1. Optimization of a neutrino factory for large  13 Golden 07 IFIC, Valencia June 28, 2007 Walter Winter Universität Würzburg

2. June 28, 2007Golden 07 - Walter Winter2 Contents Introduction Introduction Challenges for large  13 Challenges for large  13 Optimization of a high-energy neutrino factory Optimization of a high-energy neutrino factory Alternative: Low-energy neutrino factory? Alternative: Low-energy neutrino factory? … combined with superbeam? … combined with superbeam? Comparison to “competitors”: WBB, BB etc. Comparison to “competitors”: WBB, BB etc. Summary and conclusions Summary and conclusions

3. June 28, 2007Golden 07 - Walter Winter3 The setting What are „large  13 “? Assume: Decision for future program after T2K, Double Chooz, etc. Choose: sin 2 2  13 > 0.01 What are „large  13 “? Assume: Decision for future program after T2K, Double Chooz, etc. Choose: sin 2 2  13 > 0.01 Which performance indicators are relevant? Which performance indicators are relevant? –sin 2 2  13 discovered (by assumption) –sin 2 2  13 discovered (by assumption) –Mass hierarchy not a problem (for sin 2 2  13 > 0.01, at least for beta beam and NF with reasonably long L) –Mass hierarchy not a problem (for sin 2 2  13 > 0.01, at least for beta beam and NF with reasonably long L) –Sensitivity to CP violation? Or: For what fraction of all possible (true)  CP can CP violation be discovered by a given experiment? (FNAL Proton Driver study) GLoBES 2005

4. June 28, 2007Golden 07 - Walter Winter4 The „competitors“ … and how to make a selection? Wide band beam (WBB) Wide band beam (WBB) NOvA-like off-axis beam NOvA-like off-axis beam T2KK-like two detector setup T2KK-like two detector setup Beta beam (different configs) Beta beam (different configs) Neutrino factory? Neutrino factory? Possible optimization goals: 1. Physics potential optimal, effort ignored 2. Effort x Physics potential optimal 3. Robustness (systematics,  m 31 2, exposure, …) 4. …

5. June 28, 2007Golden 07 - Walter Winter5 Straightforward comparison … for sensitivity to CP violation Superbeam upgrades can easily outperform a „straightforward“ NF Superbeam upgrades can easily outperform a „straightforward“ NF How can one optimize a neutrino factory for large  13 ? How can one optimize a neutrino factory for large  13 ? (Barger, Huber, Marfatia, Winter, hep-ph/0703029)  =350 beta beam Burguet-Castell et al, 2005 Neutrino factory 3000 +7500 km 50 kt + 50 kt NuMI beam to 100kt LArTPC FNAL - DUSEL 100kt LArTPC 270kt+270kt WC detector

6. June 28, 2007Golden 07 - Walter Winter6 Designed as a discovery instrument: Flux ~ E  2, cross sections ~ E Designed as a discovery instrument: Flux ~ E  2, cross sections ~ E  As high E  as possible to obtain high event rates First oscillation maximum at E, max [GeV] ~ 2 x 10 -3 x L [km] (in vacuum,  m 31 2 = 0.0025 eV 2 ) L = 3000 km : E, max = 6 GeV L = 1000 km : E, max = 2 GeV First oscillation maximum at E, max [GeV] ~ 2 x 10 -3 x L [km] (in vacuum,  m 31 2 = 0.0025 eV 2 ) L = 3000 km : E, max = 6 GeV L = 1000 km : E, max = 2 GeV  For high E , event peak is off the osc. max. Charge ID difficult for low E if optimized for low backgrounds Charge ID difficult for low E if optimized for low backgrounds  Overall design for small  13, i.e., low backgrounds  How can that be optimized for large  13 ? Neutrino factory challenges (1) (Fig. from Huber, Lindner, Winter, 2002; Gray curve from Cervera et al, 2000)

7. June 28, 2007Golden 07 - Walter Winter7 Neutrino factory challenges (2) Matter density uncertainties <= 5% relevant for large  13 Matter density uncertainties <= 5% relevant for large  13 Reason: long L, high E (unlike superbeams with E  E res  Reason: long L, high E (unlike superbeams with E  E res   and energy threshold main impact factors for large  13  and energy threshold main impact factors for large  13 (from: Ohlsson, Winter, 2003) (from: Huber, Lindner, Winter, 2002) sin 2 2  13 =0.01,  CP =  /4

