Search for correlated
event with GW170817 in
KamLAND
Takahiko Hachiya* for KamLAND collaboration*RCNS, Tohoku univ.

1/27

KamLAND

Kamioka Liquid scintillator Anti-Neutrino Detector
池ノ山 - Google マップ

7/14/16, 13:02

池ノ山

Gifu, Japan

1000 m underground.
Muon flux 1/105 of surface-level.

~180 kmfrom reactors

•
•

50 km

§ Variable physics targets:o Reactor neutrinoso Geoneutrinoso Solar neutrinoso Supernova neutrinoso 0ν double beta decayo etc...

Shield external gamma-rays.
Detect Cherenkov-lightfrom muon.
17” PMT 1325
20” PMT 554

Page 1 of 1

fe

r

oi

l

water
uf

https://www.google.co.jp/maps/place/池ノ山/@35.7127326,136.72544…2f4376ffeb1:0x140bc5bfbb0ad6af!8m2!3d36.4273255!4d137.3110342

20 m

B

地図データ ©2016 Google、SK telecom、ZENRIN

池ノ山

since 2002

PRD 88 (2013) 033001.
PRC 92 (2015) 055808.
APJ 818 (2016) 91.
PRL 117 (2016) 082503.

§ Realized by low BG environment &low BG Liquid Scintillator(LS)ü 238U: ~10-18 g/gLS, 232Th: ~10-17 g/gLS

m

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i
ad

us

5
6.
Liquid Scintillator
1kton

20” Outer-PMT 140

Balloon(Nylon/EVOH
multi layer film)
2/27

Zen400からZen800へ - リーク
KamLAND-Zen 800
Zero neutrino double beta decay search
!"
#

!"

$
$
Majorana?

#① balloon install
Xe-LS
Xe 750 kg
136Xe 91%

② dummy-LS
filling
20 m

IB

φ3.84 mXe-LS
Xe 750 kg
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φ3.84 mBalloon construction finished!!
@Mar. 6th

3/27

ν detection methods
Invers Beta Decay (IBD)§ anti-νe only§ Eν reconstruction§ Reaction threshold 1.8 MeV§ Cross section higher than ES
"!#

%

&'

Electron Scattering (ES)§ Sensitive to all ν(especially νe)§ Eν cannot be reconstructed.
§ No threshold§ Directional info. (not in Liquid Scint.)

PromptEvisible~Eν- 0.78 MeV

BG rejection by
Delayed Coincidence(DC)Delayedn capture on p (γ2.2 MeV)$
or on 12C(4.9 MeV)
~200μs

"

"

&(

&(
4/27

GW170817 and ν observatory follow-up
The Astrophysical Journal Letters, 850:L35 (18pp), 2017 December 1

