SN Physics Workshop September 17 th 2009 Michael Smy UC Irvine SN Relic Neutrinos in Large Water...

SN Physics Workshop September 17th 2009

Michael SmyUC Irvine

SN Relic Neutrinos in Large SN Relic Neutrinos in Large Water Cherenkov DetectorsWater Cherenkov Detectors

Chandra/Hubble View of E0102-72

OutlineOutline• Super-Kamiokande SearchSuper-Kamiokande Search

– Published Analysis using SK-I DataPublished Analysis using SK-I Data– Analysis Improvements & Data Update: Analysis Improvements & Data Update:

increase sensitivity by ~factor twoincrease sensitivity by ~factor two– Search with Neutron TaggingSearch with Neutron Tagging

• SN Relic SN Relic Prospects with a DUSEL Water Prospects with a DUSEL Water Cherenkov DetectorCherenkov Detector– Without Neutron TaggingWithout Neutron Tagging– With Neutron TaggingWith Neutron Tagging

Chandra/Optical/Radio View of SN1006

Super-KamiokandeSuper-Kamiokande

Period Live time # ID PMTs / % coverage Comment

SK-I 1496 days 11146 / 40% Experiment start

SK-II 791 days 5182 / 19 % After accident

SK-III 291-518 days 11129/ 40% After repair

SK-IV running now 11129/ 40% New electronics

Electron energy [MeV]

10

0.1

10-3

10-5

10-7

SK

Eve

nt

Rat

e [/

year

/MeV

]

0

10 20 30 40 50

νe+ 16O 16N + e+ν

e+ 16O 16F + e -νe + e

νe + e -

νe+ p e+ + n

The main interaction mode for SRN’s in SK is charged current quasi-elastic interaction (inverse decay)

Courtesy K. Bays, UC Irvine

• oxgen spallation products from cosmic ’s (~600/day)

• atmospheric ’s– CC e’s

– sub-Cherenkov production: →stealth →e

• radioactivity

• solar ’s

• reactor ’s

• spallation limits the energy threshold & cuts to reduce it causes greatest signal loss

• sub-Cherenkov threshold muons from atmospheric neutrinos are irreducible without neutron tagging

SK Main BackgroundsSK Main Backgrounds

atm. → stealth ±→e±

relic ’s

spallationproductsfromcosmic ’s

μ

O

e

γ

X

Xe

Michael Smy, UC Irvine

Spallation ProductsSpallation Products

11Be

11Li12N

14B

energy resolution

8B

9Li

8Li

12B13B13O12Be

12C

8He9C

15C

16N

Energy in MeV

half

life

in s


Spallation ProductsSpallation ProductsIsotope Halflife Decay Kinetic Energy16

6C 0.7478s -n ~4 MeV15

6C 2.449s - 9.82 MeV16

7N 7.134s - 10.44 MeV11

4Be 13.8s - 11.5 MeV8

2He 0.122s n/- 11.65 MeV12

4Be 0.0114s - 11.66 MeV9

6C 0.127s +p 3~13 MeV8

3Li 0.84s - 12.5~13 MeV12

5B 0.0204s - 13.37 MeV13

5B 0.0173s - 13.42 MeV9

3Li 0.178s n/- ~10,13.5 MeV8

5B 0.77s + 13.73 MeV13

8O 0.0090s +p 8~14 MeV12

7N 0.0110s + 16.38 MeV14

5B 0.0161s - 20.16 MeV11

3Li 0.0085s --n ~16/20.77MeV

• form time diff. t between muon and relic candidate

• reconstruct muon track• calculate residual charge

ResQ: total light minus charge expect. from length

• find distance of closest approach lTransverse of muon to relic candidate

• use arrival time of each hit to calculate emission point along track: lLongitudinal is difference of point of max. light emission and relic candidate projection

