# Investigation of Colour Reconnection in WW Events with the DELPHI detector at LEP-2

## TL;DR

This study investigates Colour Reconnection effects in WW events at LEP-2 using DELPHI data, analyzing particle flow and W mass estimators, and compares results to models to understand soft gluon exchange during hadronization.

## Contribution

It provides the first detailed experimental investigation of Colour Reconnection effects in fully hadronic W pair decays at LEP-2, constraining model parameters.

## Key findings

- Reconnection probability P_reco estimated between 0.31 and 0.68.
- Best-fit SK-I model parameter kappa_{SK-I} = 2.2^{+2.5}_{-1.3}.
- Results support soft gluon exchange influence during hadronization.

## Abstract

In the reaction e+e- -> WW -> (q_1 qbar_2)(q_3 qbar_4) the usual hadronization models treat the colour singlets q_1 qbar_2 and q_3 qbar_4 coming from two W bosons independently. However, since the final state partons may coexist in space and time, cross-talk between the two evolving hadronic systems may be possible during fragmentation through soft gluon exchange. This effect is known as Colour Reconnection. In this article the results of the investigation of Colour Reconnection effects in fully hadronic decays of W pairs in DELPHI at LEP are presented. Two complementary analyses were performed, studying the particle flow between jets and W mass estimators, with negligible correlation between them, and the results were combined and compared to models. In the framework of the SK-I model, the value for its kappa parameter most compatible with the data was found to be: kappa_{SK-I} = 2.2^{+2.5}_{-1.3} corresponding to the probability of reconnection P_{reco} to be in the range 0.31 < P_{reco} < 0.68 at 68% confidence level with its best value at 0.52.