Kouji Narita Nagoya University, Japan CHORUS collaboration Study of charm production in neutrino interactions

CHORUS Experiment CERN Hybrid Oscillation Research AapparatUS ν τ appearance in pure ν μ beam by CERN SPS Direct observation of τdecay in nuclear emulsion target Flavor abundance (GeV)   e  e Mean distance from source : 600m Short Baseline Experiments / ~ 2 x km/GeV 0.1 prompt   CC event expected in CHORUS

air core-magnet calorimeter muon spectrometer target emulsion Neutrino target Active nuclear emulsion target (770kg emulsion) Scintillating fiber trackers 150  m resolution,   =2mrad Hadrons Sign and momentum air-core magnet spectrometer  p/p = p(GeV/c)  0.22 lead&fibers “spaghetti” calorimeter  E/E=32%/  E (hadrons)  E/E=14%/  E (electrons)  hadr ~60 GeV Muon ID, sign and momentum iron-core muon spectrometer  p/p~10%-15% (p<70 GeV/c) CHORUS Detector Beam exposure 1994~1997

Emulsion target Scintillating fiber tracker Emulsion target (36 plates) ~4cm Interface emulsion Scintillating fiber tracker ⇒ Interface emulsion ⇒ Target emulsion Target emulsion + S.F.T

Hardware video processors reconstruct tracks as frame-to-frame emulsion grain coincidence. 90  m plastic support 350  m emulsion sheet microscope stroke tomographic 16 images x50 magnification ~3  m focal depth 512x512 pixels 120x150  m view 350  m emulsion sheet emulsion plate CCD camera CCD camera 100  m Automatic Emulsion Data Taking (pioneered by the Nagoya CHORUS group)

Fiber Tracker  Interface emulsion  Target emulsion 100  m most upstream of each target plate are scaned μ-μ- ν τ CC interaction  τdecay vertex ν μ CC interaction  νinteraction vertex No τ decay found … ~140,000 ν μ CC interactions located ! Automatic Vertex Location

CHORUS Phase Ⅱ Analysis About 140,000 ν μ CC interactions have been located in emulsion ! (~60,000 NC interaction also located) Applying New Scanning Method (Netscan) All tracks in vertex region (1.5mm×1.5mm×6.3mm) will be scanned. Track pick up speed in emulsion increase year by year and current data storage speed is 15 minutes / vertex region ⇒ Charm physics Improvement on oscillation limit

NetScan

NetScan Data 1Plate ~800 track segments 1.5mm Beam

NetScan Data 8Plates 1.5mm 8plates (6.3mm)

NetScan Data Reconstruct tracks 1.5mm 8plates (6.3mm)

NetScan Data reject penetrating tracks 1.5mm 8plates (6.3mm)

NetScan Data reconstruct vertex νint.vtx + D 0 decay vtx 1.5mm 8plates (6.3mm)

NetScan Data Position accuracy μm X projection Mean = 0.27 μm Y projection Mean = 0.29 μm Plate Position accuracy is Checked plate by plate Average σ= 0.3μm

Prospect on Charm Physics in CHORUS Phase Ⅱ About 10,000 charm associated event is expected in 200,000 ν μ CC (final sample) Charm decay vertex is reconstructed in very good accuracy ~1µm and can be confirmed by human eye ~ BG free analysis ⇒ Charm production in Neutrino interactions can be studied ! (so far,only E531 studied)

Analysis status ~100,000 CC ev.have been data taken (NetScan). 25,693 CC ev. analyzed for D 0 production study ⇒ Phys.Lett B527: , ,292 CC ev. analyzed for Λ c production study

D 0 search Offline selection Tracks confirmed by fiber tracker at downstream of emulsion Big impact parameter to 1ry vertex r >  ( ( 2σdz) 2 ) µm ⇒ checking decay topology in emulsion by human eye 3 µm Impact parameter (Data) μ-μ- I.P

D 0 production rate 226(2prong)+57(4prong) candidates with 9.2 BG contamination from K 0, Λ 0. ( E531: 57 D 0 ) ε(tot) 58.6  0.7 (2prong), 70.1  1.3 (4prong) ⇒ σ(D 0 )/σ cc =1.99  0.13(stat.)  0.17(syst.)% =27GeV,P  < 30GeV/c) Phys.Lett B527: ,2002

Λc production study Charged charm : Λc, D, Ds Particle ID is impossible in CHORUS detector …… ⇒ Statistical analysis by flight length distribution Mass(MeV/c 2 ), cτ(µm )  Λc , 62  D , 315  Ds , 149

Charged Charm Flight Length D : Λc : Ds = 6 : 3 : 1 Λc D Ds MC (E531 result)

Stop same plate as μ - Minimum distance between μ and other tracks > 5 µm No fiber tracker confirmation required ⇒ High detection fl<400 µm ⇒ Check decay topology in emulsion by human eye Λc Search Offline Selection Minimum distance (data) 5 µm μ-μ- depth depth(µm)

Λc Analysis status 49,292 ev. analyzed 79 (1prong) + 84 (3prong) candidate found. ( E531: 62 charged charms)

Flight length MC DATA Λc Λc + D + Ds

Λc Analysis daughter momentum measurement by multiple scattering every 1pl Pmax = 1.4 GeV/c every 2pl Pmax = 4.0 GeV/c every 3pl Pmax = 7.4 GeV/c Measurable momentum is limited by measurement error Momentum resolution ~ Typically ~30 % in this analysis

Λc Analysis 1prong decay events. Decay Pt distribution MC Λc→ 1prong (a.u) GeV/c

Λc Analysis BR(Λc →Σ ± any) = 10±5 % Σ + cτ= cm Σ + → p + π 0 ~ 50 % Σ + → n + π + ~ 50 % Σ - cτ= cm Σ - → n + π - ~ 100 % Λc →Σ ± search ~100μm Λc Σ ~ cm p or π Follow daughter tracks to downstream… ⇒ 10 candidate decay found !!

Run : 7894 Event : 7004 Σ Σ Σ Λc μ μ μ P or π F.L = 60μm F.L = 1.1cm Λc Analysis Λc →Σ ± candidate Σ Θ kink = 90 mrad Pt = 171±45 MeV/c

Λc production rate 79 (1prong) + 84 (3prong) found B.G (D,Ds) ~ 21±5 ε(tot) 10.2 % (1prong), 30.2 % (3prong) ⇒ σ(Λc )/σ cc =1.39  0.18(stat.)  0.27(syst.)% =27GeV,P  < 30GeV/c) preliminar y

Conclusions CHORUS has ~ 10,000 Charm events in the emulsion target (final statistics) New scanning method (NetScan) allow CHORUS to analyze Charm physics too.(not only Neutrino oscillation) D 0 production rate have been studied using CC events. ⇒ Phys.Lett B527: ,2002 Λc production rate analysis is in progress. NetScan method can measure the momentum by multiple scattering in the emulsion target. (1prong event decay Pt was measured, and consistent with MC ) Λc →Σ ± candidates found. ⇒ Good evidence of Λc ⇒ will be published this year.