• peak light emission QPeak

Tagging Spallation EventsTagging Spallation Events

μ entry point

μ track

lTransverse

maximumlight emission

lLongitudinal

Relic Candidate

K. Bays, UC Irvine

Example of a dE/dx PlotExample of a dE/dx Plot

distance along muon track (50 cm bins)

QPeak = sumof charge inwindow

spallationexpectedhere


A Simple Example ofA Simple Example ofSpallation RemovalSpallation Removal

LTRAN (cm) LTRAN (cm)

Spallation


entry point

muonpeak of dE/dx

relic candidate LTRAN

LLONG

Previous and Improved Spallation Previous and Improved Spallation TagTag

• three-variable likelihood cut for successful single track fits– t – lTransverse

– ResQ• two-variable likelihood cut

for unsuccessful single track fits– t – ResQ

• 150ms cut on t

• 18 < E < 34: 36 % signal inefficiency

• for each muon type (single , bundle, stopping ):

• four-variable likelihood cut if single, well-fit track– t– lTransverse

– lLongitudinal

– QPeak

• three-variable likelihood otherwise– t– lTransverse

– Qtotal

• 18 < E < 24 MeV: 18.5 % ineff.• 16 < E < 18 MeV: 22.5 % ineff.

Previous Improved


Removal of SpallationRemoval of Spallation

12

black – before likelihood cut, red – after likelihood cutdt (seconds) LTRAN (cm)

(dt < 10 s)stopping muonssingle muons


• Deadtime 18% (Improved from 36%)

• Increase in Exposure of 28%

• Further Tuning may be possible…

• Solar 8B and hep neutrino 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

• improved cut is 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 MeV Solar Solar νν Events Events

7Be

16 18


Solar Solar cut cut

17-18 MeVε = 86.5%

16-17 MeVε = 72.5%

18-19 MeVε = 95.5%

Inefficiency: Previous: 7% for 18-34MeV Improved: 4.5% for 18-19MeV, 0% above 19MeV

solar candidates


External BackgroundsExternal Backgrounds

Energy in MeV

remove events with small effective wall to kill radioactive decays originating outside the detector but reconstructing within the fiducial volume of SK

Signal Inefficiency:: Previous: 7% Improved: 2.5%

Signal Inefficiency:: Previous: 7% Improved: 2.5%

reconstructed event vertexreconstructed

event direction

effective wall

Inner detector wall

Eff

ectiv

e W

all i

n cm


Efficiency ImprovementEfficiency Improvement• new cuts more

efficient AND at least as effective

• > 34MeV, efficiency increase < 1.0 due to new background reducing cuts (new pion cut especially)

• 18 – 34 MeV, large efficiency increase due mostly to new spallation and solar cuts.

• 16-18 MeV region is now usable as well!

efficiency increase > 18 MeV:(# events new/previous)

Energy [MeV]

unnormalized relic (Ando)unnormalized stealth Michels

new!


Future of this SearchFuture of this Search• New cuts improve efficiency, re-analyzing now

• More planned improvements:– Fiducial volume enlargement

– Finalizing event selection

• Combine SK-I, SK-II and SK-III data.

• Extract new combined limit.

• Hope to publish result within 1 year.

• Future phase: neutron tagging with Gd.


Possibilities of Possibilities of ee tagging tagging

2.2MeV -ray

T = ~ 200sec

Possibility 1

n+Gd →~8MeV T = ~30 sec

Possibility 2

(ref. Vagins and Beacom)

ee could be identified by delayed coincidence. could be identified by delayed coincidence.

Positron and gamma ray vertices are within ~50cm.

n+p→d +

Number of hit PMT is about 6 in SK-IV

e

e+

pn

p

Gd

Add 0.2% Gd2(SO4)3 in water

GADZOOKS!GADZOOKS!

νe+ p e+ + nInverse beta decayInverse beta decay

Courtesy Iida, ICRR

Gadzooks!Gadzooks!• dissolve Gd salts

into SK water to detect gamma by neutron capture

• need to investigate– water transparency– water recirculation– material effects

• test tank for Gadzooks! is now being constructed!!

