e in Soudan 2

Soudan 2 has much better granularity than MINOS but much lower mass, how can it do in picking out e charged current events?

•PROCEDURE:

•Events generated with the LOW energy MINOS beam, MEDIUM energy might be better, still to come. Events include detector noise.

• Hits associated with an event gathered by the shower processor. All matched hits are fed to the processor, including noise. It works well in assigning hits from an event to one group.

•A shower axis is fitted to all hits in the event

•SHOWER calculates the longitudinal and transverse distances of hits from the axis.

•Set of cuts applied to reject nc and cc events and keep e cc events.

•Only a two flavour analysis attempted, I.e. no e background.

Cuts(1)

•Containment: Standard Soudan 2 containment, < 3 hits outside containment volume

•Length: Distance between first and last hit along the cluster axis 340>L>110

•Number of Hits: 200>Nh>40, lower limit removes small nc events, higher limit removes high energy electron events (beam events) and high energy muon and nc events from the beam tail. All the interesting

oscillation action is happening below 5GeV.

Cuts(1)

Unoscillated low energy beam events

e charged current events

Cuts(2)

•Track/Shower cut: based on the fact that tracks are linear in hits, showers produce blob-like clusters. Therefore the number of close by hits for a track is smaller than for a shower. Calculate the average number of other hits within 8 cm of each hit. Events with < 6 average nearby hits are rejected.

•Longitudinal hit distribution: Showers tend to have more hits close to the vertex. Average distance of hits along the shower axis > 56 rejected.

•Pulse height ratio: Shower events deposit a large fraction of their pulse height close to the vertex. Ratio of pulse height in first 150cm to total pulse height < 0.76 rejected

•Angle with beam: Cosine angle between shower axis and beam <0.82 rejected.

Cuts(2)

22 events (out of 2713) remain and were scanned

Cut table

Expected event rate for a two year run 1324 Number of e events, no oscillations 8.8

unoscillated e cc

All events generated 2713 1754

Containment 692 868

Length 350 739

Number of hits 259 539

Track/shower cut 42 354

Longitudinal hit distribution 38 351

Pulse height ratio 29 309

Angle with beam 22 273

Scan 18 273% rejection, of all events 0.7% 15.6%

% rejection of contained events 2.6% 31.5%

Scan truth beam e 4

neutral current 11

charged current 3

Selection efficiencies

Upper plot: efficiency for contained events

Lower plot: efficiency for all events

Mean efficiency 31.5%

Mean efficiency 0.7%

Oscillation analysis

•The unoscillated events were weighted to correspond to 2 years running (1324 total events). In this total we expect 8.8 “identified” electron cc events.

•For each m2 and sin2(2) on a grid both the unoscillated events and the electron cc events were additionally weighted by the oscillation probability and the total number of “identified” electron cc events calculated.

•A 2 to find this number of events, expecting 8.8 events was calculated.

•The 90% confidence level contour was calculated.

e limits

Comparison Hugh-Peter

Summary

•I get a high m2 limit of sin2(2)~ 0.08.

•Hugh found a significantly better limit. This was almost entirely because his fiducial volume cut accepted a factor of two more events. Our cut efficiencies for contained events are very similar. He accepted a larger fiducial volume because he scanned the events and could deduce from scanning that the body of the shower was contained. This is probably valid for high energy beam events, within a beam spill cut, for which background due to rock events is negligible.

•A theoretical detector with 100% rejection for background and 100% acceptance of electron cc events would obtain 321 events at m2 =3 10-3 and sin2(2)=1.0 while expecting 13.0 events from beam electron cc events, corresponding to a 90% confidence limit of 0.024. Exploiting the energy distribution difference might reduce the limit by a factor of 2? This represents the ultimate limit on the sensitivity of a 1 kton detector in a two year run.

Event length

Event length defined as the distance between the first and last hits projected onto the fitted axis

e cc all events

e cc contained events

all unoscillated events

contained unoscillated events

cut

energy v number of hits

We are only interested in energies below 5 GeV

For e cc event this gives a maximum of 200 hits

Cut there to reduce high energy nc events

Cuts

40-200 0-56

0.76-1.0 0.82-1.0

e cc unoscillated

Selected events, energy

Before scan

After scan

2

m2

sin2 2

2