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

NetScan Data1Plate ~800 track segments

1.5m

m

1.5mm

Beam

NetScan Data8Plates

1.5m

m

1.5mm

8pla

tes

(6.3

mm

)

NetScan DataReconstruct tracks

1.5m

m

1.5mm

8pla

tes

(6.3

mm

)

NetScan Datareject penetrating tracks

1.5m

m

1.5mm

8pla

tes

(6.3

mm

)

NetScan Datareconstruct vertex

νint.vtx + D0 decay vtx

1.5m

m

1.5mm

8pla

tes

(6.3

mm

)

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

Charged Charm Flight Length

D : Λc : Ds = 6 : 3 : 1

Λc

DDs

MC

(E531 result)

• 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)

Flight length

MC

DATA

Λc Λc + D + Ds

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 Analysis1prong decay events. Decay Pt distribution

05.0θsin kink

MC Λc→ 1prong (a.u)

GeV/c

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 .