Brick Finding Ankara CM 2/4/2009 Dario Autiero

1. Brick Finding Ankara CM 2/4/2009 Dario Autiero

2. A large effort was put in the last months by a team of people in order to recover the events pending due to reconstruction problems and to improve the ED reconstruction • See presentations by Antoine and Anselmo We had the goals: Solve all the 2008 events before the 2009 run Improve the reconstruction and efficiency Have a more reliable reconstruction (more automatic) The events which were suspended, about 300 at the end of 2008 had evident reconstruction problems bringing predictions many tents of cm away from the core activity of the event We managed to digest the pending events by completing the debugging of the reconstruction Once fixed the events behave more or less like the standard ones, we did not observe a degradation of efficiency for recovered events wrt standard one Many problems were fixed at the level of the spectrometer connection, RPC clustering etc …

3. Still pending problems: Having an independent (and precise) pattern recognition at the level of the HPT (the actual onedoes not exploit the accuracy of HPT and does not well correct for the magnetic field) Having a correct treatment of tracking errors (Claudia, Anselmo and Stefano)  see next page All these improvements are necessary also for other aspects in the experiment, like the muon ID and not only for the BF. We also started a comparison with a TT pattern recognition based on the Hough transform, provided by Dubna. This process was launched at the September CM. A file in the standard Oprec root format was finally available two weeks ago  Two presentations are foreseen in the PC session

4. Residual Kalman-CS 19 mrad 20 mrad 7 mm 8 mm Typical tracking errors are of the order of 1mm, one order of magnitude smaller this is a long-standing problem

5. First and Second bricks Getting data from second bricks to complete efficiency estimation from real data. At the moment still poor statistics of 2nd bricks (data from EU only) Last data: First bricks raw eff: 467/715 = 65.3% Second bricks raw eff: 29/65 = 44.6% Removal of interactions in dead materials 715 - 3.8% = 688  1st brick corrected eff: 467/688 / (1 -6.8%) = 72.8% (72% MC) Correlation with 2nd brick: Unfound raw after first brick (100% - 65.3%) Unfound related to BF inefficiency (100% - 72.8%) foundable in 2nd brick  Second brick corrected eff: = 29/65 * (100 – 65.3) / ( 100 - 72.8) = 56.9% 1st brick BF eff = 72.8% +- 1.7% 2nd brick BF eff = 56.9% +- 6.1% Total efficiency 1st + 2nd: 72.8% + (100% - 72.8%)*56.9% = 88.3 % +- 5% (80% MC) Still too large uncertainty on 2nd bricks

6. Comments and warnings: • Predictions were made time ago for these events. Taking the latest version of the reconstruction for about 1/3 (9 events) now the brick is predicted directly as first brick, reconstruction problems fixed • For 8 events the second brick suffers from the underestimation of tracking errors. This has to be fixed in order to predict correctly the lateral probability • For 8 events the second brick was in another wall with large probability (30-40%), this looks higher (~ a factor 2) than on average prediction for second bricks. It is a fluctuation in this first sample • Too few NC • We need a larger sample to draw some more solid conclusions We should get a large sample from the last couple of weeks of extractions

8. Wall 14 (first) 60% Wall 15 40% Important backscattering

9. We should have a clearer view with the increase in statistics of the last weeks (gather all possible second brick results, also from Japan) • Re-evaluation of last version of the reconstruction on all events • A deeper comparison per events categories is needed (QE,NC,CC, electromagnetic-like) • So far the algorithms have been kept untouched, the main work has been concerning the debugging of the reconstruction. On the basis of these results it will be possible to have a second version • BF efficiency was optimized for tau events (the efficiency is about 5% larger than for standard numu NC or CC events) , in order to check it we should look for events which are tau like CC QE and with low energy muons, events with dominant electromagnetic activity, like taue and taurho. • First priority: increase the efficiency as much as possible, There are ideas about that on the side of BF and also on the possibility of concentrating the efforts on a tau signal enriched sample. We should first advance with the analysis of the event sample and understand why it goes wrong (reconstruction, 2nd bricks, …)

10. Re-evaluation campaign (bricks finding CS tagging part): Integrate in the simulation the CS tagging absent in the past: acceptance effect with respect to the total surface behind the bricks (7.4% uncovered area) + CS base track efficiencies measured from real data, implement also the 3/4)  Complete efficiency evaluation from real data (convolution of BF + CS)  Evaluate CS tagging efficiency from full MC (including the CS intrinsic efficiency as a function of the angle measured in real data, provided by Giovanni for base tracks)

11.  Better errors evaluation in tracking, important for probability maps • Re-evaluate MC BF efficiency per categories of event including the interplay of CS tagging efficiency, compare to data per categories of events: DIS, QE, NC, NC with e.m. component. • Possible tau enriched sample to maximize the efficiency •  Estimate possible bias of CS tagging inefficiency (~ 25%) on muon matching: are all muons found at the vertex even if not followed by scan-back ? even a residual inefficiency of 2% could change a lot the charm background.