identiﬁed for energies above ∼1017 eV
background of UHE cosmic rays (Aabconsists of 1660 water-Cherenkov statof ∼3000 km2 following a triangular
GW170817 ⌫ (cm 2 )ApJ Lett., 848:L12, 2017
grid spacing (Aab et al. 2015b). The
from FC+PC only
UPMU
only throughpassagefromof shower
particles+0.7
4
recorded as time⌫µ
5.6 ⇥ 1016.0traces
0.6 in 25 ns interv
Cosmic rays
interact+1.1 shortly after e⌫¯µ1.3 ⇥ 105
21.3
0.8
induce850:L35,
extensive
air2017
showers.
ApJandLett.,⌫e
4.8 ⇥ 104
directions their electromagneticcompo
to the large grammageof atmosphere f⌫¯e1.2 ⇥ 105
point to the ground. As a consequenfrom low-energy only
ground level is dominated by muons
flat spectrum
Fermi-Dirac
Eave =20 MeV
tracesin the withwater-Cherenkov
stati
7
7
showers
inducedby⌫¯e
1.2 ⇥10
6.6 ⇥10downward-goingangles can start their9 development d⌫e
1.0 ⇥1093.4 ⇥10producing traces that spread over long
solar
⌫¯x
7.5 ⇥1092.6⇥1010fraction of elec
have a considerable
9
undergomoreinteractions
than muo⌫x
6.3 ⇥10
2.1 ⇥1010
spreading more in time as they pass th
Table 2. Limits at 90% C.L. on the fluence of neutrinos from
GW170817
a spectral ind
is alsothe case given
for Earth-skimmings
MeV–10 GeV for FC+PC and 1.6 GeV–100 PeV for UPMU data.
error of(nUPMU
limit is mby tauTheneutrinost ) that traverse
zenith angle of NGC4993. Low-energy limits assume a flat spectrum
well andas ainteract
Fermi-Dirac
spec
Earth’sascrust,near theexfrom 3.5 MeV to 100 MeV. ⌫x (¯⌫x ) represents ⌫e (¯⌫e ) and ⌫µ (¯⌫µlepton).
that escapes the Earth and d
atmosphere above the SD.
Dedicated and efﬁcient selection
different time proﬁles of the signal
Figure 2. Upper limits (at 90% conﬁdence level) on the neutrino spectral
created by hadronic and neutrino primfrom GW170817 during a ±500 s window centered on SK
the GWlimit,
trigger arXiv:1802.04379
ApJ Lett., 850:L35, 2017ﬂuencefor Earth-skimmingν as well as dow
time (top panel), and a 14 day window following
the GW trigger (bottom
1012
x
panel). For each experiment, limits are calculated separately for each energy
arXiv:1802.04379
induced showers (Aabet al. 2015a).
νx
decade, assuming a spectral ﬂuence F (E ) = Fup ´ [E GeV]-2 in that decadeward-going showersνeinitiated by neutri
11
10
only. Also shown are predictions by neutrino emission
models. In the upper
efﬁciently identiﬁedνefor zenith angles
plot, models from Kimura et al. (2017) for both extended emission (EE) andet al. 2015a). For the Earth-skimming
prompt emission are scaled to a distance of 40Mpc10 and shown for the case of
10 off-axis angles to indicate
the on-axis viewing angle (qobs 1 qj ) and selectednt -induced showers with zenith ang
the dependence on this parameter. The shown off-axis angles are measured in
ApJ Lett., 850:L35, 2017
trigger the SD. This is the most sen
9
the redshift of the hostexcess of the jet opening half-angle qj . GW data10and
neutrinos, mainly due to the larger
arXiv:1802.04379
galaxy constrain the viewing angle to qobs Î [0 , 36 ] (see Section 3). In thedensity of the target (the Earth) where
lower plot, models from Fang & Metzger (2017) are
scaledtoadistanceof
108 sum of neutrino and anti40 Mpc. All ﬂuences are shown as the per the ﬂavor
and where tau leptons can travel teneutrino ﬂuence, assuming equal ﬂuence in all ﬂavors, as expected for standard
et al. 2015a). The angular resolution
neutrino oscillation parameters.
107
inclined showers is better than 2°. 5, im
the number of triggered stations incre
0
20
40
60
80
100
Auger
Collaboration2009).
100 PeV, the upper limit on an E-2 power-law spectral ﬂuence
total energy(MeV)*just my calculation
5/27
Auger performed
a search for UHE n
is F (E ) = 0.23 ´ (E GeV)-2 GeV-1 cm-2 .

6§ GW170817 (GRB 170817A)

o Multi-messenger detection of Binary NeutronStar(BNS) merger.
o Luminosity distance: 40 Mpc
o Radiated energy > 0.025 Msolar~4.5x1052 erg• ΔM < 0.2̶0.8 M

o tGRB ‒ tGW= 1.7 sec§ MeV neutrino wasnʼt observed by IceCubeʼsnoise rate and SK.
o anti-ν flux limit on the earth < 6.6x107/cm2(luminosity at source ~<4x1056 erg*)

90% fluence limit(cm-2)§ No high energy neutrino (GeV̶EeV) was
found by ANTARES, IceCube, PAO, and SK.

BNS merger and thermal ν emission
Y. Sekiguchi et al., PRL 107, 051102 (2011)§ Thermal ν from BNS mergerLighto Temp. gets to O(10) MeV after mergerØ e-/e+ pair creation, capture on nuclei
àνe/ anti-νe emission.
ü more anti-νe due to neutron richness.
Ø Energy: O(10) MeV§ Thermal ν detectiono Motivation

Rise time<10ms.
Peak lum. ~1053 erg/s.

Mediumν-oscillation not included yet
in current simulation models.

