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)

nn ,, EEEEee

NC onlyCC+NCmoreneutrons Livermore numerical model

ApJ 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 ’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)

Even

t ra

te (

/yr/

MeV

)

Astroparticle Physics 3 (1995) 367-376

Triggering, DAQ14

• 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 SK16

• 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.

’sSpallation 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)

sign

ifica

nce

solarNS /Significance:

= cut efficiency = cut effectivenessNsolar = # solar ev = # background ev* 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 s; 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) n CC events– muons from atmospheric n’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) /p events– combination of muons and pions

remaining after cuts

all SRN cutsapplied

# e

vent

s es

timat

ed in

SK-

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 ▫ /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 /p

L(r) L’(r,)

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() =c1PDF1(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

MeVSK-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.• dark = dark noise, tail = 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 78-90º5.6% 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

014N

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 OMost importantbasically Michelcan be modeled linear comb.other backgroundsignore

atm n fluxhttp://arxiv.org/abs/1102.2688v1