Search for X WZ 0  evjj Paper Seminar

1. Search for XWZ0  evjjPaper Seminar David Toback & Chris Battle Texas A&M Henry Frisch University of Chicago

2. Outline • Theory and Signature • Overview of Analysis; Event Selection and What signal would look like; Acceptance • Backgrounds • Comparing Data, Signal and Backgrounds • Fitting and Systematics • Limits • Conclusions

3. XWZ0  evjj • We want to search for new physics in a model independent manner • Many models predict new particles which decay via XWZ0 • The Wen and Z0jj have advantages: • Electrons are straightforward to trigger on and identify • Z0jj has a large branching fraction

4. Feynman Diagram X 0

5. Example Feynman Diagram • Heavy Charged Vector Boson: W’ WZ0 • Technicolor Rho: rT WZ0 W’ width, G(W’), can vary greatly Search for X as a function of mass and width 0

6. Outline • Theory and Signature • Overview of Analysis; Event Selection and What signal would look like; Acceptance • Backgrounds • Comparing Data, Signal and Backgrounds • Fitting and Systematics • Limits • Conclusions

7. W+2jets Event Selection & Summary • 1 electron • Missing ET • 2 Jets • 110 pb-1 of data from Run 1A and 1B

8. Looking for Signal • Model X production using W’  WZ0 in Pythia • Look for X WZ0 mass bumps in both Mjj and MW+jj

9. Overview of Analysis • Constrain PZn using W mass • Reconstruct dijet and W+dijet masses • Look for bumps in dijet vs. W+dijet mass plane using a fit Reconstruction procedure does a good job of reproducing W’

10. Acceptance vs. Mass Good Acceptance as a function of mass G(X)<< MX

11. Outline • Theory and Signature • Overview of Analysis; Event Selection and What signal would look like; Acceptance • Backgrounds • Comparing Data, Signal and Backgrounds • Fitting and Systematics • Limits • Conclusions

12. Backgrounds • W+jets ( W  eν, W τν  eννν ) • Non W+jets • Fakes • `tt • `bt • WW • WZ0 • Z0 ( ee) + jets • Z0 (ττ) + jets

13. Background Normalization • All but W+jets have an absolute normalization • W+jets has a large normalization error • Take normalization from the data: Ndata= NW+jets + Nother + Nsignal

14. Summary of Backgrounds Estimated from data { Use PYTHIA and normalize to known cross sections Combination of VECBOS and PYTHIA. Norm to measured Z0ee data Use VECBOS for shape. Large k factor uncertainty. Take normalization from fit to data. Agrees with Duke Group results

15. Outline • Theory and Signature • Overview of Analysis; Event Selection and What signal would look like; Acceptance • Backgrounds • Comparing Data, Signal and Backgrounds • Fitting and Systematics • Limits • Conclusions

16. Dijet Mass Distributions • No evidence of Z0 produced in association with a W • W+jets normalized to data and non-W+jets (no signal assumption)

17. W+dijet Mass Distributions • No evidence of W’ or other new particle production • W+jets normalized to the data and non-W+jets (no signal assumption)

18. W+dijet in 3 Mass Regions • Use previous normalization and check Z0 region • Data outside Z0 mass region is well modeled telling us that the background estimate inside the Z0 mass region is well modeled (both norm & shape). • No evidence for WZ0 production. ( *Figure 1 in PRL)

19. Outline • Theory and Signature • Overview of Analysis; Event Selection and What signal would look like; Acceptance • Backgrounds • Comparing Data, Signal and Backgrounds • Fitting and Systematics • Limits • Conclusions

20. Turning the Crank • Searching the data for X • Look for excess in dijet vs. W+dijet mass plane • Fit the data to signal, W+jets and non-W+jets • Fix non-W+jets background • Allow W+jets and signal to float • Binned likelihood fit in the 2-d dijet vs. W+Dijet mass plane • Normalization mostly comes from outside signal region • Same technique as Dijet Mass bump search (R. Harris) • No evidence for signal (as seen in previous plots and in the fit results) • Get 95% C.L. cross section upper limit from the fit • Incorporate systematic errors

21. Example Signal Fits I Data vs. background with no signal from “reference model” W’ with a mass of 300 GeV .

22. Example Signal Fits II Data vs. expectations (back & signal) with best fit amount of signal from reference model W’ with a mass of 300 GeV .

23. Example: Signal Fits III Data vs. expectations (back and signal): signal level which is excluded at the 95% C.L. (reference model, MW’= 300 GeV) .

24. Example: Signal Fits IV Data vs. expectations (back & signal) with reference model; theoretical production cross section Excluded at the 95% C.L.

