Discovery potential of a high energy beta beam

Discovery potential of a high energy beta beam J. Burguet, D. Casper, F. García, P. Hernández, JJ CERN Neutrino working group 19 -11 -03 1

Introduction n n The physics potential of the beta beam for the low gamma option (6 He ~60, 18 Ne 18~100, L~130 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 2

Higher gamma: why? n As in the Nufact increasing the energy for fixed E/L is advantageous: q q q 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 Dm 23, that is the neutrino hierarchy increase the energy easier to measure the spectral information in the oscillation signal important to reduce the intrinsic degeneracies 3

Observing matter effects • At O(1000) km matter effects and true CP are of the same order d =0 d =90 E/L = Dm 23/2 p 4

Solving degeneracies Use energy dependence to disentangle the true solution from fake solution. Fake solution (at <E>) True solution 5

How to accelerate? (Matts dixit) n Refurbished SPS can achieve g ~ 600. Super conducting magnets in the SPSC but same storage ring of the present design n For higher gamma one could inject ions in the LHC, up to: g(6 He) = 2488 and g(18 Ne) = 4158 n 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 6

Detectors n n n The obvious technique at low energies is water. q Good e/m separation q Good energy resolution q Clear pattern recognition for low multiplicity events q Large mass (beta-beam low gamma option ~ Mton) As the energy increases the rates increase linearly (at fixed E/L): q 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 7

Beta-beam Fluxes: The electron energy spectrum produced in the decay at rest of a He 6 ion is very well described by the simple formula: Where Eo is the end-point electron energy: 8

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: 9

Fluxes Error on previous results identified (end point 2 g(E 0 -me) rather than 2 g. E 0 10

Setups n Three setups considered q n Two detectors q q n Low (60) medium (350) and high (1500) g for near (130 km) medium (730 km) and far (3000 km) baselines 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 11

Setup-I Note: Given the different g for 6 He and 18 Ne it is not necessary to have 3 bunches for 18 Ne. On the contrary it would be better to have 3 bunches for the 6 He 6! Detector: UNO type (400 Kton) water cerenkov Efficiency: 0. 4 -0. 5 Background fraction: 10 -3 Running time: 10 years 12

Setup-II Detector: (a) SK type (40 Kton) water cerenkov (b) UNO type (400 Kton) 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 Possibility to improve (to be explored): run at two or more g (200, 250, 300, 350. . ) to reduce feed down backgrounds 13

eff Ne 18 He 6 bkg eff bkg 14

Setup-III Today Only statistical errors 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 (400 Kton) water cerenkov seems very hard at this energies but can be tried anyway (perhaps with g cascade trick) 15

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) 16

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

Results UNO • Exclusion plot shows capability of observing sign of Dm 23 in the q 13 -d plane at 730 km • At 3000 Km matter effects are very large. Sign resolved in all parameter space. SK Setup-II (730 Km) • At 130 km matter effects are negligible. Sign NOT resolved in all parameter space. 18

Conclusions n n n 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 Nu. Fact 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 19