1 / 20

Cover

Cover. Outline. Cross Talk in WW  4 jets DELPHI at LEP2 Colour Reconnection (CR) Particle Flow The D m W Method Bose-Einstein Correlations (BEC) Conclusions. Cross Talk in WW  4 jets.

afra
Télécharger la présentation

Cover

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Cover

  2. Outline • Cross Talk in WW 4 jets • DELPHI at LEP2 • Colour Reconnection (CR) • Particle Flow • TheDmWMethod • Bose-Einstein Correlations (BEC) • Conclusions

  3. Cross Talk in WW  4 jets Is there any interference between the two evolving hadronic systems from the decays of the W’s? Perturbative QCD Fragmentation Stable Hadrons BECpossible CRsupressed CRpossible betweensoft particles CRand BEC • Fundamental probesof the • dynamicsof hadronisation • Contribute to theW mass • systematic errorin the • fully hadronic channel Electroweak phase Q p+p+ e+ W+ _ p0p0 Q q p-p- e- W- _ ... q ~ 0.1 fm <~ 1 fm <~ 10-100 fm Overlap Interference is possible!

  4. The DELPHI Detector @ LEP 2 About5,000WW 4qeventscollected: DELPHI detector at LEP2 e+ e- 4 jet topology 4 well separated, high multiplicity jets, balanced event, no qq radiative return.

  5. Colour Reconnection CR: Colour rearrangement between differentcolour singlets Example: Hadronic decay ofB mesons B  J/Y + X CRinWW decays: some hadrons cannot be assigned to either W CR is suppressed in the perturbative phase 1) Group structure of QCDrequires the exchange of2 gluons 2) CRmay be possible during hadronisation 1)Average multiplicity and particle distributions 2) W mass BRexp ~1% BRfullCR ~3-5% BRnoCR ~0.3-0.5%

  6. CR Phenomenological Models DMW~O(100 MeV) • Sjöstrand & Khoze (PYTHIA): • Type I: (SK I) flux tubes • Probrecon • = 1-exp(-kIVol. Overlap) • Type II, II’ : vortex lines SK-I kI .18 0.66 1.26 2.34 4.9 100 • Gustafson & Häkkinen: minimizesstring length • Lönnblad(ARIADNE):CR between dipoles, min.stringlength • Webber et al. (HERWIG):CR if smaller cluster sizes

  7. The Particle Flow Method No CR CR Cross-Talk between W systemsshould result in some depletionand/orenhancement of soft particles in some phase space regions All results are preliminary! • Select only events withwell- definedregions:low efficiency • Count the particles betweeneach pair of jets • Compare the Inside W’s and Between W’sparticle flow

  8. Measuring the Particle Flow Project all charged particlesPi in the plane ( jet 1, jet 2) Inside W’sand Between W’s A Rescale the angles to have an equal amount of phase-space between the jets : FJ,i FJ,i . (1/FJK) D B C ( ) DELPHI preliminary data at 189 GeV #( A+C ) #( A+C ) d Z  qq(g) dF #( B+D ) #( B+D ) WW qqln no CR A B C D SK1 100% SK1 100% 0.2 0.8

  9. The Ratio of Particle Flow In the systematic error, were considered: • Bose-Einstein effects (0.7%) • Fragmentation modelling (2.6%) Work • Background subtraction/modelling (1.2%) • Extrapolation to 189 GeV (1.4%) <R>189 = 0.979 0.032(sta)  0.030(sys) Data: 183-209 GeV R DELPHI preliminary

  10. Particle Flow Results Comparison of LEP Particle Flow results DELPHI Particle Flow results DELPHI preliminary R

  11. The DmW Method Start with the standard mW analysis and mass estimator, mW(std) Bias of mW estimators: DELPHI preliminary MC prediction SK1

  12. DmW Results Dmw(std,Rcone= 0.5rad) = 59 35(sta)  21(sys) MeV/c2 Data: 189-209 GeV 2 MC prediction SK1 DELPHI preliminary +1 sigma centr. kI -1 sigma DELPHI preliminary Syst. error kI

  13. Combination of DELPHI Measurements Correlationbetween the twomethods is small Combine both DELPHI measurements 2 kI

  14. Bose-Einstein Correlations • Quantum-mechanical effect:Bose-Einstein statistics • Symmetrisation of thewave functionofn identical bosons • Enhanced production of identical bosonsclose in phase-space two-particle correlations BEC in light quark Z decays identical to BEC inside a hadronically decaying W Phase-space (projected into 1 dimension) Inclusive two-particle density Normalised two-particle density Reference Sample: MC,Unlike sign,Mixed events

  15. Measuring Inter-W BEC Observables BEC between separately hadronising strings? Assuming independent WW decay No Inter-W BEC:1 Hadronic events Semi-hadronic Events No Inter-W BEC:0 Mix 2 Semi-hadronic events DELPHI preliminary data-data comparison

  16. Monte Carlo Simulation of BEC Local Models:Reshuffle the 4-momentum of particles - LUBOEI • Has 2input parameters: correlation strength Land source size R • Reproduces BEC insideZand W decays (BEins) • Has a switch to allow inter-string BEC(BEfull)DmW35MeV • Implemented in PYTHIA (BE32 variant used here) Global Models:Generate weights for a given event - Andersson et al. • Based in Lund Area Law • No arbitraryinput parameters • Reproduces BEC insideZand W decays • No BEC between two strings • Nomature MC - Kartvelishvili & Kvatadze • Allows inter-string BEC(DmW15MeV) • Not tested yet

  17. Measured BEC Distributions 550 pb-1 s = 189 – 209 GeV 2567 qqln events 3252 qqqqevents DELPHI preliminary Dlike-sign Drlike-sign DELPHI preliminary Dunlike-sign DELPHI preliminary Drunlike-sign

  18. WW BEC Results Systematic error: Fixing R to BE full value DELPHI preliminary Fit R and L simultaneously DELPHI preliminary c2=9 -BE full -BE ins like-sign Source size c2=4 c2=1 Data BE full Measured correlation strength: L = 0.241 0.075(sta)  0.038(sys) Correlation strength

  19. LEP Combination of WW BEC Results Combine observed fraction of BE full Result of combination: 23% of LUBOEI BE32 with BEC between W’s is observed Corresponding W mass shift: 8  5 MeV/c2

  20. Conclusions • CRand BECinvestigated inWWqqQQevents in DELPHI at LEP2 • Colour Reconnection: • Two uncorrelated observables are studied: • Comparing theparticle flowbetween jets ( R ) • Modifying the kinematics of the jets ( DmW[std,cone] ) • Preliminary results indicatesmall amountof Colour Reconnection • The observables arenot sensitiveto theARIADNE model • Work continues onfragmentation error in theparticle flow • Bose-Einstein Correlations: • Model independent measurement of inter-W BEC developed • Mixed reference sample built from semi-hadronic data events • Inter-W BEC in like sign pairs found at 2.9slevel • LEP combination:23% BE32 inter-W, DmW=8  5 MeV/c2

More Related