1. Performance of a Water Cherenkov Detector for e Appearance Shoei NAKAYAMA (ICRR, University of Tokyo) November 18-19, 2005 International Workshop on a Far Detector in Korea for the J-PARC Neutrino Beam @ KIAS, Seoul, Korea

2. Motivation  SK : OA 2.5 o  A far detector in Korea has the option to choose a site for a smaller off-axis angle.  higher energy neutrino beam  Check the signal/BG separation performance for higher energy neutrinos   0 BG is dominant for e search.  efficient  0 BG rejection   

3. Current T2K Selection Criteria for e Appearance  Standard SK cuts : fiducial volume, fully-contained, Evis > 100 MeV single-ring electron-like PID no decay-e 0.35 < E rec < 0.85 GeV E rec = (m N E e -m e 2 /2)/(m N -E e +P e cos-e )  Further  0 cuts : cose < 0.9 L < 80, M 0 < 100 MeV/c 2 of  0 fitter (POLfit)

4. POL(Pattern of Light)fit –  0 fitter – 500 MeV/c  0 true P  2 = 55.5MeV/c rec.M  0 =140.4MeV/c 2 11 22 standard fitter POLfit Target: FCFV 1R-elike events L ≡ Likelihood(2 assump.) – Likelihood(electron assump.) Try to reconstruct two  rings Input: vertex, visible energy, and the 1 st  direction by the standard fitter Compare observed & expected (direct+scatter) charge Vary the 2 nd  direction and the energy fraction until the best match found  M 0 etc.

5. Events vs. Selections Event selections: 1.FCFV, E vis > 100 2. 1 ring 3. e-like 4. no decay-e 5. 0.35 < E rec < 0.85 6.  0 cuts: - cos < 0.90 - L < 80, M 0 < 100 events/22.5kt/5yrs event selections  BG e signal e BG 10 10 4 m 2 = 2.5x10 -3 eV 2 sin 2 2 13 = 0.1 S. Mine (UCI) @ NP04

6. Events vs. Selections (cont ’ d)  CC BG  NC BG beam e BG e (CC) Signal FCFV E vis >100 28491082248290 1ring 1313 (46%)277 (26%)114 (46%)243 (84%) e-like 51 (1.8%)219 (20%)111 (45%)240 (83%) no decay-e 15 (0.5%)195 (18%)92 (37%)222 (77%) 0.35 < E rec < 0.85 2.2 (0.1%)58 (5%)27 (11%)173 (60%) cos < 0.9 L < 80 M < 100 12±0.8 (0.3%) 16±0.4 (6%) 122±3 (42%) (events / 22.5kt / 5yrs) m 2 = 2.5x10 -3 eV 2 sin 2 2 13 = 0.1 S. Mine (UCI) @ NP04 ~20% ~70%

7. This study uses …  the SK-I atmospheric MC sample to study the higher neutrino energy range than that of the OA2.5 beam MC contains both e and  events livetime: 100yrs  the maximum-likelihood analysis to select e CC signals efficiently pre-cut : FCFV, Evis>100MeV single-ring e-like no-decay-e

8. Dist. for making a e CC-enriched likelihood (1) E vis : 100 ~ 250 MeV 250 ~ 400 MeV  CC + NC e CCQE 400 ~ 600 MeV 600 ~ 900 MeV 900 ~ 1500 MeV 1500 ~ MeV ring-counting parameter

9. Dist. for making a e CC-enriched likelihood (2) 250 ~ 400 MeV  CC + NC e CCQE 400 ~ 600 MeV 600 ~ 900 MeV 900 ~ 1500 MeV 1500 ~ MeV PID parameter E vis : 100 ~ 250 MeV

10. Dist. for making a e CC-enriched likelihood (3) 250 ~ 400 MeV  CC + NC e CCQE 400 ~ 600 MeV 600 ~ 900 MeV 900 ~ 1500 MeV 1500 ~ MeV cos -e E vis : 100 ~ 250 MeV

11. Dist. for making a e CC-enriched likelihood (4) 250 ~ 400 MeV  CC + NC e CCQE 400 ~ 600 MeV 600 ~ 900 MeV 900 ~ 1500 MeV 1500 ~ MeV  0 mass by POLfit E vis : 100 ~ 250 MeV

