Measurement of charm production and decay properties by CHORUS Francesco Di Capua University of Napoli and INFN Italy GRAVITY, ASTROPHYSICS AND STRINGS AT THE BLACK SEA kiten – Bulgaria June 2005

Outline The CHORUS experiment The CHORUS detector Automatic analysis of nuclear emulsions Physics motivation What do we measure and why it is interesting Results on charm analysis D 0 production in neutrino charged current interaction D *+ production in neutrino charged current interaction Fragmentation properties of charmed particles Anti-neutrino charm production Muonic branching ratio B  of charmed particles (preliminary results) Associated charm production (CC and NC) Dimuon analysis in the calorimeter Conclusions and perspectives

c |V cd | 2,|V cs | 2 d,s ----  Beam knowledge Quark density functions, strange sea (  ) ,h E had h Charm fragmentation f D0 ; f D+ ; f Ds ; f  c z = p D /p c, p T 2 DIS charm production Production from d(anti-d) quarks Cabibbo suppressed  large s contribution:  50% in and  90% in anti-

Physics motivation Measure strange content of the nucleon Possible strange/anti-strange asymmetry  non-p QCD effects Crucial role in relating charged-lepton and neutrino F 2 structure function Knowledge of the strange sea is important to search for stop at hadron colliders (largest background: g+s  W+c ) Constrain/study charm production models in NLO pQCD is a challenging theoretical problem R.Demina et al., Phys. ReV. D 62 (2000) S.J.Brodsky and B.Ma, Phys. Lett. B 381 (1996) 317  2 scales,  QCD and charm mass (J.Conrad et al. Rev.Mod.Phys. 70 (1998) ) Measure charm mass and V cd “Charm Physics with neutrinos”, G.De Lellis, P.Migliozzi, P.Santorelli, Phys. Rept.399: ,2004

Dimuon available statistics CDHS (CERN WBB) CCFR (NuTeV) CHARMII (CERN WANF) Zeitschr. Phys. C (1982) Zeitschr. Phys. C (1995) Eur. Phys. J., C11 (1999) NOMAD (CERN WANF) Phys.Lett.B486:35-48,  -  +, 2123  +  - events 5044  -  +, 1062  +  - events 4111  -  +, 871  +  - events 2714  -  +, 115  +  - events Background due to , K, K o s Cross section measurement depends on knowledge of BR (C   ) ~ 10% and on the uncertainty on it High statistics, but: CHORUS (CERN WANF) 8919  -  +, 430  +  - events To be published

Emulsion experiments These experiments study charm production by looking “directly” at the decay topology of the charmed hadron with micrometric resolution  Contra: till few years ago the charm statistics was limited by the scanning power (but this is not the case anymore) ; the anti- statistics is very poor  Pro: low background; sensitivity to low E  m c thr. effect; reconstruction of the charmed hadron kinematics (direction and momentum)  fragmentation studies are possible

 p/p = p (GeV/c)  0.22  p/p = 10 – 15% (p < 70 GeV/c) (with lead and scintillating fibers, 112 ton )  E/E = 32 %/  E (hadrons) = 14 %/  E (electrons)  h = GeV E ~ 27 GeV Air-core magnet Active target Muon  spectrometer Calorimeter WB Neutrino beam :: :   :  : e : e ::: 1.00 : 0.06 : : nuclear emulsion target (770kg) scintillating fiber trackers CHORUS experiment CHORUS experiment (CERN Hybrid Oscillation Research ApparatUS)

Calorimeter Air-core magnet beam Muon spectrometer  Emulsion target Interaction vertex Electronic detector prediction

All track segments in fiducial volume After a low momentum tracks rejection (P > 100 MeV) and number of segments  2 After rejection of passing-through tracks Tracks confirmed by electronic detectors Nuclear emulsion analysis

