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Study of charm physics in neutrino scattering

Study of charm physics in neutrino scattering. Di Capua Francesco University of Napoli, Italy Heavy Quarks and Leptons 2004 San Juan, Puerto Rico. Outline. Physics motivation. What do we measure and why it is interesting. The CHORUS experiment. The CHORUS detector

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Study of charm physics in neutrino scattering

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  1. Study of charm physics in neutrino scattering Di Capua Francesco University of Napoli, Italy Heavy Quarks and Leptons 2004 San Juan, Puerto Rico

  2. Outline Physics motivation • What do we measure and why it is interesting The CHORUS experiment • The CHORUS detector • Automatic acquisition of nuclear emulsions Results on charm analysis • Measurement of c, D0 and quasi-elastic charm production • Semi-leptonic branching ratio B • Associated charm production (CC and NC) • Anti-neutrino charm production Conclusions and perspectives

  3. A short theoretical introduction

  4. Beam knowledge -   |Vcd|2,|Vcs|2 ,h Charm fragmentation fD0; fD+; fDs; fc z = pD/pc, pT2 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

  5. 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 F2 structure function • Knowledge of the strange sea is important to search for stop • 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 pQCD is 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

  6. Dimuon available statistics CDHS (CERN WBB) 9922 -+ , 2123 +- events Zeitschr. Phys. C (1982) 19-31 CCFR (NuTeV) 5044 -+ , 1062 +- events Zeitschr. Phys. C (1995) 189-198 CHARMII (CERN WANF) 4111 -+ , 871 +- events Eur. Phys. J., C11 (1999) 19-34 NOMAD (CERN WANF) 2714 -+ , 115 +- events Phys.Lett.B486:35-48,2000 High statistics, but: Background due to p, K, Kos Cross section measurement depends on knowledge of BR (C  m) ~ 10% and on the uncertainty on it

  7. 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-n statistics is very poor • Pro: low background; sensitivity to low Enmc thr. effect; reconstruction of the charmed hadron kinematics (direction and momentum) fragmentation studies are possible

  8. nm :nm : ne : ne 1.00 :0.06 : 0.017 : 0.007 CHORUS experiment(CERN Hybrid Oscillation Research ApparatUS) Active target Air-core magnet • nuclear emulsion target (770kg) • scintillating fiber trackers p/p = 0.035 p(GeV/c)  0.22  Muonspectrometer p/p= 10 – 15% (p < 70 GeV/c) E ~ 27 GeV Calorimeter WB Neutrino beam (with lead and scintillating fibers, 112 ton ) E/E = 32 %/ E (hadrons) = 14 %/ E (electrons)  h = 60 mrad @ 10 GeV

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

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

  11. Visual inspection to confirm the event ~ 100 m

  12. Charm production by  interactions in emulsions 122 charm events in emulsion only measurement of D0 : D+ : Ds+ : c+ (no anti-neutrino charm events) B(c) crucial for other experiments E531 (Fermilab, Nagoya) Phys. Lett. B 206 (1988) 375-379 CHORUS (CERN WANF) Just got the final statistics : 2059 charm events! The analysis is in progress!

  13. Measurement of c production Phys. Lett. B. 555 (2003) 156-166 based on 50414  CC Strategy: Analysis is based on statistical approach using flight length distribution D:Λc:Ds=6:3: 1 (E531 result) Short flight decay: c enriched sample Long flight decay: Λc D+, Ds dominated sample D Analysis has been performed applying two different selections Ds

  14. A: 40 m < FL < 400 m B: 400 m < FL < 2400 m 1 prong 62 133 3 prong 66 195 Measurement of c production Short flight decay (A): Daughter track: Distance to the muon 5 m to 30 m 1614 events were selected for visual inspection Long flight decay (B): Parent track: distance to the muon < 5 m Distance between daughter and parent 5 m to 30 m 586 events were selected for visual inspection After flight length cut:

  15. +140 -54 c = 861 ± 198 (stat) ± 98 (syst) (QE) Measurement of c production Combining short (A) and long (B) decay search and taking into account efficiencies and background: BR(c  3 prong) = ( 24 ± 7 (stat) ± 4 (syst) ) x 10-2  (c) /  (CC) x BR (c  3 prong) = ( 0.37 ± 0.10 (stat) ± 0.02 (syst) ) x 10-2  (c) /  (CC) = ( 1.54 ± 0.35 (stat) ± 0.18 (syst) ) x 10-2

  16. Quasi-elastic charm production Phys. Lett. B. 575 (2003) 198 based on 46105  CC Topological and kinematical selection criteria: Require 2 or 3 tracks at primary vertex Flight length < 200 m (enriched c sample) Calorimeter energy < 10 GeV and electromagnetic energy < 2 GeV  165º (angle between muon and charm in transverse plane)

  17. Quasi-elastic charm production Azimuthal angle 13 events with a background of 1.7±0.6 (mainly from DIS c) QE production is about 15% of c production

  18. D0 V4 D0 V2 = (22.7 ± 1.8) x 10-2 Measurement of D0 production Phys. Lett. B. 527 (2002) 173 based on ~25% of statistics NOW full sample: 95450 CC events Candidate selection Primary track matched to detector muon Daughter track matched to detector track 3~13 m < I.P. wrt. 1ry vtx < 400 m Selection efficiencies V2 : (56.3 ± 0.5) x 10-2 V4 : (74.2 ± 0.9) x 10-2 Confirmed D0 sample V2 : 841 V4 : 230 BG subtracted, efficiency corrected V2 : 1428 ± 49 V4 : 310 ± 20

  19. Measurement of D0 production Fully neutral D0 decay mode: Preliminary BR4/BR2 measured BR4 = 0.1338 ± 0.0058 (PDG) BR(D0 neutrals) = 1 – BR4 x ( 1 + BR2/BR4 ) = (27.3 ± 4.5) % Total production cross section: All D0 ’s Relative detection efficiency D0/CC = 0.87 (D0) / (CC)= ND0 / 95450 / 0.87 = (2.97 ± 0.24) x 10-2

  20. Bas measured in CHORUS Phys. Lett. B. 549 (2002) 48 based on ~50% of statistics Number of selected events1055 90.6% selection purity 956  35 2ry Muon identification (Average efficiency ~ 55 %) Dimuon sample88  10 (stat)  8 (syst) B = 9.3  0.9 (stat)  0.9 (syst) % Revised result (D0  neutrals effect) B = 8.1  0.8 (stat)  0.8(syst) % Analysis with full statistics is in progress! only ‘direct’ measurement available

  21. Charged-current Gluon bremsstrahlung Associated charm production in CC • In the past this search was based on the observation of trimuon events -(+ -) and same-sign dimuons; • 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) A new analysis with full statistics is in progress (5 events on 95450 CC); The discrepancy between data and prediction should be clarified soon.

  22. Associated charm production in CC Event 77891071 E=35.4 GeV P=-13.5 GeV/c Evis=48.9 GeV 1ry@pl7 Ns=6, Nh=1 V2 @pl 6 fl= 257.0mm kink @pl 4 fl= 2271.6 mm Dq = 67.4mrad Pl 7 Pl 6 pl 4

  23. +3.1 -1.1 Production rate 1.3 x 10-3 normalised to CC +0.83 -0.36 mc = (1.40 ±0.26) GeV, in agreement with other measurements Associated charm production in NC In the past only one event observed in the E531 emulsion: Neutral-current 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 Z-gluon fusion + Currently a search is in progress in CHORUS: 3 candidates on 26568 NC have been found and the cross-section measurement will be finalised by the end of this year Gluon bremsstrahlung

