Transcript Data handling in the CHORUS emulsion experiment at CERN

Charm in emulsion
Bart Van de Vyver (VUB,Brussels)
WIN02, Christchurch (NZ), Jan’02
• CHORUS detector & emulsion
•Automatic event location,
‘analysis-driven’ vertex
analysis
•Charm in opposite-sign dimuons
•Dedicated searches (manual)
•Net scan technique,
‘general’ vertex analysis
•Semi-inclusive D0 search
•Associated charm production
CHORUS detector
Nucl. Instr. Meth. A 401 (1997) 7-44
-
Calorimeter
T=5°
hMuon
spectrometer
Heart of the detector:
Air core
Nuclear emulsion
target
spectrometer and
emulsion tracker
Veto plane
770 kg emulsion
target and
scintillating fibre
tracker
CHORUS emulsion
350 m
90 m
-54 m
-36 m
~ 800 kg active target
MIP : 30  40 grains / 100 m
transverse resolution ~ 0.5 m
depth of focus : 1 to 3 m
-21 m
0 m
Nucl. Instr. Meth. A 447 (2000) 361-376
Automatic Scanning
microscope
stroke
CCD
camera
Tracks reconstructed
by a hardware video
processor
frame to frame emulsion
grains coincidence
150x150 m view
CCD
camera
X50 magnification
~3m focal depth
tomographic
image
emulsion plate
350  m (175  m)
emulsion sheet
90 m plastic backing
350  m (175  m)
emulsion sheet
T.Nakano, Ph.D. Thesis, Nagoya Univ., 1997
Neutrino charm production

Beam
knowledge
-
|Vcd|2,|Vcs|2
Charm fragmentation
D0 : D+ : Ds+ : c+
z = pc/pD
d,s
c
Quark density functions,
strange sea ()


+ NLO effects
g
s
c
s

g

B(c)

h
Ehad

c

+ radiative gluon
c and self energy
diagrams
s
Previous experiments
CDHS (CERN WBB)
9922 -+ , 2123 +- events Zeitschr. Phys. C (1982) 19-31
CCFR (NuTeV)
5044 -+ , 1062 +- events
Zeitschr. Phys. C (1995) 189-198
CHARMII (CERN WANF)
4111 -+ , 871 +- events
Eur. Phys. J., C11 (1999) 19-34
NOMAD (CERN WANF)
2714 -+ , 115 +- events
CERN EP 2000-072,
submitted to Phys.Lett.B
E531 (Fermilab, Nagoya)
131 charm events in emulsion
only measurement of D0 : D+ : Ds+ : c+
B(c) crucial for other experiments
Phys. Lett. B 206 (1988) 375-379
CHORUS Phase I : dimuons
+
Zoom
D+
h
-
‘Proof of principle’
94/95 sample
5 plates manual follow down
96/97 sample
(N)TS automatic kink finding
25
20
15
Charged
10
Neutral
5
A.U.
0
sc
94
95
96
97
Event selection
fit
dc
0.2
0.4
0.6
E  2.3 GeV
 < 400 mrad
kink > 0.1 
flightlength > 10 m
xBjorken O. Melzer, Ph.D. Thesis, NIKHEF, 1997
Diffractively produced Ds event
- N’
Ds+ 
 N  Ds*
+ 
+ 
Phys. Lett. B 435 (1998) 458-464
CHORUS Phase II : net scan
All track segments ( < 0.4 rad) in
Fiducial volume: 1.5 x 1.5 mm2 x 8 plates
Offline analysis of emulsion data
Reconstruct full
vertex topology
At least 2-segment
connected tracks
Track segments from 8
plates overlapped
Eliminate passingthrough tracks
Charm selection
• matching to electronic detectors
1.5 mm
1.5 mm
8 plates
• track and vertex fitting (MCS)
• displaced vertex with at least
one or more matched tracks
OR
• isolated, matched track with
large impact parameter
Manual checks
• Sample of 25,693  CC interactions, ~15% of final statistics
• selection efficiency : V2  58.60.7% , V4  70.11.7%
• 851 (3.3%) selected events
Neutral ~ 33 %
V2
226
V4
57
Charged ~ 30 %
C1
121
C3
124
C5
7
Backgr ~ 37 %
2ry int. 68
e+ e-,  ray 44
low p 204
D0 production rate
 (D0) / σ (CC) = 1.99  0.13 (stat.)  0.17 (syst.) %
<E>=27GeV, P < 30GeV/c
D0  V4 / D0  V2
= 23.1  4.0 %
E531
 (D0) / σ (charm)
= 53  11 %
CHORUS
Slow rescaling model
mc = 1.3 GeV/c2
E (GeV)
To appear in Phys.Lett.B (Measurement of D0 production in …, A.Kayis-Topaksu et al.)
Associated charm production
30
29
21
Ns = 2
Nh = 6

6735 m
1010 m
transverse plane
D0 f.l. = 340 m
1st vertex
2ry vertex
kink = 420 mrad
f.l. = 1010 m
pb = 500
dE/dx
+180
- 110
2 = 310 mrad
f.l. = 7560 m
kink parent
D0
MeV/c
P = 0.78 GeV/c
proton
P > 330
MeV/c
-
Outlook
• D0 production rate
Data taking ongoing : 25k CC  200k CC
Improved selection : purity 65%  90%
No need for manual?
• Inclusive charm, including charged
~ 4,000 neutrino-induced charm events
Fragmentation fractions D0 : D+ : Ds+ : c+
B(c), Vcd, s(x), ...
• Associated charm production
Background evaluation based on CHORUS data and FLUKA
Improved selection : efficiency 1%  25%
• Exclusive channels
Proton identification
MCS momentum measurement
 detection
c absolute BR,QE c production,D*+D0+
High purity selection
selected
charm
secondary
background
not checked
primary
e+epassing
fake vee
unrelated 2ry
original
338
261
29
48
14
13
6
8
3
4
loose
291
242
28
21
0
5
5
6
1
4
tight
261
236
13
12
0
3
3
2
1
3
The CKM matrix
Vud
0.1 %
d’
s’ =
b’
nuclear beta decay
Vus
Vub
1%
25 %
Ke3 decay
bul
Vcd
Vcs
Vcb
7%
15 %
5%
 charm production
De3 decay
Be3 decay
Vtd
Vts
Vtb
d
s
b
30 %
tbl
Review of particle physics, 98 edition
Measuring Vcd


had
charm

~

had
Difficulties
charm
CC
allCC


d(x) |Vcd|2 + s(x) |Vcs|2
d(x) + s(x)
|Vcd|2
+
1 + s/d
 |Vcd|2
s|Vcs|2
d+s
s  0 for large xBjorken
No antineutrino data in emulsion
(5 % contamination in neutrino mode)
No invariant mass reconstruction or particle ID
(inclusive analysis)
Biases in the sample of vertices located in Nagoya
(CERN microscopes)
Too low statistics for the time being
(Phase II rescan of all events)
Hadronic decays more interesting than muonic ones, but harder
(Net scan both in Nagoya and at CERN)
A microscope view
3 m focal depth
nuclear fragments
Plates are orthogonal to the
neutrino beam
An AgBr emulsion grain has
about 0.5 mm diameter
120 m
Large angle nuclear
fragments (if any) are seen
as a ‘star’ of heavy ionizing
‘tracks’ in the vertex view
Interaction tracks are seen
as the coincidence of a single
grain from each view
10 m
150 m