FUTURE EXPERIMENTAL PROGRAM
for neutrino cross sections
Sara Bolognesi (CEA Saclay)
2/14
A hot topic...

Oscillation measurements in far detector constrained from near detector (xsec x flux) :
aim to ~1% uncertainty on signal normalization at future long baseline (T2K 2016 ~5-8 %)
ND→FD extrapolation :
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different Eν distribution
νµ → νe, νµ
different acceptance and target
→ rely on models to extrapolate : neutrino interactions on nuclei (C,O, Ar) → need to
model nuclear effects on initial and final states

Measurement of ν xsec at ND is experimentally complicated:
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Eν not known: xsec measurement always convoluted with flux
Eν inferred from final state leptons/hadrons which have limited angular acceptance,
threshold on low energy particles, very small info on recoiling nucleus...
Many experiments
3/14
(?) = not yet funded
(!) = running now
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Near detectors for long baseline oscillation experiments:
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T2K (T2K-2, T2HK): ND280 (!) → ND280 upgrade, INGRID (!), WAGASCI
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NOVA ND
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DUNE ND under discussion: NOMAD-like and/or Liquid Argon TPC and/or HP Ar TPC
Future intermediate detectors for HyperKamiokande
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TITUS (?)
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NuPRISM (?)

Short baseline program at FNAL : MicroBooNE, SBND (previous talk)
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Dedicated xsec experiments:
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Minerva (!)
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ArgoNEUT (!)
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Emulsion T60 experiment at T2K flux
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→ Captain-MINERVA (?)
COHERENT, CONNIE: ν Neutral Current interactions
through nuclear recoil at MeV scale (SuperNova ν physics)
Accessory measurements: LARIAT, DUET (!) : pion FSI
Annie : neutron capture in Gd
Different approaches
4/14
Argon TPC (liquid or HP)
MicroBooNE
SBND
Multipurpose
ND280 (T2K):
precise tracking
(magnetized)
7m
Mainly scintillators
INGRID
(T2K):
NOVA
near
detector
Minerva
WAGASCI (T2K):
(can be filled of water)
CaptainMinerva
ArgoNEUT (MINOS)
Water-cherenkov detectors
TITUS
NuPrism
5/14
What do we need to measure?
Uncertainties in ND→FD extrapolation :
●
different target
A-scaling: measure cross-sections on different
targets (and/or on the same target of FD)
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different acceptance
measurement of cross-section in the larger possible
phase-space: increase angular acceptance of ND
different Eν distribution
(because of oscillation)
measure all particles in the final state: low
threshold for protons, calorimetric approach
(neutrons?)
different neutrino flavor
(because of oscillation)
ν (ν) flux has typically a
wrong sign component
measure cross-section asymmetries between different
neutrino species → ν vs ν (magnetization, Gd doping)
measure xsec for νe (calorimetry)
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6/14
A-scaling: water target
Super(Hyper)-Kamiokande use water as target → need to control nuclear effects on Oxygen

Water as target but passive material
Fine Graned
Scintillator
in ND280
H2O
CH
PiZero detector
in ND280
water bags can be
emptied: water-in vs
water-out →
absolute Oxygen
xsec measurement
but larger statistical
uncertainty
carbon interactions
as background to
oxygen intreactions
→ mainly C/O xsec
constrain
WAGASCI concept: (to be installed in
T2K flux on axis)
threshold: particles have
to reach scintillator
(compromise: small granularity
vs H2O/C mass ratio)
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Water doped with scintillator (under discussion for ND280 upgrade)

