Cross section measurements in CHORUS

1
Cross section measurements in CHORUS
Andrei Artamonov ITEP, Moscow
NuInt04, Gran Sasso , Italy 17 21 March 2004
2
CHORUS detector
Air-core magnet
Active target
?p/p 0.035 p (GeV/c) ? 0.22
-nuclear emulsion target (770kg) -scintillating
fiber tracker
?
?p/p 10 15 (p lt 70 GeV/c)
muon spectrometer
27 GeV
Calorimeter
WB Neutrino beam
?E/E 32 /? E (hadrons) 14 /? E
(electrons) ?? h 60 mrad _at_ 10 GeV
nm nm ne ne 1.00
0.06 0.017 0.007
3
Targets

• Emulsion (1 ?m precision -gt decay topology)
  ET
• 770 kg, 4 X0
• 2x106 CC ? interactions, 1994-1997
• Calorimeter CT
• 112 ton, lead, 5.2 ?,
• 1.5x107 CC ? interactions, 1994-1998
• Special 4 targets 4T
• 100x4 kg, marble, plastic, Fe, Pb
• 106 CC ? interactions, 1998

4
Non-oscillation physics in CHORUS

• Charm
• D0, ?c, QE charm production
• cc CC/NC production
• BR-gtm, fragmentation functions
• anti-neutrino charm production
• total charm production cross section
• Structure functions
• Dimuons
• Trimuons
• J/? NC production
• Z/A dependence of CC cross-section

(ET) (CT) (CT) (CT) (CT) (4T)
5
Trimuon events in ?m CC interactions

• CDHS and HPWF (1978) 100 m- m- m events
• - origin largely unknown
• CHORUS
• 6x106 2m calorimeter triggers
• observed 42 m- m- m, 3 m- m m (Pm gt 5
  GeV/c)
• Detailed Monte-Carlo (LEPTO/JETSET/GEANT)
• 4x106 events with full detector simulation
• present knowledge of production rates and
• m-decays of h, r,
  w, h, f
• data-MC validation using 2m events (known
  origin)
• data-MC comparison for 3m event sample

6
Trimuons

• lt 900
• no int. bremsstrahlung

7
Trimuons
Conclusions MC predictions on 3? rate are in
agreement with measurements
8
Z/A dependence of ?mCC cross-section
Eur. Phys. J. C30 (2003) 159-167

• for the first time 4 targets in the same
  experiment
• were exposed
  simultaneously
• positions rotated to avoid acceptance
  differences
• ?mCC interactions in calorimeter used to monitor
  neutrino
• flux and for relative
  normalisation of events
• empty target period recorded for background
  subtraction
• only muons used in event reconstruction
• events are assigned to particular target by
• extrapolating muon trajectory to the target
  plane

9
Z/A
Relative total cross sections
?(?n)/?(?p) 1.71
Predictions are based on GRV98LO PDF and
modifications according
to
A.Bodek-U.K.Yang model Predictions equalized to
measurements at marble point
10
Z/A
Comparison with previous experiments
Conclusions the result is in agreement with
previous experiments and with
predictions obtained by parton
model calculations
11
?c production
Phys. Lett. B. 555 (2003) 156-166

• Analysis is based on statistical approach using
  flight length distribution

• Short flight decay
• (40 mm lt FL lt400 mm)
• ? c enriched sample
• Long flight decay
• (400 mm lt FL lt 2400 mm)
• D, Ds dominated sample

? c
D
Ds
Flight length in µm

• Analysis has been performed applying two
  different selections.

