Based on:

1

• Optimal ß-beam
• at the CERN-SPS

presented by Elena Couce NuFact05, June 24th,
Frascati

• Based on
• J.Burguet-Castell, D.Casper, E.C.,
  J.J.Gómez-Cadenas, P.Hernández,
  arXivhep-ph/0503021.

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Contents
What are we doing?
Presentation
Procedure
Optimization
Optimal distance for CERN-SPS
Optimal boost for CERN ? Frejus
Optimal ß-beam (refurbished SPS)
Reference setups
Comparison
Conclusions
3
Presentation

• We know neutrinos oscillate.
• But we still dont know enough about how they
  do it
• The Unknowns
• How far can a ?-beam go in the measurements of
  the unknowns?
• What is the best ?-beam we can do with the SPS
  accelerator? How good is it?

absolute masses, ?13, ?, ?23 octant, mass
hierarchy
4
Presentation

• In this study we have analyzed the potential of a
  ?-beam based on the CERN-SPS, trying to optimize
  its sensitivity in three different scenarios
• For a fixed existing baseline of L130 km
  (Frejus)
• With a simultaneous optimization of the baseline
• For an improved SPS

5
Presentation

• We have explicitly performed the sensitivity
  comparison of 4 setups
• SPS ? Frejus, at atmospheric peak
• (M. Mezzetto, J. Phys. G.29, 2003)
• SPS ? Frejus, at optimal boost
• SPS, at optimal baseline and boost
• Refurbished SPS, with ? 350, L 730 km
• (J. Burguet-Castell et al, hep-ph/0312068)

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Contents
Presentation
How are we doing it?
Procedure
Optimization
Optimal distance for CERN-SPS
Optimal boost for CERN ? Frejus
Optimal ß-beam (refurbished SPS)
Reference setups
Comparison
Conclusions
7
Procedure

• For this study we assume
• Atmospheric and solar parameters
• Intensities
• Run time 10 years
• 440 kton water Cherenkov detector

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Procedure

• Measurements
• Golden
  detected µ
• Disappearance
  detected e
• Fluxes

• Energy bins
• 0-500 MeV
• 500-750 Mev
• and every 250 Mev
• (first bin is discarded for high ?)

9
Procedure

• Signal/background
• Intrinsic background background on appearance
  signal from misidentified ?e

10
Procedure

• Signal/background
• Atmospheric background
• Very large!
• Additional cuts

? Selection
120 32
150 32
350 32

• End point of spectrum

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Procedure

• Signal/background
• Atmospheric background
• Very large!
• Additional cuts

? Selection Emax cut
120 32 19
150 32 24
350 32 30

• Low energy cut (for higher ?)

• End point of spectrum

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Procedure

• Signal/background
• Atmospheric background
• Very large!
• Additional cuts

? Selection Emax cut Emin cut
120 32 19 19
150 32 24 24
350 32 30 19

• Directional cut

• End point of spectrum

• Low energy cut (for higher ?)

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Procedure

• Signal/background
• Atmospheric background
• Very large!
• Additional cuts

? Selection Emax cut Emin cut cos?l cut
120 32 19 19 15
150 32 24 24 15
350 32 30 19 5

• Directional cut

• End point of spectrum

• Low energy cut (for higher ?)

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Procedure

• Signal/background
• Atmospheric background
• Its still too large
• 100 times more than the intrinsic
• An additional rejection factor of 104 seems
  feasible, from bunching of the parent ions.
• (from M. Mezzetto, J. Phys. G.29, 2003)

atmospheric background negligible
15
Procedure

• Signal/background
• Energy reconstruction

Bias between true and reconstructed energies
Efficiency matrices to account for migrations
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Procedure

• Signal/background
• Efficiency matrices
• For appearance signal
• For disappearance

17
Procedure

• Systematic errors
• 5 uncertainty in fiducial mass of detectors
• 1 uncertainty in cross-section ratio for

