Atmospheric Neutrinos MINOS MINOS Far Detector Type of Atmospheric Neutrinos at MINOS Two MINOS Atmospheric Analyses 1
Produced in the atmosphere from interactions of primary cosmic rays. p + N π ± + X p,he #,$ Zenith Down-! Detector % " Zenith π ± µ ± + ν µ ( ν µ ) µ ± e ± + ν e ( ν e ) + ν µ ( ν µ ). µ ( ) -!e ( ) - µ! ( ) -! µ " Up-! % #&" L ν e + ν e = 1/ ν µ + ν µ ν µ / ν µ 1 Detector Earth
First evidence of neutrino oscillations came from Super Kamiokande (1998). Number of Events Number of Events 600 500 400 300 00 0 Sub-GeV e-like 0-1 -0.5 0 0.5 1 00 180 Multi-GeV e-like 160 140 10 0 80 60 40 0 0-1 -0.5 0 0.5 1 cos! 600 500 400 300 00 0 350 300 50 00 150 0 Sub-GeV µ-like 0-1 -0.5 0 0.5 1 50 up down Multi-GeV µ-like + PC 0-1 -0.5 0 0.5 1 cos! ν μ ν τ OSCILLATIONS ( ) ( νµ cos θ sin θ = ν τ sin θ cos θ ) ( ν1 ν ) P (ν µ ν τ ) = sin θ sin (δm L/4E) 3
Demonstrate the oscillation behaviour Provide very high statistics discrimination against other models for neutrino disappearance, e.g. decoherence, neutrino decay,...? Measure 3 to better than % Search for sub dominate ν appearance e θ 13 3σ discovery limit is factor improvement on CHOOZ current limit. In addition: MINOS Far Detector capable of first direct observation of atmospheric ν and ν oscillations 4
(Main Injector Neutrino Oscillation Search) ν μ 735km Near (unosc) Far (oscillated) Depth of minimum sin θ Position of minimum Δm 5
MINOS Far Detector beam event 6
Located in former iron mine in northern Mn, USA. Also the home of Soudan1& (ret.) and CDMS. MINOS is 341 ft. (070 mwe) below the surface. shaft MINOS Soudan /CDMS II 7
8m octagonal steel scintillator tracking calorimeter. Two 15m sections (supermodules) 5.3 kton total mass. Each supermodule has a 1.5T toroidal magnetic field Hadronic energy resolution ~55%/ E A Completed in Aug 003. single supermodule 8
Steel-Scintillator sandwich, each layer (plane) consists of a.54 cm steel +1 cm scintillator Each scintillator plane divided into 19 x 4cm wide strips steel Alternate planes have orthogonal strip orientations, U and V 3D tracking U V U V U V U V scintillator orthogonal orientations of strips Scintillation light collected by fibres glued into each strip and read out by multi pixel PMTs 9
The Far Detector (3) v y u x The Far Detector during construction.
The Far Detector (4) The completed Far Detector. 11
Since completion in August 003 the Far Det has been taking cosmics data. Beam switched on 1st March 005 at which point the Far Detector had collected 40 days of physics quality data, excellent for a detector still in commissioning stage. Total live time 500 400 300 00 MINOS PRELIMINARY 0% live time live time Total of 5.99 kton-years of data suitable for atmospheric neutrino studies, c.f. Soudan 's 7.36 ktonyears 0 0 0 0 00 300 400 500 Days since 003-07-01 Will still take cosmics data during beam running. 1
Two Views (U-Z and V-Z) are combined to give 3D tracks and showers. Event timing information Calorimeteric information Event charge and muon momentum from curvature of tracks in B-field. UZ VZ Timing (.4 ns) Calorimetic DATA 13
ν MINOS Far Detector has a lot going for it: Deep (070 mwe) 0,000 reduction in cosmic muon and large. Magnetic field, event charge and muon momentum, even muons that leave the detector. Potential problem, 80% of the detector surface is uninstrumented. Hit in Veto Shield Event appears to start 1m from detector edge 14
Fully Contained FC ν µ Sneaky Stopping Cosmic Muons Cut: Containment, topology ν Partially Contained Downward-going PCDN µ Sneaky Thru-going Cosmic Muons Cut: Containment, topology Partially Contained upward-going PCUP µ Stopping Cosmic Muons (Direction Wrong) neutrino induced rock muon νinducedµ ν ν µ Cut: timing Thru-going Cosmic Muons (Direction wrong) Cut: timing 15
