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Higgs Sensitivity Study

Outline Committee and Charge Road Map Event Yields Dijet Mass Resolution Extraction of Limit and discovery limits. Summary and Schedule. Higgs Sensitivity Study.

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Higgs Sensitivity Study

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  1. Outline Committee and Charge Road Map Event Yields Dijet Mass Resolution Extraction of Limit and discovery limits. Summary and Schedule Higgs Sensitivity Study NOTE: We are not yet to the point where we have final numbers…please consider the trends and topics…not necessarily the specific numbers. From the Higgs-SUSY Working Group Report. CDF Collaboration Meeting May 2003

  2. Committee and Charge Provide an update to the SUSY-Higgs Working Group evaluation (http://fnth37.fnal.gov/susy.html) of the Tevatron's Standard Model Higgs search potential. This should be done in coordination with a similar committee formed by D0. The studies are to be divided by Higgs decay channel with CDF focusing on WH production and D0 on ZH production. The results of these studies should be combined, assuming approximately equal detector performance, producing a determination of the integrated luminosity required for 95% confidence level exclusion limits, 3 sigma and 5 sigma discovery versus Higgs mass. The studies should use the experience gained by early Run2 CDF detector performance, simulation of the detector and relevant physics processes and build on the work reported by the SUSY-Higgs Working group. The committee should explore analysis techniques that could improve the reach of the Higgs sensitivity. The studies should assume Tevatron operation at 396ns, with instantaneous luminosities as high as 4xE32 /cm**2/s . The committee is encouraged to draw upon resources of the CDF collaboration, especially those individuals with expertise in critical areas. The Committee's responsibility is to direct and coordinate the preparation of this study, however it is understood that significant contributions by other members of our collaboration will be recognized in the final report. A preliminary report should be prepared by June 1, 2003 with the goal of blessing the document by the CDF collaboration in the Joint Physics Meeting. A final combined CDF and D0 document should be ready for public circulation by the end of June and availability for the Fermilab Accelerator DOE review expected latter in summer 2003. The final combined report, containing the work of CDF and D0, will be presented to Ray Orbach, Director of the DOE Office of Science, who requested that CDF and D0 perform these studies for him. • Committee:Tommaso Dorigo, Tom Junk, Joseph Kroll (co-chair), Mario Martinez, Pete McNamara, Fumi Ukegawa, Brian Winer (co-Chair), Weiming Yao • Other workers:Henri Bachacou, John Conway, Martin Hennecke, Jason Nielsen, Michael Schmitt, Luca Scodellaro CHARGE ~ In a convenient unreadable font! CDF Collaboration Meeting May 2003

  3. Searching for SM Higgs • Background (~irreducible) • W+Jets • tt : • Single Top • WZ • Signal Processes: • CDF: • D0: • HSWG: • Decay Channels: • H • Cross Section x BR CDF Collaboration Meeting May 2003

  4. Detecting the Signal • Backgrounds are from real bb • Improving B-Tagging helps • Counting Experiment • Inside a mass window (HSWG) • Normalization of Bkg Important • Use Kinematic/topological Cuts • tt: should have extra jets/MET • Wbb: different jet properties. • Fit Dijet Mass distribution • Help Normalization of Bkg. • Dijet Mass Resolution Critical • Understand from data Z bb PT of bb System GeV/c CDF Note 6309: Run 1 NN search for Higgs (Chris Neu) CDF Collaboration Meeting May 2003

  5. Plenty of Publications • We have not been idle in this area • The CDF Collaboration, Phys. Rev. Lett. 90, 081802 (2003). Search for W' Boson Decaying to a Top and Bottom Quark Pair in 1.8 TeV p anti-p Collisions • The CDF Collaboration, Phys. Rev. D65, 091120 (2002) Search for Single-Top-Quark Production in p anti-p Collisions at s**(1/2) = 1.8 TeV • The CDF Collaboration, Phys. Rev. Lett. 84, 5273 (2000) Search for Scalar Top Quark Production in p anti-p Collisions at s**(1/2) = 1.8 TeV • The CDF Collaboration, Phys. Rev. Lett. 81, 5748 (1998). Search for Higgs Bosons Produced in Association with a Vector Boson in p anti-p Collisions at s**(1/2) = 1.8 TeV • The CDF Collaboration, Phys. Rev. Lett. 79, 3819 (1997) Search for New Particles Decaying into b anti-b and Produced in Association with W Bosons Decaying into e nu and mu nu at the Tevatron • Plus a series of SUSY Higgs Search papers. CDF Collaboration Meeting May 2003

