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MiniBooNE and Sterile Neutrinos

MiniBooNE and Sterile Neutrinos. M. Shaevitz Columbia University NOW2004 Workshop Extensions to the Neutrino Standard Model: Sterile Neutrinos MiniBooNE: Status and Prospects Future Directions if MiniBooNE Sees Oscillations. LSND D m 2 = 0.1 – 10 eV 2 , small mixing

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MiniBooNE and Sterile Neutrinos

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  1. MiniBooNE and Sterile Neutrinos M. Shaevitz Columbia University NOW2004 Workshop • Extensions to the Neutrino Standard Model: Sterile Neutrinos • MiniBooNE: Status and Prospects • Future Directions if MiniBooNE Sees Oscillations

  2. LSNDDm2 = 0.1 – 10 eV2 , small mixing AtmosphericDm2 = 2.510-3 eV2 , large mixing SolarDm2 = 8.210-5 eV2 , large mixing Three Signal Regions

  3. How Can There Be Three Distinct Dm2 ? • One of the experimental measurements is wrong • Many checks but need MiniBooNE to address LSND • One of the experimental measurements is not neutrino oscillations • Neutrino decay  Restriction from global fits • Neutrino production from flavor violating decays  Karmen restricts • Additional “sterile” neutrinos involved in oscillations • Still a possibility but probably need (3+2) model • CPT violation (or CP viol. and sterile n’s) allows different mixing for ’s and ’s • Some possibilities still open

  4. Excess of candidatee events 87.9  22.4  6.0 events (3.8s) P(m e) = 0.264  0.081 % Also Karmen Experiment Similar beam and detector to LSND Closer distance and less target mass  x10 less sensitive than LSND Joint LSND/Karmen analysis gives restricted region (Church et al. hep-ex/0203023) LSND Result Also, from Karmen exp. m+  e+ne nunlikely to explain LSND signal

  5. Global Fits to high Dm2 oscillations for Short-Baseline exps including LSND positive signal. (M.Sorel, J.Conrad, M.S., hep-ph/0305255) Best Fit: Dm412=0.92 eV2 Ue4=0.121 , Um4=0.204 Dm512=22 eV2 Ue5=0.036 , Um4=0.224 Best fit: Dm2=0.92 eV2 Ue4=0.136 , Um4=0.205 with Compatibility Level = 3.6% with Compatibility Level = 30% Experimental Situation:Fits of 3+1 and 3+2 Models to Data Is LSND consistent with the upper limits on active to sterile mixing derived from the null short-baseline experiments?

  6. Booster MainInjector Next Step Is MiniBooNE Use protons from the 8 GeV booster Neutrino Beam <En>~ 1 GeV • MiniBooNE will be one of the first experiments to check these sterile neutrino models • Investigate LSND Anomaly • Investigate oscillations to sterile neutrino using nm disappearance 12m sphere filled withmineral oil and PMTslocated 500m from source

  7. MiniBooNE Collaboration Y. Liu, I. Stancu Alabama S. Koutsoliotas Bucknell E. Hawker, R.A. Johnson, J.L. Raaf Cincinnati T. Hart, R.H. Nelson, E.D. Zimmerman Colorado A. Aguilar-Arevalo, L.Bugel, L. Coney, J.M. Conrad, J. Formaggio, J. Link, J. Monroe, K. McConnel, D. Schmitz, M.H. Shaevitz, M. Sorel, L. Wang, G.P. Zeller Columbia D. Smith Embry Riddle L.Bartoszek, C. Bhat, S J. Brice, B.C. Brown, D.A. Finley, R. Ford, F.G.Garcia, P. Kasper, T. Kobilarcik, I. Kourbanis, A. Malensek, W. Marsh, P. Martin, F. Mills, C. Moore, P. Nienaber, E. Prebys, A.D. Russell, P. Spentzouris, R. Stefanski, T. Williams Fermilab D. C. Cox, A. Green, H.-O. Meyer, R. Tayloe Indiana G.T. Garvey, C. Green, W.C. Louis, G.McGregor, S.McKenney, G.B. Mills, H. Ray, V. Sandberg, B. Sapp, R. Schirato, R. Van de Water, N.L.Walbridge,D.H. White Los Alamos R. Imlay, W. Metcalf, S.Ouedraogo, M. Sung, M.O. Wascko Louisiana State J. Cao, Y. Liu, B.P. Roe, H. Yang Michigan A.O. Bazarko, P.D. Meyers, R.B. Patterson, F.C. Shoemaker, H.A.Tanaka Princeton B.T. Fleming Yale MiniBooNE consists of about 70 scientists from 13 institutions.

