Higher  and smaller detectors for the beta beams Strength and weakness of the baseline (“low gamma”) energy option for the Beta Beam: a critical appraisal Prospects for a higher energy beta beam: ● A medium gamma beta beam at CERN or Fermilab with a 40kt scale detector ● A very high gamma beta beam through the LHC with a 3kt size detector Conclusions F. Terranova, INFN-Frascati Many thanks to G.Fogli, J.J.Gomez-Cadenas, M.Lindroos, M.Mezzetto, P.Migliozzi, A.Rubbia, F.Ronga, M.Spinetti and many others contributing to the discussion on the high-  beta-beams

Why Beta beams and not just Neutrino Factories? Easier: technology for radioactive ion boosting has evolved enormously Cheaper: particularly at CERN, most of the acceleration facilities exists Cleaner: only e in final state; the e   topology is experimentally much easier than   e (an enormous advantage compared with superbeam) and we do not need sign identification (no strong E cut as in NF) Most of these advantages are spoiled by the need for an UNO like detector which is difficult (site construction and PM production), expensive (kind of 500 M$) and intrinsically coarse (Fermi motion at sub GeV scale) It has additional physics items (see tomorrow's talks) but it brings the time-schedule ~2020 BUT

The root of this weakness Beta beams are evolution of radioactive ion facilities for nuclear studies (small E per nucleon) and not of heavy ion machines for dense nuclear matter (quark-gluon plasma: high E per nucleon) Energy optimisation should follow the same logic as for NF At fixed L/E, if we increase E: Flux increases as  2 and decrease as L -2 Cross section Grows like E The higher gamma the better (linear gain of sensitivity) until matter effects spoil CP violation (as NF)

Higher gamma setups Several are (in principle) available (all gammas refer to 6 He): SPS at its maximum rigidity  =150 the LHC  =2488 Could be available during the luminosity/energy upgrade of LHC: the 1 TeV SPS (useful both for lumi  =350 and E upgrade) the present LHC (coexists with the new  =2488 HE-LHC ring in the same tunnel after dipole upgrade) In the US (see talk of S.Geer and APS Snowmass, Jun 04): What happens to the decay ring? What happens to the intensity (integrated decay per year)? Can we imagine an affordable scenario for machine sharing?

What you (re)gain from them? We gain statistics (~E) We gain energy resolution (multi-GeV range): help solving ambiguities We gain sensitivity to matter effect (sign  m 2 ) 40 Kton 730 km  =350 ( 6 He) / 580 ( 18 Ne) 40 Kton iron 3000 km  =1550 ( 6 He) / 2500 ( 18 Ne) Baseline option (Frejus) J.Burguet-Castell et al., hep-ph/ Fully exploitation of the detector technology: e.g. LAr – see A. HIF04 (to appear in the Proceedings)

The most extreme case (LHC:  >1000 and E >5GeV) S ignal: an excess of horizontal muons in the rock in coincidence with the beam spill Number of unoscillated events: increase linearly with E Range of muons: increase linearly with E as well. The effective volume of rock contributing to the statistics increase linearly with E The cost of the detector increase with the surface and not with the volume We gain a quadratic increase of the sensitivity if we increase gamma and we reduce the detector cost by order of magnitudes! We loose the possibility to fully reconstruct the events This consideration holds in general: for a BB detector located at the peak of the oscillation probability, off the peak (see later), and even for neutrino factories (if the detector is magnetized). However you get best value at BB, where the detector costs more than the machine. F.T., A. Marotta et al., hep-ph/ Rock Hall

A specific case: CERN - to Gran Sasso A deep, existing (!), well equipped laboratory at a baseline of L=732 km (  = 350/580 i.e. E=1-2 GeV) Too small for 40 kton of WC or LAr Energy slightly too small for effective use of iron detectors BUT What happens for  > 350/580 (off the peak of the oscillation maximum) ? O 1 (leading term) O 2 (~ sin  ) O 3 (~ cos  ) O 4 (suppressed by   

