CP violation and mass hierarchy at medium baselines in the large 13 era A large value of 13 is a major opportunity for precision neutrino physics: what changes at medium baselines? Can we access mass hierarchy and CPV much more easily? Medium baselines at large 13 Superbeams: the case of CERN-to-LNGS and CERN-to-Phyasalmi Liquid argon detectors and the exploitation of 2° maximum Performances: CPV coverage, Mass hierachy sensitivity Conclusions S. Dusini, A. Longhin M. Mezzetto L. Patrizii, M. Sioli, G. Sirri, F. Terranova

The large 13 era After 10 years of experimental searches we know the value of the 13 angle: it is surprisingly large and, by now, known with excellent precision D. Dwyer [Daya Bay Coll.] @ Neutrino 2012 T. Nakaya [T2K Coll.] @ Neutrino 2012 13 = 8.9  0.4 Best fit before Neutrino 2012: Fogli et al., arXiv:1205.5254

A few key questions: A large 13 ease substantially the discovery of CP violation? Addressed in this talk (*) for Superbeam with medium and large baselines A large 13 ease substantially the discovery of mass hierarchy? Addressed in this talk for Superbeam with medium and large baselines In the framework of Superbeam, do we still need multi-MW drivers or we can adapt present facilities? Addressed in this talk Should we spend our money to increase the power of the driver or the quality/size of the detector? Addressed in this talk Can we build an “all-in-one” Superbeam for CPV and MH? Addressed in this talk (*) Special emphasis on European/CERN-based facilities

nm ne transitions at medium baselines A nuisance for CP; an opportunity for MH. In year 2002 [mostly inspired by tri-bimaximal mixing] In year 2012 [data driven] a0.03 comparable (or larger) than sin 213 a = 10-1 sin 213 Perturbative expansion appropriate Perturbative expansion quite rough (*) O1 and O2 of comparable size O1 is the dominant contribution (*) See e.g. Asano, Minakata JHEP 06(2011) 022

Beam simulation Dedicated proton driver (50 GeV) Primary target interaction: Focusing system: Decay tunnel: Two horns: scan on horn parameters and distance 90 m long and 2.2 m radius (optimized values). Tracing by GEANT4 Graphite 1m long GEANT4 QGSP package CERN-SPS (400 GeV) Primary target interaction: Focusing system: Decay tunnel: Pre-scan with BMPT parameterization (*) Graphite 1m long GEANT4 QGSP package Two horns: scan on horn parameters and distance 1 km long and 1.2 m radius (CNGS values). Tracing by GEANT4 Optimization method: the beam paramenters are optimized using the 13 sensitivity as figure of merit. Such sensitivity is evaluated by Globes 3.1 assuming a LAr far detector of 100 kton. (*) M. Bonesini et al., Eur. Phys. J. C20 (2001) 13

2° oscillation peak Difficult to be exploited at medium baseline 2° oscillation peak Difficult to be exploited at medium baseline. Main strenght of long baseline facilities Main Region of Interest (ROI)

Detector simulation Updated detector description in the framework of GLOBES 3.1.11 NC background contamination (conservative): 0.1% of nmCC Error on signal and background normalization: 5% Energy resolution and efficiency for ne and bar-ne implemented through smearing matrices obtained from GENIE Monte Carlo generator : Quasi elastic (QE) 80% efficiency smearing of true-level e-momentum 2-body formula for Erec yields s(En)/En~ 0.05/√En DIS+RES 90 % efficiency s(Ehad)/Ehad = 20%/√Ehad Migration matrices calculated for ne and anti-ne separately.