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Contents
Presentation
Procedure
Optimization
Optimization
Optimal distance for CERN-SPS
Tunning up Frejus!
Optimal boost for CERN ? Frejus
Optimal ß-beam (refurbished SPS)
Reference setups
Comparison
Conclusions
19
Optimal Boost for CERN ? Frejus

• Standard scenario (M. Mezzetto, J. Phys.
  G.29, 2003)
• ?60/100 (atmospheric peak)
• HOWEVER
• Poor energy resolution

bad for sensitivity, degeneracies
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Optimal Boost for CERN ? Frejus

• Can we do BETTER?
• Moving off the atmospheric peak
• Osc. prob. goes down ? bg grows faster ?
• Energy resolution increases ?
• Sowhat is the optimal boost?
• Sensitivity to CP-violation vs ?
• Sensitivity to ?13?0 vs ?

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• Sensitivity to CP-Violation vs ?

Minimum value of true ? (in the first quadrant)
for which we can establish that THERE IS
CP-violation at 99 CL or better, as a function
of ?
That is We can distinguish ? from
non-CP-violating ? (0º and 180º), for any best
fit value of ?13
22

• Sensitivity to ?13?0 vs ?

Minimum value of true ?13 for which we can
establish that ?13 ? 0 at 99 CL or better, as a
function of ?
That is We can distinguish a non-zero value for
?13 for any best fit value of ?
23

• Sensitivity to CP-Violation vs ?
• Sensitivity to ?13?0 vs ?

24
Optimal Boost for CERN ? Frejus

• Can we do BETTER?
• Moving off the atmospheric peak
• Osc. prob. goes down ? bg grows faster ?
• Energy resolution increases ?
• Sowhat is the optimal boost?
• Sensitivity to CP-violation vs ?
• Sensitivity to ?13?0 vs ?

?gt100 much better for CP-vio
And with the same SPS!
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Contents
Presentation
Procedure
Optimization
Optimization
Heating up the SPS!!
Optimal distance for CERN-SPS
Optimal boost for CERN ? Frejus
Optimal ß-beam (refurbished SPS)
Reference setups
Comparison
Conclusions
26
Optimal distance for CERN-SPS

• The observed signal is proportional to the ?
  boost, if the baseline is varied simultaneously
  (so as to stay on the atmospheric peak)
• Flux
• Cross sections (at least)
• (as we will see shortly, this is valid only while
  ?lt400)

(bg as well)
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Optimal distance for CERN-SPS

• Whats the best the SPS can do??
• Maximum boost ? 150 (250)
• Moving beyond Frejus
• Osc. prob. goes up ?
• Sowhats the optimal distance?
• Sensitivity to CP-violation vs L
• Sensitivity to ?13?0 vs L

• ? Energy resolution is SPS-optimal ?

28

• Sensitivity to CP-violation vs L
• Sensitivity to ?13?0 vs L

29
Optimal distance for CERN-SPS

• Whats the best the SPS can do??
• Maximum boost ? 150 (250)
• Moving beyond Frejus
• Osc. prob. goes up ?
• Sowhats the optimal distance?
• Sensitivity to CP-violation vs L
• Sensitivity to ?13?0 vs L

• ? Energy resolution is SPS-optimal ?

L 300 km (symmetric option)
30
Contents
Presentation
Procedure
Optimization
Optimization
Optimal distance for CERN-SPS
Optimal boost for CERN ? Frejus
Looking beyond!
Optimal ß-beam (refurbished SPS)
Reference setups
Comparison
Conclusions
31
Optimal ß-beam (J. Burguet-Castell et al,
hep-ph/0312068)

• Refurbished SPS could reach ? 500-600
• whats the best ß-beam we can do??
• Restriction 440 kton water detector
• Maximum boost ? 350
• afterwards
• non-elastic cross section begins to dominate
• single-pion background increases
• Optimal distance L 730 km (atm. peak)
• BUT
• it needs a refurbished SPS or a more powerful
  accelerator LHC? Tevatron?

