On the measurements of neutrino energy spectra andnuclear effects in neutrino-nucleus interactions

Xianguo LU ( 盧 顕国 )University of Oxford
Kyoto HE Seminar
29 July 201629 July 2016

X.-G. Lu, Oxford1Outline
1. Introduction
2. Measuring nuclear effects w/ minimal dependence on neutrino energy
3. Measuring neutrino energy independent of nuclear effects
4. Theory predictions
5. Measurement in MINERvA
6. Measurement in T2K
7. Summary
References: arXiv:1512.05748 and 1507.00967, unless otherwise specified.

29 July 2016

X.-G. Lu, Oxford

21. Probing the antimaterial world with neutrino interactions
material world

antimaterial world

violation of CP-symmetry(to be found)

Wiki: NGC 4414⇑

leptonic CP violation

29 July 2016

X.-G. Lu, Oxford

31. Probing the antimaterial world with neutrino interactions
material world

antimaterial world

violation of CP-symmetry(to be found)

Wiki: NGC 4414⇑

leptonic CP violation=, ≠,29 July 2016≠

X.-G. Lu, Oxford

41. Probing the antimaterial world with neutrino interactions
material world

antimaterial world

violation of CP-symmetry(to be found)

Wiki: NGC 4414

accelerator

detector=, ≠,29 July 2016≠

X.-G. Lu, Oxford

51. Probing the antimaterial world with neutrino interactions

detector
Quasi-elastic scattering (QE):
Resonance production (RES):
Rev.Mod.Phys. 84 (2012) 1307
Rev.Mod.Phys. 84 (2012) 1307≠
Charged-current cross section per nucleon
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X.-G. Lu, Oxford

61. Probing the antimaterial world with neutrino interactions
detector

T2K, PRL 112, 061802 (2014)

Neutrino energy reconstruction
Convert to flux via cross section
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X.-G. Lu, Oxford

71. Neutrino interactions on static nucleon➢

Static nucleon target ν

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X.-G. Lu, Oxford

81. Neutrino interactions on static nucleon➢

Static nucleon target, charged current (CC) ν → l', quasi-elastic (QE) N → N'
✔ Detection via charged lepton✔ Neutrino energy ← charged lepton kinematics

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X.-G. Lu, Oxford

91. Neutrino interactions on static nucleon➢

Static nucleon target, charged current (CC) ν → l', quasi-elastic (QE) N → N'
✔ Detection via charged lepton✔ Neutrino energy ← charged lepton kinematics✔ Lepton and hadron transversely balanced

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X.-G. Lu, Oxford

101. Neutrino interactions on bound nucleon➢

Nucleus (bound nucleon) target ν✗
Fermi motion (FM) biases neutrino energy reconstruction

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X.-G. Lu, Oxford

111. Neutrino interactions on bound nucleon➢

Nucleus (bound nucleon) target ν✗
Fermi motion (FM) biases neutrino energy reconstruction✗
Multinucleon correlations: cross section unknown, strong bias to all final state kinematics

Science 320 (2008) 1476-1478

initial nucleon in correlation withanother in large relative motion
Properties largely unknown, for simplicity no further
discussion here. See more detail in arXiv:1512.05748.

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121. Neutrino interactions on bound nucleon➢

Nucleus (bound nucleon) target, CC ν → l', QE N → N'✗
Fermi motion (FM) biases neutrino energy reconstruction✗
Multinucleon correlations: cross section unknown, strong bias to all final state kinematics✗
QE-like: QE faked by resonance production (RES) ∆ → N'π
π absorbed in nucleus ← final state interaction (FSI)
PRL 111, 221802 (2013)29 July 2016

X.-G. Lu, Oxford

131. Neutrino interactions on bound nucleon➢

Nucleus (bound nucleon) target, CC ν → l', QE N → N'✗
Fermi motion (FM) biases neutrino energy reconstruction✗
Multinucleon correlations: cross section unknown, strong bias to all final state kinematics✗
QE-like: QE faked by resonance production (RES) ∆ → N'π
π absorbed in nucleus ← final state interaction (FSI)✗
FSI → energy-momentum transferred in nucleus, possible nuclear emission

nuclear emission

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X.-G. Lu, Oxford

141. Neutrino interactions on bound nucleon➢

Nucleus (bound nucleon) target ν✗
Nuclear effects: FM, multinucleon correlations, FSI, etc.
✗
Transverse momenta NOT balanced

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151. Nuclear effects in neutrino interactions
nuclear targets
Effects associated with nuclear
targets in neutrino interactions– highly convoluted

