First ν μ → ν e Oscillation Results from MiniBooNE Morgan Wascko Imperial College London April 12, 2007 MO Wascko, Imperial HEP Seminar April 12, 2007
Outline 1. Motivation & Introduction 2. Description of the Experiment 3. Analysis Overview 4. Two Independent Oscillation Searches 5. First Results MO Wascko, Imperial HEP Seminar April 12, 2007
Motivation: Neutrino Oscillations if neutrinos have mass, a neutrino that is produced as a ν µ (e.g. π + → µ + ν µ ) has a non-zero probability to oscillate Pontecorvo, 1957 and some time later be detected as a ν e (e.g. ν e n → e - p) ν µ e - ν e π + X µ + ν detector ν source MO Wascko, Imperial HEP Seminar April 12, 2007
Motivation: Neutrino Oscillations ν µ ν 1 ν 2 In a world with 2 neutrinos, ϴ if the weak eigenstates ( ν e , ν µ ) ν e are different from the mass eigenstates ( ν 1 , ν 2 ): � � � �� � ν e cos θ sin θ ν 1 = ν µ − sin θ cos θ ν 2 The weak states are mixtures of the mass states: | ν µ > = − sin θ | ν 1 > + cos θ | ν 2 > | ν µ ( t ) > = − sin θ ( | ν 1 > e − iE 1 t )+ cos θ ( | ν 2 > e − iE 2 t ) The probability to find a ν e when you started with a ν µ is: P oscillation ( ν µ → ν e ) = | < ν e | ν µ ( t ) > | 2 MO Wascko, Imperial HEP Seminar April 12, 2007
Motivation: Neutrino Oscillations In units that experimentalists like: � 1 . 27 ∆ m 2 ( eV 2 ) L ( km ) � P oscillation ( ν µ → ν e ) = sin 2 2 θ sin 2 E ν ( GeV ) Oscillation probability between 2 flavour states depends on: 1. fundamental parameters Δ m 2 = m 1 2 -m 2 2 = mass squared difference between states sin 2 2 θ = mixing between ν flavours 2. experimental parameters L = distance from ν source to detector E = ν energy ν ν ν ν ν ν ν ν ν ν ν MO Wascko, Imperial HEP Seminar April 12, 2007
Motivation: Oscillation Signals Solar ν : measured by Homestake, ..., SNO confirmed by KamLAND hep-ex/0406035 Atmospheric ν : measured by K-II, ..., Super-K confirmed by K2K, MINOS Accelerator ν : measured by LSND unconfirmed hep-ex/0404034 hep-ex/0104049 MO Wascko, Imperial HEP Seminar April 12, 2007
Motivation: The Problem � 1 . 27 ∆ m 2 ( eV 2 ) L ( km ) � P oscillation ( ν µ → ν e ) = sin 2 2 θ sin 2 E ν ( GeV ) M. Sorel A standard 3 neutrino picture: increasing (mass) 2 Δ m 23 2 = m 2 2 - m 3 2 Δ m 12 2 = m 1 2 - m 2 2 Δ m 13 2 = Δ m 12 2 + Δ m 23 2 The oscillation signals cannot be reconciled without introducing physics beyond the Standard Model. MO Wascko, Imperial HEP Seminar April 12, 2007
Motivation: LSND MiniBooNE was proposed in 1997 to address the LSND result. LSND observed a 4 σ excess of ν e events in a ν µ beam: 87.9 ± 22.4 ± 6.0 interpreted as 2-neutrino oscillations, P( ν µ → ν e ) = 0.26% PRD 64, 112007 � 1 . 27 ∆ m 2 ( eV 2 ) L ( km ) � P P oscillation ( ν µ → ν e ) = sin 2 2 θ sin 2 E ν ( GeV ) MiniBooNE strategy: Keep (L/E ν ) same as LSND but change systematics, including event signature: - Order of magnitude higher E ν than LSND - Order of magnitude longer baseline L than LSND - Search for excess of ν e events above background MO Wascko, Imperial HEP Seminar April 12, 2007
The MiniBooNE Collaboration MO Wascko, Imperial HEP Seminar April 12, 2007
Motivation: MiniBooNE and LSND 5 2 = m 4 2 - m 5 2 Δ m 45 4 If MiniBooNE observes LSND-type ν oscillations... 2 = m 3 2 - m 4 2 Δ m 34 increasing (mass) 2 The simplest explanation is to add more ν s , to allow more independent Δ m 2 values. Δ m 23 2 = m 2 2 - m 3 2 The new ν s would have to be sterile, otherwise Δ m 12 2 = m 1 2 - m 2 2 they would have been seen already. ν s If MiniBooNE does not observe LSND-type oscillations... The Standard Model wins again! Today: MiniBooNE’s initial results on testing the LSND anomaly • A generic search for a ν e excess in our ν µ beam, • An analysis of the data within a ν µ → ν e appearance-only context MO Wascko, Imperial HEP Seminar April 12, 2007
MiniBooNE Summary MiniBooNE Final Sensitivity MiniBooNE performed a blind analysis for the ν µ → ν e appearance search - Did not look at ν e events while developing reconstruction, particle identification algorithms - Final cuts made with no knowledge of the number of ν e events in the box Final sensitivity to ν e appearance shown for two independent analyses - “Primary” analysis chosen based on slightly better sensitivity MO Wascko, Imperial HEP Seminar April 12, 2007
MOW (blinded) c.2002 We opened the box on March 26, 2007 MO Wascko, Imperial HEP Seminar April 12, 2007
And the answer is... Primary Analysis Cross-check Analysis Counting Experiment: Counting Experiment: 300<E ν QE <1500 MeV 475<E ν QE <1250 MeV expectation: 1070 ± 33 (stat) ± 225(sys) expectation: 358 ± 19 (stat) ± 35 (sys) data: data: significance: significance: MO Wascko, Imperial HEP Seminar April 12, 2007
And the answer is... Primary Analysis Cross-check Analysis Counting Experiment: Counting Experiment: 300<E ν QE <1500 MeV 475<E ν QE <1250 MeV expectation: 1070 ± 33 (stat) ± 225(sys) expectation: 358 ± 19 (stat) ± 35 (sys) data: data: 380 significance: significance: 0.55 σ MO Wascko, Imperial HEP Seminar April 12, 2007
And the answer is... Primary Analysis Cross-check Analysis Counting Experiment: Counting Experiment: 300<E ν QE <1500 MeV 475<E ν QE <1250 MeV expectation: 1070 ± 33 (stat) ± 225(sys) expectation: 358 ± 19 (stat) ± 35 (sys) data: 971 data: 380 significance: 0.55 σ significance: -0.38 σ MO Wascko, Imperial HEP Seminar April 12, 2007
And the answer is... MiniBooNE observes no evidence for ν µ → ν e appearance-only oscillations. MiniBooNE First Result The two independent oscillation analyses are in agreement! The rest of this talk is a presentation of the experimental methods used to get here. MO Wascko, Imperial HEP Seminar April 12, 2007
Outline 1. Motivation & Introduction 2. Description of the Experiment -Beam -Detector 3. Analysis Overview 4. Two Independent Oscillation Searches 5. First Results MO Wascko, Imperial HEP Seminar April 12, 2007
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