Neutrino and Charm Physics with CHORUS

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Neutrino and Charm Physics with CHORUS

• Francesca Spada
• NIKHEF Annual Scientific Meeting - 13/12/2001

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CHORUS Emulsion PhysicsMeasurement 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

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The CERN neutrino beamReminder

• 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)

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The CHORUS detectorHybrid 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

• Lead and fibre Calorimeter
• DE/E 32 / ÖE (hadrons)
• 14 / ÖE (electrons)
• Dqhadrons 60 mrad _at_ 10 GeV
• Muon spectrometer
• Dp /p 10 15 up to 70 GeV

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Emulsion data acquisitionThe 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 120150 µm
• Focal depth 3 µm

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Emulsion data acquisitionThe Nikhef/CERN
scanning facility
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CHORUS Oscillation PhysicsResults and
perspectives

• Design purpose
• Oscillation physics at large mass square (Dm2
  eV2) and small mixing (sin2(2q) 10-4)
• Current limit on oscillation
• Pµt lt 3.4 10-4 _at_90 CL
• Phase 2 analysis has started
• Outlook to reach the proposal
  sensitivity
• sin2(2q) 10-4
• after scanning is completed (2002)

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Non-Emulsion physics with CHORUSNIKHEF 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)

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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 gt80 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

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NETSCAN
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
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Charm physics with CHORUSD0 production

• 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) (1.990.130.11)10-2

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Charm physics with CHORUSAssociated c production

• From a dedicated search
• We observed a candidate event for associated
  charm production
• Event topology in emulsion V2 Kink

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Charm physics with CHORUSCharmed hadron fractions
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Charm physics with CHORUSWorks in progress

• Bm
• charm in antinu
• Double charm search
• ???

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Conclusions