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