1. MINOS in 2010 Peter Litchfield HEP Seminar March 2 nd 2010  MINOS is a mature experiment with a number of published results. I will  give you a short introduction to MINOS and neutrino oscillations  show you the published results from the last ~1 year on,,sterile neutrinos  show you something of what further will come from the current data

2. MINOS Timeline The Soudan 2 collaboration had the first thoughts of a long baseline neutrino experiment at Soudan around 1989. The detector would be Soudan 2.  But the Main Injector was still years in the future In 1994 Fermilab requested letters of intent for neutrino experiments at the Main Injector. The MINOS collaboration formed to design and construct a new, bigger detector Final approval was given in 1998 and construction started The far detector was completed in 2002 and started collecting data on atmospheric neutrinos and cosmic ray muons The near detector and the beam were completed at the end of 2004 First data March 2005 First oscillation publication, July 2006 Neutrino running ended June 2009 Antineutrino running started September 2009

3. MINOS running  The exposure of MINOS is measured in terms of the number of 120GeV protons delivered to the target (POT)  ~7.2 x 10 20 POT have been accumulated for the neutrino oscillation data  ~1.5 x 10 20 POT for the antineutrino data which is still running

4. Neutrino Phenomenology We assume that there are three neutrinos (if there are more things are more complicated yet) Neutrinos can be described as eigenstates of flavour (e, ,  ) or of mass, they are not necessarily the same. The flavour eigenstates ( e, ,  ) are a mixture of the mass eigenstates ( 1,2,3 ) When they are produced neutrinos are eigenstates of flavour, e.g. When neutrinos propagate they do so as the mass eigenstates  This is what produces neutrino oscillations

5. Why do Oscillate? Quantum mechanical phenomenon, not a special property of neutrinos Initial state has pure flavor, e.g.   But is a mixture of mass states Each mass state has the same initial energy but different mass, therefore different velocity After traveling some distance the particle wave packets will have changed phase  Now a different mixture of mass states Therefore a different mixture of flavor states when it interacts 1 2 3   + e +  Time t Distance L later

6. Three Neutrino Phenomenology The Matrix U can be decomposed into three submatrices with elements which are the sines and cosines of 3 angles  12,  13,  23 and a phase  (responsible for CP violation) MINOS/Super-K NO A/T2K/ Double-CHOOZ SNO-Kamland

7. Formalism: 3 Flavour Oscillations Probability of   →   P=1.0-sin 2 2  23 sin 2( 1.27  m 23 2 L/E)+small terms Probability of  oscillating to e in vacuum:  P=P 1 +P 2 +P 3 +P 4  P 1 =sin 2 θ 23 sin 2 2θ 13 sin 2 (1.27  m 13 2 L/E) “atmospheric”  P 2 =cos 2 θ 23 sin 2 2θ 12 sin 2 (1.27  m 12 2 L/E) “solar”  P 3 = Jsinδsin(1.27  m 12 2 L/E)  P 4 =Jcosδcos(1.27  m 12 2 L/E)  J=cosθ 13 sin 2 θ 12 sin 2 θ 13 sin 2 θ 23 sin(1.27  m 12 2 L/E)sin(1.27  m 13 2 L/E) “atmospheric- solar interference” At the distance of Soudan and the known oscillation parameters the blue terms are dominant for MINOS Nova, with its increased mass and off axis location will be more sensitive to  13 and possibly , if  13 is large enough.

8. Matter effects Matter is not CP invariant, it is made up of matter, not antimatter.  Neutrinos passing through matter interact differently than anti- neutrinos All flavours of neutrinos can interact with electrons via Z exchange, only e interact via W exchange The effect depends on the sign of  m 2, i.e whether nature has the normal or inverted heirachy In matter at oscillation maximum, P 1  P 1 (1 ± 2E/E R ). E R  11GeV for the earths crust. The + sign is for neutrinos with normal mass hierarchy and antineutrinos with inverted mass hierarchy. Z e e e e W x x ee

9.  In principle we want to determine all the elements of the mixing and mass matrices for neutrinos and anti-neutrinos  MINOS was designed 15 years ago when neutrino oscillations were an unproved speculation  We went for the easiest and at that point the defining oscillation property, the disappearance of    Coarse, magnetised detectors to measure  We measure very well  m 23 2 and reasonably well sin 2 2  23  Having done that we would like to measure and sin 2 2  13  Do oscillate in the same way as   ? Is CPT conserved?  Are there more than 3 neutrinos, extras have to be sterile? What is MINOS doing?