Measured Gd n capture Spectrum in SK

Astrophys. J. 697, 730-734 (2009)Michael Smy, UC Irvine

GdClGdCl33 Source in Super-Kamiokande Source in Super-Kamiokande• measure Gd n capture gamma

cascades:– Spectrum

– Vertex Resolution

– Capture Time


0123456789

10

10 15 20 25 30 35 40 45 50

relic+B.G.(inv.mu 1/5)

B.G. inv.mu(1/5)

atmsph.–

e

Visible energy (MeV)

even

ts/1

0yea

rs/2

MeV

Possibility of SRN detectionPossibility of SRN detectionRelic model: S.Ando, K.Sato, and T.Totani, Astropart.Phys.18, 307(2003) with NNN05 flux revision

If invisible muon background can be reduced by neutron tagging

Assuming invisible muon B.G. can be reduced by a factor of 5 by neutron tagging.

With 10 yrs SK data,Signal: 33, B.G. 27(Evis =10-30 MeV)

SK10 years (=67%)

Assuming 67% detection efficiency.

Courtesy Iida, ICRR

Gadolinium Water “Band-Pass” FilterGadolinium Water “Band-Pass” Filter

Ultrafilter Nanofilter

De-Ioniziation/Reverse Osmosis

pure water plusGd from tank

Gd plus smallerimpurities

(UF product)

Gd-sized impuritiesonly (NF reject)

impurities smaller thanGd (NF product)

impurities bigger thanGd (UF reject)

impurities to drain (DI/RO reject)

pure water(DI/RO product)

M. Vagins, ICMU

Filtration/Transparency Studies in IrvineFiltration/Transparency Studies in Irvine

IDEAL

“band pass”water system

IDEALIDEAL

pure Hpure H22O O

SystemSystem““band pass”band pass”SystemSystem

ExtraDI

DI

DI


usual stylewater

filtrationsystem

SimpleFilter

DIDI

DI

Measuring Water TransparencyMeasuring Water Transparency


• idea based on a IMB device • measure light intensity continuously as a function

of light travel distance• vertical pipe for quick & easy change of distance• pipe is necessarily short (< height of lab)

• look for changes when GdCl3 / Gd2(SO4)3 is introduced

• plastic pipe and tank (no metal effects)• use integrating spheres and a focal lens to stabilize

intensity measurements of Si photodiodes • use laser pointers (small, cheap & good beam quality)

Pulsed Laser Pointers

Experimental SetupExperimental Setup

Beam Splitter & Steerer

Integrating Sphere & Photodiode

Adjustable Mirrors


Reject 0.2% Gd(NOReject 0.2% Gd(NO33))33: UV (337nm): UV (337nm)Pure Water Measurement Gd(NO3)3 Measurement

linear scale linear scale

log scale

125.8±5.9m 94.87±0.46cm


Endorse GdClEndorse GdCl33 Solution Solution

360nm 337nm

650nm

595nm

532nm

478nm

405nm

0.8% Solution: 4xGadzooks! Concentration


66.8±0.9m69.8±3.2m21.08±0.51m6.422±0.014m

2.864±0.004m 33.00±0.23m 27.74±0.26m

Gadolinium Compound SelectionGadolinium Compound Selection

• GdCl3 is considered too corrosive for stainless steel tank/PMT support structure

• Gd(NO3)3 is opaque in the UV

• Gd2(SO4)3 is not as corrosive and (from spectro-photometer measurements) should have good water transparency

• However, it dissolves not nearly as fast: must first solve selective water filtration


GdGd22(SO(SO44))33 Filtering Progress Filtering Progress• took data with ultrafilter and two types of

nanofilters• basic principle is sound

• UF passed ~100% of Gd2(SO4)3

• NF rejected ~100% of Gd2(SO4)3

• actually use try multiple stages of NF; clean up product with DI & RO units

• so far, cannot reproduce transparency even without Gd; need to tune the bandpass; check for impurities from additional components

• when filtration is working, measure resulting water transparency of Gd2(SO4)3 solution

M. Vagins, ICMU

Make 100 ton class test tank and demonstrate the GADZOOKS! Idea.