  6. Road Map for Study Event Yields Dijet Mass Resolution • Establish baseline event selection • Use the Run 2A Winter Conference Select (Top/EWK) • B Tagging • Estimate Extensions to acceptance. • Impact of multiple interactions. • Explore other selection cuts to reduce backgrounds…this needs more work. • IMPORTANT: We must use every part of our detector and reducing the sys. Error on background is key. • What can we achieve? • Use of Tracking Information • Full Corrections for b-quarks • Advanced Techniques using full event information. Extracting Luminosity Thresholds • Establishing thresholds for 95%CL, 3s, 5s discovery. • Use full Mjj Spectrum • How do we quote the result? CDF Collaboration Meeting May 2003

  7. Event Yield~Introduction Lepton Selection: (CEM, CMUP, CMX) Winter 2003 Conference Cuts Missing ET > 20 GeV (raw) Jet Counting: ET > 10 GeV (raw) |hd| < 2.0 Z-Veto: Winter 2003 Top Cuts Additional Kinematic Cuts: One Jet ET > 25 GeV No third Jet ET > 20 GeV No second Isolated Track • Establish a Solid Baseline first: • Lepton Selection (Winter 2003) • Loose Jet Selection • Use Run 2A detector Simulation • Not perfect…would have preferred a Run 2B Simulation • But offline Alg. are tuned for current detector and L…no time to optimize. • Additional Kinematic Cuts • Attempt to clean up backgrounds • Followed approach similar to HSWG • More optimization possible • e.g. Variables from CDF6309 CDF Collaboration Meeting May 2003

  8. Event Yield ~ Signal Events • Monte Carlo Sample: • Alpgen: WH Productions • MH 110, 115, 120, 130, 140 • 500K events at each mass • All decays W and H. • Standard Winter 2003 approach for generation and simulation • Cross Section and BR • PPHV T.Han, S Willenbrock Phys. Lett. B273 (1991) 167. • HDECAY: A.Djouadi,J.Kalinowski, M. Spira Comp. Phys. Commun 108C (1998) 56 CDF Collaboration Meeting May 2003

  9. Signal Distributions WH110 WH120 WH140 CDF Collaboration Meeting May 2003

  10. B-Tagging • Baseline: • Use Winter 2003 Secvtx • Uses Beamline…not optimal • Is “tight” tag for both b’s not optimal • Eta range ~ < 1.0 • Additional Requirement that one of the tags in a jet with ET > 25 • Clearly we must • Use event-by-event vertex • Have a loose tag for second leg • JETPRB (More Later) • extend to higher eta? • More Later • …other good ideas CDF Collaboration Meeting May 2003

  11. Summary of Signal Yields Preliminary CDF Collaboration Meeting May 2003

  12. Yields Don’t run screaming from the room…yet. There are a lot of improvements that are possible on these numbers: e.g. extended lepton coverage loose b-tagging. etc.This is just a (low) reference point to work from …More details after looking at the backgrounds. CDF Collaboration Meeting May 2003

  13. Event Yields ~ Backgrounds • Monte Carlo: • Relied on much of the background Monte Carlo generated for the top group for the winter conferences. • ttbar • Alpgen, Herwig, Pythia • Wbb, Wcc • Alpgen • WZ • Alpgen • Single Top • Pythia CDF Collaboration Meeting May 2003

  14. Background Distributions Wbb ttbar W*  tb CDF Collaboration Meeting May 2003

  15. Summary of Background Yields Preliminary CDF Collaboration Meeting May 2003

  16. Event Yield ~ Extensions/Improvements Improve S/B Improve Acceptance • Lepton Coverage • Include Plug Electrons • Include Muons in the IMU • Tau’s • Isolated Tracks • B-Tagging • Loose tagging • Extension to higher h • Can we get away with a single tag? • Kinematic Selection • Beat down individual backgrounds. • Avoid Shaping the Mjj • Improve Mjj…more later. • Techniques • Neural Networks • Recent Analysis got an effective 30% increase in Lum. We have investigated some of these…but it is a never ending list of ideas. CDF Collaboration Meeting May 2003

  17. Primary Lepton (h) Coverage • Looking for electrons in the plug and muons in the IMU/BMU. • The HWG Report assumed coverage out to |h|<2.0 • We will have to do this. • Estimated the increase in the acceptance • Look where the HEPG level lepton from W decay fell in the detector. • Ratio of the leptons that fall in our current coverage (CEM,CMUP,CMX) to the ones that fell in Plug (|h|<2.0) and IMU (|h|<2.0). CDF Collaboration Meeting May 2003

