Response of a Large Water Detector to Superbeams

D. CasperUniversity of California, Irvine

Long-Baseline Experiments Today

Experiment Source

Baseline

(km)

E(GeV

)

Power

(MW)Rate(yr -1)

K2K KEK 250 1 0.005 50

MINOS FNAL 732 3 0.4 1000

CNGS CERN 730 17 0.17 3700

Note: “1 year” is defined as 107 seconds

View from the Crystal BallNear-term long-baseline experiments focused on dominant channel

Expect ~few percent measurementsPossible direct observation of appearance

Sensitivity to sin2213 around few % level

Sensitivity of all limited if m232 small

Kamland may find LMA solar solutionCritical to CP violation searches

Mini-BOONE will test LSNDPrecision mixing measurements imperative if confirmed

Next Generation Goals

Precision measurement of dominant oscillation channel

Determine sign of m232

Sensitivity to sub-dominant e channel at 1‰ levelSensitivity to CP

Probably a “phase 2” goal, after 13

Dependent on solar neutrino solution

Neutrino FactoriesThe ultimate tool for probing neutrino oscillation

Enormous luminosityExceptional purityPerfect knowledge of spectrumFlavor of initial neutrino tagged by charge

Caveats:Technical challenges to muon accelerationCost

Not considered here

SuperbeamsExploit extremely intense proton sources to produce beam from -decayIntermediate step to neutrino factory

beam necessary for beamSensitivity intermediate between near-term experiments and neutrino factoryCost also intermediateTechnical hill less steep to climb

Proton drivers essentially designed (or existing)Radiation damage near target station may be important

Possible Future Proton Drivers

Source Location

Proton Energy(GeV)

Power(MW)

Upgraded Booster

FNAL 16 1?

UpgradedNUMI

FNAL 120 1.6

50 GeV PS

JHF 500.77(4)

SPL CERN 2.2 4

Upgraded NUMI BeamsExpect four-fold luminosity increase of MINOS neutrino beame contamination: 0.5%Beam direction fixed by existing MINOS experimentGo off-axis to suppress high-energy tail?

MINOS

Off-axis/Dipole NUMI beamsVariations on NUMI:

Off-axis detector with MINOS low-energy beam? (D. Harris)Use dipole after second horn? (F.DeJongh)

Higher energy implies matter effects

JHF 50 GeV PSApproved:

50 GeV PS0.77 MW

Proposed: Neutrino beamline to KamiokaUpgrade to 4 MW

Outlook:Completion of PS in 2006/2007

JHF Neutrino BeamsWide-band beam

Horn-focusing onlyLong high-energy tail

Narrow-band beamPions momentum-selected with dipoleLower intensity

Off-axis beamIntense, narrowLess tail than WBB0.2% e around peak energy

CERN/SPLProposed:

Recycle LEP RF cavities into proton linacProton kinetic energy: 2.2 GeVPower: 4 MW

Outlook:Not yet approvedRecommendation by ECFA considered likely

SPL Neutrino BeamMARS Monte CarloLiquid Hg jet target20 m decay tunnelKaon production negligibleFew ‰ e contentE ~ 250 MeV

Beta BeamRecall talks of Zucchelli and MezzettoLook for numu appearance:

Exploit low-energy to avoid pion productionUse muon mass and Cherenkov threshold to avoid e/mu confusion

Possibility to run with neutrino and anti-neutrino sourcesSensitivity to few degrees in 13

Comparing SuperbeamsUpgraded NUMI

High energy (3-15 GeV)Large event rates/kton, requires long baselineMatter effects visibleBackgrounds probably worst at high-energy

JHFIntermediate energy (0.7-1 GeV)

Good compromise between backgrounds, baseline and rateMatter effects small1% e in off-axis beam (0.2% on peak)

SPLLow energy

Requires short baseline, large detectorNo matter effectsBackgrounds probably smallest

