Short Baseline neutrino experiments Outline Status of oscillation

Short Baseline neutrino experiments Outline Status of oscillation experiments Charm production Summary Jaap Panman, CERN Neutrino 2004, Paris, 15 June 2004

Oscillation searches In this talk concentrate on CERN programme, other experiments are covered by other speakers. MOTIVATION of the CERN - t programme: At proposal time: • Cosmologically relevant region (few e. V scale) • Seesaw mechanism could accommodate e. V scale masses and relatively small mixing After Super. K: • Smaller mass-differences more likely • But, LSND …

Neutrino beam West Area Neutrino Facility at CERN SPS 450 Ge. V CHORUS, NOMAD Wide Band Beam – 5. 06 1019 POTs (1994 -1997) – <E > ~ 27 Ge. V – <L> ~ 0. 6 km <L>/<E> ~ 2 10 -2 km/Ge. V Dm 2 > 1 e. V 2 – Prompt t : negligible

NOMAD t detection by kinematical selection

CHORUS t tp at h t ve t detection by decay KINK recognition , ( o’s) -, h- Calorimeter kink Air-core magnet ex rt beam Spectrometer -54 mm -36 mm Red frame: ~30 x 40 m 2 Active target -21 mm 0 mm Veto • Nuclear emulsion • Sci-Fi tracker

Status of oscillation into t – t e – t NOMAD data: final - CHORUS phase-II not yet finished

Search for • • • – e oscillation in NOMAD Motivated by LSND result Final results available Due to electron neutrino component in beam (1%) – careful simulation of beam line needed Exploit powerful electron identification Study energy spectra (enhanced at low energy) and radial distributions (enhanced in the center)

Final results NOMAD result rules out the LSND allowed region with Dm 2 above 10 e. V 2 Define ratio of electron and muon neutrino CC events Events are compatible with known sources No evidence for oscillations

Charm production Additional results of NOMAD and CHORUS: • Charm physics • (for other results see Camilleri’s talk) NOMAD charm physics • D* production and fragmentation study • Exploiting mass resolution CHORUS charm physics • Neutral and charmed particle production • Decay properties, fragmentation studies • Exploiting topological decay recognition • Charm studies only possible with PHASE-II Net. Scan technology

Automatic emulsion data acquisition -II) 1 Location of interaction vertex 1 2 guided by electronic detector. 2 (phase Full data taking around interaction vertex called Netscan Volume : 1. 5 x 1. 5 mm 2 x 6. 3 mm Angular acceptance : 400 mrad ~ 11 minutes / event 3 Offline tracking and vertex reconstruction Reconstruct full vertex topology At least 2 -segment connected tracks Track segments from 8 plates overlapped Eliminate passing through tracks

y r 0 a n i Measurement of D production m i l e r P Phys. Lett. B 527 (2002) 173, based on ~25% of statistics NOW: full sample: 95450 CC events I. P. Candidate selection Primary track matched to detector muon Daughter track matched to detector track 3 ~ 13 μm < I. P. wrt. 1 ry vtx < 400 μm Confirmed D 0 sample 2 prong (V 2) 841 (background: 35) 4 prong (V 4) 227 (no background) Detector muon Selection efficiencies V 2 : 56. 3 ± 0. 5 x 10 -2 V 4 : 74. 2 ± 0. 9 x 10 -2 BG subtracted, efficiency corrected V 2 1426 ± 52 V 4 305 ± 21 (D 0 V 4 ) / ( D 0 = 21. 4 ± 1. 6 x 10 -2 V 2)

m i l re P y r a in Fully neutral D 0 decay modes: BR 4/BR 2 – measured BR 4 = 0. 1338 ± 0. 0058 BR(D 0 PDG neutrals) = 1 -BR 4 x(1+ BR 2/BR 4 ) = 24. 1 ± 4. 5% (6 prong negligible) Total production cross section: All D 0’s = NV 4/BR 4 = 2280 ± 151(stat. ) ± 26(stat. eff. ) ± 99(BR 4 err. ) Relative detection efficiency D 0/CC = 0. 88 σ(D 0)/σ(CC) = 2280/95450/0. 88 = = 2. 71 ± 0. 22 x 10 -2

Study of fragmentation Different strategies to study fragmentation Properties of charm production: NOMAD isolates D* using invariant mass reconstruction For these events, kinematic quantities are well measured, but statistics is low CHORUS uses a high statistics and pure sample of D 0 events obtained by isolating neutral particle decays. However, distributions have to be obtained by an unfolding method.

Nomad D*+ measurement Use decay chain: Step 1: exploit invariant mass combinations Step 2: kinematical cuts Step 3: neural network to reduce combinatorial background Cleanest sample: Neural Net estimator cut at K=0. 8735 35+-7. 2 events (12 background) Larger statistics: K>0. 6

Study larger statistics sample: Background is combinatorial D* mass in clean sample MC: S+B D* yield in CC events (T): Compatible with BEBC Data

p. T 2 distribution of charmed particles The transverse momentum of charmed particles wrt the direction of the hadronic system is usually parametrized as NOMAD Phys. Lett. B 206 (1988) 380 -384 • NOMAD 47 -12 events Phys. Lett. B 526 (2002) 278 -286

Measurement of D 0 momentum Use correlation between opening angle of decay daughters and charm Inverse of momentum to obtain momentum geometrical distribution mean of opening angle of daughters D Momentum distribution of D 0 can be measured by unfolding opening angle distribution (curve is the model in the CHORUS MC) P m li re y r ina

Z-distribution NOMAD Fits to Collins-Spiller and Peterson: CHORUS: Fit to Peterson formula (dotted curve is MC model) Ø Ø Also an E 531 measurement Indirect measurements from dimuon data: v CDHS, CCFR, CHARMII, Nu. Te. V, CHORUS NOMAD CHORUS lim e Pr y r ina

