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: 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? LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni

This work: FLUKA + NUX with 3-f oscillations with matter effects (A.Rubbia) FLUKA + NUX with 3-f oscillations with matter effects Earth density profile: PREM model 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 LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni

Event selection and definition LAr Super-Kamiokande Thresh. for e event 10 MeV 100 MeV (single prong) Thresh. for muon event 50 MeV 200 MeV 600 MeV (Multi-prong) LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni

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) Pp = 401 MeV/c En = 340 MeV Pe = 241 MeV/c Pp = 336 MeV/c En = 961 MeV Pe = 493 MeV/c Pp = 416 MeV/c Pp = 399 MeV/c Pp = 424 MeV/c En = 534 MeV Pe = 416 MeV/c Pp = 303 MeV/c En = 840 MeV Pe = 509 MeV/c Pp = 504 MeV/c En = 585 MeV Pe = 433 MeV/c Pp = 398 MeV/c En = 949 MeV Pe = 479 MeV/c En = 653 MeV Pe = 500 MeV/c Pp = 525 MeV/c Pp = 278 MeV/c En = 568 MeV Pe = 493 MeV/c En = 323 MeV Pe = 294 MeV/c En = 806 MeV Pe = 789 MeV/c LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni

ne CC Simulated Event Gallery En = 549 MeV Pe = 609 MeV/c Pp = 198 MeV/c En = 978 MeV Pe = 528 MeV/c Pp = 543 MeV/c En = 510 MeV Pe = 471 MeV/c En = 220 MeV Pe = 195 MeV/c Pp = 136 MeV/c En = 849 MeV Pe = 595 MeV/c En = 743 MeV Pe = 727 MeV/c En = 799 MeV Pe = 745 MeV/c En = 422 MeV Pe = 378 MeV/c Pp = 116 MeV/c En = 770 MeV Pe = 409 MeV/c En = 954 MeV Pe = 637 MeV/c LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni

The “standard” nm analysis: Beware of containment: but we have good news about the possibility of using MS to measure muon energy LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni

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 LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni

The Precision Physics case Solar n and KamLAND experiments contributed to determine with relatively high precision Dm212 and 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>| LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni

The determination of q23 in 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 (in SK ~ 6 ev/Kton yr) 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 LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni

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 LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni

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 LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni

Cryodet Workshop, G.Battistoni To give an idea: osc. web calculator based on the code of F.V. (thanks to V.Vlachoudis CERN) http://pceet075.cern.ch/neutrino/oscil/ q12 = 34° q13 = 3° q23 = 50° ne  ne ne  nm ne  nt q12 = 34° q13 = 0° q23 = 50° ne  ne ne  nm ne  nt q12 = 34° q13 = 0° q23 = 40° ne  ne ne  nm ne  nt n’s from nadir LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni

Cryodet Workshop, G.Battistoni 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? LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni

Cryodet Workshop, G.Battistoni 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…) LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni

ne + ne SubGeV CC interaction rates (kton yr)-1 No Osc.: 51.3 (62.8) 40o 45o 50o 0o 52.2 (63.9) 51.3 (62.8) 50.2 (61.7) 3o 51.7 (63.3) 50.9 (62.5) 49.7 (61.2) 5o 51.4 (63.0) 50.6 (62.2) 49.6 (61.1) 10o 50.8 (62.00) 50.4 (61.9) 49.3 (60.8) q23 q13 En<1 GeV Plepton<1 GeV/c LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni

Cryodet Workshop, G.Battistoni In graphic form... q13 = 0o q13 = 3o q13 = 5o q13 = 10o LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni

Cryodet Workshop, G.Battistoni Results for q13 = 0 q23 = 40o q23 = 50o LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni

Cryodet Workshop, G.Battistoni Results for q13 = 0 Ratio Ne/Ne0 q23 = 40o q23 = 50o 0.037 +/- 0.006 LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni

Cryodet Workshop, G.Battistoni Results for q13 > 0 q13 = 5o q13 = 10o LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni

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? LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni

Cryodet Workshop, G.Battistoni 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 LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni

For example (q13 = 0) : it could be possible to achieve a 3 s separation even for ~500 kton yr LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni

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 LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni

Cryodet Workshop, G.Battistoni 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,...). LNGS 13 Mar 2006 Cryodet Workshop, G.Battistoni