晨光杯Observation of ?c decay into ?+?- and ?+?

Observation
of
_
_ ηc decay into
Σ+Σ- and Ξ-Ξ+ final states
Phy. Rev. D87, 012003 (2013)
耿聪(Cong Geng)
中国科学技术大学近代物理系
2014/4/20 武汉
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Outline
Motivation
• Intermediate charm meson loop mechanism
• Prediction for ηc→baryon pairs
_
_
Search for ηc→Σ+Σ-, Ξ-Ξ+ at BESIII
Results and Comparison
Discussion
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Motivation
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QCD - A big picture
Confinement
Asymptotic freedom
Nobel Prize 2004
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Charmonium
• Annihilation decays of
charmonia below open charm.
_
• c and c annihilate
at the origin
_
of the (cc) wave function
Relatively large energy scale ~ 2mc
Short-distance, Perturbative QCD ？
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Helicity Selection Rule
Relatively large energy scale ~ 2mc
pQCD asymptotic behaviors are expected
Helicity Selection Rule (HSR) !!!
•
An alternative description of this
selection rule with the quantum number
named “naturalness”
•
The selection rule requires that
The masses of light
quarks from the gluons
could be ignored.
Helicity conservation is not a
consequence of a particular
symmetry but is a dynamical
consequence of leading twist
pQCD
Chernyark and Zitnitsky, Phys. Rept. 112, 173 (1984); Brodsky and Lepage, PRD24, 2848 (1981).
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1. “ρπ puzzle”
pQCD expects :
However, the measured value is orders of magnitude smaller than
the approximate “12%”(even consider the HSR)
_
2. ψ(3770) non-DD decay
Unclarified!!!!
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Intermediate charm meson
loop mechanism (IML)
_
cc pair first couples to an intermediate charm meson pair, and
then these two mesons re-scatter into two light mesons.
IML to account for “ρπ puzzle”
IML for ψ(3770) non-DD decay
Y. J. Zhang et al, PRL102, 172001 (2009)
Q. Wang et al, PRD85, 074015 (2012)
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c1 VV
Long-distance contribution via intermediate meson loops
X. H. Liu and Q. Zhao,
PRD81, 014017 (2010)
Quite well consistent !
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Prediction for ηc→baryon pairs
X. H. Liu and Q. Zhao
J. Phys. G38, 035007,2011
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IML for baryon pair production in ηc
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_
_
Search for ηc→Σ+Σ-, Ξ-Ξ+ at BESIII
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BESIII and Data Sets
𝟐. 𝟐𝟓 × 𝟏𝟎𝟖 J/ψ events collected
with BESIII detector at BEPCII
from June 12nd to July 28th in
the year of 2009.
The analysis depends on the decay
mode J/ψ→γηc.
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Event Selections (I)
𝑱/𝝍 → 𝜸𝜼𝒄 , 𝜼𝒄 → 𝜮+ 𝜮− , 𝜮 → 𝒑𝝅𝟎
𝑱/𝝍 → 𝜸𝜼𝒄 , 𝜼𝒄 → 𝚵 − 𝚵+ , 𝚵 → 𝚲𝝅
Common criteria for 𝜮 pair and 𝜩 pair:
• Vertex constraints for charged tracks and the requirement
on their solid angles
• dE/dx and TOF are combined to do particle identification
• Photon pre-selections : requirements on minimum energy
and time information in EMC
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Event Selections (II)
For 𝜮 pair :
For 𝜩 pair :

 𝝅𝟎

Kinematic fit on energy-momentum
conservation is applied on
J/𝜓 →∗→ 𝛾𝑝𝑝𝜋 0 𝜋 0
 𝜮
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
Vertex fit and Second vertex fit tool is
used to reconstruct the long-life Λ
and Ξ
to distinguish the two pions
 Kinematic fit on energy-momentum
conservation is applied on
J/𝜓 → 𝛾𝛯 − 𝛯+ → 𝛾𝑝𝑝2(𝜋 + 𝜋 − )
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Invariant mass
𝚵
𝚺
ηc
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ηc
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Background Studies
Kinematic Fit to suppress the background
with one more or one mis-detected photon.
The background can be well understood !
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Number of Signals
Fit Function
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Systematic Uncertainties
Dominant
PDG
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Results and Comparison
Theoretical prediction
Consistent !
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Discussion
 Theoretical predictions are on the basis of
intermediate charm meson loop mechanism.
 First Experimental observation of 𝜼𝒄 → 𝜮+ 𝜮− and
𝜼𝒄 → 𝚵− 𝚵+ . The BRs are order of magnitude 10-3 and
agree with with the predictions.
 Future, to improve the precisions of both experiment
and theory.
 Theory also predicted the similar decays in χc0 and hc.
This is the opportunity for the BESIII after getting
high statistics.
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My Major Contribution at BESIII
Publications:
International Conference:
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Thanks for your attention !
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