Study of neutrino oscillations with ANTARES J. Brunner.

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


• 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


• 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


Multi Line Sample

Simulated Muon Rates

Simulated Muon Rates

2727


Multi Line Sample

Simulated Neutrino Rates

Simulated Neutrino Rates

2828


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

Study of neutrino oscillations with ANTARES J. Brunner.

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