Coincidence analysis in ANTARES: Potassium-40 and muons Brief overview of ANTARES experiment ...

Coincidence analysis in ANTARES:Potassium-40 and muons

Brief overview of ANTARES experiment Potassium-40 calibration technique Adjacent floor coincidences as very basic atmospheric muon signal

ITEP winter schoolFeb 12, 2008

Dmitry Zaborov(ITEP, Moscow, Russia)

Feb 12, 2008 D. Zaborov. Coincidence analysis in ANTARES 2

Detection principle

č

43°Sea floor

p

104

atm

p, 107

at

m

Reconstruction of trajectory (~ ) from timing and position of PMT hits

interaction

Cherenkov light from

3D PMTarray

1-100 cosm

effective area ~ 0.1 km2 in TeV rangeangular resolution ~ 0.3º at 10 TeVHadronic showers

from CC/NC interactions can be detected as well


Detector layout

~70 m

12 lines (900 PMTs) 25 storeys / line 3 PMTs/storey

350 m

100 m

14.5 m

Junctionbox

Readout cables

40 km toshoreHorizontal layout

Sea bed ~ -2500 m

a storey


Current status

L11

L9

L12

L7

L8

L6

L4

L2

L3

L5

L1

IL07

seismometer

100 m

N

Junction box

Submarinecable

to shore

42°50’ N

6°10’E

10 detector lines +

instrumentation line

operational (since December 07)

(Feb. 2008)

2 more lines coming soon

~ 2 muons/sec

~ 5 neutrino/day (atmospheric) L10

* Cable path is shown only indicatively


Basic detection and calibration elements

Hydrophone:acoustic positioning

Optical Module:10” PMT in 17” glass sphere

photon detection

Local Control Module(in Ti container):Front-end ASIC, Clock, DAQ/SC,

compass/roll/pitch

Optical Beaconwith blue LEDs:timing calibration


In situ calibration with Potassium-40

40K

40Ca

e- ( decay)

Cherenkov

Gaussian peak on coincidence plot

Peak offset

Rate of correlated coincidences

High precision (~5%) monitoring of OM

efficiencies

time calibration confirmed

15 Hz

MC prediction 13+/-4 Hz

(“NIM” angular acceptance)Mean ≈ 0

RMS 0.7 nsNo dependence on bioluminescent activity has been observed - this confirms the single photon character of bioluminescent emission


Example: calibration of Line 8Three OM sensitivity factors si can be extracted using 3 equations

rateij = k * si * sj

factor k gives absolute scale;k can be determined from Monte-Carlo (or, in opposite, used to constrain parameters of Monte-Carlo)

OM-OM time offsets determined using K-40 (basically single photoelectrons)w.r.t Dark room calibration (high amplitude laser pulse)

* No charge calibration used* No walk correction included

Unofficial technical plot


I,j=1,2,3


Time evolution (example)

Time delays seem stable (within our accuracy)

Gradual decrease is probably due to PMT gain drift

Steep changes are threshold tunings



K40 runs are taken once a week

K40 trigger can run in parallel with other triggers (e.g. GRB trigger or

directional triggers) and can be even used for physics analysis as is


Time evolution of average K-40 coincidence rate

start at 12 Hz “degradation”

tuning 2

One year of “degradation” could be fully compensated by the tuning

tuning 2-> 15.5 Hz

* Other Lines show similar behavior

tuning 1



Delay between adjacent floors (theory)

Δt = L / c ≈ 50 ns Δt ~ L n / c ~ 70 ns

L

Δt ~ 0

But light hits back of the OM

≈ fixed number for exactly vertical muons a wide distribution in general

from

to

The most basic signal of physics events in ANTARES

Delay between storeys No systematic

errors from trigger or

reconstruction algorithms

No background


Adjacent floor coincidences: measurementIntegral under the peak ~ muon flux

Shape is sensitive to angular acceptance of optical modules and angular distribution of muon flux

The effect of muon flux reduction with depth is directly (!) measured

Low energy threshold(compared to full reconstruction)

The analysis can be repeated for every detector storey separately

This plot is preliminaryActual comparison of peak amplitude with Monte Carlo will be made after OM angular acceptance issues are fixed, OM efficiency is well known and all dead time corrections applied


Summary

• A calibration technique using Cherenkov light from Potassium-40 decays in sea water has been developed– Sensitivity of optical modules is now controlled using K-40– K-40 is also a useful tool for time calibration

• A simple but powerful technique for atmospheric muon measurement is developed based on the idea of adjacent floor coincidences– First results allowed to reject one of the models of OM angular

acceptance– Depth dependence and absolute normalization of atmospheric

muon flux can be extracted using this new approach– Possibility to reject certain hadronic interaction models or (less

likely) primary flux models is being investigated– Promising prospects to use adjacent floor coincidences in the

trigger

Coincidence analysis in ANTARES: Potassium-40 and muons Brief overview of ANTARES experiment ...

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