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Study of neutrino Study of neutrino oscillations with oscillations with
ANTARESANTARES
J. BrunnerJ. Brunner
Method : Use event ratiosMethod : Use event ratios
MC events with oscillations
Split intoNon-oscillation event rate
Oscillation correction
Rate of observed events in 2 channelsCan be expressed in these terms
Analytical calculation of mixing angle for eachΔm2, error propagation (stat&syst) from R
Many systematic effects cancel or attenuate for R 22
Choose two appropriate Choose two appropriate channelschannels
• Single line eventsSingle line events lower energy and more vertical lower energy and more vertical
• Multi-line eventsMulti-line events higher energy & more isotropic higher energy & more isotropic
• Strong effect of oscillations for single line events Strong effect of oscillations for single line events – marginal for multiline events– marginal for multiline events
Elevation Neutrino Energy
2322 104.2;12sin eVm
E/L : differences enhancedE/L : differences enhanced
• R1 = 0.82 (with osc/no osc)R1 = 0.82 (with osc/no osc)• R3 = 0.97 (with osc/no osc)R3 = 0.97 (with osc/no osc)• Fit mixing angle (linear) for each Fit mixing angle (linear) for each ΔΔmm22 for ratio R1/R3 for ratio R1/R3• In practice : R3 supplies flux normalizationIn practice : R3 supplies flux normalization
2322 104.2;12sin eVm
Track reconstructionTrack reconstruction
• Good efficiency down to low energies Good efficiency down to low energies – 20 GeV = 100m muon track for oscillation 20 GeV = 100m muon track for oscillation
analysisanalysis
• Good rejection of downgoing muonsGood rejection of downgoing muons
• Reliable zenith angle resolution Reliable zenith angle resolution – few degreesfew degrees
• Azimuth determination / pointing accuracyAzimuth determination / pointing accuracy– not needednot needed
Reconstruction conceptReconstruction concept
1.1. Select “hot spots” at each detector Select “hot spots” at each detector string string should correspond to point of closest should correspond to point of closest approach of muon track and detector approach of muon track and detector lineline
2. Add hits from neighboring floors in narrow 2. Add hits from neighboring floors in narrow time windowtime window
3. Perform minimization of time/distance/amplitude 3. Perform minimization of time/distance/amplitude related function with all selected hit using a related function with all selected hit using a simplified geometry simplified geometry obtain track parameters obtain track parameters
Recent clean lowE single-line Recent clean lowE single-line eventeventClose to vertical
Good fit
No correlated activity in any other line
1010
Recent clean lowE single-line Recent clean lowE single-line eventevent
Point of closest approachCannot be atm muon
7 storeys hit8 storeys high100m = 20 GeVTotal signal: 17 p.e.
1111
Recent clean lowE single-line Recent clean lowE single-line eventevent
Point of closest approachCannot be atm muon
7 storeys hit8 storeys high100m = 20 GeVTotal signal: 17 p.e.
1212
Tried now for also for Deepcore
SANTA project (Juan Pablo & Rolf)
Data sampleData sample• 4 years of ANTARES data taking 2007-20104 years of ANTARES data taking 2007-2010
• 2007 : 5 lines active2007 : 5 lines active
• 2008-2010 : 10,11,12 lines active2008-2010 : 10,11,12 lines active
• Use Physics runs which fulfill basic quality Use Physics runs which fulfill basic quality criteriacriteria
• Total active time : 830 daysTotal active time : 830 days
1313
Acceptance to Atmospheric Acceptance to Atmospheric nu’snu’s
• Two MC samples combinedTwo MC samples combined
• Trigger and Reconstruction requiredTrigger and Reconstruction required
• No quality cutsNo quality cuts
1414