0.2%Gd water in 100 ton class water tank

PMTs

Water system Transparency measurement

EGADS Evaluating Gadolinium’s Action on Detector Systems

Figure by A.Kibayashi

Courtesy A. Kibayshi, Okayama University

Current status of Gadzooks!Current status of Gadzooks!

• Excavation has started• Test tank is currently designed• Construction will start soon• Material compatibility test• Study selective water filtration at Irvine• transparency measurement at Irvine• test a large-scale water system and measure the

water transparency performance with EGADS soon


Supernova Relic Supernova Relic Neutrino RequirementNeutrino Requirement

of DUSEL Water of DUSEL Water DetectorDetector

K. Bays, UC Irvine

RequirementsRequirements• sufficient depth to avoid being

overwhelmed by spallation background

• need above about six photo-electrons/MeV for sufficient energy resolution (and threshold for Gd n capture events)

• need low PMT dark noise (same reason): cooling of the PMT environment

• good radiopurity


Expected Threshold for DUSEL Expected Threshold for DUSEL Detector at 4850ft LevelDetector at 4850ft Level

• assume spallation background is dominant issue

• assume spallation spectrum scales with muon rate when varying depth

• ignore correlation between spallation energy and lifetime

• keep signal/background ratio to the same level as SK


I Relic SpectrumI Relic SpectrumIncrease in relic rate in watercompared to present SK analysisas energy threshold changes


II Muon Intensity as Function of DepthII Muon Intensity as Function of Depth

98.13/227.124.11/64.2131018.2)( kmhkmh eehI


III Spallation Spectrum at SKIII Spallation Spectrum at SK• The unnormalized

spallation spectrum from SK data can be parameterized by a simple formula:

• The increase in spallation as the energy threshold is lowered can be calculated by:

En (MeV)

25

2

25

1)(/)(

EEEnSEnS

MeVEneEnS /894.058.18)(


III Spallation Spectrum With Gd: III Spallation Spectrum With Gd: Guess Spallation Rate with nGuess Spallation Rate with n

• shorter livetime, less products, less energy

• …but what are production rates?

• what if spallation list is not complete?

• if reduced by ~1 order of magnitude: shift spectrum by 2.6MeV (ln(10)MeV/0.894)


Energy Threshold ResultsEnergy Threshold Results• Some particular values:

4050 (4850 ft) = 15.5/12 MeV

2930 (3500 ft) = 17.5/15 MeV

2700 m.w.e. (SK) = 18/15.5 MeV

1680 (2000 ft) = 20.5/18 MeV

250 (300 ft) = 25/22.5 MeV• since SK will lower the

threshold, a DUSEL detector should be able to employ the same techniques, so this is very conservative

Energy Threshold (MeV)

w/o Gd

with Gd


ConclusionsConclusions• SK is improving the sensitivity of the SN relic search• spallation tagging is critical for this• together with data update, sensitivity should improve by up to a

factor of two• SK will lower the energy threshold of the search to 16 MeV• SK investigates introduction of Gd salt to detect anti-neutrinos via

delayed coincidence using n capture on Gd:– water filtration system is currently designed in Irvine– large-scale test and material effects are studied soon in a especially built test

tank next to SK

• with Gd, SK should see SN relics within ten years• DUSEL detector has excellent prospects to measure and study the

SN relic signal– must have sufficient photocathode coverage– must have cool enough PMT environment– must have radiopurity

• DUSEL depth is sufficient with or without Gd

SN Physics Workshop September 17 th 2009 Michael Smy UC Irvine SN Relic Neutrinos in Large Water...

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