supernova relic neutrinos kirk bays december 8, 2011 uc irvine
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Supernova relic neutrinosKirk BaysDecember 8, 2011UC Irvine
OUTLINE.• 1) Theory and background: supernovae, SN
neutrinos, and what has come before
• 2) Super-K: what is it, how does it work
• 3) Tools: software used to study neutrinos
• 4) Event selection: cut out the backgrounds!
• 5) Remaining backgrounds: understand, model
• 6) Analysis methodology: fits fits fits
• 7) Results: getting this is the whole point
• 8) Discussion: What does it all mean?
1: Theory and background
www.smbc-comics.com
Supernovae• Stars are fueled by nuclear fusion• Mostly fuse H into He, as the universe
began full of hydrogen• When hydrogen is used up, it collapses • If the star is massive enough, begins
fusing He, becomes layered• Stars > ~8 solar masses can fuse
elements all the way to iron• Iron doesn’t fuse, and without fusion
the core collapses on itself• This makes the core super-hot and
dense; also the collapse rebounds when it becomes dense enough to hit neutron-neutron interactions
• Rebound shock + emissions from superhot core = supernova
Supernova neutrinos• Released E: En~99%, Ekinetic~1%, Elight~0.1%• As the core collapses, high temperature and
pressure make electron capture favorable:▫ e + p n + ne
(neutronization burst, ~1044 J, ~10 ms, ne)• After the rebound, the core is superheated
(~100 billion K), and releases neutrino-antineutrino pairs of all flavors equally. These neutrinos are trapped by the collapsed core, and leak out; they also fuel the explosion (rebound not enough alone)(thermal burst, ~1046 J ,~10 s, all flavors)
,,EEEE
ee
NC onlyCC+NCmore
neutrons Livermore numerical modelApJ 496 (1998) 216
SN neutrino bursts
• SN1987A: first neutrinos definitely seen from farther than the sun
• Galactic supernova: ~3/century
2140 tons
6800 tons
200 tons scintillator
SN 1987A
~10k eventsGal. center
in SK today:
arXiv:hep-ph/0412046v2
The DSNB• Even though we would not see
the n burst from far away supernovae, the neutrinos from all supernovae in the history of the universe combined should be a diffuse, detectable signal.
• This is called the Diffuse Supernova Neutrino Background (DSNB), or Supernova Relic Neutrinos (SRN, `relics’). These terms are interchangeable.
• This signal has never been seen.• Many theorists have constructed
models of the DSNB• Only a few events/year are
expected at SK. This is a rare signal
Cosmic Gas Infall – Malaney - R. A. Malaney, Astroparticle Physics 7, 125 (1997)Chemical evolution - D. H. Hartmann and S. E.Woosley, Astroparticle Physics 7, 137 (1997)Heavy Metal Abundance - M. Kaplinghat, G. Steigman, and T. P. Walker, Phys. Rev. D 62, 043001 (2000)Large Mixing Angle - S. Ando, K. Sato, and T. Totani, Astroparticle Physics 18, 307 (2003) (updated NNN05)Failed Supernova - C. Lunardini, Phys. Rev. Lett. 102, 231101 (2009) (assume Failed SN rate = 22%, EoS = Lattimer-Swesty, and survival probability = 68%.)6/4 MeV FD spectrum - S. Horiuchi, J. F. Beacom, and E. Dwek, Phys. Rev. D 79, 083013 (2009).