8. June 28, 2007Golden 07 - Walter Winter8 Optimization options for large  13 Opt. goal 1: Physics potential optimal, effort ignored Magic baseline (MB) Magic baseline (MB) Better detector: Golden* Better detector: Golden* Platinum channel: Plat* Platinum channel: Plat* Instead of platinum: Combination with superbeam? Instead of platinum: Combination with superbeam? Better known matter density? Better known matter density? … (from: Huber, Lindner, Rolinec, Winter, 2006) COMPETITIVE!   ~ 20 – 50 GeV

9. June 28, 2007Golden 07 - Walter Winter9 Impact of matter density uncertainties? The more information added, the less important … The more information added, the less important … In fact: at L >> 6000 km, one can measure the matter density at the level of 0.5% (Winter, hep-ph/0502097; Minakata, Uchinami, hep-ph/0612002; Gandhi, Winter, hep-ph/0612158) In fact: at L >> 6000 km, one can measure the matter density at the level of 0.5% (Winter, hep-ph/0502097; Minakata, Uchinami, hep-ph/0612002; Gandhi, Winter, hep-ph/0612158) (from: Huber, Lindner, Rolinec, Winter, 2006) Dashed: 2% Solid: 5%

10. June 28, 2007Golden 07 - Walter Winter10 Magic baseline Idea: Yellow term = 0 independent of E, oscillation parameters (Huber, Winter, 2003) Idea: Yellow term = 0 independent of E, oscillation parameters (Huber, Winter, 2003) Purpose: “Clean” measurement of  13 and mass hierarchy Purpose: “Clean” measurement of  13 and mass hierarchy Drawback: No  CP measurement at magic baseline Drawback: No  CP measurement at magic baseline  combine with shorter baseline, such as L=3 000 km Effect for large  13 : Reduces correlation  13 -  CP -  3000 Effect for large  13 : Reduces correlation  13 -  CP -  3000

11. June 28, 2007Golden 07 - Walter Winter11 Platinum channel, superbeams Compare to antineutrinos: Compare to antineutrinos:  Antineutrino channel without matter effect suppression/enhancement  Supports information on  CP for large  13 Main challenge for platinum: Requires CID, but electrons are showering for high energies Main challenge for platinum: Requires CID, but electrons are showering for high energies  So far, Plat* with 40% eff. and no upper threshold purely speculative!

12. June 28, 2007Golden 07 - Walter Winter12 Combination: NF plus superbeam? Idea: combine superbeam with neutrino factory Idea: combine superbeam with neutrino factory Superbeam peaks at much lower energies L SB ~130 km, E ~ 0.25 GeV Superbeam peaks at much lower energies L SB ~130 km, E ~ 0.25 GeV For large  13 : L NF ~ 730 km sufficient (E  = 50 GeV) For large  13 : L NF ~ 730 km sufficient (E  = 50 GeV) L/E+matter effect complementary! Matter effect + high statistics from NuFact versus operation close to vacuum osc. maximum at superbeam L/E+matter effect complementary! Matter effect + high statistics from NuFact versus operation close to vacuum osc. maximum at superbeam (Burguet-Castell et al, 2002)

13. June 28, 2007Golden 07 - Walter Winter13 Lower appearance threshold CC/NC Backgrounds: Assume BG fraction  x E -2 such that ~ 5 x 10 -6 integrated over spectrum (  ~ 10 -3 ) Lower appearance threshold CC/NC Backgrounds: Assume BG fraction  x E -2 such that ~ 5 x 10 -6 integrated over spectrum (  ~ 10 -3 )  Background increases at low energies Possibly for large  13 : (not included yet!) Use different cuts to increase efficiency (CID error at the level of ~1% OK!?) Possibly for large  13 : (not included yet!) Use different cuts to increase efficiency (CID error at the level of ~1% OK!?) Better energy resolution Was: 0.15 x E (approximation) Improve to: ? Better energy resolution Was: 0.15 x E (approximation) Improve to: ? Better detector: Golden* ?

14. June 28, 2007Golden 07 - Walter Winter14 Effort matters! Low-E neutrino factory? Opt. goal 2: Effort x physics potential optimal Lower threshold allows for lower E  - but how low? Lower threshold allows for lower E  - but how low? For example: E  = 4.12 GeV, L=1280 km: For example: E  = 4.12 GeV, L=1280 km: Effort Fraction of  CP for CPV (WW @ KEK talk, Jan. 2006) (Geer, Mena, Pascoli, 2007) How does that compare to the other competing options? How does that compare to the other competing options?

