Low Energy Background Study of the KamLAND DetectorTatjana Miletić

advisor: Dr. Charles Lane

Outline Neutrino Discovery Mass and

Oscillations KamLAND

Experiment First KamLAND

Results Low Energy

Background Study Summary

Neutrino Discovery

-1930 Wolfgang Pauli, theoretical prediction-1933 Enrico Fermi, named the particle-1953 to1959 Reines and Cowan, discovery of particle fitting the expected characteristics of neutrino, detected anti-neutrino via the inverse decay

nepνe

-1962 Danby, muon neutrino discovery-1975 tau lepton discovered by Perl, implied the existence of tau neutrino- 2001 Kodama directly observed tau neutrino

Mass and Oscillations

-Standard Model prediction(postulated that neutrinos are mass less, consistent with observation that individual

lepton flavors seemed to be conserved and total lepton number as well)

-Phenomenon of neutrino oscillations (direct tests for neutrino mass lack at present required sensitivity, the recent hints for neutrino mass are indirect,based on phenomena of neutrino oscillations)

Phenomenon of Neutrino Oscillations

- neutrinos are massive particles which behave in analogy to quarks, the states with definite mass, “mass eigenstates” , are not necessarily the partners of the charged leptons

The weak eigenstates the mass eigenstates

lare linear superpositions ofwhere coefficients i

liU ,

form the leptonic mixing matrix.

ee

,

,

(1)(1)

(2)(2)

Phenomenon of Neutrino Oscillations

Consider the time development of the mass eigenstate i

where L is the flight path and it is assumed that the laboratory momenta and energies are much larger than neutrino rest mass.If we consider propagation of a neutrino which was createdat L=0 as a weak eigenstate ,at distance L this statewill be described by

l

Thus, the neutrino of flavor l acquired components correspondingto the flavors l’. This is the consequence of coherence in the superposition of the states in equation 2.

(4)

(3)

Phenomenon of neutrino oscillations

Probability that “transition” l → l’ happens at L is

This is an oscillation function of a distance L. Neutrino oscillationexperiments are often analyzed in a simplified way by assuming only two neutrino flavor mix, e.g. e and μ. Mixing matrix is then simplified as well as oscillation probability.

cossin

sincosU

(5)

(6)

22

21

2 mmm

Phenomenon of neutrino oscillations

To test for oscillation, one can perform:

-appearance search (looking for neutrino flavor – e.i. deviations of from 0)

-disappearance search (looking for a change in flux normalization – e.i. deviation from unity)

The oscillation length is:

(7)

Numerous searches for neutrino oscillations were performed in lasttwo decades. Most of them resulted in exclusion plot, based on them certain ranges of parameters and can be excludedfrom future consideration.

2m 2sin 2

),( LP e

),( LP ee

Exclusion plot Two isolated islandson a exclusion plot ~two solutions, bothcorresponding to 2510 eVm

22 102sin (SMA)

5.02sin 2 (LMA)

Various solutions for solar neutrino problem

Phenomenon of neutrino oscillations

At present time, there are three groups of measurements thatsuggest the existence of neutrino oscillations:

-”atmospheric neutrino anomaly” (cosmic rays impinging on the N and O nuclei at the top of the earth’s atmosphere produce mostly pions which decay via the chain )

-”solar neutrino puzzle” (the Sun produces an intense flux of electron neutrinos as a byproduct of the fusion reactions, the most popular solution scenario MSW – effect which explains neutrino oscillations in matter)

- involving man-made neutrinos (first indication came from LSND experiment and finally – )

ee ,

KamLAND Experiment

Kamioka Liquid scintillator Anti-Neutrino Detector

-The largest low-energy anti-neutrino detector built so far-Located at the site of former Kamiokande experiment-High concentration of nuclear reactors at the right distance

1000 ton Liquid Scintillator

Balloon made of transparentnylon/EVOH composite film,supported by cargo net structure.

Stainless steel tank filled withparaffin oil (0.04% lighter than LS).

