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Neutrinos and Charm Production in Physics: Motivation, Results, and Outlook

Explore the motivation, results, and future outlook of charm production in physics with neutrinos. Learn about quark density functions, experimental techniques, and current research findings from the CHORUS Collaboration.

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Neutrinos and Charm Production in Physics: Motivation, Results, and Outlook

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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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