~ 100  m Visual inspection to confirm the event

The CHORUS charged current data sample and charm subsample Located CC events Selected for visual inspection 2752 C1452 C3491 C522 V2819 V4226 V63 Total charm candidates2013

Measurement of D 0 production and of decay branching fractions in -N scattering Phys. Lett. B. 613 (2005) 105 Candidate selection Primary track matched to el. detector muon Daughter track matched to el. detector track 3~13  m < I.P. wrt. 1ry vtx < 400  m After BG subtraction and efficiency correction: = ± ± B(D 0  V4) B(D 0  V2) The relative rate is:  (D 0 )/  (CC)= ± ± Assuming B(D 0  V4)=0.1339± (PDG);

D 0 topological branching fractions INCLUSIVE measurement in CHORUS: B(D 0  V2) = ± ± B(D 0  V6) = (1.2 ± 0.2)x B(D 0  V2) B(D 0  V4) B(D 0  V0)=1- B(D 0  V4)[1+ + ] B(D 0  V6) B(D 0  V4) B(D 0  V0) = 0.218±0.049±0.036 very important for B  measurement!!! B(D 0  V0)  5% (PDG) Sum over all exclusive channel for which measurement exist B(D 0  V2) = ± (PDG) Sum over all exclusive channel for which measurement exist B(D 0  V6) = (0.59 ± 0.12)x10 -3 (FOCUS coll.) sum of all exclusive measured channel To be compared with:

Energy dependence of the cross section ratio and charm mass CHORUS data E531 data Fit to a theoretical model m c =(1.42  0.08 (stat)  0.04 (syst) ) GeV/c 2 Fit parameters for the model curve (M.Gluk,E.Reya and A.Vogt, Z.Phys.C (1955) 433) (  s p as measured in CHORUS, see next slides)

Accepted by Phys. Lett. B. - CERN-PH-EP Looking for events in the channel: D *+  D 0  +  D 0 fl>100  m     <60 mrad 0.4 <p(  + )<4 GeV/c 10.< p T <50. MeV/c Number of candidates Background prediction (1)Expected shape of the candidates normalized to the observed events; (2-3-4) shape normalized to the total number of D 0 and C + respectively; D *+ signal in the D 0 h + sample No signal in the D 0 h - sample as expected No signal in the C + h - sample as expected No signal in the C + h + sample as expected  D0D0  D *+ Measurement of D *+ production in CC -N scattering

Assuming B(D *+  D 0  + ) =0.677±0.005 (PDG) the relative rate is:  (D *+ )/  (D 0 )=0.38 ± 0.09 (stat) ± 0.05 (syst) assuming that the D *+ and D *0 production rate are equal and recalling that D *0 always decays into D 0 :  (D *  D 0 )/  (D 0 )=0.63 ± 0.17 By using the measure of  (D 0 )/  (CC) made in CHORUS:  (D *+ )/  (CC)=(1.02 ± 0.25 (stat) ± 0.15 (syst) )% To be compared with: At similar neutrino energy beam: NOMAD  (D *+ )/  (CC)=(0.79 ± 0.17 (stat) ± 0.10 (syst) )% BEBC  (D *+ )/  (CC)=(1.22 ± 0.25)% At the higher energy of the Tevatron beam:  (D *+ )/  (CC)=(5.6 ± 1.8)% Defining f V =V/(P+V), V= vector production and P pseudoscalar production of D meson f V =0.51 ± 0.18 Consistent within the error: with V:P=3:1, as expected from simple spin arguments; with measurements in e + e -,  N,  N experiments.