12. Dist. for making a e CC-enriched likelihood (5) 250 ~ 400 MeV  CC + NC e CCQE 400 ~ 600 MeV 600 ~ 900 MeV 900 ~ 1500 MeV 1500 ~ MeV L by POLfit E vis : 100 ~ 250 MeV

13. Likelihood distribution  CC + NC e CCQE Likelihood FCFV, Evis>100MeV single-ring e-like no decay-e  good separation

14. Likelihood distributions for each energy range 250 ~ 400 MeV 400 ~ 600 MeV 600 ~ 900 MeV 900 ~ 1500 MeV 1500 ~ MeV E vis : 100 ~ 250 MeV Likelihood  CC + NC e CCQE

15. Events vs. Selections (100yr atm- MC) FCFV,evis : 44073 44408 28071 39884 1ring : 32339 31059 18170 23668 e-like : 522 572 577 1187 no decay-e : 166 177 234 516 likelihood : 43 (25.9%) 70 (39.5%) 59 (25.2%) 116 (22.5%) FCFV,evis : 26678 36401 18921 25904 1ring : 20444 28583 13189 14432 e-like : 20294 28316 13091 14333 no decay-e : 19278 26667 12001 12437 likelihood : 17502 (90.8%) 22201 (83.3%) 9379 (78.2%) 7328 (58.9%) FCFV,evis : 21872 11274 3851 5549 1ring : 4734 3379 1397 1967 e-like : 2622 2857 1342 1919 no decay-e : 2374 2611 1183 1379 likelihood : 290 (12.2%) 667 (25.5%) 325 (27.5%) 545 (39.5%) e CC  CC NC rec E : 0~0.35 0.35~0.85 0.85~1.5 1.5~

16. Likelihood distributions for each sample rec E: 0~0.35 0.35~0.85 0.85~1.51.5~ e CC  CC NC

17. Efficiency by the likelihood cut e CC  CC NC rec E : 0~0.35 0.35~0.85 0.85~1.5 1.5~ Efficiency Likelihood>0.0 Likelihood>0.5

18. Composition of e CC interactions in the final sample True neutrino energy (GeV) Fraction e CC QE e CC single  e CC multi  WC detector cannot reconstruct the neutrino energy of these events.

19. Summary  The signal/BG separation in a water Cherenkov detector for the e appearance experiment has been developed based on a likelihood analysis.  The performance of the signal/BG separation was checked in the higher neutrino energy for a smaller off-axis site of a far detector in Korea.  In the higher energy region, the performance of the separation is worse. In addition, the fraction of CC non-QE interaction in the final sample is larger, whose parent neutrino energy cannot be reconstructed correctly.

20. Supplement

21. Events vs. Selections (100yr atm- MC) FCFV,evis : 343 44358 42139 69596 1ring : 325 41521 31935 31455 e-like : 7 527 709 1615 no decay-e : 4 192 243 654 likelihood : 1 (25.0%) 61 (31.8%) 79 (32.5%) 147 (22.5%) FCFV,evis : 15212 32525 21705 38462 1ring : 14305 29203 15765 17375 e-like : 14210 28936 15637 17251 no decay-e : 14168 27630 13998 14587 likelihood : 13144 (92.8%) 23517 (85.1%) 10931 (78.1%) 8818 (60.5%) FCFV,evis : 261 4551 7177 30557 1ring : 52 1363 2426 7636 e-like : 51 1254 1814 5621 no decay-e : 51 1240 1717 4539 likelihood : 2 ( 3.9%) 204 (16.5%) 356 (20.7%) 1265 (27.9%) e CC  CC NC true E : 0~0.35 0.35~0.85 0.85~1.5 1.5~

22. Likelihood distributions for each sample true E: 0~0.35 0.35~0.85 0.85~1.51.5~ e CC  CC NC

23. Efficiency by the likelihood cut e CC  CC NC true E : 0~0.35 0.35~0.85 0.85~1.5 1.5~ Efficiency Likelihood>0.0 Likelihood>0.5