BETA-BEAMSBETA-BEAMS Piero Zucchelli On leave of absence from: High Energy Physics and INFN - Sezione di Ferrara M. Mezzetto D. Casper M. Lindroos A. Blondel U. Koester S. Hancock B. Autin M. Benedikt H. Haseroth M. Grieser A. Jansson S. Russenschuck F. Wenander Physics Letters B 532 (3-4) (2002) pp An idea

GUIDELINES A. Neutrino beams from a different perspective B. The “Beta-Beam” Concept C. Experimental Scenario D. Beta-beams and neutrino physics E. The Value question

The focussing properties are given only by: - the divergence of the parent “beam” - the Lorentz transformations between different frames P T = p T P L =  ( p + p  cos  ) from which, on average (if spinless)  1/  (it depends ONLY on parent speed!) E  E 0 E 0 =daughter particle energy when parent is at rest where. In the forward direction, E  2  E 0 (I.e. same rest-frame spectrum shape multiplied by 2  ) Focussing Properties  are produced by weak “decay” of a parent: ,K,nucleus. We assume the decay to be isotropic at rest and call E 0 the rest frame energy of the neutrino.

LBL Scope maximum neutrino flux for a given  m 2  E/L  E 0 /L. The neutrino flux onto a “far” detector goes like  2 /L 2 ; Therefore  (  m 2 ) 2 /E 0 2. At a given parent intensity, low energy decays in the CMS frame are the most efficient in achieving the “LBL requirement”, and independently of the  factor. But we want to observe neutrino interactions: N=  If we assume to be in the regime where  E (>300 MeV for  ) N  (  m 2 ) 2  /E 0 And acceleration enters into the game; The “Quality Factor” of a “non-conventional” neutrino beam is therefore  /E 0

The BETA-BEAM 1. Produce a Radioactive Ion with a short beta-decay lifetime 2. Accelerate the ion in a conventional way (PS) to “high” energy 3. Store the ion in a decay ring with straight sections. 4. It will decay. e ( e ) will be produced. - SINGLE flavour - Known spectrum - Known intensity - Focussed - Low energy - “Better” Beam of e ( e ) The “quality factor” QF=  /E 0 is bigger than in a conventional neutrino factory. In addition, ion production and collection is easier. Then, X more time to accelerate. Muons:  ~500 E 0 ~34 MeV QF~15 6 He Beta-:  ~150 E 0 ~1.9 MeV QF~79 18 Ne Beta+:  ~250 E 0 ~1.86 MeV QF~135

Possible  - emitters ( e )

Anti-Neutrino Source Consider 6 He ++  6 Li +++ e e - E 0  MeV T/2  s 1. The ion is spinless, and therefore decays at rest are isotropic. 2. It can be produced at high rates, I.e. 5E13 6 He/s 3. The neutrino spectrum is known on the basis of the electron spectrum. DATA and theory: =1.578 MeV =1.937 MeV RMS/ =37% B.M. Rustand and S.L. Ruby, Phys.Rev. 97 (1955) 991 B.W. Ridley Nucl.Phys. 25 (1961) 483

Bunched? 2500 m R=300 m The interactions time structure in the detector is identical to the time structure of the parents in the decay ring in a given position. The beta decay position does not matter, since the parents have the same speed of the neutrinos The far detector duty cycle is bunch length / ring length A B Interactions time Ion intensity time

Next decades neutrino physics A. Imagine that there will be a next generation neutrino detector. An R&D, design and construction phase will lead us into next decade. B. Imagine to explore non-accelerator physics first. C. Imagine that this program is compatible with a superbeam shooting muon neutrinos onto it. If this will expand the neutrino knowledge of the period , you’re ready to do it (known technology). D. Imagine that you have PREPARRED and STUDIED an option to shoot electron neutrinos onto the same detector. If the next decade neutrino physics will demand it, you’re ready to do it.

A Dream? A. the ~600 Kton UNO detector. B. Supernovae, Solar, Atmospheric, Proton Decay:  12,m 12,  23,m 23. C. Frejus site and SPL Super-Beam: possibly  13 D. Frejus site and SPS Beta-Beam: possibly  13, possibly CP (2) and T Is this physics program less visionary than a muon-based neutrino factory program? The objectives are wider, the discovery potential for some specific assumptions is smaller. Speculations and fashions on the  value will also last many years!

SuperBeam: a competition? The proton requirements of the Beta-Beam are part of the (100uA for 1s every 2-5 s). The plans 100 uA protons overall. The Superbeam uses 2mA from the SPL. Therefore: The BetaBeam affects the SuperBeam intensity by 3% at most.

