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Atmospheric n ’s in a large LAr Detector

Atmospheric n ’s in a large LAr Detector. G.Battistoni, A.Ferrari, C.Rubbia, P.R.Sala & F.Vissani. Motivations to continue the study of atmospheric neutrinos. There is still interest in continuing the study of atmospheric neutrinos:

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Atmospheric n ’s in a large LAr Detector

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  1. Atmospheric n’s in alarge LAr Detector G.Battistoni, A.Ferrari, C.Rubbia, P.R.Sala & F.Vissani

  2. Motivations to continue the study of atmospheric neutrinos • There is still interest in continuing the study of atmospheric neutrinos: • the confirmation of SK results with a technology having a large reduction of experimental systematics with respect to water Čerenkov • the search for subleading contributions in the mixing matrix; • a possible (in principle) precision measurement of q23 • a possible discrimination of Normal vs Inverted Hierarchy of masses Tiny effects!! • Can a very large LAr detector be the tool to perform these new investigations (“Precision Physics”)? How does it compare to SK? Cryodet Workshop, G.Battistoni

  3. (A.Rubbia) Earth density profile: PREM model This work: FLUKA + NUX with 3-f oscillations with matter effects Atmospheric neutrino Fluxes (2002) @LNGS • Dm223 = 2.5 x 10-3eV2 (positive) • Dm212 = 8.x10-5eV2 • q12= 34o • q23 = 40o, 45o , 50o • q13 = 0o, 3o , 5o , 10o • dCP = 0o A.Strumia & F.V. hep-ph/0503246 1000 Kton year exposure Cryodet Workshop, G.Battistoni

  4. Event selection and definition Cryodet Workshop, G.Battistoni

  5. En = 961 MeV En = 949 MeV Pe = 509 MeV/c Pe = 500 MeV/c Pe = 416 MeV/c Pe = 479 MeV/c En = 653 MeV En = 585 MeV Pe = 789 MeV/c En = 806 MeV En = 840 MeV En = 340 MeV En = 323 MeV En = 568 MeV Pe = 493 MeV/c Pe = 493 MeV/c Pp = 401 MeV/c Pp = 504 MeV/c Pp = 336 MeV/c Pe = 433 MeV/c Pp = 424 MeV/c En = 534 MeV Pp = 398 MeV/c Pp = 416 MeV/c Pe = 241 MeV/c Pe = 294 MeV/c Pp = 303 MeV/c Pp = 399 MeV/c Pp = 278 MeV/c Pp = 525 MeV/c ne CC Simulated Event Gallery How SubGeV ne events will appear in ICARUS in one of its projective views (full detector desponse simulation using FLUKA) Cryodet Workshop, G.Battistoni

  6. En = 849 MeV En = 978 MeV En = 510 MeV En = 799 MeV En = 770 MeV En = 422 MeV En = 954 MeV En = 743 MeV En = 220 MeV En = 549 MeV Pp = 198 MeV/c Pe = 595 MeV/c Pp = 116 MeV/c Pe = 609 MeV/c Pe = 195 MeV/c Pe = 745 MeV/c Pe = 471 MeV/c Pp = 543 MeV/c Pe = 637 MeV/c Pe = 528 MeV/c Pe = 378 MeV/c Pp = 136 MeV/c Pe = 727 MeV/c Pe = 409 MeV/c ne CC Simulated Event Gallery Cryodet Workshop, G.Battistoni

  7. Beware of containment: but we have good news about the possibility of using MS to measure muon energy The “standard” nm analysis: Cryodet Workshop, G.Battistoni

  8. A slightly less standard opportunity Direction reconstruction using lepton+recoiling proton • In general: • a superior capability • in pointing • a better resolution • in L/E Minimum Goal: ~50-100 kton yr Cryodet Workshop, G.Battistoni

  9. The Precision Physics case • Solar n and KamLAND experiments contributed to determine with relatively high precision Dm212and q12 • At present the only determination of q23 come from atmospheric neutrinos and has a large uncertainty. How close is q23 to /4? Is it larger or lower than /4? (“octant ambiguity”) q23 < /4|<nm|n3>|>|<nt|n3>| Cryodet Workshop, G.Battistoni

  10. (in SK ~ 6 ev/Kton yr) The determination of q23in atm. neutrino exp. DIscussion previously proposed by P.Lipari Essentially the best determination of 2 q23 comes from the analysis of Multi-GeV muon-like events At present: 36° < q23 < 54° The “solar” (12) sector generates significant effects on Sub-GeV neutrinos which might help resolve the octant ambiguity. This is true even in case q13 = 0 Cryodet Workshop, G.Battistoni