Anatomy of a DSNB model
• Main ingredients: star formation history, spectrum
• Star formation history well measured in recent years
• As most SN ns thermally produced, use Fermi-Dirac spectrum:
• Leaves 2 free parameters: = n luminosity, T = n temperature
• Downside: FD imperfect description
f= DSNB fluxz = red shift parameterRSN = CC SN rate
RSF = star formation rate
S. Horiuchi, J. F. Beacom, and E. Dwek, Phys. Rev. D 79, 083013 (2009)
Current knowledge
• In 2003, SK published a paper detailing the first SRN search at SK
• Final 90% CL flux limit:▫ 1.2 n cm-2s-1 19.3<En<83.3
MeV• 100x previous limit• Most stringent limit ever• Methodology: implement cuts to
remove most backgrounds• Model remaining backgrounds• c2 fit (SNR + 2 backgrounds)• No indication for SNR events• Many theories predict the SRN
signal to be on the edge of this limit
• I have now improved this study significantly
L. Strigari, M. Kaplinghat, G. Steigman, T. Walker, The Supernova Relic Neutrino Backgrounds at KamLAND and Super-Kamiokande,JCAP 0403 (2004) 007
‘Our best estimate for the flux at Super-K is slightly below, but very close to the current SK upper limit. …We estimate that the SRN background should be detected (at 1σ) at Super-K with a total of about 9 years (including the existing 4 years) of data.’
Phys. Rev. Lett. 90, 061101 (2003)
decay e’s from`invisible’ n m m’s
ne CC
90% CL SRN
2. The Super-Kamiokande detector
Super-Kamiokande
‘Inner Detector’, ID• ~11,150 inward facing
photomultiplier tubes • single photon sensitivity• ~40% surface coverage
11
39.3 m
41.4 m
‘Outer Detector’, OD• Optically separate from ID• 1885 outward facing PMTs
Water system:filtration, degasification, water flowwater entering tank 18.2 MΩ*cmleaving tank 11 MΩ*cm35-70 tons/hour water flow
Radon system:• 99.98% effective at reducing radon• reduces background, worker health
26 Helmholtz coilsreduce Earth’s magneticfield by factor of 9
ID fiducial volume two meters from PMTs;32.5 ktons -> 22.5 Ktons
Kamioka neutrino detection experiment
underground2700 m.w.e.
50 ktons
Detector History
• April 1 1996: begin data taking• July 15 2001: stop for maintenance• Nov 11 2001: Accident destroys ~60% of
PMTs while refilling• Oct 8 2002: Masatoshi Koshiba
awarded Nobel Prize in physics (25%)• Dec 6 2002: Surviving PMTs
repositioned, start data taking again• Feb 2003: First SRN paper published• Late 2005: begin full repair• 2006: Kirk joins the team!• June 2006: Full repairs complete,
start new data taking• Aug 2008: Full electronics upgrade• Sep 2008: continue data taking• Nov 2011: SRN paper submitted to PRD!
12
SK-I(40% coverage, 1497 live days
11,146 PMTs)
SK-III(40% coverage, 562 live days)
SK-II(19% coverage, 794 live days)
SK-IV(40% coverage)
Physics in SK
• High energy particles interact in the water, create light via the well known Cherenkov effect
• For DSNB events, inverse beta decay is by far the dominant mode
arXiv:hep-ph/0412046v2
e- kinetic E (MeV)
Eve
nt
rate
(/y
r/M
eV
)
Astroparticle Physics 3 (1995) 367-376
Triggering, DAQ
14
• Dark noise: 3-5 KHz.• PMT timing resolution ~3
ns• Lower trigger thresholds
can detect lower energy events
• Limited by computing power
• 2 channels/PMT keep detector mostly dead-time free
• SK-IV electronics different,not discussed here
The Super-Kamiokande Detector The Super-Kamiokande Collaboration, Nucl. Instrum. Meth. A501(2003)418-462
.3 p.e.