Feynman x distribution Most charmed particles are produced in the forward region NOMAD CHORUS m P li re y r a n i

Charm fragmentation results Large spread in values Maybe due to different mixtures of charm final states: • E 531: all charm decays • Nomad: D* • CHORUS: D 0 • Dimuon experiments: weighted by muonic decay mode

Measurement of Λc production Strategy Phys. Lett. B 555 (2003) 156 based on 50414 CC A statistical approach using flight length distribution MC Short flight decay : Λc enriched sample Λc Long flight decay : D+, Ds dominant Two different set of criteria Ds D+ have been adopted. Flight length in μm

Measurement of Λc production Candidate selection (A) Short flight decay (A) Daughter track : Distance to the muon 5 µm to 30 µm 1614 events from 50, 414 CC events were selected for visual inspection Long flight decay (B) Parent track : distance to the muon < 5 µm Detector muon Distance between daughter and parent 5µm to 30 µm 586 events from 56, 761 CC events were (B) selected for visual inspection Samples after flight length cut (A) 40 mm < FL < 400 mm (B) 400 mm < FL < 2400 mm 1 prong 3 prong 62 133 66 195 Detector muon

Λc • Combining short (A) and long (B) decay search, and taking into account efficiency and background: • c = 861 198 (stat. ) 98 (syst. )+140 (QE) • Br( c -54 3 prong) = (24 7 (stat. ) 4 (syst. )) 10 -2 σ ( c)/σ(CC) Br( c 3 prong)=(0. 37 0. 10(stat) 0. 02(syst))X 10 -2 σ ( c) /σ(CC)= (1. 54 0. 35(stat) 0. 18 (syst)) 10 -2

Quasi-elastic charm production Phys. Lett. B 575 (2003) 198 based on 46105 CC a) n - c+ b) n - c+ ( c*+) c) p - c++( c*++) Topological and kinematical selection criteria: • Require 2 or 3 tracks at primary vertex • 165° (angle between muon and charm in the transverse plane) • Flight length < 200 m (enriched c sample) • Calorimeter energy < 10 Ge. V and electromagnetic energy < 2 Ge. V 13 events with a background of 1. 7 0. 6 (mainly from DIS c) QE production is about 15% of c production

Kinematical selection of QE candidates Energy measured in calorimeter Azimuthal angle Events in first bin

Associated charm production In CC interactions One event has been observed and published. Charged-current Gluon bremsstrahlung W g c– c – D+D+X Phys. Lett B 539 (2002) 188, CHORUS Coll.

NEW Associated charm production In NC interactions Z-gluon fusion Z g c– – D+D+X c In the past only one event • Observed in E 531 emulsion Indirect search performed by Nu. Te. V • Production rate (2. 6 x 1. 6)x 10 -3 of CC Systematic search for double decay topologies Events observed in NC and CC interactions with very low background (order 0. 1 event) AND Gluon bremsstrahlung Z g c– c – D+D+X

example of NC event E=29. 9 Ge. V Both neutral decays inconsistent with two-body decay (acoplanarity) TT #5, Pd 1> 1. 39 Ge. V/C @ 90 CL. TT #8, Pd 2>4. 66 Ge. V/C @ 90 CL. Pd 3>3. 33 Ge. V/c @ 90 CL. TT #3 Pd 4>2. 72 Ge. V/c @ 90 CL. pl 23 pl 22 TT #6 PP>0. 66 Ge. V/C @ 90 CL.

example of CC event Evis= 53. 8 Ge. V E=36. 9 Ge. V P=-16. 9 Ge. V/c Both neutral decays inconsistent with two-body decay (acoplanarity) Pd 1>4. 70 Ge. V/c @ 90 CL. (TT #2) Pd 2>0. 67 Ge. V/c @ 90 CL. Pd 2>1. 92 Ge. V/c @90 CL. (TT #5) Pd 3>2. 32 Ge. V/c @90 CL. (TT #7) Pl 31 pl 30

Charm production in antineutrino interactions N + = 2725 “ 1 spectrometer events” N - = 93890 Selected events = 82 kink> 50 mrad, F. L > 50 m found charm = 61 after reconstruction cut = 32 N = 4374 ± 135 + 1. 9 f. Co = 2. 9 - 1. 2 (stat) f. Cry a n i m i l + e Pr ( N c. X) + 1. 2 = 4. 8 + - 0. 9 % ( N X) Energy dependence

Trimuon events in CC interactions CDHS and HPWF (1978): ~100 - - + events - origin largely unknown CHORUS: ~6 x 106 2 calorimeter triggers observed: 42 - - +, 3 - + + (P > 5 Ge. V/c) Detailed Monte-Carlo (LEPTO/JETSET/GEANT) 4 x 106 events with full detector simulation present knowledge of production rates and -decays of h, r, w, h’, f data-MC validation using 2 events (known origin) data-MC comparison for 3 event sample

Trimuons DATA All MC Charm-> + -/ Int. bremsstrahlung Angle between leading - and sum of two others j>900 no int. bremsstrahlung

Trimuons MC 2 validation P and well reproduced main 3 sources MC - - + predictions Charm-> + -/ - decay Internal bremsstrahlung (theoretical) Conclusions – MC predictions on 3 rate are in agreement with measurements 8. 3 2. 8 8. 6 4. 5 40 Observed in experiment: 42 - - +

SUMMARY • SBL oscillation programme at CERN: – NOMAD final data – CHORUS, final statistics, but phase-II analysis ongoing • Many additional measurements (in this talk concentrated on charm physics) – Production cross-sections – Fragmentation functions – Decay properties • Other results will be shown by Camilleri