supernova relic neutrinos ( srn ) are a diffuse neutrino signal from all past supernovae
DESCRIPTION
Supernova Relic Neutrinos ( SRN ) are a diffuse neutrino signal from all past supernovae that has never been detected. Expected number SRN events in SK 0.8 -5.0 events/year/22.5kton (10-30MeV) 0.5 -2.5 events/year/22.5kton (16-30MeV) 0.3 -1.9 events/year/22.5kton (18-30MeV). - PowerPoint PPT PresentationTRANSCRIPT
Supernova Relic Neutrinos (SRN) are a diffuse neutrino signal from all past supernovaethat has never been detected.
Motivation SRN measurement enables us to investigate the history of past Supernovae. The SRN flux is related to the supernova rate in galaxies and the cosmic star formation history
Predicted Predicted SRN fluxSRN flux
Expected number SRN events in SK0.8 -5.0 events/year/22.5kton
(10-30MeV)
0.5 -2.5 events/year/22.5kton(16-30MeV)
0.3 -1.9 events/year/22.5kton(18-30MeV)
Ando et al (2005) (LMA)R. A. Malaney (1997)Kaplinghat et al (2000)Hartmann, Woosley (1997)Totani et all (1996) (constant SN rate)
SK-ISK-IDATADATA
Atmospheric e (dot dashed)
Invisible -e decay (dashed)
(1496 days)
OLDOLD 90% C.L. Flux limit: 90% C.L. Flux limit: SK-I : < 1.2 /cm2 /sec
Two Irreducible backgroundsTwo Irreducible backgrounds:1) Atmospheric νe cc interactions
2) Decay of sub-Cherenkov ‘invisible μ’s’ from atmospheric νμ interactions
From 2003 published resultFrom 2003 published result:SK-I result:
M. Malek, et al, Phys. Rev. Lett. 90, 061101 (2003)
This study used:binned χ2 limit extraction18 MeV lower energy thresholdSK-I data only0th order inverse beta cross sectiontwo irreducible backgroundsThese things have now been improved!
+ 90% c.l. relic
both backgrounds (solid)
solar e recoil energy (total) (MeV)
energy resolution at: 16 MeV 18 MeV
7Be
16 18
8B
pep
hep
pp Nuclear Spallation from cosmic ’sSolar neutrinos
Radioactive backgroundsCosmic ray muons, decay electrons
Pions from neutrino interactionsElectronics effects
• many backgrounds, cuts• solar ’s and spallation: largest at low energy, set energy threshold• dominant background is spallation: spa-cut has largest inefficiency• crude solar and spallation cuts in published analysis: improvement needed for lower E threshold
Reducible Backgrounds
Spallation and Solar CutsSpallation and Solar Cuts11Be
11Li12N14B
energy energy resolutionresolution
8B
9Li
8Li
12B13B13O
12Be
12C
8He9C
15C
16N16 MeV
18 MeV
New threshold 18 16 MeV!
Lowering threshold < 16 MeV too difficult due to “wall” of spallation products with long half-lives that enter sample
• SPALLATION is cut using correlation to cosmic ray muons• Original cut used 2-D spatial correlation, time and charge• New method allows 3-D spatial correlation, muon categorization• Stricter cut < 18 MeV
• SOLAR events are cut by correlation to solar direction• New technique estimates multiple scattering, which dominates angular resolution• New cut is optimized in 1 MeV bins using MC, better reduction
16-18 MeV N/A 23% N/A 18% 18-20 MeV 7% 9% 36% 9% 20-24 MeV 7% 0% 36% 9%24-34 MeV 7% 0% 36% 0%
Energy range 2003 cut new cut
Solar and Spallation cut inefficiency
SOLAR CUT SPALLATION CUT2003 cut new cut
Total signal inefficiency: SK-I (1497 days) SK-II (794d) SK-III (562d) NEW (now) 22% (16-90) 31% 23%OLD (2003) 48% (18-90) N/A N/A
(now more data included!)
Atmospheric backgroundνμ CCνe CCμ/πNC elastic
E of background (MeV)
20032003: two channels:νμ CC spectrum modeled by decay electrons from cosmic ray ’s νe CC spectrum from MC
NowNow: four channels: νμ CC νe CCNC elastic required by lower E threshold; spectrum from MCμ/π prod.: reduced by cuts; helps constrain NC in signal fit
SK-I/III combined final data sample
Cherenkov angle distribution degrees
νe CCμ/π NC elastic
low region(μ/π)
isotropic region(NC elastic)
signal region(relic //e)
MC (without contribution)
low region(μ/π)
signal region(relic //e)
isotropic region(NC elastic)
e e+p
n (invisible)
Signal region
42o
μ, π
Low angle events
25-45o
Isotropic region
N
reconstructedangle near 90o
20-38 degrees 38-50 degrees 78-90 degrees E (MeV)
SK-I/III dataνμ CCνe CCNC elasticμ/π > C. thr.all backgroundrelic
20032003: binned χ2 fit to center region, two background channels
NowNow: simultaneous unbinned maximum likelihood fit, four background channels,three Cherenkov angle regions.Each channel has freefloating normalization
Combined Fit
combined 90% c.l.: < 5.1 ev / yr / 22.5 ktons interacting < 2.7 /cm2/s (>16 MeV) < 1.9 /cm2/s (scaled to >18 MeV)
combined90% c.l.
