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Charm production and its impact on
future neutrino experiments
Francesco Di Capua – INFN Napoli
NuFact - Valencia
3/07/08
 DIS charm production

Beam
knowledge
|Vcd|2,|Vcs|2
d,s
-

Charm fragmentation
fD0 ; fD+ ; fDs ; fc
z = pD/pc, pT2
c
Quark density functions,
strange sea ()
Production from d(anti-d) quarks Cabibbo suppressed
 large s contribution: 50% in  and 90% in anti-

,h
h
Ehad
pQCD LO CC charm
production
• Production from d(anti-d) quarks Cabibbo suppressed
• large s contribution: 50% in n and 90% in anti-n
d 4 (  N   CX )
ddydzdp
2
T

d 2 (  N    cX )
ddy
 h f h  Dch ( z, pT2 )
=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,c) in 
charm production
D probability for a charm quark to fragment into a charmed hadron
h with a given z and p2T
Intrinsic interest
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
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
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  ) ~ 10%
and on the uncertainty on it
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mc thr. effect;
reconstruction of the charmed hadron
kinematics (direction and momentum)
fragmentation studies are possible
CHORUS experiment
(CERN Hybrid Oscillation Research ApparatUS)
Active target
• nuclear emulsion target (770kg)
• scintillating fiber trackers

WB Neutrino beam
 :
e
p/p = 0.035 p (GeV/c)  0.22
Muon spectrometer
E ~ 27 GeV
 :
Air-core magnet
: e
1.00 : 0.06 : 0.017 : 0.007
Calorimeter
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
Air-core magnet
Calorimeter
 beam
Muon spectrometer

Emulsion target
Electronic
detector
prediction
Interaction vertex
Nuclear emulsion analysis
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
Visual inspection to confirm the event
~ 100 m
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
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)
(sp as measured in CHORUS, see
next slides)
The relative rate is:
(D0)/(CC)=0.0269 ± 0.0018 ± 0.0013
At 27 GeV average
neutrino beam
Measurement of D*+ production in
CC -N scattering


D0
fl>100m
<60 mrad


D*+
D0
Assuming B(D*+  D0 p+)=0.677±0.005 (PDG) the relative rate is:
By using the measure of (D0)/(CC) made in CHORUS:
(D*+)/(CC)=(1.02 ± 0.25(stat) ± 0.15 (syst))%
K
p+
p+
(D*+)/(D0)=0.38 ± 0.09(stat) ± 0.05(syst)
p+
0.4 <p(p+)<4 GeV/c
10.< pT<50. MeV/c
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 / 
d 4 (  N   CX )
ddydzdpT2

d 2 (  N  cX )

ddy
 1  z  c 2  z  
+


z
1

z
 1+ z2
Dc ( z )  N 
2
c 
1

1  

z 1 z 


Dp ( z) 

h
2
f

D
(
z
,
p
h h c
T)
Collins-Spiller
J.Phys. G 11 (1985) 1289
N
p 

1
z
1  z  1  z  



2
Peterson et al.
Phys.Rev. D 27 (1983) 105
Measurement of fragmentation properties of charmed
particle production in CC neutrino interaction
Momentum distribution of D0’s
produced inclusively in CHORUS
CHORUS data
Z distribution
CHORUS data
Peterson
Collins-Spiller
Prediction
<z> = 0.63 ± 0.03(stat) ± 0.01(syst)
Fit to Collins-Spiller distribution:
+0.05
cs = 0.21 -0.04 ± 0.04
Fit to Peterson distribution:
P = 0.083 ± 0.013 ± 0.010
Measurement of inclusive charm production
CHORUS
E531
(Charm)/(CC)=(5.9±0.4)%
At 27 GeV average
neutrino beam
Charmed fractions anf inclusive
topological branching ratios
fD0 = (45.23.8)%
fD+ =
(28.94.3)%
fc+ =
(16.4=
4.2)%
f
(9.45.4)%
Ds+
Likelihood fit to flight length over
momentum distribution to obtain the
charm production fractions
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.)
B muonic branching ratio of
charmed particles
B (All Charm)= (7.30.8(stat))%
B (D0)= (6.51.2(stat))%
Measurement of charm production in
antineutrino charged-current interactions
( N  +cX)
( N  +X)
TOT
1.4
= 5.0 +- 0.9
±0.7%
32
CHORUS DATA
Derived from di-lepton data
Theoretical prediction obtained
from leading order calculation
with mc=1.31 GeV/c2
Associated charm production
boson gluon fusion
gluon bremsstrahlung
3 observed events in NC sample
topologies
C1+V2
V2+V2
C3+V4
Background= 0.18±0.06
+2.9

