Charm production and its impact on future neutrino experiments

1. Charm production and its impact on future neutrino experiments Francesco Di Capua – INFN Napoli NuFact - Valencia 3/07/08

2.  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

3. pQCD LO CC charm production • Production from d(anti-d) quarks Cabibbo suppressed • large s contribution: 50% in n and 90% in anti-n • =x(1+m2c/Q2)(1-x2M2-Q2), for kinematical effects of heavy charm • z: fraction of the charm momentum carried by the charmed hadron • p2T transverse momentum of Ch wrt to the charm direction • fh mean multiplicity of the charmed hadron h(D0,D+,Ds,Lc) in n charm production • D probability for a charm quark to fragment into a charmed hadron h with a given z and p2T

4. Physics motivation Intrinsic interest 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 Constrain/study charm production models • in NLO pQCD is a challenging theoretical problem Measure charm mass and Vcd Future and present neutrino experiments interest Charm production represents one of main background in golden and silver channel investigated in future experiments

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) 8910 -+ , 430+- events Nucl..Phys.B798:1-16,2008 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. Dimuon cross-section (CHORUS)

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. The CHORUS charged current data sample and charm subsample Located CC events 93807 Total confirmed charm candidates 2013 452 C1 819 V2 491 C3 226 V4 22 C5 6 V6

13. The relative rate is: (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 Charm mass fit mC=1.42±0.08 GeV/c2 Fit parameters for the model curve (M.Gluk,E.Reya and A.Vogt, Z.Phys.C (1955) 433) (spas measured in CHORUS, see next slides) At 27 GeV average neutrino beam

14. Measurement of D*+ production in CC -N scattering m- n D0fl>100mm p+ q<60 mrad K- m- n p+ 0.4 <p(p+)<4 GeV/c 10.< pT<50. MeV/c D*+ D0 p+ 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)

15. From charm quark to charmed hadrons Z definedas the ratio of the energy of the charmed particle E D and the energy transfer to the hadronic system n: z = E D / n Collins-Spiller J.Phys. G 11 (1985) 1289 Peterson et al. Phys.Rev. D 27 (1983) 105

16. Measurement of fragmentation properties of charmed particle production in CC neutrino interaction CHORUS data Peterson Collins-Spiller +0.05 -0.04 ecs = 0.21 ± 0.04 CHORUS data Prediction Z distribution Momentum distribution of D0’s produced inclusively in CHORUS <z> = 0.63 ± 0.03(stat) ± 0.01(syst) Fit to Collins-Spiller distribution: Fit to Peterson distribution: eP = 0.083 ± 0.013± 0.010

17. Measurement of inclusive charm production CHORUS E531 At 27 GeV average neutrino beam (Charm)/(CC)=(5.9±0.4)%

18. Charmed fractions anf inclusive topological branching ratios fD0 = (45.23.8)% Likelihood fit to flight length over momentum distribution to obtain the charm production fractions fD+ = (28.94.3)% fc+ = (16.44.2)% fDs+ = (9.45.4)% BR(C+  1 prong) =(64.7  6.4)% BR(C+  3 prong) =(34.3  3.5)% BR(C+  5 prong) =(1.00.2)% BR(D0  fully neutrals) =(21.8  4.9)% BR(D0  2 prong) =(64.7  4.9)% BR(D0  4 prong) =(13.390.61)% (LEP meas.)

19. Bmmuonic branching ratio of charmed particles B (D0)= (6.51.2(stat))% B (All Charm)= (7.30.8(stat))%

20. Derived from di-lepton data 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) Measurement of charm production in antineutrino charged-current interactions

21.  +2.9 (cc)/(NC)=(3.6 )x10-3 -2.4 Associated charm production gluon bremsstrahlung boson gluon fusion 3 observed events in NC sample C1+V2 V2+V2 C3+V4 Background= 0.18±0.06 topologies

22. Charm in present and future neutrino experiments First Charm event in OPERA data!!! P=3.9+1.7-0.9 GeV kink=0.204 rad Shower

23. Applyng charm production measurement to silver channel background predictions

24. Charm cross-section at Neutrino Factory energies • muon antineutrino • electron neutrino E (GeV) Calculation inputs: • Neutrino Factory Flux from 50 GeV muon decay with polarization P=0 • Oscillation probability • Charm cross section as function of energy from CHORUS • world average neutrino CC cross-section

25. Charm cross-section at Neutrino Factory energies (eN->e- Charm X)/(CC)=(5.85±0.36)% neutrino charm production (eN->e-C+X)/(CC)=(3.12±0.20)% _ Anti-neutrino charm production (N->+ Charm X)/(CC)=(4.89±1.72)%

26. 1 mm - n ne t e » ¸ ( 0 . 1 0 . 3 )% miss charge Pb Emulsion layers Silver channel signal topology in Emulsion Cloud Chamber detector (Opera-like) Muon spectrometers: p/p < 20% for p<50 GeV n beam Two supermodules

27. Charge current interactions x Oscillation probability • P=0 muon polarization • E= 50 GeV • 2x1020 useful muons/year x 5 year       13 =5º =90º   1 Kton detector    

28. Charm background A crucial point is represented by muon identification and right charge assignment capability Opera spectrometer (RPC + drift tubes) Assume: Muon identification ID= 98% At NuFact spectrum (50 GeV muons) Wrong charge assignment P(+-)=0.3% (Opera Proposal) P(+-)=1.0% To be conservative

29. 1 mm + e C+ e- Pb Emulsion layers Charm background(1) 1 mm • + from primary  CC interactionnot identified • muonic decay of charm fake  decay - _  C- + Pb Emulsion layers 21.1±7.4 at 732 Km (1.1+0.5 at 3000Km) • electron from primary e CC interactionnot identified • muonic decay of charm with wrong charge assignment fake  decay 2.80 at 732 Km (0.16 at 3000Km)

30. Charm background(2)  _  + • Neutral charmed particle decay vertex mistaken as primary vertex • + from  CC faking  because of its large impact parameter _  3.0 event at 732Km (0.15 at 3000Km)

31. - neutrino direction Charm Kinematical cuts  Invariant Mass hadronic system  Charm

32. Signal/background energy dependence 732 Km Silver channel signal Charm background hadrons 5 Kton _ _  oscillation 3000 Km D. Autiero et al. Eur. Phys. J. C33 (2004) 243

33. Conclusions • More than 2000 charm events collected by CHORUS experiments out of 93807 CC events • Charm (charged and neutrals) inclusive cross-section, Semi-leptonic branching ratio, D* production, Fragmentation parameters, associated charm production measured • First direct measurement of charm induced by anti-neutrino (32 events) • CHORUS measurements can be used for charm background prediction in the future golden and silver channel investigations

34. Backup slides

35. 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)

36. D0topological branching fractions After BG subtraction and efficiency correction: B(D0 V4) B(D0 V2) = 0.207 ± 0.016 ± 0.004 +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+ + ]