The SAND detector in the DUNE near detector system
Laura Pasqualini (University of Bologna and INFN)
on behalf of the DUNE Collaboration
20th Lomonosov Conference
23rd August 2021

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The Deep Underground Neutrino Experiment

DUNE Far Detector

DUNE Near Detector and neutrino source• A new generation Long Baseline oscillation experiment with a rich physics research program: threeflavor oscillation measurements, supernovae, BSM studies• An intense wide-band νµ/ νµ neutrino beam 1.2 MW (1.1 x 1021 pot/year), upgradable to 2.4 MW
high-intensity produced at Fermilab• Two neutrino detectors are foreseen: a Near Detector complex (ND) at Fermilab and a FarDetector, consisting of four Liquid Argon Time Projection Chamber (LArTPC) modules 17 kton
each, located 1.5 km underground and 1300 km away from neutrino source at Sanford
Underground Research Facility in South Dakota
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The Near Detector complex
Near Detector will be located 574 mdownstream of neutrino beam and will include
three main components with standalonefeatures:• ND-LAr: a 67 ton LArTPC• ND-GAr: a high pressure gaseous argon
TPC surrounded by an electromagnetic
calorimeter in a 0.5 T magnetic field• SAND: the System for on-Axis Neutrino
Detection
3Laura Pasqualini | The SAND detector in the DUNE Near Detector system

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The Near Detector physics goals
To extract oscillation parameters DUNE
interactions rates both at FD and ND

will measure neutrino

𝑁𝑋 𝐸𝑟𝑒𝑐 = න 𝑑𝐸𝜈 Φ 𝐸𝜈 𝑃𝑜𝑠𝑐 (𝐸𝜈 )𝜎𝑋 (𝐸𝜈 )𝑅𝑝ℎ𝑦𝑠 (𝐸𝜈 , 𝐸𝑣𝑖𝑠 )𝑅𝑑𝑒𝑡 (𝐸𝑣𝑖𝑠 , 𝐸𝑟𝑒𝑐 )𝐸𝜈To predict the expected oscillating νµ and νe spectra at FD themeasurements done at ND must be propagated to FD but systematic
uncertainties on modeling of cross section, nuclear effects and fluxes
are not consistent with the precision required by DUNEThe ND will play the role of:• measure with high precision:‒ flux Φ(Eν)  low density detector to provide high resolution and precise energy scales‒ cross section σ (Eν) and calibrate detector response  same Ar target as FD• constrain nuclear effects Rphys using both Ar and lighter targets
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DUNE PRISM
PRISM (Precision Reaction-Independent SpectrumMeasurement) concept to control systematic uncertainties
on neutrino-argon interactions model ND-LAr + ND-Gar
will move to collect data at different off-axis positions:• disentangle effects due to mismodeling of neutrino
flux and interaction cross-section, as well as
mapping of reconstructed vs true neutrino energy
response of the detectorSAND

ND-LArND-GArBeam νµ flux at ND fordifferent off-axis angles• predict oscillated neutrino event spectra at FD with
reduced model dependence

arXiv:2103.13910
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Laura Pasqualini | The SAND detector in the DUNE Near Detector system

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SAND
The only component of the ND that will permanently belocated on-axis

SAND

ND-LArND-GAr

SAND consists of:- Electromagnetic Calorimeter (ECAL)- Superconducting magnet

inherited from
KLOE
experiment

KLOE- Lar active target- Inner tracker
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SAND primary goals• On-axis ν-spectrum monitor to detect any potential changes in the beam over time on a weekly
basis that can affect the FD oscillation analysis• Provide an independent in-situ measurements of νµ, anti- νµ, νe, anti- νe fluxes and energy spectra• Constrains systematics from nuclear effects by measuring the ν and anti-ν cross sections on nuclei
other than argon (carbon and hydrocarbons)• Exploit the unprecedented high statistics to perform a rich physics program besides the oscillation
program

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The KLOE detector• SAND is largely based on a reuse of themagnet and calorimeter of the KLOE
experiment which took data from 1999 to2018 with a very stable detector
performance to study CP violation in neutralkaon decays at the DAFNE Φ-factory inFrascati• Drift chamber in the inner volume will be replaced by atarget/tracker system• Electromagnetic calorimeter: leadand scintillating fiber sampling
calorimeter + 4880 PMTs

Energy resolution:𝝈Τ𝑬 = 𝟓. 𝟕%Τ 𝑬(𝑮𝒆𝑽)• Magnet: superconducting coil (5 mbore) inside the yoke produced B=0.6 T
8Laura Pasqualini | The SAND detector in the DUNE Near Detector systemtime resolution:
𝝈 = 𝟓𝟒Τ 𝑬(𝑮𝒆𝑽) 𝒑𝒔

NIM A 482 (2002) 364
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SAND detector

Liquid Argon Active volume• The upstream part of SAND will be instrumented with
1-ton LAr active target, so called “LAr meniscus”• It will be instrumented with an optical system tocollect UV scintillation light on fine segmented focalplanes• The outer vacuum vessel of the cryostat will bemade of C-composite material reinforced with aninternal Al foil, the inner vessel containing the LAr will
be made of Al, to keep the overall radiation length ~ 1X0ν

