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Neutrino DIS measurements in CHORUS DIS2004 Strbske Pleso 14-4-2004 Alfredo G. Cocco INFN – Napoli
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CHORUS detector p/p = 0.035 p (GeV/c) 0.22 p/p = 10 – 15% (p < 70 GeV/c) -nuclear emulsion target (770kg) -scintillating fiber tracker E/E = 32 %/ E (hadrons) = 14 %/ E (electrons) h = 60 mrad @ 10 GeV ~ 27 GeV Air-core magnetActive target muon spectrometer Calorimeter WB Neutrino beam :: : : : e : e ::: 1.00 : 0.06 : 0.017 : 0.007
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Neutrino targets ET Emulsion ( 1 m precision decay topology ) ET 770 kg, 4 X 0 2x10 6 CC ν interactions, 1994-1997 CT Calorimeter CT 112 ton, lead-scint.fiber, 5.2 1.5x10 7 CC ν interactions, 1994-1998 4T Special 4 targets 4T 100x4 kg, marble, plastic, Fe, Pb ~10 6 CC ν interactions, 1998
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Charm D 0, Λ c, QE charm production cc CC/NC production BR , fragmentation functions anti-neutrino charm production total charm production cross section Structure functions J/Ψ NC production Dimuons Trimuons Z/A dependence of CC cross-section Non-oscillation physics in CHORUS (ET) (CT) (4T)
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Dimuons analysis To extract: m c (fragmentation) B (charm into decay fraction) Dimuons
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Data selection
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Data sample Data taken from 1995 to 1998 with a dedicated trigger setup 6.6 10 6 triggers At least 2 reconstructed muons 5 10 5 events Dimuons
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Selection criteria 5 E sh 200 GeV ngap1 5 ngap2 5 E 1 5 GeV E 2 5 GeV d 12 15 cm q 2 4 GeV 2 V y,z 120 cm 295 cm V x 394 cm 20 E 200 GeV x bj 1.0 y bj 1.0 Dimuons
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Final sample 2 selected : N = 2801 N + = 13132 N + = 1224 N ++ = 70 The leading muon is that one with the highest P T (96 % efficiency) Leading muon 2nd muon Dimuons
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MCDIS generator Dimuons
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MCDIS 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 Dimuons
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MCDIS Leading Order cross section F = helicity structure functions (m t m c V CKM pdf( )) = Lorentz boost between lepton and hardon configurations Aivazis et al. (1994) Dimuons
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MCDIS Leading Order cross section Where in the limit of M 2 /Q 2 0 is the “slow rescaling” variable For charm neutrino production and neglecting initial quark mass Dimuons
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MCDIS Fragmentation function z Z=P(h c )/P max (h c ) = 0.05 Peterson parametrization Dimuons
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MCDIS Transverse momentum PT2PT2 = 1.1 W+W+ PTPT hchc N Dimuons
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MCDIS Parton Distribution Functions = 1 for a flavour SU(3) symmetric sea Used: GRV94LO and CTEQ3L Strangeness parametrization: Dimuons
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Data – MC comparison E (GeV) E sh (GeV) E 1 (GeV) E 2 (GeV) P 2 (GeV/c) P 1 (GeV/c) data MC Dimuons
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Data – MC comparison x y Q 2 (GeV 2 ) z V z (cm) V y (cm) data MC Dimuons
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Data – MC comparison V x (cm) d 12 (cm) cos 2 12 Invariant mass (GeV) data MC cos 1 Dimuons
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Evaluation of N charm
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Background 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 Dimuons
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Background MonteCarlo: High statistics (10 6 ) fully simulated CC interaction sample to evaluate Dimuons
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Background 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 Dimuons
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Same sign Data-MC comparison E (GeV) E sh (GeV) E 1 (GeV) E 2 (GeV) P 2 (GeV/c) P 1 (GeV/c) data MC Dimuons
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induced opposite sign dimuon events 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 Dimuons
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4 parameters Maximum Likelihood fit Event by event (unbinned) likelihood function in order to extract m c B Probability density given by MonteCarlo as a function of the unknown parameters Dimuons
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ML fit result Correlation coefficients Systematic uncertainties Dimuons
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Dimuon analysis result (preliminary) m c = 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) Dimuons
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Dimuon Analysis Summary Largest sample of neutrino induced dimuons to date Results from LO analysis in agreement with other experiments Slow Rescaling model confirmed Dimuons
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CDHS and HPWF (1978): ~100 events - origin largely unknown CHORUS: ~6x10 6 2 calorimeter triggers observed: 42 , 3 (P > 5 GeV/c) Detailed Monte-Carlo (LEPTO/JETSET/GEANT) 4x10 6 events with full detector simulation present knowledge of production rates and -decays of ’ data-MC validation using 2 events (known origin) data-MC comparison for 3 event sample Trimuon events in CC interactions
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Angle between leading and sum of two others DATA All MC Charm -> + Int. bremsstrahlung Trimuons < 90 o no int. bremsstrahlung
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Trimuons MC 2 validation P and well reproduced Charm -> + decay 8.3 2.8 Internal bremsstrahlung (theoretical) 8.6 4.5 40 main 3 sources MC predictions Observed in experiment: 42 Conclusions – MC predictions on 3 rate are in agreement with measurements
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Z/A dependence of CC cross-section for the first time 4 targets in the same experiment were exposed simultaneously positions rotated to avoid acceptance differences 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 Eur. Phys. J. C30 (2003) 159-167
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Z/A Pb Fe M P Relative total cross sections Predictions are based on GRV98LO PDF and modifications according to A.Bodek-U.K.Yang model Predictions equalized to measurements at marble point ( n)/ ( p) = 1.71
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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
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