On colour rearrangement in hadronicW +W− evemts

Abstract

We discuss the possibility of colour rearrangement in e + e − → W + W − → q 1 q 2 q 3 q 4 events, i.e. that the original colour singlets q 1 q 2 and q 3 q 4 may be transmuted, for instance, into new singlets q 1 q 4 and q 3 q 2. The effects on event properties could be quite large if such a rearrangement would occur instantaneously, so that gluon emission would be restricted to each of the new singlets separately. We argue that such a scenario is unlikely for two reasons. Firstly, the W + and W − usually decay at separate times after the W + W − production, which leads to large relative phases for energetic radiation off the two constituents of a rearranged system, and a corresponding dampening of the QCD cascades. Secondly, within the perturbative scenario the colour transmutation appears only in order α 2 s and is colour-suppressed. Colour reconnection at longer time scales is quite feasible, however, and may affect the fragmentation phase. If so, the nature of non-perturbative QCD can be probed in a new way. We formulate several alternative toy models and use these to estimate the colour reconnection probability as a function of the event kinematics. Possible consequences for LEP 2 events are illustrated, with special attention to systematic errors in W mass determinations.

Measurement of the W boson mass and ${\rm W^+W^-}$ production and decay properties in ${\rm e}^+{\rm e}^-$ collisions at ${\sqrt s = 172}$ GeV

“…In contrast, significant interference in the hadronisation process is considered to be a real possibility. With the current knowledge of non-perturbative QCD, such interference can be estimated only in the context of specific models [19,20,[33][34][35][36][37].…”

“…Direct measurements of M W from hadron colliders currently yield 80.33 ± 0.15 GeV [1][2][3]. Ultimately it is believed [4] that LEP2 can achieve a precision on the W mass of approximately [30][31][32][33][34][35][36][37][38][39][40] MeV. The mass dependence of the W + W − production cross-section at threshold, √ s ∼ 161 GeV, was used to extract the first measurements of M W from LEP2 data [5][6][7][8].…”

Coalescence model for Θc pentaquark formation

“…During development of the final state, HERWIG assigns to each unstable object with four-momentum q an exponentially distributed proper lifetime, with mean value τ given by [15] …”

$\mathrm{W^+W^-}$ production and triple gauge boson couplings at LEP energies up to 183 GeV

“…This effect is investigated at 183 GeV with Monte Carlo samples generated with Pythia, in two classes of reconnection models called type I and type II [45], and with Ariadne [46]. g) Finally, a possible presence of biases in our analysis or fit method is checked by analysing Monte Carlo events generated with known values of the couplings, ranging from -2 to +2.…”