Enrique Fernández Univ. Autónoma Barcelona/IFAE

1. Neutrino Physics with Accelerators Enrique Fernández Univ. Autónoma Barcelona/IFAE Corfu Summer Institute on EPP, Corfu, Greece, Sept. 4-26, 2005

2. Neutrino properties Neutrinos are particles that only interact weakly (and gravitationally), that is, they are truly neutral: The cross-section for interacting with matter is very small, ~ 10-40 cm2 (for MeV n’s). This implies that they are “invisible” in most cases. The charged current weak interaction is also very peculiar: it does not conserve P (nor CP). The interaction is strongly dependent on the spin orientation. They also have a very small mass, compared with that of any other elementary particle.

3. Neutrinos in the SM In the SM there are 3 lepton families, each containing a charged lepton and a neutrino. Neutrinos are massless particles and each family lepton number (as well as global lepton number) is conserved. The neutrino has three states (weak eigenstates): ne, nm, nt. By definition these are the states that couple to the W together with the corresponding charged leptons. These assumptions, in particular the massless assumption, were built up from experiments.

4. Massive neutrinos and neutrino oscillations In 1998 there was a breakthrough in neutrino physics. Data from atmospheric neutrinos collected by the Superkamiokande detector showed that there were neutrino oscillations. As we will see neutrino oscillations requires that the neutrinos have mass and that there is lepton mixing.

5. Massive neutrinos and neutrino oscillations What do we mean by oscillation?(ref.: B. Kaiser, hep-ph/0506165). A neutrino of flavor a, na, is produced at the source. When it interacts at the target it does so as a neutrino of a different flavor, nb.

6. Neutrino Oscillations: Oscillation requires both mixing between the leptons and massive neutrinos. Suppose that there are several neutrino mass statesni. Mixing means that the state produced together with charged lepton la is a superposition of differentni: U*ai= amplitude of W+ decay to la ni The set of all U*ai (for 3 ni) form a unitary matrix. Inverting it: Pontecorvo-Maki-Nakagawa-Sakata matrix

7. Neutrino Oscillations: The oscillation probability is given by the square of the amplitude:

8. Neutrino oscillations. Squaring the amplitude: The oscillation implies that lepton family number is no longer conserved.

9. Neutrino Oscillations: This is entirely similar to what happens in the case of the quarks, where favor is not conserved in weak decays, e.g L (uds) p (uud)+ p- (du) The reason for the non-conservation of “quark family number” or “flavor” is quark mixing, the fact that weak and mass eigenstates are different. u d’ c s’ t b’ The difference is that we produce weak-interaction quarks (in the weak decay of the L) but observe them as mass states (in the p or p).

10. Neutrino oscillations. Squaring the amplitude: From this expression we see that: 1) as required by CPT invariance. 2) In general (if U complex): CP violation. 3) The sin2[..L/E] gives “oscillatory” pattern. The above formula is very complicated but nature has been kind enough as to make it simple in certain cases of interest.

11. Neutrino oscillation: To gain some understanding of the above formula write: For a given term to be relevant the argument of sin2() should not be much smaller than 1, otherwise sin2( ) is too small. It can also be that for a given experiment only one mixing angle is relevant. The bottom line is that in some cases the oscillation can be treated as a two-family mixing.

12. Neutrino oscillation: Oscillation probabilities (2 neutrino case; relevant for CNGS beam):

13. The first clear signature of oscillations came from the SuperKamiokande experiment in 1998

14. SuperKamiokande detector principle Detect Cherenkov light produced by charged lepton l  from reacction n+Nl  +X (l =e,m), or e- from n+e-n+e- . Detector operates in real time and has directional information.

15. SuperKamiokande events (fairly typical) muon electron

16. Evidence for neutrino oscillations SK atmospheric n

17. Evidence for oscillatory signature in atmospheric neutrino oscillation (SK: PRL, 93, 101801 (2004)) 1.9x10-3eV2<Dm2<3.0x10-3eV2 L/E ~ 500 km/GeV

18. Evidence for neutrino oscillations Solar n Experiments Many experiments, for many years, observed a deficit on the number of neutrinos coming from the Sun,with respect to the Standard Solar Model. Solar experiments observed e-neutrino disappearance. The SNO experiment measured the total flux of neutrinos coming from the Sun and found it consistent with the Standard Solar Model.

