Dead time Vs Data collection for AMS

Dead time Vs Data collection for AMS P. Zuccon – INFN Perugia P.Zuccon -- INFN Perugia

The Problem • As the dead time after a trigger increases the data collection efficiency becomes smaller. • What is the fraction of the data collected by AMS02 as function of the dead time? • Let’s assume that the time difference between the arrival of two cosmic rays is distributed as an exponential with constant equal to the average delta t (t) or the average rate (n). let’s indicate with T the trigger dead time. The fraction of collected events will be: Average number of events within the time T if the physical rate is t P.Zuccon -- INFN Perugia

Fraction of collected events P.Zuccon -- INFN Perugia

The Problem • To complete the picture we must know • what is the range of rates AMS will be exposed to • how much time AMS will be exposed to each rate • Combine everything to get the collected statistics vs dead time The rate seen by AMS depends on: The AMS acceptance geometry trigger configuration The cosmic rays spectrum geomagnetic latitude Solar activity P.Zuccon -- INFN Perugia

Trigger for Protons from AMS MC Cfr: P.Zuccon AMS Analysis meeting 31 March 2005 P.Zuccon -- INFN Perugia

Time spent at various geomagnetic latitudes • ISS orbit spans uniformly the region lat [-51.7,51.7] lon [-180,180] • The time spent in a given latitude interval is proportional to the selected area • Consider 10 geomagnetic latitude intervals as for AMS-01 and map they to the geographical coo (see plot) • Calculate the area corresponding to the various geomagnetic latitude bands ref: P.Zuccon PhD thesis P.Zuccon -- INFN Perugia

Evaluate the rate Integral rate from Ek Threshold to INF • From AMS-01 data evaluate: • the cut-off value vs the geomagnetic latitude • the fractional contribution of the under cut-off protons • Cosmic protons flux parameterization Vs solar activity: M.Honda et al . (HKKM) ICRC07 • The flux is parameterized w.r.t. the counts of the Climax neutron monitor. • The average Climax count for 1988-1989 (same solar cycle as 2010-2011) is 3768 • Take the trigger acceptance as 1 m2 sr, and calculate the trigger rate for the spectrum in the range [cut-off value, INF] • Correct for the contribution of under cut-off protons • Add further 10% to account for He flux P.Zuccon -- INFN Perugia

Rates Calculation AMS-01 1998 (1 m2sr) AMS-02(1 m2sr) (2010-11) P.Zuccon -- INFN Perugia

Collected Statistic Trigger efficiency as function of the dead time and the geomagnetic latitude Cosmic protons P.Zuccon -- INFN Perugia

Collected Statistic Trigger efficiency as function of the dead time and the geomagnetic latitude Cosmic protons A=1 m 2 sr A=2 m 2 sr P.Zuccon -- INFN Perugia

P.Zuccon -- INFN Perugia

Dead time Vs Data collection for AMS