If  increases beyond the golden value 350/580: The oscillation probability decreases as  -2 The flux increases as  2 The cross section and the effective rock volume increase both as  A specific case: CERN - to Gran Sasso Leading term: signal rate suppressed Matter effects cancel out at leading order even if the baseline is large We recover the quadratic increase of sensitivity but we test now CP-even terms and no matter effects P(   e )     sin     sin     sin    cos 

Beam related background: Pion punch-through deep hadron plug Early  /K decays in flight energy cut (charge id) Charm backgroundonly for the highest , energy cut (charge id) Beam unrelated background: Atm. neutrinosenergy cut (beam timing) Cosmicsangular cut (huge slant depth near the horizon) Can we handle background with such a rough detector? Beam unrelated background is so small that we can release by two order of magnitudes the request on the bunch length of the beta-beam An enormous technical simplification

Event rate  13 =0 (only the O 4 term survives) Instrumented surface: 15x15 m 2 (one LNGS Hall) Iron detector interleaved with active trackers (about 3kton) 2 GeV energy cut in a 20 deg cone decays per year of 18 Ne ; decays per year of 6 He 100 % oscillated events per year: (  =2500) (anti  =1500) (  =4158) (anti  =2488)

Sensitivity A killer application to test  13 values on the range solve ambiguities in combination with an on-peak facility

Machine issues: decay ring Main cost is civil engineering Low gamma: 6.8km, 5T, useful decay fraction 37% Higher gammas: Use the acceleration ring also for storage and build a small straight section pointing toward the detector and a curved section to reconnect (very high gamma 3km straight section, 9T, 8km curved) Pros: cost of civil engineering higher but not prohibitive Cons: full occupancy of the machine (interference with the LHC) useful decay fraction 10%: can be easily recovered instrumenting more than one LNGS hall Intermediate gammas: Both possibilities can be considered for a dedicated decay ring  =350, 11km, 9T, useful decay fraction is 22% The actual cost mainly depends on the outcome of the R&D for the energy upgrade of the LHC or the VLHC (maximum field available)

Machine issues: occupancy Not a problem for an intermediate gamma with dedicated decay ring (LHC/S-SPS used only in the accelerating phase) Not a problem for a very high gamma BB (VHG) if postponed to the energy upgrade of the LHC (two rings coexisting in the same tunnel and sharing the same cryogenics) Very unlikely for a VHG unless we can store >> ions Machine issues: intensity Intermediate gamma: reduction of a factor of 5 of the decays per second can be recovered by a faster PS and ion collection time VHG: reduction of a factor of but no need of asymmetric merging (no background from atm): multibunch stacking in the LHC before acceleration or re-optimise the choice of the isotope (fast PS!)

Conclusions An increase of the energy of the beta beam will surely imply an increase of their physics potential:  On peak with 40kton detectors: CP violation, matter effect, improved sensitivity to  13  Off-peak with <10kt detector: outstanding sensitivity to  13 and different pattern of oscillations (ambiguity solver) The combination of the two (possible only if a machine scenario for the LHC can be foreseen) is a killer application for the determination of the PMNS An increase of the energy of the beta beam could also imply a strong reduction of the costs (no massive detectors). But a complete machine scenario is not available, yet.

None of these studies is more than 6-month old Neutrino factory Low  Beta beamHigh  Beta beam

Exploiting the  CC topology at the Beta-Beams? QE dominance: strong contamination from atm sub-GeV (WC/LAr) Transition region between QE and non- QE dominance DIS dominance Iron detectors Multi GeV  CC events can be: Fully reconstructed by an iron detector (like MONOLITH but without a magnetic field) Partially reconstructed by an instrumented surface (do you remember the through-going muons of MACRO?) Interaction vertex Muon Rock

Sensitivity  =4158/2488  =2500/1500

40 LNGS km