19. Evidence for neutrino oscillations SK atmospheric n Solar experiments KAMLAND reactor exp. K2K

20. Neutrino oscillation: In addition to the Solar (+Kamland) and Atmospheric (+K2K), there are two other very relevant experiments: Chooz reactor experiment. Sees no oscillation of reactor ne over a baseline of 1 Km. LSND accelerator experiment. Sees positive signal of oscillations of nm→ ne over 30 m baseline conveniently ignored Excess of 87.9±22.4±6.0 events!

21. Results of the analysis of the oscillation data

22. Results of the analysis of the oscillation data

23. Oscillation parameters Dm2atm≡ Dm232=m23-m22= [2.40.3)x10-3 eV2] dm2sol≡ Dm221=m22-m21= (0.80.3)x10-5 eV2 Mixing angles: q12  qsol  34º2º q23 qatm 45º3º q13 < 12º (at 3s) sin2q13≡|Ue3|2 < 0.04 n12/3 ne n21/3 ne n30% ne

24. CP violation phase atmospheric solar Links atmospheric & solar sectors Parameterization of the PMNS matrix In view of the results it is convenient to parameterize the PMNS matrix as: cij≡cosqij sij≡sinqij

25. Accelerator experiments and their primary goals: MiniBoone (FNAL):prove or disprove LSND K2K (KEK-Kamioka):check SK, improve Dm MINOS (FNAL-Soudan)check SK, improve Dm, q13? OPERA (CERN-LNGS)see nt appearance in nm beam T2K (KEK-Kamioka)try to measure q13 Nona (FNAL-Nth Minn.)try to measure q13 Many ideas for futureq13, CP-violation, ...

26. MiniBoone Experiment (FNAL): Look for ne appearance in nmbeam

27. Long Base Line Experiments MINOS KEK to Kamioka (K2K) CNGS (CERN to Gran Sasso)

28. K2K (KEK to Kamioka) ~1 event/2days ~1011nm/2.2sec (/10m10m) ~106nm/2.2sec (/40m40m) 1º tilt downwards nm 12GeV protons nt SK p+ m+ Target+Horn 100m ~250km 200m decay pipe p monitor Near n detectors (ND) m monitor (monitor the beam center) • Signal of n oscillation at K2K • Reduction of nm events • Distortion of nm energy spectrum

29. GPS SK Tspill TSK TOF=0.83msec SK Events Decay electron cut. 500msec 20MeV Deposited Energy No Activity in Outer Detector Event Vertex in Fiducial Volume More than 30MeV Deposited Energy 107 events Analysis Time Window 5msec for 0.89x1020 p.o.t. -0.2<TSK-Tspill-TOF<1.3msec (BG: 1.6 events within 500ms 2.4×10-3events in 1.5ms) TDIFF. (ms)

30. K2K near-detector complex • 1KT Water Cherenkov Detector (1KT) • Scintillating-fiber/Water sandwich Detector (SciFi) • Lead Glass calorimeter (LG) before 2002 • Scintillator Bar Detector (SciBar) after 2003 • Muon Range Detector (MRD)

31. The same detector technology as Super-K. Sensitive to low energy neutrinos. Flux measurement done with the 1Kton detector Far/Near Ratio (by MC)~1×10-6 M: Fiducial mass MSK=22,500ton, MKT=25ton e: efficiency eSK-I(II)=77.0(78.2)%, eKT=74.5% NSKexp=151 +12 -10 NSKobs=107

32. Dqp m Near Detector Samples assuming that the neutron is at rest, En can be calculated from the E and the angle of the m-. Focus on QE: nmn→m-p • 1KT • Fully Contained 1 ring m (FC1Rm) sample. • SciBar • 1 track, 2 track QE (Dqp≤25), 2 track nQE (Dqp>25)where one track ism. • SciFi • 1 track, 2 track QE (Dqp≤25), 2 track nQE (Dqp>30) where one track ism.

33. SciBar neutrino interaction study • Fully Active Fine-Grained detector (target: 16 tons of scint.). • Sensitive to a low momentum track. • Identify CCQE events and other interactions (non-QE) separately.