  18. Primary Lepton Type • Consider other lepton signatures. • Hadronic Tau Decays of W • Isolated Tracks • Leptons that have failed our standard cuts, and taus. • Taus: • Purity Good. • Efficiency not as high • Isolated Tracks • PT>15 Isol < 1.0 (R=0.4) • MET > 35 GeV • WH Acceptance Increase: 44% (MH = 120 GeV/c2) Note: If these samples have lower S/B, we can combine them as a separate channel in the end. CDF Collaboration Meeting May 2003

  19. B-Tagging ~ Loose Tagging (|h|<~1) • We want the tagging on the second leg to be loose. • We have parameterized the OR between Secvtx and JETPRB. • We are in the progress of investigating the impact on all the signal and backgrounds. • Signal Double Tag: Factor of 1.45 to 2.0 CDF Collaboration Meeting May 2003

  20. B-Tagging ~ Extended (1<|h|<2) • The HSWG Report assume b-tagging out to |h|<2.0. • Our current algorithms drop off rapidly after ~1.0 to 1.1. • Based on the distribution of the b-quarks in the events there is acceptance to be gained. • We are trying to quantify • Of course we have not yet developed such an algorithm…how we do it is a harder question. CDF Collaboration Meeting May 2003

  21. Impact of Multiple Interactions • On the debit side, we must accomplish all this in an environment of many multiple interactions per crossing. • This will involve reoptimizing track reconstruction, b-tagging, lepton-ID, and general event selection (e.g. extra jet veto) • What we have done is try to identify where things go bad. • Monte Carlo Datasets with multiple interactions. • The MC may not have the proper tuning but we can look at trends. • Used our standard reconstruction, tagging, etc. which is tuned at low luminosity. • The degradation that we see is worse than it will be after reoptimizing for that environment. CDF Collaboration Meeting May 2003

  22. Impact of Multiple Interactions • Kept standard event reconstruction and event selection: • Except jet veto…more in a minute. • Monte Carlo: • Pythia WH enbb Production • Added minimum bias interactions using “mbr” • Samples with 0,2,4,6,8, and 10 additional minimum bias. SecVtx Tagging Tagging Rates are per taggable Jet… We will need to reoptimize the tagging! CDF Collaboration Meeting May 2003

  23. Example of Changing our Approach • One of the kinematic cuts is the removal of events with a third jet with ET > 20 GeV. (Part of Full Jet Selection Below) • This will clearly be sensitive to extra events. • Demand Veto Jet is consistent with Lepton Primary Vertex by looking at the z0 of tracks in the jets. Several Competing effects in the Jet selection. CDF Collaboration Meeting May 2003

  24. Impact of Multiple Interactions • We have examined a variety of scenarios…here is one example table. Degradation Primarily Cal Isolation CDF Collaboration Meeting May 2003

  25. Dijet Mass Resolution • Dijet Mass “peak” is important • Excellent Resolution is essential • Counting events in a window • Fitting Mjj • Use as much information as possible. • Dijet Mass Group • A lot of work • Including tracking information, etc. • It’s all about the Jet Corrections. • Good Test Sample: CDF Collaboration Meeting May 2003

  26. Including Other information • Dijet Mass Group has been working hard developing algorithms which correct the energy using tracking information. From a talk by Steve Kuhlmann at a Higgs Working Group Meeting Mbb = 120 GeV Jets in the central and no b-specific corrections. CDF Collaboration Meeting May 2003

  27. Incorporation Corrections for b-quarks • We have studied corrections that are derived on WH events considering the b-quark jets in these events. • These corrections are applied on top of the tracking corrections from the dijet mass group. • Cone Size R=0.4 • But look at tracks R=1.0 • Use Charge Fraction and ET • In principle we could derive these as a function of MH Jets matched to b-quarks Central – Central Jets so tracking info can be used on both jets. CDF Collaboration Meeting May 2003

  28. B-Jets in Plug Plug – Plug B-Jets Central – Plug B-Jets Second Gaussian larger CDF Collaboration Meeting May 2003

  29. Other Interesting Approach Note: No H1 Correction Here • Do other event quantities help? • “Hyperball Method” (CDF-6450) • Tommaso Dorigo and Luca Scordellaro • Use N Kinematic Variables • e.g. • Determine the average mass reconstruction error for small regions of N-dimensional space • Use this to correct events that fall in that region of phase space Must Avoid Shaping Peak in Bkg. Test on data. (e.g. Z bb) CDF Collaboration Meeting May 2003