Water Cherenkov (TITUS, NuPrism)
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same target and acceptance as Far Detector
limited reconstruction capability: Cherenkov threshold, no pion discrimination, no
sign discrimination by itself (need muon spectrometer or Gd doping)
7/14
Acceptance
Far Detectors have typically 4π coverage while Near Detectors optimized for forward going
particles → need to enlarge ND acceptance to high angle and backward tracks
ND280 event display
●
v
Most of the
events are
forward
tracks
●
v
Backward tracks: if only 1 muon track
observed, need to distinguish between Still vertical tracks difficult (lot of
material and no TPC coverage)
forward µ+ and backward µ→ TOF between detectors
(NEW results soon: 4pi CCincl xsec!)
Possibility for ND280 upgrade:
horizontal targets
surrounded by TPCs
to get 4p acceptance
+ scintillators all around for TOF
+ calorimetry (νe)
TPC
TPC
Scintillator
target
TPC
TPC
TPC
Water
target
TPC
TPC
Measurement of outgoing protons

NEW Measurements expected from ND280: proton kinematics and
transverse variables (proton threshold for good tracking/ID ~500 MeV)
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ArgoNEUT: small statistics but powerful Ar technology → MicroBooNE!
Gas Ar would give even smaller threshold:
NEW results from ND280 TPC will come (small stat) → HP TPC under discussion
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T60: emulsion detector in front of INGRID at T2K flux (high stat: few thousands νµ)
Emulsion

INGRID
Main limitation:
Very limited predictivity of proton kinematics from models!
And difficult interpretation of the results: disentangling nuclear effects on initial state
(Fermi momentum, 2p2h, ...) from Final State re-interactions
9/14
'Calorimetric' approach

Measurement of all the energy around the vertex or all the energy in the event
Minerva Collaboration, Phys.Rev.Lett. 111 (2013) 022502,
Minerva
- inclusive energy for low
momentum particles
ν µ Q2<0.2 GeV2
- Eν from total deposited
energy (and q3 from muon
kinematics) ~ electron
scattering data
Main limitation:
● Calibration issues (no sensitivity
to neutrons, energy threshold...)
● Very limited predictivity from models!
The two problems are tightly
convoluted and difficult to disentangle

Example from NOVA:
OLD
NEW: xsec
re-tuning
A taste of the future → DUNE:
● need to reconstruct precise E shape for good sensitivity (two oscillation maxima)
ν
● capability of full reconstruction of tracks and showers down to very low threshold
→ need to reach very good control on detector calibration/uniformity and on
neutrino interaction modelling which have convoluted effected in E ν

10/14
Future long baseline experiments: ν e and ν xsec

HK
In future (HK, DUNE) large samples
of 4 ν species → the uncorrelated
uncertainties are relevant
●
HK needed uncertainty to have
negligible impact on δCP:
5% ± 1%
ν e-ν e uncorrelated 1-2%
5% ± 2%
5% ± 3%
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For DUNE assumed: uncorrelated
ν µ - ν µ 5% and ν e - ν e 2%
DUNE
→ equivalent
to factor 2 in
exposure!
DUNE and HK talks @ NuFact 2015

We are interested to ν e
appeareance and δ CP
from ν – ν comparison
ν versus ν
Neutrino flux has always a background component from wrong sign component → need to
distinguish muon charge (or n vs p) in order to measure ν versus ν xsec precisely

Very well measured in multipurpose magnetized detectors like ND280
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Large water cherenkov detectors: eg, TITUS
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Side magnetised MRDs (1.5T):
iron interleaved with air gaps and scintillators
Doping with Gadolinium (0.1%):
tag the presence of
neutron in the final state
(Gd doping will be implemented in SK in next years:
stay tuned!)
(Annie experiment on FNAL beam to test technology)
Limitation: need to model properly the neutron multiplicity in ν and ν events which
is affected by initial and final state effects
11/14
νµ CCQE: νµ + n → µ- + p
νe CCQE: νe + n → e- + p

νµ versus νe
Measurement of electrons and separation from muons well done in all mentioned
detectors: TPC PID (+calorimeters), cherenkov rings
Main limitation is due to
statistics: standard neutrino
fluxes are dominated by νµ
(protons on target → K,π → µνµ)

Neutrinos from Stored Muons
(nuSTORM): beams from the decay
of 3.8 GeV muons confined within a
storage ring
 Monitor the production
of electrons in standard
ν beam: uncertainty on
νe flux improved by one
order of magnitude
(ν flux from muon
decays precisely
known)
12/14
Alternative concept: NuPRISM
Flux at different off-axis angle = different Eν spectra
Combine measurements at
different angles to
● build monochromatic flux →
measure xsec vs energy
● build flux shape similar to oscillated
flux at far detector
should decrease the ND → FD extrapolation
uncertainty but cannot reconstruct the details
of the final state (no precise measurement of xsec:
µ charge, low momentum hadrons, different targets...)
13/14
14/14
The way out?