10. The 2 Detector Paradigm  The principle of MINOS is very simple. One detector at Fermilab measures the beam composition there. Another detector in Soudan measures the composition after it has travelled 735km. If it is different the neutrinos have oscillated. BUT;  The near detector is close to the end of the beam decay pipe and thus sees an extended line source of neutrinos. The far detector is far away and sees a point source. The energy distributions are different independent of oscillations  Although designed as closely similar as possible there are differences in the detectors and the beam conditions are different  Have to make corrections to the near detector spectrum to predict the far

11. Near-Far Beam Extrapolation 1)Far/Near: 2)Beam Matrix: The truth far energy distribution is expressed as a function of the near (previous slide) as a matrix. The near detector measured energy distribution vector is converted to a truth distribution by efficiency and background matrix corrections, multiplied by the far-near matrix, and converted back to a far detector measured distribution vector by far detector efficiency and background matrices 3)Event-by-Event: The beam MC calculates the relative probability of the neutrino from each beam decay hitting the near and far detectors. The near detector MC is corrected using the near detector data. Far detector distributions are built up event by event from the corrected near MC using the relative probabilities of hitting the two detectors  The Far/Near is the simplest and adequate for low statistics data  For the best sensitivity we need to allow for details of the beam extrapolation.

12. →e→e  When  e interact they produce electrons  Ignoring smaller components, the oscillation probability for   →  e is given by  We know that sin 2 2  13 is small (<~0.15) from the CHOOZ experiment, there will not be many events  MINOS is a coarse detector, not designed to identify electrons  There is a large background of electrons coming from  0 →   THIS IS A REALLY TOUGH JOB IN MINOS  We need NO  A (and/or T2K), but we have tried anyway

13.   →  e Analysis Strategy  Develop a selection procedure using MC and the near detector data to select  e events and reject background  Measure the rate of selected events in the near detector. Assuming no oscillated events in the near detector this rate is  Intrinsic beam  e (calculated from the beam MC)  Background misidentified NC and   events  Extrapolate the near detector data to the far detector (need to do the NC and   separately as the   oscillate)  Compare the far detector prediction with the data.  Hope for an excess due to oscillations.

14.   →  e Near Detector Background  Selection of  e events is done using an Artificial Neural Network  11 different properties of  e events describing the shower length, width and shape are fed into the network Selected Area normalised output of the ANN  Signal efficiency: 41% Total CC background rejection: 99.4% Total NC background rejection: 92.3%  Predicted FD MC Background, 3.2x10 20 pot 69% NC, 19% CC, 8% beam  e, 4%  

15. Far Detector Background  The Far detector background is predicted from the near detector data by the Far/Near method  The strength of a two detector experiment is that many systematics cancel (e.g. background cross-sections)  Have to extrapolate the different background components separately as the Charged Current background will oscillate, the NC will not  Separate background components using different beam configurations  Horn on, pions are focussed and we have a low energy peak  Horn off, no focussing, only the very forward (high energy) neutrinos are detected

16. Horn on-off NC/CC decomposition

17. 17 e Selected Far Detector Data  We observed a total of 35 events  We expect 27±5(stat)±2(sys) background events.  The data is 1.5  above expected background.  Published PRL 103:261802 (2009)

18. MINOS 90% CL in sin 2 2  13  A Feldman-Cousins method was used.  Fit simply to the number of events from 1-8 GeV, no shape or correlation information used.  Best fit and 90% CL limits are shown:  as a function of  CP  for both mass hierarchies  at MINOS best fit value for  m 23 2 and sin 2 2  23 allowed region  Limits for Normal (Inverted) hierarchy for (  CP =0) sin 2 2  13 <0.29 <0.42 (90% CL)

19. 7.0 x10 20 POT Future limit if excess goes away with more data. Future measurement if data excess persists.  We have already doubled the data in current running!  Expect new results shortly Future 90% Contours

20. Is CPT conserved?  If CPT is conserved then, the oscillation parameters of must be the same as   Unfortunately are harder to study the   The production of  - is lower than  +  The cross sections for are lower than for   Only about 1/3 the events per POT  There is no previous data on separated  and interactions.  Super-K has produced unseparated limits  A global fit produces the limits in the plot M.C. Gonzalez-Garcia & M. Maltoni, Phys. Rept. 460:1-129 (2008)

21. Beam Antineutrinos  Standard NuMI focuses positive mesons, parents of   are mostly produced by mesons going through the field free center of the horns  NuMI beam composition: –91.7% peak at 3 GeV –7.0% peak at 8 GeV –1.3%  e and π−π− π+π+ 120 GeV p + Target Focusing Horns 2 m 675 m νμνμ νμνμ 15 m 30 m Decay Pipe

22.  Most true are high energy and come from unfocussed  -  Most events in the oscillation region around 2-3 GeV are background events  Neutral Current events with a fake muon  Mis-reconstructed or Mis- identified   CC events   + are selected with cuts based on three parameters;  CC/NC separation parameter  2 curvature measurements Selecting

23. Far Detector Spectrum  The near detector data was projected to the far detector using the beam matrix method  64.6  8.0(stat)  3.6(syst) events were predicted with no oscillations  58.3  7.6(stat)  3.6(syst) with CPT conserving oscillations  42 data events were obtained, a 1.9  deficit  The deficit is at high energies, NOT where we expect to see oscillations  Checked by examining  + events produced in the rock upstream, find ~1  excess. Conclude the deficit is statistical

24. Oscillation Fit  Allowed region contours were calculated using the Feldman Cousins prescription including systematics.  The best fit point is at high because of the deficit at high energy.  The CPT conserving point from the MINOS   analysis is within the 90% contour.  A previously allowed CPT violating region (unshaded) is excluded at 99.7% C.L.

