Nick van Remortel University of Antwerpen, Belgium On behalf of the LEP experiments W W BEC in
Jan 09, 2016
Nick van RemortelUniversity of Antwerpen, Belgium
On behalf of the LEP experiments
WWBEC
in
Nick van Remortel Moriond QCD 2003
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
BEC in WW events at LEP
Why study BEC between different W’s in
Separation between W’s ~ 0.1 fm
Hadronization size: 0.5 to several fm
If two particle sources overlap: Inter-W BEC possible
Potential bias in direct measurement of MW
MW = 0 – 100 MeV
Colour Reconn.
Inter-W BEC
Syst. Uncert. On MW
Hadronisation models: In absence of CR no inter-W BEC is possible
Other syst.
Coherent particle production inside strings = independent
But maybe incoherent BEC à la HBT between two W’s
Nick van Remortel Moriond QCD 2003
BEC in WW events at LEP
Modeling of BEC in WW events
Global Reweighting Models:
V. Kartvelishvili and R. Kvatadze, Phys. Lett B 514 (2001) 7.
S. Todorova-Nova and J. Rames, hep-ph/9710280
Estimate matrix elements for permutation of identical bosons
In Lund Area Law:Predict small shifts in MW : ~ 10 MeV
Nick van Remortel Moriond QCD 2003
BEC in WW events at LEP
Local Models: LUBOEI
Pairs get shift Q, according to
Where
BE0
BE32
Nick van Remortel Moriond QCD 2003
BEC in WW events at LEP
LEP WW statistics
~ 10k WW events in each experiment
45.6% are
43.9% are
Ranging in CM energies from 160 – 209 GeV
Selection Performances
4q : E ~ 80%, P ~ 85%2q: E ~ 62%, P ~ 96%
15% of qq() background has to be subtracted using Models
BEC inside one W
BEC between W’s
Nick van Remortel Moriond QCD 2003
BEC in WW events at LEP
Measurement of inter-W BEC
In case of independent WW decay
• S. V. Chekanov, E. A. De Wolf and W. Kittel, Eur. Phys. J. C6 (1999) 403.• E. A. De Wolf, hep-ph/0101243
Mix 2 semi-hadronic events
Two observables
• 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
BEC in WW events at LEP
Results from L3
NO Inter-W BEC found
Big enhancement at low Q forInter-W BEC
Nearly flat and zero for no inter-W BEC
Nick van Remortel Moriond QCD 2003
BEC in WW events at LEP
Fit D’(Q):
D’(Q) = Ddata(Q)/DMC no inter-W (Q)
Big enhancement at low Q forInter-W BEC
Nick van Remortel Moriond QCD 2003
BEC in WW events at LEP
Results from ALEPH
(Q) = (Q)data – (Q)MC no BE
No D(Q) and no numbers given yet !
(Q) is consistent with zero
BUT
Nick van Remortel Moriond QCD 2003
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
BEC in WW events at LEP
Increased sensitivity analysis
Fraction of pairs coming from different W’s
very low
SA
ME
WD
IFF
W
Give pair weights, using 2 extra variables
Typical gain in sensitivity : 20%
Nick van Remortel Moriond QCD 2003
BEC in WW events at LEP
Result
BEins Model
BEfull Model
DATA FIT
Fraction of pairs from different W’sis enhanced
By fitting D(Q) with
DELPHI finds a non-zero value of at 3 (stat + syst)
1.4 lower than BEfull
Final paper in preparation !
Nick van Remortel Moriond QCD 2003
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 ?
BEC in WW events at LEP
Nick van Remortel Moriond QCD 2003
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