– Pb
– Fe
– Ar

gas dynamics+ shell structure–O
Neutrino
energy–C–– binding energy– Fermi motion

qu
a

–

interaction dynamics

–
re
DI
s
S
on
sie
an
las
t
tic

– multinucleon correlations– Final state interactions
Previous discussion
nuclear effects
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161. Nuclear effects in neutrino interactions
T2K, PHYSICAL REVIEW D 91, 072010 (2015)

nuclear targets
– Pb
– Fe
– Ar

gas dynamics+ shell structure

–O
–C
–

– binding energy– Fermi motion

interaction dynamics

–
–
qu
re
DI
so
S
as
na
iel
nt
as
tic

– multinucleon correlations– Final state interactions

nuclear effects
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X.-G. Lu, Oxford

171. Nuclear effects in neutrino interactions
T2K, PHYSICAL REVIEW D 91, 072010 (2015)

nuclear targets
– Pb
– Fe
– Ar

gas dynamics+ shell structure

–O
–C
–

– binding energy– Fermi motion

interaction dynamics

–
–
qu
re
DI
so
S
as
na
iel
nt
as
tic

– multinucleon correlations– Final state interactions

nuclear effects
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X.-G. Lu, Oxford

18

1. Nuclear effects in neutrino interactions
T2K, PHYSICAL REVIEW D 91, 072010 (2015)

nuclear targets
– Pb
– Fe
– Ar

gas dynamics+ shell structure

–O
–C
–

– binding energy– Fermi motion

interaction dynamics

–
–
qu
re
DI
so
S
as
na
iel
nt
as
tic

– multinucleon correlations– Final state interactions

nuclear effects
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X.-G. Lu, Oxford

19Outline
1. Introduction
2. Measuring nuclear effects w/ minimal dependence on neutrino energy
3. Measuring neutrino energy independent of nuclear effects
4. Theory predictions
5. Measurement in MINERvA
6. Measurement in T2K
7. Summary

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X.-G. Lu, Oxford

202. Minimal energy dependent measurement of nuclear effects
nuclear targets
– Pb
– Fe
– Ar

gas dynamics+ shell structure–O
Neutrino
energy–C
X–– binding energy– Fermi motion

interaction dynamics

–
–
qu
re
DI
so
S
as
na
iel
nt
as
tic

– multinucleon correlations– Final state interactions

nuclear effects
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X.-G. Lu, Oxford

212. Energy dependence of final state kinematics
4-momentum transfer: Q2
Invariant mass of N': W
Ignoring binding energy,(

Quasi-elastic scattering (QE):●●

Resonance production (RES):

effect of Fermi motion)

Lepton retains most of the increase of neutrinoenergyHadronic kinematics much less Eν-dependent
than leptonic ones

For QE and RES, Q2<<mN2 (interaction length)
W is nucleon or resonance mass.
ω “saturates” when Eν > Ο (mN/2)
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222. Energy dependence of nuclear medium response
N' mom. saturates with large neutrino energy.
FSI all determined by N' momentum:
1. In-medium interaction probability τf saturates=

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N' mom. saturation

×

X.-G. Lu, Oxford

τf23

2. Energy dependence of nuclear medium response
N' mom. saturates with large neutrino energy.
FSI all determined by N' momentum:
1. In-medium interaction probability τf saturates
2. Energy-momentum transferfrom N'to the nucleus also saturate=

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N' mom. saturation

×

X.-G. Lu, Oxford

τf24

2. Energy dependence of nuclear medium response
N' mom. saturates with large neutrino energy.
FSI all determined by N' momentum:
1. In-medium interaction probability τf saturates
2. Energy-momentum transferfrom N'to the nucleus also saturate

N' mom. saturation

Medium response:
Nuclear emission: nucleus being excited or
broken-up, emitting particles.
Probability: P(∆E)

=

×

τf
P(∆E)

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252. Energy dependence of nuclear medium response
N' mom. saturates with large neutrino energy.
FSI all determined by N' momentum:
1. In-medium interaction probability τf saturates
2. Energy-momentum transferfrom N'to the nucleus also saturate.

N' mom. saturation

Medium response:
Nuclear emission: nucleus being excited or
broken-up, emitting particles.
Probability: P(∆E)●

fully determine nuclear response – ideal variables to characterize FSI.

=

×

τf
P(∆E)

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26

2. State-of-the-art probes of nuclear effects✔

✔

Neutrinos produced by accelerators have wellunderstood directions.
Momentum conservation applies in all directions of
the neutrino-nucleus interaction system.
→ neutrino-nucleon kinematic imbalance=
nuclear effects
Neutrino energy unknown, use transverse projection→
To first order, nuclear effects can be determined
independently on neutrino energy.

