Doubly Heavy Baryons
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Doubly Heavy Baryons
Likhoded A.K.IHEP, Protvino, Russia
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Contents
Introduction Mass spectrum Decays Production Conclusion
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Double-heavy BaryonsThe only experimental information about DHB
gives SELEX collaboration:
There are several questions to SELEX results:1) Lifetime2) Cross sections
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Theoretical information about DHB:
1) Mass spectrum Potential Models (two step calculation) QCD Sum Rules QCD Effective field theory Lattice QCD
2) Life time and leading decay modes OPE Exclusive decays in NRQCD sum rules
3) Cross section Perturbative QCD + nonrelativistc ME
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Mass spectrum
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Potential models
Heavy Quark Symmetry
q
Q 1
QCD
QCDQm
Diquark approximationDiquark approximation
Simplification in (QQ’q) dnamics in Born-Oppenheimer or adiabatic approximations:
VQ,VQ’ << Vq
Two step calculation in Potential Model
Heavy Quark-Diquark Symmetry
q
1
QCD
QCD2 vmvmm QQQ
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Potential modelsThree-body problemThree-body problem
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Ground states mass predictions
[20]
[20]
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PM predictions for ground state cc-diquark 3c are
+
* +
3478MeV, 1S1S 1/2
3610MeV, 1S1S 3/2
cc
cc
M
M
~ 40MeVM
[V. Kiselev, A.Onishchenko, A.L.]
Metastable state (2P1S) ½-(3702) have L=1, S=0 for diquark.
Transitions to the ground state (L=0, S=1) requires simultaneous change of orbital momentum and spin.
PM predictions
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SR and Lattice QCD
NRQCD Sum RulesM(cc)=3.470.05 GeV
M(bc)=6.800.05 GeV
M(bb)=10.070.09 GeV
Lattice QCDM(cc)=3.600.02 GeV
[V. Kiselev, A.Onishchenko, A.L.]
[R.Lewis et al]
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Spin-dependent corrections
For heavy diquark:
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Spin-dependent corrections
Taking into account interaction with the light quark gives (S=Sd+Sl )
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cc spectrum
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bb spectrum
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Hyperfine mass splittings
[N.Brambilla et al]
[R.Lewis et al]
[V. Kiselev, A.Onishchenko, A.L.]
Hyperfine splitting for cc: PM: =(130±30) MeV QCDEFT =(120±40) MeV Lat.QCD =76.6 MeV
[20]
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Summary
1) Ground state mass predictions depend on the model (~200 MeV)
2) Uncertainties in PM are mainly connected with different value of heavy quark masses.
3) The lightest S- and P-wave exitations of the diquark are quasistationar.
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Lifetimes
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OPE
(*)
(*)
(*) (*)1
2cc
cc
cc ccMT
4Im 0eff effd x T H x HT
Where
is standard hamiltonian of weak c-quark transitions
1 1
* . .2 2
Feff uq cq
GH V V C O C O h c
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OPE
In decays of heavy quarks released energy is significant, so it is possible to expand Heff in the series of local operators suppressed by inverse powers of heavy quark mass
spectator
Pauli interference
EW scattering
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OPEFor example, for semileptonic decay mode
2 52
3
2
(*) (*) (*) (*)2
,192
, ,2
F cc cs
c cc v v cc c cc v v cc c c cc
G mV
iDK v c c v G v c G c v E G K
m
where
In numerical estimates we have used following parameter values:
mc=1.6 GeV ms=0.45 GeV mq=0.3 GeV
M(++cc)=M(+
cc)=3.56 GeV MHF=0.1 GeV
|diq(0)| = 0.17 GeV3/2
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OPE
0.43ps, 0.12pscc cc
16%, 4%,cc ccBr l X Br l X
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OPE
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Exclusive decays in NRQCD sum rules
Semileptonic DHB decaysHeavy Quark Spin Symmetry makes possible to describe
semileptonic decays close to zero-recoil point
HQSS put constraints on SL FF
2 2 2 2b c b cq m m m m
2 2 2
12
b c l
b c
m m m
m m
'v v
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Exclusive decays in NRQCD sum rules
Quark loop for 3-point correlator in the baryon decay
For 1/21/2 transition there are 6 form-factors:
1 2 3 5 1 2 3V I V F V A I A F A
F F I I F Ip J p u p G v G v G G v G v G u p
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Exclusive decays in NRQCD sum rules
These 6 FF are independent. However, in NRQCD in LO for small recoil it is possible to obtain following relations:
1 2 3 1,V V V IW A IWG G G G
Only 2 FF are not suppressed by heavy quark mass:
1 1V A IWG G
Vector current conversation requires
1 1IW
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NRQCD Sum RulesIn the case of zero recoil IW(1) is determined from Borell
transfromation
For calculation of exclusive widths one can adopt pole model
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NRQCD Sum Rules
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Production of cc-baryons
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In all papers it was assumed, that
This is quite reasonable assumption in the framework of NRQCD, where, for example, octet states transforms to heavy quarkonium. Analogously, we have to assume, that dissociation of (cc)3 into DD is small.