Green: anti-νe
Red: νe
Blue: νxHeavy

K. Kyutoku, K. Kashiyama, arXiv:1710.05922• Information btw merger to jet.
• ν-mass measurement by time diff. fromGW.

o ~3x1052 erg anti-νe emission(Integrated over 1sec)t ⇠ 0.51 s✓

D
100 MPc◆⇣m⌫ ⌘2
100 meV✓

10 MeVE⌫o Exposure of 80 Mt*yr is necessary...

• assuming merger rate ~50/yr at ~200 Mpc

6/27

◆2

(10 s 145 t) for energy intervals (0.25 − 15) MeV and(0.4 − 15) MeV, respectively (Table I).

±500 s time windows around GW150914, GW151226 and
GW170104 where the expected background is close tozero, so the 90% C.L. upper limits on the number of GW
correlated events N90 (Eν , nobs , nbkg ) is 2.44 [39]. The
IBD cross-section for antineutrinos was calculated according to [42]. The results are shown on Fig. 4, line
5 and in table II, column 6.

Ref.: Limits on ν from BBH merger
GW event Threshold,Count rate,
Detected
MeV
ev/1000 s
GW150914 0.25/0.4 2.07±0.06/1.68±0.06
2/0
GW151226 0.25/0.4 2.15±0.06/1.72±0.06
1/1
GW170104 0.25/0.4 2.28±0.07/1.72±0.06
2/1

Mono-energetic ν assumed 1015

1 - Bx νe ES+/- 500 sec window searched

The upper limits on the fluence without oscillation formonoenergetic (anti-)neutrinos with energy Eν are calculated as follows:
central engine active

centralN90 (Eν , nobs , nbkg
) engine activeΦ=ϵNe σ(Eth , Eν )(c) 250s

Φ, cm-2 GW -1

Table I: Average Borexino count rate in 7 day runs containApJs 850:21,
ing the GW events in terms of events per 1000
interval for2017
0.25 MeV and 0.4 MeV thresholds. The number of registered1014
events inside ±500 s interval is shown in the rightmost column.
13

10

2 - Bx νe ES
3 - Bx νµ,τ ES

where N90 (Eν , nobsgamma, n ) is the 90 % C.L. upper limit
HENbkgon the number of GW
GW-correlated events in (Eth , Eν )(a) 100s(b)(b) (d)electron
gamma > 100 deMeV
range
per single
GW event, (a)ϵ is100s
the recoil
31
(e)
500s
tection eﬃciency, Ne = 4.79 × 10 is the number of elecB. Baretet fiducialal., Astropart.
trons in the
Borexino
volume, Phys.
σ(Eth , 35,
Eν ) 1is (2011)
theFigureSummary of upper bound ofcross-section
GRB emission process
durations taken
into accounttotal1:neutrino-electron
integrated
overthein the total GW+HEN coincidence time window. (a) active central engine before the(Eth , Eνjet) has
interval.
electroneﬃciency
relativistic
broken outTheof therecoil
stellar envelope;(b) detection
active central engine
with therelativistic
brokenprecisionout of the envelope;(c) delay
between theonset of theof
precursor
equals 1jetwithof fiducial
volumedefinition
4%.
and the main burst; (d) duration corresponding to 90% of GeV photon emission; (e) time
Theof upper
limitactivity.
N90 (E
nbkg ) is
calculatedtheν , nobs
span
central engine
Overall,the ,considered
processes
allow for aformaximumof500s between
the observationof a HEN
and a GW
transient,setting
the known
coincidence
total
numberof observed
eventsnobs
and forthetime window to [ 500s, 500s]. The time window for GW or HEN signals from the onset
mean
backgroundaccordance
withprocedure
bkg inofthe GRB
is tGW tGRB ⇡n
tHEN
tGRB
2 [ 350s, +150s].
Notethethat weshow a period
between
the
end
of
the
precursor
emission
and
the
start
of
the
main
GRB
with by
no GW[39]. The total cross-section σ(Eth , Eν ) is obtainedin-or
HEN emission. While we cannot exclude the possibility of GW or HEN emission in thistegrating
the would(ν, e)-scatteringcross-sectiondσ(Eν )/dEeperiod,such emission
have no e↵ect on ourestimated time window.
The
top of the
figureschematicelectron
drawing of aenergies
plausible emission
scenario.
[40] shows
overa recoil
Ee between
the electron
threshold energy Eth and the neutrino energy Eν :4 - Bx νµ,τ ES

2

Bx1

5 - Bx νe IBD

1012

4

(1)

150s

3

KL

1011

7
10

10

9

10

8

10

(Bx: Borexino)

6 - S-K νe ES
7 - S-K νµ,τ ES
8 - S-K νe IBD
9 - K-L νe IBD
1

5

SK
8
10
Eν, MeV69• SK good at expected
thermal ν region.
• KamLAND good below
5 MeV.