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27

2. State-of-the-art probes of nuclear effects✔

✔

Neutrinos produced by accelerators have wellunderstood directions.
Momentum conservation applies in all directions of
the neutrino-nucleus interaction system.
→ neutrino-nucleon kinematic imbalance=
nuclear effects✔

Neutrino energy unknown, use transverse projection→
To first order, nuclear effects can be determined
independently on neutrino energy.

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28

2. State-of-the-art probes of nuclear effects
No nuclear effects

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2. State-of-the-art probes of nuclear effects
Limited energy evolution with FSI strength

invariant w/ neutrino energy

FM
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FSI
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30

2. State-of-the-art probes of nuclear effects
Counterexample
Strong – inverted – energy evolution contains lepton kinematics δφT ~ δpT/qT

Neutrino energy dependence can counteracts nuclear effects.

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2. State-of-the-art probes of nuclear effects
Extension
Proton momentum
Counterexample

invariant w/ nucleon-level physics

FM
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FSI
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2. State-of-the-art probes of nuclear effects
Application●

Directly showing initial state, useful to study new
target material

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2. State-of-the-art probes of nuclear effects
Application

In RES, N' = proton + pion, sensitive to pion FSI● Useful to study FSI in anti-neutrino interaction (anti-nu CCQE N'=neutron)●

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2. State-of-the-art probes of nuclear effects
No FSI (i.e. FM only)

Isotropic FM

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2. State-of-the-art probes of nuclear effects

Decelerating FSI

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2. State-of-the-art probes of nuclear effects

Accelerating FSI(real example in Section 4)

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Outline
1. Introduction
2. Measuring nuclear effects w/ minimal dependence on neutrino energy
3. Measuring neutrino energy independent of nuclear effects
4. Theory predictions
5. Measurement in MINERvA
6. Measurement in T2K
7. Summary

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X.-G. Lu, Oxford

38

3. Nuclear effect-independent reconstruction of neutrino energy
nuclear targets
– Pb
– Fe
– Ar

gas dynamics+ shell structure–O
Neutrino
energy–C
X–– binding energy– Fermi motion
Xinteraction dynamics

–
–
qu
re
DI
so
S
as
na
iel
nt
as
tic

– multinucleon correlations– Final state interactions

nuclear effects
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X.-G. Lu, Oxford

393. Hydrogen as neutrino interaction target
nuclear targets

HWith
target,nuclear
Eν

=
≠

– Pb
∑ final-state energy.

A problem of detector resolution .
nuclear phy. + d.r.

– Fe
– Ar

gas dynamics+ shell structure–O–C

Neutrino
energyH– binding energy– Fermi motion
X–interaction dynamics

–
–
qu
re
DI
so
S
as
na
iel
nt
as
tic

– multinucleon correlations– Final state interactions

nuclear effects
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X.-G. Lu, Oxford40

3. Hydrogen as neutrino interaction target●

Pure hydrogen–

Technical requirement:●

bubble chamber (historical: 73, 79, 78, 82, 86)
Chin. Phys. C 38, 090001 (2014)

H2–

Safety issue: explosive
LBNE design report, FERMILAB-PUB-14-022●●“Since the use of a liquid H2 bubble chamber is excluded in the ND
hall due to safety concerns, ...”In the last ~30 years there has been no new measurement of neutrino interactions onpure hydrogen.

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3. Double-transverse kinematic imbalance
Lepton-proton interaction → 3 charged particles: l p → l' X Y– Leading order realization in standard model:

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423. Double-transverse kinematic imbalance
Lepton-proton interaction → 3 charged particles: l p → l' X Y– Leading order realization in standard model:

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43

3. Double-transverse kinematic imbalance
Lepton-proton interaction → 3 charged particles: l p → l' X Y– Leading order realization in standard model:

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3. Hydrogen doping

Double-transverse momentum imbalance
Hydrogen: 0● Heavier nuclei: irreducible symmetric broadening● by Fermi motion O(200 MeV)
● further by FSI●

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3. Hydrogen doping

Double-transverse momentum imbalance
Hydrogen: 0● Heavier nuclei: irreducible symmetric broadening● by Fermi motion O(200 MeV)
● further by FSI● Hydrogen doping: adding hydrogen atoms in target material.
● Hydrogen shape is only detector smearing.
● With good detector resolution, hydrogen yield can be extracted.
● With very good res., event-by-ev. selection of nu-H interaction is possible.
● In situ nuclear-free flux measurement with current technology is possible via“bin-and-fit” method (arXiv:1512.09042, see new demonstration in Section 6).
●

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Outline
1. Introduction
2. Measuring nuclear effects w/ minimal dependence on neutrino energy
3. Measuring neutrino energy independent of nuclear effects
4. Theory predictions
5. Measurement in MINERvA
6. Measurement in T2K
7. Summary

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47

4. Theory predictions for transverse kinematic imbalancecollinear enhancement* suggested by GENIE Collaboration to examine
removing elastic component of hA FSI.