-11 mV
Final trigger records data in 1.3 μs range (one ‘event’)
Calibration• LINAC:
Most important calibration source Old medical linear accelerator, on site Shoots mono-energetic electrons ( 5 – 18 MeV) into known positions Energy known to within 20 KeV Primary calibration of absolute energy scale (accurate to within 1%) Also useful for energy resolution, angular resolution, spatial resolution
• Xe/laser source and scintillator ball: Helps fine tune high voltage to regulate individual PMT gain
• N2 laser and diffuser ball: Relative PMT timing, ‘tq map’
• Deuterium-tritium neutron generator (DT): double check absolute energy scale, trigger efficiency
• Decay electrons: determines water transparency for LE group, stability of energy scale
15
Nucl. Instrum. Meth. A501(2003)418-462
Signals in SK
16
• Atmospheric neutrinos up to TeV• Reactor, solar, relic ns (all < 21 MeV)• Cosmic ray muons (~2Hz) • Spallation (<24 MeV)• Stopping muon decay electrons• ….
solar
atmospheric
3. Tools
e-/e+ reconstructionVertex fitting:
• Electrons travel ~10 cm before stopping• This is on the order of resolution; can
consider a point-like event• Reconstructed with BONSAI (by Michael)
▫ uses only the PMT timing information▫ fits a dark noise component▫ constructs likelihood, compares to likelihood
derived from LINAC data▫ best resolution of all SK fittersEnergy fit:
• Charge determination for PMTs poor at low levels, assume 1 p.e. per hit
• Takes into account dark noise, water transparency, geometry, occupancy correction
• E resolution ~10% @ 18 MeVDirection Fit:
• Likelihood fit; resolution ~20 degrees
• Vertex, direction, and energy reconstruction tools are the same as used for the long established SK solar analyses
• All energies quoted are total electron equivalent energy
18
M.B. Smy, Low Energy Challenges in Super-Kamiokande-III, Nuc. Phy. B, 168, pg 118-121 (2007)
Cherenkov angle
• Reconstructing the Cherenkov angle important for particle ID
• Reconstruction algorithm takes 3 hit PMTs, forms a cone with an opening angle; looks at all 3-hit combinations, fits to peak of distribution
• Events with multiple particles, gammas, emit light more isotropically; algorithm biases these to high angles
• Width of distribution also can be used to discriminate e’s vs p’s
ep
Muon fitting
• Main muon fitter name Muboy• Better track resolution than fitter
used in 2003 (entry point resolution ~100cm, direction resolution ~6 deg.)
• Can categorize muons by type:▫ Single through-going (~82%)▫ Stopping (~7%)▫ Multiple muons (2 types) (~7%)▫ Corner clipper (~4%)▫ Can’t fit (<1%)
• We can make a dE/dx distribution of muon track based on Muboy fit
• Also developed an alternate fitter (Brute Force Fitter, BFF) for when Muboy fails; can refit ~75% of misfit singles
dE/dx
get dE/dx using timing infoassume light travels at v=c/n and muon at v = c; determine
where along track light originatedquadratic Eqn w/ 2 solutions, keep both
Take into account corrections based onwater transparency, coverage
Multiple Coulomb scattering
• Electrons can multiple Coulomb scatter in the detector
• It can be useful to estimate how much an electron scatters
• Select PMT, construct cone w/ 42o angle from vertex to PMT; intersection points of cones gives unit vectors
• Do this for all combination of 2 hit PMTs
• Vector adding all the direction unit vectors/ # unit vectors gives a value between 0 (completely unaligned) to 1 (all perfectly aligned)
• This value is used as a `goodness’; estimates multiple Coulomb scattering
Best Fit Direction
4. Event selection
First reduction
• SK records immense amount of data• Much of this can be removed with some
simple cuts• Eliminates major backgrounds and makes
the rest of the data more manageable• Similar to solar first reduction
