model dependent

2. Constrain σ(νe)/σ(νμ)

• No experimental constraint on σ(νe) exists at the few percent level

νμ μ-

??

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6Eν (GeV)

0

10

20

30

40

50

60

d(E ν,E

ν) (1

0-39 cm

2 /GeV

)

0.20.61.0

Eν (GeV)

FIG. 1: (Color online) The spreading function d(Eν , Eν) of Eq. (4) per neutron of 12C in the

case of electrons evaluated for three Eν values. The genuine quasielastic (dashed lines) and the

multinucleon (dotted lines) contributions are also shown separately.

III. APPLICATIONS

A. T2K

Here the situation is relatively simple as one deals with a long baseline experiment [10, 11]

with oscillation mass parameters already known to a good accuracy. We have pointed out

[4] the interest of the study for T2K of the muon events spectrum both in the close detector

and in the far detector since the two corresponding muonic neutrino beams have different

energy distributions. The study of the reconstruction influence on the electron events in

the far SuperKamiokande detector was performed in our Ref. [4], it is discussed again here

in our new reversed perspective. The two muon beams in the close and far detectors and

the oscillated electron beam at the far detector having widely different energy distributions,

the effect of the reconstruction is expected to differ in all three. The muon neutrino energy

distribution in the close detector, normalized with an energy integrated value of unity,

Φνµ(Eνµ) is represented in Fig. 2 as a function of Eνµ. At the arrival in the far detector it

is reduced by a large factor which depends on the oscillation parameters and its expression

8

Martini et al. arXiv:1211.1523

Constraints from Typical Near Detectors

• Shouldn’t cross section systematics cancel in a near/far fit?

• Some errors, like total normalization, will cancel

• However, multi-nucleon and pion absorption events feed-down into oscillation dip

• Cannot disentangle with near detectors

• Energy spectrum is not oscillated

• More multi-nucleon = smaller dip

• Multi-nucleon effects are largely degenerate with mixing angle effect!

at SK

at SKSK Oscillated Flux Eν→Erec Smearing

(Eν=0.8 GeV)

Eν→Erec Smearing (Eν=0.8 GeV)

ND280 Flux

Mixing Angle Bias!Near detectors lack sensitivity

SYSTEMATIC ERRORS 21

• Updates to the cross-section systematic error model, primarily accounting for neutrino/antineutrino differences:

• Uncertainty to parameterize the relative rate of interactions on nucleon pairs by neutrinos and antineutrinos

• This parameter is constrained by ND280 data

• Correlations between the νe and νe cross section systematic parameters

• Improved estimates of the uncertainties on the relative rates of neutrinos and antineutrinos, which are important for CP violation measurements

Source of Uncertainty ν 1Re ν 1Re ν 1Re/ν 1Re

SK Detector 2.3% 3.1% 1.6%

SK Final State and Secondary Interactions 2.6% 2.4% 3.5%

Flux and X-sec constrained by ND280 2.9% 3.2% 2.3%

NC 1γ 1.5% 3.0% 1.5%

νe and νe 2.6% 1.5% 3.1%

NC Other 0.2% 0.3% 0.2%

Total 5.5% 6.3% 5.9%

Theoretical estimate

Inclusion of FGD2, anti-neutrino mode samples improve constraint

2016 T2K νe Uncertainties

• CPV sensitivity depends on the uncertainty in the νe/anti-νe ratio (5.9%)

• Dominant uncertainties come from theoretical estimates

• SK Final State Interactions (model extrapolation ofπ

±-N scattering data to nuclear environment)

• σνe/σνμ (no experimental constraint below ~20%)

• Current uncertainty in Multi-nucleon events contains no shape uncertainty

• Adding shape uncertainty may increase this error

See Talk byM. Scott formore details

Detector Concept

(GeV)νE0 0.5 1 1.5 2 2.5 3 3.5

Arb

. Nor

m.

