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Systematic studies on mw

Systematic studies on mw. D. BOUMEDIENE – P. PEREZ – E. LANCON CEA/ Saclay O. BUCHMÜLLER. 1- Reminder (cone, P cut, PF cut) 2- P Flow cut analysis 3- Cone analysis 4- No typ6 objects analysis 5- Charged only analysis 6- Mjet=0 analysis 7- Conclusion. Reminder. Leukerbad:

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Systematic studies on mw

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  1. Systematic studies on mw D. BOUMEDIENE – P. PEREZ – E. LANCON CEA/ Saclay O. BUCHMÜLLER 1- Reminder (cone, P cut, PF cut) 2- P Flow cut analysis 3- Cone analysis 4- No typ6 objects analysis 5- Charged only analysis 6- Mjet=0 analysis 7- Conclusion D. BOUMEDIENE

  2. Reminder • Leukerbad: • Pcut analysis (cutting on all Eflow objects) is unstable for all channels • The instability is due to some neutral objects (ECAL residuals : typ6 Eflow objects ) • the analysis is stable either : • if typ6 objects are not considered at all, • or if no cut is applied on typ6 objects • However the two analyses lead to incompatible mw measurements • Pisa / W meeting 06-07-01: • Particle Flow based cut analysis is not stable in the 4q channel (it motivated the test of Pcut on 4q and lnqq) D. BOUMEDIENE

  3. Aim • mw measurement stability is tested for the following algorithms • Pcut (see Leukerbad meeting) • PF cut (4q+lnqq) • Cone (4q+lnqq) • Absolute ALEPH mw measurement scale is tested with • Charged only (4q+lnqq) • Typ6 suppression (updated) • Mjet=0 (4q+lnqq) New today Mw is measured 23 times (4 channels) D. BOUMEDIENE

  4. Techniques • 4q channels: 3D fit • lnqq channels: • The lepton is not used (because not concerned by the effect): 2D fit • All the channels are used (except lnln) • Parametrisations/jet corrections are systematically recomputed • Correlations are evaluated at 2 energies (4q+lnqq merged) • shifts on mw derived from observed errors. D. BOUMEDIENE

  5. Pflow Cut Analysis • PF in 4q channel is given by Thomas's code P Flow cut An equivalent distribution is  defined in the 3 lnqq channels D. BOUMEDIENE

  6. Pflow cut analysis • tendency: slope is 2.0 s far from 0 (jetset) • discrepancy wrt flat: 1.6 s D. BOUMEDIENE

  7. Pflow cut analysis: no cut on typ6 obj. • tendency: 1.2 s from slope=0 • discrepancy wrt flat: 0.4 s tendency: 2.0 s  1.2s discrepancy wrt flat: 1.6 s 0.4s D. BOUMEDIENE

  8. PFcut Summary • PF cut analysis (cutting on all objects) is unstable (2.0 s) • It is difficult to use it to measure CR • The size of the effect is compatible with what was observed with the P cut. • -82  51 MeV/c2 (excluding [0.1,0.9], lnqq+4q) • The physical source of the problem in Pcut/Pfcut analyses comes from the same source: cutting on typ6 objects • PF cut analysis without cutting on typ6 objects is stable D. BOUMEDIENE

  9. the cone analysis Rcone 0.6 0.75 1.0 1.25 2.0 r (%) 73 7883 90 95 • Hugo’s cone Algorithm is used for the reconstruction (http://alephwww.cern.ch/~ruizh/aleph-only/cones/cones.html) • jet parametrisations are recomputed • Jet energy corrections are done ( Patrice talk) • All energies, all channels (except lnln) are used • Correlations between analyses are computed with • 2 x 200k evt (@ 2 energies) • The difference 4q / lnqq and energy dependence are neglected D. BOUMEDIENE

  10. Parametrisation (Rc=0.6) sb: angular resolution D. BOUMEDIENE

  11. Parametrisation (Rc=2.0) sb: angular resolution D. BOUMEDIENE

  12. Dmw versus RC • tendency: 2.6 s far from expectations (jetset) • discrepancy wrt flat: 2.4 s • better probability for the slope Durham analysis (RC=3.0) taken as reference D. BOUMEDIENE

