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Chris Hays Duke University

W Mass Measurement at the Tevatron. D Ø. Chris Hays Duke University. CDF. TEV4LHC Workshop Fermilab 2004. Past, Present, and Future. Precision of direct measurements:. x. x. x. x. x. x. 2004: LEP 42 MeV. 1990: UA2 900 MeV. 2000: D Ø 91 MeV. 1989: UA1 2.9 GeV. 1995:

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Chris Hays Duke University

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  1. W Mass Measurement at the Tevatron DØ Chris HaysDuke University CDF TEV4LHC Workshop Fermilab 2004

  2. Past, Present, and Future Precision of direct measurements: x x x x x x 2004: LEP 42 MeV 1990: UA2 900 MeV 2000: DØ 91 MeV 1989: UA1 2.9 GeV 1995: CDF 180 MeV 1983: UA1 5 GeV Tevatron 59 MeV W mass now known to better than 5 parts in 10,000 (MW=34 MeV) Looking forward: * Tevatron Run 2 has quadrupled Run 1 CDF, DØ data sets * CDF has analyzed first 200 pb-1 of data and determined uncertainties CDF: 79 MeV DØ: 84 MeV x x x x x x 2011: Tevatron <15 MeV 2006: CDF/DØ <34 MeV 2004: CDF 76 MeV 2005: CDF/DØ <59 MeV 2008: CDF/DØ <20 MeV 2010: ATLAS/CMS <20 MeV LHC <15 MeV ~1 fb-1 ~0.4 fb-1 ~0.2 fb-1 ~4 fb-1 ~10 fb-1 C. Hays, Duke University, TEV4LHC

  3. W Mass Fit Distributions Transverse mass * mT2 = 2pTET(1-cos(Df)) * m ~ 2 pT + u|| * Low sensitivity to pTW * Recoil modelling crucial ET = -(pT + u) u^ Lepton pT * m ~ 2 pT * Insensitive to recoil * pTW modelling crucial (u) u|| CDF RUN II PRELIMINARY pT mT CDF RUN II PRELIMINARY C. Hays, Duke University, TEV4LHC

  4. CDF Run 2 Uncertainties Scale and resolution: m: W = + 30 MeV e: W = + 70 MeV Tower removal: m: W = + 10 MeV e: W = + 20 MeV Transverse mass fit Backgrounds: m,e: W = + 20 MeV Production and decay model: m,e: W = + 30 MeV CDF RUN II PRELIMINARY Statistics: m: W = + 50 MeV e: W = + 45 MeV Scale and resolution: m,e: W = + 50 MeV C. Hays, Duke University, TEV4LHC

  5. Production and Decay Model Uncertainties CDF RUN II PRELIMINARY Parton Distribution Functions QED Radiative Corrections e Uncertainty determined from CTEQ eigenvectors + MRST e W charge asymmetry will reduce uncertainty e Single-photon FSR modelled l + W ~ 5 MeV with 4 fb-1 v LHC: No charge asymmetry v Constrain PDFs with lepton h distributions from W and Z e 2-photon FSR needs to be added W~ 5 MeV with 4 fb-1 W ~ 10 MeV achievable (also at LHC) C. Hays, Duke University, TEV4LHC

  6. Production and Decay Model Uncertainties pTW Model e Uncertainties determined from RESBOS parameters g1, g2, g3 e Parameters constrained by Run 1 Z pT distribution g2 = 0.68 + 0.12 GeV2 g3 = -0.60 + 0.30 pT fit: W = + 27 MeV mT fit: W = + 13 MeV CDF RUN II PRELIMINARY W ~ 5 MeV with 4 fb-1 (pT fit: 10 MeV) v LHC: Large Z statistics W ~ 5 MeV achievable (also for pT fit) GW e 70 MeV uncertainty from world average of direct measurements W~ 5 MeV with 4 fb-1 (also at LHC) C. Hays, Duke University, TEV4LHC

  7. CDF Run 2 Muon Momentum Calibration Set momentum scale using J/ and upsilon decays to muons e Uncertainty from difference in scales: CDF RUN II PRELIMINARY W= + 15 MeV p/p e Post-alignment-correction uncertainty: W= + 20 MeV J/ e Resolution uncertainty (from Z decays): W= + 12 MeV W~ 5 MeV with 4 fb-1 <1/pT()> (GeV-1) (also at LHC) CDF RUN II PRELIMINARY CDF RUN II PRELIMINARY Upsilon Z C. Hays, Duke University, TEV4LHC

  8. CDF Run 2 Electron Calibration Set energy scale using E/p peak W= +35 MeV Tune upstream passive material using tail of E/p distribution W= +55 MeV CDF RUN II PRELIMINARY CDF RUN II PRELIMINARY Correct for non-linearity W= +25 MeV e Resolution uncertainty (from Z decays): W= + 12 MeV CDF RUN II PRELIMINARY W~ 15 MeV with 4 fb-1 (also at LHC) C. Hays, Duke University, TEV4LHC

  9. CDF Run 2 Recoil Measurement Measure hadronic recoil by summing over all calorimeter towers * Remove towers with energy deposited by lepton 0.1 x 0.25  Estimate removed recoil energy using towers separated in  438 1243 92 m: W= +10 MeV e: W= + 20 MeV 9 MeV W~ 5 MeV with 4 fb-1 (also at LHC) CDF RUN II PRELIMINARY Removed muon towers C. Hays, Duke University, TEV4LHC

  10. CDF Run 2 Recoil Model * Parametrize hadronic response: R = umeas/utrue * Resolution model incorporates terms from underlying event and jet resolution utrue given by pT(Z) W= +20 MeV  Tune parameters using Z  events   u Resolution at low pT(Z) dominated by underlying event Resolution at high pT(Z) dominated by jet resolution CDF RUN II PRELIMINARY W= +42 MeV Model underlying event with minimum-bias data (inelastic collisions) W~ 10 MeV with 4 fb-1 (also at LHC) C. Hays, Duke University, TEV4LHC

  11. CDF Run 2 Backgrounds Muons CDF RUN II PRELIMINARY Muons Electrons W= + 20 MeV W~ 5 MeV with 4 fb-1 (also at LHC) C. Hays, Duke University, TEV4LHC

  12. Milestones * Improve understanding of passive material (E/p tail) * Improve COT alignment * Understand W/Z differences in recoil model * W pT constrained with ZpT CDF RUN II PRELIMINARY * Detailed understanding of upsilon/Z systematics * PDF constrained with W charge asymmetry * Include 2-photon FSR C. Hays, Duke University, TEV4LHC

  13. Ratio Method Can also measure mass by measuring Z transverse mass for each lepton W transverse mass measurement gives ratio of W to Z masses Potentially removes energy calibration uncertainty Lower Z statistics (not an issue at LHC) Are there additional systematics? pTW uncertainty could be larger than mT measurement DØ Run 1 Experience (82 pb-1) C. Hays, Duke University, TEV4LHC

  14. Summary Now have Run 2 experience (first milestone hit) Most systematics shrinking with increasing data Experimental issues (CDF) Recoil differences between W's and Z's Electron energy calibration (passive material) Should be soluble (still early) Preliminary Run 2 results available Theoretical issues Modelling 2-photon FSR (in progress) Update PDFs (need input from W charge asymmetry measurement) Update pTW parameters (need input from Z pT measurement) Potential Improvements at the LHC Can large Z statistics get recoil model below 10 MeV uncertainty? Can PDF uncertainty get below 10 MeV? C. Hays, Duke University, TEV4LHC

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