CASE STUDY:

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CASE STUDY Exotic Charmed Hybrids at
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Lowest energy charmonium hybrid (spin-exotic)

C.Bernard, Phys.Rev. D56
(1997) 7039 F.E.
Close, Phys. Rev. 1998

P.R. Page, Acta Phys. Polon.
1998
Narrow!(?)
Non-relativistic selection rule if X and Y have
the same non-relativistic structure and L0
are not allowed
P. Page, Phys Lett.B402(1997)
Suppressed decay or sub-threshold decay into
charmed mesons Decay into hidden charm and light
hadrons
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HYBRID PRODUCTION
Two-body reaction cross section
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HYBRID DECAY INTO OPEN CHARM
Decay into two s-waves suppressed First charmed
possibility _at_4286MeV Width
depends strongly on hybrid mass
s-wave
PDG
Selection rule based on symmetry
symmetry breaking by 4 gives decay widths of 1-4
MeV P. Page Phys.Lett. B402 (1997)
183-188
Slow decays
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HYBRID DECAY INTO CLOSED CHARM
HYBRID DECAY INTO HIDDEN CHARM
First excited gluonic field
Relativistic decay L and S preserved, excitation
energy goes into light hadrons
Lowest mass with L1, S1
Scalar light hadrons
Pseudoscalar light hadrons
Scalar rate Pseudoscalar UKQCD,
McNeile, Phys. Rev. D56 (2002)
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Production in annihilations _at_ p15 GeV
Production mode (exotic spin-quantum numbers)
We start with the channel and neutral
pions
Trigger!!
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Production of exotics in
Crystal Barrel _at_ LEAR
Spin exotic Possibly hybrid
Amplitude square from Partial Wave Analysis of
nucleon annihilation data Crystal Barrel 1997.
Here Hybrid production amplitude as large as
meson production amplitude
We assume this to be true for


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E760, R.Cester Workshop on Physics
at SuperLEAR
Charmonium meson production
Hybrid production (lower limit)
We expect
HESR _at_ GSI
1700 hybrids per day 4 BR 70/day if decay
to hidden charm 100
Keep in mind
Annihilation background
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Barrel calorimeter

• Forward calorimeter (not in picture)
• Not yet implemented in software
• Increase acceptance in the (important)
• forward region

• Neutral pions and
• Only EMC required
• Little background from annihilations
• Significant combinatorics

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Acceptance loss (forward region)
Pair production from the 7 roughly Poisson
distributed with extra pairs
Mass-shift due to energy losses 20 MeV Spread due
to measurement uncertainties 40 MeV
Low energy background which can be easily cut out
resulting in a noise level of 0.4
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5 degree beam pipe P(hole) 5.8 All detected 68
Number of photons

• EM-processes (photon loss gain)
• Pair production
• Roughly Poisson distributed for 7 photons
• P(all detected)87
• P(one pair production)11.4
• Bremsstrahlung
• Readout threshold effects (1 MeV)
• Photons hitting the same crystal
• Opening angle (0.03 radians in forward direction)

Pure phase space
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Events with at least 7 photons and three
non-overlapping pions 28

• Mass shift 10 MeV
• 7.8 MeV width
• Energy and angular
• resolution of the EMC

Energy leakage due to dead region between
crystals 2 mm between crystals 5.5 of the area
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Combinations
Gaussian fit of lower peak Mass 4.13 GeV Width
196 MeV
Signal in 30 of events Background to
signal (combinatorics only) 490
200 days
CUT
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Stricter cuts on quality of intermediate particle
s gives a better hybrid peak quality but with
less statistics
Detection in 18 of the events Background/signal
162
What if we require the detection of the third
pion and make new cuts from there?
CUT
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After Geant4 detector simulation
Signal
Only combinatorics No noise!
CUT
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Invariant mass cut
Background Signal
Mass 4.17 GeV Width 74 MeV Background/signal 60
Signal in 5 of events (only lower peak)
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Detection in 18.9 of the events Background/signal
195
CUT
Basically the same detection efficiency
(depending on cut choice)
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SUMMARY The lowest mass charmonium hybrid
is investigated in production from
with or at p15 GeV The detection of the
decay chain is simulated in the EMC and the
tracker for lepton tagging
TO BE DONE (pretty soon) Redo the study with the
all-important forward EMC Investigate how the
spatial and energy resolution of the EMC crystals
effect the hybrid detection Investigate decay
into open charm Partial wave considerations Etc..