7/27

(blue
ergy
291 s
GW1
the e

GW151226 and GW170104 detection times is applied forfurther analysis. This time window covers the possible
delay of a neutrino which propagates slower than GW(for a claimed distance of d ≈ 440 Mpc for GW151226[2] the delay reaches 440 s for a 0.5 MeV neutrino with
•70Highemission< 1 sec.
meVmass 3period), as wellas possible earlier emission of• TOF effect dominant for MeV neutrinos.
neutrinos due✓ to poorly
constrained◆ ✓◆2 details of black holeheaviest 2m⌫
1.0 MeVMoreover, the choice is-Window
black =holemerger.
10 s (BH-BH)

Time window for thermal ν search
Figure from ApJ, 846:114, 2017.
This is likely to be underestimated
The Astrophysical Journal, 846:114 (15pp), 2017 September 10(mentioned in arXiv:1710.05922).

Fujibayashi et al.

70 meVE⌫detectable(40 Mpc case)

Calculation for ES:
EthE⌫detectable =
2

✓

1+

r

me
1+2
Eth

2 Position reconstruction precision increases with energy due toThis logic is from Borexinoʼs GW paper (ApJ 850:21, 2017).

◆

statistical reasons
3 The P lanck 2015 CMB temperature and polarization power
spectra in combination with the baryon acoustic! oscillations data
gives a limit on the sum of neutrino massesmν ≤ 0.17 eV at
95% C.L. [37]. Together with the measured oscillation mass differences [38] it leads to a constraint on the maximum neutrinomass m1 , m2 , m3 of 70 meV.

Ap
cand
GW1
respe
0.267
291
GW1
extra
of ±
neut
GW1

And also, if BG is high, O(0.1 sec)-burst is worth being searched.
8/27

KamLAND DATA Quality

9/27

Detector condition
No mini-balloon for KL-Zen.
Full volume available.
Preliminary

0.002

Deadtime(trigger disable) distribution

Deadtime ratio in 1 sec bin

Deadtime ratio in 1 sec bin

Deadtime(trigger disable) distribution

0.0015

0.002

Zoom

0.00150.001

0.000500.001

0.0005

−400

−200

0

200

400
t-tgw [s]

0

−40

−20

0

20

40
t-tgw [s]10/27

Event selection (IBD)§ Veto muon & events 2-msec after the muon.
§ 2-sec veto after showering muonßDifferent from usual analysis*.
§ Likelihood selection*PRD 88 (2013) 033001.
§ Prompt Energy (Ep):0.9̶100 MeV (Eν 1.8̶100 MeV).
§ Delayed Energy (Ed):
1.8̶2.6 MeV || 4.4̶5.6 MeV§ Time correlation (dT): < 1000 μs.
§ Space correlation (dR): < 200 cm.

Overalldetection eff.
~98%
11/27

BG rate for IBD search
2

10

10

Blue: Selections
other than theparameters
Skyblue:
DC candidates

event/bin

DC related parameters

event/bin

Event selection• Run014495̶014546• 2017/8/1̶2017/8/30(w/o 8/17): 24.4 livedays• Rp, Rd < 6.0 m

1

1
20

40

60

10

80
100
Ep [MeV]

1

2

3

4

5
6
Ed [MeV]200300dR [cm]event/bin

Event rate:
120 evts/24day ~ 5.7e-5 evts/sec• Almost all are accidental BG.
• Negligible in 1000 sec window.

event/bin

Preliminary
10

1
0

10

1
1000

2000

3000
dT [µs]

0

100

12/27

Event selection (ES)§ Veto muon & events 2-msec after the muon.
§ 2-sec veto after showering muon
§ Visible Energy: 0.5̶100 MeV(Eν: 0.67̶100 MeV)
§ Veto DC tagged events.
o Anti-neutrino candidates.
o Rn daughters.

