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

2. 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

3. The CERN neutrino beam Reminder
CHORUS was exposed during 4 years to the WBB from SPS at CERN
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

4. 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 = 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 = GeV
Muon spectrometer:
Dp /p = 10 – 15% up to 70 GeV

5. 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

6. Emulsion data acquisition The Nikhef/CERN scanning facility

7. 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 < @90% CL
“Phase 2” analysis has started:
Outlook to reach the proposal sensitivity
sin2(2q) ~ 10-4
after scanning is completed (2002)

8. 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)

9. 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

10. 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

11. 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 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!

12. 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 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)

13. Charm physics with CHORUS Charmed hadron fractions

14. Charm physics with CHORUS Works in progressBm
charm in antinu
Double charm search
???

15. Conclusions