  30. Extracting Luminosity Thresholds • To quantify our sensitivity we would like to know how much luminosity is required to: • Exclude (95% CL) the existence of the SM Higgs at the certain mass. • This is based on the theoretical cross section. • Observe a 3s excess of events. • Consistent with having a higgs decay (i.e. mass “bump”). • Observe a 5s excess of events. • We want a method that can easily “sum” over different channels and CDF and Dzero data. • Note: it will be extremely difficult to see 3s or 5s excesses in individual channels for individual experiments • Rough “Rule of Thumb”…multiply the L-Threshold by 4. CDF Collaboration Meeting May 2003

  31. Method • Statistical Analysis Using Pseudoexperiments • Input: • Predicted Event Yield for each background source and signal • Dijet Mass Distribution. (Binned) • We are using the shape information • Scan through Integrated Luminosity. • At each Luminosity, generate a large number of pseudoexperiments both with and without signal. • For each pseudoexperiment ask “Do we find a Ns excess or 95% CL” • Keep Track of the Fraction of pseudoexperiments that satisfy the condition • For the last step we have investigated two approaches • Bayesian Integration (with a flat prior) • CLS Frequentist Approach (used at LEP) • Methods include external constraints and sys. Errors. Give similar Results CDF Collaboration Meeting May 2003

  32. …50% of Experiments… • Where do we set the Luminosity threshold for a given higgs mass? • To set a threshold we must define that threshold as requiring X% of the pseudoexperiments satisfy the condition (e.g. 3s excess) • The HSWG Report required 50% of the pseudoexperiments satisfy the condition. • It does matter. CDF Collaboration Meeting May 2003

  33. Explore Sensitivity to Various Effect Impact of Dijet Mass Resolution • These methods allow us to explore our sensitivity to various effects. • Dijet Mass Resolution • Uncertainty on background. • Different event selection. CDF Collaboration Meeting May 2003

  34. Impact of Systematics • Important conclusion: When the S/B is very low we need to tightly control the systematic error on the backgrounds (normalization and shape.) 10% CDF Collaboration Meeting May 2003

  35. Combining with Dzero • The method is setup so that we can “easily” combine the results with Dzero. • Each experiment would provide the expected Mjj distributions and the distributions from data. • The method uses likelihoods so it can combine the two experiments. • Need to think carefully about the common systematic errors. • As mentioned earlier Dzero is working on the ZH channel. We plan to combine our results using this approach. CDF Collaboration Meeting May 2003

  36. Summary and Schedule • We have attacked the WH channel search for the SM higgs boson on three major fronts: • Event Yields including B-Tagging: • One Conclusion: We must use every part of the detector and every handle possible to increase the event yield. • Dijet Mass Resolution: • One Conclusion: This is perhaps where we “win” the fastest. • Luminosity Thresholds: • One Conclusion: Life is really hard sometimes. • Remember that we will be looking for the higgs as we accumulate data. • Setting Limits as we go. • Our techniques will become more refined. CDF Collaboration Meeting May 2003

  37. Summary and Schedule • Schedule: • Planned to “Prebless” at June 6th Joint Physics Mtg. • Had planned on May 30th but we need more time. • Bless at June 20th • Will include ZH study from DZero. • Meeting with Ray Orbach on June 24th at 1 pm. • Hey that gives us the morning to work right? • Having a definitive statement for Orbach is not possible. • We can’t precisely predict what our abilities will be 5 years from now. • We can communicate to him our general level of our sensitivity and relate the critical issues. • We should emphasize our understanding of the problem only gets better with time and data! CDF Collaboration Meeting May 2003

  38. Final Comments • The top discovery in Run I took several years and an enormous amount of work. • It was a complicated analysis in several different channels. • Our reach was much higher than we expected at the start of the Run 1. • Our ability to measure the top mass was much better than we expected at the start of the Run 1. • To a great extend it was not that sensitive to systematic errors. • The higgs search is much more complicated than the top analysis. • Primarily due to the poor S/B. • Bringing in many more “channels” to increase acceptance. • We will probably be sensitive to systematic errors. • …hopefully our reach will be better than we think… CDF Collaboration Meeting May 2003

  39. Final Thought I’m confident that given the data and the time, the collaboration will find a way to squeeze the most sensitivity out of our data sample…we have very creative people on this collaboration and that is perhaps our biggest asset. CDF Collaboration Meeting May 2003

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