Elena Couce (IFIC - U. Valencia)Based on a collaboration with D. Casper, JJ Gomez-Cadenas and P.

Hernandez

April 27 2006ISS meeting at RAL (UK)

Experimental ChallengeExperimental Challenge

Next generation neutrino oscillation Next generation neutrino oscillation experiments:experiments:

Need for precision measurements of very small Need for precision measurements of very small oscillation probabilities oscillation probabilities at E/L at E/L mm22

atmatm :: High StatisticsHigh Statistics Low SystematicsLow Systematics

CP-VIO??? 2

23

23

sign

octant

?

?

m

13 ?

So why a Water Cherenkov So why a Water Cherenkov Detector?Detector?

Because water is cheap… so we can make it Because water is cheap… so we can make it large!large!

Let’s say… 20 x !Let’s say… 20 x !

It has other uses: It has other uses: atmospherics, proton decay, atmospherics, proton decay, supernova…supernova…

However it cannot detect the charge…However it cannot detect the charge…

Is signal/background ratio good enough?Is signal/background ratio good enough?

SK

≈ 1000 kTon

SuperBeamSuperBeam -Factory-Factory β-beamβ-beam√ √

At least ~10 times larger than for any other technology!

In this talk we’re presenting the results of a complete and In this talk we’re presenting the results of a complete and realistic realistic

MC simulation of a MC simulation of a Water CherenkovWater Cherenkov detector exposed to a detector exposed to a β-β-beambeam

ProcedureProcedure Fluxes:Fluxes:

Nature’s oscillation parameters:Nature’s oscillation parameters:

Analysis cuts:Analysis cuts:

L = 700 Km = 350 5 + 5 years 5.8 1018 d.p.y. of 6He 2.2 1018 d.p.y. of 18Ne

L = 130 Km = 100 5 + 5 years 5.8 1018 d.p.y. of 6He 2.2 1018 d.p.y. of 18Ne

High High β-Beam β-BeamLow Low β-Beam β-Beam

mm221212 sinsin22θθ1212 mm22

2323 sinsin22θθ2323 sinsin22θθ1313 7.92 10-5 eV2 0.314 2.4 10-3 eV2 0.44 2.74 10-3 40º

G.L. Fogli hep-ph/0506083

Fiducial:Fiducial:

Selection:Selection: PID Michel e-

Distance to walls > 2 m Maximum of 10 hits in outer det.

Fiducial cuts: Fiducial cuts: Signal and Background spectra

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66HeHe

66HeHe1818NNee

1818NNee

-- oo++ -- oo++

-- oo++ -- oo++

PID cutPID cut

Electron/muon separation:Electron/muon separation:μ-like event e-like event

Selecting 1 ring -like events

PID cut : PID cut : Signal and Background spectra

High- -beam:

PID cut

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PID cut

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66HeHe

66HeHe1818NNee

1818NNee

-- oo++ -- oo++

-- oo++ -- oo++

Michel e- cutMichel e- cut

ee

Signal

Selecting events with a second delayed ring after the

first

Michel e-

t ~ decay time

Michel e- cut: Michel e- cut: Signal and Background spectra

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Delayedring cut

Delayedring cut

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PID

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66HeHe

66HeHe1818NNee

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-- oo++ -- oo++

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Low- -beam after fiducial + PID + Michel e- cuts:

66HeHe

66HeHe1818NNee

1818NNee

-- oo++

-- oo++ -- oo++

-- oo++

Michel e- cut: Michel e- cut: Absolute # of events

Signal/Bkgd final compositionSignal/Bkgd final composition

High- -beam after fiducial + PID + Michel e- cuts:

Low- -beam after fiducial + PID + Michel e- cuts: 1818NN

ee

66HeHe

BKGNDSIGNAL SIGNAL BKGND

SIGNAL BKGND

1818NNee

BKGNDSIGNAL

66HeHe

SIGNAL BKGND

High- -beam after fiducial + PID + Michel e- + Energy > 500 MeV cuts:

Low- -beam after fiducial + PID + Michel e- cuts: 1818NN

ee

66HeHe

BKGNDSIGNAL SIGNAL BKGND

SIGNAL BKGND

1818NNee

BKGNDSIGNAL

66HeHe

SIGNAL BKGND

Signal/Bkgd final compositionSignal/Bkgd final composition

Cuts evaluationCuts evaluation: : Relative effect of each cut

Low- -beam:

1818NNee

66HeHe

0%

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Normalized to fiducial events

Cuts evaluationCuts evaluation: : Relative effect of each cut

Low- -beam

Cuts evaluationCuts evaluation: : Signal to noise ratio

High- -beam

ConclusionsConclusions

AA β-beamβ-beam with a Water Cherenkov should have with a Water Cherenkov should have good signal to noise ratio well below good signal to noise ratio well below θθ13 13 = = 3º 3º (s/n = 60)(s/n = 60)

Water Ckov detectors might not be the best Water Ckov detectors might not be the best choice in terms of performance for β-beam choice in terms of performance for β-beam experiments (particularly at high experiments (particularly at high ). However ). However the increase in statistics compensates, up to the increase in statistics compensates, up to ~ ~ 350350

The s/n is better for high The s/n is better for high β-beam, particularly β-beam, particularly for for . In addition it allows energy binning.. In addition it allows energy binning.

ConclusionsConclusions

From this study we know the relevant From this study we know the relevant processes contributing to signal and processes contributing to signal and background. With some knowledge on the background. With some knowledge on the corresponding corresponding cross section errorscross section errors it it should be possible to obtain, if not a good should be possible to obtain, if not a good estimate, at least an educated guess on the estimate, at least an educated guess on the systematic errors… possibly good enough?systematic errors… possibly good enough?

HELP WANTED!

Study of T2HK signal and backgroundand

Realistic comparison of β-beam and Superbeam performances

to be continued…