CHORUS data Prediction simulation The momentum of D 0 can be inferred by the geometrical average ( ) of the angle of the decay daughters with respect to the direction of the D 0 (as described in S.Petrera, G.Romano, Nucl.Instrum. And Meth.174 (1980) 61 ) Measurement of fragmentation properties of charmed particle production in CC neutrino interaction Phys. Lett. B 604 (2004) 145 Momentum distribution of D 0 ’s produced inclusively in CHORUS

From charm quark to charmed hadrons Defined z as the ratio of the energy of the charmed particle E D and the energy transfer to the hadronic system  z  E D /  we measure = 0.63 ± 0.03 (stat) ± 0.01 (syst) Collins-Spiller J.Phys. G 11 (1985) 1289 Peterson et al. Phys.Rev. D 27 (1983) 105

Z distribution CHORUS data Peterson Collins-Spiller Fit to Collins-Spiller distribution:  cs = 0.21 ± Fit to Peterson distribution:  P = ± ± To be compared with: To compare results: If z s = E D / string energy  S P = ± ± If z Q = P charmed particle / P charm quark  Q P = ± ± 0.008

Fragmentation properties X F is defined as: X F = 2  p L D –  E D W p L D longitudinal momentum of D 0 E D energy of D 0 W invariant mass From the distribution we mesure : =0.38 ± 0.04 (stat) ± 0.03 (syst) To be compared with NOMAD: = 0.47 ± 0.05 forward-backward asymmetry: =0.79 ± 0.14 (stat) ± 0.05 (syst) To be compared with E531: = ± From the distribution production angle out of the lepton plane we mesure: =0.030 ± 0.002

Analysis based on the full statistics B  muonic branching ratio of charmed particles Preliminary B  = (7.3  0.8 (stat) )% The results takes into account the new CHORUS measurement of B(D 0  V0)  22% B  = (8.3  1.6 (stat) )% Considering only events with visible energy above 30 GeV B  x |V cd | 2 LO =(0.474  )x10 -2 (CDHS,CHARM II, CCFR average value) |V cd | LO =(0.239  0.046) B  x |V cd | 2 NLO =(0.534  )x10 -2 (CCFR) |V cd | NLO =(0.254  0.066) To be compared with: 0.221< |V cd |<0.227 at 90% CL Obtained imposing CKM unitarity and only 3 generations

Phys. Lett. B. 604 (2004) Measurement of charm production in antineutrino charged-current interactions Strategy: look for the  + generated in the antienutrino CC interaction After  reconstruction cut and charm topology selection TOT 32  (  N   + cX)  (  N   + X) = 5.0 ±0.7% Theoretical prediction obtained from leading order calculation with m c =1.31 GeV/c 2 Derived from di-lepton data ( G.de Lellis et al., J.Phys.G28 (2002), 713 ) CHORUS DATA

Associated charm production in CC Charged-current Gluon bremsstrahlung Currently a search is in progress in CHORUS: 1 event observed and confirmed by kinematical analysis (Phys. Lett. B. 539 (2002) 188) A new analysis with full statistics is in progress (5 events on CC); The discrepancy between data and prediction should be clarified soon. In the past this search was based on the observation of trimuon events  - (  +  - ) and same-sign dimuons; Large background from p and K decays Observed rate 60 times larger than expected from theoretical calculations! (K.Hagiwara Nucl.Phys.B 173 (1980) 487

Event Event E=35.4 GeV P=-13.5 GeV/c Pl 7 Pl 6pl 4 Pl 7 Pl 6pl 4 Evis=48.9 GeV Associated charm production in CC Ns=6, Nh=1 6 fl=  m 4 fl=  m  = 67.4mra d

Associated charm production in NC Neutral-current Z-gluon fusion In the past only one event observed in the E531 emulsion: Currently a search is in progress in CHORUS: 3 candidates on NC have been found and the cross-section measurement will be finalised by the end of this year Production rate 1.3 x normalised to CC Indirect search performed by NuTeV: Production rate (2.6±1.6)x10 -3 normalised to CC at 154 GeV m c = (1.40 ±0.26) GeV, in agreement with other measurements (A. Alton et al., Phys. Rev. D64 (2001) 539) Gluon bremsstrahlung +