Look for events coming from below the horizon. The flat overburden at Soudan means can also look for events slightly above horizon. Event selection is based on event timing, timing resolution.4ns per channel. Require 0 planes and m tracks, look at event timing 1/β (c/v). Downward going cosmic ray muons Upward going events Select 91 events. B. Rebel (FNAL) 16
UZ VZ Timing µ + Timing 17
NUANCE Monte Carlo: Bartol'96 flux MC normalised to data Event Charge ID Use the charge of the muon to separate ν and ν events Efficiency is a function of, muon momentum, track length and vxb Charge ID is a work in process B. Rebel (FNAL) 18
FC and PC-Down have same background: sneaky cosmic muons. Therefore, use same cuts. Rejection factor of 1 in 7 required to achieve a signal to background ratio of :1. Use Monte Carlo signal (Barr et al.) and cosmic muon background to develop cuts based analysis to reduce signal: background to 1:1, then apply veto shield (~97% efficient). Use veto shield to measure remaining background in sample. 19
Define a fiducial volume: 0.5m from detector edge Events 6 5 MINOS PRELIMINARY Data ( livedays) Cosmic Muon MC 5 planes from each supermodule end 4 3 " µ CC MC! 00 Cuts: FC - require both ends be 'contained' PCDN - require upper end 'contained' and lower end non-contained. 0 0.5 1 1.5.5 3 3.5 4 Fiducial Distance / m Muons entering through coil hole. Removed with 40cm radial cut. Signal:Cosmic ~ 1:300 0
Background dominated by steep cosmic ray muons Cut out sneaky muons Δ z Events 3 MINOS PRELIMINARY data MC cosmic µ MC atmos " 1-1 0 0. 0.4 0.6 0.8 1 1. 1.4 1.6 Signal:Cosmic ~ 1:15! Z / m 1
Remaining background is steep, highly curving cosmic ray muons Deposit lots of charge in first plane (Q vtx) / PE Q vtx MC atmos " 300 50 00 / PE Q vtx MC cosmic µ 300 50 00 150 0 50 0 0 0.1 0. 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 cos! z 150 0 50 0 0 0.1 0. 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 cos! z y (zenith) / PE Q vtx MC atmos " 300 50 00 150 0 / PE Q vtx MC cosmic µ 300 50 00 150 0 z 50 0-1 -0.8-0.6-0.4-0. 0 0. 0.4 0.6 0.8 1 cos! zenith 50 0-1 -0.8-0.6-0.4-0. 0 0. 0.4 0.6 0.8 1 cos! zenith
Define 'steep' to be: cos θ zenith > 0.7 or cos θ z < 0.5 Then require Qvtx<0 Events 00 180 160 140 10 0 80 60 40 0 cos# zenith >0.7, cos# z <0.5 Data MC cosmic µ MC atmos "! MINOS PRELIMINARY 0 0 50 0 150 00 50 300 Signal:Cosmic ~ 1:1.5 Q vtx /PE 3
FC/PCDN:Veto Shield Added after detector construction, rather odd shape due to readout cables. Event so: 99.9% acceptance. Same scintillator strips used in detector, but parallel to Z axis. 4 sections ( per supermodule) each 8 meters long. East West B-Field Y V U Coil hole Shield Layer X Z out of page 4
An event is 'vetoed' if energy is deposited in the shield with 0ns of the event. Measure veto shield efficiency using steep stopping cosmic ray muons. Veto Efficiency = 97.1±0.(sys) % The signal rejection is dominated by shield noise: Signal Inefficiency =.5±0.(sys) % 5
Applying veto shield: Data Total MC (no oscillations) Total MC (Δm =0.005eV ) Total 94 10.1±4.0 94.3±18.9 PCDN 5.6±4.3 0.5±4.1 FC 69 98.5±19.7 73.8±14.8 MC predictions include all backgrounds Know veto shield efficiency and number of vetoed events, therefore can estimate cosmic ray muon background in selected sample. Measured Cosmic Muon BG MC Cosmic Muon BG Events 4.4±0.4(stat)±0.3(sys) 4.9±0.5(stat)±0.7(sys) 6
Very different backgrounds to FC/PCDN. Stopping cosmic ray muons with incorrect direction from timing, therefore timing cuts do the work here. However still need a containment and a Δz cut to remove upgoing neutrino induced muons (reduced to 1% of signal) Signal:BG ~ 1:15 7