32
Contents
Presentation
Procedure
Optimization
Optimal distance for CERN-SPS
Optimal boost for CERN ? Frejus
Optimal ß-beam (refurbished SPS)
The players
Reference setups
Comparison
Conclusions
33
Reference Setups
Setup III
Setup II
Setup 0
Setup I
Optimal Frejus
Optimal SPS
Optimal ß-beam
Original Frejus
?60/100 L130 km
? 120 L130 km
? 150 L300 km
? 350 L730 km
34
Contents
Presentation
Procedure
Optimization
Optimal distance for CERN-SPS
Optimal boost for CERN ? Frejus
Optimal ß-beam (refurbished SPS)
Reference setups
Let the game begin!
Comparison
Conclusions
35
Comparison

• Looking for CP-violation

Region of the ? - ?13 plane where we can
establish, at 99 CL or better, that THERE IS
CP-violation

• Sensitivity for Setup III
• 10º for delta
• 10-4 for sin2(2 ?13)

And again this means We can distinguish ? from
non-CP-violating ? (0º and 180º), for any best
fit value of ?13
36
Comparison
Comparison

• Looking for ?13?0

Region of the ?13 - ? plane where we can
establish, at 99 CL or better, that ?13 ? 0.
One order of magnitud between the sensitivities
of setups 0 and III
Which means We can tell ?13 ? 0 for any best fit
value of ?
37
Comparison

• Looking at ?13 and ?

38
Comparison

• Looking at ?13 and ?

39
Discrete degeneracies
Comparison
Sensitivity to ?m223 sign Sensitivity to ?23 octant
Setup 0 None None
Setup I None None
Setup II Low A little better for ?150/250 Low A little better for ?150/250
Setup III Good for ?13 gt 4º Some A little better for ?350/580
40
Discrete degeneracies
Comparison
Sensitivity to ?m223 sign Sensitivity to ?23 octant
Setup 0 None None
Setup I None None
Setup II Low A little better for ?150/250 Low A little better for ?150/250
Setup III Good for ?13 gt4º Some A little better for ?350/580
Region of the ? - ?13 plane where we can
establish, at 99 CL or better, the sign of
?m223 That is We can distinguish the true sign
from the wrong one for any best fit value of ?
and ?13
41
Discrete degeneracies
Comparison
Sensitivity to ?m223 sign Sensitivity to ?23 octant
Setup 0 None None
Setup I None None
Setup II Low A little better for ?150/250 Low A little better for ?150/250
Setup III Good for ?13 gt4º Some A little better for ?350/580
42
Discrete degeneracies
Comparison
Sensitivity to ?m223 sign Sensitivity to ?23 octant
Setup 0 None None
Setup I None None
Setup II Low A little better for ?150/250 Low A little better for ?150/250
Setup III Good for ?13 gt4º Some A little better for ?350/580
Region of the ? - ?13 plane where we can
distinguish between ?23 40.7º and ?23 49.3º,
at 99 CL or better And again for any best fit
value of ? and ?13
43
Contents
Presentation
Procedure
Optimization
Optimal distance for CERN-SPS
Optimal boost for CERN ? Frejus
Optimal ß-beam (refurbished SPS)
Reference setups
Comparison
And the winner is
Conclusions
44
Conclusions

• For the CERN ? Frejus baseline
• ? ? 100 shows more sensitivity
• same accelerator, same detector, same place,
• better results!

45
Conclusions

• While thinking on expending lots of on a 440
  kTon detector
• farther appears to be better!
• (L 300 km)
• same accelerator, same detector
• better results!
• Is there a suitable baseline?

46
Conclusions

• And while we are at it
• why not go for the best?
• different accelerator, same detector, more money
• Yes, it is more expensive, but
• Setup III is comparable with NuFact!
• Refurbished SPS? LHC? Tevatron? Somewhere else?
• RD!

• Caveats
• We need precise measurements of atmospheric
  parameters!
• (T2K-I atmospheric data)
• Are the fluxes assumed here really possible?

47
Conclusions

• If Frejus baseline ? ? 100

• L300 km looks more promising

• Some further RD on ?-beams could be worth our
  time!