Multi-line event selectionMulti-line event selection
• Cuts are chosen for extremely high purity against atm Cuts are chosen for extremely high purity against atm contributioncontribution
• Final cuts Final cuts Fit Quality<1.3Fit Quality<1.3 && && sinsinθθ<-0.15<-0.15 (8.6 (8.6ºº below horizon) below horizon)
• Vary MC input: water parameters & angular DOM acceptanceVary MC input: water parameters & angular DOM acceptance
• Data/(Data/(++)MC between )MC between 0.970.97 to to 0.8150.815– compatible with flux uncertainty and total detector acceptance compatible with flux uncertainty and total detector acceptance
tolerancetolerance
• Numbers are for 2008 only hereNumbers are for 2008 only here
data 491 MC 504 603 MC 1.2 3.5
cut
sinθ<-0.15 tchi2<1.3
cut 1515
Multi-Line Events for Full data Multi-Line Events for Full data setset
• 1518 1518 Event candidates in totalEvent candidates in total
• Neutrino Oscillation: reduce sample by Neutrino Oscillation: reduce sample by 3.3%3.3%
• Muon impurity Muon impurity ~1%~1%
• MC MC 14% 14% high for all years within high for all years within statistical fluctuationsstatistical fluctuations
• Reminder: Absolute normalisation cancels in Reminder: Absolute normalisation cancels in event ratioevent ratio
• Following plots: MC scaled by 0.857 Following plots: MC scaled by 0.857
1616
Year by YearYear by YearNumber of Used StoreysNumber of Used Storeys
1919
Single Line Event SelectionSingle Line Event Selection2007-20102007-2010
• Nstorey>7 : hard cut to suppress muonsNstorey>7 : hard cut to suppress muons
• tchi2<0.95tchi2<0.95
• tcosth > 0 (upward going) tcosth > 0 (upward going)
2020
Single Line Event SelectionSingle Line Event Selection2007-20102007-2010
• Nstorey>7 : hard cut to suppress muonsNstorey>7 : hard cut to suppress muons
• tchi2<0.95tchi2<0.95
• tcosth > 0 (upward going) tcosth > 0 (upward going)
2121
Single-Line MCSingle-Line MCYear by YearYear by Year
• Muon impurity ~5%Muon impurity ~5%
• Neutrino oscillationsNeutrino oscillations– 18% reduction 18% reduction – Suppression of ~90 eventsSuppression of ~90 events– Corresponds to ~4-sigma effect w.r.t. Corresponds to ~4-sigma effect w.r.t.
statistical error (23 events)statistical error (23 events)
2323
Single Line Event SelectionSingle Line Event Selection2007-20102007-2010
• Elevation angle in log and linearElevation angle in log and linear
2424
Systematic error & Systematic error & Selection StabilitySelection Stability
• MethodMethod– Use both “Test” MC & “average” MCUse both “Test” MC & “average” MC
•MCMC11 : “low count” MC : “low count” MC
•MCMC2 2 : “high count” MC: “high count” MC
•MCMCmm : “average” MC with MC : “average” MC with MCmm = (MC = (MC11 + MC + MC22)/2)/2
– Consider Multi-Line and Single-Line SelectionConsider Multi-Line and Single-Line Selection– Vary Fit quality cut around chosen valueVary Fit quality cut around chosen value
– Evaluate ratios X = MCEvaluate ratios X = MC11 / MC / MCmm for various cuts for various cuts
– Evaluate double ratios XEvaluate double ratios XML ML / X/ X1L1L
– Systematic error from variations of XSystematic error from variations of XML ML / X/ X1L1L
2525
Systematic errorSystematic errorSingle Line Sample
Multi Line Sample
Fit quality cut varied
Fit quality cut varied
2626
Systematic errorSystematic errorSingle Line Sample
Multi Line Sample
Simulated Muon Rates
Simulated Muon Rates
2727
Systematic errorSystematic errorSingle Line Sample
Multi Line Sample
Simulated Neutrino Rates
Simulated Neutrino Rates
2828
Systematic errorSystematic errorSingle Line Sample
Multi Line SampleVariation w.r.t. average MC
18% between MC1 & MC2
9% variation to MCm
Very stable against cut variations
Very stable between single-line and multi-line sample
cancellation of systematics in R confirmed !
