Latest Physics Results from ALEPH: QCD Studies & Beyond

1. Latest Physics Results from ALEPH Paolo Azzurri CERN - July 15, 2003

2. What’s new ? • QCD Studies • Four fermions & Gauge Couplings • Jet reconstruction & radiative Z peak • SUSY searches • Conclusions & Prospects P.Azzurri - Latest physics results from ALEPH

3. QCD studies

4. FINAL ! αS @ 91-209 GeV Consistent analysis at all energies using six event shape variables in hadronic events NLO + NLL Theory Theory syst error evaluated with the lepwg method (uncertainty band method) P.Azzurri - Latest physics results from ALEPH

5. Reference of mixed pions from different events Reference of unlike-sign pions from the same event Two-dimensional BE correlations QL : longitudinal component of Dp QT: transverse component of Dp Selection of two-jet events with large thrust Q= Dp= p1 - p2 p1 Data/MC double ratio of the distribution of like-sign tracks to reference samples q p2 String = Pion source q P.Azzurri - Latest physics results from ALEPH

6. source size andstrength depend on the reference sample ! Two-dimensional BE correlations Fit double ratio to: Lund Model predicts RT<RL P.Azzurri - Latest physics results from ALEPH

7. rapidity gap with no charged particles q Jets with 1.5 rapidity gap gluon – jet (softest) rapidity gap q MC with CR (GAL) MC without CR The charge of the third softest jet (most likely gluon) is sensitive to CR models High purity quark jets : data/mc agreement Rapidity gaps in gluon jets From OPAL proposal to test CR at Z peak P.Azzurri - Latest physics results from ALEPH

8. Models with no CR agree with data only at zero rapidity gap : data shows an effect ! Tested CR models not in agreement with data at all rapidity gaps (overestimate of CR effects) Rapidity gaps in gluon jets (data-MC)/MC New ALEPH measurement as a function of the rapidity gap P.Azzurri - Latest physics results from ALEPH

9. Four fermions & Gauge Couplings

10. Zee production New analysis of the hadronic decay channel eeqq: 4f signal defined by lepwg convention Selection efficiency=24%, purity =82% P.Azzurri - Latest physics results from ALEPH

11. W-pair production Consistent event selections at all energies 183-207 GeV Latest data reprocessing and event reconstructions More stringent evaluations of systematic uncertainties FINAL ! P.Azzurri - Latest physics results from ALEPH

12. Lepton universality W decay couplings Lepton non-universality P.Azzurri - Latest physics results from ALEPH

13. MC BEI = BE Inside W decay MC BEB = BE Between W decays BE correlations in W pairs 4q W pairs Double ratio: four jet decays compared to two mixed hadronic parts of semileptonic decays 2q 2q P.Azzurri - Latest physics results from ALEPH

14. disfavoured at the 3.7 sigma level BE correlations in W pairs Fit double ratio to: like –sign pairs unlike –sign pairs P.Azzurri - Latest physics results from ALEPH

15. Integral of the BE enhancement disfavoured at the 3.3 sigma level BE correlations in W pairs like –sign pairs Double difference Complementary measurement: unlike –sign pairs P.Azzurri - Latest physics results from ALEPH

16. 1-D, 2-D & 3-D 95% CL contour limits Triple Gauge Couplings W pairs, single W and single photons combined New multi-parameter fits with correct O(α) treatment in W-pair analysis P.Azzurri - Latest physics results from ALEPH

17. NEW ! Generic Triple Gauge Couplings updated P.Azzurri - Latest physics results from ALEPH

18. Form Factor for Vector Resonance Enhancement of mass & width of technirho excluded at 95% CL For at 95% C.L. Generic Triple Gauge Couplings NEW ! T.L.Barklow et al. hep-ph/9704217 P.Azzurri - Latest physics results from ALEPH

19. Limits @ 95% CL: Quartic Gauge Couplings Analysis of acoplanar photon pairs with high transverse momentum (ννγγ final state) P.Azzurri - Latest physics results from ALEPH

20. Jet reconstruction improvements& radiative Z peak

21. Jet 1 Jet 2 Rescaled di-Jet mass Radiative Z event: Jet angles and jet velocities are the fundamental ingredients of radiative Z and W mass measurements with kinematic fits P.Azzurri - Latest physics results from ALEPH

22. Removing low energy neutrals (<1.5 GeV , and <2 GeV if mixed) Jet boost (and mass) now well calibrated ! Jet velocity & mass Last jet reconstruction (with ECAL cleaning) Z peak jets boost (T>0.8) P.Azzurri - Latest physics results from ALEPH

23. Simulation of forward charged tracks Loss of forward tracks in data (nuclear interactions in Vdet material) Year 2000 Z peak hadronic events Affects regions with at low polar angle (4% max deficit in forward directions) Deficit parametrized as a function of the track cosθ and PT Monte Carlo tracks corrected P.Azzurri - Latest physics results from ALEPH

24. Systematic uncertainties Radiative Z peak Unbinned likelihood fit to a pdf built with a fit to the MC reference P.Azzurri - Latest physics results from ALEPH

25. SUSY searches final results

26. Constraints on the MSSM Combination of searches for charginos, neutralinos, sleptons, higgs limits on the LSP mass Improvement of the selectron search in the gaugino region New scan of low tanβ with stau mixing (without Higgs constraints) P.Azzurri - Latest physics results from ALEPH

27. Summary of LSP limits NEW ! improved Limits on the LSP mass with stau mixing LSP limit at 95% CL with any stau mixing P.Azzurri - Latest physics results from ALEPH

28. Conclusions & Prospects ALEPH is coming to an end … • Searches for new physics completed with the LSP limits • Many Standard Model analyses completed or close to being published • Archiving of ALEPH data and Monte Carlo (~3Tb) for long term analysis completed (June 2003) P.Azzurri - Latest physics results from ALEPH

29. Two-dimensional BE correlations Comparison with other LEP experiments P.Azzurri - Latest physics results from ALEPH

30. BE correlations in W-pairs Fit results without fixing the source radius P.Azzurri - Latest physics results from ALEPH

31. @95% C.L. O(α) correction sytematic now evaluated as the difference between schemes Triple Gauge Couplings W-pairs, single W and single photons combined P.Azzurri - Latest physics results from ALEPH

32. Quartic Gauge Couplings P.Azzurri - Latest physics results from ALEPH

33. Jet velocity & mass Last jet reconstruction with ECAL cleaning ECAL cleaning with full egs simulation: Z peak jets boost (T>0.8) Jet boost (and mass) calibrated ! P.Azzurri - Latest physics results from ALEPH

34. Radiative Z peak • Main effective changes • wrt observation large data/MC shift : • Strict cut on beam background • ECAL cleanning in jets • Removal of low energy neutrals • Correction of forward tracks P.Azzurri - Latest physics results from ALEPH