University of Antwerpen, Belgium On behalf of the LEP experiments Nick van Remortel University of Antwerpen, Belgium On behalf of the LEP experiments BEC in W

Two-particle correlations are studied by Two-particle densities, BEC in WW events at LEP Measurement of BEC in High-Energy Physics Two-particle correlations are studied by Two-particle densities, Often in the variable Q Enhancement at small Q when BEC is there Nick van Remortel Moriond QCD 2003

Hadronisation models: In absence of CR no inter-W BEC is possible BEC in WW events at LEP Why study BEC between different W’s in Separation between W’s ~ 0.1 fm If two particle sources overlap: Inter-W BEC possible Potential bias in direct measurement of MW Inter-W BEC D MW = 0 – 100 MeV Other syst. Colour Reconn. Hadronization size: 0.5 to several fm Syst. Uncert. On MW Hadronisation models: In absence of CR no inter-W BEC is possible Coherent particle production inside strings = independent But maybe incoherent BEC à la HBT between two W’s Nick van Remortel Moriond QCD 2003

Modeling of BEC in WW events BEC in WW events at LEP Modeling of BEC in WW events Global Reweighting Models: Estimate matrix elements for permutation of identical bosons Predict small shifts in MW : ~ 10 MeV In Lund Area Law: S. Todorova-Nova and J. Rames, hep-ph/9710280 V. Kartvelishvili and R. Kvatadze, Phys. Lett B 514 (2001) 7. Nick van Remortel Moriond QCD 2003

Pairs get shift dQ, according to BEC in WW events at LEP Local Models: LUBOEI Pairs get shift dQ, according to Where BE0 BE32 Nick van Remortel Moriond QCD 2003

~ 10k WW events in each experiment BEC in WW events at LEP BEC inside one W LEP WW statistics ~ 10k WW events in each experiment 43.9% are 45.6% are Ranging in CM energies from 160 – 209 GeV Selection Performances 4q : E ~ 80%, P ~ 85% 2q: E ~ 62%, P ~ 96% 15% of qq(g) background has to be subtracted using Models BEC between W’s Nick van Remortel Moriond QCD 2003

Measurement of inter-W BEC BEC in WW events at LEP Measurement of inter-W BEC S. V. Chekanov, E. A. De Wolf and W. Kittel, Eur. Phys. J. C6 (1999) 403. E. A. De Wolf, hep-ph/0101243 In case of independent WW decay Two observables Mix 2 semi-hadronic events OPAL: still working on this method L3: Phys. Lett. B547 (2002) 139. ALEPH: EPS Budapest 2001 DELPHI: ICHEP Amsterdam 2002 and about to publish Nick van Remortel Moriond QCD 2003

Big enhancement at low Q for Nearly flat and zero for BEC in WW events at LEP Results from L3 Big enhancement at low Q for Inter-W BEC Nearly flat and zero for no inter-W BEC NO Inter-W BEC found Nick van Remortel Moriond QCD 2003

Big enhancement at low Q for BEC in WW events at LEP Big enhancement at low Q for Inter-W BEC D’(Q) = Ddata(Q)/DMC no inter-W (Q) Fit D’(Q): Nick van Remortel Moriond QCD 2003

Dr(Q) = Dr(Q)data – Dr(Q)MC no BE BEC in WW events at LEP Results from ALEPH Dr(Q) = Dr(Q)data – Dr(Q)MC no BE Dr(Q) is consistent with zero BUT No D(Q) and no numbers given yet ! Nick van Remortel Moriond QCD 2003

Enhancement at low Q is followed by BEC in WW events at LEP Results from DELPHI LUBOEI does not change charge multipl. Enhancement at low Q is followed by dip at higher Q Nick van Remortel Moriond QCD 2003

Fraction of pairs coming from BEC in WW events at LEP Increased sensitivity analysis Q* g Fraction of pairs coming from different W’s very low SAME W Give pair weights, using 2 extra variables Typical gain in sensitivity : 20% DIFF W Nick van Remortel Moriond QCD 2003

Fraction of pairs from different W’s BEC in WW events at LEP Result Fraction of pairs from different W’s is enhanced BEfull Model DATA FIT By fitting D(Q) with DELPHI finds a non-zero value of L at 3 s (stat + syst) 1.4 s lower than BEfull Final paper in preparation ! BEins Model Nick van Remortel Moriond QCD 2003

Inter-W BEC, observed in DELPHI BEC in WW events at LEP Inter-W BEC, observed in DELPHI seems to be concentrated in very small Q region Corresponds to a bigger R value than expected from MC with inter-W BEC Good news for MW : smaller amount of pairs participate in the effect Interesting for BEC guru’s: Is it HBT or not ? Nick van Remortel Moriond QCD 2003

BEC in WW events at LEP Summary Indications for inter-W Bose-Einstein Correlations seen by DELPHI Final publication is in preparation. Not confirmed by L3, although raw data agree qualitatively well with DELPHI Other LEP experiments are working hard to provide final results on the subject Nick van Remortel Moriond QCD 2003