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

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-

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+m 2 c /Q 2 )(1-x 2 M 2 -Q 2 ), for kinematical effects of heavy charm  z: fraction of the charm momentum carried by the charmed hadron  p 2 T transverse momentum of C h wrt to the charm direction  f h mean multiplicity of the charmed hadron h(D 0,D +,D s,  c ) in charm production  D probability for a charm quark to fragment into a charmed hadron h with a given z and p 2 T

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

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: CHORUS (CERN WANF) 8910  -  +, 430  +  - events Nucl..Phys.B798:1-16,2008

Dimuon cross-section (CHORUS)

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

 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)

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

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

~ 100  m Visual inspection to confirm the event

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

Measurement of D 0 production and of decay branching fractions in -N scattering Phys. Lett. B. 613 (2005) 105 The relative rate is:  (D 0 )/  (CC)= ± ± At 27 GeV average neutrino beam m C =1.42±0.08 GeV/c 2 Charm mass fit Fit parameters for the model curve (M.Gluk,E.Reya and A.Vogt, Z.Phys.C (1955) 433) (  s p as measured in CHORUS, see next slides)

Measurement of D *+ production in CC -N scattering  D 0 fl>100  m     <60 mrad 0.4 <p(  + )<4 GeV/c 10.< p T <50. MeV/c  D0D0  D *+ Assuming B(D *+  D 0  + ) =0.677±0.005 (PDG) the relative rate is:  (D *+ )/  (D 0 )=0.38 ± 0.09 (stat) ± 0.05 (syst) By using the measure of  (D 0 )/  (CC) made in CHORUS:  (D *+ )/  (CC)=(1.02 ± 0.25 (stat) ± 0.15 (syst) )%

From charm quark to charmed hadrons Z defined as the ratio of the energy of the charmed particle E D and the energy transfer to the hadronic system  z  E D / Collins-Spiller J.Phys. G 11 (1985) 1289 Peterson et al. Phys.Rev. D 27 (1983) 105

Measurement of fragmentation properties of charmed particle production in CC neutrino interaction CHORUS data Prediction Momentum distribution of D 0 ’s produced inclusively in CHORUS CHORUS data Peterson Collins-Spiller Z distribution = 0.63 ± 0.03(stat) ± 0.01(syst) Fit to Collins-Spiller distribution:  cs = 0.21 ± Fit to Peterson distribution:  P = ± ± 0.010

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

Charmed fractions anf inclusive topological branching ratios 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(D 0  fully neutrals) =(21.8  4.9)% BR(D 0  2 prong) =(64.7  4.9)% BR(D 0  4 prong) =(13.39  0.61) % (LEP meas.) f D+ = (28.9  4.3)% f Ds+ = (9.4  5.4)% f  c+ = (16.4  4.2)% f D0 = (45.2  3.8)% Likelihood fit to flight length over momentum distribution to obtain the charm production fractions

B  muonic branching ratio of charmed particles B  (All Charm)= (7.3  0.8 (stat) )% B  (D 0 )= (6.5  1.2 (stat) )%

Measurement of charm production in antineutrino charged-current interactions TOT 32  (  N   + cX)  (  N   + X) = 5.0 ±0.7% Theoretical prediction obtained from leading order calculation with m c =1.31 GeV/c 2 Derived from di-lepton data CHORUS DATA

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

Charm in present and future neutrino experiments First Charm event in OPERA data!!! Shower  kink =0.204 rad P= GeV

Applyng charm production measurement to silver channel background predictions

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 Charm cross-section at Neutrino Factory energies Calculation inputs: E (GeV) muon antineutrino electron neutrino

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

 beam Two supermodules Muon spectrometers:  p/p < 20% for p<50 GeV )%3.01.0( miss charge  Pb Emulsion layers   1 mm -- e Silver channel signal topology in Emulsion Cloud Chamber detector (Opera-like)

Charge current interactions x Oscillation probability + + N events (L=732Km) N. events (L=3000Km) e   248 e  e e        e    -- e   e  e e   8673      e               P  =0 muon polarization E  = 50 GeV 2x10 20 useful muons/year x 5 year  13 =5º  =90º 1 Kton detector

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

Charm background(1)  + from primary  CC interaction not identified muonic decay of charm fake  decay  21.1±7.4 at 732 Km ( at 3000Km) electron from primary e CC interaction not identified muonic decay of charm with wrong charge assignment fake  decay  2.80 at 732 Km (0.16 at 3000Km) Pb Emulsion layers 1 mm --  C-C- _ ++ Pb Emulsion layers 1 mm ++ e C+C+ e-e-

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)  _ +

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

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

Conclusions More than 2000 charm events collected by CHORUS experiments out of 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

Backup slides

Chorus dimuon analysis result (calo)  m c = 1.26  0.16 (stat)  0.09 (syst)   = 0.33  0.05 (stat)  0.05 (syst)   P =  (stat)  (syst)  B  =  0.004(stat)  (syst) N leading  - =8910  180 N leading  + = 430  60

D 0 topological branching fractions INCLUSIVE measurement in CHORUS: B(D 0  V2) = ± ± B(D 0  V6) = (1.2 ± 0.2)x B(D 0  V2) B(D 0  V4) B(D 0  V0)=1- B(D 0  V4)[1+ + ] B(D 0  V6) B(D 0  V4) B(D 0  V0) = 0.218±0.049±0.036 very important for B  measurement!!! B(D 0  V0)  5% (PDG) Sum over all exclusive channel for which measurement exist B(D 0  V2) = ± (PDG) Sum over all exclusive channel for which measurement exist B(D 0  V6) = (0.59 ± 0.12)x10 -3 (FOCUS coll.) sum of all exclusive measured channel After BG subtraction and efficiency correction: = ± ± B(D 0  V4) B(D 0  V2)