ev/yr interacting in 22.5 ktons
logL
ikel
ihoo
d
SK-I/II/IIIcombinedlikelihood
Comparison to Published /cm2/s >18 MeV
Published limit 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 MeVε = 52% 78 %(small statistical correlation in samples)improved fitting method takes into account NC
1.91.6
New SK-I/II/III combined fit 1.6 1.9
BACKUP
Period Live time # ID PMTs / % coverage Comment
SK-I 1497 days 11146 / 40% Experiment start
SK-II 793 days 5182 / 19 % After accident
SK-III 562 days 11129/ 40% After repair
SK-IV running now 11129/ 40% New electronics
Super-Kamiokande (Super-Kamiokande (SKSK))
SK is 50 kton water Cherenkov detector in the Kamioka mine, Japan (2700 m.w.e). The data is divided into segments: SK-I, II, III, and IV.
Electron energy [MeV]
10
0.1
10-3
10-5
10-7
SK E
vent
Rat
e [/
year
/M
eV]
0
10 20 30 40 50
νe+ 16O 16N + e+ν
e + 16O 16F + e -νe + e ν
e + e -
νe+ p e+ + n The main interaction mode for SRN’s in SK is charged current quasi-elastic interaction (inverse decay)
• 4 variable likelihood cut• The 4 variables:
– dlLongitudinal
– dt– dlTransverse
– QPeak
• Use new, better μ fitters• Tuned for each muon type (i.e.
single, multiple, stopping μ)• Improvements allow lowering of
energy threshold to 16 MeV!
distance along muon track (50 cm bins)
Spallation CutSpallation Cut
QPeak = sumof charge inwindowspallationexpectedhere
New Cut: 16 < E < 18 MeV: 18.2% signal inefficiency 18 < E < 24 MeV: 9.2% signal inefficiencyOld cut (likelihood + 150 ms hard cut) 18 < E < 34: 36% signal inefficiency
μ entry point
μ track
dlTransverse
where peakof DE/DX plotoccurs
dlLongitudinal
dE/dx Plot
Relic CandidateOLD likelihood
NEW!
Effwall cutEffwall cut
Energy (MeV)
oldnew
Some ray events originating from outside of fiducial volume have possibility of being reconstructed within fiducial volume of SK. In order to remove these events, we applied effwall cut which uses travel distance from tank wall.
Signal Inefficiency:: Old: 7% New: 2.5%
Signal Inefficiency:: Old: 7% New: 2.5%
reconstructed event vertexreconstructed
event direction
Effwall
Inner detector wall
Final Backgrounds (after all relic cuts)
E (MeV)
These 3 can be modeled as a combination of other backgrounds, and thus aren’t considered separately
CC Backgroundsinvisible μ decay eνe CCμ > C. threshold μ/π
νμ CCνe CCμ/πNC elastic
Combined Fit
combined 90% c.l.: = 5.1 ev / yr / 22.5 ktons interacting = 2.7 /cm2/s (>16 MeV) = 1.9 /cm2/s (scaled to >18 MeV)
combined90% c.l.
ev/yr interacting in 22.5 ktons
logL
ikel
ihoo
d
SK-I/II/IIIcombinedlikelihood
SK-I (~1500 days)SK-II (~790 days)SK-III (~560 days)combined
SK-I
best fit is negativefit shown is 0 relic contribution
20-38 degrees 38-50 degrees 78-90 degrees
E (MeV)
SK-Idataνμ CCνe CCNC elasticμ/π > C. thr.all backgroundrelicSK-I only 90% c.l. limit:
< 2.4 /cm2/s (>16 MeV)< 1.6 /cm2/s (scaled to >18 MeV)
SK-IIBest fit (shown):3.5 ev/yr interacting
20-38 degrees 38-50 degrees 78-90 degrees
E (MeV)
SK-II only 90% c.l. limit:< 7.4 /cm2/s (>16 MeV)< 5.2 /cm2/s (scaled to >18 MeV)
dataνμ CCνe CCNC elasticμ/π > C. thr.all backgroundrelic
SK-IIIBest fit (shown) :6.5 ev/yr interacting
20-38 degrees 38-50 degrees 78-90 degreesE (MeV)
SK-III only 90% c.l. limit:< 8.1 /cm2/s (>16 MeV)< 5.7 /cm2/s (scaled to >18 MeV)
dataνμ CCνe CCNC elasticμ/π > C. thr.all backgroundrelic
Systematics: Inefficiency
19
• 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: 4.5% SK-III: 3.1%
Cuts: efficiencies and sys errors
20
• SK-I:effwall : 98% (0.5%)C. angle: 95% (0.4%)pion like: 98% (0.2%)spall+solar: 89% (1%)2-peak, 2-ring: >99%Correlation cut: 99% (0.3%)1st reduction: 99% (2%)
(includes: electronic noise cuts, 50 us cut)
Total: 78 %
• SK-II95% (0.3%)88% (0.3%)97% (0.5%)87% (1.4%)>99%99% (0.3%)99% (2%)
• SK-III96% (0.3%)94% (0.3%)98% (0.5%)89% (1%)>99%99% (0.3%)99% (2%)
69% 77%