Measurement of charm production and decay properties
by CHORUS
Francesco Di CapuaUniversity of Napoli and INFN
Italy
GRAVITY, ASTROPHYSICS AND STRINGS AT THE BLACK SEAkiten – Bulgaria June 2005
Outline
The CHORUS experiment• The CHORUS detector
• Automatic analysis of nuclear emulsions
Physics motivation• What do we measure and why it is interesting
Results on charm analysis• D0 production in neutrino charged current interaction• D*+ production in neutrino charged current interaction • Fragmentation properties of charmed particles• Anti-neutrino charm production
• Muonic branching ratio B of charmed particles (preliminary results)
• Associated charm production (CC and NC)• Dimuon analysis in the calorimeterConclusions and perspectives
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
“Charm Physics with neutrinos”, G.De Lellis, P.Migliozzi, P.Santorelli , Phys. Rept.399:227-320,2004
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:
CHORUS (CERN WANF)CHORUS (CERN WANF) 8919 -+ , 430 +- events To be published
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
The CHORUS charged current data sample and charm
subsampleLocated CC events 93807Selected for visual
inspection2752
C1 452
C3 491
C5 22
V2 819
V4 226
V6 3
Total charm candidates
2013
Measurement of D0 production and of decay branching fractions in -N scattering
Phys. Lett. B. 613 (2005) 105
Candidate selectionPrimary track matched to el. detector muonDaughter track matched to el. detector track3~13 m < I.P. wrt. 1ry vtx < 400 m
After BG subtraction and efficiency correction:
= 0.207 ± 0.016 ± 0.004B(D0 V4)B(D0 V2)
The relative rate is:
(D0)/(CC)=0.0269 ± 0.0018 ± 0.0013
Assuming B(D0 V4)=0.1339±0.0061 (PDG);
D0 topological branching fractions
INCLUSIVE measurement in CHORUS:
B(D0 V2) = 0.647 ± 0.049 ± 0.031
B(D0 V6) = (1.2 ± 0.2)x10-3+1.3- 0.9
B(D0 V2)B(D0 V4)
B(D0V0)=1- B(D0V4)[1+ + ]B(D0 V6)B(D0 V4)
B(D0V0) = 0.218±0.049±0.036 very important for B measurement!!!
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
To be compared with:
Energy dependence of the cross section ratio and charm mass
CHORUS data
E531 data
Fit to a theoretical model
mc=(1.42 0.08(stat) 0.04(syst)) 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)
Accepted by Phys. Lett. B. - CERN-PH-EP-2005-010.
Looking for events in the channel: D*+ D0 +
D0 fl>100m
<60 mrad
0.4 <p(+)<4 GeV/c10.< pT<50. MeV/c
Number of candidates
Background prediction(1) Expected shape of the candidates normalized
to the observed events;(2-3-4) shape normalized to the total number of D0
and C+ respectively;
D*+ signal in the D0 h+
sample
No signal in the D0h-
sample as expected
No signal in the C+h-
sample as expected
No signal in the C+h+
sample as expected
D0
D*+
Measurement of D*+ production in CC -N scattering
Measurement of D*+ production in CC -N scattering
Assuming B(D*+ D0 +)=0.677±0.005 (PDG) the relative rate is:
(D*+)/(D0)=0.38 ± 0.09(stat) ± 0.05(syst)
assuming that the D*+ and D*0 production rate are equal and recalling that D*0 always decays into D0:
(D* D0)/(D0)=0.63 ± 0.17By using the measure of (D0)/(CC) made in CHORUS:
(D*+)/(CC)=(1.02 ± 0.25(stat) ± 0.15 (syst))%To be compared
with:At similar neutrino energy beam:
•NOMAD (D*+)/(CC)=(0.79 ± 0.17(stat) ± 0.10 (syst))%•BEBC (D*+)/(CC)=(1.22 ± 0.25)%
At the higher energy of the Tevatron beam: • (D*+)/(CC)=(5.6 ± 1.8)%
Defining fV=V/(P+V) , V= vector production and P pseudoscalar production of D meson
fV=0.51 ± 0.18Consistent within the error: with V:P=3:1, as expected from simple spin arguments; with measurements in e+e-, N, N experiments.
