GADZOOKS! project at Super-Kamiokande

M.Ikeda (Kamioka ICRR, U.of Tokyo)for Super-K collaboration2015,6,9@WIN2015

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Contents• GADZOOKS! project• Supernova Relic Neutrino search• R&D status and Plan• Summary

• Identify n̄ep events by neutron tagging with Gadolinium in SK.

•Gadolinium has large neutron capture cross section and emit 8MeV gamma cascade.

γ

p

n

Gde+

8 MeVΔT~30μsVertices within 50cm

ne

GADZOOKS! project

Physics targets:(1) Supernova relic neutrino (SRN)(2) Improve pointing accuracy for

galactic supernova(3) Precursor of nearby supernova by

Si-burning neutrinos(4) Reduce proton decay background(5) Neutrino/anti-neutrino

discrimination(6) Reactor neutrinos

Capt

ures

on

Gd

Gd in Water

100%

80%

60%

40%

20%

0%0.0001% 0.001% 0.01% 0.1% 1%

0.1% Gd gives~90% efficiencyfor n captureIn Super-K this means ~100 tons of water solubleGd2(SO4)3

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Gadolinium Antineutrino Detector Zealously Outperforming Old Kamiokande, Super!

Beacom & Vagins PRL.93, (2004) 171101

Supernova Relic Neutrino (SRN)

Beginning of the universe

NOW

１ billion years ago

10 billion years ago

S.Ando, Astrophys.J. 607, 20(2004)

Theoretical flux prediction : 0.3~1.5 /cm2/s (17.3MeV threshold) 3

Neutrinos from past SNe

Supernova Relic Neutrino (SRN)

Beginning of the universe

NOW

１ billion years ago

10 billion years ago

S.Ando, Astrophys.J. 607, 20(2004)

Theoretical flux prediction : 0.3~1.5 /cm2/s (17.3MeV threshold) 4

Neutrinos from past SNe

First goal is discovery of SRN

Search for SRN at Super-KSearch window for SRN at SK : From ~10MeV to ~30MeV

Now SRN search is limited by BG. We need BG reduction by the neutron tagging which can be achieved by GADZOOKS! 5

Evaluating Gadolinium’s Action on Detector Systems200 m3 tank with 240 PMTs

15m3 tank to dissolve Gd Gd water circulation system(purify water with Gd)

Transparency measurement(UDEAL)

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EGADS

One of main goals for EGADS is to study the Gd water quality with actual detector materials. Thus, the detector fully mimic Super-K detector.: SUS frame, PMT and PMT case, black sheets, etc.

Gd dissolving test has been performed since Oct.2014. (see next page)

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EGADS detector: Baby-Kamiokande

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The light left at 15 m in the 200m3 tank was ~75% for 0.2% Gd2(SO

4)

3 ,

which corresponds to ~92% of SK-IV pure water average.

Transparency of Gd water with PMTs

Where we are now?

• Now, we are summarizing the R&D results and making a proposal.

• A committee which was formed to review and evaluate the proposal has started the review.

• After the review of the committee, we will start collaboration wide discussion in this June.

• If the proposal is approved, more detailed plan will be made also with T2K members.

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Summary

• GADZOOKS! is a project to upgrade Super-K, so that SRN ν ̄e can be tagged by the delayed coincidence signal from a neutron capture of Gd.

• EGADS detector was build for R&D of Gd water purification system and check Gd effect to Super-K.

• EGADS has been keeping a good water quality with the target Gd concentration after PMT installation.

• Collaboration wide discussion to decide the Gd installation to Super-K will start in June (two weeks).

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Improvement for Proton decay

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Neutron multiplicity for

Pe+p0 MC

92.5%Zero n

Atmospheric n BG

Accompany many n

If one proton decay event is observed at Super-K after 10 yearsCurrent background level: 0.58 events/10 yearsBackground with neutron anti-tag: 0.098 events/10 years

Background probability will be decreased from 44% to 9%.

Supernova burst case

ne+p

n+e

ne+p

n+e

Improve pointing accuracy e.g. 4~5° 3°(90%C.L.) for 10kpc.

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By identifying ne+p events enhance n+e events in angular distribution.Also, it enables us to extract ne + nx spectrum.

W/O n-tag With n-tag

10 kpc supernova

tag eff. = 1.0tag eff. = 0.8tag eff. = 0.0

Num

ber o

f sup

erno

vae

Pointing accuracy (1000 simulations for 10kpc supernova)

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20-38 degrees 38-50 degrees 78-90 degrees

E (MeV)

SK combined 90% C.L. (SK4 is not included yet)

E (MeV)E (MeV)

ne e+

p

n (invisible)

Signal region42o

μ, π

Low angle events Isotropic region

n Nn

reconstructedangle near 90o

dataνμ CCνe CCNC elasticμ/π > C. thr.all backgroundrelic

< 5.1 ev / yr / 22.5 ktons = < 2.7 /cm2/s (>16 MeV) (using LMA model spectrum (Ando et.al, 2005)

SRN upper limit from SK  PRD 85, 052007 (2012)

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Effect of Star formation rate• Nakazato et al. ApJ 804 (2015) 75

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