(cc)/(NC)=(3.6 -2.4 )x10-3
Charm in present and future neutrino
experiments
First Charm event in OPERA data!!!
kink=0.204 rad
P=3.9+1.7-0.9 GeV
Shower
Applyng charm production
measurement to silver channel
background predictions
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
Charm cross-section at Neutrino
Factory energies
neutrino charm
production
Anti-neutrino
charm production
(eN->e- Charm X)/(CC)=(5.85±0.36)%
(eN->e-C+X)/(CC)=(3.12±0.20)%
_
(N->+ Charm X)/(CC)=(4.89±1.72)%
Silver channel signal topology in
Emulsion Cloud Chamber detector
(Opera-like)
1 mm
e
-


Pb
Emulsion layers
Muon spectrometers:
miss ( 0 . 1 0 . 3 )%
charge
p/p < 20% for p<50 GeV
Charge current interactions x
Oscillation probability
+
N events
(L=732Km)
N. events
(L=3000Km)
• P=0 muon polarization
e
248
248
• E= 50 GeV
ee
1476332
87497
• 2x1020 useful muons/year
x 5 year
e
 

173
147
874240
46852
101
63
5178
4849
750066
44450
110
50
86
73

1720759
92219
e
189
153

10357
9698
13
=5º =90º
1 Kton detector


 
e
 


-
 
e


 

e
e
 
e
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
Charm background(1)
1 mm
• + from primary  CC interaction not
-
_

identified
C-
• muonic decay of charm fake  decay
+
Pb
Emulsion layers
 21.1±7.4 at 732 Km
(1.1+0.5 at 3000Km)
1 mm
+
e
• electron from primary e CC interaction
not identified
C+
e-
Pb
• muonic decay of charm with wrong
charge assignment fake  decay
Emulsion layers
 2.80 at 732 Km
(0.16 at 3000Km)
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)
Kinematical cuts
Invariant Mass hadronic system
-

neutrino
direction
Charm
Charm

Signal/background energy dependence
Silver
channel signal
732 Km
Charm background
hadrons
5 Kton
_
_
 oscillation
3000 Km
D. Autiero et al. Eur. Phys. J. C33 (2004) 243
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
Backup slides
Chorus dimuon analysis result (calo)
Nleading - =8910180
Nleading + = 43060
mc

 P
 B

=
=
=
=
1.26  0.16 (stat)  0.09 (syst)
0.33  0.05 (stat)  0.05 (syst)
0.065  0.005 (stat)  0.009 (syst)
0.096  0.004(stat)  0.008 (syst)
D0 topological branching fractions
INCLUSIVE measurement in CHORUS:
B(D0  V2) = 0.647 ± 0.049 ± 0.031
-3
B(D0  V6) = (1.2 +1.3
- 0.9 ± 0.2)x10
B(D0V0)=1-
B(D0V4)[1+
B(D0  V2) B(D0  V6)
+
]
B(D0  V4) B(D0  V4)
B(D0V0) = 0.218±0.049±0.036
very important for B measurement!!!
After BG subtraction and efficiency correction:
B(D0  V4)
= 0.207 ± 0.016 ± 0.004
B(D0  V2)
B(D0  V0) 5%
(PDG) Sum over all exclusive channel for
which measurement exist
B(D0  V2) = 0.485 ± 0.020
(PDG) Sum over all exclusive channel for
which measurement exist
B(D0  V6) = (0.59 ± 0.12)x10 -3
(FOCUS coll.) sum of all exclusive
measured channel