First Result of Borexino Experiment andKamLAND Solar Phase
Sei Yoshida
Reserch Center for Neutrino Science, Tohoku Univ.

for the KamLAND Collaboration2007 November 2ndNeutrino Meeting @ ICRR

1Solar neutrino physics
Two types of solar neutrino experiments
Radiochemical experiments (low energy threshold, integrated flux)
Water experiments (real-time information, higher energy threshold ~ 5 MeV: Only~10-4 of total flux)

νBorexino and KamLAND solar phase: 1st real-time experiment at lowenergies solar neutrinoe-KamLAND

νNeutrino Meeting @ ICRRBorexino
2007 November 2nd2

Solar neutrino spectrum
Current neutrino date is consistent with MSW/LMA solution, which predicts
transition from matter enhanced oscillations at 8B energy to vacuum oscillation atlow energy.
The survival probability increases from ~0.33 at high energy to up to ~0.6 at lowenergy.

Vacuumoscillations

Transition regionΔm2 ≈ 8·10-5
eV2
27° < θ < 38°

Mattereffects

Measurement of 7Be solar neutrino flux will test the predicted increase in the νesurvival probability.
Neutrino Meeting @ ICRR

2007 November 2nd3

Prediction of solar ν flux
Heavy elements abundanceStrong disagreement with helioseismological measurement

Nuclear reaction cross sections (by LUNA)
3He(α, γ)7Be, 14N(p, γ)15O

The prediction of 7Be flux depends both on the solar model and the crosssection of 3He(α, γ)7Be reaction. Å test of standard solar model
Neutrino Meeting @ ICRR

2007 November 2nd4

Solar neutrino status
Borexino succeeded firstly 7Be observation.
KamLAND plans to measure 7Be and pep/CNO ν(purification work in progress)
arXiv:0708.225lv2 [astro-ph]Neutrino Meeting @ ICRR

2007 November 2nd5

First Result of Borexino
Talk based onarXiv:0708.225lv2 [astro-ph]talk presented on TAUP2007@sendai

2007 November 2nd

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6

Borexino Detector
Borexino is located on Gran Sasso Underground Lab. (4000 m water equivalent).
278 tons of LS contained in nylon
vessel of 4.25 m radius (PC + PPO)
890 tons of ultra-pure buffer (PC +DMP quencher) contained in stainlesssteel sphere of 6.75 m radius
External nylon vessel against Rn
emanated from PMTs and stainless2214 PMTs of 8 inch (1843 with opticalconcentrater)
2100 tons of ultra-pure water containedin a cylindrical dome
200 PMTs for detecting cherenkov lightemitted by OD water

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2007 November 2nd7

Observed spectrum in Borexino
210Po (only, not in eq. with 210Pb!)

14C

85Kr+7Be ν
11Cμ cut
μ are not relavant BG for 7Be

Fiducial cut
External background is the dominant background component in NW, except in the210Po peak region

spallation cut ( within 2 msec after μ )214Bi-Po and Rn daughters removal
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2007 November 2nd8

Energy calibration and stability
Borexino group have not calibrated with inserted sources (yet)Planned for the near future

So far, energy calibration determined from 14C end point spectrum
Energy stability and resolution monitored with 210Po α peak
Difficult to obtain a very precise calibration because:
14C intrinsic spectrum and electron quenching factor poorly known

Light yield determined from 14C fit

Light yield monitored with210Po peak position
190
188

Po peak (nhits)

186
184
182
180
178
176
174
172
170
28-AprNeutrino Meeting @ ICRR

18-May7-Jun

27-Jun2007 November 2nd17-Jul

6-Aug

9

Position reconstruction
Position reconstruction algorythms (we have 4 codes right now)time of flight fit to hit time distribution
developed with MC, tested and validated in CTF
cross checked and tuned in Borexino with 214Bi-214Po events and 14C eventsz vs Rc scatter plot

Resolution
214Bi-214Po (~800 KeV)

14±2 cm
14C(~100 KeV):
41±4 cm

Rc = x 2 + y 2
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2007 November 2nd10

Fiducial volume cut
External background is large at the periphery of the IV
γ from materials that penetrate the buffer
They are removed by a fiducial volume cut

214Bi-214Po

R < 3.276 m (100 t nominal mass)
Another volumetric cut, z < 1.8 m, was done to remove
some Rn events caused by initial scintillator termalstabilization (87.9 t)

238U: < 2. 10-17 g/g

Radial distribution

z vs Rc scatter plot

R2gauss

FV

R = x2 + y2 + z 2

Rc = x 2 + y 2

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2007 November 2nd11

7Be signal: fit without α/β subtraction
Strategy:
Fit the shoulder region only
Use between 14C end point and 210Popeak to limit 85Kr content
pep neutrinos fixed at SSM-LMA value

210Po peak not included in this fit

Fit components:
7Be ν85Kr

CNO+210Bi combined
very similar in this limited energy
regionLight yield left free

7Be ν

CNO + 210Bi85Kr

These bins used to limit 85Kr content in fit

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2007 November 2nd12

7Be signal: fit α subtraction of 210Po peak
The large 210Po background is subtracted
in the following way:

2 gaussians fitαFor each energy bin, a fit to the α/β Gatti
variable is done with two gaussians
From the fit result, the number of α
particles in that bin is determined
This number is subtracted
The resulting spectrum is fitted in theenergy range between 270 and 800 KeV

βA small 210Po residual background isallowed in the fit
Results are totally consistent with thoseobtained without the subtraction

The two analysis yield fully compatible results
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2007 November 2nd13

Comments on errors
Statistical:
Right now, it includes combined the effect of statistics itself, the lack ofknowledge of 85Kr content, and the lack of a precise energy calibration
These components are left free in the final fit, and contribute to the statistical error

Systematic:
Mostly due to fiducial volume determination
With 45 days of data taking, and without an internal source calibration, we
estimate an upper limit of 25% for this error
Can be much improved even without internal calibration with more statistics and better
understanding of the detector response

Neutrino Meeting @ ICRR

2007 November 2nd14

Conclusions
Borexino has performed the first real time detection of 7Be solar neutrinos
A clear 7Be neutrino signal is visible after a few cuts
7Be ν Rate:

47 ± 7 (stat) ± 12 (sys) counts/day/100t

The central value is well in agreement with MSW/LMA.
Significant improvements are expected shortly
Increase of Statistics ÅEnergy calibration
Off-line 85Kr measurement by mass spectroscopy

Neutrino Meeting @ ICRR

2007 November 2nd15

KamLAND solar phase2007 November 2ndNeutrino Meeting @ ICRR

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KamLAND Detector
Kamiokamine overburden : 2700m.w.e.
Muon rate : 0.34Hz
1000 tons of Liquid Scintillator

1 kt Liquid Scintillator

PMTs

KamLANDDetector

Mineral Oil : Buffer against external BG
1979 PMTs(17” 1325 + 20” 554)
Photocathod coverage : 34%
Outer water Cherenkov detector for muon
vetoPurification Work in Progress

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2007 November 2nd17

Internal Background of KamLAND
Single Energy Spectrum Observed in KamLAND Before Purification

Fiducial R < 4 m

Main sources of background in the range of 7Be neutrino
210Pb(Æ 210Bi Æ 210Po ) , 40K
Í by distillation
85KrÍ by N2 purging
pep/CNO neutrino ; 11CÍ by tagging neutron

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2007 November 2nd18

Required Reduction by Purification

T1/2Activities(Before purif.)

Purification
Goal

RequiredReduction

210Pb

22.3 y40 mBq/m3

1 μBq/m3

10-4 ~ 10-540K

109 y2・10-16 g/g

10 -18 g/g

10-2

238U

109 y

3・10-18 g/g

10 -18 g/g

OK232Th

1010 y5・10-17 g/g

10 -16 g/g

OK85Kr11 y

400 mBq/m3

1 μBq/m3

10-5 ~ 10-6

222Rn

3.8 d

< 1mBq/m3---

Neutrino Meeting @ ICRR

2007 November 2nd19R&D Study for Distillation
Achievement
Test Apparatus @ Tohoku Univ.

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ImpurityReduction
210Pb~7×10-5 (for 212Pb)
40K< 4×10-285Kr< 1×10-5 (for natKr)
222Rn~ 6×10-4
Almost achieved required level2007 November 2nd20

Expected Spectrum after Purification
210Pb :7.7×10-5
40K:3.8×10-2
85Kr :1.0×10-6
39Ar :1.0×10-6

11C

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2007 November 2nd21

New Purification System
2002~ 2006
R&D study with small and middle size test benchSummer in 2006 ~Construction
Winter in 2006 ~Test operation to tune up parameters
Spring in 2007 ~Online purification of KamLAND LS
Suspended on August 2007

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2007 November 2nd22

Concept of New Purification System
Distillation against metals and ionsN2 purge against Kr, Ar, and Rn.
pure N2 gas

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2007 November 2nd

N2 Generator

23

Distillation System

Dodecane(NP) isfinally.
secondly.
LiquidPseudocumene(PCPPOLS
Purging
is mixed(blendedisscintillator(LSdistilledby pureNdistilled)is)withdistilled
is feddistilledinto
firstly
small
PC,NP,buffer
andtank
PPO.
(2m3)from KamLAND.
2) gasOperatingpressure~2kPa.
Operatingpressurepressure~2kPa.
~0.6
40Density
kPa
kPa.
Different
Temperatureboilingsenserpoint
andmeter
B
point
~ 60
100
BoilingNoilingpoint
ratemixture
~
190
30℃
~℃℃
Nm3/h by pre-small tank.
PCand NP
is35adjusted
2 flow
Restat thethebottomofPCNP
tower
Dodecane+
PPO(little“Gaswith– Liq. PPO
Mixer”wt%,, andÆ“ÆGas-Liqinto. Separator” tank. concentrated)
PPO
isofmixed~ 10thenfed
mixtureRestSeries
atbottomofPC
towertowerÆDodecane
Exhaust+ PPO
Æ send to PPO concentrator (~140℃ under 2kPa), NP is evaporated back to NPÆsend to next tower
tower.
Neutrino Meeting @ ICRR

2007 November 2nd29

N2 Generator

Newly developed/constructed N2 generator
Supply air : Rn less air from outside of mineN2 supply capacity : 40 Nm3/h
Emergency 5 Nm3/h

PurityAr 0.02 ~ 0.03ppm (measured)Kr ~10-15 (not measured yet)
222Rn ~ 5μBq/m3 (measured at purif. Area)
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2007 November 2nd30

Status during 1st Purificationz LS purification rate: F=0.9t/h
z Parameters were well controlled .