0

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1510×

Off-axis Flux°1.0

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Off-axis Flux°2.5

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Off-axis Flux°4.0

WC Detector

ν-Beam ν Interactions

ν Interactions

ν Interactions

1° 2.5°

4.0°

Muon p&θ

Muon p&θ

Muon p&θ

Take linear combinations!

-0.5 *

+1.0*

-0.2*

600 MeV Monoenergetic Beam using 60 slices

in off-axis angle

30/01/15 Mark Scott, TRIUMF 3

ννPPRRIISSMM νPRISM detector concept

ν beam

νPRISMMuon p-θ

+1.0

-0.5

-0.2

● Combine slices of νPRISM

● Produce desired flux

● Create observable distribution

Muon p&θ from a

monoenergetic beam

Benefits of a Monoenergetic Beam• Fully specified initial state!

• Electron-scattering-like measurements with neutrinos!

• Can now fully map Etrue to Erec

• No longer rely on final state particles to determine Eν

• First ever measurements of σNC(Eν)

• Much better constraints on NC oscillation backgrounds

• It is now possible to separate the various components of single-μ events!

Near Detector “Oscillations”

(GeV)νE0 0.5 1 1.5 2 2.5 3 3.5

Arb

. Nor

m.

0

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Off-axis Flux°1.0

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Off-axis Flux°2.5

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Off-axis Flux°4.0

WC Detector

ν-Beam ν Interactions

ν Interactions

ν Interactions

Muon p&θ

Muon p&θ

Muon p&θ

Take different linear

combinations!

+1.0*

-0.8*

+0.2*

Measured oscillated p&θ spectrum in a near detector!

{This is the procedure

used for the νμ disappearance

analysisSystematic errors due to nuclear effects are

reduced to ~1%

Match Super-K Oscillated Flux

Oscillated Flux Produced at the Near Detector!

Oscillated p&θ Measured at the Near Detector!

“Oscillations” in a Near Detector•Red region is directly

measured by NuPRISM

•Blue region is flux difference correction

•Green is SKnon-CC0π background

•Partially cancels with already-subtracted NuPRISM CC0π background

•Magenta is acceptance correction

•(geometric muon acceptance)

•SK prediction is largely from directly measured component

(GeV)νE0 0.2 0.4 0.6 0.8 1 1.2 1.4

1e2

1 PO

T]⋅

100

MEV

⋅2

Flux

/[cm

0

10000

20000

30000

40000

50000

60000

70000

80000

Oscillated SK flux

Oscillated SK flux

NuPRISM flux fit

(GeV)νE0 0.2 0.4 0.6 0.8 1 1.2 1.4

1e2

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T]⋅

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MEV

⋅2

Flux

/[cm

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20000

40000

60000

80000

Oscillated SK flux

Oscillated SK flux

NuPRISM flux fit

(GeV)νE0 0.2 0.4 0.6 0.8 1 1.2 1.4

1e2

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T]⋅

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MEV

⋅2

Flux

/[cm

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310×

Oscillated SK flux

Oscillated SK flux

NuPRISM flux fit

Reconstructed neutrino energy (GeV)0 0.5 1 1.5 2 2.5 3

Even

ts

0

1

2

3

4

5

Oscillated SK events

Measured NuPRISM events

NuPRISM acceptance correction

Fitted flux difference correction

backgroundπNon-CC0


Even

ts

0

0.5

1

1.5

2

2.5

3

3.5

4Oscillated SK events




backgroundπNon-CC0


Even

ts

0

1

2

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5

6Oscillated SK events




backgroundπNon-CC0

νe Appearance (CPV)

• Step 1 is the νe version of the νμ disappearance analysis

• Reduces FSI/SI and SK detector uncertainties, and improves ND280 flux+xsec constraint

• Step 2 uses only the near detector to measure σ(νe)/σ(νμ)

• Constrains the σ(νe)/σ(νμ) uncertainty

• Step 3 uses the 2.5° slice of the Near Detector to measure NC backgrounds with the same energy spectrum as the far detector (reduces background systematics)

3 step approach:Step 1: Measure Super-K νe response

with Near Detector νμ

Step 2: Measure Near Detector νe response with Near Detector νμ

High-E is above muon acceptance

If σ(νe)/σ(νμ)=1 this fit is all

that is needed Measure σ(νe)/σ(νμ)

Near Det.

