SpillServer and FD neutrino events

SpillServer and FD neutrino events D. A. Petyt 13/10/05 • As part of my CC analysis studies, I have been attempting to isolate beam neutrino candidates in the FD using both scanning and event timing/topological cuts. • I was asked to summarise my findings as relates to the possible effect of SpillServer downtime on the recording of neutrino events in the FD. • This topic has already been covered in detail by Niki at the 21/09/05 ND phone meeting. I will show very similar plots here and will draw the same conclusions – the principle one being that with the system in place in batch processing, all beam induced events should appear in the “spill” stream and the only events that will be “missing” when the SpillServer is down are very low energy NC events that we probably can’t reconstruct very well (or at all…)

SpillServer and batch processing • The SpillServer efficiency is high (a rough, and probably biased estimate from data is ~98%, but I expect Nathaniel has a better number). • This inefficiency is dominated by a single period in mid-June when the SpillServer was effectively down for 10 days • When the Spill Server is running, all true spill-tagged snarls (100 us of detector activity around the predicted time of the spill in the FD) are written to the “spill” stream in the offline batch processing. • When the spill server is not running, snarls that pass either (or both) of the existing plane or E4 triggers that are coincident with spill times derived from ND SGATE timestamps in the database are written to the “spill” stream. Niki has verified for June and July data that entries exist in the database for all ND SGATE spills with pot>0 • The only events that are “lost” when the SpillServer is down are therefore events which fail the E4 and 4/5 triggers – i.e. very low energy NC events with total ph<1500 ADC counts.

Event scan • Scanned reconstructed FD “spill” files (with blinding applied) from Jun 1 – 19 Sept (LE-10 running, 5.1e19 p.o.t). • 1348 events scanned and classified into the following categories: • Sample is dominated by “junk” events, which are primarily radioactive noise • 26/1348 events do not have spill trigger bit set (trigsrc!=131072) • 6/140 neutrino candidates do not have trigger bit set

Neutrino candidates with trigsrc!=131072 • As expected, the events are clustered around the period 10/06-20/06, which was (by far) the single largest period of SpillServer downtime.

Scan of events with trigsrc!=131072 Network problems at Soudan on this day

CC event with trigsrc!=131072

NC event with trigsrc!=131072

Event time relative to Near SGATE • There is a difference in event timing when the spill trigger bit is not set: • the snarl time for spill triggers is set to the start of the Spill Trigger window (typically 40(?)us before the predicted time of the spill at the FD • The snarl time for events without the spill trigger bit is the trigger time of the event (4/5 or E4 trigger) • By calculating the difference between the snarl trigger time and the earliest digit of the reconstructed event, this offset can be removed. Junk event Junk event Events with trigsrc!=131072

Neutrino candidates vs time • All neutrino events, with the exception of one incorrectly-classified junk event, are in the expected time window. • No significant clustering of events in time. Junk event

“Junk” events as a function of time • Rate of “junk” events much lower when SpillServer is down – as expected • Most “junk” events are low ph noise, but there are other categories (such as incoming showers and other pathologies) which pass the E4/plane trigger…

LI events as a function of time • LI events in spill trigger window tend to correlate with LI gain curves (higher flashing rate) • No LI events during 1st gain curve in this plot as SS was down at this time. • 15 of 17 LI events were accompanied with trigger PMT hits

Neutrino candidates vs p.o.t. • The absolute rate of neutrinos in the FD is unknown (due to blinding and, presumably, oscillations), but the ratio of events to p.o.t. in a given time period should be a constant, given stable beam conditions. • The plot at right shows that this is indeed the case for the time period in question.

R1.18 SR shower finding efficiency • What about the low ph NC events that are “lost” when the SpillServer isn’t running? • From FD (LE) Monte Carlo, I calculate that 136/26522 (~0.5%) of true NC events have raw ph<1500 ADC counts and therefore fail the E4 trigger. • However, given the current R1.18 SR shower reconstruction, no NC events below 2000 ADC reconstruct at all. • In order to ‘rescue’ these events, special reconstruction algorithms would be required.

Low ph junk events • However, the aforementioned “junk” events, which have a much higher rate than true low energy NC events, also congregate in this low PH region. • We would need to find a way of rejecting these events and retaining the NC signal. Timing helps – but not enough in this case…

True energies of low ph NC events • Assuming we can isolate these low energy NC events, what is their utility in a physics analysis? • The plots at right show that these events are typically low y. This implies that they do not carry much “memory” of the parent neutrino energy and would therefore not add much spectral information in a nu_sterile fit. • You could always count them, but I am personally dubious that they would add much to a NC analysis. It would be interesting to see a more complete study of this.

Summary and conclusions • Definite (& hopefully final) comments about the SpillServer: • Efficiency is high (>98%) • Even when SpillServer is down, spill-coincident events are recovered in the “spill” stream by using SGATE times from the database • The only events we “lose” are low energy NC events with <1500 ADC counts • The number of events “lost” is then <0.5%*2% - hardly a large number… • It’s not clear we can even use these events for physics analysis anyway… • Status after 19/10/05? • Looked at late Sep spill files and found 1/201 snarls with trigsrc!=131072 (event scanned as cosmic)…

SpillServer and FD neutrino events