2929
Systematic errorSystematic error
• Consider all 25 Consider all 25 combinations of single-combinations of single-line and multi-line cutsline and multi-line cuts
• Plot double ratio Plot double ratio – XXML ML / X/ X1L1L
• Distribution well Distribution well centered around 1centered around 1
• Spread totally contained Spread totally contained within 3%within 3%
• Propose 3% as Propose 3% as conservative syst. errorconservative syst. error
Ratio of Ratios25 entriesXML / X1L
3030
ResultsResults
• Assuming “standard” Assuming “standard” oscillations, coherent oscillations, coherent data/MC ratio of 0.86data/MC ratio of 0.86
• Larger year-by-year Larger year-by-year fluctuations for 1L fluctuations for 1L due to smaller due to smaller statisticsstatistics
• Ok within statistical Ok within statistical errorerror
Single-line events
Multi-line events
3131
Data R = 472/1518 = 0.311+/-0.019 (stat&syst)MC Non-Osc: R = 636/1837 = 0.346Non-oscillation hypothesis at 1.8 sigma from measured ratio
ResultsResults
• Assuming “standard” Assuming “standard” oscillations, coherent oscillations, coherent data/MC ratio of 0.86data/MC ratio of 0.86
• Larger year-by-year Larger year-by-year fluctuations for 1L fluctuations for 1L due to smaller due to smaller statisticsstatistics
• Ok within statistical Ok within statistical errorerror
Single-line events
Multi-line events
3232
Data R = 472/1518 = 0.311+/-0.019 (stat&syst)MC Non-Osc: R = 636/1837 = 0.346Non-oscillation hypothesis at 1.8 sigma from measured ratio PRELIMINARY
Single-Line MCSingle-Line MCYear by YearYear by Year
• Muon impurity ~5%Muon impurity ~5%
• Neutrino oscillationsNeutrino oscillations– 18% reduction 18% reduction – Suppression of ~90 eventsSuppression of ~90 events– Corresponds to ~4-sigma effect w.r.t. Corresponds to ~4-sigma effect w.r.t.
statistical error (23 events)statistical error (23 events)
3333
Example result from MCExample result from MC• Active time 2007-2010 : 830 days (220 days with 5 lines Active time 2007-2010 : 830 days (220 days with 5 lines
only)only)
• Assumed true values: Assumed true values: ΔΔmm22=2.4 10=2.4 10-3-3 eV eV22 & max. mixing & max. mixing
• Reachable 1-sigma precision in Reachable 1-sigma precision in ΔΔmm22 for maximal mixing 33% for maximal mixing 33%
Best fit1 sigma90% C.L.
1 sigma
N1/N2 : 5.7% Δm2 : 33%
ResultResult
• 1-sigma in 1-sigma in ΔΔmm22 for maximal mixing: for maximal mixing: 1.4-3.0 101.4-3.0 10-3-3 eV eV22
• ΔΔmm22=2.2 +/- 0.8 10=2.2 +/- 0.8 10-3-3 eV eV22
• Active time 2007-2010 : 830 days (220 days with 5 lines Active time 2007-2010 : 830 days (220 days with 5 lines only)only)
• Non-oscillations excluded at 1.8 sigmaNon-oscillations excluded at 1.8 sigma
N1/N2 : 6.1% Δm2 : 36%
3535
ResultResult
• 1-sigma in 1-sigma in ΔΔmm22 for maximal mixing: for maximal mixing: 1.4-3.0 101.4-3.0 10-3-3 eV eV22
• ΔΔmm22=2.2 +/- 0.8 10=2.2 +/- 0.8 10-3-3 eV eV22
• Active time 2007-2010 : 830 days (220 days with 5 lines Active time 2007-2010 : 830 days (220 days with 5 lines only)only)
• Non-oscillations excluded at 1.8 sigmaNon-oscillations excluded at 1.8 sigma
N1/N2 : 6.1% Δm2 : 36%
3636
PRELIMINARY
Next stepsNext steps• Go from event ratio to fit of E/L Go from event ratio to fit of E/L
distributiondistribution
• Even better: 2-dim grid in E versus LEven better: 2-dim grid in E versus L
• Further cleaning of low Energy sample Further cleaning of low Energy sample from atmospheric muons neededfrom atmospheric muons needed
15 30 45 GeV
Differential Effect of oscillations well visibleFind magic cut to get rid of this
BackupBackup
Tau Neutrino appearance ? Tau Neutrino appearance ?
• Cascade-like events effectively Cascade-like events effectively suppressedsuppressed
• 17% branching ratio into muons17% branching ratio into muons
• Nutau CC cross section much lowerNutau CC cross section much lower
• Negligible effect for present analysisNegligible effect for present analysis