Parameter

Pressure [kPa]

Temperature [C]PC tower

2.00 (Max-min: 0.08%)

62.4 (Max-min: 3.1%)

NP tower

2.00(Max-min: 0.17%)

96.9(Max-min: 0.85%)

PPO tower

0.60(Max-min: 0.48%)

174.8(Max-min: 0.69%)

Purge tower

40.0(Max-min: 0.00%)

29.0+3.2-2.8 (Tower A)
29.5+2.9-2.5 (Tower B)(F=30Nm3/h)
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2007 November 2nd31

1st Purification PeriodTotal 1699m3 of LS was purified till Aug. 1st, 2007.
Purified Volume / KamLAND volume = 1.4
Reactor and geo neutrino observation ware continuing .

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2007 November 2nd32

Monitoring Quality
Background Reduction
Reduction factors for 210Pb and 40K were monitored by KamLAND
The data were continuously taken during purification.

Rn concentration in purified LS ( Å less than 10 mBq/m3 ; OK)
Delayed coincidence of Bi-Po Æ miniLAND
Electrostatic collection method after trapping

Reduction factor of 85Kr
Cold trap + RGA

Optical propertyAttenuation length after distillation
Light output
LS density
PPO concentration
GCNeutrino Meeting @ ICRR

2007 November 2nd33

Status during 1st Purification
222Rnmeasurement →OK (<10mBq/m3)

miniLANDElectro static collection method
Nat.Krmeasurement

Cold trap + RGA

Light yield and attenuation length of LS
222Rn and 85Kr are counted with KamLAND

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2007 November 2nd34

Status during the 1st purification
Vertex distribution (Jun. 1)(0.45 MeV < E < 0.70 MeV)

Preliminary

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2007 November 2nd35

Status during the 1st purification
Vertex distribution (Aug. 1-17)(0.45 MeV < E < 0.70 MeV)Lighter LS was installed.
Δρ ~ 0.03%
Last 173m3
14.4% of KamLAND(Z>3.4m)

Succeeded to keep LS boundary.

Preliminary

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2007 November 2nd36

Lower partz [m]Status after purification

x2+y2 [m2]Preliminary
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2007 November 2nd37

Status after purificationz [m]Upper partx2+y2 [m2]Preliminary
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2007 November 2nd38

Status after the 1st purification (cont.)
210Bi

210Po

85Kr

39Ar

40K

232Th

Before

34.9

39.5

421.3

108.0

18.4

1.0(0.1)

mBq/m3

(0.5)

(0.7)

(2.2)

(2.9)

(0.5)

μBq/m3After

2.5 (0.1)
7.1(0.1)

8.8(0.1)
15.1(1.9)

4.5(0.3)
111.3(0.2)

6.4(0.3)
100.7(0.3)< 3.7

1.2(2.3)

mBq/m3Ratio[%]

7.2(0.3)
20.3(0.4)

20.3(0.5)
38.2(4.9)

1.07(0.08)
26.4(0.2)

5.9(0.4)
93.2(2.5)

90%CL

μBq/m3<20%

Need morestatistics.

After/Before

Red figure: Upper region (Z>4m)
Blue figure: Lower region (Z<3m)

The activities are still high for 7Be and pep/CNO ν, but 210Po reduction helps
reactor and geo ν measurement a lot because of less 13C(α, n) background.
Neutrino Meeting @ ICRR

2007 November 2nd39

2nd purification campaign
We stopped our 1st purification activities .
Old LS

Blasting in Kamioka mine by next spring

We are going to upgrade our apparatus .
13℃

To prevent mixing Æ install cooling system
more careful distillation ; for small ΔΤ, Δρ, ……

And we start 2nd purification campaign after blasting.
10℃
Purified LS

temperature controller(~ 25℃ Æ ~ 10℃)

Neutrino Meeting @ ICRR

2007 November 2nd40

For pep/CNO neutrino measurement
pep/CNO ν are far below
11C background, even if
purification will be
successfully done.
New electronics is being
developed.

Muon Spallation Backgrounddead time free electronics
for tagging neutron after μ

Point-like veto (spherical cut) around 2.2 MeV γ

Triple coincidence events
Cosmic μ
Neutron (Capture time ~210μsec)
11C(Lifetime=29.4min.)μ + 12C Æ μ + 11C + n
11B + e+ + νen captureγ (2.2 MeV)

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2007 November 2nd41

Energy spectra after 11C rejection

Prototype was tested.

Expected CNO ν+ pep ν flux error ~ 6% (Stat. error)
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2007 November 2nd42