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Motivation Color reconnection Standard variables

C o l o r R e c o n n e c t i o n in Hadronic WW Events at LEP. Motivation Color reconnection Standard variables Particle production between jets, Particle flow distributions Summary. Thomas Ziegler, Johannes Gutenberg Universität, Mainz Moriond conference, 17-24 march 2001 1.

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Motivation Color reconnection Standard variables

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  1. ColorReconnectionin Hadronic WW Events at LEP Motivation Color reconnection Standard variables Particle production between jets,Particle flow distributions Summary Thomas Ziegler, Johannes Gutenberg Universität, Mainz Moriond conference, 17-24 march 2001 1

  2. Motivation Interesting physics where we might learn something about the QCD vacuum MW( ) = 80,442 ± 0,034stat ± 0,028syst GeV/c2 MW( ) = 80,460 ± 0,031stat ± 0,054syst GeV/c2 ± 40 MeV/c2 uncertainty from colourreconnection in hadronic channel

  3. primaryquarks independentdecay perturbative crc non-perturbative crc

  4. Description of color reconnection beforepartonshower Dynamical rearrangement of color charges as distance of decay vertices of W  0,1 fm perturbative QCD* * T. Sjöstrand, V.A. Khoze, Phys. Rev. Lett. 72 (1994) 28.

  5. Time scale of fragmentation corresponds  1fm !!! Processes in partonshower and hadronisation might be important!!! Simulation with phenomenological models!!! These depend on the description of the QCD-vacuums!!!

  6. phenomenologicalmodels: • models of Sjöstrand/Khoze (skI/skII/skII‘):framework of string fragmentation(strings overlap/cross, implemented in JETSET) • model of Gustafson/Häkkinen (GH):framework of string fragmentation(minimize total string length, implemented in JETSET) • models of Lönnblad(ar2/ar3):framework of dipole cascade model(minimize string length, implemented in ARIADNE) • model of Webber et.al.(hcr):framework of cluster fragmentation(minimize cluster s-t-distance, implemented in HERWIG) • new model of Rathsman:based on area law between string pieces, will be implemented

  7. Investigatesome standardvariables momentum distribution: Similiar analyses of all four experiments, no evidence for crc

  8. Theideaoftheparticleflow Color reconnection leads to rearrangements of particle production Careful ! very simple picture !

  9. The event selection A D 100o - 140o < 100o < 100o C 100o - 140o B • preselection based on energymeasured in calorimeters • cuts on ISR events • jet clustering • Low efficiency (> 15 %) • very clean topology

  10. Particle production between jets 1 plane / 4 planes

  11. L3 Consider the ratio: and the two observables:

  12. ALEPH: Rn189GeV(0.2-0.8) = 0.820  0.038  0.026 =2.8 L3: Rn189GeV(0.3-0.7) = 0.771  0.049  0.029 =3.3 OPAL*: 1/ Rn189GeV(0.2-0.8) = 0.83  0.03  0.01 =3.1 sensitivity Slightly different selections, object definition and reconstruction, 1/4 planes, nevertheless the method shows high sensitivity in framework of sk1 model (0-100%) (similiar numbers for Sr) *using charged tracks only

  13. comparison of different colorreconnection models at 189 GeV

  14. HERWIG systematically higher than JETSET large systematic uncertainty for Rn/Sr further work on observables to make them more robust against fragmentation effects

  15. Summary Low sensitivity of standard variables for color reconnection / no evidence is found particle flow analysis is very promising with high sensitivity for effects in sk1 model,all experiments work on this method most important uncertainty comes from fragmentation systematics, but still room for improvements in observables

  16. Results are not yet conclusive but combination of energies and experiments will come soon to extract best description of the hadronic final states in WW events

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