• OD triggered events• > 2,000 p.e. (1,000 SK-II)• > 800 hit tubes (400 SK-II)• Calibration events• Outside fiducial volume• < 16 or > 90 MeV• Electronics noise
remove:
muons
reduces data volumeby ~2 orders of magnitude
Spallation
• Even at 2700 m.w.e., cosmic ray muons enter detector at ~2Hz
• The muons can spall on oxygen nuclei, create radioactive products whose decays (mostly beta decays) can mimic SRNs
• Spallation occurs < 24 MeV; lower the energy, the more spallation
• Dominant low energy background• Want final sample spallation free, as
it is hard to model; determines analysis lower energy threshold
• Spallation eliminated by correlating to preceding muons
spallationproductsexpected
in SK
Spallation cut in 2003:• lose 36% signal
efficiency• uses cut tuned for solar• only down to 18 MeV
• 4 variable likelihood cut• The 4 variables:
▫ dlLongitudinal▫ dt▫ dlTransverse
▫ Qpeak
• Muboy: better resolution μ fit• Tune separate likelihoods for each muon
type (single, multiple, stopping)
distance along muon track (50 cm bins)
p.e
.’s
Spallation Cut
QPeak = sumof charge inwindowspallationexpectedhere
μ entry point
μ track
dlTransverse
where peakof dE/dx plotoccurs
dlLongitudinal
dE/dx
Relic Candidate
old likelihood
new
• Correlate events to all muons within previous 30 seconds
• Muons within 30 seconds after relic candidates make final sample
• Data sample – random sample = spall sample• Make likelihoods (PDFs) for each variable
Spallation cut
• SK-I/III cut combined; SK-II different
• Additional tracks for multiple muons have own special PDFs
• If Muboy fails fit, check BFF
Examples forSK-I/III singles
QPEAK
p.e. (x 103)
Spallation cut
• Improvements allow lowering of energy threshold• Requires 2-stage cut• Inefficiency calculated for all detector (position
dependent)• SRN MC vertex distribution used to get overall
inefficiency
2003 Old cut 18 < E < 34: 36% signal ineff.New Cut (SK-I/III): 16 < E < 18 MeV: 18% signal ineff. 18 < E < 24 MeV: 9% signal ineff.New Cut (SK-II): 17.5 < E < 20 MeV: 24% signal ineff. 20.0 < E < 26 MeV: 12% signal ineff.
• Solar 8B and hep neutrinos are a SRN background (hep at 18 MeV, and both at 16 MeV, because of energy resolution)
• Cut criteria is optimized using 8B/hep MC
• 2003: 1 cut < 34 MeV• New cut is now energy
dependent, tuned in 1 MeV bins
hep
8B
pep
pp
e recoil energy (total) (MeV)
energy resolution for an event of energy:
16 MeV
18 MeVSolar ν Events
7Be
16 18
Solar n cut• Solar events cut using qsun
• cos(qsun) = 1 if reconstructed direction matches sun
• 2003 cut: remove cos(qsun)>0.87 for all events E < 34 MeV
• ~15 degree resolution from the physics; multiple scattering of electron makes resolution worse
• Use multiple Coulomb scattering estimator `MSgood’ to improve efficiency by using a separate cut for each MSgood bin, for each 1 MeV energy bin
combinedMSgood < 0.40.4 < MSgood < 0.50.5 < MSgood < 0.60.6 < MSgood
integrated cos(θsun)
• Determine optimal cut points using `significance’ function
• Significance assumes dominant decay-e background only, represents signal/sqrt(background)
• Number of solar events modeled using MC spectrum, normalized using data < 16 MeV
• SK-I/III solar cut same, SK-II different
Solar n cut
cos(θsun)
sig
nifi
can
ce
solarNS /
Significance:
e = cut efficiency k = cut effectivenessNsolar = # solar ev a = # background evk* Nsolar = # solar events after cut applied
Incoming event cut
• Large amounts of background exists near the walls
• Much is removed by the fiducial volume cut; some survives
• The deff variable can help discriminate these events without the inefficiency of removing more volume
• Incoming events will have smaller deff; also incorrectly fit events that are really near the wall tend to have small deff