Near Det.

Near Det.

νe Selection•Use 2.5°-4° portion of detector ➜ Higher νe purity!

•6 m inner detector diameter (increase to 8 m soon)

•3500 events with 71% purity

•Can already achieve ~5% total error

•Further improvements expected from reconstruction tuning (e.g. π

0 rejection & e/μ

PID) and in-situ background constraints

•Current uncertainty is dominated by flux

•Hadron production uncertainties can be reduced with NA61 kaon and replica target measurements

•T2K is working to reduce the horn current uncertainty

•Goal is to achieve 3% uncertainty with the above improvements

NuPRISM Reco

(MeV)recE0 500 1000 1500 2000

Even

ts/(2

00 M

eV)

0

500

1000

1500-CCeν

0πNCγNC-CCµν

1-Ring e Candidates

POT Weighted Signal (New Cuts/MC Stats)

16

• Weighting to 1.5e21 neutrino mode POT for each off-axis position between 2.5 and 4.0 degrees

Purity for Erec<1.2 GeV = 71(73)% Nue Signal for Erec<1.2 GeV =3501(3184)

20 inch PMT Results

NuPRISM Reco

(MeV)recE0 500 1000 1500 2000

Frac

tiona

l Err

or

0

0.05

0.1

0.15

0.2

0.25

Total

Statistical (S-B)

Background Systematics

Signal Efficiency

)µν/eνFlux (

(MeV)recE0 500 1000 1500 2000

Frac

tiona

l Err

or

0

0.05

0.1

0.15

0.2

0.25TotalStatistical (S-B)Background SystematicsSignal Efficiency

)µν/eνFlux (

Old vs New Total Error Size

17

• The total uncertainty below 1 GeV is only slightly reduced with cut optimization on large MC statistics

• Configuration changes are likely needed to get any significant improvments

New Old

nuPRISM Status 10

Achieving High νe Purity• From the T2K analysis, we have an example of the νe purity that can be achieved in

a WC detector with a 2.5 degrees off-axis flux

• 3.50 intrinsic νe events vs. 0.96 NC events - 77% νe purity

• There are challenges in nuPRISM: events are closer to the wall and more muon background

• Optimization of PMT size/granularity for PID is ongoing

• But, nuPRISM has an advantage due to the more off-axis flux

Off-axis angle (º)

νe Flux 0.3-0.9 GeV

νμ Flux0.3-5.0 GeV

Ratio νe/νμ

2.5 1.24E+15 2.46E+17 0.507%3.0 1.14E+15 1.90E+17 0.600%

3.5 1.00E+15 1.47E+17 0.679%

4.0 8.65E+14 1.14E+17 0.760%

50% increase in νe fraction from 2.5 to 4.0 degrees off-axis

TITUS Gd Studies• Super-K is planning to add Gd to the detector to

tag final state muons

• This information can be useful for ν/ν separation

• νμ + n ➜ μ- + p typically produces 0 final

state neutrons

• νμ + p ➜ μ+ + n typically produces 1 final

state neutron

• The neutron emission cross section, and the n-Gd capture probability are not precisely known

• Sensitive to nuclear modeling

• Neutron capture rates can be calibrated with an intermediate water detector

• With off-axis technique, we can measure neutron signal rates for ν and ν as a function of Etrue and muon kinematics

HK Intermediate WC Detector

Gd Doping

11

• 0.1% Gd2(SO4)3 allows tagging of final state nucleons

– νµ CCQE: νµ + n → µ− + p 0 neutrons 74% → 83%

– νµ CCQE: νµ + p → µ+ + n 1 neutron 61% → 73%

• Clear n signals can be modified by nuclear effects: re-scattering, charge exchange, and absorption in the nuclear media

