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Measurement of charm production and decay properties by CHORUS

Measurement of charm production and decay properties by CHORUS. Francesco Di Capua University of Napoli and INFN Italy GRAVITY, ASTROPHYSICS AND STRINGS AT THE BLACK SEA kiten – Bulgaria June 2005. Outline. Physics motivation. What do we measure and why it is interesting.

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Measurement of charm production and decay properties by CHORUS

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  1. Measurement of charm production and decay properties by CHORUS Francesco Di Capua University of Napoli and INFN Italy GRAVITY, ASTROPHYSICS AND STRINGS AT THE BLACK SEA kiten – Bulgaria June 2005

  2. Outline Physics motivation • What do we measure and why it is interesting The CHORUS experiment • The CHORUS detector • Automatic analysis of nuclear emulsions Results on charm analysis • D0 production in neutrino charged current interaction • D*+ production in neutrino charged current interaction • Fragmentation properties of charmed particles • Anti-neutrino charm production • Muonic branching ratio Bm of charmed particles (preliminary results) • Associated charm production (CC and NC) • Dimuon analysis in the calorimeter Conclusions and perspectives

  3. 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

  4. 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 “Charm Physics with neutrinos”, G.De Lellis, P.Migliozzi, P.Santorelli , Phys. Rept.399:227-320,2004

  5. 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 CHORUS (CERN WANF) 8919 -+ , 430 +- events To be published 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

  6. 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

  7. 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

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

  9. 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

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

  11. The CHORUS charged current data sample and charm subsample

  12. After BG subtraction and efficiency correction: B(D0 V4) B(D0 V2) = 0.207 ± 0.016 ± 0.004 Candidate selection Primary track matched to el. detector muon Daughter track matched to el. detector track 3~13 m < I.P. wrt. 1ry vtx < 400 m The relative rate is: AssumingB(D0 V4)=0.1339±0.0061 (PDG); (D0)/(CC)=0.0269 ± 0.0018 ± 0.0013 Measurement of D0 production and of decay branching fractions in -N scattering Phys. Lett. B. 613 (2005) 105

  13. D0topological branching fractions +1.3 - 0.9 INCLUSIVE measurement in CHORUS: B(D0 V6) B(D0 V4) B(D0 V2) B(D0 V4) B(D0 V2) = 0.647 ± 0.049 ± 0.031 B(D0 V6) = (1.2 ± 0.2)x10-3 B(D0V0) = 0.218±0.049±0.036 very important for Bm measurement!!! B(D0V0)=1- B(D0V4)[1+ + ] To be compared with:

  14. CHORUS data Fit parameters for the model curve (M.Gluk,E.Reya and A.Vogt, Z.Phys.C (1955) 433) E531 data Fit to a theoretical model (spas measured in CHORUS, see next slides) Energy dependence of the cross section ratio and charm mass mc=(1.42  0.08(stat)  0.04(syst)) GeV/c2

  15. Measurement of D*+ production in CC -N scattering Number of candidates Background prediction Accepted by Phys. Lett. B. - CERN-PH-EP-2005-010. Looking for events in the channel:D*+  D0p+ m- n D0fl>100mm p+ D*+ signal in the D0 h+ sample No signal in the D0h- sample as expected q<60 mrad K- m- n p+ 0.4 <p(p+)<4 GeV/c 10.< pT<50. MeV/c D*+ D0 p+ No signal in the C+h+ sample as expected No signal in the C+h- sample as expected • Expected shape of the candidates normalized to the observed events; • (2-3-4) shape normalized to the total number of D0 and C+ respectively;

  16. Measurement of D*+ production in CC -N scattering assuming that the D*+ and D*0 production rate are equal and recalling that D*0 always decays into D0: (D*  D0)/(D0)=0.63 ± 0.17 By using the measure of (D0)/(CC) made in CHORUS: Assuming B(D*+ D0p+)=0.677±0.005 (PDG)the relative rate is: (D*+)/(CC)=(1.02 ± 0.25(stat)± 0.15 (syst))% (D*+)/(D0)=0.38 ± 0.09(stat)± 0.05(syst) • At similar neutrino energy beam: • NOMAD (D*+)/(CC)=(0.79 ± 0.17(stat)± 0.10 (syst))% • BEBC (D*+)/(CC)=(1.22 ± 0.25)% • At the higher energy of the Tevatron beam: • (D*+)/(CC)=(5.6 ± 1.8)% To be compared with: Defining fV=V/(P+V) , V= vector production and P pseudoscalar production of D meson Consistent within the error: with V:P=3:1, as expected from simple spin arguments; with measurements in e+e-, pN, gN experiments. fV=0.51± 0.18

