Online Reconstruction used in the Antares-Tarot alert system J ü rgen Brunner The online reconstruction concept Performance Neutrino doublets and high energy events DAQ data flow and implementation of alert system

Reconstruction concept

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

2. Add hits from neighboring floors in narrow time window

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

Purity of neutrino selection Plot  2 for all upward going tracks  clear double structure visible Plot  2 for all upward going tracks  clear double structure visible Simple  2 cut allows to choose high purity sample Simple  2 cut allows to choose high purity sample Good coverage of full zenith angular range Good coverage of full zenith angular range

Angular resolution Mirror solution in azimuth do not permit good pointing accuracy if fit is done on only two lines Mirror solution in azimuth do not permit good pointing accuracy if fit is done on only two lines Minimum 3-line fit required Minimum 3-line fit required Brightest (HE) events can be as good as 0.5º Brightest (HE) events can be as good as 0.5º Atmospheric Neutrinos / Muons Minimum 3-lines in reco 1 degree Median Angular resolution

Avoid explosion of alert rates Example: Example: –sparking OM Handful cases seen Handful cases seen Monitored via trigger rate of pure trigger Monitored via trigger rate of pure trigger Typical rate 5Hz Typical rate 5Hz Alert sending veto: Alert sending veto: –~ 20 Hz Online reco distinguishes between tracks and “Bright points” Online reco distinguishes between tracks and “Bright points”

Doublet search Select 2 events coming from the same direction in a time windows of 15 min. t0t0 t 0 + δt t0t0 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. 2 events coincidence rate: ΔΩ = 3° x 3° Δt = 15 min 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 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 Data Filter Data writer BBalert ligier

Trigger time Ethernet switch off-shore on shore ARS Data flow to onshore farm

Trigger time Ethernet switch off-shore on shore ARS Data flow to onshore farm

Trigger time Ethernet switch off-shore on shore ARS Data flow to onshore farm

Delay of alert sending Time slices of 100msec are treated by each trigger node (unreducable delay) Time slices of 100msec are treated by each trigger node (unreducable delay) Online reconstructions gets data from shared memory of data filter farm output stream Online reconstructions gets data from shared memory of data filter farm output stream 10msec CPU to process one event 10msec CPU to process one event Up to 100Hz output rate data processed in real time on a single computer Up to 100Hz output rate data processed in real time on a single computer ~1000 TimeSlices are buffered in each trigger node ~1000 TimeSlices are buffered in each trigger node –Useful for excternal alerts (GRBs) –Induces for ToO an avoidable delay of ~100sec –Redesign under study

BBalert Launch the on-line reconstruction ligier Monitoring GCN format Server TAROT Chile Interactive Webpage Monitoring “I am alive” ANTARES data Trigger Reconstruction Pointing telescope + data acquisition Internet Test messages Implementation BBpaper