charmed hadrons from fragmentation and b decays
DESCRIPTION
Charmed Hadrons from Fragmentation and B Decays. Sören Lange Johann Wolfgang Goethe-Universität Frankfurt * for the BELLE Collaboration CHARM 2006, June 5-7, 2006, Beijing. * Present Address: Justus Liebig Universität Gießen. KEK-B Asymmetric Accelerator. E(e – )=8 GeV, E(e + )=3.5 GeV. - PowerPoint PPT PresentationTRANSCRIPT
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Charmed Hadrons from Fragmentation and B Decays
Sören LangeJohann Wolfgang Goethe-Universität Frankfurt*
for the BELLE Collaboration
CHARM 2006, June 5-7, 2006, Beijing
*Present Address: Justus Liebig Universität Gießen
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 2
KEK-B Asymmetric Accelerator
E(e–)=8 GeV, E(e+)=3.5 GeV
Tsukuba, Japan
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 3
Charm Production at BELLE
integrated luminosity1/fb recorded per day(106 events for =1 nb)
~90% of time on-resonance: s=10.58 GeV continuum + Y(4S) Y(4S) decays 99% toBB ~99% of B mesons
decay into charm particles ~10% of time off-resonance:
s=10.52 GeV only continuum (c, off-resonance)~1.3 nb
is as high as (b, on-resonance)~1.2 nb
10.58 10.52
~3.0 nb
~4.2 nb
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 4
D from B decay direct D production (continuum)
On- vs. Off-Resonance: Charm production
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 5
Motivation
• fragmentation as a QCD process• theoretical aspect:
• how does a quark transform into a hadron ?• from emission of one gluon to emission of n gluons • how do the infinite number of gluons self-organize ?• how do all the spins align to exactly spin-0 or spin-1 ?• are there differences between mesons and baryons ?
(formfactor)• understand the dynamics
(as a function of quark momentum ?)• non-perturbative effects ?
• practical aspect:• improve Monte-Carlo• B meson fragmentation measured well (LEP, SLD), but D meson not • comparison to PYTHIA 6.2• important for other analyses of direct charm production
D**, DsJ etc.
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 6
An Example of Calculating an QCD Process in e+e–
Ratio of di-quark to di-muon events Perturbative Expansion in S
+ higher order
LO NLO NNLO
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 7
Fragmentation
parton cascade hadronization
c
relevant variable
momentum fraction
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 8
Data Set
on-resonance 87.7/fb off-resonance 15.0/fb Monte-Carlo 217.0/fb
QQ98 event generator+ Peterson model fragmentation+ PYTHIA 6.2+ GEANT 3.21
Phys. Rev. D73(2006)032002
hep-ex/0506068
decay modes used in reconstruction
efficiency and misidentification probability
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 9
History of Charm Fragmentation Data
fragmentation data from e+e- cc, s=10.52 GeV before 2000
ARGUS, 31.4/pbZ. Phys. C52 (1991) 353CLEO, 35.8/pb Phys. Rev. D37(1988)1719nowadays equivalent dataare recorded in ~50 min
after 2000CLEO, D,D*, 8.9/fbPhys. Rev. D70(2004)112001CLEO, Ds,Ds*, 4.7/fbPhys. Rev. D62(2000)072003
BELLE 2005: integrated luminosity 10 xP bin size 1/3 baryon fragmentation c precision in high xP region
Ds
x+
Ds
xP
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 10
On-resonance vs. Off-resonance
Do D*
Ds c
B decay
continuum
p(Do)=2 GeV/c
momentum resolution << XP bin width: no need for deconvolution
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 11
Mass distributions
0.68<xP<0.70(near peak of fragmentationfunction off-resonance)
for full xP rangeincreasing preceeding statistics by factor 10
Ds
Do
c
D*
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 12
Average number of charmed hadrons per B decay
from integrated yield on-resonance minus off-resonance
~1-2 deviation due to D** feeddown
error of branching ratio and luminosity
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 13
Fragmentation Functions
• vs. momentum fraction x• continuum• high precision
up to x=1• estimated
syst. errorfrom D** feeddowne.g. broad p-wave Do*(2308)D´1(2427)is 13%
xP
xP xP
Do
Ds c
D*
xP
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 14
QCD Fragmentation Models
Term (1-z) from kinematics:
# not available in PYTHIA:re-weighting =store z and pand re-calculate ansatz
#
#
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 15
Comparison to QCD Fragmentation Models
deviationsin high xregion
Example: Do fragmentation function
“fit” MC vs. data:define fragmentation ansatz(re-weighting if necessary)+ full parton shower+ full detector resolution
e.g.
