Charm production with neutrinos Physics motivation Results Outlook Giovanni De Lellis University of Naples (on behalf of the CHORUS Collaboration)

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-

measure strange content of the nucleon Possible s/anti-s asymmetry  non-p QCD effects crucial role in relating F 2 structure function for charged- and neutral-lepton strange sea is important for “stop” searches at hadron colliders: largest background: g+s  W+c R.Demina et al., Phys. ReV. D 62 (2000) S.J.Brodsky and B.Ma, Phys. Lett. B 381 (1996) 317 constrain/study charm production models –in NLO pQCD is a challenging theoretical problem »2 scales,  QCD and charm mass (J.Conrad et al. Rev.Mod.Phys. 70 (1998) ) measure charm mass and V cd Physics motivation

Experimental techniques –massive high density detectors (CDHS, CCFR, CHARMII, NuTeV, NOMAD, CHORUS Calo): Pro: large statistics Contra: background from p, K decays; not sensitive to low- neutrino energies (E n <15GeV); not possible to study separately the different charmed types; B  is needed –bubble chamber filled with heavy liquid (BEBC, Fermilab 15-ft) –nuclear emulsions (E531, CHORUS)

Emulsion experiments Look “directly” at the decay topology of the charmed hadron with sub-micron resolution Contra: the anti- statistics is still poor Pro: –low background; sensitivity to low E –  m c threshold effect –hadron species identification –reconstruction of charmed hadron kinematics –  fragmentation studies 100  m

Inclusive charm production cross-section induced by Inclusive charm-production cross-section measurement possible only with nuclear emulsions So far only E531: 122 events CHORUS is currently analysing about 1000 events Final statistics (~1year from now) about events!

 p/p = p (GeV/c)  0.22   p/p = 10  15% (p < 70 GeV/c) -nuclear emulsion target (770kg) -scintillating fiber tracker CHORUS detector  E/E = 32 %/  E (hadrons) = 14 %/  E (electrons)  h = GeV E ~ 27 GeV Air-core magnet Active target muon spectrometer Calorimeter Neutrino beam :: :   :  : e : e : : : 1.00 : 0.05 : : 0.007

0  m -21  m -36  m -54  m MIP: 30  40 grains/100  m Resolution ~ 0.3  m Focal depth: 1 to 3  m S. Aoki et., Nucl. Instr. Meth. A 447 (2000) 361 CHORUS emulsion  350  m  90  m

8 plates 1.5 mm All tracks (θ<400mrad) in the scanning volume (1.5X1.5X6.3mm 3 ) are recorded at 11 min./event scanning speed CHORUS Phase II

All track segments (  < 0.4 rad)All track segments (  < 0.4 rad) Fiducial volume: 1.5 x 1.5 mm 2 x 8 platesFiducial volume: 1.5 x 1.5 mm 2 x 8 plates Offline analysis of emulsion dataOffline analysis of emulsion data Track segments from 8 plates overlapped At least 2-segment connected tracks Eliminate passing- through tracks Reconstruct full vertex topology Emulsion data acquisition

Selection criteria At least one among daughter particle and muon tracks formed by at least 2 segments and reconstructed by the fiber tracker systems Tracks with big impact parameter with respect to vertex point  visual inspection for decay confirmation impact parameter vs. vertex depth dz = vertex depth parameterize the angular error θ=0.4 rad θ=0. rad Selected events

 N  D s *  - N’ D s +   +   +   Diffractive D s production Phys. Lett. B 435 (1998) 458, CHORUS Coll.

D 0 production rate D 0  V4 / D 0  V2 =  ,693  CC analyzed (~15% of the full statistics) 25,693  CC analyzed (~15% of the full statistics) 851 (3.3%) selected events for visual inspection851 (3.3%) selected events for visual inspection Confirmed D 0 sample: 226 V2, 57 V4Confirmed D 0 sample: 226 V2, 57 V4 σ(D0)/σ(CC) E (GeV) Phys. Lett. B 527 (2002) 173, CHORUS Coll. J.Phys.G28 (2002) 713 (all channels): all existing data are combined σ(D 0 )/σ(CC) = 2.58  0.26(stat.)  0.13(syst.) % E531 CHORUS σ (D 0 )/σ (CC)x Br(D 0  V2+V4 ) = 1.99  0.13 (stat.)  0.17 (syst.)%