Oscillations with SuperbeamsPrecision measurement of sin2223 and m23

2 by high-statistics disappearanceSearch for 13 by e appearance

Measure sign of m232 using matter

effects on neutrino/anti-neutrino beamsSearch for CP violation using e appearance in neutrino/anti-neutrino beams

Water DetectorsLarge mass (UNO 440 kton fiducial)Excellent performance on simple events

Lepton ID from pattern recognitionGood lepton momentum, directionTopological rejection of some NC

Difficult to identify neutrino flavor without contamination in complex events

Require single-ring topology = loss of efficiency for high-energy (E > 1 GeV) neutrinosEfficiency less important than background rejection due to large size

Upgraded NUMI StudiesExhaustive scans of parameter space for several detector scenarios, beams, and baselines performed by Barger, et al

Parameterize detector performance

This study:Use two different proposed beamsFull simulation of detectorFull reconstruction

NUMI Beams in UNOOff-axis NUMILow-energy beam

Dipole Beam

Mis-ID background: about 5% of single-ring CC rateEfficiency for signal at 2 GeV ~ 25%(single ring cut)Next talk will discuss NUMI beam physics reach

Bkgd Bkgd

AppearanceSignal (Posc=1)

AppearanceSignal (Posc=1)

JHF Super-Kamiokande295 km baselineSuper-Kamiokande:

22.5 kton fiducialExcellent e/ IDAdditional 0/e ID

Hyper-Kamiokande20 fiducial mass of SuperK

Matter effects smallStudy using fully simulated and reconstructed data

JHF SK: Precision

5 years, JHFSuperK

OA 2°LE1.5LE3

JHF SK: θ13 Sensitivity

5 years, OA 2°sin2213 = 0.1

sin2213 90% CL sensitivity ~ 0.01 for 1.610-3 < m2 < 410-3 eV2 (5 years)

SPL UNOSPL beam to Fréjus

130 km baseline

UNO: Next-generation water Cerenkov nucleon decay and neutrino detector20 fiducial mass of SuperK (445 ktons)

Study using fully-simulated and reconstructed data

/e Background Rejection

Particle Identification CutUse Cerenkov light pattern (including opening angle, if possible) as primary rejectionTighten cut to reduce mis-ID furthere CC Efficiency: 79%

CC Contamination:~0.6%

Neutral Current 0 Production

Data very sketchyANL

p n + (7 events)

n n 0 (7 events)

Gargamelle p p 0 (178 events)

p p 0 (139 events)

No cross-section

BNL p p – / p p +

Hope to measure with 1kton detector (K2K)

K2K Preliminary1-kton, single 0’s

0 beam angle

0 momentum(MeV/c)

Energy Flow Fitter

0/e Background Results

Apply energy-flow fitter to surviving eventsCut:

M < 45 MeV

Most 0 background eliminated

Oscillated beam

Beam Contamination

NC 0

Cut (45 MeV)

CERN UNO: θ13 Sensitivity

Search for e appearance90% CL sin2213 sensitivity at ‰ level in favored m2 region

Beta Beam (Ne18)Apply simple cuts

Fiducial volumeSingle-ringParticle IDDirectional cut possible in principle for 6He

Assume atmospheric neutrinos are excluded by event time

Mu-like SignalE-like Bkgd

Ne18 Beta Beam with Decay Cut

Decay cut eliminates most mis-ID

Remaining events are NC charged pi

About 3 events background in 5-year 18Ne runOne event background in 10-year 6He run

Efficiency for Beta BeamInefficiency is essentially due to energy transfer leaving lepton below thresholdClose to 100% for muon momentum > 200 MeV/cNeed to tune beam energy with oscillation parameters and efficiency

SummaryLong-baseline experiments with superbeams offer:

1% measurements of oscillation1‰ sensitivity to sin2213

Low or intermediate energy beams combined with large water detectors could also detect CP violation in favorable LMA scenariosHigher energy beams at very long baselines can measure sign of m23

2

Superbeams fall short of a neutrino factory, but could bring us a step closer to building one