Precision Neutrino Oscillation Measurements & the Neutrino Factory

1. Precision Neutrino Oscillation Measurements & the Neutrino Factory Scoping Study for a Future Accelerator Neutrino Complex – Discussion Meeting Steve Geer, 6 May 2005

2. Introduction • Neutrino physics is exciting • The main accelerator-based neutrino physicsquestions we want to address are: • What is the rough value of sin22q13 ? • Is the Mass Hierarchy Normal or Inverted ? • What is the value of d (Is there CPV in the n sector) ? • What is the precise value of q23 (Is sinq23 =1) ? • Is three-flavor mixing the whole story ? • Answering these questions will be challenging

3. _ _  e e 50% e , 50% - e- e 50% e , 50%  Muon decay kinematics very well known: _ _ Neutrino Factory Beam Properties Precisely known neutrino fluxes & spectraPrecise comparison between neutrino & antineutrino properties possiblee and  beams (a wealth of measurements)

4.  ee  CC   - CC Low Backgrounds Neutrino factories provide electron neutrinos (antineutrinos)in addition to muon anti-neutrinos (neutrinos). e oscillations at a neutrino factory result in the appearance of a “wrong-sign” muon … one with opposite charge to those stored in the ring: Backgrounds to the detection of a wrong-sign muon are expected to be at the 10-4 level background-freee oscillations with amplitudes as small as O(10-4) can be measured !

5. Rates Many groups have calculated signal & background rates. Example: Hubner, Lindner & Winter; hep-ph/0204352 JPARC-SK: Beam = 0.75 MW, Mfid = 22.5 kt, T = 5 yrs JPARC-HK: Beam = 4 MW, Mfid = 1000 kt, T = 8 yrs NUFACT: Beam = 2.6  1020 decays/yr, Mfid = 100 kt, T = 8 yrs m322 = 0.003 eV2 , m212 = 3.710-5 eV2 , sin2 2q23 = 1, sin2 2q13= 0.1, sin2 2q12= 0.8, d = 0 Superbeams Neutrino Factory JPARC-SK JPARC-HK Signal 140 13000 65000 Background 23 2200 180 S/B 6 360

6. Measurements 10 kt LAr detector, L = 7400 km, 30 GeV nu-factory with 1021m+decays. There is a wealth of information that can be used at a neutrino factory. Oscillation parameters can be extracted using events tagged by: • right-sign muons • wrong-sign muons • electrons/positrons • positive t-leptons • negative t -leptons • no leptons Bueno, Campanelli, Rubbia; hep-ph/00050007 2 (m+ stored and m- stored)

7. The Challenge

8. Huber, Winter; Phys. Rev. D68, 2003 7500 km + 3000 km sin22q13 Mass Hierarchy CP Violation 10-5 10-4 10-3 10-2 10-1 sin22q13 Neutrino Factory Sensitivity The Neutrino Factory provides hope that the full program (measuring q13, determining the mass hierarchy, & searching for CPV) can be accomplished if sin22q13 > O(10-4) ! • As q13  0, • P(nenm)  0 If sin22q13 < O(10-4) a NF would make the first observation of nenm appearance important test of three-flavor mixing.

9. nent and Other Channels If sin22q13 > O(10-3) the nentchannel enables elimination of false solutions for combined NF + SB scenarios (Donini et al; hep-ph/020940, and others). The nent channel is unique to NFs  the only direct test of nentmixing. To analyze the full NF potential the nentchannel must be analyzed together with right-sign & wrong-sign muons, and the two NC rates or the two ne rates.

10. sin22q13 Reach (3s) YEAR “Short-Term” Program Ability to observe non-zero q13 versus time Calculations ofW. Winter Within bands dvaries Substantial uncertainties on time-axis … but thetrend is clear

11. sin22q13 Reach (3s) YEAR “Longer-Term” Program ? Calculations ofW. Winter Even greater uncertainties on time-axis Need to develop a clearer picture: NF timescale ? Branching point(s) ? Alternative paths and basis for choice ?

12. sin22q13 YEAR Mass Hierarchy Sensitivity Figures like thiscan help us developthe neutrino physics“road map” It would be good to develop an agreed on list of figures and experiments to beplotted, and timelinesto be used.

13. Wish-List for Study There have been a series of neutrino physics studies in Europe, Japan and the US, aimed at understanding future needs and options. Lots has been done, but there are still some questions to be nailed … for example: • Is a NF needed if sin22q13 is large ? • What is the minimum NF energy that will deliver the physics (cost issue) ? • How do we best test the three-flavor frameworkand how do we quantify the test? • How can we best articulate the physics case for precision measurements of the neutrino parameters if sin22q13 > O(0.01), & continuing the program if sin22q13 < O(0.01) ?

14. Final Remarks Neutrino Factories offer great physics potential If, within our lifetimes, we want answers to the basic neutrino questions then, beyond the foreseen programwe will need to make a big step in detectors and facilities.We must continue to work on articulating the physicscase for this big step  plots, numbers, road-map. We also need to work on consensus within the neutrinocommunity (proton drivers, beta beams, neutrino factories). The physics drives us (not the facility).Cost is an issue for all our desired future facilities. For NFs muon acceleration is a cost driver. The NF energy needed must be considered carefully.