• It will reconstruct the events in combination with theECAL and the tracker• Its role is constraining nuclear effects on argon andhave a complementary Ar target permanently locatedon axis for cross-calibration
9Laura Pasqualini | The SAND detector in the DUNE Near Detector system

preliminary CADs
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SAND inner tracker
The internal magnetized volume of SAND will be instrumented with an Inner Tracker to: separate
neutrino and antineutrino events (charge ID), identify primary leptons(beam flavor composition),
reconstruct event-by-event and all charged and neutral (π0, n) particles tracks

Three different detector technologies are under investigation for the inner tracker:- 3-Dimensional projection Scintillator Tracker (3DST) as active neutrino target- TPCs as low density tracker to measure particles escaping the scintillator- Straw Tube Trackers (STT) as low density tracker interleaved with carbon or hydrocarbon layers as target

The possible main configurations with these detectors are:- 3DST + TPCs
- STT only

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SAND inner tracker – 3DST+TPC• 3DST (active target) is made of many 1.5 x 1.5 x 1.5 cm3 plastic
scintillator cubes each readout by three orthogonal wavelength-shifting
fibers optically coupled to SiPMs

TPCs • TPCs are rectangular chambers surrounding the 3DST filled with an
optimized gas mixture and instrumented with resistive Micromegas
detectors (200-600 μm spatial resolution  2-4% momentum resolution)~2m3DST• 3DST: particle identification by energy deposit and momentum
reconstruction by range (Δp/p < 4% for μ and p) + event-by-event
neutron kinetic energy measurement with Time of Flight• Momentum reconstruction of particles
leaving 3DST by TPCs
• Fully active target (11.8 ton mass)

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SAND inner tracker – STT
90 modules with planes of 5 mm diameter straw tubes (Xe/CO2gas at 1.9 atm) arranged in XXYY layers, radiator ofpolypropylene foils and a target (CH2, C,…)

12 out of 90
STT planesνThis design provides:• Accurate reconstruction of transverse plane kinematics

variables from particle 4-momenta( Δp/p ≤ 3%, Δθ/θ ≤ 1.5 % mrad)• e/π separation via transition radiation (e/π ~ 10-3) and

p/π/K identification with dE/dx and range• 4π detection of π0 from γ conversion (~ 49 %) within STT

volume• Neutron detection is ensured by combination of STT with

ECAL
12fiducial volume mass 4.7 t CH2, 557 kg C
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Background rejection
Backgrounds at ND site arise mainly from:• cosmic radiation and ambient radioactivity  suppressed to negligible
level requiring a time coincidence with the beam spill

simulation of νinteraction in a spill• beam related neutrino interactions in the material surrounding thedetector  most critical background source
Expected CC + NC event rate per beam spill are 84 events/spill ( ν )and 45 events/spill ( ν )External background is rejected using a combination of simple cuts
and a neural network jointly applied to timing and topologicalinformation from the subdetector and reconstructed quantities
STT option

13Signal efficiency (%)

Background efficiency (%)

Purity (%)

92.8

0.003

99.6

Laura Pasqualini | The SAND detector in the DUNE Near Detector system

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Beam monitoring capability• The beam is monitored by measuring variations of νμ CC interaction energy spectrum and event
distribution in space• Expected sensitivity are evaluated comparing the distribution of reconstructed neutrino energy
expected from nominal (Ninorm) and varied (Nivar) beam using the test statistic T:𝑛(𝑁𝑖𝑛𝑜𝑟𝑚 − 𝑁𝑖𝑣𝑎𝑟 )2
𝑇=෍∼ Δ𝜒 2𝑛𝑜𝑟𝑚𝑁𝑖
𝑖=1

1 week data taking• In one week SAND has enough sensitivity (√Χ2 > 3) to detect the majority of beam variations and thecases with less sensitivity don’t contribute significantly to the beam spectrum
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SAND physics program• Reducing systematics for long baseline oscillation analysis:-Flux measurements-

Constraints on the nuclear effects in Ar using a combination of different nuclear targets• SAND will turn the ND site to a physics facility for precision measurements andsearches exploring many different topics:-Precision isospin physics-Measurements of sin2θW and electroweak physics-Measurements of strangeness content of the nucleon (s(x), s(x), Δs, etc)-

Study of QCD and structure of nucleons and nuclei-

Measurements of nuclear physics and ν-nucleus interactions-Search for new physics: sterile neutrinos, NSI, etc…

arXiv:1910.05995
Nucl. Phys. A765, 126(2006), hep-ph/0412425
Phys. Rev. D76, 094023 (2007), hep-ph/0703033

