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 charm mass and V cd 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) Physics motivation

Experimental techniques –massive high density detectors (CDHS, CCFR, CHARMII, NuTeV, NOMAD, CHORUS Calo): Pro: large statistics Contra: background from , K decays; not sensitive to low- neutrino energies (E <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 –not depending on muonic branching ratio which in turn depends on fragmentation fractions (energy) –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 has just got the final statistics: ~ 2000 charms! Analysis finalized by the end of the year!

CHORUS detector  p/p = 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 = 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 emulsions  350  m  90  m

Automatic emulsion data acquisition (phase-II) Angular acceptance : 400 mrad Track segments from 8 plates overlapped At least 2-segment connected tracks Eliminate passing through tracks Reconstruct full vertex topology Volume : 1.5 x 1.5 mm 2 x 6.3 mm 1 2 Location of interaction vertex guided by electronic detector. Full data taking around interaction vertex called Netscan Offline tracking and vertex reconstruction ~ 11 minutes / event

Selection criteria Emulsions have no time information: at least one among charm daughter particles must be reconstructed by the tracker systems (necessary for D 0 search) Emulsion-electronic tracker matching for the  track as well Tracks with large impact parameter with respect to vertex point  visual inspection for decay confirmation impact parameter vs. vertex depth θ=0.4 rad θ=0. rad Selected events dz = vertex depth parameterize the angular error

Neutrino-induced charm sample Decay topology (prong)Sample Kink461 Vee841 Trident501 4Vee230 C523 6Vee3 Total sample2059 final sample of located interactions with a  -

Fully neutral D 0 decay mode No measurement so far, 5% value by comparison with charged modes Essential to extract the D 0 production cross-section Essential to get the correct muonic branching ratio and hence the inclusive charm production cross-section from dimuon data PDG Ingredients: CHORUS new results New measurements! preliminary assumed to be 5%!!!

Measurement of D 0 production Phys. Lett. B 527 (2002) 173, based on ~25% of statistics 2 prong (V2) 841 (background: 37) 4 prong (V4) 230 (no background) Observed D 0 events NOW: full sample: CC events and D0  fully neutral taken into account 6 prong (V4) 3 (no background)  (D 0 )=0.145  ry location and 2ry detection Preliminary

Measurement of D 0 momentum Use correlation between opening angle of decay daughters and charm momentum to obtain momentum distribution D Momentum Inverse of geometrical mean of opening angle of daughters Momentum distribution of D0 can be measured by unfolding opening angle distribution (curve is the model in the CHORUS MC) Preliminary

Z-distribution Preliminary  Also an E531 measurement  Indirect measurements from dimuon data:  CDHS, CCFR, CHARMII, NuTeV, CHORUS Feynman x distribution Peterson formula Preliminary dotted curve is MC model

Charm fragmentation results Remark: u,d from sea and valenceu from sea incorrect to put all charms together, but difficult to tag separately Large spread in values due to different mixtures of charm final states: E531: all charm decays Nomad: D* CHORUS: D 0 Dimuon experiments: weighted by muonic decay mode

Statistical approach using flight length distribution Λ c DsDs D+D+ Flight length in μm  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 Phys. Lett. B 555 (2003) 156

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

 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.)% -54 Preliminary

a)  n   -  c + b)  n   -  c + (  c *+ ) c)  p   -  c ++ (  c *++ ) Quasi-elastic charm production Require 2 or 3 tracks at primary vertex   165° (angle between muon and charm in the transverse plane) Flight length < 200  m (enriched  c sample) Calorimeter energy < 10 GeV and electromagnetic energy < 2 GeV Topological and kinematical selection criteria: 13 events with a background of 1.7 (mainly from DIS  c) QE production is about 15% of  c production Phys.Lett.B 575 (2003) 198 (based on  CC)

Anti-neutrino studies Charm production mainly from anti-s sea quark  combined analysis with neutrino data can separate valence and sea quark contributions Different production and hadronization mechanisms  no quasi-elastic process and suppressed due to baryon number conservation About 5% contamination in the neutrino beam  limiting factor is still the low statistics Final data sample: 2704 interactions with a  ±2.1% contamination from measured interaction ratio: consistent with a measurement done using interactions in the calorimeter (2.2±0.1%), consistent with beam contamination and the different energy spectrum and cross-section

Anti-neutrino induced charm production Decay topology Candidate events background Vee161.4±0.3 V460.13±0.06 Kink40.8±0.2 Trident40.3±0.2 C520.02±0.01 Total322.7±0.4 background is essentially from charm in neutrinos 0.97±0.15 in neutrinos (suppression of ) 6.0% in neutrinos (higher energy and presence of QE process)

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

Associated charm production in CC In the past, observation of tri-muon events  - (  +  - ) and same-sign di-muons (controversial interpretation) 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 larger statistics is in progress. Four candidates found and the first cross-section estimation reported

 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

Newly found CC event E=36.9 GeV P=-16.9 GeV/c Evis= 53.8 GeV Both neutral decays inconsistent with two-body decay (acoplanarity) P d1 > CL.(TT #2) P d2 > CL. P d2 > CL. P d3 >2.32 CL.(TT #7) P d2 >1.92 CL.(TT #5) P d2 >1.92 CL.(TT #5) Pl31 pl30 Pl31 pl30

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 3 candidates have been found and the preliminary measurement of the cross-section is reported

An event in NC 120µm 210µm PLATE 18 PLATE µm TT Ns = 6 Nh = 1 (gray) pl 17 FL = 884 µm pl 17 FL = 426 µm

Associated charm production cross-section ProcessObserved events Estimated background CC40.79±0.10 NC30.12 ±0.02 preliminary agreement with the theory for the CC process agreement with NuTeV for NC (different energy spectrum) first direct measurement! Background in CC comes from single charm + hadronic “white” interaction Background in NC comes from single charm + hadronic “white” interaction + missed muon

Conclusions and Outlooks 150K events in CHORUS emulsions for Charm analysis 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) (Phys.Lett.B 575 (2003) 198) –QE  c production (Phys.Lett.B 575 (2003) 198) –Anti-neutrino charm production (being submitted to the journal) –D 0 decay  all neutrals (being submitted to the journal) Analyses in progress with preliminary results: –Associated charm production cross-section in CC and NC –Z and x-Feynman distributions –Charm topological branching ratios