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

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Presentation on theme: "Study of charm physics in neutrino scattering Di Capua Francesco University of Napoli, Italy Heavy Quarks and Leptons 2004 San Juan, Puerto Rico."— Presentation transcript:

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 The CHORUS experiment The CHORUS detector Automatic acquisition of nuclear emulsions Physics motivation What do we measure and why it is interesting Results on charm analysis Measurement of  c, D 0 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 c |V cd | 2,|V cs | 2 d,s ----  Beam knowledge Quark density functions, strange sea (  ) ,h E had h Charm fragmentation f D0 ; f D+ ; f Ds ; f  c z = p D /p c, p T 2 DIS charm production Production from d(anti-d) quarks Cabibbo suppressed  large s contribution:  50% in and  90% in anti-

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 F 2 structure function Knowledge of the strange sea is important to search for stop at hadron colliders (largest background: g+s  W+c ) Constrain/study charm production models in NLO pQCD is a challenging theoretical problem R.Demina et al., Phys. ReV. D 62 (2000) S.J.Brodsky and B.Ma, Phys. Lett. B 381 (1996) 317  2 scales,  QCD and charm mass (J.Conrad et al. Rev.Mod.Phys. 70 (1998) ) Measure charm mass and V cd

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

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- statistics is very poor  Pro: low background; sensitivity to low E  m c thr. effect; reconstruction of the charmed hadron kinematics (direction and momentum)  fragmentation studies are possible

8  p/p = p (GeV/c)  0.22  p/p = 10 – 15% (p < 70 GeV/c) (with lead and scintillating fibers, 112 ton )  E/E = 32 %/  E (hadrons) = 14 %/  E (electrons)  h = GeV E ~ 27 GeV Air-core magnet Active target Muon  spectrometer Calorimeter WB Neutrino beam :: :   :  : e : e ::: 1.00 : 0.06 : : nuclear emulsion target (770kg) scintillating fiber trackers CHORUS experiment CHORUS experiment (CERN Hybrid Oscillation Research ApparatUS)

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

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

11 ~ 100  m Visual inspection to confirm the event

12 Charm production by interactions in emulsions Phys. Lett. B 206 (1988) E531 (Fermilab, Nagoya) 122 charm events in emulsion only measurement of D 0 : D + : D s + :  c + (no anti-neutrino charm events) B(c  ) crucial for other experiments CHORUS (CERN WANF) Just got the final statistics : 2059 charm events! The analysis is in progress!

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

14 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: A: 40  m < FL < 400  m B: 400  m < FL < 2400  m 1 prong prong

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

16 Quasi-elastic charm production Phys. Lett. B. 575 (2003) 198 based on  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 13 events with a background of 1.7±0.6 (mainly from DIS  c ) QE production is about 15% of  c production Quasi-elastic charm production Azimuthal angle

18 Measurement of D 0 production Phys. Lett. B. 527 (2002) 173 based on ~25% of statistics NOW full sample: 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 V4 : (74.2 ± 0.9) x V2 : 841 V4 : 230 Confirmed D 0 sample V2 : 1428 ± 49 V4 : 310 ± 20 BG subtracted, efficiency corrected D 0  V4 D 0  V2 = (22.7 ± 1.8) x 10 -2

19 Measurement of D 0 production Fully neutral D 0 decay mode: BR4/BR2 measured BR4 = ± (PDG) BR(D 0  neutrals) = 1 – BR4 x ( 1 + BR2/BR4 ) = (27.3 ± 4.5) % Total production cross section: All D 0 ’s Relative detection efficiency D 0 /CC = 0.87  (D 0 ) /  (CC) = N D0 / / 0.87 = (2.97 ± 0.24) x Preliminary

20 Number of selected events % selection purity 956  35 Dimuon sample 88  10 (stat)  8 (syst) B  = 9.3  0.9 (stat)  0.9 (syst) % only ‘direct’ measurement available B  as measured in CHORUS 2ry Muon identification (Average efficiency ~ 55 %) Revised result (D 0  neutrals effect) B  = 8.1  0.8 (stat)  0.8 (syst) % Phys. Lett. B. 549 (2002) 48 based on ~50% of statistics Analysis with full statistics is in progress!

