Neutrino DIS measurements in CHORUS

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Neutrino DIS measurementsin CHORUS
DIS2004
Strbske Pleso 14-4-2004
Alfredo G. Cocco INFN Napoli
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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
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Neutrino targets

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

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Non-oscillation physics in CHORUS

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

(ET) (CT) (CT) (CT) (CT) (4T)
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Dimuons analysis
Dimuons
To extract ? mc ? ? ?
(fragmentation) ? B? (charm into ? decay
fraction)
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Data selection
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Data sample
Dimuons
? Data taken from 1995 to 1998 with a dedicated
trigger setup ?
6.6?106 triggers ? At least 2 reconstructed
muons ? 5?105
events
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Selection criteria
Dimuons
? 5 ? Esh ? 200 GeV ? ngap1 ? 5
ngap2 ? 5 ? E?1 ? 5 GeV E?2 ? 5 GeV ? d12 ?
15 cm ? q2 ? 4 GeV2 ? ?Vy,z ? ? 120 cm
295 cm ? Vx ? 394 cm ? 20 ? E? ? 200 GeV
xbj ? 1.0 ybj ? 1.0
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Final sample
Dimuons
2? selected N?? 2801 N?
13132 N? 1224 N 70 The leading
muon is that one with the highest PT (96
efficiency)
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MCDIS generator
Dimuons
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MCDIS
Dimuons
? A new complete event generator for neutrino CC
DIS has been implemented ? Based on Aivazis
helicity formalism ? Leading Order cross
section ? Strange quark parametrization (?,?) ?
Implements JETSET for hadronization ? Fermi
motion, radiative correction (Bardin) ? Full
control on each step via runcards
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MCDISLeading Order cross section
Dimuons
Aivazis et al. (1994)
F helicity structure functions (mt mc VCKM
pdf(?)) ? Lorentz boost between lepton and
hardon configurations
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MCDISLeading Order cross section
Dimuons
For charm neutrino production and neglecting
initial quark mass
Where ? in the limit of M2/Q2? 0 is the slow
rescaling variable
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MCDISFragmentation function
Dimuons
Peterson parametrization
? 0.05
ZP(hc)/Pmax(hc)
z
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MCDISTransverse momentum
Dimuons
? 1.1
N
PT
hc
W
PT2
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MCDISParton Distribution Functions
Dimuons
? Used GRV94LO and CTEQ3L ? Strangeness
parametrization
? 1 for a flavour SU(3) symmetric sea
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Data MC comparison
Dimuons
E? (GeV)
Esh (GeV)
data
MC
E?1 (GeV)
E?2 (GeV)
P?2 (GeV/c)
P?1 (GeV/c)
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Data MC comparison
Dimuons
data
MC
y
x
z
Q2 (GeV2)
Vz(cm)
Vy(cm)
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Data MC comparison
Dimuons
data
MC
d12(cm)
Vx(cm)
cos ?2
cos ?1
?12
Invariant mass (GeV)
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Evaluation of Ncharm
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Background
Dimuons
Background is due to ? and K decay into ? in CC
interactions This can be evaluated using same
sign dimuons in data and the ratio between
opposite and same sign events in CC MonteCarlo
Selection efficiencies and neutrino-antineutrino
cross contamination also to be taken into account
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Background
Dimuons
MonteCarlo ? High statistics (106) fully
simulated CC interaction sample to
evaluate
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Background
Dimuons
In order to subtract background using this
procedure it is crucial to verify that MC
reproduces the distributions of the same sign
dimuon events in the data
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Same sign Data-MC comparison
Dimuons
data
MC
Esh (GeV)
E? (GeV)
E?2 (GeV)
E?1 (GeV)
P?2 (GeV/c)
P?1 (GeV/c)
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induced opposite sign dimuon events
Dimuons
neutrino
antineutrino CDHS
9922 2123 CHORUS
10718 ? 288 420 ?
63 NOMAD 2714 ? 227
115 ? 40 CHARM II 3100
700 CCFR
5030 1060 NUTEV
5102 1458
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4 parameters Maximum Likelihood fit
Dimuons
? Event by event (unbinned) likelihood function
in order to extract mc ? ? B? ? Probability
density given by MonteCarlo as a function of
the unknown parameters
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ML fit result
Dimuons
? Correlation coefficients
? Systematic uncertainties
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Dimuon analysis result(preliminary)
Dimuons
? mc 1.46 ? 0.15 (stat) ? 0.10 (syst) ?
? 0.56 ? 0.05 (stat) ? 0.045 (syst) ? ?
0.040 ? 0.003 (stat) ? 0.015 (syst) ? B?
0.098 ? 0.005(stat) ? 0.014 (syst)
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Dimuon Analysis Summary
Dimuons
? Largest sample of neutrino induced dimuons to
date ? Results from LO analysis in agreement
with other experiments ? Slow Rescaling
model confirmed
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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

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Trimuons

• lt 90o
• no int. bremsstrahlung

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Trimuons
Conclusions MC predictions on 3? rate are in
agreement with measurements
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Z/A dependence of ?m CC 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
• ?m CC 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

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Relative total cross sections
Z/A
?(?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
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Z/A
Comparison with previous experiments
Conclusions the result is in agreement with
previous experiments and with
predictions obtained by
parton model calculations
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Many analyses are still in progress NEW
RESULTS WILL BE AVAILABLE WITHIN 2004