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Performance of a Water Cherenkov Detector for n 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. Motivation. SK : OA 2.5 o
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Performance of a Water Cherenkov Detector for ne 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
Motivation • SK : OA 2.5o • 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 • p0 BG is dominant for ne search. efficient p0 BG rejection g g g g
Current T2K Selection Criteria for ne Appearance • Standard SK cuts : • fiducial volume, fully-contained, Evis > 100 MeV • single-ring • electron-like PID • no decay-e • 0.35 < Enrec < 0.85 GeVEnrec = (mNEe-me2/2)/(mN-Ee+Pecosqn-e) • Further p0 cuts : • cosqne < 0.9 • DL < 80, Mp0 < 100 MeV/c2 of p0 fitter (POLfit)
POL(Pattern of Light)fit –p0 fitter – • Target: FCFV 1R-elike events • DL≡Likelihood(2g assump.) – Likelihood(electron assump.) • Try to reconstruct two g rings • Input: vertex, visible energy, and the 1stg direction by the standard fitter • Compare observed & expected (direct+scatter) charge • Vary the 2ndg direction and the energy fraction until the best match foundMp0 etc. POLfit g2 g1 standard fitter 500 MeV/c p0 true Pg2 = 55.5MeV/c rec.Mp0 =140.4MeV/c2
S. Mine (UCI) @ NP04 Events vs. Selections Dm2 = 2.5x10-3 eV2 sin2 2q13 = 0.1 104 nm BG • Event selections: • FCFV, Evis > 100 • 2. 1 ring • 3. e-like • 4. no decay-e • 5. 0.35 < Enrec < 0.85 • 6. p0 cuts: • - cos < 0.90 • - DL < 80, Mp0 < 100 events/22.5kt/5yrs ne signal ne BG 10 event selections
S. Mine (UCI) @ NP04 Events vs. Selections (cont’d) Dm2 = 2.5x10-3 eV2 sin2 2q13 = 0.1 (events / 22.5kt / 5yrs) ~20% ~70%
This study uses … • the SK-I atmospheric n MC sample • to study the higher neutrino energy range than that of the OA2.5 beam MC • contains both ne and nm events • livetime: 100yrs • the maximum-likelihood analysis • to select neCC signals efficiently • pre-cut : FCFV, Evis>100MeV single-ring e-like no-decay-e
Dist. for making a neCC-enriched likelihood (1) nmCC + NC neCCQE ring-counting parameter Evis : 100 ~250 MeV 250 ~ 400 MeV 400 ~ 600 MeV 600 ~ 900 MeV 900 ~ 1500 MeV 1500 ~ MeV
Dist. for making a neCC-enriched likelihood (2) nmCC + NC neCCQE PID parameter Evis : 100 ~250 MeV 250 ~ 400 MeV 400 ~ 600 MeV 600 ~ 900 MeV 900 ~ 1500 MeV 1500 ~ MeV
Dist. for making a neCC-enriched likelihood (3) nmCC + NC neCCQE cos qn-e Evis : 100 ~250 MeV 250 ~ 400 MeV 400 ~ 600 MeV 600 ~ 900 MeV 900 ~ 1500 MeV 1500 ~ MeV
Dist. for making a neCC-enriched likelihood (4) nmCC + NC neCCQE p0 mass by POLfit Evis : 100 ~250 MeV 250 ~ 400 MeV 400 ~ 600 MeV 600 ~ 900 MeV 900 ~ 1500 MeV 1500 ~ MeV
Dist. for making a neCC-enriched likelihood (5) nmCC + NC neCCQE DL by POLfit Evis : 100 ~250 MeV 250 ~ 400 MeV 400 ~ 600 MeV 600 ~ 900 MeV 900 ~ 1500 MeV 1500 ~ MeV
Likelihood distribution FCFV, Evis>100MeV single-ring e-like no decay-e Likelihood neCCQE nmCC + NC good separation
Likelihood distributions for each energy range nmCC + NC neCCQE Likelihood Evis : 100 ~250 MeV 250 ~ 400 MeV 400 ~ 600 MeV 600 ~ 900 MeV 900 ~ 1500 MeV 1500 ~ MeV
Events vs. Selections (100yr atm-n MC) rec En: 0~0.35 0.35~0.85 0.85~1.5 1.5~ nmCC 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%) NC 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%) neCC 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%)
Likelihood distributions for each sample nmCC NC neCC rec En: 0~0.35 0.35~0.85 0.85~1.5 1.5~
Efficiency by the likelihood cut nmCC rec En: 0~0.35 0.35~0.85 0.85~1.5 1.5~ NC neCC Likelihood>0.0 Efficiency Likelihood>0.5
Composition of neCC interactions in the final sample neCC multi p neCC single p Fraction WC detector cannot reconstruct the neutrino energy of these events. neCC QE True neutrino energy (GeV)
Summary • The signal/BG separation in a water Cherenkov detector for the ne 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.
Events vs. Selections (100yr atm-n MC) true En: 0~0.35 0.35~0.85 0.85~1.5 1.5~ nmCC 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%) NC 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%) neCC 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%)
Likelihood distributions for each sample nmCC NC neCC true En: 0~0.35 0.35~0.85 0.85~1.5 1.5~
Efficiency by the likelihood cut nmCC true En: 0~0.35 0.35~0.85 0.85~1.5 1.5~ NC neCC Likelihood>0.0 Efficiency Likelihood>0.5