• Retune SK-I to increase efficiency• SK-II and SK-III separately tuned;
not enough statistics for energy dependent tuning
remainingremoved (2003)recovered (now)
More cuts
• multiple timing peak• multiple rings• Pion cut
▫ uses width of 3-hit combination distributions
• OD correlated▫ check hit ID tubes for
correlations in time and space to OD hit tubs, even if no OD trigger
• Pre-post activity▫ remove events +/- 50 ms;
for SLE events require 5 m correlation
Efficiency
• Efficiency greatly increased from 2003• With lower energy threshold,
efficiency is 87% greater in SK-I• Including new SK-II and SK-III data,
efficiency is increased by 227%• Sensitivity improvement:
▫ sqrt(3.3) 80% better sensitivity• Systematic errors calculated on
efficiency; mostly from studying LINAC data vs LINAC MC
final efficiency (sys error)
SK-I
5. Remaining backgroundswww.smbc-comics.com
Cut backgrounds
single muons
dt (s)
final sample datarandom sample
• After cuts, want final sample `free’ of these backgrounds (spallation, solar, pions, decay electrons, etc)
• Check many distributions to try and determine if this is true
• Due to low statistics, very difficult to be sure backgrounds completely gone; can only so no statistically significant amount remaining
• Estimated remaining in SK-I/II/III• Spall: < 4• Solar: < 2• deff cut: < 2
• Any remaining background likely to make limit more conservative
Remaining Backgrounds
• Final sample still mostly backgrounds, from atmospheric n interactions; modeled w/ MC
• 1) nm CC events– muons from atmospheric nm’s
can be sub-Cherenkov; their decay electrons mimic SRNs
– modeled with decay electrons• 2) ne CC events– indistinguishable from SRNs
• 3) NC elastic– low energy mostly
• 4) m/p events– combination of muons and pions
remaining after cuts
all SRN cutsapplied
# e
ven
ts e
stim
ate
d i
n S
K-I
Backgrounds 1) and 2) were considered in the 2003 study.
Backgrounds 3) and 4) are new!
SK-I backgrounds
• SRN events expected (98% SK-I) in the central, signal region (38-50o)
• ‘Sidebands’ previously ignored• Now that we consider new
background channels, sidebands useful▫ NC elastic events occur at high C.
angles ▫ m/p events occur at low C. angles
• Sidebands help normalize new backgrounds in signal region
not used
ne
e+p
n (invisible)
Signal region42o
μ, π
Low angle events
25-45o
NC regionn
N nreconstructedangle near 90o
6. Analysis methodology
Maximum likelihood fit
• 2003 study used binned c2 to fit final sample
• Found that changing the binning could change answer (up to 20%)
• Instead use unbinned maximum likelihood fit
• Fit all 4 backgrounds in all three Cherenkov regions, (for SK-I/II/III each), make PDFs
• Also make PDFs for all relic models
• Loops over all combinations of events, maximize likelihood
)(
1
5
1
5
1)( )(
jjevents c
ij
N
i j
j eEFcL
F is the PDF for a particular channel;E is the event energy;c is the magnitude of each channel;i represents a particular event, andj represents a channel (SRN + 4 backgrounds)
Systematic errors
• Many systematics considered, were not considered in 2003
• All the systematics operate by distorting the likelihood
• 1) Energy resolution/ E scale▫ Error on MC▫ considered independent▫ distortions added in quadrature
• 2) Energy independent efficiency▫ Systematic from cut reduction▫ Also cross section, FV errors
• Spectral shape systematics▫ Apply very conservative errors to
NC elastic, ne CC channels. ▫ decay electron background from
data, no error; neglect m/p
L(r) L’(r,e)
Make likelihood function of amount of distortion
Then sum all combinations ofdistorted likelihoods, weighed
by Gaussian envelope
example: E res/scale
L =c1PDF1(E) + c2p2(E) ….SRN decay-e
apply E res/scale distortion to PDF1:
L(e) =c1PDF1(E,e) + c2p2(E) ….
