DIS 2004 Strbske Pleso 14 4 2004 Neutrino

DIS 2004 Strbske Pleso 14 -4 -2004 Neutrino DIS measurements in CHORUS Alfredo G. Cocco INFN – Napoli

CHORUS detector Active target -nuclear emulsion target (770 kg) -scintillating fiber tracker WB Neutrino beam : e p/p = 0. 035 p (Ge. V/c) 0. 22 muon spectrometer ~ 27 Ge. V : Air-core magnet : e 1. 00 : 0. 06 : 0. 017 : 0. 007 Calorimeter E/E = 32 %/ E (hadrons) = 14 %/ E (electrons) h = 60 mrad @ 10 Ge. V p/p = 10 – 15% (p < 70 Ge. V/c)

Neutrino targets Emulsion (1 m precision decay topology) ET 770 kg, 4 X 0 2 x 106 CC ν interactions, 1994 -1997 Calorimeter CT 112 ton, lead-scint. fiber, 5. 2 1. 5 x 107 CC ν interactions, 1994 -1998 Special 4 targets • 100 x 4 kg, marble, plastic, Fe, Pb • ~106 CC ν interactions, 1998 4 T

Non-oscillation physics in CHORUS Charm (ET) Structure functions J/Ψ NC production Dimuons Trimuons Z/A dependence of CC cross-section (CT) (4 T) D 0 , Λc, QE charm production cc CC/NC production BR , fragmentation functions anti-neutrino charm production total charm production cross section

Dimuons analysis To extract: mc (fragmentation) B (charm into decay fraction)

Data selection

Dimuons Data sample Data taken from 1995 to 1998 with a dedicated trigger setup 6. 6 106 triggers At least 2 reconstructed muons 5 105 events

Dimuons Selection criteria 5 Esh 200 Ge. V ngap 1 5 ngap 2 5 E 1 5 Ge. V E 2 5 Ge. V d 12 15 cm q 2 4 Ge. V 2 Vy, z 120 cm 20 E 200 Ge. V 295 cm Vx 394 cm xbj 1. 0 ybj 1. 0

Dimuons 2 selected : N = 2801 N += 13132 N+ = 1224 N++= 70 The leading muon is that one with the highest PT (96 % efficiency) 2 nd muon Final sample Leading muon

Dimuons MCDIS generator

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

MCDIS Dimuons Leading Order cross section Aivazis et al. (1994) F = helicity structure functions (mt mc VCKM pdf( )) = Lorentz boost between lepton and hardon configurations

MCDIS Dimuons Leading Order cross section For charm neutrino production and neglecting initial quark mass Where in the limit of M 2/Q 2 0 is the “slow rescaling” variable

MCDIS Dimuons Fragmentation function Peterson parametrization = 0. 05 Z=P(hc)/Pmax(hc) z

Dimuons MCDIS Transverse momentum PT N = 1. 1 hc W+ PT 2

MCDIS Parton Distribution Functions Used: GRV 94 LO and CTEQ 3 L Strangeness parametrization: = 1 for a flavour SU(3) symmetric sea Dimuons

Data – MC comparison E (Ge. V) Dimuons Esh (Ge. V) data MC E 1 (Ge. V) E 2 (Ge. V) P 1 (Ge. V/c) P 2 (Ge. V/c)

Data – MC comparison x y Q 2 (Ge. V 2) z Vy(cm) Vz(cm) Dimuons data MC

Data – MC comparison Vx(cm) cos 1 Invariant mass (Ge. V) d 12(cm) cos 2 12 Dimuons data MC

Evaluation of Ncharm

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 Monte. Carlo Selection efficiencies and neutrino-antineutrino cross contamination also to be taken into account

Dimuons Background Monte. Carlo: High statistics (106) fully simulated CC interaction sample to evaluate

Dimuons 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

Same sign Data-MC comparison Dimuons data MC E (Ge. V) Esh (Ge. V) E 1 (Ge. V) E 2 (Ge. V) P 1 (Ge. V/c) P 2 (Ge. V/c)

Dimuons induced opposite sign dimuon events neutrino CDHS 9922 antineutrino 2123 CHORUS 10718 288 420 63 NOMAD 2714 227 115 40 CHARM II 3100 700 CCFR 5030 1060 NUTEV 5102 1458

4 parameters Maximum Likelihood fit Dimuons Event by event (unbinned) likelihood function in order to extract mc B Probability density given by Monte. Carlo as a function of the unknown parameters

ML fit result Dimuons Correlation coefficients Systematic uncertainties

Dimuon analysis result (preliminary) mc B = = 1. 46 0. 15 (stat) 0. 10 (syst) 0. 56 0. 05 (stat) 0. 045 (syst) 0. 040 0. 003 (stat) 0. 015 (syst) 0. 098 0. 005(stat) 0. 014 (syst) Dimuons

Dimuons Dimuon Analysis Summary Largest sample of neutrino induced dimuons to date Results from LO analysis in agreement with other experiments Slow Rescaling model confirmed

Trimuon events in CC interactions CDHS and HPWF (1978): ~100 + events - origin largely unknown CHORUS: ~6 x 106 2 calorimeter triggers observed: 42 +, 3 + + (P > 5 Ge. V/c) Detailed Monte-Carlo (LEPTO/JETSET/GEANT) 4 x 106 events with full detector simulation present knowledge of production rates and -decays of h, r, w, h’, f data-MC validation using 2 events (known origin) data-MC comparison for 3 event sample

Trimuons DATA All MC Charm-> + / Int. bremsstrahlung Angle between leading and sum of two others j< 90 o no int. bremsstrahlung

Trimuons MC 2 validation P and well reproduced main 3 sources MC predictions Charm-> + / decay Internal bremsstrahlung (theoretical) Conclusions – MC predictions on 3 rate are in agreement with measurements 8. 3 2. 8 8. 6 4. 5 40 Observed in experiment: 42 +

Z/A dependence of CC cross-section Eur. Phys. J. C 30 (2003) 159 -167 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

Relative total cross sections ( n)/ ( p) = 1. 71 Pb Fe M P Predictions are based on GRV 98 LO PDF and modifications according to A. Bodek-U. K. Yang model Predictions equalized to measurements at marble point Z/A

Z/A Comparison with previous experiments Conclusions: the result is in agreement with previous experiments and with predictions obtained by parton model calculations

Many analyses are still in progress NEW RESULTS WILL BE AVAILABLE WITHIN 2004