A given cross-section
measurement is affected by
many different effects
To disentangle them we need to
compare different measurements
(C, O, ν species, different variables …)
→ long term plan & collaboration btw
experiments at different flux
The role of theoreticians is fundamental here !
Slide credit to Laura Fields
FUTURE EXPERIMENTAL PROGRAM
for neutrino cross sections:
BACKUP
Sara Bolognesi (CEA Saclay)
Neutrino energy

We do not know Eν event by event. Eg, SuperK measures the outgoing muon and
infers the neutrino energy on the basis of available ν-nucleus interaction models
Martini et al
Spreading of reconstructed Eν for
fixed true Eν due to nuclear effects
eg: low energy
tails due to 2p2h

One possible way out: measure also outgoing proton (or more in general full
hadronic final state)
9/16
7/16
A-scaling (2)
Measure on different targets and scale with A relying on models:
most of measurement on C (CH scintillators) and few on iron, lead...
but scaling of nuclear effects with A not straightforward. Few examples:
low energy: scaling of 2p2h contribution depends on fraction of nn / np initial correlated
pairs in the nucleus which is not well known
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high energy (Deep Inelastic Scattering): uncertainty on nuclear PDF → A-scaling not well reproduced
Importance of large Ar TPC (MicroBooNE, SBND, Captain-Minerva) for DUNE program
Very important to have large Ar target in DUNE near detector
DUNE ND reference design:
strawtubes (filled with HP Ar) with
radiators walls (C3H6) interleaved
with different targets
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a lot of interactions will
not be on Ar
combined analysis: target
subtractions etc. → large
systematics due (eg) to
uncertainties on acceptance
due to xsec modeling
→ HP Ar TPC under
discussion
Pions fate
Final state effects on pions: very sparse data available
ABS π+
CX π+
inelasti π+
c
New measurement from DUET experiment at TRIUMF
LARIAT: ArgoNEUT repourposed in FNAL charged
test beam
(large potential also from DUNE prototypes at CERN test beam!)
Coherent eleastic ν-nucleus scattering (CEνNS)
Large xsec (1-100 MeV) but never observed
SuperNova n detection
modeling energy transport in SuperNova
irreducible background to Dark Matter
Measure of nuclear
recoil in neutral current
events
monitoring of neutrino reactors
CHOERENT: three detector technologies
at neutron spallation source at Oak Ridge
Xenon double phase
high purity Germanium
Cesium Iodide scintillator
CONNIE: Charged Coupled Device at Angra Nuclear Power Plant (Brasil)
Cross-sections
T2K flux
NOVA flux
Formaggio, Zeller
arXiv:1305.7513
3/21
Moving to larger energies ...
T2K flux
13/21
DUNE
Moving to larger energies ...
T2K flux
14/21
DUNE
Moving to larger energies ...
15/21
Need to control well
all different xsec,
each process has
very different
detector acceptance
T2K flux
DUNE
2p2h at near and far detector
Far Detector
Near
Detector
(after oscillation)
(before
oscillation)
2p2h uncertainty is mainly on the overall normalization at ND
while at FD 2p2h biases the shape of neutrino energy spectrum (fill the oscillation deep)

At ND 2p2h is slightly lower
muon momentum than 1p1h
… but is also the region where the
CC1π background is larger ...
Martini et al
CCQE
2p2h
CCQE+2p2h
CC1π
There is no clear enhancement of
2p2h for backward muon angles
muon momentum < 1.2GeV
2p2h: ν vs ν
●
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
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