Study of charm physics in neutrino scattering
Di Capua FrancescoUniversity of Napoli, Italy
Heavy Quarks and Leptons 2004San Juan, Puerto Rico
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, D0 and quasi-elastic charm production
• Semi-leptonic branching ratio B
• Associated charm production (CC and NC)• Anti-neutrino charm production
Conclusions and perspectives
A short theoretical introduction
cc
|Vcd|2,|Vcs|2
d,sd,s
-- Beam
knowledge
Quark density functions,strange sea ()
,h,h
EEhadhad
hh
Charm fragmentationfD0
; fD+ ; fDs
; fc
z = pD/pc, pT2
DIS charm production
Production from d(anti-d) quarks Cabibbo suppressed large s contribution: 50% in and 90% in anti-
Physics motivationMeasure 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+sW+c )
Constrain/study charm production models • in NLO pQCD is a challenging theoretical problem
R.Demina et al., Phys. ReV. D 62 (2000) 035011S.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) 1341-1392)Measure charm mass and Vcd
Dimuon available statistics
CDHS (CERN WBB)CDHS (CERN WBB)
CCFR (NuTeV)CCFR (NuTeV)
CHARMII (CERN WANF)CHARMII (CERN WANF)
Zeitschr. Phys. C (1982) 19-31
Zeitschr. Phys. C (1995) 189-198
Eur. Phys. J., C11 (1999) 19-34
NOMAD (CERN WANF)NOMAD (CERN WANF) Phys.Lett.B486:35-48,2000
9922 -+ , 2123 +- events
5044 -+ , 1062 +- events
4111 -+ , 871 +- events
2714 -+ , 115 +- events
Background due to , K, Kos
Cross section measurement depends on knowledge of BR (C ) ~ 10%
and on the uncertainty on it
High statistics, but:
Emulsion experiments These experiments study charm production
by looking “directly” at the decay topology of the charmed hadron with micrometric resolutionContra: 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 Emc thr. effect;
reconstruction of the charmed hadron kinematics (direction and momentum) fragmentation studies are possible
p/p = 0.035 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 = 60 mrad @ 10 GeV
E ~ 27 GeV
Air-core magnetActive target
Muonspectrometer
CalorimeterWB Neutrino beam
:: : : e : : e
1.00 :: 0.06 :: 0.017 :: 0.007
•nuclear emulsion target (770kg)•scintillating fiber trackers
CHORUS experimentCHORUS experiment(CERN Hybrid Oscillation Research ApparatUS)
CalorimeterAir-core magnet
beamMuon spectrometer
Emulsion target
Interaction vertex
Electronic detector
prediction
All track segments infiducial volume
After a low momentumtracks rejection(P > 100 MeV) and numberof segments 2
After rejection ofpassing-through tracks
Tracks confirmedby electronic detectors
Nuclear emulsion analysis
~ 100 m
Visual inspection to confirm the event
Charm production by interactions in emulsions
Phys. Lett. B 206 (1988) 375-379
E531 (Fermilab, E531 (Fermilab,
Nagoya)Nagoya)
122 charm events in emulsion
only measurement of D0 : D+ : Ds+ :
c+
(no anti-neutrino charm events)
B(c) crucial for other experiments
CHORUS (CERN CHORUS (CERN
WANF)WANF)Just got the final statistics :
2059 charm events!
The analysis is in progress!
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+, Ds dominated sample
Analysis has been performed applying two different
selections
Phys. Lett. B. 555 (2003) 156-166 based on 50414 CC
D : Λc : Ds = 6 : 3 : 1(E531 result)
Λc
D
Ds
Measurement of c production
Short flight decay (A):
Daughter track: Distance to the muon 5 m to 30 m1614 events were selected for visual inspection
Long flight decay (B):
Parent track: distance to the muon < 5 mDistance between daughter and parent 5 m to 30 m586 events were selected for visual inspection
After flight length cut:
A: 40 m < FL < 400 mB: 400 m < FL < 2400 m
1 prong62133
3 prong66195
Combining short (A) and long (B) decay search and taking into account efficiencies and background:
c = 861 ± 198 (stat) ± 98 (syst) (QE)+140-54
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
Measurement of c production
Quasi-elastic charm productionPhys. 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)
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
Measurement of D0 productionPhys. Lett. B. 527 (2002) 173 based on ~25% of statistics
NOW full sample: 95450 CC eventsCandidate selection
Primary track matched to detector muonDaughter track matched to detector track3~13 m < I.P. wrt. 1ry vtx < 400 m
Selection efficienciesV2 : (56.3 ± 0.5) x 10-2
V4 : (74.2 ± 0.9) x 10-2
V2 : 841V4 : 230
Confirmed D0 sample
V2 : 1428 ± 49V4 : 310 ± 20
BG subtracted, efficiency correctedD0 V4D0 V2
= (22.7 ± 1.8) x 10-2
Measurement of D0 production
Fully neutral D0 decay mode:
BR4/BR2 measuredBR4 = 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
Preliminar
y
Number of selected events 1055
90.6% 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 (D0 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!
Associated charm production in CC
Charged-current
Gluon bremsstrahlungCurrently 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.