sum with weights for new likelihood
dLeNL )(' 2/2
7. Results
Fit results
Ando et al.’s LMA model; SRN best fit 0
Fit results• SK-II and SK-III give a
positive fit for SRN signal• This positive indication is
not significant
New Results: flux limits (n cm-2s-1, 90% cl)
Ee+ > 16 MeV
SK-I SK-II SK-III Combined Predicted
LMA (03)
<2.5 <7.7 <8.0 <2.9 1.7
Cosmic gas Infall (97)
<2.1 <7.5 <7.8 <2.8 0.3
Heavy Metal (00)
<2.2 <7.4 <7.8 <2.8 0.4 - 1.8
Failed Supernova
(09)
<2.4 <8.0 <8.4 <3.0 0.7
Chemical Evolution
(97)
<2.2 <7.2 <7.8 <2.8 0.6
6 MeV (09) <2.7 <7.4 <8.7 <3.1 1.5
LMA = Ando et al (LMA model)HMA = Kaplinghat, Steigman, Walker(heavy metal abundance)CGI = Malaney (cosmic gas infall)FS = Lunardini (failed SN model)CE = Hartmann/Woosley (chemical evolution)4/6 MeV = Horiuchi et al n temp
Kamiokande 1987A allowed
IMB 1987A allowed
8. Discussion
/cm2/s >18 MeV
Published limit (SK-I only) 1.2
cross section update to Strumia-Vissani 1.2 1.4
Gaussian statistics Poissonian statistics in fit 1.4 1.9
New SK-I Analysis:ETHRESH 18 16 MeV (2.5 1.7)ε = 52% 78 % (LMA)(small statistical correlation in samples)improved fitting method takes into account NC
1.7
New SK-I/II/III combined fit 1.7 2.0(2.9 > 16 MeV)
COMPARISON TO PUBLISHED LIMIT
2003
now
What’s next for SRNs?
•Analysis already includes 176 ton-years of data•Now highly optimized•Further improvements will be slow•There is some hope for background reduction in
SK-IV with new electronics (neutron tagging)•Still, it is unlikely that a discovery can be made at
SK in the near future•Gd doping could be a solution
▫neutron tagging allows background reductions▫removes most spallation, lower energy threshold
•Otherwise wait for next generation detectors
49
END.
Backups:
Energy reconstruction
• Start with Nhit = number hit PMTs (within 50 ns window)
• Assume 1 p.e. per PMT• Convert to `Effective’ # hits = # p.e.• edark = dark noise, etail = MCS tail
• Nall/Nnorm = bad channel correction
• Rcover = cathode coverage• S = angular coverage correction• l = water transparency• r = distance from vertex to PMT• G = gain factor• X = occupancy
• Occupancy:▫ search surrounding PMTs to guess
true # p.e.’s in PMT• Take PMT as center of 3x3 patch• Use Poissonian probability:
▫ P(k;l)=lke-l/k!• Assume all hit PMTs see same #p.e.• N = total # p.e.’s seen; l=N/9• xi = fraction hit in 3x3 patch
• P(>=1)=1-P(0)=1-e-l=xi
• = l log(1/(1-xi))=#p.e./9PMTs• Not all PMTs hit; want #p.e./hit PMT• #p.e./hit PMT = l/xi=log(1/(1-xi))/xi
LINAC
DT generator:
2H+3H4H+n(n = 14.2 MeV)
n + 16O 16N + p
16N decay (7.13 s halflife)
1) (66%) 6.13 MeV g + b2) (28%) b
10.4 MeV total Q
(isotropic)
Solar Cut16-17 MeV 26.2%/0.11 17-18 MeV 17.9%/0.1218-19 MeV 12.2%/0.0419-20 MeV 3.5%/0.08TOTAL 15%/.35
20 MeV ~ 0.05 events in total no cut necessary
SK-I/III ineff/#remain
16 17 18 19 20
cut 1
cut 1
cut 2
cut 2
cut 3
cut 3
cut 4
cut 4
SK-I/III
SK-II+ ~1MeV
E (MeV)
SK-I
SK-II
Near Invisible Muon Sample