Far detector location CERN to Gran Sasso (L=730 km) CERN to Gran Sasso 7 km off -axis Existing facilities  Moderate size of the Halls (10 kton of LAr at most)  Larger masses in a shallow lab  Flux limitation due to the use of the SPS off-axis  CERN to Phyasalmi (L=2290 km) Minimal option: SPS based with 20 kton LAr Ultimate option: 100 kton with a dedicated 50 GeV driver

CPV coverage (on-axis 50 GeV) 5% systematic error on flux normalization 5 n + 5 anti-n years Normal (known) Inverted (known) Normal (unknown) Inverted (unknown) Max power @ SPS Benchmarks (vertical lines): 10 kt Ä 0.77 MW Ä 10 y Þ 0 % 10 kt Ä 1.0 MW Ä 10 y Þ 0 % 10 kt Ä 2.4 MW Ä 10 y Þ 30-40 % Domain of sign ambiguity Max mass @ LNGS

CPV coverage (off-axis 10 km 400 GeV) 5% systematic error on flux normalization 5 n + 5 nbar years Normal (known) Inverted (known) Normal (unknown) Inverted (unknown) Max power @ SPS Benchmarks (vertical lines) 20 kt Ä 0.77 MW Ä 10 y Þ 0 % 30 kt Ä 0.77 MW Ä 10 y Þ 15-25 % 100 kt Ä 0.77 MW Ä 10 y Þ 45-55 %

Mass hierarchy coverage 5 % systematic error on flux normalization 5 n + 5 nbar years On-axis 50 GeV 10 kt Ä 0.77 MW Ä 10 y Þ 20-30 % 10 kt Ä 1.0 MW Ä 10 y Þ 30-40 % 10 kt Ä 2.4 MW Ä 10 y Þ 50 % Normal Inverted The mass hierarchy coverage is better for the on-axis configuration since the on-axis neutrino spectrum includes most of the ROI. In general, wide-band beam offers more sensitivity to MH and, hence on-axis configurations are better suited than off-axis (very narrow). It was the opposite for the 13 sensitivity Off-axis 10 km 400 GeV 20 kt Ä 0.77 MW Ä 10 y Þ 30 % 30 kt Ä 0.77 MW Ä 10 y Þ 35 % 100 kt Ä 0.77 MW Ä 10 y Þ 50 % For a discussion see e.g. Coloma, Fernandez, Labarga, arXiv:1206.0475

The “bimagic” baseline (e.g. CERN to Phyasalmi at 2290 km) HOWEVER: The bimagic baseline is very well suited for MH: MH coverage is nearly CP independent and large even at modest exposures. Medium baselines outperform but need to know a priori the mass hierarchy Both medium and long baseline can measure mass hierarchy. Long baselines slightly outperform due to 2nd maximum 20 kton , SPS-based See A. Rubbia @ Neutrino 2012

Systematics ON-AXIS As a general rule, medium baseline superbeams saturate their CPV overage at about 70%. The reason is due to systematics. Normal hierachy, known The CP phase d induce firstly a change in the normalization. Hence, the CP coverage at large exposure is dominated by the systematics on the overall normalization In fact, 5 % :is widely used but the T2K super-beam nowadays is still above the 10% level Control of systematics will be crucial for the design of future experiments; in fact, improving the systematic error pays much more than boosting mass/beam power for exposures larger than 2 MW yeff Mton

Conclusions (i.e. answers) A large 13 ease substantially the discovery of CP violation? It makes CPV accessible to Superbeams but CPV remains a major task due to the dominance of O1 A large 13 ease substantially the discovery of mass hierarchy? Enormously! Thanks, again, to O1. Medium baselines can achieve full coverage for exposure larger than 1 MW y Mton. Longer baslines much before. In the framework of Superbeam, do we still need multi-MW drivers or we can adapt present facilities? We need it for CPV in any realistic configuration Should we spend our money to increase the power of the driver or the quality/size of the detector? For exposures larger than 2 MW yeff Mton we are systematic limited.

Well.. systematics are not unbeatable. Can you remember this?  Can we build an “all-in-one” Superbeam for CPV and MH? Yes if the exposure is larger than 1 MW yeff Mton . But to get coverage > 70% we need new ideas to cope with systematics Well.. systematics are not unbeatable. Can you remember this?  Daya Bay 2012 CHOOZ 1997