• Statistical information remains – powerful approach for H2O

• Cross section measurements

GENIE v2.8.0 simulations of neutrino/antineutrino interactions with C target

ν ν


Gd Doping

11








ν ν

GENIE v2.8.0 simulations ofneutrino/antineutrino

interactions with C target


Gd Doping

11








ν ν

Phase 0• The intermediate detector program will

proceed in a phased approach

• In Phase 0, the instrumented portion of the detector will be constructed, and placed on the surface near ND280

• In phase 0, we will perform a high-purity measurement of σ(νe)/σ(νμ)

• Off-axis angles of ≥6.6° are accessible

• The flux ratio of νe/νμ grows with off-axis angle

• Performance of reconstruction (PID, ring counting, etc.) can also be demonstrated

• An easily accessible surface detector will allow access to refine detector calibration as needed

NuPRISM Phase 0

Flux Histograms

5 (GeV)νE

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-410

-310

-210

-110

1ND280

(GeV)νE0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

-410

-310

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-110

1Proton Module

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-410

-310

-210

-110

1 Off-axis°6

numu (Integral=1) nue (Integral=1) nue/numu Ratio

The nue/numu ratio is largest between the pion and kaon “peaks”

For more off-axis bins, this region is around 1 GeV or less

νμ flux (integral = 1) νe flux (integral = 1)

νe/νμ ratio

NuPRISM Phase 0

Flux Histograms

5 (GeV)νE

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-410

-310

-210

-110

1ND280

(GeV)νE0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

-410

-310

-210

-110

1Proton Module

(GeV)νE0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

-410

-310

-210

-110

1 Off-axis°6


The nue/numu ratio is largest between the pion and kaon “peaks”

For more off-axis bins, this region is around 1 GeV or less

6° off-axis

ND280

NuPRISM Phase 0

Flux Histograms, Cont.

6


For the 12 degree off-axis position the nue/numu maximum is in the 0.5-1.0 GeV range

After peaking at 200-300 MeV, the nue flux is relative flat out to 1 GeV (GeV)νE

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-410

-310

-210

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1 Off-axis°9

(GeV)νE0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

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1 Off-axis°12

12° off-axis

νe Selection in Phase 0• Increased off-axis angle results in:

• Increased νe purity

• Decreased event rate

• For >6°, event pileup at the 280m site becomes manageable

• Even at 12°, a 2% statistical error is achievable

• In addition, the high statistics νμ sample can be used to study full lepton phase space (at a fixed Eν), and Gd capture

• Phase 0 can produce important physics results prior to the construction of the complete detector!

59

(GeV)νE0 0.5 1 1.5 2 2.5 3

/50

MeV

/1e2

1 PO

T2

Flux

/cm

1010

1110

1210

OA°ND280 2.5 OA°6.0 OA°9.0 OA°12.0

FluxµνNeutrino Mode,

(GeV)νE0 0.5 1 1.5 2 2.5 3

/50

MeV

/1e2

1 PO

T2

Flux

/cm

810

910

1010

OA°ND280 2.5 OA°6.0 OA°9.0 OA°12.0

FluxeνNeutrino Mode,

FIG. 74. The 6�, 9� and 12� o↵-axis ⌫µ

(top) and ⌫e

(bot-tom) spectra. The 2.5� o↵-axis spectrum is also showed forcomparison.

the 9� and 12� o↵-axis positions with a low energy peakand a second peak around 800 MeV. The second peakcomes from neutrinos produced in kaon decays and itsrelative fraction is enhanced as the peak from pion de-cays moves to lower energy where the cross-section issuppressed. The lower energy peak from pion decays pro-vides the opportunity to study ⌫

µ

-CC interaction nearthe threshold where nuclear e↵ects are expected to besignificant. The peak from kaon decays can be used tostudy interactions that are relevant for the acceleratorand atmospheric neutrino measurements. In particular,with Gd loading in the detector, the neutron multiplic-ities can be studied both for events near the thresholdand for O(1 GeV) events, the energy region of interestfor atmospheric neutrinos.

