1. The Low-Energy Neutrino Factory Alan Bross, Malcolm Ellis, Steve Geer, Olga Mena, Silvia Pascoli “Olga and Silvia did all the clever stuff ” IPPP/06/85; DCPT/06/170; Roma-TH-1443; FERMILAB-PUB-07-021-E

2. Alan Bross IDS Meeting RAL January 16, 20082 Neutrino Factory – ISS Preliminary Design  Proton Driver  Target, Capture, Decay     Bunching, Phase Rotation u Reduce  E  Cooling  Acceleration  103 MeV  25 & 50 * GeV  Storage/Decay ring * Still under study Why Study Low-Energy Neutrino Factory?

3. Alan Bross IDS Meeting RAL January 16, 20083 Well, Cost is Certainly a Motivation ISS Preliminary  Going from 25 GeV (maybe 50) to 4 GeV u Eliminates FFAGs u Fewer RLAs u Smaller and possibly cheaper storage ring(s) u Saves 25-40% s $1B USD?

4. Alan Bross IDS Meeting RAL January 16, 20084  Up to now, the NFMCC has focused on neutrino factories with energies of 20-50 GeV  The collaboration has not studied lower energy neutrino factories because, until recently, the proposed NF detectors have had muon energy thresholds (for measuring wrong-sign muons with adequate background rejection) of a few GeV, which imposes a minimum threshold on the desirable neutrino energy, and hence a minimum NF energy  ~20 GeV.  In the ISS there was progress on understanding how to reduce the detector thresholds for measuring wrong-sign muons … so we can now consider lower energy neutrino factories. But, Can the Physics Goals be Accomplished with a LE-NF?

5. Alan Bross IDS Meeting RAL January 16, 20085 Fine-Resolution Totally Active Segmented Detector Simulation of a Totally Active Scintillating Detector (TASD) using No a and Miner a concepts with Geant4 3 cm 1.5 cm 15 m u 3333 Modules (X and Y plane) u Each plane contains 1000 slabs u Total: 6.7M channels  Momenta between 100 MeV/c to 15 GeV/c  Magnetic field considered: 0.5 T  Reconstructed position resolution ~ 4.5 mm 15 m 150 m B = 0.5T

6. Alan Bross IDS Meeting RAL January 16, 20086 “Special” Detector Has to be Magnetized  Magnetized Totally Active Sampling Calorimeter 25kT  Magnets  15m  X 15m long -0.5T u Times 10! u Cost estimate s $140-680M –Conventional SC  New Ideas u High T c SC s No Vacuum Insulation u VLHC SC transmission line s Technically proven s Might actually be affordable

7. Alan Bross IDS Meeting RAL January 16, 20087 Superconducting Transmission Line makes this concept possible (affordable)  SCTL not a “concept” – prototyped, tested and costed for the VLHC Project at Fermilab

8. Alan Bross IDS Meeting RAL January 16, 20088 Parameters $1000/m  $50M 100 kA op demonstrated

9. Alan Bross IDS Meeting RAL January 16, 20089 TASD Performance  Event Reconstruction Efficiency Muon charge mis-ID rate Excellent  E

10. Alan Bross IDS Meeting RAL January 16, 200810  E of TASD With the expected energy resolution of TASD it, can fully exploit the rich oscillation pattern at low energy  0.5 to 1.5 GeV (and go to E threshold of 0.5 GeV)

11. Alan Bross IDS Meeting RAL January 16, 200811 Detector Performance Issues What are the sensitivities to detector backgrounds?  At low energy  background rates grow substantially  How does this affect the sensitivity of the analysis and the potential physics reach?  and K decay in flight become the main background concerns u 1-5 X 10 -4 level.  Figure of merit u Ratio of particle decay lengths to interaction lengths. s For TASD R= 1; for the Magnetized Fe-Scintillator detector it is 8. s So TASD 10 times worse than in Fe-Scint  But, TASD will have vastly superior kink detection (40 hits on  track before decay, continuous dE/dx meas. better  E s We believe that these properties will allow us to control backgrounds to the 10 -3 level or better.

12. Alan Bross IDS Meeting RAL January 16, 200812 The Physics Study  Baseline: 1480km (FNAL-Henderson) u Also did Homestake to Fermilab  Choose NF Energy ~ 4 GeV (Actually 4.12 GeV). This is motivated by the realization that for baselines O(1000km), if  13 is not very small, the oscillation pattern is extremely rich below ~4 GeV.  Will divide the simulated data into 3 energy bins, and fit the wrong-sign muon rates for each bin with positive- & negative- muons stored in the ring (6 rates to fit). Can also fit 6 right-sign muon rates.  Energy bins: En = [0.8,1.5], [1.5,3.5], [3.5,4.12] GeV.  Bins chosen to optimize ability to resolve degenerate solutions.