25. Search for transitions  If   could transform into during the flight from Fermilab we would observe an enhancement in the  + energy spectrum.  Assuming that the transition probability has the same form as the the oscillation probability, we can define a transition probability   <0.0206 at 90% conf

26. Reverse Horn Current Running  The beam setting for the analysis just described selected negative tracks and thus    By reversing the horn currents we can select positives and thus  MINOS is currently running in this mode  Event rate is ~1/3 lower than in  mode  But spectrum peaks in the oscillation region and thus is more sensitive to oscillations  With the full data sample we expect to collect we will reduce the error on by about a factor of 4

27. Sterile Neutrinos  We know from LEP data that there are only three low mass neutrinos with standard model interactions  However this does not exclude neutrinos that do not couple to normal matter (sterile).  Some models beyond the standard model can include such objects  If only standard model interactions exist the rate of neutral current interactions does not change in oscillations since all neutrinos have the same neutral current cross sections  If sterile neutrinos exist and neutrinos can oscillate to them, as well as a deficit of charged current interactions there will be a deficit of neutral current interactions.

28. Sterile Neutrinos  Select events with no reconstructed  or which are rejected by the charged current selection  Observed 388 events  Far/Near extrapolation predicts 377  19.4(stat)  18.5(syst)  Small correction if  13  0  No evidence for NC disappearance  Fraction of   that disappear by converting to sterile neutrinos given by <51% at 90% confidence  Oscillations to sterile neutrinos will reduce the number of NC events

29. New Oscillation analysis  CC events have the most statistics and best resolution on the neutrino energy, analysis of these events is the money analysis  Measure muon energy E  by range or curvature in the field  Measure the hadronic shower energy E shw by summing scintillator pulse height.  E  =E  +E shw  The 2008 analysis used 3.2 x 10 20 protons on target  Currently we have more than doubled this exposure to ~7.2 x 10 20 POT  A new analysis is in process with results this summer.  The 2008 analysis used only selected  (  - ) CC events with interaction vertices in the fiducial volume, 848 events. Only ~40% of our total events  The new analysis will have ~4,500 events of which ~1700 will be CC and will include all the extra events

30. Published CC Analysis  MINOS 2008 Result (3.2 10 20 POT) Phys. Rev. Lett. 101, 131802 (2008)  m 2 = (2.43±0.13) x 10 -3 eV 2 sin 2 (2  ) > 0.95  Decay disfavoured at 3.9   Decoherence disfavoured at 5.7 

31. New, improved, Oscillation Analysis  The extra events that will be included are;  CC  + events: combining the  and analyses  NC events: contain a significant component of true CC events with low energy muons  Events with production vertices outside the fiducial volume: only ~20% of events and with worse resolution but another source of true CC events  Events with  produced in the rock upstream of the detector: we only see the muon in general and it has lost energy in the rock so very poor resolution on E  but the total rate is sensitive to oscillations.  The rock and anti-fiducial volume events are the subject of Matt Strait’s thesis. Seminar to come in a few weeks.  Although the CC events are only ~40% of the data they have by far the most statistical weight, adding the remainder will gain 15-20% in sensitivity

32. New, improved, Oscillation Aanlysis  Analysis improvements include;  A new CC selection which will improve the efficiency for low energy events  A new method of estimating the shower energy using a knn nearest neighbour method  Fitting will be made as a function of event resolution to increase sensitivity  The event-by-event extrapolation method will be used along with the beam matrix method for the extrapolation.  Fitting can be done as a function of E  and E shw instead of just E  which implements the resolution fitting, improves the separation of true CC and NC events in the NC selected sample and reduces some systematics

33. MC plots of event energies: CC fiducial  The following plots show a MC Generated Fake experiment with 7.0x10 20 pot and the previous best fit oscillation parameters. The predictions for no oscillations and truth oscillations are also shown.

34. MC plots of Event energies: NC Predicted events True NC True CC 2)In fiducial NC events. Note the different distributions for true CC and NC events

35. MC event energies: Anti-fiducial events  The out of fiducial volume CC events have a strong oscillation signal but the total of events is only ~1/7 of the fiducial events

36. MC plots of event energies: Rock events  All data will be fitted simultaneously to give the final oscillation parameters.  Results out this summer….

37. Summary  MINOS has published results on several oscillation channels based on 3.2 x 10 20 pot  We have by far the best measurement of  m 2 and have searched for oscillations in anti-neutrinos, sterile neutrinos and in   →  e  Results on the full 7.2x10 20 pot   →  e will appear shortly  Results from this data and hot off the press anti-neutrino data is being analysed and results should appear this summer (Neutrino 2010 is in Athens in June)  Don’t forget the other analyses being done on MINOS  Near detector data on neutrino interactions, by far the highest statistics in the world with the Minerva fine grain detector just coming on stream  Cosmic ray muon and neutrino data  Onward to Nova and a detector designed for   →  e