21 Associated charm production in CC Charged-current Gluon bremsstrahlung 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 CC); The discrepancy between data and prediction should be clarified soon. 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

22 Event Event E=35.4 GeV P=-13.5 GeV/c Pl 7 Pl 6pl 4 Pl 7 Pl 6pl 4 Evis=48.9 GeV Associated charm production in CC Ns=6, Nh=1 6 fl=  m 4 fl=  m  = 67.4mra d

23 Associated charm production in NC Neutral-current Z-gluon fusion In the past only one event observed in the E531 emulsion: Currently a search is in progress in CHORUS: 3 candidates on NC have been found and the cross-section measurement will be finalised by the end of this year Production rate 1.3 x normalised to CC Indirect search performed by NuTeV: Production rate (2.6±1.6)x10 -3 normalised to CC at 154 GeV m c = (1.40 ±0.26) GeV, in agreement with other measurements (A. Alton et al., Phys. Rev. D64 (2001) 539) Gluon bremsstrahlung +

24 Associated charm production in NC

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

26 Charm production rate as a function of energy Theoretical prediction

27 Analyses in progress - From charm quark to charmed hadrons Charmed fractions f h (present results based on the 122 E531 events and a reanalysis discussed in T. Bolton hep-ex/ ) Fragmentation functions (z and P T 2 distribution) - Total charm production cross-section - Charm mass m c, Muonic branching ratio B , V cd - x distribution charm (anti-charm) events - D * production, D *  D 0 + 

28 Conclusion Charm physics in interactions very interesting So far, from a subsample of charm data in CHORUS we have measured: Λ c production QE charm production D 0 production CC associate charm production BR   Diffractive D s * production 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 Many analyses are still in progress New results will be available within 2004

29 Backup slides

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

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

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  p or  c (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 pp cc E  NOMAD    0.08  0.11 CDHS   --- CCFR 0.22   0.12 CHARMII  NuTeV  0.31 All the above numbers have been obtained with a LO analysis At e + e - exps s 1/2  10 GeV  P  0.16(D + )  0.27(  c ) O.Biebel, P.Nason, B.R.Webber hep-ph/

34 p T 2 distribution of charmed particles The transverse momentum of charmed particles wrt the direction of the hadronic system is usually parametrized as Available statistics in exp E events Phys. Lett. B 206 (1988) NOMAD47 events Phys. Lett. B 526 (2002)

35 E531 Phys.Lett.B 206 (1988) 380 NOMAD Phys.Lett.B 526 (2002) 278 b 3.25  0.37 (GeV/c)  0.40 (GeV/c) -2 Analysis in progress of the CHORUS data: Results should be available in a couple of months New analysis of the NOMAD data in progress 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 p T 2 distribution of charmed particles

36 The strange sea distribution No new results Both at LO and NLO  ~0.5 At LO  is not zero  =2.5  0.7, while it is at NLO  =  ’ =-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<  <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 V cs (In the following we use 0.996±0.024 Riv.NuovoCim. 23(2000)1)    BR(C   ) (In the following 9.31±0.95% for E  >30 GeV) Output parameters Charm mass: m c Element of the CKM matrix: V cd Fragmentation parameter:  Two parameters for each mode ( and anti- ) 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)  is the shape of the s-quark PDF

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

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

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

41 Chorus dimuon analysis result (calo) (preliminary)  m c = 1.46  0.15 (stat)  0.10 (syst)   = 0.56  0.05 (stat)  (syst)   =  (stat)  (syst)  B  =  0.005(stat)  (syst)

42 V ud V ud 0.1 % 0.1 % nuclear beta decay The CKM matrix V cb V cb 5 % 5 % B e3 decay V cs V cs 15 % 15 % D e3 decay V ub V ub 25 % 25 % b  u l V us V us 1 % 1 % K e3 decay V cd V cd 7 % 7 % charm production V td V td V ts V ts V tb V tb 30 % 30 % t  b l Review of particle physics, 98 edition d’ s’ b’ d s b =


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