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
Event Event 7789107177891071
E=35.4 GeVE=35.4 GeV P=-13.5 P=-13.5 GeV/cGeV/c
Pl 7Pl 7 Pl 6 Pl 6 pl 4pl 4
Evis=48.9 Evis=48.9 GeVGeV
Associated charm production in CC
11ry@pl7ry@pl7
NNs=6, Nh=1s=6, Nh=1
V2 @V2 @pl 6pl 6
fl= 257.0fl= 257.0mm
kink @pl 4kink @pl 4
fl= 2271.6 fl= 2271.6 mm
= 67.4mra= 67.4mradd
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 26568 NC have been
found and the cross-section measurement will be finalised by the end of this year
Production rate 1.3 x 10-3 normalised to CC
+3.1-1.1
Indirect search performed by NuTeV:
Production rate (2.6±1.6)x10-3 normalised to CC at 154 GeV
mc = (1.40 ±0.26) GeV, in agreement with other measurements
+0.83-0.36
(A. Alton et al., Phys. Rev. D64 (2001) 539)
Gluon bremsstrahlung
+
Associated charm production in NC
N+ = 2704
N- = 93768= 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 %+ 1.4- 1.0
fC-
fCo= 2.4 + 1.5
- 1.0(stat)
Estimated background = 2.7mainly due to the muon wrong sign identification
Preliminar
y
Charm production in antineutrino interactions
Charm production in antineutrino interactions
Charm production rate as a function of energy
Theoretical prediction
Analyses in progress
),( 2)(2
2
4 )(T
hch hdyd
cXNd pzDfTdydzdpd
CXNd
- 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 +
ConclusionCharm physics in interactions very interesting
So far, from a subsample of charm data in CHORUS we have measured:
Λc production
QE charm production
D0 production
CC associate charm production
BR
Diffractive Ds* production
Phys. Lett. B. 555 (2003) 156Phys. Lett. B. 575 (2003) 198Phys. Lett. B. 527 (2002) 173Phys. Lett. B. 539 (2002) 188Phys. Lett. B. 549 (2002) 48Phys. Lett. B. 435 (1998) 458
Many analyses are still in progressNew results will be available within 2004
Backup slides
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 eventsResults should be available in a couple of months
Fragmentation functionsThe z distribution can be parametrized as follows
2
2 1
11
1
121
)( z
zz
zz
zz
NzDc
c
c
Collins-SpillerJ.Phys. G 11 (1985) 1289
2
11
1
)(
zzz
NzD
p
p Peterson et al.
Phys.Rev. D 27 (1983) 105
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
Determination of p and c
p c
E531 0.0760.014 ---
NOMAD 0.0750.028 0.036 0.130.08 0.11
CDHS 0.02-0.14 ---
CCFR 0.220.05 0.880.12
CHARMII 0.0720.017 ---
NuTeV --- 2.070.31
All the above numbers have been obtained with a LO analysis
At e+e- exps s1/210 GeV P0.16(D+)0.27(c)O.Biebel, P.Nason, B.R.Webber hep-ph/0109282
pT2 distribution of
charmed particles
The transverse momentum of charmed particles wrt thedirection of the hadronic system is usually parametrized as
2
2Tbp
T
edp
dN
Available statistics in exp• E531 122 eventsPhys. Lett. B 206 (1988) 380-384• NOMAD 47 eventsPhys. Lett. B 526 (2002) 278-286
E531Phys.Lett.B 206 (1988)
380
NOMADPhys.Lett.B 526 (2002)
278
b 3.250.37 (GeV/c)-2 3.38 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 = 1.10.3 (GeV/c)-2
M.Aguilar-Benitez et al., Phys. Lett B 123 (1983) 103
pT2 distribution of
charmed particles
The strange sea distribution
No new results Both at LO and NLO ~0.5 At LO is not zero =2.50.7, while it is at
NLO =’=-0.460.420.360.650.17
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
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) BR(C ) (In the following 9.31±0.95% for E>30 GeV)
Output parameters Charm mass: mc
Element of the CKM matrix: Vcd 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
Vcd determinationAt LO order severalexperiments extracted
)006.0224.0( cdV
At NLO only CCFR analysis
)015.0239.0( cdV
As expected LO and NLO give consistent results!
)225.0(
)014.0224.0(013.0011.0
cd
cd
V
VPrevious estimates
mc determination
At LO order severalexperiments extractedthe charm-quark mass
GeV )13.040.1( cm
At NLO only CCFR analysis
GeV )19.070.1( cmincludes also kinematic effects associatedwith heavy quark productions
GeV )74.1( 13.018.0
cmg fusion
E691 Phys. ReV. Lett. 65 (1990) 2503
determinationAt LO order several experiments extracted
)031.0405.0(
At NLO only CCFR analysis
)036.0484.0( LO and NLO give consistent results at 1.2
A fit to all available data (N,eN,N) gives
)045.0714.0(
)044.0667.0(
Barone,Pascaud,Zomer E.Phys.J.C 12, 243
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)
VVudud
0.1 %0.1 % nuclear beta decay
The CKM matrix
VVcbcb 5 %5 %
Be3 decay
VVcscs 15 %15 %
De3 decay
VVubub 25 %25 %
b u l
VVusus 1 %1 %
Ke3 decay
VVcdcd 7 %7 %
charm production
VVtdtd VVtsts
VVtbtb 30 %30 %
t b l
Review of particle physics, 98 edition
d’d’
s’s’
b’b’
dd
ss
bb
==