12
?c
50000 CC events half of full statistics

• Short flight decay (A)
• Daughter track distance to the muon 5 µm to 30
  µm
• 1614 events were selected for visual inspection
• Long flight decay (B)
• Parent track distance to the muon lt 5 µm
• Distance between daughter and parent 5µm to 30 µm
• 586 events were selected for visual inspection

(A)
(B)
Samples after flight length cut
1 prong
3 prong
(A) 40 mm lt FL lt 400 mm
62
66
(B) 400 mm lt FL lt 2400 mm
133
195
13
results
?c

• Combining short (A) and long (B) decay
  search,and taking into account efficiency and
  background
• Lc 861 ? 198 (stat.)?? 98 (syst.)140 (QE)
• Br(Lc 3prong) (24 ? 7 (stat.) ? 4 (syst.))
  ? 10-2

-54
s (Lc)/s(CC)?Br(Lc 3prong)(0.37 ? 0.10(stat)
? 0.02(syst))X10-2
s (Lc) /s(CC) (1.54 ? 0.35(stat) ? 0.18 (syst))
? 10-2
14
Quasi-elastic charm production
Phys.Lett.B 575 (2003) 198 based on 46105 ?? CC
a) ?? n ? ?- ?c b) ?? n ? ?- ?c
(?c) c) ?? p ? ?- ?c(?c)
Topological and kinematical selection criteria

• Require 2 or 3 tracks at primary vertex
• ? ? 165 (angle between muon and charm in the
  transverse plane)
• Flight length lt 200 ?m (enriched ?c sample)
• Calorimeter energy lt 10 GeV and electromagnetic
  energy lt 2 GeV

13 events with a background of 1.7?0.6 (mainly
from DIS ?c)
QE production is about 15 of ?c production
15

• Measurement of D0 production
• 
  Phys. Lett. B 527 (2002) 173, based on 25 of
  statistics
• NOW full sample 95450 CC events

NEW
Candidate selection

• Primary track matched to detector muon
• Daughter track matched to detector track
• 3 13 µm lt I.P. wrt. 1ry vtx lt 400 µm

Selection efficiencies

• V2 56.3 0.5 x 10-2

• V4 74.2 0.9 x 10-2

Confirmed D0sample

• 2 prong (V2)

841
227

• 4 prong (V4)

(D0 V4) / (D0 V2) 21.4 1.6 x 10-2
BG subtracted, efficiency corrected
V2 1426 52 V4 305 21
16
D0
NEW
Fully neutral D0 decay mode
BR4/BR2 measured BR4 0.1338 0.0058
PDG BR(D0 neutrals) 1-BR4 x(1 BR2/BR4 )
24.1 4.5
Total production cross secton
All D0s NV4/BR4 2280 151(stat.)
26(stat.eff.) 99(BR4 err.) Relative detection
efficiency D0/CC 0.88
s(D0)/s(CC) 2280/95450/0.88 2.71 0.22
x 10-2
17
NEW
Associated charm production in CC
One event has been observed and published. Phys.
Lett B 539 (2002) 188, CHORUS Coll.
Charged-current
Gluon bremsstrahlung
18
Associated charm production in NC

• In the past only one event
• observed in the E531 emulsion
• Production rate 10-3 normalised to CC
• Indirect search performed by NuTeV
• Production rate (2.6?1.6)x10-3 normalised to CC
  at 154 GeV
• Currently a search for this process is in
  progress in CHORUS

19
Event 81332312
V2V2 in 0mu
1ry_at_pl23 Ns1, Nh3 V2(1) _at_pl 23 Dq 96.3
mrad fl 62.8mm V2(2) _at_pl 22 fl 976.6mm Dq
203.4 mrad
TT 5
TT 8
TT 3
TT 6
pl23
pl22
20
Event 77393952
Ns 6 Nh 1 (gray)
4Vee _at_ pl 17 FL 884 µm
C3 _at_ pl 17 FL 426 µm
21
charm production in antineutrino interactions
PRELIMINARY
Nm 2725 Nm- 93890 Selected events 82 found
charm 61 after m reconstruction cut 32
1m spectrometer events
Qkinkgt 50 mrad, F.L gt 50 mm
22
Charm production rate as a function of n energy
23
Many types of analysis are still in progress
MORE NEW RESULTS WILL BE AVAILABLE IN COURSE
OF 2004