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4. Theory predictions for transverse kinematic imbalancecollinear enhancement

acceleration peak

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49

4. Theory predictions for transverse kinematic imbalance

inverted evolution

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4. Theory predictions for transverse kinematic imbalance

arXiv:1606.04403

collinear enhancement
similar in pπ- and pπ0 systems
Conclusion: large room to improve theories
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Outline
1. Introduction
2. Measuring nuclear effects w/ minimal dependence on neutrino energy
3. Measuring neutrino energy independent of nuclear effects
4. Theory predictions
5. Measurement in MINERvA
6. Measurement in T2K
7. Summary

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X.-G. Lu, Oxford

525. Measurement in MINERvA
Nucl.Instrum.Meth. A743 (2014) 130-159

ν

Phys.Rev. D91 (2015) no.7, 071301

NuMI on-axis neutrino beam, 3 GeV peak energy● Fine grained scintillator tracker as target●
Event selection: 1 µ, ≥ 1 p, 0 π (CCQE-like)➢µ reconstruction: tracker, matched to MINOS ND, momentum by range andcurvature➢ p reconstruction: ID and momentum by tracker dE/dx profile, momentum threshold
450 MeV➢
π veto: cut on untracked energy and Michel electrons●

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5. Measurement in MINERvA – selecting ESC protons
After cuts

Chin. Phys. C, 38, 010009 (2014)

Cut on dE/dx near end point
to select ESC protons.

Elastically scattering contained = ESC
Nominal end point:
ESC protons true end point (p → 0)or exiting or inelastic interaction(p ≠ 0 w/ different dE/dx profile)

ESC

non-ESC
E5

non-ESC protons
have missing ranges→ works also for
p by range

E0

Non-ESC true end point (p → 0)
Neutrino2016 P2.043

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545. Measurement in MINERvA – selecting ESC protons
After cuts

E
T
AF

R

S
T
CU

SpreadStatistics

default

100%

100%

dE/dx

60%

40%

χ2

70%

60%

dE/dx + χ2

50%

30%

Neutrino2016 P2.043

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5. Measurement in MINERvA – pT scale corrections

BEFORE CORRECTIONS
Non-unity pT scales:
instrumental apparent acceleration or
deceleration of the final-state particles.
Correction recipe: find a pT-scale related
distribution that can be describedanalytically.

Neutrino2016 P2.043

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5. Measurement in MINERvA – pT scale corrections

AFTER CORRECTIONS
Non-unity pT scales:
instrumental apparent acceleration or
deceleration of the final-state particles.
Correction recipe: find a pT-scale related
distribution that can be describedanalytically.

Neutrino2016 P2.043

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5. Measurement in MINERvA – final-state momentum spectra

In given acceptance, overall spectral shapes not sensitive to FSIs.
● Nuclear effects are difficult to observe on top of kinematics originating from neutrinonucleon interaction level. Direct observables are therefore needed.
●

Neutrino2016 P2.043

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5. Measurement in MINERvA – single-T kinematic imbalance

GENIE predictions in MINERvA
acceptance show collinear enhancement
discussed previously (Section 4).
● Sensitivity achieved by momentum
improvement cuts and corrections.
●

Neutrino2016 P2.043

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Outline
1. Introduction
2. Measuring nuclear effects w/ minimal dependence on neutrino energy
3. Measuring neutrino energy independent of nuclear effects
4. Theory predictions
5. Measurement in MINERvA
6. Measurement in T2K
7. Summary

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60

6. Measurement in T2K
Nucl.Instrum.Meth. A659 (2011) 106-135

TPC

ν

FGD1

TPC1

FGD2

TPC2

(not signal
event display)

J-PARC off-axis neutrino beam, 600 MeV peak energy● Fine Grained Detector (FGD1) as CH target● Event selection: 1 µ, ≥1 p, 1 π+
● PID and tracking: TPC1●

arXiv:1605.00154

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616. Measurement in T2K – double-T kinematic imbalance

