1. 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

2. 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

3. 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

4. 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/
V. Kartvelishvili and R. Kvatadze, Phys. Lett B 514 (2001) 7.
Nick van Remortel
Moriond QCD 2003

5. 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

6. ~ 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

7. 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/
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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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