Study of the eightfold degeneracy at a b -beam/SuperBeam complex

Study of the eightfold degeneracy at a b-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/0406132

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 NB we are able to reproduce NUANCE results within 5% once its cross-section is used

BB SB q23=45°

BB SB 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 BB+SB Parameter extraction in presence of signal (I)

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

3.5 q13 0.5 1.0 1.5 2 2.5 3 0. BB+SB vs NuFact golden after 10 years data taking BB + SB NuFact golden The eightfold degeneracy for both 68% 90% and 99% are shown

Comments (I) • By using the BB or the SB alone is not possible to solve any of the degeneracies, although for large enough q13 a first estimate of the two continuous parameters q13 and d 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/0310059: “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 q13 and d • NuFact golden is able to solve the sign(Dm223) 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(Dm223) and q23) has been discussed in several papers(see Nucl.Phys.B669:255-276,2003 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 q13>1°

Exclusion plots in absence of signal • So far the c2 method was adopted to compute the sensitivity • It works fine when a large number of back. events is expected. OK for SB and n from BB • This is not true for anti-n 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

sin22q13~0.0004 sin22q13~0.0003 q13 sensitivity vs d(10 years BB) c2

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 q13 a first estimate of the two continuous parameters q13 and d 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 n and anti-n • The performance of a BB+SB in measuring q13 and d is similar to the one of the NuFact golden for q13 > 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.

(d,q13) input value Dq13 = q13-q13 The intrinsic clone flow BB and SB have almost the same clone flow  Weak synergy in removing the intrinsic clone S.Rigolin Moriond 04

n back. anti-n back Evts vs q13 vs d n signal anti-n signal n+anti-n signal BB SB

sin22q13~0.0034 sin22q13~0.0004 sin22q13~0.00046 sin22q13~0.0003 q13 sensitivity vs d(10 years BB) F&C c2

2+8 years SB F&C sin22q13~0.0024 sin22q13~0.0014 q13 sensitivity vs d 2+8 years SB c2

Study of the eightfold degeneracy at a b -beam/SuperBeam complex