MiniBooNE Oscillation Searches Steve Brice (Fermilab) for the - - PowerPoint PPT Presentation
MiniBooNE Oscillation Searches Steve Brice (Fermilab) for the MiniBooNE Collaboration Neutrino 2008 Outline Electron Neutrino Appearance Oscillation Result 0 Rate Measurement Combining Analyses Compatibility of High
Steve Brice (Fermilab) for the MiniBooNE Collaboration Neutrino 2008
Neutrino 2008 Steve Brice (FNAL) 2
– Oscillation Result – π0 Rate Measurement – Combining Analyses – Compatibility of High m2 Measurements – Low Energy Electron Candidate Excess – Data from NuMI Beam
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2 National Laboratories, 14 Universities, 80 Researchers
University of Alabama Bucknell University University of Cincinnati University of Colorado Columbia University Embry-Riddle Aeronautical University Fermi National Accerator Laboratory University of Florida Indiana University Los Alamos National Laboratory Louisiana State University University of Michigan Princeton University Saint Mary’s University of Minnesota Virginia Polytechnic Institute Yale University
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Test the LSND indication of anti-electron neutrino oscillations Keep L/E same, change beam, energy, and systematic errors
P(ν→νe) = sin22θ sin2(1.27m2 L/Ε)
neutrino energy (E): MiniBooNE: ~500 MeV LSND: ~30 MeV baseline (L): MiniBooNE: ~500 m LSND: ~30 m
Booster
detector dirt decay region absorber
primary beam tertiary beam secondary beam
(protons) (mesons) (neutrinos)
π+
e
98.1%, 0.6%, 1.2%, 0.03%
ν ν ν = = = =
Event rates:
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541 meters downstream of target 3 meter overburden of dirt 12 meter diameter sphere Filled with 800 t of pure mineral oil (CH2--density 0.86, n=1.47) Fiducial volume: 450 t 1280 inner 8” phototubes-10% coverage, 240 veto phototubes (Less than 2% channels failed during run)
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trackbased analysis: Counting Experiment: 475<Eν<1250 MeV data: 380 events expectation: 358 ±19 (stat) ± 35 (sys) significance: 0.55 σ
No evidence for ν ν ν ν
ν ν νe appearance in the analysis region
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arXiv: 0803.3423, accepted by Phys. Lett. B
28,600 π0 events mπ ~ 20 MeV/c2
π0 rate measured to a few percent Critical input to oscillation result → without it, π0 background errors would be ~25%
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Two algorithms were used:
Uses direct reconstruction of particle types and likelihood ratios for particle-ID
Set of low-level variables combined with BDT algorithm -> PID “score”
better sensitivity, so was used for primary results.
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Limits from fits to open data
10%-30% improvement in 90% C.L. limit below ~1eV2.
The combination of the two νe samples gives an increase in coverage in the region m2<1 eV2. Differences in the details are due to the specific fluctuations in the data samples and the interplay with correlations among them.
The combination yields a consistent result.
paper at draft stage
Preliminary
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– How probable is it that all experimental results come from the same underlying 2-ν osc. hypothesis? – Assessed by combining the χ2 surface of each experiment
– Indicate where oscillation parameters would lie, at a given CL, assuming all expt. results can arise in a framework of 2-ν osc. – The compatibility is the metric for the validity of this assumption.
arXiv:0805.1764 [hep-ex], submitted to Phys. Rev. D
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0.012 0.221 27.37
0.147 0.052 73.44
0.023 0.253 2.14
0.256 0.072 16.00
0.023 0.242 3.94
0.256 0.072 25.36
Sin22θ θ θ θ
Max. Compat % Bugey MB
KARMEN2
LSND
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– 25.36% compatibility at m2 = 0.072 eV2, sin22θ = 0.256
– 3.94% compatibility at m2 = 0.242 eV2, sin22θ = 0.023 Colors represent χ 2
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reconstructed neutrino energy bin (MeV) 200-300 300-475 475-1250 Data 375±19 369±19 380±19 total background 284±25 274±21 358±35 νeintrinsic 26 67 229 ν induced 258 207 129
higher E, where νe bkgd dominates.