§ Veto badly reconstructed events.

Overalldetection eff.
~99%
13/27

Event selection• 2017/8/1̶2017/8/30(w/o 8/17): 24.4 livedays

R

events/m3/sec/0.01MeV

BG rate for ES search
10−4
10−5

Energy spectrum
40K

Preliminary

208Tlfrom balloon

from PMTs

10−6
10−7

R< 600 cm
R< 550 cm−8

10

R< 500 cm
R< 450 cm
R< 400 cm

10−9

1

11C

10C

2

3
EnergyKat (MeV)

14/27

BG rate for ES search10

R< 500 cm
R< 450 cm
R< 400 cm

R< 600 cmth

R< 550 cm−3

Integrated BG rate

N(E )/s

R< 600 cm

th

N(E )/s/m3

Integrated BG rate/volume

1

10−4

10−1

−5

10−2

10

10−6

Preliminary

1

2
3
4
Visible Energy Threshold [MeV]
Energy Threshold (MeV)
Kat
Event selection• 2017/8/1̶2017/8/30(w/o 8/17): 24.4 livedays

10−3

Modifying window andvolume,BG free with 1.0 MeV
threshold.

R< 550 cm
R< 500 cm
R< 450 cm
R< 400 cm

BG free with 3.5 MeV
threshold if
1000 sec window

Preliminary
1234Visible Energy Threshold [MeV]
Energy Threshold (MeV)

Window = 10 s✓Katmheaviest⌫
70 meV◆2 ✓1.0 MeVE⌫detectable

◆2

15/27

Fiducial volume decision (ES)<latexit sha1_base64="ZkwmayHsCJoutnboqYGq+ueb4Zc=">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</latexit>

✓

1 MeV
E⌫

R< 600 cm◆2

1.64sigma=90% C.L.
arXiv:physics/0308063+1

R< 600 cm

R< 550 cm

1

R< 500 cm
R< 450 cm

0.5

R<

5

th

R< 400 cmcm
00Preliminary1∈ / 1.64/2 + N(E ) , ∈=(R/6 m)3

Window[sec] = 10th

∈ / 1.64/2 + N(E ) , ∈=(R/6 m)3(R/600cm)3
Figure of merits relative to 600-cm-radius analysis: F OM = 1.64 p
B(R, Eth )
2 +

2

3

Visible Energy Threshold (MeV)

4

Fixed 1000 sec window

0.6

R< 600 cm

R<

R< 550 cm
R< 500 cm

600

cm

R< 450 cm
R< 400 cm

0.4

0.2

0

R<

cm
0
45
Preliminary

1

2

3

Visible Energy Threshold (MeV)

4
16/27

Unblind

17/27

Eprompt [MeV]IBD search
102

Preliminary
No events in +/- 500 sec window.
Consistent with expectation: 5.7e-2.

101−20000020000
t - tgw [sec]18/27

Evis_single [MeV]ES search R<600cm, higher energy
102 Preliminary

No events above 3.5 MeV in +/- 500 sec window.
Consistent with expectation: 0.7.

100<<latexit sha1_base64="Ol0Wb7p4wWCc6F2Y89JCnAXffas=">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</latexit>

−1000
✓

t [sec] < 10

1 MeV
Evis

◆2

0
+1

1000
t - tgw [sec]19/27

ES search R<500 cm, lower energy
Evis_single [MeV]Preliminary

BG

co• Eth 1-MeV analysisnsist• BG rate: 0.025/secent• 10-sec expected: 0.25 evt.
• Nobs: 1 evt.
• Probability(Nobs>0): 22%

3

2

1
−100
0<
<latexit sha1_base64="Ol0Wb7p4wWCc6F2Y89JCnAXffas=">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</latexit>−50

t [sec] < 10

✓

0

50

◆2

t - tgw [sec]

1 MeV
Evis

+1

100

• Eth 0.5-MeV analysis• BG rate: 0.045/sec• 20-sec expected: 0.89 evt.
• Observed: 1 evt.
• Probability(Nobs>0): 59%
20/27

Occurred at
Thu Aug 17 12:41:05.449 2017 UTC
1.02 sec after GW(0.72 sec before GRB).