Lund string fragmentation
PYTHIA default a = 0.30“fit” vs. data a = 0.68
xP
xP
xP
xP
xP
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 16
Which fragmentation model fits best ?
d.o.f. = #bins - #parameters
Bowler and Lund appear favoured ~
similar trend as for B fragmentatione.g. SLD, Phys. Rev. D 65 (2002)092006
2 depends on size of data and re-weighted MConly relative comparison
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 17
Ratio of D*/D Spin-1/Spin-0 Fragmentation
naïve spin countingprobability for spin-1
PV=0.75
data (off-resonance)
MC Peterson
MC Bowler PV=0.75
MC Bowler PV=0.59
deviations in high x region
PV<0.75 predicted by theorybecause m(D*)m(D)
see Braaten et al.Phys. Rev. D51(1995)4819
in PYTHIAPV = PARJ(13)
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 18
Ratio of c/D Baryon/Meson Fragmentation
deviations in high x region
data (off-resonance)
MC Peterson
MC Bowler PV=0.75
MC Bowler PV=0.59
total cross section
(c)/(D+D*+Ds) =8.10.30.2%
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 19
What is remarkable in the high x region ?
• limit x=1: quark and meson have identical momentum• pointlike formfactor• QCD self-organization of infinite number of partons• where is the energy coming from ?
1 valence c quark
1 valence u,d quark
N= sea quarks (u,d,s,c)
N= sea gluons
1 hadron
1 quark ? =
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 20
Is there a Non-Perturbative Contribution ?
preliminary data were used by theory: Cacciari, Nason, Oleari hep-ph/0510032, JHEP0604(2006)6
high x = soft gluons xgluon~(1-xP) higher order in s (e.g. NNNLO) but also non-perturbative (s high)
Ansatz: calculate fragmentation function
perturbative in NLO take BELLE and CLEO data and fit
perturbative + non-pertubative (motivated by QCD sum-rules)
determine non-perturbative fraction
FIT
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 21
Is there a Non-Perturbative Contribution ?
result: ~25% is non-perturbative, except Do
why ?
decay D* Do is close to thresholdidentical velocitywe „see“ transition between the formfactors(gluon cloud transition from spin-1 to spin-0)
Do highly non-perturbative ~60%
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 22
Cross check: limit x=1 on two sides
exclusive 2-body e+e–DD(*)
consistent withBelle, Phys. Rev. D70(2004)071101 = 0.550.030.05 pb (D*+D–) = 0.620.030.06 pb (D*+D*–)
e+e–D*+D–
e+e–D*+D–, e+e–D*+D*–
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 23
Summary
Charm Fragmentation Functions were measured at s10.6 GeV with a data set of 87.7/fb + 15.0/fb
Bowler and Lund models are favoured Default PYTHIA parameters seem not suited for charm fragmentation,
best fit:
Evidence for non-perturbative effects at high x1 All results posted in Durham Reaction Database
http://durpdg.dur.ac.uk/cgi-bin/hepdata/testreac/11582/FULL/q
Phys. Rev. D73(2006)032002
hep-ex/0506068
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 24
Additional Slides
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 25
Radiation of a gluon
•
PYTHIA 6.2 manualthis is origin of (1-z) terms in fragmentation function
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 26
Non-uniformity in on-resonance xP distribution
• peak at xP=0.3-0.35 is due to two-bodyBD(*)DBR1%
• not seen in Ds
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 27
Estimate of contribution from D**
• difference of primary Do and D+
(after D* correction)• difference ~13%
must be compared to uncertainty in branching ratio ~6%
Do
D+
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 28
Ratio vs. primary D „primary“ = Do corrected for D* decay
Ds enhanced in B decay c enhanced in continuum
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 29
Total Cross Sections
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 30
neutral vs. charged
strange vs. light quark baryon vs. meson
Where in xP does the Peterson model fail ? Ratios.
spin1 vs. spin 0
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 31
CDCTrack Finder+ dE/dxHe/C2H5
/ KL detection14 layer RPC+Fe
Aerogel Cherenkov n=1.015~1.030
SVD
TOF
Superconducting Solenoid B=1.5T
The Belle Detector
8 GeV e -
3.5 GeV e+EM CalorimeterCsI(Tl) 16X0
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 32
Title
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 35
D**
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 36
D**
• assume heavy quark symmetrymcharm
• light quark couples to L first
• thenL=1 states are 2 doublets
jq=1/2broad (decay by S wave)
jq=3/2narrow (decay by D wave)
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 37
D**
• BELLE observes the two broad D** (jq=1/2) statesPhys. Rev. D69(2004)11200265.4 Mill. BB
• mass widthD*0(J=0) 2308171528 MeV 276211860 MeV D´1(J=1) 2427262015 MeV 384+107
-752470 MeV
D2* can decay to D and D*
D+K+
D*+Do+
DoK+
DoK++
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 38
History of Charm Fragmentation Data
fragmentation data from e+e- cc, s=10.5 GeV before 2000
ARGUS, 31.4/pbZ. Phys. C52 (1991) 353
CLEO, 35.8/pb Phys. Rev. D37(1988)1719
nowadays equivalent dataare recorded in ~50 min
D* Ds
D+ c
x+ x+
x+ x+
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 39
Why is Do more non-perturbative than D+ ?
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Sören Lange (Frankfurt Univ.) BELLE Charm Fragmentation June 6, 2006 40
Fragmentation Functions in PYTHIA 6.2