15. June 28, 2007Golden 07 - Walter Winter15 Neutrino factory superbeam (NF-SB) Idea: Use on-axis superbeam from secondary pion/kaon beam in addition to NF beam (same accelerator facility!) p    e  SB appearance  e NF Platinum e  NF Golden p    e  SB appearance  e NF Platinum e  NF Golden  4 MW superbeam basically coming for free?  Same detector might be used at same baseline (if out-of-phase bunches from SB and NF)  Compared to platinum channel, no CID is required; higher efficiencies possible  Correlated matter effect between NF and superbeam if same L  Can be combined with low-E neutrino factory idea (arXiv:0706.2862 [hep-ph])

16. June 28, 2007Golden 07 - Walter Winter16 NF-SB schematics Drawback: Target station challenging Conservative assumption: only half the muons go in NF channel (recycler?) Drawback: Target station challenging Conservative assumption: only half the muons go in NF channel (recycler?) Degrees of freedom: E p, E , L Degrees of freedom: E p, E , L (Huber, Winter, 2007) Target station/decay pipe(s): How can this be done?

17. June 28, 2007Golden 07 - Walter Winter17 NF-SB requirements E , L varied E , L varied Assume: P target ~ 4 MW leading to 0.5 10 21 useful muon decays/year (50% of „standard-NF“) Assume: P target ~ 4 MW leading to 0.5 10 21 useful muon decays/year (50% of „standard-NF“) Detektor: 50 kt Golden* Detektor: 50 kt Golden* 5 yr running time in each polarity = 10 yr total 5 yr running time in each polarity = 10 yr total 80% electron detection efficiency (without CID!) 80% electron detection efficiency (without CID!) 5% systematics (except for normalization errors 2.5%) – as usual 5% systematics (except for normalization errors 2.5%) – as usual (high-Z target; Zisman @ IDS CERN, March 2007) E p : Tested MiniBOONE-like (E p =8 GeV) and AGS-like (E p =28 GeV) WBB for the superbeam E p : Tested MiniBOONE-like (E p =8 GeV) and AGS-like (E p =28 GeV) WBB for the superbeam  E p ~ 28 GeV better choice E p window

18. June 28, 2007Golden 07 - Walter Winter18 Comparison of appearance rates NF Golden-SB appearance-NF Platinum E p chosen such that SB peaks at lower E E p chosen such that SB peaks at lower E Platinum peaks at higher E (spectrum!) Platinum peaks at higher E (spectrum!) (Huber, Winter, 2007) 2.5 10 21 useful muon decays Golden E  =5 GeV L=1250 km

19. June 28, 2007Golden 07 - Walter Winter19 Synergy: NF – Superbeam? Synergy ~ Improvement of physical potential beyond a simple addition of statistics (hep-ph/0211300) Synergy ~ Improvement of physical potential beyond a simple addition of statistics (hep-ph/0211300) Comparison neutrino factory versus NF-SB: Use double luminosity in neutrino factory, because both polarities may be used simultaneously = 10 21 useful muon decays/year for NF alone = 0.5 10 21 useful muon decays/year for NF-SB alone ~ similar effort assumption Comparison neutrino factory versus NF-SB: Use double luminosity in neutrino factory, because both polarities may be used simultaneously = 10 21 useful muon decays/year for NF alone = 0.5 10 21 useful muon decays/year for NF-SB alone ~ similar effort assumption Comparison WBB versus NF-SB: more difficult since detector effort versus accelerator effort Use WBB with E p =28 GeV and 500 kt WC detector for comparison Comparison WBB versus NF-SB: more difficult since detector effort versus accelerator effort Use WBB with E p =28 GeV and 500 kt WC detector for comparison Open questions: Open questions: –What option has the better absolute performance? –L-E  Optimization? –What if two baselines used for the NF-SB? (similar to Burguet-Castell et al)

20. June 28, 2007Golden 07 - Walter Winter20 L-E  Optimization: CPV discovery Geer et al. choices are sufficiently close to optimum Geer et al. choices are sufficiently close to optimum NF-SB synergistic, better performance than NF alone NF-SB synergistic, better performance than NF alone Our choices : L = 900 km, E  = 5 GeV and L=1250 km, E  =5 GeV (given the low energy ~ minimum effort ~ constraint) Our choices : L = 900 km, E  = 5 GeV and L=1250 km, E  =5 GeV (given the low energy ~ minimum effort ~ constraint) CP fraction for discovery (3  ), sin 2 2  13 =0.1 (Huber, Winter, 2007)