lower E are ν-induced, in particular:
Preliminary
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Nearing the end of a comprehensive review of the νe appearance backgrounds and their uncertainties → Not Quite Ready for Release Yet
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Arrows indicate whether effect is to increase or decrease the low energy data excess The effects have different magnitudes despite the arrows all being the same size
Nearing the end of a comprehensive review of the νe appearance backgrounds and their uncertainties → Not Quite Ready for Release Yet
removes one of the gammas from a ν-induced NC π0 → γγ
– Photonuclear absorption was missing from our GEANT3 detector Monte Carlo – Reduces size of excess
Effect of photonuclear interactions
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– Absent from GEANT3 – creates background from π0s
– e.g. uncertainties in final state following photonuclear interaction
Arrows indicate whether effect is to increase or decrease the low energy data excess The effects have different magnitudes despite the arrows all being the same size
Nearing the end of a comprehensive review of the νe appearance backgrounds and their uncertainties → Not Quite Ready for Release Yet
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– Absent from GEANT3 – creates background from π0s
– e.g. uncertainties in final state following photonuclear interaction
– Errors propagated in model-independent way
Arrows indicate whether effect is to increase or decrease the low energy data excess The effects have different magnitudes despite the arrows all being the same size
Nearing the end of a comprehensive review of the νe appearance backgrounds and their uncertainties → Not Quite Ready for Release Yet
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– Absent from GEANT3 – creates background from π0s
– e.g. uncertainties in final state following photonuclear interaction
– Errors propagated in model-independent way
– e.g. finer momentum binning
Arrows indicate whether effect is to increase or decrease the low energy data excess The effects have different magnitudes despite the arrows all being the same size
Nearing the end of a comprehensive review of the νe appearance backgrounds and their uncertainties → Not Quite Ready for Release Yet
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– Absent from GEANT3 – creates background from π0s
– e.g. uncertainties in final state following photonuclear interaction
– Errors propagated in model-independent way
– e.g. finer momentum binning
– No longer need to rely on more uncertain past results
Arrows indicate whether effect is to increase or decrease the low energy data excess The effects have different magnitudes despite the arrows all being the same size
Nearing the end of a comprehensive review of the νe appearance backgrounds and their uncertainties → Not Quite Ready for Release Yet
Neutrino 2008 Steve Brice (FNAL) 20
– Absent from GEANT3 – creates background from π0s
– e.g. uncertainties in final state following photonuclear interaction
– Errors propagated in model-independent way
– e.g. finer momentum binning
– No longer need to rely on more uncertain past results
– Comprehensive review of how the 0,+ radiative decay rate is inferred from the measured π0 rate
Arrows indicate whether effect is to increase or decrease the low energy data excess The effects have different magnitudes despite the arrows all being the same size
Nearing the end of a comprehensive review of the νe appearance backgrounds and their uncertainties → Not Quite Ready for Release Yet
Dirt events tend to be at large radius, heading inward Add a new cut on “Distance to Wall backward” to reduce these.
significant background from neutrino interactions in the dirt outside the tank
Removing dirt events
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MC upgrades and new cuts have no appreciable effect above 475 MeV
“Distance to Wall Backwards” cut:- Reduces dirt events by ~80% Reduces νe events by ~20% Plot has no dirt removal cuts
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NuMI event rates:
ν ν ν ν
ν ν νe: 5% ν
ν ν ν
ν ν νe: 1% The beam at MiniBooNE from NuMI is significantly enhanced in νfrom K decay because of the 110 mrad off-axis position. MiniBooNE is 745m from NuMI target
Work in collaboration with MINOS
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PRELIMINARY PRELIMINARY
Good agreement between data and Monte Carlo:the MC is tuned well. Very different backgrounds compared to MB (Kaons vs Pions) Ongoing effort to reduce ν ν ν ν ν ν ν νe
e
CCQE sample systematics 1.26σ excess < 900 MeV
PRELIMINARY PRELIMINARY
paper at draft stage
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sensitivity (NOT limit from data)
CCFR 90% CL
SciBooNE data will significantly improve this sensitivity
Preliminary
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– Making suite of cross-section measurements – Searching for various neutrino oscillations – Publications coming out
– Making suite of cross-section measurements – Searching for anti-neutrino disappearance
– LSND result was an indication of anti-nue appearance – Extra ~2.5 x 1020 POT (making grand total of ~5 x 1020 POT) – Should take FY2008 and FY2009 running
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Region allowed at 90% C.L. by joint analysis of LSND and KARMEN
Only antineutrinos allowed to oscillate
Preliminary
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– Combining Analyses
– Compatibility of High m2 Measurements
– Low Energy Electron Candidate Excess
– Data from NuMI Beam
excess seen with current uncertainties
– Result this summer
– Doubling current POT for result
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– 2 papers expected
– Reconstruction challenges overcome – 1 paper expected
– 1 paper submitted PLB – Coherent/resonant in nu and anti-nu modes – Flux averaged cross-section measurement – 2 further papers expected
– Flux averaged cross-section measurement – 1 paper expected
– Nu mag. Mom – 1 paper expected.
– Refined Nue appearance – Nuebar appearance – Numu and numubar disappearance – 1 PRL, ~3 further papers expected
– Big effort – 2+ papers expected
– Phenomenology – CP violation, Lorentz violation, ... – 3+ papers expected
– Large event rate from NuMI beam – Check on osc. and Low E – 1 paper being written
– 1 PRL, 2 further papers expected
= PhD Student (6 already graduated)
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NC EL
Results (from 10% nu sample):
(per nucleon, n+p averaged, flux averaged)
= 8.8 ±0.6(stat) ±2.0(syst) x10-40 cm2
= 1.34 +0.38–0.25 GeV
reducing systematic errors in progress (D. Perevalov, Alabama)
NC/CCQE ratio measurement and antinu data
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– Values to R are excluded at a given CL
!"#$%
1 J! x |lnj(x)|
J=0 n-1
P(x) =
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⇒ Under active investigation, prediction of ~140 (gω/10)4 events, where gω is 10 to 30.
prediction. (Harvey, Hill, and Hill, arXiv:0708.1281[hep-ph])