Direction of track is determined from timing of hits along its length. The rms of the hits times about the track is calculated for the two hypotheses of +c or -c. The hypothesis with smallest rms is selected as track direction. +c hypothesis +c hypothesis 8
Use difference in RMS to selected events with good timing MINOS PRELIMINARY data MC cosmic µ MC atmos! 1-1 - -9-8 -7-6 -5-4 -3 - -1 0 RMS up - RMS down / ns Remaining background is estimated from high statistics Monte Carlo studies <0.36 (68% c.f.). A x-check is made by extrapolating data distribution into signal region giving 0.5 events. Data Total MC (no oscillations) Total MC (0.005eV ) Events 13 19.3±3.9.7±.1 9
Summary of selected events Data MC ν µ /ν µ CC no oscillations MC ν µ /ν µ CC 0.005eV Cosmic Muon MC Other Backgrounds Total 7 18.9±5.8 93.5±19 4.9±0.7 5.6±1.1 Barr et al flux. Sys error dominated by (flux and cross-section) Assumes no oscillations Other Backgrounds: ν τ CC Rock muons ν e CC Neutral Current 30
FC PCDN PCUP 31
Define a 'high resolution' sample for FC events, by applying similar timing cuts to PCUP. Place 30 events into a 'low resolution' sample which have an ambiguous direction. Correct Track Direction Before Cut = 96.0 % After Cut = 99.9 % FC events 3
Events 30 5 0 Data MC null oscillations MC " m 3 = 0.005 ev MC Background MINOS PRELIMINARY 15 5 0-1 -0.8-0.6-0.4-0. 0 0. 0.4 0.6 0.8 1 cos! zenith For high-resolution events can calculate the up-down ratio (R obs ) and compare it to MC expectation in the absence of oscillations (R MC ). R obs /R MC = 0.6±0.15(stat)±0.03(sys) 33
Measure charge from curvature of track in magnetic field. Track length Muon momentum vxb Require that Q/P / σ Q/P >.0 5000 0000 15000 000 5000 Stopping cosmic ray muons Data + MC µ - MC µ - + MC µ + µ MINOS PRELIMINARY μ - μ + agreement. Good data/mc 0-0 -15 - -5 0 5 15 0 Q/P/! Q/P 34
ν ν ν/ν Data 34 18 55 MC (no oscillations) MC (0.005 ev ) Charge Purity = 98.7% 45.6±8.9 4.9±4.7 68.5±14 33.8±6.6 18.7±3.4 51.9± Events 4 0 18 16 14 1 8 6 4 0 - -8-6 -4-0 4 6 8 Data MC Expectation (no oscillations) MC Expectation ("m =0.005 ev MC background MINOS PRELIMINARY ) Q/P/! Q/P N+/N- = 0.53±0.15(stat)±0.0(sys) Expected N+/N- = 0.55 35
Events 30 5 MINOS PRELIMINARY Events 30 5 Data MC nill oscil " µ 0 15 " µ 0 15 MC (#m =0.005 ev ) MC background 5 5 0-1 -0.8-0.6-0.4-0. 0 0. 0.4 0.6 0.8 1 cos! zenith 0-1 -0.8-0.6-0.4-0. 0 0. 0.4 0.6 0.8 1 cos! zenith R obs /R MC ν ν 0.7±0.35(stat)±0.03(sys) 0.83±0.9(stat)±0.03(sys) 36
MINOS has collected 5.99 kton-years of cosmic data before beam switched on in March 005. Have observed a total of 198 atmospheric neutrino events, 7 contained vertex and 91 upward-going muons. Contained event up-down ratio excludes no oscillations to.5σ. Contained events can be charged id'ed with 98% purity. Measured N+/N- = 0.53±0.15(stat)±0.0(sys), c.f. expectation 0.55. No enough statistics yet to make any statement about charge separated oscillation parameters. Acknowledgements: A. Blake, J. Chapman, B. Rebel and M. Thomson 37
`Thus I descended from the first circle down into the second, which girdles less space, and so much more woe that it goads to wailing. There abides Minos horribly, and snarls; he examines the sins at the entrance; he judges, and he sends according as he entwines himself.' Dante Alighieri - Divina Commedia Gustave Dore
/ ev 3 m!! -3 m -1 - = 0.005 ev,! m = 0.005 ev MINOS PRELIMINARY ) (ev!+!m - MINOS PRELIMINARY 90% 68% 99% -3-4 90% C.L. 95% C.L. Input Value -5-5 -4-3 - FC Expected! m 3-1 / ev -4-4 -3 -!m!- upmu Expected (ev ) -1 39
Can accommodate LSND, solar and atmos results with CPT violation giving different masses for neutrino and antineutrino. Use a none zero theta 13 component to measure sign of deltam "Because it's there." - George Mallory, 194 40