Discovery potential of a high energy beta beam

1
Discovery potential of a high energy beta beam

• J. Burguet, D. Casper, F. García, P. Hernández,
  JJ
• CERN Neutrino working group
• 19-11-03

2
Introduction

• The physics potential of the beta beam for the
  low gamma option (6He 60, 18Ne18100, L130 km)
  has been extensively explored.
• We want to address the question that we asked in
  Golden'' what is the optimal baseline and
  energy for the beta-beam? In particular we want
  to consider higher gamma options and
  correspondingly longer baselines

3
Higher gamma why?

• As in the Nufact increasing the energy for fixed
  E/L is advantageous
• statistics increases linearly with E (due to the
  cross section) ? reduce the detector mass
  keeping the same rates
• longer baseline ?enhance matter effects ?
  possibility to measure the sign of Dm23, that is
  the neutrino hierarchy
• increase the energy ? easier to measure the
  spectral information in the oscillation signal ?
  important to reduce the intrinsic degeneracies

4
Observing matter effects

• At O(1000) km matter effects and true CP are of
  the same order

d 0
d 90
E/L Dm23/2p
5
Solving degeneracies
Use energy dependence to disentangle the true
solution from fake solution.
Fake solution (at ltEgt)
True solution
6
How to accelerate? (Matts dixit)

• Refurbished SPS can achieve g 600. Super
  conducting magnets in the SPSC but same storage
  ring of the present design
• For higher gamma one could inject ions in the
  LHC, up to g(6He) 2488 and g(18Ne) 4158
• This possibility looks more futuristic due to the
  complexity of the storage ring and also looses
  would be unavoidable we assume a lose of a
  factor 10 in the number of ions

7
Detectors

• The obvious technique at low energies is water.
• Good e/m separation
• Good energy resolution
• Clear pattern recognition for low multiplicity
  events
• Large mass (beta-beam low gamma option Mton)
• As the energy increases the rates increase
  linearly (at fixed E/L)
• Thus one could, a priory, afford a lighter (more
  granular) detector for the same rate.
• Note that an important advantage of the beta-beam
  is that we do not need to measure the muon
  charge, thus no need to magnetize

8
Beta-beam Fluxes
The electron energy spectrum produced in the
decay at rest of a He6 ion is very well described
by the simple formula
Where Eo is the end-point electron energy
9
In the ion rest frame the spectrum of the
neutrinos is
After performing the boost and normalizing the
total number of ion decays to be Nb per year, the
neutrino flux per solid angle in a detector
located at a distance L aligned with the straight
sections of the storage ring is
Where
10
Fluxes
Error on previous results identified (end point
2g(E0-me) rather than 2gE0
11
Setups

• Three setups considered
• Low (60) medium (350) and high (1500) g for near
  (130 km) medium (730 km) and far (3000 km)
  baselines
• Two detectors
• Water detector (SK, UNO) like. Includes full
  simulation of efficiencies and backgrounds
• Granular detector (SCIBAR, Minerva). Simulation
  and final analysis still in progress
• Today ? shown only water results

12
Setup-I
Note Given the different g for 6He and 18Ne it
is not necessary to have 3 bunches for 18Ne. On
the contrary it would be better to have 3 bunches
for the 6He6!
Detector UNO type (400Kton) water cerenkov
Efficiency 0.4-0.5 Background fraction 10-3
Running time 10 years
13
Setup-II
Detector (a) SK type (40 Kton) water
cerenkov (b) UNO type (400Kton) water cerenkov
Running time 10 years
Efficiency Takes into account migrations due to
resolution and CC background to QE Backgrounds
Takes into account feed-down backgrounds Possibili
ty to improve (to be explored) run at two or
more g (200,250,300,350..) to reduce feed down
backgrounds
14
eff
eff
Ne18
He6
bkg
bkg
15
Setup-III
Running time 10 years
Detector (a) Light detector of O(50) kton
(tracking calorimeter a la Minerva, liquid argon
TPC). Simulation and analysis in progress (b)
UNO type (400Kton) water cerenkov seems very hard
at this energies but can be tried anyway (perhaps
with g cascade trick)
Today ? Only statistical errors
16
Results

• Notice
• Light water detector at 730 km performs
  similarly than Mton at 130 km (improves on
  degeneracies)
• Mton class detector at 730 km spectacular
• Not a sizeable improvement at 3000 km (Mton
  detector, stat only)

17
Results
Setup-II (SK like detector)
Separate sin(d)1 from sin(d) 0 at 99 CL
Setup-I
Setup-III Uno like detector (stat only)
Setup-II Uno like detector
18
Results
UNO

• Exclusion plot shows capability of observing sign
  of Dm23 in the q13-d plane at 730 km
• At 3000 Km matter effects are very large. Sign
  resolved in all parameter space.
• At 130 km matter effects are negligible. Sign NOT
  resolved in all parameter space.

SK
Setup-II (730 Km)
19
Conclusions

• Setup-I suffers from low cross section, muon
  threshold and Fermi motion that makes energy
  binning very difficult
• Setup-II seems optimal. It requires a moderate
  increase in g (feasible at SPS) and a longer
  baseline. Water technique can be used, thus
  sinergy with UNO physics. Physics potential
  comparable with the NuFact
• Setup-III needs to be explored in more detail, in
  particular concerning baseline, detectors and the
  possibility of cascading the g. Water looks
  unlikely. It requires LHC acceleration. Not
  obvious benefit wrt Setup-II