Evis
x
y
z
r

= 1.4 MeV
= -137 cm= -81 cm
= 7 cm= 159 cm

Relatively inside vertex.

Evis_single [MeV]

About the event

3

Preliminary

2

1
−100

−50

0

50

100

t - tgw [sec]21/27

runs (usually 1 day long), to the average rate of its
neighbors.
(3) The effective event rate is then used to classify eachpartition into one of seven different ranks, which
are defined in Table I. As an example, the rank
classification for one data-taking run (∼24 h long) isshown in Fig. 3. We find that the rank assignment ofeach volume generally varies slowly with time except

by other independent KamLAND data. A fit to the candidate
event spectrum then determines the partial contributions.
This section describes how the background model isconstructed and what is known about its constituents. Background sources are classified into three categories: radioactive
impurities in the LS, spallation products, and radioactivity inthe surrounding materials.

1.4 MeV: 11C dominant

PHYSICAL REVIEW C 92, 055808 (2015)

Be SOLAR NEUTRINO MEASUREMENT WITH KamLAND
1

2

3

4

5

6

7

Z (m)

3
TABLE III. Summary of signal andbackground in the FV. The
est-fit signal and background rates in2 the whole energy range (w/o1cut) and the 7 Be solar neutrino energy range (0.5 MeV < E <0
8 MeV) are shown.
-1

otope

-2

Event rate w/o E cut -3

Event rate in 0.5–0.8 MeV-4

R 4.5 m

2

Bi
Kr
Ar
K

Be

2

210

Events/(kt d 10keV)

0

Data
Total
(extrapol.)
7Beν
11C
210Bi
85Kr
7Be
Pile-UpAll ranks
Rank 1 0 2 All
ranks
Rank
118 20
4
6
8
10
12
14
16
210Po
Be SOLAR NEUTRINO MEASUREMENT(ktρ d)(m−1) WITH KamLAND(kt d)−1
14C
U,Th
Solar neutrinos
FIG. 3. (Color online) Rank classification of partitions in the FV
during a short data-taking
interval.
Minor Spal.
Rank
Po(α)
582 ± 94117 ± 191
purification, we collected samples from a location within the
Otherν
10
2 055808-4
FV at10z 0= +1.5 m. These samples were analyzed for their Kr
pepν
1443
14.9
3
content using a helium purge, a cold trap to retain the Kr, and4CNOν
a residual gas analyzer to measure its partial pressure. BasedRadioactive impurities
in the LS510on these measurements, the 85 Kr decay rate was estimated at
Bi(β )
6-1µBq/m3 , assuming a recent isotopic ratio of 85 Kr in
8.3 ±
4.2
23974 ± 883 3955 ± 238 4557 ± 168 578 ± 35 7
1085
air [19]. Asa third crosscheck for the
0.2
0.4
0.6 Kr content
0.8of the LS,1
1.2
1.4
85
85m
10
858 ± 59453 ± 10257 ± 430 ± 7a Kr- Rb delayed coincidence analysis was performed,
utilizing the β decay into the metastable,
514-keV
excited state(MeV)
VisibleEnergy11C
3±3
2±30.04 ± 0.04 0.02 ± 0.04
of 85 Rb. This analysis yielded 17.3 ± 5.9 µBq/m3 , averaged
10
over the entire FV. 85 Kr undergoes a unique first forbidden
β+ decay
181 ± 293 ± 3848 ± 8
1 ±C (β10)
β decay. The β spectrum contained in the background model7(τ=
29.4 min,ofQselected= 1.98MeV)
Beν(GS98)
FIG.
5.
(Coloronline)Energyspectrum
Be solarwascalculated
usinga
relativistic
Fermi
function
plus
a
shape
Spallation products
10
Producedby muon spallation.
correction accounting for the forbiddenness following
theneutrino
candidates
forspectral
theparametrization
rank 1 data set together with the best-fit
0.4
0.6
0.2
lifetime.
procedure Long
outlinedin Ref.
[20]. This
167 ± 17320.8± 2 1 1.2 1.4
was found to fit well the high-statistics β spectrum collected
Visible Energy (MeV)
curvesfrom the simultaneous fit to all rank’s spectra. The22/27
fit range
7