  24. Associated charm production in NC

  25.  induced charm = 32 All  ‘s = 4975 ± 187 s(n N  m+cX) + 1.4 = 5.1 % - 1.0 s(n N  m+X) Charm production in antineutrino interactions Preliminary Strategy: observed events with 1+ from spectrometer N+ = 2704 N- = 93768 = 1 spectrometer events After  reconstruction cut: Estimated background = 2.7 mainly due to the muon wrong sign identification fCo + 1.5 = 2.4 (stat) fC- - 1.0

  26. Charm production rate as a function of  energy Charm production in antineutrino interactions Theoretical prediction

  27. Analyses in progress - From charm quark to charmed hadrons • Charmed fractions fh (present results based on the 122 E531 events and a reanalysis discussed in T. Bolton hep-ex/9708014) • Fragmentation functions (z and PT2 distribution) - Total charm production cross-section - Charm mass mc, Muonic branching ratio B, Vcd - x distribution charm (anti-charm) events - D* production, D* D0 + 

  28. Conclusion Charm physics in  interactions very interesting • So far, from a subsample of charm data in CHORUS we have measured: Phys. Lett. B. 555 (2003) 156 Phys. Lett. B. 575 (2003) 198 Phys. Lett. B. 527 (2002) 173 Phys. Lett. B. 539 (2002) 188 Phys. Lett. B. 549 (2002) 48 Phys. Lett. B. 435 (1998) 458 • Λc production • QE charm production • D0 production • CC associate charm production • BR   • Diffractive Ds* production Many analyses are still in progress New results will be available within 2004

  29. Backup slides

  30. Charmed fractions • fh can only be measured in emulsions! • Present results based on the 122 E531 events and a reanalysis discussed in T. Bolton hep-ex/9708014 Analysis in progress of the CHORUS data: 2000 events Results should be available in a couple of months

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

  32. 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 ep or ec (depends on the choice) is one of the free parameters of the fit to the dimuon data, see later

  33. Determination of p and c All the above numbers have been obtained with a LO analysis At e+e- exps s1/210 GeV eP0.16(D+)0.27(Lc) O.Biebel, P.Nason, B.R.Webber hep-ph/0109282

  34. The transverse momentum of charmed particles wrt the direction of the hadronic system is usually parametrized as • Available statistics in n exp • E531 122 events • Phys. Lett. B 206 (1988) 380-384 • NOMAD 47 events • Phys. Lett. B 526 (2002) 278-286 pT2 distribution of charmed particles

  35. pT2 distribution of charmed particles One measurement available with 360 GeV pp interactions b = 1.10.3 (GeV/c)-2 M.Aguilar-Benitez et al., Phys. Lett B 123 (1983) 103 • Analysis in progress of the CHORUS data: • Results should be available in a couple of months • New analysis of the NOMAD data in progress

  36. The strange sea distribution • No new results • Both at LO and NLO k~0.5 • At LO a is not zero a=2.50.7, while it is at NLO • Da=a-a’=-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< Da<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

  37. Relevant parameters of the fit to dimuon data • Input parameters • Charmed fractions and decay model constrained by other experiments • Vcs (In the following we use 0.996±0.024 Riv.NuovoCim. 23(2000)1) • BmBR(C m) (In the following 9.31±0.95% for En >30 GeV) • Output parameters • Charm mass: mc • Element of the CKM matrix: Vcd • Fragmentation parameter: e • Two parameters for each mode (n and anti-n) 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)ais the shape of the s-quark PDF

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

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

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

  41. Chorus dimuon analysis result (calo)(preliminary)  mc= 1.46  0.15 (stat)  0.10 (syst)   = 0.56  0.05 (stat)  0.045 (syst)  =0.040  0.003 (stat)  0.015 (syst)  B=0.098  0.005(stat)  0.014 (syst)

  42. Vud 0.1 % nuclear beta decay The CKM matrix • Vus • 1 % • Ke3 decay • Vub • 25 % • b  u l  d’ d • Vcd • 7 % •  charm production • Vcs • 15 % • De3 decay • Vcb • 5 % • Be3 decay s’ = s b’ b • Vtd • Vts • Vtb • 30 % • t  b l  Review of particle physics, 98 edition

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