21. June 28, 2007Golden 07 - Walter Winter21 Use two baselines? What happens if NF and SB have two detectors (50 kt each) at L NF and L SB ? What happens if NF and SB have two detectors (50 kt each) at L NF and L SB ? Matter effect uncorrelated between L NF and L SB Matter effect uncorrelated between L NF and L SB  Same baseline close to optimal!  In addition: correlated matter effect helps: ~ 2% improvement in CP fraction (Huber, Winter, 2007) E  = 5 GeV 0.82 0.8 Our choice

22. June 28, 2007Golden 07 - Walter Winter22 Comparison to competitors NF-SB can outperform any of the discussed setups except from beta beam NF-SB can outperform any of the discussed setups except from beta beam But: Luminosity choice for beta beam arbitrary in this context! Parameters:  =350, L=712 km, 5 yr x 5.8 10 18 useful 6 He decays/yr, 5 yr x 2.2 10 18 useful 18 Ne decays/yr (Burguet-Castell et al, 2005) But: Luminosity choice for beta beam arbitrary in this context! Parameters:  =350, L=712 km, 5 yr x 5.8 10 18 useful 6 He decays/yr, 5 yr x 2.2 10 18 useful 18 Ne decays/yr (Burguet-Castell et al, 2005) (Huber, Winter, 2007) E p =28 GeV 500 kt WC

23. June 28, 2007Golden 07 - Walter Winter23 What does it take to outperform any setup? (… neglecting „effort“) Additional platinum channel: small effect Additional platinum channel: small effect Additional MB or higher E  ~10 GeV: especially useful for small sin 2 2  13 ~ 0.01 Additional MB or higher E  ~10 GeV: especially useful for small sin 2 2  13 ~ 0.01 Additional large (500 kt) WC detector at same site: largest effect for large  13 Additional large (500 kt) WC detector at same site: largest effect for large  13  Luminosity matters to outperform beta beam!

24. June 28, 2007Golden 07 - Walter Winter24 Potential further improvements Better golden efficiency (possibly traded in for higher backgrounds) Better golden efficiency (possibly traded in for higher backgrounds) Muon recycling from SB decay pipe? Muon recycling from SB decay pipe? Further E p optimization/SB horn Further E p optimization/SB horn Larger detector? Detector hybrid? Larger detector? Detector hybrid? Optimization of „magnetization fraction“ (part of the detector to be magnetized) Optimization of „magnetization fraction“ (part of the detector to be magnetized) Staged concepts? Such as 1. WBB Golden*, 2. NF-SB, 3. NF-SB Golden*+WC Staged concepts? Such as 1. WBB Golden*, 2. NF-SB, 3. NF-SB Golden*+WC Up to ~ 4 x NF luminosity Maximum synergy? Optimized NF-SB statistics Optimized funding?

25. June 28, 2007Golden 07 - Walter Winter25 A short note on the Mass hierarchy measurement Requirement: Determine mass hierarchy for all possible values of  CP (Fraction of  CP =1) @ 3  Requirement: Determine mass hierarchy for all possible values of  CP (Fraction of  CP =1) @ 3  Results: Results: –Low-E NF: L > 800 km, almost indep. of E  –NF-SB: L > 500 km sufficient Reason: Schwetz-effect (hep-ph/0703279)  Since we find L > 900 km for CPV, any of these requirements is fulfilled! TALK THIS AFTERNOON

26. June 28, 2007Golden 07 - Walter Winter26 Summary Optimization goals: Optimization goals: –Cost x Physics potential optimal: NF-SB? –Physics potential optimal: Beta beam? NF-SB WC ? High-E NF? Discovery machine (sin 2 2  13 0.01) : Different requirements for Discovery machine (sin 2 2  13 0.01) : Different requirements for –Machine: Target station, muon energies, baseline(s) –Detector: Optimization for high effs versus low backgrounds But: Better low-energy threshold useful for both! (though no prerequisite for high-E NuFact) Optimize for two different NuFacts until T2K, Double Chooz, NOvA etc. finished? Optimize for two different NuFacts until T2K, Double Chooz, NOvA etc. finished?