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SAND physics program“solid” hydrogen concept
STT option provide a compact modular layout with a flexible design to control configurations, chemicalcomposition and mass of neutrino targets similar to e± DIS experiments will provide a “solid” hydrogenconcept:
arXiv:1910.05995

model independent subtraction ofmeasurements on dedicated graphite(pure C) targets from main CH2 targetto extract high statistics samples ofν(anti-ν) CC interactions on H by akinematic analysis
Keep under control systematic uncertainties:• Flux measurements• Constrain models on nuclear effects
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Likelihood function incorporating multi-dimensional correlations
among kinematic variables to separate C and H samples

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SAND physics program - flux measurements
The measurement of ν flux is a mandatory condition to extract oscillation probability from measured
neutrino interaction

𝑁𝑋 𝐸𝑟𝑒𝑐 = න 𝑑𝐸𝜈 Φ 𝐸𝜈 𝑃𝑜𝑠𝑐 (𝐸𝜈 )𝜎𝑋 (𝐸𝜈 )𝑅𝑝ℎ𝑦𝑠 (𝐸𝜈 , 𝐸𝑣𝑖𝑠 )𝑅𝑑𝑒𝑡 (𝐸𝑣𝑖𝑠 , 𝐸𝑟𝑒𝑐 )𝐸𝜈A large sample of ν(anti-ν) on H allows an accurate determination of absolute and relative ν fluxes
using νμp→μ-pπ+, νμp→μ+pπ- and νμp→μ+n process on hydrogen• interaction on H are free from typicalproblems
arising
fromnuclear
smearing• selecting small momentum transfer (cuton v < 0.25 GeV) flattens crosssections allowing to measure the flux

systematics uncertainties for the flux measurement

5 years (STT-only)
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arXiv:2103.13910
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SAND physics program - flux measurements
Relative νμ and νμ fluxes can be measured by selecting inclusive CC interactions with small energy
transfer (< 0.25 GeV) in the 3DST (CH)• large target mass provides sizable number of interactions (1.5 x 107 νμ CC and 5.5x106 νμ CC / year)• uncertainties introduced by nuclear effects and by corresponding smearing on the reconstructed
hadronic energy can be partially mitigated by the neutron reconstruction with ToF

3DST + TPC

Reconstructed versus true ν energy

5 years
STT-only

neutron energy
reconstructed with ToF

50 MeV

500 MeV
arXiv:2103.13910
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SAND physics program - constrain nuclear effects
DUNE will face the challenge of modelling neutrino-nucleus interaction which requires the knowledgeof large and complex nuclear effects on Ar affecting the re-scattering of final state particles within thenucleus  this smearing introduces uncertainties on the reconstruction of neutrino energy• Argon detector alone cannot resolve nuclear smearing and related systematics• H + Ar target integrated with the SAND detector with STT option offers valuable information toreduce systematics:

𝑁𝑋 𝐸𝑟𝑒𝑐 = න 𝑑𝐸𝜈 Φ 𝐸𝜈 𝑃𝑜𝑠𝑐 (𝐸𝜈 )𝜎𝑋 (𝐸𝜈 )𝑅𝑝ℎ𝑦𝑠 (𝐸𝜈 , 𝐸𝑣𝑖𝑠 )𝑅𝑑𝑒𝑡 (𝐸𝑣𝑖𝑠 , 𝐸𝑟𝑒𝑐 )𝐸𝜈

1 % on H

Measured from highstatistic sampleRphys ≡ 1

δp/p 0.2 % calibrated in-situ
from K0 π+π- in STT volume

constrain the product σXRphys on Ar from a direct comparison between Ar and H interactions within
the same detector
 reduce beam model uncertainties affecting DUNE PRISM
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Conclusions• SAND is an excellent beam monitoring to spectral changes that would impact on long-baseline
measurements• SAND adds robustness to the ND complex: measuring the flux and constraining nuclear effects, iscapable of control systematics uncertainties on ν spectrum in order to provide the initial state of thebeam and to compare it with the observations at the Far Detector• SAND can explore many different physics topics within the ND complex, from precision
measurements to searches for new physics• Dedicated studies were carried out to finalize the design of SAND as an integrated on-axis detector
and currently the choice between the different technologies is under decision process20

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Thank you for your attention!

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Backup22

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SAND physics – test of isospin• The Adler integral provide the ISOSPIN of thetarget:
1𝑆𝐴 𝑄

2𝑑𝑥 ഥ𝜈𝑝𝜈𝑝
𝐹2 − 𝐹2 = 𝐼𝑝
0 2𝑥=න• Large statistics of ν interaction on H will provide
precision test of SA at different Q2 values• Only measurements available fro BEBC based on
5000 νp and 9000 νp (D. Allasia et al., ZPC 28(1985) 321)
• Direct measurements of F2,3νn/F2,3νp free from
nuclear uncertainties

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SAND physics – electroweak measurements
Complementary with colliders & low energy
measurements: DUNE ND can determine sin2θW
from the ratio of NC and CC interactions induced byneutrinos in different channels:• Rν = σNCν/ σCCν in ν-N DIS ( ~ 0.35 %)• Rνe = σNCν/ σNCν in ν-e- NC elastic ( ~ 1 %)Independent cross-check of NuTeV sin2θW anomaly(3σ from SM prediction) in a similar Q2 range

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