Online Reconstruction used in the Antares-Tarot alert system

Jürgen Brunner

•The online reconstruction•concept•Performance

•Neutrino doublets and high energy events•DAQ data flow and implementation of alert system

Reconstruction conceptReconstruction concept

1.1. Select “hot spots” at each detector Select “hot spots” at each detector string string should correspond to point of closest should correspond to point of closest approach of muon track and detector approach of muon track and detector lineline

2. Add hits from neighboring floors in narrow 2. Add hits from neighboring floors in narrow time windowtime window

3. Perform minimization of time/distance/amplitude 3. Perform minimization of time/distance/amplitude related function with all selected hit using a related function with all selected hit using a simplified geometry simplified geometry obtain track parameters obtain track parameters

Purity of neutrino selectionPurity of neutrino selection

• Plot Plot 2 2 for all upward for all upward going tracks going tracks clear clear double structure double structure visiblevisible

• Simple Simple 2 2 cut allows cut allows to choose high purity to choose high purity samplesample

• Good coverage of full Good coverage of full zenith angular rangezenith angular range

Angular resolutionAngular resolution

• Mirror solution in Mirror solution in azimuth do not azimuth do not permit good permit good pointing accuracy if pointing accuracy if fit is done on only fit is done on only two linestwo lines

• Minimum 3-line fit Minimum 3-line fit requiredrequired

• Brightest (HE) Brightest (HE) events can be as events can be as good as 0.5good as 0.5ºº

Atmospheric Neutrinos / MuonsMinimum 3-lines in reco

1 degreeMedian Angular resolution

Avoid explosion of alert Avoid explosion of alert ratesrates

• Example: Example: – sparking OMsparking OM

• Handful cases seenHandful cases seen• Monitored via trigger Monitored via trigger

rate of pure triggerrate of pure trigger• Typical rate 5HzTypical rate 5Hz• Alert sending veto: Alert sending veto:

– ~ 20 Hz ~ 20 Hz

• Online reco Online reco distinguishes between distinguishes between tracks and “Bright tracks and “Bright points”points”

Doublet search

Select 2 events coming from the same direction in a time windows of 15 min.

t0

t0 + δt

t0

At the end, we want to send the alert position with an error box of ~1°

→ angular resolution of the 2 events is around 1.5°

→ maximum angular distance between the 2 events is around 3°

Doublet search

Estimation of background rate.

212 22 atmatm RtR

2 events coincidence rate:

1atm yrR 300

1

ΔΩ = 3° x 3°Δt = 15 min

1atm yrR 0.007

2

Reconstruction on art least 3 lines

More than 3-sigma effect in 1 year !Not sufficient to obtain acceptable number of fake alerts

Selection of High Energy Neutrinos• Events from multi-line reconstruction are shown here• Use only basic parameters no sophisticated energy fit

– Number of storeys used in fit– Total amplitude of hits used in fit

• Exponential fall-off• Allows smooth selection of cut values to adjust to a

desired fake-alert rate of 1-2 alerts per months

Number of storeys used in fit

Total amplitude of hits used in fit

Candidates for ToOCandidates for ToO

Selection of HE events

• MC sample of selected events

• Median neutrino energy: 4 TeV

• Angular resolution : 0.75 degrees

• Several alerts already sent

• Some images taken

Implementation

BBalert runs in shore station

- connects into data stream after data filter but before writing to disk

- Turns in infinite loop (start-stop controlled by AlertControl)

- Needs less than 10msec to process one event

All data

DataFilter

Data writer

BBalert

ligier

Trigger Trigger Trigger

time

Ethernet switch

off-shore

on shore

ARS ARS ARS ARS ARS ARS

Data flow to onshore farm

Trigger Trigger Trigger

time

Ethernet switch

off-shore

on shore

ARS ARS ARS ARS ARS ARS

Data flow to onshore farm

Trigger Trigger Trigger

time

Ethernet switch

off-shore

on shore

ARS ARS ARS ARS ARS ARS

Data flow to onshore farm

Delay of alert sendingDelay of alert sending

• Time slices of 100msec are treated by Time slices of 100msec are treated by each trigger node (unreducable delay)each trigger node (unreducable delay)

• Online reconstructions gets data from Online reconstructions gets data from shared memory of data filter farm output shared memory of data filter farm output streamstream

• 10msec CPU to process one event10msec CPU to process one event• Up to 100Hz output rate data processed in Up to 100Hz output rate data processed in

real time on a single computerreal time on a single computer• ~1000 TimeSlices are buffered in each ~1000 TimeSlices are buffered in each

trigger nodetrigger node– Useful for excternal alerts (GRBs)Useful for excternal alerts (GRBs)– Induces for ToO an avoidable delay of ~100secInduces for ToO an avoidable delay of ~100sec– Redesign under studyRedesign under study

BBalert

Launch the on-line

reconstruction

ligier

Monitoring

GCN format

Server TAROT Chile

Interactive Webpage

Monitoring“I am alive”

AN

TA

RE

S d

ata

TriggerReconstruction

Pointing telescope+ data acquisition

Internet

Test messages

Implementation

BBpaper