ν
Zeyuan Yu
IHEP
First Workshop on Reactor neutrino Experiments
Oct. 16 – Oct. 19, Seoul National University
Neutrino oscillation: neutrino energy
P(ne->nm) = sin2(2q) sin2(1.27Dm2L/E)
Measured: reconstructed prompt energy
• Neutrino oscillation is based on neutrino true energy
• What we measured is reconstructed prompt energy
• Energy response model: connection between the true and measured
ne  p  e  n

• The positron has a kinetic energy about Eν-1.8MeV
• Neutron has a kinetic energy of tens keV, studied with MC
• The true prompt energy equals to the positron kinetic energy plus two 0.511
MeV annihilation gamma
• However, reconstructed prompt energy is not linear to the true one
• MC is used to generate
the Etrue to Edep
conversion matrix
• Some IBD reaction occur
around or in the acrylic,
which will absorb the
energy of e+ and
annihilation gamma,
without photon generated.
E+ traversed
acrylic
e+ stopped
in acrylic
• Non-linearity sources
• LS converts the deposit energy to optical photons: non-linear
• Particle dependent non-linear light yield of LS: from Etrue to visible energy Evis
• PMT converts optical photon to charge: linear
• Electronics records PMT output and PMT charge reconstruction: non-linear
• Charge dependent non-linearity from electronics: from Evis to Erec
• What we have
• Calibration sources, and most of them are γ
• 12B β spectrum from muon spallation
• 212Bi, 214Bi, 208Tl β+γ spectrum from natural radioactivity
• What we want
• Energy response of positron from Erec to Etrue
• Question
• How to get the positron response from gamma and electron data?
• 1) Tune the MC
• 2) Build an Energy model (DYB)
• The kernel
• Electron non-linearity in LS
• Electronics non-linearity model
An example
• Quenching curves are generated according to different kB
• Cherenkov curve is generated with MC, but the
Cherenkov/Scintillation ratio is unknown, and described with kC
• kB and kC will be free parameters in the energy model fitting
Electron quenching example.
kB = 6.0e-3 cm/MeV
Cherenkov contribution curve
• LS scintillation has slow components
• Several tens percent with τ ~ 30ns
• Several percent with τ larger than 100ns
• The CR-(RC)4 circuit is not effective enough to capture the late hits
• τ = 25ns. Hits with difference time separations have different measured charge
• MC shows that the electronics non-linearity can be modeled with an exponential function
• The non-linearity model has been crosschecked with FADC
Simulated PMT waveform
Simulated electronics response
Integral 1
Integral 2
• Gamma deposits energy in LS
via Compton scattering and
e+/e- pair production
• GEANT4 based MC is used to
connect electron and gamma
• Multiple gamma is naturally
handled
At detector
center
At detector
center
• The calibration source analysis has two major systematics:
• Optical shadowing of the source enclosure and weights, corrected with MC
• Energy loss in the enclosure, contributing to the Compton tail. Fit the spectra
with MC inputs.
• Most of gamma peaks have been assigned an about 1% systematic
uncertainty due to enclosure effects
Single gamma
137Cs
source
68Ge
54Mn
source
60Co
40K
source
Natural 208Tl
n-H capture
n-12C inelastic scattering from PuC source
16O*
Multiple gamma
de-exciting from PuC source
n-56Fe capture from AmC source
n-12C capture
n-Gd capture
• Construct a Chi2 function to fit the gamma and 12B data
simultaneously
• Free parameters: absolute energy scale, kB and kC for LS, α and τ for
electronics
• Fit the 208Tl, 212Bi and 214Bi continuous β+γ spectrum.
• Two fitting results are also crosschecked with
• LS electron non-linearity bench measurement
• PMT readout measured by a FADC
• 53MeV endpoint in the Michel electron spectrum
• Assume positron deposit its kinetic energy in the same way to electron
• e+ e- pair generation during the e+ flight has negligible effects
• Two methods give consistent results.
• 1% uncertainty in most energy ranges (larger than 2MeV)
Positron non-linearity
model in the GdLS
• The energy model uncertainty is
propagated to the neutrino
oscillation fitter
• 4 curves selected from 1 sigma
phase space to parameterize the
shape uncertainty
• 4 corresponding pull terms in the
Chi2 fitting function
4 curves selected to parameterize shape uncertainty
Black: nominal model
Others: selected 4 curves
• The energy response model is critical in the measurement of Δm2
• Convert the Etrue to Erec
• With the gamma calibration sources and 12B β spectrum, DYB has
built the energy model with 1% uncertainties over most energy ranges
• Energy model uncertainty is dominated by gamma source enclosures
and the coupling between LS and electronics uncertainty
• We plan to deploy gamma sources with different enclosures
• A FADC readout system has been installed at Dec. 2015. Preliminary results
show good agreements with the energy model.