Neutrino and Charm Physics with CHORUS Francesca Spada NIKHEF Annual Scientific Meeting - 13/12/2001

CHORUS Emulsion Physics Measurement principles Neutrino interactions take place in a target/detector of nuclear emulsions direct observation of short lived particle decays 770 Kg of nuclear emulsions divided in 4 stacks perpendicular to the beam Very high spatial resolution (~1µm) with 300 tridimensional hits/mm Suitable to detect the decay signature: Interaction vertex Short t or charm path ~ 1 mm A kink as decay topology Oscillation physics: search for nt appearance in a pure nm beam nm energy well above t production threshold An electronic detector reconstructs the kinematics and allows trace-back to the interaction vertex in emulsion

The CERN neutrino beam Reminder CHORUS was exposed during 4 years to the WBB from SPS at CERN 5 . 1019 POTs leading to 840,000 nµ CC interactions in emulsion Eprotons = 450 GeV Intense nµ beam with En ~ 27 GeV Prompt nt unavoidable but negligible (~0.1 bg events expected in total) Ricorda di mettere gli anti su nu_mu e nu_e

The CHORUS detector Hybrid emulsion/electronic tracking Active target: nuclear emulsion target scintillating fibre tracker Air-core magnet + tracker: Hadron momentum (up to 20 GeV) Dp /p = 0.035 p (GeV) Å 0.22 Active target Calorimeter Spectrometer Air-core magnet Honeycomb Chambers 4-Target setup Lead and fibre Calorimeter: DE/E = 32% / ÖE (hadrons) = 14% / ÖE (electrons) Dqhadrons = 60 mrad @ 10 GeV Muon spectrometer: Dp /p = 10 – 15% up to 70 GeV

Emulsion data acquisition The Nagoya Track Selector Shift each plane by the angle given in predictions Take 16 tomographic images per plate at different focal depths The most upstream 100 µm of each plate are scanned Sum up the ph. A track is recognized as a peak CCD image: 120×150 µm Focal depth: 3 µm

Emulsion data acquisition The Nikhef/CERN scanning facility

CHORUS Oscillation Physics Results and perspectives sin2(2q) Dm2 [eV2] 0.6 eV2 Design purpose: Oscillation physics at large mass square (Dm2 ~ eV2) and small mixing (sin2(2q) ~ 10-4) Current limit on oscillation: Pµt < 3.4 10-4 @90% CL “Phase 2” analysis has started: Outlook to reach the proposal sensitivity sin2(2q) ~ 10-4 after scanning is completed (2002)

Non-Emulsion physics with CHORUS NIKHEF activities Deep inelastic scattering - Measurement of structure functions (R. Oldeman, ‘98 data) Charm production in the calorimeter (C. v/d Poel, R. van Dantzig) DIS Workig Group ® finalize data for publication 4-Target data - Study neutrino cross section in different materials (R. Oldeman, I. Hristova, R. van Dantzig, M. de Jong)

CHORUS Phase II Scanning speed increased from 0.01 frames/sec in 1994 to 10,000 in 2000 Automatic scanning of a large emulsion volume is now feasible! New predictions/locations (mainly 0µ) to increase by >80 Kevents the current sample of ~164 Kevents (scan-back started) For each (old and new) located event ® full event analysis in the vertex region (data-taking started, current speed is ~10 Kevents/month) Improvement of oscillation search to reach the proposal sensitivity We will have a big sample of events fully analyzed in the vertex region Unbiased study of charm production in neutrino interactions About 600 charm events already identified

NETSCAN An innovating scanning technique! Use already located events Fiducial Volume An innovating scanning technique! Use already located events Pick up all track segments in an 8-plates deep fiducial volume around scan-back track Decay search is not limited to the scan-back track Offline analysis of emulsion data Reconstruct full vertex topology At least 2-segment connected tracks Track segments from 8 plates overlapped Eliminate passing-through tracks

Charm physics with CHORUS D0 production Interaction vertex Decay D0 TT-matched tracks Sample: 25,693 events analyzed with Netscan Charm selection: based on Impact Parameter analysis and track matching in the Target Tracker Purity: 63% (background: 2ry interactions, d rays, g conversions, low momentum tracks) After manual scanning 283 D0 candidates Efficiency: 58% on V2, 70% on V4 Expected bg ~ 9 events (mainly K0 and L0 decays) s(D0)/s(CC) = (1.99±0.13±0.11)·10-2 CHORUS E531 PRELIMINARY!

Charm physics with CHORUS Associated c production From a dedicated search: We observed a candidate event for associated charm production Event topology in emulsion: V2 + Kink 30 29 21 µ 2 1 3 790 µm V2 ® decay of a D0 1 - kink parent (flight ~ 1010 µm) 2 - kink daughter (flight ~ 7560 µm) undergoing kink or 2ry interaction 3 - ionization ~ 3xMIP ® proton (~780 MeV from multiple scattering) Candidate for (neutral + charged) double charm production Background evaluation under work (¾)

Charm physics with CHORUS Charmed hadron fractions

Charm physics with CHORUS Works in progress Bm charm in antinu Double charm search ???

Conclusions