Current objective:
Develop signal extraction techniques;
Measure ν-H cross section – first one since 30 years.

arXiv:1605.00154

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626. Prospects for Current Experiments

Simple performance projection of T2K-like detector using NuWro+T2K flux on CH (ideal acceptance)

arXiv:1512.09042

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6. Prospects for Current Experiments

Simple performance projection of T2K-like detector using NuWro+T2K flux on CH (ideal acceptance)
The hydrogen event selection can be improved by●
Veto nuclear emission●
Veto π0, γ background●
Improve tracking resolution → most critical
Requirement on nuclear physics decreases as resolution improves!
✔
Now only need to look at |δpTT|<O(10 MeV) region.
✔
In future even a less burden; can be measured w/ pure nuclear target, e.g. graphite.
arXiv:1512.09042

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6. In situ nuclear-free flux measurement via “bin-and-fit”
Previous setting (ideal accpt.) but w/ ideal tracking+PID
3-particle final state: µ, p, π+Eν reconstructed as sum of final-state energy
H excl. pπ+ signal➢
Fraction: ~ 20% (blue-shifted peak) – 10% (tail)29 July 2016

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6. In situ nuclear-free flux measurement via “bin-and-fit”
Previous setting (ideal accpt.) but w/ ideal tracking+PID
3-particle final state: µ, p, π+Eν reconstructed as sum of final-state energy
H excl. pπ+ signal➢
Fraction: ~ 20% (blue-shifted peak) – 10% (tail)➢No (nuclear) bias in reconstructed Eν

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6. In situ nuclear-free flux measurement via “bin-and-fit”
Previous setting (ideal accpt.) but w/ ideal tracking+PID
3-particle final state: µ, p, π+Eν reconstructed as sum of final-state energy
H excl. pπ+ signal➢
Fraction: ~ 20% (blue-shifted peak) – 10% (tail)➢No (nuclear) bias in reconstructed Eν
➢Can be extracted (statistically in realistic case)

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6. In situ nuclear-free flux measurement via “bin-and-fit”
Previous setting (ideal accpt.) but w/ ideal tracking+PID
3-particle final state: µ, p, π+Eν reconstructed as sum of final-state energy
H excl. pπ+ signal➢
Fraction: ~ 20% (blue-shifted peak) – 10% (tail)➢No (nuclear) bias in reconstructed Eν
➢Can be extracted (statistically in realistic case)➢σ only nucleon cross section, Φ=N/(σ ∆Εν)➔

both Φ and Eν nuclear-free➔require tracking, PID (only needed for Εν
calculation), νH excl. pπ+ x-sec

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686. Potentials in Near-Future Experiments●

T2K-II ND for in situ nuclear-free flux measurement–

Has free hydrogens (CH and H2O)–

Capable of momentum and PID measurement of muons, protons, pions–

Need to optimize configuration for momentum resolution, and for acceptancefor high statistics. A higher B-field is a more expensive but very effective way
to improve the resolution.

–

Calorimetry capability to veto nuclear emission and electromagnetic
background.

–

Nuclear physics in |δpTT|<O(10 MeV) can be measured in situ with embedded
graphite target.

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Outline
1. Introduction
2. Measuring nuclear effects w/ minimal dependence on neutrino energy
3. Measuring neutrino energy independent of nuclear effects
4. Theory predictions
5. Measurement in MINERvA
6. Measurement in T2K
7. Summary

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7. Summary
●

●

●

●

Understanding nuclear effects is crucial for neutrino physics at GeV regime, deeply
related to solving matter-antimatter asymmetry of our current universe.
For neutrinos provided by accelerators, one can use transverse kinematic imbalance
to maximally disentangle nuclear effects and neutrino energy uncertainty.
Experimental efforts are under way. By exploring this new technique, we aim toprovide critical physics input in neutrino interactions, and demonstrate/apply novel
flux constraining techniques for future experiments.
Outlook–

Current measurements:●–

Potential measurements in current experiments:●–

T2K-ND, MINERvA
TK2-INGRID, T60, NOvA, µBooNE

Potential measurements in future experiments:●

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T2K-II-ND, DUNE-ND

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BACKUP

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PHYSICAL REVIEW C 73, 065502 (2006)

Neutrino energy 1 GeV

QE

RES

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736. Measurement in T2K
Nucl.Instrum.Meth. A659 (2011) 106-135

FGD target:
polystyrene (CH)TPC: momentum,
dE/dx

ν

ν beam: off-axis, peak ~ 600 MeV
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END

4785; 4948

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