Study of the eightfold degeneracy at a  -beam/SuperBeam complex (F.Terranova on behalf of) Pasquale Migliozzi INFN – Napoli Work mainly based on A. Donini, E. Fernandez-Martinez, P.M., S. Rigolin, L. Scotto Lavina hep-ph/

S.Rigolin Moriond 04

The cross-section problem The present knowledge of neutrino and anti-neutrino cross-sections is rather poor below 1 GeV (see plot) On top of that, the few available data are not on water Very difficult the extrapolation from different nuclei due to nuclear effects Therefore, it is not astonishing that different calculations can differ up to a factor 2 In the following we compare two calculations on water: NUANCE and one from P. Lipari (adopted in this work)

Cross-section comparison NUANCE Lipari

Expected rates/kton/year This work Nuance Mezzett 04 anti- This work anti- Nuance anti- Mezzett 04 BB SB NB we are able to reproduce NUANCE results within 5% once its cross-section is used

BB SB  23 =45°

Parameter extraction in presence of signal (I) SB BB+SB BB Continuous line: intrinsic degeneracy Dashed line: sign ambiguity Dot-dashed line: octant ambiguity Dotted line: mixed ambiguity NB The black dots show the theoretical clone location computed following Ref. JHEP 0406:011,2004

Parameter extraction in presence of signal (II) Continuous line: intrinsic degeneracy Dashed line: sign ambiguity Dot-dashed line: octant ambiguity Dotted line: mixed ambiguity

BB+SB vs NuFact golden after 10 years data taking  The eightfold degeneracy for both 68% 90% and 99% are shown BB + SB NuFact golden

Comments (I) By using the BB or the SB alone is not possible to solve any of the degeneracies, although for large enough  13 a first estimate of the two continuous parameters  13 and  can be attempted Even when the two beams are combined the two discrete parameters cannot be measured These results are in contrast with the statement of hep- ex/ : “We stress the fact that an experiment working at very short baselines has the smallest possible parameter degeneracies and ambiguities and it is the cleanest possible environment where to look for genuine leptonic CP violation effects” The correct statement is that “in many cases the discrete ambiguities, although not solved, does not affect in a significant way the measure of the continuous parameters”

Comments (II) Assuming 10 years data taking and a single detector BB + SB and NuFact golden give comparable results in measuring the continuous parameters  13 and  NuFact golden is able to solve the sign(  m 2 23 ) clones but not the octant ones BB+SB is not able to solve any of these clones How to get rid of clones?

What about the CERN scenario? The possibility to exploit atmospheric neutrinos in large WC or Magnetized Iron Detectors to measure the discrete parameters (sign(  m 2 23 ) and  23 ) has been discussed in several papers (see Nucl.Phys.B669: ,2003 and refs. therein) We believe that by combining atmospheric neutrinos with BB and SB the number of clones can be drastically reduced (work in progress) If this attempt works, it would be the demonstration that with a single detector it is possible to solve all the degeneracies for  13 >1°

Exclusion plots in absence of signal So far the  2 method was adopted to compute the sensitivity It works fine when a large number of back. events is expected. OK for SB and from BB This is not true for anti- from BB where 1 back. event is expected after 10 years! We tried the Feldman and Cousins approach, which is particularly suitable to deal with small number of events

22  13 sensitivity vs  (10 years BB) sin 2 2  13 ~ sin 2 2  13 ~0.0003

Comparison of some of future projects BB+SB

Conclusion Degeneracies are unavoidable and they should be taken into account in computing the sensitivity of a project The cross-sections at low energy (below 1 GeV) are both badly predicted and measured By using the BB or the SB alone is not possible to solve any of the degeneracies, although for large enough  13 a first estimate of the two continuous parameters  13 and  can be attempted The combination of a BB and a SB (as proposed in the CERN scenario) is not a real synergy (i.e. NO degeneracy is solved). Indeed, it only determines an increase of statistics for both and anti- The performance of a BB+SB in measuring  13 and  is similar to the one of the NuFact golden for  13 > 1° By using a Mton detector the synergy of the BB and atmospheric signals could help in resolving the degeneracies (under studies) The sensitivity of a BB+SB is comparable to JPARC-HK, while the Neutrino Factory is better.

The intrinsic clone flow ( ,  13 ) input value  13 =  13 -  13 BB and SB have almost the same clone flow  Weak synergy in removing the intrinsic clone S.Rigolin Moriond 04

Evts vs  13 vs  back. signal anti- signal +anti- signal BBSB anti-n back

F&C 22  13 sensitivity vs  (10 years BB) sin 2 2  13 ~ sin 2 2  13 ~ sin 2 2  13 ~ sin 2 2  13 ~0.0003

 13 sensitivity vs  2+8 years SB F&C sin 2 2  13 ~ sin 2 2  13 ~ years SB 22