25. Systematic Errors Use same (conservative) methods as dijet mass bump search and `bb mass bump search • Find the no-systematic 95% C.L. upper limit • Vary background or signal (depending on effect) by +1σ and –1σ and re-fit • Recalculate new limit • Take absolute value of % change in limit (even if the cross section limit goes down!) • Take the larger % of the two variations (+1σ and –1σ) as the % smearing • Take all variations and add them in quadrature • Use this as a Gaussian smearing to the likelihood

26. Systematic errors Vary both signal and background separately to over-estimate the magnitude of the effect • Amount of non-W+jets (vary background) • Absolute jet energy scale (vary signal) • Energy resolution (vary signal) • Radiation (vary signal) • Q2 scale of W+Jets (vary background) • Structure functions (vary background) • Acceptance (add % error) • Luminosity (add % error)

27. Systematic Errors • Absolute energy scale dominates the error • Shifts signal into region with lots more background • Checked with Pseudo-Expts

28. Errors Cont.:Extended Gauge Model • Narrower width = less signal in high background region • Absolute energy scale again dominates the error

29. Systematic Error Summary • Systematic errors for lots of effects • Conservative estimation methods • We are not pulled unreasonably by an unexpected fluctuation in the data • Data is well modeled • Set limits

30. Outline • Theory and Signature • Overview of Analysis; Event Selection and What signal would look like; Acceptance • Backgrounds • Comparing Data, Signal and Backgrounds • Fitting and Systematics • Limits • Conclusions

31. Setting Limits • We set generic 95% C.L. cross section limits on X production as a function of mass and width • Use W’ production as a good approximation • Use W’ production as a model (determines production cross sections) and set mass limits • Begin with an theoretical overview of W’

32. Reference Model • Simplest W’ Model • W’ is the same as W only heavier (same couplings to quarks and leptons) • No new neutrinos • Call this “Reference Model” • Consequences • Large production cross sections • Γ(W’  WZ0)  M5W’ • Large branching fraction to WZ0 • Large total width, Γ(W’) • Model becomes unphysical at approx. MW  Γ(W’) which occurs at approx. MW’  425 GeV/c2

33. Extended Gauge Model • Simplest W’ model unphysical (can be no W’WZ0 vertex in SM) • Simplest extension is W’-W mixing as in extended gauge models (e.g. L-R symmetry) • Effective W’WZ vertex; same as in reference model but vertex multiplied by  , which is estimated (non-trivially) by  = C(MW / MW’)2 where C is of order 1 • Γ(W’ WZ0)  MW’ • Narrow width  Small Br; most previous W’ searches assume this (e.g. W’  eν ) • Use  = C(MW / MW’)2 as general Г(W’) << MW’ • Large production cross section

34. Theoretical Consequences • Comparison of the reference and extended gauge models • Drastic differences in width and branching ratios Wide Widths Small Br Narrow Widths Large Br

35. Branching Ratio for W’WZ0 • Reference Model • W’ is the same as the SM W only heavier • Large width large branching ratio • Extended Gauge Model • Mixing factor between W and W’ • Small width • Small branching ratio

36. Mass Dist. For Reference Model • 1000 PYTHIA generated events for the reference model • Width increases as a function of mass

37. 95% C.L. Limits: Reference Model • We exclude the reference model of W’ from 200 to 480 GeV. • Taken in conjunction with low mass exclusions from the W’lν , we exclude the entire model

38. 95% C.L. Limits: Ext. Gauge Model • 95% C.L. upper limits on cross section vs. W’ mass for the extended gauge model • No mass limits for very small factors (branching ratio is tiny) • Cross section limits applicable for any new particle production with narrow width XWZ0

39. Cross Section vs. Mixing Factor 95% C.L. upper limits on cross section vs. W – W’ mixing factor

40. Cross Section vs. W’ Width • 95% C.L. upper limits on the cross section vs. W’ width • These limits are good for any new particle production with XWZ0; narrow or wide width * PRL Figure 2

41. Limits on Mixing Factor vs. W’ Mass 95% C.L. exclusion region for W-W’ mixing factor vs. W’ mass * PRL Figure 3

42. Outline • Theory and Signature • Overview of Analysis; Event Selection and What signal would look like; Acceptance • Backgrounds • Comparing Data, Signal and Backgrounds • Fitting and Systematics • Limits • Conclusions

43. Conclusions • No evidence forXWZ0in the enjjdecay channel • Narrow and width width approximations • Most comprehensive limits on direct W’ WZ0 • Reference model completely excluded • Large exclusions in an extended gauge model • Web page at -hepr8.physics.tamu.edu/hep/wprime/ • Documentation in CDF Note 5610 • PRL draft in CDF Note 5629

44. Backups

45. Acceptance vs. W’ Mass • Good Acceptance for W’ • Reference Model • Large width at large mass • Lots of low mass events • Lower acceptance

46. Pseudo-Experiments: Check Re-run entire analysis on fake data generated from backgrounds only • Generate fake data set • Allow number of events to float • Re-estimate the effect of all systematic errors for the fake data set • Add errors in quadrature as for data • Re-estimate the limit from the fake data set • Repeat many times • Repeat for different masses and mixing factors

47. Pseudo-Exp: Jet Energy Error • The effect on the limit (in %) of the jet energy scale uncertainty for a set of pseudo-experiments with W’ mass of 200, 300, 400, 500, & 600 GeV respectively. This is for the extended gauge model with C=1.

48. Pseudo-Experiments: Total Error • The total effect on the limit (in %) due to all systematic uncertainties for a set of pseudo-experiments with W’ mass of 200, 300, 400, 500, & 600 GeV respectively. This is for the extended gauge model with C=1.

49. Pseudo-Experiments: Limit • 95% cross section upper limit from a set of pseudo-experiments with W’ mass of 200, 300, 400, 500, & 600 GeV respectively. This is for the reference model.

50. Pseudo-Experiments: Total Error • The total effect on the limit (in %) due to all systematic uncertainties for a set of pseudo-experiments with W’ mass of 200, 300, 400, 500, & 600 GeV respectively. This is for the reference model.