Physics reach of CERN-based SuperBeam neutrino oscillation experiments
Pilar Coloma
2
Enrique Fernandez-Marntez
Open Access
0
CERN Physics Department, Theory Division
, CH-1211 Geneva 23,
Switzerland
1
Departamento de Fsica Toerica, Universidad Auotnoma de Madrid
, Cantoblanco 28049 Madrid,
Spain
2
Center for Neutrino Physics, Department of Physics
, Virginia Tech, Blacksburg,
VA 24061, U.S.A
We compare the physics potential of two representative options for a SuperBeam in Europe, studying the achievable precision at 1 with which the CP violation phase ( ) could be measured, as well as the mass hierarchy and CP violation discovery potentials. The rst setup corresponds to a high energy beam aiming from CERN to a 100 kt liquid argon detector placed at the Pyhasalmi mine (2300 km), one of the LAGUNA candidate sites. The second setup corresponds to a much lower energy beam, aiming from CERN to a 500 kt water Cerenkov detector placed at the Gran Sasso underground laboratory (730 km). This second option is also studied for a baseline of 650 km, corresponding to the LAGUNA candidate sites of Umbria and the Canfranc underground laboratory. All results are presented also for scenarios with statistics lowered by factors of 2, 4, 8 and 16 to study the possible reductions of ux, detector mass or running time allowed by the large value of 13 recently measured.
1 Introduction 2 3 4
Summary and discussion
Daya Bay [1] and RENO [2] have recently conrmed the previous hints from T2K [ 3],
MINOS [4], Double-CHOOZ [5] and the interplay between solar and KamLAND data [6, 7]
with the discovery of a large value of 13 which saturates previous upper bounds [8]. Recent
global ts [ 9, 10] give a best t for 13 between sin2 13 = 0:024 and 0:027 (with the larger
values for an inverted hierarchy) and a 1 error close to a 10%. Such a large value opens the
window to fundamental measurements such as the existence of leptonic CP violation and
the neutrino mass hierarchy, critical for a comparison with double neutrinoless beta decay
searches probing the Majorana nature of the neutrino elds. The value of 13 currently
favoured would allow these searches to be performed at relatively modest upgrades of
conventional neutrino beams to SuperBeam setups, characterized with a beam power close
to (or above) 1 MW. In this work we will explore and compare the physics potential and
performance of two representative setups for a European SuperBeam experiment with a
neutrino ux produced at the CERN accelerator complex.
Seven possible detector sites have been studied within the LAGUNA [11] project:
Ferjus (France), Canfranc (Spain), Umbria (Italy), Sierozsowice (Poland), Boulby (UK),
Slanic (Romania) and Pyhasalmi (Finland). In addition there is the Gran Sasso (Italy)
underground laboratory, which presently hosts the CNGS [12] physics program and is
studying the only existing neutrino beam in Europe. Here we will concentrate in two
extreme setups: the longest possible baseline of 2300 km corresponding to the distance from
CERN to Pyhasalmi, and a shorter baseline of 730 km which corresponds to the present
beamline between CERN to Gran Sasso. We will also discuss the physics performance of
alternative LAGUNA sites with similar baselines to Gran Sasso such as Canfranc (650 km)
or Umbria (665 km).
An even shorter baseline of 130 km matching the CERN to Ferjus distance has also been
extensively studied [13{19]. The low energies needed to match this short baseline imply
correspondingly low cross sections and, typically, less statistics than other setups. If a high
beam power around 4 MW is achievable in order to compensate the reduced cross section
at these energies, this setup would provide an excellent sensitivity to leptonic CP violation,
given the negligible matter eects that could mimic its presence. However, the small matter
eects also imply no sensitivity to the mass hierarchy from the study of the oscillations
of the neutrino beam alone, although some sensitivity can be gained in combination with
atmospheric neutrino oscillations at the same detector [18, 20]. For the large values of
13 currently favoured, an even more attractive option implies the observation of this low
energy beam at its second oscillation peak, which would increase the CP violation discovery
potential as well as the determination of the mass hierarchy, at a 650 km baseline [21].
However, as these high beam powers are not expected to be achieved in the near future,
in this work we will instead assume a more modest ux of 0:8 MW, similar to what is
being considered for LAGUNA-LBNO [22]. For the high energy and long baseline option
of 2300 km we will consider a 100 kt liquid argon (LAr) detector, while the lower energies
required for the oscillation at 730 km match better the water Cerenkov (WC) technology,
for which we consider a 500 kt ducial volume. In order to explore if the large value of 13
allows for more conservative setups with reduced power, detector mass or running time,
we will present all our results with reductions in the statistics by f (...truncated)