Search for hb in two-photon collisions with L3 Detector at LEP

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Search for hb in two-photon collisions with L3
Detector at LEP

• Carmen Palomares
• CERN
• On behalf of L3 Collaboration

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The Charmonium System
_ cc
Mass
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The Bottomonium System
---- Uncertain states Based on charmonium
system hb meson is expected
_ bb
Mass
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hb ( ) 1S state, JPC 0- not yet seen

• Mass should be close to ? (1S) mass (9.46 GeV)

hypothesis m(hb) (GeV)
QCD calculations
Lattice NRQCD Lattice potential 1/m expansion Potential model pQCD 9.38 9.37 9.40 9.36 9.41 A.El-Khadra hep-ph/9508266 G.S. Bali et al. Phys Rev D56 (97) S.Narison, Phys Lett B387 (96) T. Barnes hep-hp/0103142 N.Brambilla et al. Phys Lett B513
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Experimental expectations

• High statistics of gg collisions at LEP II
• In L3 Lee- 610 pb-1 , 189 GeV lt ?s lt
  209 GeV
• Predicted cross-section

QCD Potential model ? Ggg(hb) ? 0.5 keV
(predictions for hc compatible with the
measurements) s(ee-? ee-hb) 0.26 pb at lt?sgt
197 GeV hb decays BR(4 charged particles)
3 ? 5 expected events A.Böhrer, Search for the
hb meson, PHOTON 2001 (eff 100)
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Previous searches

• In radiative decay of the ?(3S) ? g hb (CUSB
  CLEO)
• CLEO(1994)
• BR(?(3S)?pp hb) x BR(hb? g hb) lt 0.1 at 90
  C.L.
• for hb mass range from 9.32 GeV to 9.46 GeV
• Phys. Rev. D49(1994) 40

• In two-photon collisions
• ALEPH(2002)
• Ggg(hb) x BR(4 charged part) lt 48 eV at 95
  C.L.
• 0 events found (background 0.300.25)
• Ggg(hb) x BR(6 charged part) lt 132 eV at 95
  C.L.
• 1 candidate m9.300.04 GeV (background
  0.700.34)
• Phys. Lett. B530 (2002)

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Selection
Studied decays 4 charged particles and 4
charged particles po 6 charged particles and
6 charged particles po
Charged particles are p and/or K

• Preselection to define good tracks with pTgt150
  MeV
• and e.m. cluster compatible with photons
  from po
• (Eggt 80 MeV)

• Selection gg? R? n charged particles
• n tracks (no other accidental tracks must be
  present)
• S pT2 lt 0.1 GeV2
• Reject photon conversions, cut m(ee-)gt50 MeV
• gg -gt tt-,
  cut m(3p) gt 1.9 GeV

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• 2 bumps from po (mass(gg) po mass (105-165
  MeV))

Data Selected 4 track po
Data Selected 6 track po
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Results
Wgg between 9 10 GeV
Channel Selected Events Eff() Expected Background Reconstructed Mass (GeV)
4 tracks 1 4.9 0.250.06 9.90.3
4 tracks po 0 1.9 0.090.01
6 tracks 1 3.6 0.650.06 9.40.3
6 tracks po 1 0.9 0.290.07 9.90.3
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4 charged particles
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6 charged particles
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6 charged particles po
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Invariant mass distribution
4 charged particles po
4 charged particles
1 candidate
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Invariant mass distribution
6 charged particles
6 charged particles po
1 candidate
1 candidate
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Invariant mass distribution
All channels combined
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Invariant mass of the candidates
Average reconstructed mass of the most
significant candidates
M 9.7 0.3 GeV
Mass resolution due to detector effects 300
MeV p/K misidentification 50 MeV
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Possible Interpretations

• The observation is found to be compatible with
• the background expectation (expectation 1.3)
• If we assume the production of hb resonance
• in the invariant mass range 9-10 GeV

Upper limits on Ggg(hb)xBR Ggg(hb) x BR(4
charged part.) lt 0.3 keV Ggg(hb) x BR(4
charged part. po) lt 0.5 keV Ggg(hb) x BR(6
charged part.) lt 0.4 keV Ggg(hb) x BR(6
charged part. po) lt 1.4 keV At 95 of C.L
Assuming the same BR for each channel Ggg(hb) x
BR(all channels) lt 0.2 keV at 95 of C.L.
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Conclusions

• We find 3 candidates in the Wgg range 9-10 GeV
• They are compatible with background (1.3 events)
• The observation is also compatible with a
  signal.
• The analysis will be slightly improved to
  increase the sensitivity