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Charm production with neutrinos

Charm production with neutrinos. Giovanni De Lellis University of Naples. Physics motivation Results Outlook. (on behalf of the CHORUS Collaboration). . Beam knowledge.  -.  . . |V cd | 2 ,|V cs | 2. Charm fragmentation f D0 ; f D+ ; f Ds ; f  c z = p D /p c , p T 2. ,h.

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Charm production with neutrinos

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

  2. Beam knowledge -   |Vcd|2,|Vcs|2 Charm fragmentation fD0; fD+; fDs; fc z = pD/pc, pT2 ,h d,s c h Ehad n DIS charm production Quark density functions, strange sea () Production from d(anti-d) quarks Cabibbo suppressed  large s contribution:50% in n and 90% in anti-n

  3. Physics motivation • measure strange content of the nucleon • Possible s/anti-s asymmetry  non-p QCD effects • crucial role in relating F2 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) 035011 S.J.Brodsky and B.Ma, Phys. Lett. B 381 (1996) 317 • constrain/study charm production models • in NLO pQCDis a challenging theoretical problem • 2 scales, LQCD and charm mass (J.Conrad et al. Rev.Mod.Phys. 70 (1998) 1341-1392) • measure charm mass and Vcd

  4. 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 (En<15GeV); not possible to study separately the different charmed types; Bm is needed • bubble chamber filled with heavy liquid (BEBC, Fermilab 15-ft) • nuclear emulsions (E531, CHORUS)

  5. Emulsion experiments • Look “directly” at the decay topology of the charmed hadron with sub-micron resolution • Contra: the anti-n statistics is still poor • Pro: • low background; sensitivity to low En •  mc threshold effect • hadron species identification • reconstruction of charmed hadron kinematics •  fragmentation studies 100 mm

  6. Inclusive charm-production cross-section measurement possible only with nuclear emulsions So far only E531: 122 events Inclusive charm production cross-section induced by n CHORUS is currently analysing about 1000 events Final statistics (~1year from now) about 3000-4000 events!

  7. CHORUS detector Active target p/p = 0.035 p(GeV/c)  0.22 Air-core magnet -nuclear emulsion target (770kg) -scintillating fiber tracker  p/p= 10 15% (p < 70 GeV/c) muon spectrometer En~ 27 GeV Neutrino beam Calorimeter E/E = 32 %/ E (hadrons) = 14 %/  E (electrons) h = 60 mrad @ 10 GeV nm :nm : ne : ne 1.00 : 0.05 : 0.017 : 0.007

  8. 350 m 90 m -54 mm -36 mm -21 mm 0 mm CHORUS emulsion 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

  9. CHORUS Phase II scanning speed 1.5 mm 1.5 mm 8 plates All tracks (θ<400mrad) in the scanning volume (1.5X1.5X6.3mm3) are recorded at11 min./event

  10. Emulsion data acquisition • All track segments (q < 0.4 rad) • Fiducial volume: 1.5 x 1.5 mm2 x 8 plates • Offline analysis of emulsion data Reconstruct full vertex topology At least 2-segment connected tracks Track segments from 8 plates overlapped Eliminate passing-through tracks

  11. 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 θ=0.4 rad Selected events θ=0. rad dz = vertex depth parameterize the angular error

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

  13. D0 production rate Phys. Lett. B 527 (2002) 173, CHORUS Coll. • 25,693 nm CC analyzed (~15% of the full statistics) • 851 (3.3%) selected events for visual inspection • Confirmed D0 sample: 226V2, 57V4 σ(D0)/σ(CC) E531 D0 V4 / D0 V2 = 0.231  0.04 σ(D0 )/σ (CC)x Br(D0V2+V4 ) = 1.99  0.13 (stat.)  0.17 (syst.)% CHORUS J.Phys.G28 (2002) 713 (all channels): all existing data are combined σ(D0)/σ(CC) = 2.580.26(stat.)0.13(syst.) % En (GeV)

  14. (A) Λ c m (B) D+ Ds Flight length inμm m Λc production rate Statistical approach using flight length distribution • Short flight decay: selection A • (40 mm < FL <400 mm): • Λ c enriched sample • 128 candidatesout of 50,414 CC • Long flight decay: selection B • (400 mm < FL < 2400 mm): • D+, Ds dominated sample • 210 candidates out of 56,761 CC parent particle track

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

  16. Lc 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) • Lc = 861  198 (stat.) 98 (syst.)+140 (QE) • Br(Lc 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(Lc) / σ (CC)= 1.54  0.35(stat)  0.18 (syst)% -54

  17. Quasi-elastic charm production a)  n  -c+ b)  n  -c+ (c*+) c)  p  -c++(c*++) QE charm production has a peculiar topology “pure” Lc sample with a small (<10%) contamination i.e. normalization error  absolute BR determination P. Migliozzi et al. Phys. Lett. B 462 (1999) 217-224 Many candidates have been found in CHORUS and the cross-section measurement is in progress

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

  19. Associated charm production in CC • In the past this search was based on the observation of tri-muon events m-(m+m-) and same-sign di-muons: • 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) • Currently a search is in progress in CHORUS • 1 event observed and confirmed by kinematical analysis (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.

  20. > 330 MeV/c First observation in CC Phys. Lett B 539 (2002) 188, CHORUS Coll. 30 29 21 Ns = 2 Nh = 6 n B.G. = 0.04±0.01 6735 mm 1010 mm D0f.l. = 340 mm 1st vertex 2ry vertex kink parent q2 qkink = 420 mrad = 310 mrad D0 f.l. = 7560 mm f.l. = 1010 mm m- P = 0.78 GeV/c pb = 500 MeV/c +180 - 110 P transverse plane dE/dx proton

  21. 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 1.3+3.1-1.1 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 • mc=(1.40+0.83-0.36 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.

  22. Event 81332312 V2&V2 in 0mu 1ry@pl23 Ns=1, Nh=3 V2(1) @pl 23 Dq =96.3 mrad fl= 62.8mm V2(2) @pl 22 fl= 976.6mm Dq =203.4 mrad TT #5 TT #8 TT #3 TT #6 pl23 pl22

  23. PLATE 18 PLATE 17 TT TT TT 210µm 140µm 120µm Event 77393952 Ns = 6 Nh = 1 (gray) 4Vee @ pl 17 FL = 884 µm C3 @ pl 17 FL = 426 µm

  24. Conclusions and Outlooks • 200K events in CHORUS for Charm analysis • From a sub-sample of data CHORUS has measured: • Diffractive Ds* production(Phys. Lett. B 435 (1998) 458) • σ(D0)/σ(CC) (Phys. Lett B 527 (2002) 173) • CC associated charm production (Phys.Lett. B 539 (2002) 188) • Bm(Phys. Lett B 548 (2002) 48): first direct measurement • σ(Lc)/σ(CC) (Phys.Lett.B 555 (2003)156) • Analyses in progress: • Associated charm production in CC and NC • D* production • D0 decay all neutrals • Charm topological branching ratio • Anti-neutrino charm production • QE Lc production

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