3cc cc
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Similar to quarkonium production cross sections factorizes into hard (pertubative) and soft (non-pertubative) parts.
In both cases second part is described by wave function of bound state at origin.
That’s why it is reasonable to compare, for example, J/cc and cc final states. In this case only one uncertainty remains – the of squared wave functions at origin.
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Fragmentation mechanism
e.g.
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In e+e-, where FM dominates, expected cross sections at is
10.6GeVs
5~ 7 10cc
cc
2( ) ~ 7 10 pbcc
At SuperB, where expected luminocity is L=1036 cm-2 s-1
* 5~ 7 10ccN
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Hadronic production
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4c sectorLO calculations for (4c) at gives
at mc=1.25 GeV s=0.24It should be compared with
This gives
At Z-pole
Main uncertainties come from errors in mc and s
10.6GeVs
372fbe e cccc
tot cc
1.03nbe e cc
44~ 3.7 10
2
cR
c
2~ 2.3 10ZR
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Violation of factorization in hadroproduction at low pT
cc total cross sections:
Tevatron: (cc)=12 nb
LHC : (cc)=122 nb
3~10bc
cc
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Conclusion
• Double heavy quark pair production is a new battle field (see, e.g. B-factories)
• Test of fragmentation approximation in production
• NRQCD factorization• Properties of weak decays
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Backup slides
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1) Fragmetation mechanism
X cc final state
, / , 1 , ',c cX cc J P
e
e
X
c
c
2
23
02 2 1
27c X s
RJD z z
m
2 XEz
s
M2/s corrections are neglected (M2/s <<1)
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X cc final state2) Complete calculations (with M2/s corrections)
(c) = 40 (49) fb,
(J/) = 104 (148) fb,
( c0) = (48.8) fb
( c1) = (13.5) fb
( c2) = (6.3) fb
Complete calculations deviate from fragmetation calculations at
M2/s terms are important
10.6GeVs
[A.Berezhnoi, A.L.]
[K.Y. Liu, Z.G. He, K.T. Chao]
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X cc final state
3) Quark-Hadron duality 2
sing
2
280fbD
c
m
ccccm
d e e cc c cdm
dm
1.25GeVcm 0.24s 0.5GeV
S=1sing204fbd e e cc c c
S=0sing76fbd e e cc c c
Q-H duality does not contradict Color Singlet model within uncertainties in mc s and
It should be compared with total sum of complete calculations.
tot 216fbQQ
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X cc final state
a) fragmentation approach
S=1 Dccc(z) similar to DcJ/(z)
Difference in wave functions |J/ (0)|2 and |cc(0)|2
Again, similar to J/ case, at complete calculations for vector (cc)3 -diquark are needed
10.6GeVs
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X cc final state
b) Quark-Hadron duality
One inclusive cross section for vector 3c in S=1
Uncertainties are caused by errors in s and
This value is close to results of complete calculations with cc(0) taken from PM.
~115 170fbcc c c
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Conclusion1) at ( at LHC )
2) For lumonocity L=1034 cm-2 s-1 it gives ~104 cc-baryons per year
3) Taking into account Br ~10-1 in exclusive modes we expect 103 cc events per year
~100fbcce e X 10.6GeVs
~122nbcce e X