Scintillation Light

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Scintillation Light
Background Rejection
and
Alternative Scintillator/PMT
Configurations
Steve Biller, Oxford
e-
g
e-e+
ne
g
e-
e+
p
n
n
n
Problematic Backgrounds
Cherenk/Scint
Discrimination ?
p
ne
9Li
(Qb = 13.6 MeV)
e-
Fiducial cuts
plus SOME
Cherenk/Scint
Discrimination ?
n
8Be* (35%)
a
a
Accidentals from
(2.5 MeV)
(2.5 MeV)
e- and/or g
(Various Decays)
For ES, troublesome, low E, long-lived,
muon spallation products mostly involve e+
Cherenk/Scint
Discrimination ?
Cherenk/Scint
Discrimination ?
Cherenkov Light:
~50% “SNO-equivalent” Photocathode Coverage
(light concentrators)
~25 hits/MeV
+ ‘fast’ Wavelength Shifter
(scaling from SNO)
Scintillation Light:
Sloooooooooow
Scintillator
Tune chemistry to yield
(pure pseudocumine: t ~ 28ns)
~25-50 hits/MeV
(Energy resolution based on total of 50-75 hits/MeV)
PC + SMALL
amount of PPO
Also add bis-MSB to shift Cherenkov light?
Why Not Use Concentrators Anyway??
Degradation?
1-2% per year in water for SNO…
should be much better for mineral oil
PLUS
neutron peak continually calibrates energy scale
Advantages:
Less scint for same light yield – better attenuation length
OR
Increased light for same scint – pulse-shape discrimination
OR
Can pursue Cherenk/scint by just changing the chemistry
More options !!
(“What’s not to like?”)
Plan of Attack:
• Benchtop tests being constructed to measure
light yield and time spectrum for various mixtures
(Gabriel Orebi-Gann)
• Identify supplier of Al strips for concentrators
• Start accelerated ageing tests for strips in mineral oil
• Input will be used for detailed simulations (SNOMAN)
SNOMAN Update
Completed: Added mineral oil as medium;
Gd cascade modelled (Nick);
PMT geometry reconfigured
Nearly
Completed:
More detailed handling of additives;
Reactor “Event Generator”;
Official policy on external distribution.
And Now For
Something
Completely
Different…
Rejection of 9Li and 8He
(Using spatial and timing information)
Half-lives:
0.1-0.2 sec
Muon rate at far site: ~5 Hz (0.2 sec between muons)
Need to deal with ~2 muon tracks on average
for each candidate neutrino event (~100/day)
Fiducial cut needs to include up to ½ meter from muon tack
Fraction of fiducial volume:
2 x [p (0.5m)2] x 5m
= 0.10
3
4/3 p (2.6m)
Thus, need to know systematics
on fiducial cut to better then ~5%
Handles
1) Direct calibration
corresponds to a vertex reconstruction systematic
of 1-2%, which about what we have for SNO
2) Comparison in limit of ‘identical’ detectors
apply same cuts to near detector – dominated by neutrino
interactions, so indicates what’s been thrown out
3) Use Spallation Products
particularly 12B, which can be tagged with muon
(0.02s half-life) and produces electrons in same
energy range
4) Compare with applying the “right cuts at the wrong time”
to try to assess the contamination based on the difference,
then just model this without making any ‘cuts’ in neutrino analysis
Summary
A separated Cherenkov measurement
would be VERY nice (and maybe we
could even do this… work in progress)
We should SERIOUSLY consider using light
concentrators in any case (preserves flexibility)
9Li and 8He should not really be a problem for us

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