  13. 4q/lnqq contributions Probability of a linear behavior (with a slope) increases when combining 4q and lnqq channels D. BOUMEDIENE

  14. Dmw versus s (Rc=0.75) D. BOUMEDIENE

  15. Cone without typ6 objects • tendency: FLAT(<1s) • discrepancy wrt flat: (<1s) RC=2.0 taken as reference  ‘Cutting’ on typ6 objects caused the instability D. BOUMEDIENE

  16. Cone Summary • Cone analysis (with all measured energy) is unstable (2.6 s) as expected • It cannot be used to measure CR • The problem is not due to 1 energy only • The effect is similar to what was observed with the P cut and PF cut analyses : • -85  31 MeV/c2 (Rc=0.6, lnqq+4q) • The physical source of the problem is the same • Cone analysis without typ6 is stable D. BOUMEDIENE

  17. Standard Durham analysis without Typ6 objects • All type6 (~5% energy) objects are removed from the jets. • Statistical sensitivity loss is < 1% in both lnqq and 4q channels • Correlation with standard analysis r =92% D. BOUMEDIENE

  18. Effect of Typ6 objects suppression D. BOUMEDIENE

  19. Typ6 Suppression Summary • mw measured without typ6 objects is shifted wrt standard analysis by: • -112  20 MeV/c2 • The effect is compatible to what was observed with the P cut / PF cut / cone analyses D. BOUMEDIENE

  20. Charged only analysis • we can test an analysis using only charged tracks. Such an analysis is reliable (all distributions for charged are in agreement between DATA/MC) • but we expect a big loss of sensitivity. Tested analysis: Charged objects only are used correlation with std analysis: r = 31 % Sensitivity loss: ~70 % D. BOUMEDIENE

  21. Charged only analysis D. BOUMEDIENE

  22. Charged Only Summary • mw measured with charged objects only is shifted wrt standard analysis by: • -120  65 MeV/c2 • The effect is compatible to what was observed with the P cut / PF cut / cone / pre typ 6 analyses D. BOUMEDIENE

  23. mjet=0 analysis • Jet masses are biased by a bad simulation of multiplicities in particular for typ6 objects. • It is known that the bias propagates to mw • A measurement with a fixed Mjet should be insensitive to a bias Tested analysis: We fix Ejet = Pjet (  same jet mass in MC and DATA)  Nothing is removed, we just forget the jet mass correlation with std analysis: r = 74 % Sensitivity loss: ~15 (4q) ~21(lnqq) % D. BOUMEDIENE

  24. mjet = 0 analysis D. BOUMEDIENE

  25. mjet=0 Summary • mw measured with mjet=0 is shifted wrt standard analysis (2D for lnqq) by: • -79  31 MeV/c2 • The effect is compatible with what was observed with • P cut / PF cut / cone / pre typ 6 / charged only analyses D. BOUMEDIENE

  26. Summary Analysis Dmw(MeV/c2)slope slope no typ6 CONE (Rc=0.6) - 85  31(2.7 s) 2.6s 0.7s Pflow - 82  51 (1.6 s) 2.0s 1.2s (exclud. [0.1,0.9]) Pcut (cut 2GeV) -125  40 (3.1s) 3.2s 0.5s Pre TYP6 -112  20(5.6 s) - - Charged only -120  65(1.8 s) - - Mjet=0 - 79  31(2.5 s) - - we have compelling evidences that the aleph w mass is overestimated by 50-100 MeV/c2 D. BOUMEDIENE

  27. Conclusion We have compelling evidences that the aleph w mass is overestimated by 50-100 MeV/c2 We have developed low correlated analyses which are stable in the lnqq channels (Minimum requirement for 4q Color Reconnection sensitive analysis) Those analyses will now be used to study Color Reconnection effect in the 4q channel mw and width analysis The code and ntuples are publicly available on Castor for all energies and all MC D. BOUMEDIENE

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