Be ν
ther ν

Rank 1, R< 450 cm
Ev/(kt d 20keV)

Rank

4

The abundance of 232 Th and 238 U and their daughtersin the LS is constrained by KamLAND data. The decay
rates of the 222 Rn- 210 Pb subchain of the 238 U series and the228
Th- 208 Pb subchain of the 232 Th series can be measured,
Fit Range
almostfree, using 214 Bi- 214 Po and 212 Bi- 212 Po
510backgroundβ-α delayed coincidences, with 94.8% and 31.9% selection
efficiencies, respectively. The inferred 238 U and 232 Th conBG subtracted
20are (5.0 ± 0.2) ×
centrations assuming secular equilibriumdata
4 (93 ± 4 nBq/m3 ) and (1.3 ± 0.1) × 10−17 g/g
10−1810g/g(59 ± 4 nBq/m3 ), respectively. Some radioactive decay chains10
are found to be out of secular equilibrium. A fit to the210
prominent
Po α peak, quenched to about 0.3 MeV visible
10in3Fig. 4, yields spatially varying activities
energyranging from0
2.4 to 4.8 mBq/m3 , depending on the rank of the analyzed
0.4 section,
0.6 this0.8
1
1.2 1.4
volume. However, as discussed in the following
backgroundcomponentisnotconsidered
in
the
fit
becauseit
VisibleEnergy(MeV)
2
10
falls below the analysis threshold. The higher-mass members
228
222
of the decay chains above
Th andRn C
are92,determinedby
PHYSICALREVIEW
055808 (2015)a spectral fit and are found to be unimportant.
the backgroundis dominateddaughters
101 1 MeV,
theBelowhighestbackgroundpartitions—those
withbyrank
7—the
210
210
210
210
of
Pb,
namely
Bi
and
Po.
Bi,
the
most
important
fit only yields an upper limit for the activity. After LS

Events/(kt d 10keV)

PhysRevC.92.055808

A. Radioactive impurities in the liquid scintillator

4

3

210

-

2

1

7

0

11

+

Evis_single [MeV]ES search R < 450 cm, lower energy+/- 500 sec
BG

Preliminary

co
n

sis
• Eth 1-MeV analysistent• BG rate: 0.0056/sec• 1000-sec expected: 5.6 evt.
• Nobs: 9 evt.

32

• Eth 0.5-MeV analysis• BG rate: 0.018/sec• 1000-sec expected: 19 evt.
• Observed: 21 evt.

1
−1000

0

1000
t - tgw [sec]23/27

Fluence Upper Limit
monochromatic energy was assumed.

24/27

Time window comparison
cm-2

ν fluence UL on the Earth (90% CL)

1017
1016

ν e LowE 1000-s

ν e HighE 1000-s

ν e LowE 20-s

1013
1010

Preliminary

Narrow window
Factor ~3 better.

107
104

•
•
•
•

(Window, Eth, Radius, 90% CL UL #)IBD:(1000 s, 1.8 MeV, 6 m, 2.4)
ES HighE: (1000 s, 3.5 MeV, 6 m, 1.8)
ES LowE: (1000 s, 0.5 MeV, 4.5 m, 11)
ES LowE: (20 s, 0.5 MeV, 5 m, 3.5)

ν e IBD 1000-s
52Min. Rad. Energy(4.5× 10 erg)

oscillation neglected

1

10

102
Eν [MeV]

25/27

Limits on all flavors (narrow window)cm-2

ν fluence UL on the Earth (90% CL)

1017
1016

ν x LowE
ν x LowE
ν e ES LowE
ν e LowE

ν x HighE
ν x HighE
ν e ES HighEν e HighE

1013

Preliminary

1010
107
104

ν e IBD
52
Min. Rad. Energy(4.5× 10 erg)

oscillation neglected

1

10

102
Eν [MeV]

26/27

Summary§ MeV-neutrinos from BNS merger: GW170817 was searchedwith KamLAND.
§ Time window for the search was modified for thermal ν.
§ No IBD was found within +/- 500 sec from tGW.
§ 1 ES candidate was found after 1 sec from GW.

o BG consistent with (500-cm-radius, 10-s-window, 1-MeV-Eth) analysis.

§ KamLANDʼs sensitivity is <1/106 of expected ν fluence.
27/27