CHORUS data Prediction
simulation
The momentum of D0 can be inferred by the geometrical average () of the angle of the decay daughters with respect to the direction of the D0
(as described in S.Petrera, G.Romano, Nucl.Instrum. And Meth.174 (1980) 61 )
Measurement of fragmentation properties of charmed particle production in CC neutrino interaction
Phys. Lett. B 604 (2004) 145
Momentum distribution of D0’s produced inclusively in CHORUS
),( 2)(2
2
4 )(T
hch hdyd
cXNd pzDfTdydzdpd
CXNd
From charm quark to charmed hadrons
Defined z as the ratio of the energy of the charmed particle E D and the energy transfer to the hadronic system zE D / we measure <z> = 0.63 ± 0.03(stat) ± 0.01(syst)
2
2 1
11
1
121
)( z
zz
zz
zz
NzDc
c
c
Collins-Spiller
J.Phys. G 11 (1985) 1289
2
11
1
)(
zzz
NzD
p
p Peterson et al.Phys.Rev. D 27 (1983) 105
Z distributionCHORUS dataPetersonCollins-Spiller
Fit to Collins-Spiller distribution:
cs = 0.21 ± 0.04 +0.05 -0.04
Fit to Peterson distribution:
P = 0.108 ± 0.017 ± 0.013
To be compared with:
To compare results:If zs = E D / string energyS
P = 0.083 ± 0.013 ± 0.010If zQ = P charmed particle / P charm quark
QP = 0.059 ± 0.010 ± 0.008
Fragmentation properties
XF is defined as: XF= 2 pLD – ED
W
pLD longitudinal momentum of D0
ED energy of D0
W invariant mass
From the distribution we mesure <XF>:
<XF >=0.38 ± 0.04(stat) ± 0.03(syst)
To be compared with NOMAD: <XF >= 0.47 ± 0.05
forward-backward asymmetry:
<A>=0.79 ± 0.14(stat) ± 0.05(syst)
To be compared with E531: <A> = 0.620 ± 0.092
From the distribution production angle out of the lepton plane we mesure:
<tanout>=0.030 ± 0.002
Analysis based on the full statistics
B muonic branching ratio of charmed particlesPrelim
inar
yB = (7.3 0.8(stat))
%The results takes into account the new
CHORUS measurement of B(D0 V0)22%
B = (8.3 1.6(stat))%
Considering only events with visible energy above 30 GeV
B x |Vcd|2LO=(0.474
0.027)x10-2
(CDHS,CHARM II, CCFR average value)
|Vcd|
LO=(0.2390.046)
B x |Vcd|2NLO=(0.534
0.046)x10-2
(CCFR)
|Vcd|
NLO=(0.2540.066)To be compared with:
0.221< |Vcd|<0.227 at 90% CL Obtained imposing CKM unitarity and only 3 generations
Phys. Lett. B. 604 (2004) 11-21
Measurement of charm production in antineutrino charged-current
interactions
Strategy: look for the + generated in the antienutrino CC interaction
After reconstruction cut and charm topology selection
TOT 32
(N +cX)(N +X)
= 5.0 ±0.7%
+ 1.4- 0.9
Theoretical prediction obtained from leading order calculation with mc=1.31 GeV/c2
Derived from di-lepton data
(G.de Lellis et al., J.Phys.G28 (2002), 713)
CHORUS DATA
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 93807 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 p 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
Chorus dimuon analysis result (calo)
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)
Nleading -
=8910180 Nleading + = 43060
Chorus dimuon analysis result (calo)
MC prediction obtained using fitted values of parameters mc, k, P, B
dimuon cross-section relative to CC events
data
Conclusion
Interesting charm physics results from CHORUS thanks to: high beam flux; Nuclear emulsion target (0.8t); Automatic emulsion analysis
D*+ production
D0 production
Antineutrino charm production
Fragmentation properties
QE charm production
Λc production
BR CC associate charm production
D0 production
Diffractive Ds* production
Accepted by Phys. Lett. B. Phys. Lett. B. 613 (2005) 105Phys. Lett. B. 604 (2004) 11Phys. Lett. B. 604 (2004) 145 Phys. Lett. B. 575 (2003) 198Phys. Lett. B. 555 (2003) 156Phys. Lett. B. 549 (2002) 48Phys. Lett. B. 539 (2002) 188 Phys. Lett. B. 527 (2002) 173 Phys. Lett. B. 435 (1998) 458
Other analyses in progress
Measured so far:
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
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
BR(C ) 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
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
==