Cherenkov? Opportunistic? The detector has to be massive, and distinguish electrons from muons in the few hundreds MeV region Same as: - SuperBeam - Proton decay - Atmospheric neutrinos! You don’t need charge identification......and therefore a magnetic detector!

The Far Detector Observables The relative neutrino flux for a spinless* parents is ONLY function of  and L, not even of the parent itself. (* as it is for 6 He and 18 Ne)

beam-related backgrounds due to Lithium/Fluorine interactions at the end of the straight sections The Far Detector Background GEANT3 simulation, 3E6 proton interactions onto a Fe dump, tracking down to 10 MeV 100 mrad off-axis and 130 km distance. DIF and DAR (K+) contributions <10 -4  =150

The Signal maximization... The signal coming from appearance  interactions after 130 km and 440 kt-year fiducial mass in the hypothesis (  13 =  /2,m 13 =2.4E-3 eV 2 ). The machine duty-cycle is assumed to remain constant. table

…and the interaction background... NC interactions potentially produce  ++ decays (almost at rest) and the  + is misidentified as a muon. Asymmetries with Superbeams start to appear (the e/  0 separation becomes  /  ) Kinematical cuts are possible, still delicate and MC dependent. Another strategy consists in having the pions below Cherenkov threshold (M. Mezzetto). Interaction Background

...and the Atmospheric “background” The atmospheric neutrino background has to be reduced mainly by “timing” on the 6He bunches (protons for the SuperBeam). The shortness of the ion bunches is therefore mandatory (10 ns for a ~SPS ring length). However, the directionality of the antineutrinos can be used to further suppress this background by a factor ~4-6X dependent on gamma. Atmospheric Background

Anue Summary Figures

The Nue case Neon production Intensity is lower, HOWEVER: Ne has charge 10 and mass For the previous reason, SPS can accelerate the ion up to  =250 (250 GeV/nucleon) WITH THE SAME MAGNETIC FIELD used for 6 He and  =150. =0.93 GeV !!! 3. For the same reasons explained for the antineutrino case, the potential oscillation signal improves despite the fact /L=7E-3 GeV/km

Nue Summary Figures

Super-Beta The Super-Beta Beams (nufact02) (Old) Super-Beam numu: 9, km Beta-Beam anue: 37, km (Old) Super-Beam anumu: km Beta-Beam nue: 18, km Obviously: the SuperBeam lower energy is “better”. Still, the oscillation probability of the Beta-Beams are 37% (anue) and 15% (nue) respectively. The SuperBeam has more beam-related background, but is much simpler to do. Beta-beam detector backgrounds to be studied. ONE DETECTOR, ONE DISTANCE, 2X2 (due) BEAMS!

A CP or a T search? J. Sato, hep-ph In the T search, ambiguities are resolved! The tunability of the beta-beam allows additional choice of the phase cot (  m 2 13 L / 4E) CP Asymmetry T Asymmetry

General Considerations A.  13 is just the starting step for super&beta-beams. B. CP violation at low energy is almost exempt from matter effect, therefore already particularly attractive (nue beta-beam, anue beta-beam). C. Who else can do T violation without magnetic field and electron charge identification? (nue beta-beam, numu super-beam). D. CPT test by anue beta-beam, numu super-beam is the ultimate validation of the 3-family mixing model and of the CP and T measurements. E. If LSND is confirmed, 6 mixing angles and 3 CP violation phases are waiting for us! The smallness of the LSND mixing parameter implies high purity beams, the missing unitarity constraints will demand sources with different flavours. H. Minakata, H. Nunokawa hep-ph CPT Asymmetry

One simple optimization (M.M.) At the same time, it maximizes the overlap with the CP-odd term (at CERN-Frejus distance) Background should not generate a Cherenkov signal!

BetaBeam “downgrading”  =75, Flux Drop, Background Drop 11X Flux Drop!!!

Poor man’s neutrino factory? Redundant measurements of CP,T,CPT (M.M. Nufact02)

Comment on BB cost estimates (nufact02)

BB Value Proposition Natural expansion of a program that starts with a 1. non-accelerator and scalable Water Cherenkov phase 2. SuperBeam phase. 3. Betabeam phase. covering in an adaptive way supernovae detection proton decay atmospheric neutrinos solar neutrinos  13 search CP asymmetry T asymmetry CPT asymmetry. (and our retirement)

Buy a BetaBeam? If somebody will prove it can be done If somebody will show it can deliver the neutrino answers we will possibly need in years from now. If those questions will be within reach at all If the neutrino program will progress in the water cherenkov direction If there will be no other - simpler, cheaper - solution that will deliver the same or more

“Se son rose, fioriranno”. CONCLUSIONS “If they're roses, they will blossom” “Si tiene barbas, San Antón, si no la Purísima Concepción” e