  8. p  m n 50m Decay Pipe MiniBooNE Neutrino Beam Variable decay pipe length (2 absorbers @ 50m and 25m) 8 GeV Proton Beam Transport One magnetic Horn, with Be target Detector

  9. The MiniBooNE Detector • 12 meter diameter sphere • Filled with 950,000 liters (900 tons) of very pure mineral oil • Light tight inner region with 1280 photomultiplier tubes • Outer veto region with 241 PMTs. • Oscillation Search Method:Look for ne events in a pure nm beam

  10. Particle Identification • Separation of nm from ne events • Exiting nm events fire the veto • Stopping nm events have a Michel electron after a few msec • Also, scintillation light with longer time constant  enhanced for slow pions and protons • Čerenkov rings from outgoing particles • Shows up as a ring of hits in the phototubes mounted inside the MiniBooNE sphere • Pattern of phototube hits tells the particle type Stopping muon event

  11. Example Cerenkov Rings Size of circle is proportional to the light hitting the photomultiplier tube

  12. Neutrino events beam comes in spills @ up to 5 Hz each spill lasts 1.6 msec trigger on signal from Booster read out for 19.2 msec no high level analysis needed to see neutrino events backgrounds: cosmic muons  NVeto<6 Cut decay electrons  NTank>200 Cut simple cuts reduce non-beam backgrounds to ~10-3 n event every 1.5 minutes • Current Collected data: • 400k neutrino candidates • for 3.7 x 1020 protons on target

  13. Michel electron energy (MeV) 15% E resolution at 53 MeV PRELIMINARY PRELIMINARY NC p0events Energy Calibration Checks Spectrum of Michel electrons from stopping muons Energy vs. Range for events stopping in scintillator cubes Mass distribution for isolated p0 events

  14. Oscillation Analysis: Status and Plans • Blind (or “Closed Box”) ne appearance analysis you can see all of the info on some events or some of the info on all events but you cannot see all of the info on all of the events • Other analysis topics give early interesting physics results and serve as a cross check and calibration before “opening the ne box” • nm disappearance oscillation search • Cross section measurements for low-energy n processes • Studies of nmNC p0 production  coherent (nucleus) vs nucleon • Studies of nmNC elastic scattering  Measurements of Ds (strange quark spin contribution)

  15. Events in MiniBooNE with Evis>100 MeV Low Energy Neutrino Cross sections  MiniBooNE 

  16. Use nm quasi-elastic eventsnm+nm-+p Events can be isolated using single ring topology and hit timing Excellent energy resolution High statistics: ~30,000 events in plot(Full sample: ~500,000) On the Road to a nm Disappearance Result • En distribution well understood from pion production by 8 GeV protons • Sensitivity to nm nm disappearance oscillations through shape of En distribution Monte Carlo estimate of final sensitivity Systematic errorson MC large nowBut will go downsignificantly Will be able to cover a large portion of 3+1 models

  17. Look for appearance of ne events above background expectation Use data measurements both internal and external to constrain background rates SignalMis IDIntrinsic ne Estimates for the nmne Appearance Search • Fit to En distribution used to separate background from signal.

  18. ne from m-decay Directly tied to the observed half-million nm interactions Kaon rates measured in low energy proton production experiments HARP experiment (CERN) E910 (Brookhaven) “Little Muon Counter” measures rate of kaons in situ p+ m+ nm e+ nenm K+p0 e+ne KLp-e+ne Monte Carlo Intrinsic ne in the beam Small intrinsic ne rate  Event Ratio ne/nm=6x10-3

  19. Background mainly from NC p0 production nm + p  nm + p + p0followed by p0 g gwhere one g is lost because it has too low energy Over 99.5% of these events are identified and the p0 kinematics are measured  Can constrain this background directly from the observed data Mis-identification Backgrounds

  20. Oscillation sensitivity and measurement capability Data sample corresponding to 1x1021 pot Systematic errors on the backgrounds average ~5% from estimates of Dm2 = 1 eV2 Dm2 = 0.4 eV2 MiniBooNE Oscillation Sensitivity