1325 17-inch + 554 20-inch PMT’sPhotosensitive coverage ~ 34%

3mm thick acrylic wall: Rn barrier

3.2Kton water Cherenkov outer detector 225 – 20inch PMT’s

KamLAND Experiment

Designed to detect:

- anti-neutrino interactions via inverse beta decay or electron scattering- neutrinos from the Sun- terrestrial anti-neutrinos- anti-neutrinos from the past Supernova

e

Reactor anti-neutrino detection in liquid scintillator

reaction process: inverse-β decay nepνe

dpn

distinctive two step signature

- prompt part:

- delayed part (2.2MeV)

- tagging: correlation of time, energy and position between prompt and delayed signal

e

KamLAND Experiment - Electronics

MACRO Electronics Trigger LBL Electronics

DAQ PMT’sw

avefo

rms

triggercommand

E-sum

triggercommand

Nsum

event data

run conditio

nsrun conditions

event data

MACRO Electronics

- borrowed from MACRO experiment

- 4 crates, 44 cards each each card has 4 channels

- constantly writing data into circular buffer

- trigger issuing Start and Stop commands

- depending on a type of interrupt DAQ reads out the buffer for fixed amount of time before the Stop.

First KamLAND Results

First results, published in December 2002, revealed the evidence for reactor anti-neutrino disappearance

- data obtained (March 4 to October 6, 2002)- total of 370 million events in 145.1 days of live time- ratio of the number of observed reactor anti-neutrino events to the expected in the absence of neutrino oscillations is

)(041.0)(085.0611.0exp

syststatN

NN

ected

bgobs

- MeVE e 4.3)(

- bgN is estimated number of background effects

Some photos…Some photos…

BackgroundsBackgrounds

Produced by:Produced by:- cosmic muon induced processes- cosmic muon induced processes- natural radioactivity- natural radioactivity

Two types of physics signatures interesting for KamLAND:Two types of physics signatures interesting for KamLAND:- double events (reactor anti-neutrino signature,- double events (reactor anti-neutrino signature,

supernova neutrino scattering on C)supernova neutrino scattering on C)- single events (low energy neutrino scattering on electrons,- single events (low energy neutrino scattering on electrons,

minimum energy deposition of 1MeV) minimum energy deposition of 1MeV)

Cosmic muons:Cosmic muons:- prompt neutrons from muon capture and muon spallation- prompt neutrons from muon capture and muon spallation- radioactive isotopes produced by cosmic ray activation- radioactive isotopes produced by cosmic ray activation

BackgroundsBackgrounds

Backgrounds from natural radioactivity in KamLAND Backgrounds from natural radioactivity in KamLAND derive from various sources:derive from various sources:

- decays chains of the long lived - decays chains of the long lived naturally naturally present in small amounts in rocks surrounding the detectorpresent in small amounts in rocks surrounding the detectorand materials used in detector construction;and materials used in detector construction;- radioactive impurities contained in scintillator - radioactive impurities contained in scintillator (including(including and and ), ), andand- decay of - decay of artificially added to steel during productionartificially added to steel during productionfor quality monitoring purposesfor quality monitoring purposes- decay of - decay of continuously produced in the disintegrationcontinuously produced in the disintegrationofof , radon readily diffuses into many materials and has , radon readily diffuses into many materials and has a life time of only few days it effectively act as a carrier thata life time of only few days it effectively act as a carrier thatdisperses the radioactivity through the entire detector.disperses the radioactivity through the entire detector.

Accidental coincidence makes another type of background, uncorrelatedAccidental coincidence makes another type of background, uncorrelatedbackground.background.

KThU 40232238 ,,

U238

Rn222 Pb210

Co60

Rn222

U238

KTh 40232 , Kr85

KamLAND DataKamLAND Data

ROOT currently used in all High Energy andROOT currently used in all High Energy andNuclear Physics laboratories to monitor,Nuclear Physics laboratories to monitor,to store and to analyze data.to store and to analyze data.

KamLAND data:KamLAND data:- converted to ROOT format- converted to ROOT format- processed to remove muon events so that data contain - processed to remove muon events so that data contain only low energy single eventsonly low energy single events

Typical ROOT file contains:Typical ROOT file contains:- event number information- event number information- time- time- approximate position- approximate position- PMT hits number (Nsum)- PMT hits number (Nsum)

Nsum gives the number of photoelectrons at PMTs, therefore Nsum Nsum gives the number of photoelectrons at PMTs, therefore Nsum information is proxy for energy deposition.information is proxy for energy deposition.To obtain Nsum we devide recorded waveforms to time bins and countTo obtain Nsum we devide recorded waveforms to time bins and countnumber of pulses from all waveforms in the corresponding time bin.number of pulses from all waveforms in the corresponding time bin.

NSUMNSUM

KamLAND DataKamLAND Data

Run numbers : 1335 to 1340 ~ 5 days of data takingRun numbers : 1335 to 1340 ~ 5 days of data taking

Expected Poisson distribution, since with no radiation background Expected Poisson distribution, since with no radiation background only thermionic PMT noise would form the signal coming from only thermionic PMT noise would form the signal coming from uncorrelated events. uncorrelated events.

