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 e in Soudan 2

 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.

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 e in Soudan 2

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  1. 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.

  2. 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.

  3. Cuts(1) Unoscillated low energy beam events e charged current events

  4. 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.

  5. Cuts(2) 22 events (out of 2713) remain and were scanned

  6. Cut table 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 Expected event rate for a two year run 1324 Number of eevents, no oscillations 8.8

  7. Selection efficiencies Mean efficiency 31.5% Mean efficiency 0.7% Upper plot: efficiency for contained events Lower plot: efficiency for all events

  8. 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.

  9. e limits

  10. Comparison Hugh-Peter

  11. 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.

  12. e cc all events e cc contained events all unoscillated events contained unoscillated events cut Event length Event length defined as the distance between the first and last hits projected onto the fitted axis

  13.  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

  14. Cuts e ccunoscillated 40-200 0-56 0.76-1.0 0.82-1.0

  15. Selected events, energy Before scan After scan

  16. 2 2 sin22 m2

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