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