E (MeV)from decay electrons that can be correlated to lowenergy muons with no OD trigger (from atm. neutrinos)`near invisible’ and most like real background
SK-II - Spallation Sample
•Invert SK-I/III spallation cut to get a ‘spallation sample’ of spallation events
•Fit spectrum to exponential
•Have SK-I, SK-II energy resolution functions from SK-II solar paper
•Solve for Sactual
•Get •Compare spectrums 55
')'()()('
dEERESESES ISKE actualISK
')'()()('
dEERESESES IISKE actualIISK
56
16 1817 (MeV)
17.4 MeV round to 17.5 MeVSK-I SK-II
SK-I
SK-II
SK-III
Systematics: Inefficiency
• Define:▫ r = # relic events we see in data▫ R = # relic events actually occurring in detector▫ ε = efficiency (SK-I/II/III dependent)▫ assume ε follows a probability distribution P(ε)▫ assume P(ε) is shaped like Gaussian w/ width σineff
▫ then we alter likelihood:
then the 90% c.l. limit R90 is such that
dPRLRL )()()('1
0
σineff
SK-I: 3.5%SK-II: 4.7% SK-III: 3.4%
Systematics: energy scale, resolution
•Method:▫Use MC, parameterize effects▫ ie for e-res, parameterize : fe-resolution(E) = (Etrue+(Erecon- Etrue)*error)
• δ(E) = (fe-scale(E)2 + fe-resolution(E)2)1/2
59
eventsN
iiii EeEmErL
1
)()(),()(
dLeNL )(' 2/2
)())(1(),()( iiii EEcEE
e-scale e-resSK-I: 1% 2.5% SK-II: 1.5% 2.5%SK-III: 1% 2.5%
Systematics: NC elastic
• Keep spectra the same• Change normalization in signal
region by 100%▫ +1s = double (14.8% SK-I)▫ -1s = 0%
• Because of physical bound, apply error asymmetrically (-1s to +3s)
• Instead of standard Gaussian weighing function (appropriate for symmetric case), use a weighted Gaussian function
• Maintain necessary properties:▫ expectation value = 0▫ variance = s2
SK-I NC elastic normalization
20-38º 38-50º 78-90º
5.6% 7.4% 87%
# s affect
Weighing function applied (weighted Gaussian)
Systematics: ne CC
• For ne CC case, keep normalization, distort spectrum
• Use large error of 50% at 90 MeV (0 distortion at 16 MeV, linear between)
• Use same range (-1 to 3 s) and weighing function as NC case
• -2 s would bring spectrum to 0 at 90 MeV, which is unphysical
No distortion-1s+1s
SK-I ne CC PDF
same weight fxn as NC case
dE/dx
BFFgood
other cuts: pre/post activity, pion, OD correlated, electronics noise
• decaye
NC study• Lots of 15.1 MeV g and
pion absorption events in MC
• 15.1 MeV g’s from mistake in NEUT code (improper branching ratio). Was 1.3% should be 0.007%
• Pion absorption also incorrect
• the g-rays from 14N are >99% < 7.6 MeV.
• Ignore both incorrect event types
all NC15.1 MeV gpion abs
15 (MeV)
10
5
0
14N
p+13
C
1+
(g.s.)
0+(2.31)
1+(3.95)
2+(7.03)
3+(11.05)
Sp=7.55MeV
Sp=7.550MeV
Sn=10.55MeV
NC background
all NC (after fixes)single pNC elasticmulti-piall NC (SK-I):
neglect
p-, p+ > 200p+ < 200
p0
p on O
Most importantbasically Michelcan be modeled linear comb.other backgroundsignore
atm n fluxhttp://arxiv.org/abs/1102.2688v1
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