The physics program of NuPRISM Phase 0 will takeadvantage of the large o↵-axis properties of the neutrinoflux to make measurements that compliment the ultimateNuPRISM physics program. Although NuPRISM Phase0 cannot study the nuclear e↵ect in detail since it does

TABLE IX. The expected number of selected 1Re and 1Rµcandidate events in the NuPRISM Phase 0 detector at di↵er-ent o↵-axis angles at a baseline of 280 m for 2⇥ 1021 protonson target in neutrino mode.

O↵-axis Angle 1Re Events (< 1.2 GeV) ⌫e

-CC Purity6� 10626 79.5%9� 5781 83.5%12� 3480 86.4%O↵-axis Angle 1Rµ Events ⌫

µ

-CC Purity6� 3.33e5 92.7%9� 1.09e5 90.4%12� 6.23e4 91.7%

not cover ranges of o↵-axis angles, it can provide interest-ing information complimentary to NuPRISM. The Phase0 provides large statistics of ⌫

e

and ⌫̄e

samples with bet-ter purity in the signal region of 0.4-1.2GeV. There aremuon neutrinos in this energy region coming from kaondecays, which can provide a constraint on this compo-nent of the flux. The o↵-axis peak energies for ⌫

e

and⌫

µ

are below 300 MeV, which will provide samples nearthreshold where nuclear e↵ects and the ⌫

e

/⌫µ

cross sec-tion di↵erence are expected to be large, allowing sensitivetest of models.

60

(MeV)recE0 500 1000 1500 2000

Even

ts/(2

00 M

eV)

0

1000

2000

3000-CCeν

0πNCγNC-CCµν

OA, 1-Ring e Candidates°6

(MeV)recE0 500 1000 1500 2000

Even

ts/(2

00 M

eV)

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500

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1500

-CCeν0πNCγNC-CCµν


(MeV)recE0 500 1000 1500 2000

Even

ts/(2

00 M

eV)

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500

1000

-CCeν0πNCγNC-CCµν


FIG. 75. The predicted 1Re candidates in bins of recon-structed energy for o↵-axis angles of 6�, 9� and 12�. The ratesare normalized to a neutrino mode exposure with 5⇥1021 pro-tons on target.

(MeV)recE0 500 1000 1500 2000

Even

ts/(1

00 M

eV)

0

50

100

310×

-CCQEµν

-CCnonQEµν

NCOther

Candidatesµ OA, 1-Ring °6

(MeV)recE0 500 1000 1500 2000

Even

ts/(1

00 M

eV)

0

10

20

310×

-CCQEµν

-CCnonQEµν

NCOther


(MeV)recE0 500 1000 1500 2000

Even

ts/(1

00 M

eV)

0

5

10

310×

-CCQEµν

-CCnonQEµν

NCOther


FIG. 76. The predicted 1Rµ candidates in bins of recon-structed energy for o↵-axis angles of 6�, 9� and 12�. The ratesare normalized to a neutrino mode exposure with 5⇥1021 pro-tons on target.

Summary• An intermediate water detector can collect high

statistics samples of neutrino interactions with the same nuclear target and similar efficiencies as HK

• By measuring neutrino interaction across a range of off-axis angles, it is possible to experimentally constrain the relationship between Erec and Etrue

• Phase 0 will consist of the instrumented portion of the detector in a surface water tank

• Precise measurement of σ(νe)/σ(νμ)

• Demonstration of reconstruction and calibration performance

• Convenient access for hardware and calibration R&D

• The program will begin in the T2K era to provide an important demonstration that systematic errors can be sufficiently controlled in Hyper-K era

an intermediate water cherenkov detector for t2k & hk · 2016-11-21 · detector conﬁguration...

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