KamLAND DataKamLAND Data

Monte Carlo simulation of Poisson Monte Carlo simulation of Poisson distribution and background withdistribution and background withenergy deposition of 30 photoelectrons. energy deposition of 30 photoelectrons.

Actual Nsum distribution.Actual Nsum distribution.

Nuclear -decay: Fermi theory

• The first weak interaction studied was the nuclear beta-decay (decay of a free or bounded neutron)

in terms of quark constituents:

• Initially this reaction was studied: Being a two-bodies decay A B+C, the electron E should have been completely determined as:

eepn

eeud

eHeH 32

31

A

eBAe m

mmmE

2

222

eepn

Ee

#

eve

nts

mn-mp-me 17 keV

epn

Ee

#

eve

nts

Not this ! But this

Nuclear -decay: Fermi theory

Probability of emission of an electron in an energy interval dE:Probability of emission of an electron in an energy interval dE:

wherewhere is the matrix element for two particle interacting: is the matrix element for two particle interacting:ifM

and wave functionsand wave functions describe the nucleus before and describe the nucleus before and after decay respectively.after decay respectively. is an extremely short range is an extremely short rangepotential so it can be replaced with potential so it can be replaced with . . and and areareintroduced for convenience of measuring energies and momenta.introduced for convenience of measuring energies and momenta.

fi ,)( ba rrV

)( ba rr

ee pE , - energy and momentum of an electron- energy and momentum of an electron

E - neutrino energy, W – total disintegration energy - neutrino energy, W – total disintegration energy ),( ZF - Coulomb interaction between nucleus and electrons- Coulomb interaction between nucleus and electrons

KamLAND DataKamLAND Data

Histogram fitted using probabilityHistogram fitted using probabilitydistribution fordistribution for , form of beta, form of betaspectrum or Kurie plot.spectrum or Kurie plot.Z=6Z=6

C14

KeV15610

Histogram fitted using probabilityHistogram fitted using probabilitydistribution for distribution for andand , form , form of beta spectrum or Kurie plot.of beta spectrum or Kurie plot.Z=36Z=36

Kr85

KeV6700

C14

C14 Kr85

SummarySummary

- Improvement of detector necessary for “Solar Neutrino Phase”- Improvement of detector necessary for “Solar Neutrino Phase”

- The calibration of detector using low energy sources needed- The calibration of detector using low energy sources needed

- Understanding of energy scale and origin of background- Understanding of energy scale and origin of background

- Development of software, analysis tools- Development of software, analysis tools

- Work in progress…- Work in progress…

ReferencesReferences

1.1. Proposal for US Participation in KamLANDProposal for US Participation in KamLAND2.2. Measurement of Electron Anti-Neutrino Oscillations with a LargeMeasurement of Electron Anti-Neutrino Oscillations with a LargeLiquid Scintillator Detector, KamLAND, Osamu Tajima, Department ofLiquid Scintillator Detector, KamLAND, Osamu Tajima, Department ofPhysics, Tohoku University, Sendai, Japan, March 2003Physics, Tohoku University, Sendai, Japan, March 20033.3. Nuclei and Particles, Emilio Serge, 1977, W.A.Benjamin, Inc., Nuclei and Particles, Emilio Serge, 1977, W.A.Benjamin, Inc., Reading, MassachusettsReading, Massachusetts4.4. Reactor-based Neutrino Oscillation Experiments, Carlo Bemporad,Reactor-based Neutrino Oscillation Experiments, Carlo Bemporad,Giorgio Gratta, Petr Vogel, Reviews of Modern Physics, volume 74,Giorgio Gratta, Petr Vogel, Reviews of Modern Physics, volume 74,April 2002April 20025. Readout Issues for the New Waveform Digitizer, Edward Kearns,5. Readout Issues for the New Waveform Digitizer, Edward Kearns,Department of Physics, Boston University, February 20, 1994Department of Physics, Boston University, February 20, 19946.6. First Results from KamLAND: Evidence for Reactor Anti-NeutrinoFirst Results from KamLAND: Evidence for Reactor Anti-NeutrinoDisappearance, Phys.Rev.Lett. 90, 021802 (2003)Disappearance, Phys.Rev.Lett. 90, 021802 (2003)7. Discovery of the Neutrino, editors; C.E.Lane and R.I.Steinberg,7. Discovery of the Neutrino, editors; C.E.Lane and R.I.Steinberg,Franklin Institute, Philadelphia, WorldScientific publishing Co, 1993Franklin Institute, Philadelphia, WorldScientific publishing Co, 1993