13. Alan Bross IDS Meeting RAL January 16, 200813  NF performance: BASIC: (5 years)  (3  10 20 useful decays/yr)  (2 signs)  (20Kt fid. Mass) = 3  10 22 Kt-decays  (2 signs) BETTER: (10 years)  (5  10 20 useful decays/yr)  (2 signs)  (20Kt fid. Mass) = 1  10 23 Kt-decays  (2 signs)  Detector efficiency  =0 for E n 0.5 GeV  Energy resolution – 30% (extremely conservative: NOVA ~ 6%, expect TASD to be better)  Central values chosen: sin 2  12 = 0.29,  m 2 21 = 8x10 -5 eV 2,  m 2 31 = 2.5x10 -3 eV 2 and  23 = 40°. Input Parameters

14. Alan Bross IDS Meeting RAL January 16, 200814  L=1480 Km  Simulate  13 =3 o,  =0 then fit e   & e   rates  Fits for 3 neutrino energy bins:  13 (degrees)  (degrees) Dark: 0.8 – 1.5 GeV Cyan: 1.5 – 3.5 GeV Magenta: >3.5 GeV  Each fit yields one correct & one additional (“intrinsic degeneracy”) solution … but the additional solutions for the 3 bins do not overlap  Unique Solution ! Illustration of how it works: 90%, 95%, 99% CL Contours Solutions corresponding to correct sign  m 2 Resolving Degeneracies

15. Alan Bross IDS Meeting RAL January 16, 200815  13 (degrees)  (degrees) Illustration of how it works:  Repeat, analysis, picking the wrong sign for  m 2.  The solutions for the 3 bins are no longer consistent  Can determine mass hierarchy.  There is a 3 rd degeneracy, arising from the same predicted rates for  23 &  /2-  23 … can show similar plots to illustrate how this degeneracy gets resolved. 90%, 95%, 99% CL Contours Solutions corresponding to incorrect sign  m 2 Resolving Degeneracies II

16. Alan Bross IDS Meeting RAL January 16, 200816 Disappearance Channel  Central values used: sin 2  23 = 0.4 and 0.44  Maximal mixing rejected at 99% CL if sin 2  23 < 0.48 (  23 < 43.8°) in the low luminosity case 90%, 95% & 99% (2 dof) CL contours resulting from the fits at L = 1480 km, 3 x 10 22 kton-decays. Only disappearance data have been used

17. Alan Bross IDS Meeting RAL January 16, 200817 Golden Channel e   90%, 95% & 99% (2 dof) CL contours resulting from the fits at L = 1480 km, 1 x 10 23 kton-decays.  13 = 1°, four central values for  = 0°, 90°, -90° & 180° No Background Background @ 10 -3

18. Alan Bross IDS Meeting RAL January 16, 200818 Mass hierarchy can be determined for all , if  13 > 3 o (sin 2 2  13 > 0.01) Mass Hierarchy L=1480 Km  Hierarchy - 99% CL (2 D.O.F.)  Red (no backgrounds) u Dotted - 1 X 10 23 KT- years u Solid – 3 X 10 22 KT-years  Black (Background @ 10 -3 ) u Short dash - 1 X 10 23 KT- years u Long dash – 3 X 10 22 KT- years

19. Alan Bross IDS Meeting RAL January 16, 200819  Reach  -CP Reach 99% CL (2D.O.F.)  Red (no backgrounds) u Dotted - 1 X 10 23 KT- years u Solid – 3 X 10 22 KT-years  Black (Background @ 10 -3 ) u Short dash - 1 X 10 23 KT-years u Long dash – 3 X 10 22 KT- years

20. Alan Bross IDS Meeting RAL January 16, 200820 95% CL Error on  13 vs. Bkg  13 = 2 o  13 = 3 o  13 = 8 o No dependence on  for the several values of  that have been studied

21. Alan Bross IDS Meeting RAL January 16, 200821 95% CL Error on  Solid:  = 0 Dashed:  = 90 o  13 = 2 o  13 = 3 o  13 = 8 o

22. Alan Bross IDS Meeting RAL January 16, 200822

23. Alan Bross IDS Meeting RAL January 16, 200823 Summary  A Low-Energy Neutrino Factory (coupled with the right detector) gives excellent capability to measure leptonic CP violation and explore the full neutrino mixing matrix, even if the mixing angle  13 is very small (  13 ~ 1°).  In the absence of backgrounds, the neutrino mass hierarchy could be resolved down to sin 2 2  13 =0.002 (0.0003) in the low (high) luminosity scenario, regardless of the value of the CP violating phase .  If we add a 10 -3 background, those limits translate into 0.005 and 0.001.  The 99% CL (2 dof) error on the CP violating phase is 0.01 (0.001) in the most pessimistic (optimistic) scenario.

24. Alan Bross IDS Meeting RAL January 16, 200824 Summary  The intrinsic degeneracy is resolved due to the energy binning analysis at the 99% CL. The  23 degeneracy is also solved in the range 2° <  13 < large as well as from  13 = 2° down to  13 = 0.5 ° in both the low and high luminosity scenarios due to the impact of the solar term at small energies and large distances.  For the intermediate values  13 ~ 2°, the  23 degeneracy is present only at the 95, 99% CL (2 dof) in the low luminosity scenario, but it does not interfere with the measurement of CP violation.  Maximal mixing is rejected at the 99% CL (2dof) if  23 > 43.8° just-by exploiting the disappearance data.  Even if  13 -> 0, from the disappearance channel data, we could determine the neutrino mass hierarchy at the 95% CL (2 dof) in the high luminosity scenario.

25. Alan Bross IDS Meeting RAL January 16, 200825 Outlook  A Low-Energy Neutrino Factory (coupled with the right detector) gives excellent capability in exploring the full neutrino mixing matrix and measure leptonic CP violation  A finely segmented TASD is quite possibly the right analysis tool for a Low-Energy NF u Much more simulation/study needs to be done, but the initial results are promising  A Low-Energy Neutrino Factory (4 GeV) is certainly cheaper than a 20-50 GeV facility (   -25-40%)  Plus with proper planning a Low-Energy Neutrino Factory might be upgradeable to higher energy

26. Alan Bross IDS Meeting RAL January 16, 200826 Target, B-rot, Cool Mu2e 8GeV 4GeV NuFact MC-R&D Hall 0.2-4GeV mu-Linac To DUSEL Low Energy NF and Project X