  21. Run Plan • At the current time have collected 3.7x1020 p.o.t. • Data collection rate is steadily improving as the Booster accelerator losses are reduced • Many improvements in the Booster and Linac (these not only help MiniBooNE but also the Tevatron and NuMI in the future) • Plan is to “open the ne appearancebox” when the analysis has been substantiated and when sufficient data has been collected for a definitive result Current estimate is sometime in 2005 • Which then leads to the question of the next step • If MiniBooNE sees no indications of oscillations with nm Need to run withnm since LSND signal wasnmne • If MiniBooNE sees an oscillation signal Then …………

  22. Map out mixings associatedwith nm ne Map out mixings associatedwith nm nt Experimental Program with Sterile Neutrinos • If sterile neutrinos then many mixing angles, CP phases, and Dm2 to include • Measure number of extra masses Dm142, Dm152… • Measure mixings Could be many small angles • Oscillations to sterile neutrinos could effect long-baseline measurements and strategy • Compare nm andnm oscillations  CP and CPT violations

  23. Precision measurement ofoscillation parameters sin22q and Dm2 Map out the nxn mixing matrix Determine how many high mass Dm2‘s 3+1, 3+2, 3+3 ………….. Show the L/E oscillationdependence Oscillations or n decay or ??? Explore disappearancemeasurement in high Dm2 region Probe oscillations to sterile neutrinos (These exp’s could be done at FNAL, BNL, CERN, JPARC) Next Step: BooNE: Two (or Three) Detector Exp. • Add Far detector at 2 km for low Dm2 or 0.25 km for high Dm2 BooNE BooNE(1 and 2s)

  24. Conclusions • Neutrinos have been surprising us for some time and will most likely continue to do so • Although the “neutrino standard model” can be used as a guide,the future direction for the field is going to be determined by what we discover from experiments. • Sterile neutrinos may open up a whole n area to explore

  25. Backup Slides

  26. Horn has performed flawlessly for two years and “world record” 96 million pulses (old record 12M)  But has failed just recently with a ground fault Expected lifetime 1 year / 200 million pulses Problem seems to be associated with debris combined with corrosion probably from water vapor. Horn is being replaced with fully tested spare Fermilab in shutdown through Nov. Horn replacement will be completed in Oct. 8 GeV Protons impinge on 71cm Be target Horn focuses secondaries and increases flux by factor of ~5 170 kA pulses, 143 ms long at 5 Hz MiniBooNE Horn  e/ 0.5%

  27. Constraints on the number of neutrinos from BBN and CMB Standard model gives Nn=2.6±0.4 constraint If 4He systematics larger, then Nn=4.0±2.5 If neutrino lepton asymmetry or non-equilibrium, then the BBN limit can be evaded.K. Abazajian hep-ph/0307266G. Steigman hep-ph/0309347 “One result of this is that the LSND result is not yet ruled out by cosmological observations.” Hannestad astro-ph/0303076 Bounds on the neutrino masses also depend on the number of neutrinos (active and sterile) Allowed Smi is 1.4 (2.5) eV 4 (5) neutrinos Nn=3 solid 4 dotted 5 dashed 0.00 0.005 0.01 0.015 0.02 0.025 0.03 Hannestad astro-ph/0303076 Sterile Neutrinos: Astrophysics Constraints

  28. LSND allowed regions compared to Null short-baseline exclusions Doing a combined fit with null SBL and the positive LSND results Yields compatible regions at the 90% CL 3 + 1 Model Fits to SBL Data Best fit: Dm2=0.92 eV2 , Ue4=0.136 , Um4=0.205 Best Compatibility Level = ~3.6%

  29. Confidence Levels: 3+1  3.6% compatibility 3+2  30% compatibility Best Fit NSBL LSND 90% CL 95% CL Also, low Dm2 regions 99% CL Combined LSND and NSBL Fits to 3+2 Models 3 + 2 Best Fit: Dm412=0.92 eV2 , Ue4=0.121 , Um4=0.204 , Dm512=22 eV2 , Ue5=0.036 , Um4=0.224 (M.Sorel, J.Conrad, M.S., hep-ph/0305255)

  30. For quasi-elastic events ( nm+nm-+p and ne+ne-+p)  Can use kinematics to find En from Em(e) and qm(e) Monte Carlo nm+nm-+p Monte Carlo ne+ne-+p energy resolution energy resolution 10% 10% Neutrino Energy Reconstruction

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