34. 3 track (NC) p0 SciBar event gallery CC-QE with a proton rescattering Large energy deposit in Electron Catcher

35. Spectrum measurement Expected shape (No Oscillation) Enrec[GeV] CC-QE assumption V: Nuclear potential

36. Oscillation analysis • Best fit values. sin22q = 1.5 Dm2 [eV2] = 2.210-3 • Best fit values in the physical region. sin22q = 1.00 Dm2 [eV2] = 2.810-3 Probability of no oscillation: 0.005% (4s) from normalization only: 0.26% (3s) from shape only: 0.74% (2.5s)

37. The MINOS experiment Stated goals:

38. The MINOS beam-line

39. MINOS detector: running since early 2005 Near detector 0.98 Kton Far detector 5.4 Kton

40. Low-energy beam after first 1020 pot.

41. CNGSCERN to Gran Sasso Neutrino ProjectA nt appearance program  beam produced at CERN and detected at LNGS after a travel of 730 km Approved by CERN and INFN in 1999, ready in 2006

42. The 2 ways of detecting t appearance @GRAN SASSO m- nt nm BR 18 % h- ntnpo 50 % e- nt ne 18 % p+ p- p- nt npo 14% nm …..nt  t-+ X oscillation CC interaction OPERA: Observation of the decay topology of  in photographic emulsion (~ mm granularity) ICARUS: detailed TPC image in liquid argon and kinematic criteria (~ mm granularity) Decay “kink” n t- nt

43. n interaction • Electronic detector • finds the brick of n interaction • m ID, charge and p Spectrometer (drift tubes-RPCs) Emulsions+lead + target tracker (scintillator strips) Basic “cell” Pb Emulsion 1 mm 8 cm OPERA: an hybrid detector • Emulsion analysis: • Vertex • Decay kink • e/gamma ID • Multiple scattering, kinematics

44. Back Dm2 = 1.8 x 10-3 Dm2 = 2.5 x 10-3 Dm2 = 4.0 x 10-3 Final Design 9.0 17.2 43.8 1.06 With improvements 10.3 19.8 50.4 0.67 OPERA CNGS (6.76 1019 pot/year in shared mode ) OPERA Nt events 5 years data taking Better efficiencies due changeable sheets Better charm background rejection with mid. from dE/dx

45. Future Accelerator Experiments: what do we want to measure? What is the value of q13? What is the value of d? Is there CP violation? Which mass spectrum? Measuring q13 is a prerequisite for measuring d and the sign of Dm32

46. Next generation experiments: SuperBeams Two experiments are now being proposed (approved): T2K (Tokai to Kamioka, 295 km) Nona (FNAL to Ash River, Minnesota, 810 km) These experiments use conventional beams but of much higher intensity (1021 p.o.t./year) than those at present: T2K (New J-Park 50 GeV accelerator) Nona (FNAL Booster) Measure (search) q13, sign of Dm223, d. Improve atmospheric parameters (5% in Dm, 1% in sin22q23).

47. Next generation experiments: SuperBeams, off-axis Both experiments use the off-axis beam configuration: the far detector is placed at an angle from the beam direction. Because of pion decay kinematics (spin-zero, 2 body...), the energy of the neutrinos at an angle from the forward direction is almost independent of the parent pion energy →

48. Next generation experiments: SuperBeams (off-axis) The energy can be tuned for the baseline of the experiment. Background rejection improves substantially with respect to wide-band beam.

49. Measurement of q13 q13is the small fraction of ne in the n3 mass eigenstate. n3 enters in the atmospheric oscillations. Therefore: do an experiment at the atmospheric scale involving ne. For example nm to ne. In general P(nm→ne) has leading and sub-leading terms:

50. P(nmne) in vacuum P(nmne) = P1 + P2 + P3 + P4 • P1 = sin2(q23) sin2(2q13) sin2(1.27 Dm232 L/E) • P2 = cos2(q23) sin2(2q12) sin2(1.27 Dm122 L/E) • P3 = J sin(d) sin(1.27 Dm232 L/E) • P4 = J cos(d) cos(1.27 Dm232 L/E) where J = cos(q13) sin(2q12) sin(2q13) sin(2q23) x sin(1.27 Dm232 L/E) sin(1.27 Dm122 L/E) for the moment