Status and Prospects of Borexino Status and Prospects of Borexino

G. RanucciG. Ranucci

NOW 2006NOW 2006Conca SpecchiullaConca Specchiulla

September 11, September 11, 20062006

Summary of the talkDescription of the architecture of the detectorStatus of the installations and operationsNear future fill and operation schedulePhysics with BorexinoCTF in the framework of the Borexino projectConclusions

Borexino is a massive calorimetric

liquid scintillation detector aimed at

the real time detection of the 7Be solar

neutrino flux

Main challenge: radiopurity !

Borexino Collaboration

-Virginia Tech (USA)

- College de France (France)

- Princeton Univeristy (USA)

- Technical University Munich (Germany)

- JINR Dubna (Russia)

- Kurchatov Institute Moscow (Russia)

- MPI Heidelberg (Germany)

- Jagellonian University Cracow (Poland)

- INFN – Milano (Italy)

- INFN – Genova (Italy)

- INFN – Perugia (Italy)

- INFN – LNGS (Italy)

Stainless steel sphere (d = 13.7 m)2200 inner phototubes - 1800 equipped with light concentratorsOuter Muon veto: 210 outer phototubes plus diffusive tyvek panelsExternal buffer of ultra-pure waterWater Tank (h and d = 18 m )Calibrations equipmentsElectronics and DAQ

Schematic view of the Borexino experimentBorexino features a shell structure - Components of the detector (from center):Scintillator: PC + PPO (1.5 g/l) (300 tons, 100 tons fiducial mass)Nylon inner vessel (d = 8.5 m) - Nylon outer vesselBuffer liquid: PC + DMP (1040 ton)

Purification and other ancillary plants (I)

Purification systems

Purification skids

Distillation

Water extraction

Nitrogen stripping

Module 0

Silica gel column

CTF purification skid

Water extraction of the concentrated PPO solution

Purification and other ancillary plants (II)

Storage vessels and associated pumping stations

Nitrogen and synthetic air plants

Regular nitrogen

Purification equipment →high purity nitrogen

LAK Nitrogen (low content argon and krypton nitrogen)

Synthetic air line (used for vessel inflation)

PPO plant – preparation of the master solution (PPO concentrated solution)

DMP plan – buffer quencher

Interconnection system – path of the scintillator through the various plants

Exhaust system – to reduce the PC vapors content in the nitrogen

PC unloading station

Purification and ancillary plants (III)

Filling Stations – for the PC and water fill of the detector

Water purification plant - to purify the raw water

Borexino water loop – to feed and re-circulate the water in the Water Tank

Emergency systems

Blow down

Fire extinguishing equipments

Centralized control system

Clean rooms

Some used in the installation phase of the detector

That on top of the Water Tank hosts part of the filling stations – access to the detector for calibration

Calibrations

A variety of calibration and monitoring systems are planned

Laser pulses distributed to all PMT’s with a fiber optics splitting system

•Timing calibration

•Gain adjustment via detection of the single photoelectron peak

External sources (Th) located in the SSS close to the light cones

•Check of the stability in time of the overall detector response

Internal sources inside the scintillator

•Position calibration

•Energy calibration

discrimination

Calibrations

CCD Cameras with capability to locate precisely (±2 cm) objects inside the detector (translates into a ≤ 2% uncertainty in the FV definition)

Laser beams with different wavelengths through the buffer and laser excitation of the scintillator

•Stability monitoring of the optical properties

Blue LED’s + fibers for the outer muon veto detector

Calibration of the overall detector response via a sub-MeV -source (51Cr)

Water Tank (1999)

Stainless Steel Sphere (2000)

Phototubes in the SSS (2001)

Vessel in SSS prior to inflation as viewed from CCD cameras (2004)

SSS – PMT’s – Vessel inflated as viewed from CCD cameras

Last phototubes on the bottom of the sphere and on the 3 m doorLast phototubes on the bottom of the sphere and on the 3 m door

Closing of the big door of the sphere (June 2004)

Muon veto: tyvek and phototubes on the external surface of the sphere

Tyvek on the lateral wall of the Water Tank

Tyvek under the dome of the Water Tank

Electronics racks

Status of the activity as September 2006

Detector installation – essentially completed (SSS closed in June 2004, only few piece of hardware missed in the Water Tank)

Purification and fluid handling systems – Installation completed, cleaning and commissioning almost completed (in 2005 and beginning of 2006, after substantial alleviation of the underground operation constraints, but water discharge not yet allowed; only some final cleaning missed)

Calibration hardware – CCD cameras and external source insertion system completed, hardware to deploy the internal sources to be finalized

Filling – Water Fill of the Sphere in progress (water discharge still by truck, full operation capability via normal discharge expected in few weeks)

CNGS – data taking during the August run accomplished successfully

Status of Borexino during the August CNGS runStatus of Borexino during the August CNGS run

The filling of the Borexino Stainless Steel Sphere (SSS) has started on August 1°, 2006

During this run, about 55 t of 55 t of waterwater were present

The height of the water from the bottom of the SSS is about 1.8 m

Active surface ~ 10.5 m2

Beam direction

Current acceptance and target massCurrent acceptance and target mass

Borexino CTF Opera

Hall-C Side view

Hall-C Top view

Water level heigth: 1.8 m Target Mass: 55 t (not relevant and not considered in this run)

