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26/07/2002C.Palomares / ICHEP02 Search for  b in two-photon collisions with L3 Detector at LEP Carmen Palomares CERN On behalf of L3 Collaboration.

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Presentation on theme: "26/07/2002C.Palomares / ICHEP02 Search for  b in two-photon collisions with L3 Detector at LEP Carmen Palomares CERN On behalf of L3 Collaboration."— Presentation transcript:

1 26/07/2002C.Palomares / ICHEP02 Search for  b in two-photon collisions with L3 Detector at LEP Carmen Palomares CERN On behalf of L3 Collaboration

2 26/07/2002C.Palomares / ICHEP02 The Charmonium System _ cc Mass

3 26/07/2002C.Palomares / ICHEP02 The Bottomonium System _ bb ---- Uncertain states Based on charmonium system  b meson is expected Mass

4 26/07/2002C.Palomares / ICHEP02  b ( ) 1S state, J PC 0 -+ not yet seen  Mass should be close to Υ  (1S) mass (9.46 GeV) hypothesis m(  b ) (GeV) QCD calculations Lattice NRQCD Lattice potential 1/m expansion Potential model pQCD A.El-Khadra hep-ph/ G.S. Bali et al. Phys Rev D56 (97) S.Narison, Phys Lett B387 (96) T. Barnes hep-hp/ N.Brambilla et al. Phys Lett B513

5 26/07/2002C.Palomares / ICHEP02 Experimental expectations   High statistics of  collisions at LEP II In L3 : L e+e- = 610 pb -1, 189 GeV <  s < 209 GeV  Predicted cross-section: QCD Potential model     b  0.5 keV (predictions for  c compatible with the measurements)  e + e -  e + e -  b ) = 0.26 pb at = 197 GeV  b decays: BR(4 charged particles) ~ 3%  5 expected events A.Böhrer, Search for the  b meson, PHOTON 2001 (eff = 100%)

6 26/07/2002C.Palomares / ICHEP02 Previous searches  In radiative decay of the Ύ (3S)   b (CUSB & CLEO)  CLEO(1994) BR( Ύ (3S)   h b ) x BR( h b   b ) < 0.1% at 90% C.L. for  b mass range from 9.32 GeV to 9.46 GeV Phys. Rev. D49(1994) 40  In two-photon collisions  ALEPH(2002) *    b  x BR(4 charged part) < 48 eV at 95% C.L. 0 events found (background: 0.30±0.25)    b  x BR(6 charged part) < 132 eV at 95% C.L.  1 candidate m=9.30±0.04 GeV (background: 0.70±0.34)  Phys. Lett. B530 (2002)

7 26/07/2002C.Palomares / ICHEP02 Selection I.Preselection: to define good tracks with p T >150 MeV and e.m. cluster compatible with photons from  o (E  > 80 MeV) Studied decays 4 charged particles and 4 charged particles +  o 6 charged particles and 6 charged particles +  o Charged particles are  and/or K II.Selection:   R  n charged particles   n tracks (no other accidental tracks must be present)   p T 2 < 0.1 GeV 2  Reject: photon conversions, cut: m(e + e - )>50 MeV      cut:  m(3  ) > 1.9 GeV

8 26/07/2002C.Palomares / ICHEP02  2 bumps from  o (mass  o mass ( MeV)) Data Selected 4 track +   Data Selected 6 track +  

9 26/07/2002C.Palomares / ICHEP02 Results W   between 9 —10 GeV ChannelSelected Events Eff(%) Expected Background Reconstructed Mass (GeV) 4 tracks ± ±0.3 4 tracks +  o ± tracks ± ±0.3 6 tracks +  o ± ±0.3

10 26/07/2002C.Palomares / ICHEP02 4 charged particles

11 26/07/2002C.Palomares / ICHEP02 6 charged particles

12 26/07/2002C.Palomares / ICHEP02 6 charged particles +  

13 26/07/2002C.Palomares / ICHEP02 Invariant mass distribution 4 charged particles 4 charged particles +  o 1 candidate

14 26/07/2002C.Palomares / ICHEP02 Invariant mass distribution 6 charged particles 6 charged particles +  o 1 candidate

15 26/07/2002C.Palomares / ICHEP02 Invariant mass distribution All channels combined

16 26/07/2002C.Palomares / ICHEP02 Invariant mass of the candidates M = 9.7 ± 0.3 GeV * * Mass resolution due to detector effects ~ 300 MeV  /K misidentification ~ 50 MeV Average reconstructed mass of the most significant candidates:

17 26/07/2002C.Palomares / ICHEP02 Possible Interpretations  The observation is found to be compatible with the background expectation (expectation 1.3)  If we assume the production of  b resonance in the invariant mass range 9-10 GeV: Upper limits on    b )xBR:    b ) x BR( 4 charged part.) < 0.3 keV    b ) x BR( 4 charged part. +  o ) < 0.5 keV    b ) x BR( 6 charged part.) < 0.4 keV    b ) x BR( 6 charged part. +  o ) < 1.4 keV At 95% of C.L Assuming the same BR for each channel:    b ) x BR(all channels) < 0.2 keV at 95% of C.L.

18 26/07/2002C.Palomares / ICHEP02 Conclusions We find 3 candidates in the W  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


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