  17. CHORUS data Prediction simulation Measurement of fragmentation properties of charmed particle production in CC neutrino interaction Phys. Lett. B 604 (2004) 145 Momentum distribution of D0’s produced inclusively in CHORUS The momentum of D0 can be inferred by the geometrical average (l) of the angle of the decay daughters with respect to the direction of the D0 (as described in S.Petrera, G.Romano, Nucl.Instrum. And Meth.174 (1980) 61 )

  18. From charm quark to charmed hadrons Defined z as the ratio of the energy of the charmed particle E D and the energy transfer to the hadronic system n: z = E D / nwe measure <z> = 0.63 ± 0.03(stat)± 0.01(syst) Collins-Spiller J.Phys. G 11 (1985) 1289 Peterson et al. Phys.Rev. D 27 (1983) 105

  19. CHORUS data Peterson Collins-Spiller +0.05 -0.04 ecs = 0.21 ± 0.04 Z distribution Fit to Collins-Spiller distribution: Fit to Peterson distribution: eP = 0.108 ± 0.017± 0.013 To be compared with: To compare results: If zs = E D / string energy eSP = 0.083 ± 0.013± 0.010 If zQ = P charmed particle / P charm quark eQP = 0.059 ± 0.010± 0.008

  20. pLD – b ED W XF= 2 g XF is defined as: Fragmentation properties pLD longitudinal momentum of D0 ED energy of D0 W invariant mass From the distribution we mesure <XF>: <XF>=0.38 ± 0.04(stat)± 0.03(syst) To be compared with NOMAD: <XF>= 0.47 ± 0.05 forward-backward asymmetry: <A>=0.79 ± 0.14(stat)± 0.05(syst) To be compared with E531: <A> = 0.620 ± 0.092 From the distribution production angle out of the lepton plane we mesure: <tanqout>=0.030 ± 0.002

  21. Bmmuonic branching ratio of charmed particles Analysis based on the full statistics Preliminary B = (7.3 0.8(stat))% The results takes into account the new CHORUS measurement of B(D0  V0)22% Considering only events with visible energy above 30 GeV B = (8.31.6(stat))% Bm x |Vcd|2LO=(0.474  0.027)x10-2 (CDHS,CHARM II, CCFR average value) |Vcd|LO=(0.2390.046) Bm x |Vcd|2NLO=(0.534  0.046)x10-2 (CCFR) |Vcd|NLO=(0.2540.066) To be compared with: 0.221< |Vcd|<0.227 at 90% CL Obtained imposing CKM unitarity and only 3 generations

  22. Measurement of charm production in antineutrino charged-current interactions Derived from di-lepton data (G.de Lellis et al., J.Phys.G28 (2002), 713) Theoretical prediction obtained from leading order calculation with mc=1.31 GeV/c2 TOT 32 CHORUS DATA s(n N  m+cX) + 1.4 = 5.0 ±0.7% - 0.9 s(n N  m+X) Phys. Lett. B. 604 (2004) 11-21 Strategy:look for the + generated in the antienutrino CC interaction After  reconstruction cut and charm topology selection

  23. 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 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) A new analysis with full statistics is in progress (5 events on 93807 CC); The discrepancy between data and prediction should be clarified soon.

  24. 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

  25. +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

  26. Associated charm production in NC

  27. Chorus dimuon analysis result (calo) Nleading - =8910180 Nleading + = 43060  mc= 1.26  0.16 (stat)  0.09 (syst)   = 0.33  0.05 (stat)  0.05 (syst)  P=0.065  0.005 (stat)  0.009 (syst)  B=0.096  0.004(stat)  0.008 (syst)

  28. Chorus dimuon analysis result (calo) dimuon cross-section relative to CC events data MC prediction obtained using fitted values of parameters mc, k, P, B

  29. Accepted by Phys. Lett. B. Phys. Lett. B. 613 (2005) 105 Phys. Lett. B. 604 (2004) 11 Phys. Lett. B. 604 (2004) 145 Phys. Lett. B. 575 (2003) 198 Phys. Lett. B. 555 (2003) 156 Phys. Lett. B. 549 (2002) 48 Phys. Lett. B. 539 (2002) 188 Phys. Lett. B. 527 (2002) 173 Phys. Lett. B. 435 (1998) 458 • D*+ production • D0 production • Antineutrino charm production • Fragmentation properties • QE charm production • Λc production • BR   • CC associate charm production • D0 production • Diffractive Ds* production Conclusion Interesting charm physics results from CHORUS thanks to: • high beam flux; • Nuclear emulsion target (0.8t); • Automatic emulsion analysis Measured so far: Other analyses in progress

  30. Backup slides

  31. 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

  32. 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

  33. 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

  34. 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

  35. Relevant parameters of the fit to dimuon data • Input parameters • Charmed fractions and decay model constrained by other experiments • Vcs • BmBR(C m) • 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

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

  37. 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

  38. 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

  39. 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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