L. Perasso

Preliminary evidence for signal (1)Preliminary evidence for signal (1)

ms

GPS clock time difference betweenBX event and nearest previous CNGS time stamp

Binning: 50 s

Preliminary evidence for signal (2)Preliminary evidence for signal (2)

GPS clock time difference betweenBX event and nearest previous CNGS time stamp

Binning: 50 sZoom of 0-100 ms interval

ms

Preliminary evidence for signal (3)Preliminary evidence for signal (3)5 events at 2.4 ms delay(binning 50 s)

No other bin but one has more than 1 except out of 3200 events in 8000 bins

Expected CNGS events: 5Expected cosmic muons: ~ 2000

Probability of bck fluctuation: < 2. 10-5

ms

Near future perspectivesFilling Operations

Sphere full of water by the middle of November 2006 (expectation is to complete the fill with the full discharge capability)

SSS and Nylon Vessel PC fill to be started by the middle of December 2006. The PC will be delivered from the production plant in Sardinia to Gran Sasso via special transportation trucks, and then passed through the distillation unit prior to be mixed with the PPO and inserted in the detector. Detector full of PC by May 2007

Water Tank water fill to be carried out in parallel with the first phase of the PC fill from the middle of December. Completed in two months

Data Taking phases

CNGS beam monitor – throughout the October 2006 run with about all the water in the SSS (and then with PC for future beam on periods)

PC runs – Preliminary runs since the beginning of the fill (radiopurity check). Run in full configuration: from middle of 2007

Meanwhile source calibrations in various steps

e Lie Be 77

Monocromatic ! E=862 keV

SSM=4.8x109 /sec/cm2

“ window” (0.25-0.8 MeV)

xx ee

=10-44 cm2

e

x

expected rate (LMA hypothesis) is 35 counts/day in the neutrino window

Physics goals for BorexinoPhysics goals for Borexino

Measure 7Be solar neutrinos (0.25-0.8 MeV) Measured vs MSW-LMA predicted event rateTime variation of solar signal in the sub-MeV range

Study CNO and pep neutrinos (0.8-1.3 MeV) (rejection of 11C cosmogenic background – proved in CTF hep-ex/0601035)

Neutrinos from the Earth Neutrinos form supernovae Neutrino magnetic moment (also in conjuction with

the 51Cr source calibration)

Radiopurity constraintsRadiopurity constraints To lower the threshold down to 250 keV, it is mandatory to reach very

high radiopurity levels in the active part of the detector ;

This translates into the following requirements on the most critical contaminants (238U , 232Th , 40K, 210Po, 210Pb, 39Ar, 85Kr) :

Intrinsic contamination of the scintillator for what concerns isotopes belonging to the U and Th chain 10-16 g/g; Intrinsic contamination of the scintillator for what

concerns 40K 10-14 g/g;

Contamination of the buffer liquid in U and Th chain 10-14 g/g;

Contamination of the nylon vessel for what concerns the U and Th chain 10-12 g/g;

Constraints on N2 used to sparge scintillator: 0.14 ppt of Kr in N2 (0.2 Bq 85Kr/m3 N2) Constraints on N2 used to sparge scintillator:

0.36 ppm of Ar in N2 (0.5 Bq 39Ar/m3 N2)

Each of these points required careful selection and clean handling of materials, + implementation of purification techniques

Contamination of the external water in U and Th chain 10-10 g/g;

14C /12C 10-18 in the scintillator

Counting Test Facility (CTF)Counting Test Facility (CTF)

• 100 PMTs

• 4 tons of scintillator

• 4.5m thickness of water shield

• Muon-veto detector

CTF high mass and very low levels of background contamination make it a unique detector to search for rare or forbidden processes with high sensitivity

CTF campaigns

1. CTF1: 95-97

2. CTF2: 2000 (pxe)

3. CTF3: 2001 still ongoing

• CTF is a prototype of BX. Its main goal was to verify the capability to reach the very low-levels of contamination needed for Borexino

CTF Radiopurity results

238U = (3.5 ± 1.3) 10-16 g/g

232Th = (4.4 ± 1.5) 10-16 g/g

14C/12C = (1.85 ± 0.13) 10-18

Breakthrough results in the field of ultra-low radioactive contaminations, opening the path toward the real time solar neutrino detection in the sub-MeV region

Furthermore, realization of the importance of the background induced by 85Kr and 210Pb – 210Po and demonstration of capability to cope with them through a suitable combination of water extraction, distillation and silica gel column purification techniques

Some physics resultsSome physics results

Limit on the neutrino magnetic moment at the level of 5.5x10-10 B

[Borexino coll., Phys. Lett. B 563 (2003)] 37

Limit on the electron stability [Borexino coll., Phys. Lett. B 525 (2002)]

Limits on nucleon decay into invisible channels [Borexino coll., Phys. Lett. B 563 (2003)] 23

Limit on the violation of the Pauli exclusion principle [Borexino coll., Eur.Phys. J. C37 (2004) 421]

Limit on antiuneutrino flux from the Sun (threshold 1.8 MeV) <1.1105 cm-2s-1

annie e26106.4

ConclusionsConclusions

-The installation of the detector is completed

-The purification and ancillary plants are essentiall all ready, cleaned and commissioned

-The first phase of the fill (water fill) is in progress - expected to be completed by beginning of November

-Final PC fill to be started in December, to be completed by May

-Overall instrument working fine as proved by the data taking during the August CNGS run

- From next Spring/Summer data taking with the From next Spring/Summer data taking with the detector in the final configurationdetector in the final configuration