Outline

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Outline

• Multiplicities in qq and WW events
• Motivation
• The ISR problemand other cuts
• Results at 183 and 189 GeV
• Energy evolution of ltngt and ltngt/D
• Multiplicities in bb and uds events
• Conclusions

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• Why Multiplicities ?
• Easy to count charged particles, Errors ? with
  ?
• Basic observable of the hadronic final state
• Evolution with energy predicted by models (QCD)
• Possible signals for
• Colour Reconnection in WW s at LEP2

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Colour Reconnection in WW
The hadronic products of WW -gt 4j can
interconnect, since

• Colour Reconnection mixes up singlets, creating
  resonances which cant be assigned to either W
• Global effect on multiplicity

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The Initial State Radiation
problem
...require
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...other cuts

• Ntrkgt9, ETgt0.2
• WW removed requiring BN lt 0.065

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• WW(4q) and WW(2q) selected

on the basis of the number of jets, their energy
and multiplicity, separation between jets,
missing momentum, etc.

• Efficiencies, purities and numbers of events

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WW(4q)
WW(2q)
4 high multiplicity jets, well separated, event
balanced, no qq radiative return.
2 jets1 low mult. and energetic jet, well
separated, event unbalanced.
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Results at 183 and 189 GeV
qq
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WW(2q)
0.1ltPlt1GeV
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but from the average of the 4 LEP experiments
(as from May99), the ratio (all P) is
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with ltngt(W)19.22?0.12st ?0.31sy
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Multiplicity difference in bb and (uu,dd,ss)
DELPHI events
Dead cone
mq
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with
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Method

• ltngtbb and ltngt uds extracted from the system of
  equations

ltngtbb29.04?1.08, ltngtuds23.07 ?1.32, ltngtcc31.47
?3.94 183 GeV ltngtbb30.14?0.65, ltngtuds26.17
?0.91, ltngtcc26.82 ?2.61 189 GeV
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ltngtbb29.04 ? 1.08st ? 0.41sy ?bl
5.07 ?1.28st ?1.07sy
183 GeV
ltngtbb30.14 ? 0.65st ? 0.33sy ?bl
3.97 ?0.83st ?0.68sy
189 GeV
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Conclusions

• Agreement DATA/QCD for the evolution with
  c.m.energy of ltngt and ltngt/D.
• Koba-Nielesen-Olesen scaling hypothesis observed
  up to 189 GeV.
• No interconnection effects observed in WW events
  at this level of statistics.
• Multiplicities in bb and in uds events measured
  and their difference incompatible with
  independent flavour fragmentation, and in
  agreement with QCD.

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