kouji narita nagoya university, japan chorus collaboration study of charm production in neutrino...
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Kouji Narita
Nagoya University, Japan
CHORUS collaboration
Study of charm production in neutrino interactions
CHORUS ExperimentCERN Hybrid Oscillation Research AapparatUS
• ντ appearance in pure νμ beam by CERN SPS
• Direct observation of τdecay in nuclear emulsion target
Flavor abundance <E>(GeV) 1.0 26.9 0.056 21.7 e 0.009 47.9e 0.002 35.3
Mean distance from source : 600m
Short Baseline Experiments
<L>/<E> ~ 2 x 10-2 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 = 0.035.p(GeV/c) 0.22
• lead&fibers “spaghetti” calorimeter
E/E=32%/E (hadrons)
E/E=14%/E (electrons)
hadr~60 mrad @10 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 trackerEmulsion 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 memulsion sheet
microscope stroke
tomographic 16 images
x50 magnification~3m focal depth
512x512 pixels120x150 m view
350 memulsion sheete
mu
lsio
n p
late
CCDcamera
CCDcamera
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-
• ντ CC interaction τdecay vertex
• νμ CC interaction νinteraction vertex
No τ decay found … ~140,000 νμ CC interactions located !
Automatic Vertex Location
CHORUS Phase AnalysisⅡ About 140,000 νμ CC interactions have been located in emulsi
on ! (~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 Data Position accuracy
μm
μm
X projection
Mean = 0.27 μm
Y projection
Mean = 0.29 μm
Plate
Plate
Position accuracy isChecked plate by plate
Average σ= 0.3μm
Prospect on Charm Physicsin CHORUS Phase Ⅱ
• About 10,000 charm associated event is expected in 200,000 νμCC (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 D0 production study
⇒ Phys.Lett B527:173-181,2002
49,292 CC ev. analyzed for Λc production study
D0 search Offline selection
Tracks confirmed by fiber tracker at downstream of emulsion Big impact parameter to 1ry vertex
r > (3.2 + ( 2σdz)2) µm
⇒ checking decay topology in emulsion by human eye
3 µm
Impact parameter (Data)
μ-
I.P
D0 production rate
226(2prong)+57(4prong) candidates with 9.2 BG contamination from K0, Λ0 . ( E531: 57 D0 ) ε(tot) 58.60.7 (2prong), 70.11.3 (4prong)
⇒σ(D0)/σcc=1.99 0.13(stat.) 0.17(syst.)%
(@<E>=27GeV ,P < 30GeV/c)
Phys.Lett B527:173-181,2002
Λc production study
• Charged charm : Λc, D, Ds
Particle ID is impossible in CHORUS detector ……
⇒ Statistical analysis by flight length distribution
Mass(MeV/c2), cτ(µm )
Λc 2284.9, 62 D 1869.3, 315 Ds 1968.6, 149
• Stop same plate as μ-
• Minimum distance between μ and other tracks > 5 µm• No fiber tracker confirmation required
⇒ High detection efficiency @ fl<400 µm
⇒ Check decay topology in emulsion by human eye
Λc Search Offline SelectionMinimum distance (data)
5 µm
μ-
depth
depth(µm)
Λc Analysis status
• 49,292 ev. analyzed
• 79 (1prong) + 84 (3prong) candidate found.
( E531: 62 charged charms)
Λc Analysisdaughter momentum measurement
by multiple scattering
1dx 2dx3dx 4dx 5dx 6dx L
X
L
pdxRMS scatt
3
16.13
0
222 σ6)()( errormeasuredscatt dxRMSdxRMS
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
22 σ6)( dxRMS scat
μmcmX 0.3σ,8.20 Momentum resolution ~N
%80
Typically ~30 % in this analysis
Λc Analysis
BR(Λc →Σ± any) = 10±5 %
Σ+ cτ= 2.396 cm
Σ+ → p + π0 ~ 50 %
Σ+ → n + π+ ~ 50 %
Σ- cτ= 4.4434 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
ΣΣ
Σ
Λc Λc
Λc
μ μ
μ
P or π P or π
P or π
F.L = 60μm
F.L = 1.1cm
Λc Analysis
Λc →Σ± candidate
Σ
09.0θsin kink
Θkink = 90 mrad
GeV/c5.09.1Pdaughter
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 )/σcc=1.39 0.18(stat.) 0.27(syst.)%
(@<E>=27GeV ,P < 30GeV/c)
prelim
inary
prelim
inary
Conclusions• CHORUS has ~ 10,000 Charm events in the emulsion targ
et (final statistics)
• New scanning method (NetScan) allow CHORUS to analyze Charm physics too.(not only Neutrino oscillation)
• D0 production rate have been studied using 25693 CC events. ⇒ Phys.Lett B527:173-181,2002
• 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 .