Associated charm production in NC

Chorus dimuon analysis result (calo)  m c = 1.26  0.16 (stat)  0.09 (syst)   = 0.33  0.05 (stat)  0.05 (syst)   P =  (stat)  (syst)  B  =  0.004(stat)  (syst) N leading  - =8910  180 N leading  + = 430  60

Chorus dimuon analysis result (calo) MC prediction obtained using fitted values of parameters m c, k,  P, B  dimuon cross-section relative to CC events data

Conclusion Interesting charm physics results from CHORUS thanks to: high beam flux; Nuclear emulsion target (0.8t); Automatic emulsion analysis D *+ production D 0 production Antineutrino charm production Fragmentation properties QE charm production Λ c production BR   CC associate charm production D 0 production Diffractive D s * production Accepted by Phys. Lett. B. Phys. Lett. B. 613 (2005) 105 Phys. Lett. B. 604 (2004) 11 Phys. Lett. B. 604 (2004) 145 Phys. Lett. B. 575 (2003) 198 Phys. Lett. B. 555 (2003) 156 Phys. Lett. B. 549 (2002) 48 Phys. Lett. B. 539 (2002) 188 Phys. Lett. B. 527 (2002) 173 Phys. Lett. B. 435 (1998) 458 Other analyses in progress Measured so far:

Backup slides

Charmed fractions f h can only be measured in emulsions! Present results based on the 122 E531 events and a reanalysis discussed in T. Bolton hep-ex/ Analysis in progress of the CHORUS data:  2000 events Results should be available in a couple of months

Fragmentation functions The z distribution can be parametrized as follows Collins-Spiller J.Phys. G 11 (1985) 1289 Peterson et al. Phys.Rev. D 27 (1983) 105

NOMAD Fit to z distribution Direct measurements E531, NOMAD, CHORUS-Emul in progress z distribution is extracted for charmed hadrons and fitted  Indirect measurements  CDHS, CCFR, CHARMII, NuTeV, CHORUS-Calo in progress  p or  c (depends on the choice) is one of the free parameters of the fit to the dimuon data, see later

The strange sea distribution No new results Both at LO and NLO  ~0.5 At LO  is not zero  =2.5  0.7, while it is at NLO  =  ’ =-0.46  0.42  0.36  0.65  0.17 The momentum distributions of s and anti-s are consistent and the difference in the two distributions is limited to –1.9<  <1.0 at 90% C.L. In the near future: NuTeV NLO analysis will be available; CHORUS-Calo and NOMAD-FCAL LO analyses will be available, too

Relevant parameters of the fit to dimuon data Input parameters Charmed fractions and decay model constrained by other experiments V cs    BR(C   ) Output parameters Charm mass: m c Element of the CKM matrix: V cd Fragmentation parameter:  Two parameters for each mode ( and anti- ) that describe the magnitude and the shape of the s and anti-s PDFs  =2S/(U+D) is the proportion of s-quarks to non strange quarks in the nucleon sea x(1-x)  is the shape of the s-quark PDF

V cd determination At LO order several experiments extracted At NLO only CCFR analysis As expected LO and NLO give consistent results! Previous estimates

m c determination At LO order several experiments extracted the charm-quark mass At NLO only CCFR analysis includes also kinematic effects associated with heavy quark productions  g fusion E691 Phys. ReV. Lett. 65 (1990) 2503

 determination At LO order several experiments extracted  At NLO only CCFR analysis LO and NLO give consistent results at 1.2  A fit to all available data (  N,eN, N) gives Barone,Pascaud,Zomer E.Phys.J.C 12, 243

V ud V ud 0.1 % 0.1 % nuclear beta decay The CKM matrix V cb V cb 5 % 5 % B e3 decay V cs V cs 15 % 15 % D e3 decay V ub V ub 25 % 25 % b  u l V us V us 1 % 1 % K e3 decay V cd V cd 7 % 7 % charm production V td V td V ts V ts V tb V tb 30 % 30 % t  b l Review of particle physics, 98 edition d’ s’ b’ d s b =