Statistical approach using flight length distribution Λ c DsDs D+D+ Flight length in μm Λ c production rate  (A) Short flight decay: selection A (40 mm < FL <400 mm): Λ c enriched sample 128 candidates out of 50,414 CC Long flight decay: selection B (400 mm < FL < 2400 mm): D +, D s dominated sample 210 candidates out of 56,761 CC  (B)(B) parent particle track

Evidence for  c production: 3-prong decays (background free) MC: D and Ds Data Background check: Pt distribution for 1-prong decays b.g. excess Data Monte Carlo Data

 c production rate Combining short (A) and long (B: only 3-prong) decay searches and correcting for efficiencies and background: 3 equations and 3 unknowns D+Ds = 1118  116(stat)D+Ds = 1118  116(stat)  c = 861  198 (stat.)  98 (syst.) +140 (QE)  c = 861  198 (stat.)  98 (syst.) +140 (QE) Br(  c  3prong) = 24  7 (stat.)  4 (syst.)%Br(  c  3prong) = 24  7 (stat.)  4 (syst.)% Phys. Lett. B 555 (2003) 156 σ(D+Ds)/σ (CC) = 2.00  0.21(stat)% by product σ (  c) / σ (CC)= 1.54  0.35(stat)  0.18 (syst)% -54

a)  n   -  c + b)  n   -  c + (  c *+ ) c)  p   -  c ++ (  c *++ ) Quasi-elastic charm production QE charm production has a peculiar topology “pure”  c sample with a small (<10%) contamination i.e. normalization error  absolute BR determination P. Migliozzi et al. Phys. Lett. B 462 (1999) Many candidates have been found in CHORUS and the cross-section measurement is in progress

Associated charm production D+D+X c c W c c D+D+X Z CC Gluon BremsstrahlungZ-Gluon Fusion NC

Associated charm production in CC In the past this search was based on the observation of tri-muon events  - (  +  - ) and same-sign di-muons: Large background from  and K decays Observed rate 60 times larger than expected from theoretical calculations! (K.Hagiwara Nucl.Phys.B 173 (1980) 487) Currently a search is in progress in CHORUS 1 event observed and confirmed by kinematical analysis (Phys. Lett B 539 (2002) 188, CHORUS coll.) (Phys. Lett B 539 (2002) 188, CHORUS coll.) A new analysis with a larger statistics is in progress. The discrepancy between data and theoretical predictions will be clarified soon.

 m 6735  m transverse plane -- D0D0 kink parent N s = 2 N h = 6  kink = 420 mrad D 0 f.l. = 340  m f.l. = 1010  m 22 = 310 mrad f.l. = 7560  m 2ry vertex p  MeV/c dE/dx proton P = 0.78 GeV/c P > 330 MeV/c st vertex Phys. Lett B 539 (2002) 188, CHORUS Coll. First observation in CC Phys. Lett B 539 (2002) 188, CHORUS Coll. B.G. = 0.04±0.01

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

Ns=1, Nh=3 23  =96.3 mrad fl= 62.8  m 22 fl=  m  =203.4 mrad TT #6 TT #3 TT #8 TT #5 pl23 pl22 Event V2&V2 in 0mu V2&V2 in 0mu

120µm 210µm PLATE 18 PLATE µm TT Event Ns = 6 Nh = 1 (gray) pl 17 FL = 884 µm pl 17 FL = 426 µm

200K events in CHORUS for Charm analysis From a sub-sample of data CHORUS has measured: –Diffractive D s * production (Phys. Lett. B 435 (1998) 458) –σ (D 0 )/σ(CC) (Phys. Lett B 527 (2002) 173) –CC associated charm production (Phys.Lett. B 539 (2002) 188) –B   (Phys. Lett B 548 (2002) 48): first direct measurement –σ(  c )/σ(CC) (Phys.Lett.B 555 (2003)156) Conclusions and Outlooks Analyses in progress: –Associated charm production in CC and NC –D* production –D 0 decay  all neutrals –Charm topological branching ratio –Anti-neutrino charm production –QE  c production