  11. Oscillation effects in e-like events in the q13 = 0 approximation Fosce = F0e P(ne  ne) + F0m P(nm  ne) F0e ,F0m : n flux w/o osc. = F0e [ P(ne  ne) + r P(nm  ne) ] r = F0m/ F0e : m/e flux ratio = F0e [ 1 – P12 + r cos2 q23 P12 ] P12 = |Aem|2 : 2n transition probability ne  nmt in matter driven by Dm212 (Fosce / F0e) – 1 = P12 (r cos2 q23 – 1) screening factor for low energy n (r ~ 2) ~ 0 if cos2 q23 = 0.5 (sin2 q23 = 0.5) < 0 if cos2 q23 < 0.5 (sin2 q23 > 0.5) > 0 if cos2 q23 > 0.5 (sin2 q23 < 0.5) Important only in SubGeV region where Dm212L/E is sufficiently large Cryodet Workshop, G.Battistoni

  12. A new measurement of q23 SubGeV: r~2 Also the nm rate is affected but this would be an extra term which adds to the “standard” 2-flavor oscillations However, the general case of non vanishing q13 (and possibly dCP) plus matter effects is more complex Cryodet Workshop, G.Battistoni

  13. To give an idea: nene nene nene nenm nenm nenm q12 = 34° q13 = 0° q23 = 50° q12 = 34° q13 = 0° q23 = 40° nent nent nent q12 = 34° q13 = 3° q23 = 50° osc. web calculator based on the code of F.V. (thanks to V.Vlachoudis CERN) http://pceet075.cern.ch/neutrino/oscil/ n’s from nadir Cryodet Workshop, G.Battistoni

  14. Implications: The knowledge of the absolute level of SubGeV ne can provide the best possible measurement of q23 and of its octant. The unique features of a large LAr detector (>50 kton?) can provide an important measurement of of SubGeV ne with null or largely reduced experimental systematics. The ICARUS tecnology can explore for the first time the region with Pe<100 MeV/c (to be demonstrated by T600) Of course, from the point of view of statistical significance, this requires a very high exposure. How large? Cryodet Workshop, G.Battistoni

  15. Other possibilities • There are q13 induced oscillations which instead affect the MultiGeV region: these could be used to discriminate the hierarchy of masses (sign of Dm223) if n and anti-n could be distinguished(MSW resonance is present for n when Dm223>0 or for anti-n (when Dm223<0) • This measurement, which requires n/anti-n separation, might be more problematic for a LAr detector (magnet…) Cryodet Workshop, G.Battistoni

  16. ne + ne SubGeVCC interaction rates (kton yr)-1 No Osc.: 51.3 (62.8) q23 q13 En<1 GeV Plepton<1 GeV/c Cryodet Workshop, G.Battistoni

  17. In graphic form... q13 = 0o q13 = 3o q13 = 5o q13 = 10o Cryodet Workshop, G.Battistoni

  18. Results for q13 = 0 q23 = 40o q23 = 50o Cryodet Workshop, G.Battistoni

  19. Results for q13 = 0 Ratio Ne/Ne0 q23 = 40o q23 = 50o 0.037 +/- 0.006 Cryodet Workshop, G.Battistoni

  20. Results for q13 > 0 q13 = 5o q13 = 10o Cryodet Workshop, G.Battistoni

  21. The problem of systematics Leaving aside for a moment the question if such an extremely large exposure can be achieved: The proposed measurement requires an absolute no-oscillation prediction affected by a systematic uncertainty not exceeding 1%.Is this achievable? (absolute level, ne/nm ratio) • Primary c.r. fluxes (maybe we can take this ~under control) • Neutrino-nucleus cross sections • Hadronic interactions and atm. shower development • is exactly 2 at low energy only if just p are there! • K/p? Cryodet Workshop, G.Battistoni

  22. A less naive method... • Of course it is hard to believe that one could rely on the absolute level of Ne prediction... (the c.r. flux normalization remains one of the most important uncertainties) • A better analysis is the ratio: so that many common systematics cancel out • The important topic remains the uncertainty as a function of energy Cryodet Workshop, G.Battistoni

  23. For example (q13 = 0) : it could be possible to achieve a 3 s separation even for ~500 kton yr Cryodet Workshop, G.Battistoni

  24. Considerations from SK • This topic has been debated at the end of 2004 in the context of a dedicated workshop http://www-rccn.icrr.u-tokyo.ac.jp/rccnws04/ • Requirements for SK: the measurement of q23 octant can be done with an exposure of at least 20 years of SK (depending on q13) to distinguish (Dc2~2) between the 2 mirror values of corresponding to sin2q23 = 0.96 with the present level of systematics Cryodet Workshop, G.Battistoni

  25. Conclusions • A very large LAr TPC, in principle, can give new important contributions to neutrino physics, also with atmospheric neutrinos • It allows to detect low energy neutrinos with null or negligible experimental systematic error. An exposure of 50-100 kton yr would allow be the minimum goal for this topic. • the sector of SubGeV ne, in particular, offers the possibility of performing new interesting measurements. • To perform new precision measurements a very large exposure (>500 kton yr) is anyway needed • Such a large exposure might be in part useless without an effort to reduce the existing systematic uncertainties (n fluxes, cross sections,...). Cryodet Workshop, G.Battistoni

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