W Mass Measurement at the Tevatron CDF Chris

W Mass Measurement at the Tevatron CDF Chris Hays Duke University TEV 4 LHC Workshop Fermilab 2004 DØ

Past, Present, and Future Precision of direct measurements: x x x 1983: UA 1 5 Ge. V 1990: 1989: UA 2 UA 1 2. 9 Ge. V 900 Me. V x 1995: CDF 180 Me. V x 2000: DØ 91 Me. V W mass now known to better than 5 parts in 10, 000 ( MW=34 Me. V) x 2004: LEP 42 Me. V Tevatron 59 Me. V CDF: 79 Me. V Looking forward: DØ: 84 Me. V * Tevatron Run 2 has quadrupled Run 1 CDF, DØ data sets * CDF has analyzed first 200 pb-1 of data and determined uncertainties x x x 2006: 2004: 2005: CDF/DØ 76 Me. V <59 Me. V <34 Me. V ~0. 2 fb 1 ~0. 4 fb 1 ~1 fb 1 x x 2008: CDF/DØ <20 Me. V 2010: ATLAS/CMS <20 Me. V ~4 fb- ~10 fb-1 1 C. Hays, Duke University, TEV 4 LHC x 2011: Tevatron <15 Me. V LHC <15 Me. V

W Mass Fit Distributions Transverse mass * m. T 2 = 2 p. TET(1 -cos( f)) * m ~ 2 p. T + u|| * Low sensitivity to p. TW * Recoil modelling crucial Lepton p. T * m ~ 2 p. T * Insensitive to recoil * p. TW modelling crucial ET = -(p. T + u) u^ (u) u|| CDF RUN II PRELIMINARY m. T p. T CDF RUN II PRELIMINARY C. Hays, Duke University, TEV 4 LHC

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

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

Production and Decay Model Uncertainties p. TW Model e e Uncertainties determined from RESBOS parameters g 1, g 2, g 3 Parameters constrained by Run 1 Z p. T distribution CDF RUN II PRELIMINARY p. T fit: W = + 27 Me. V m. T fit: W = + 13 Me. V g 2 = 0. 68 + 0. 12 Ge. V 2 g 3 = -0. 60 + 0. 30 W ~ 5 Me. V with 4 fb-1 (p. T fit: 10 Me. V) v LHC: Large Z statistics W ~ 5 Me. V achievable (also for p. T fit) GW e 70 Me. V uncertainty from world average of direct measurements W ~ 5 Me. V with 4 fb-1 (also at LHC) C. Hays, Duke University, TEV 4 LHC

CDF Run 2 Muon Momentum Calibration Set momentum scale using J/ and upsilon decays to muons Uncertainty from difference in scale W= + 15 Me. V e Post-alignment-correction uncertai W= + 20 Me. V Resolution uncertainty (from Z dec W= + 12 Me. V CDF RUN II PRELIMINARY J/ e -1 <1/p. T( )> (Ge. V ) CDF RUN II PRELIMINARY p/p e W ~ 5 Me. V with 4 fb-1 (also at LHC) CDF RUN II PRELIMINARY Upsilon Z C. Hays, Duke University, TEV 4 LHC

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

CDF Run 2 Recoil Measurement Measure hadronic recoil by summing over all calorimeter towers * Remove towers with energy deposited by lepton Estimate removed recoil energy using towers separated in 0. 1 x 0. 25 438 m: W= +10 Me. V e: W= + 20 Me. V 1243 92 W ~ 5 Me. V with 4 fb-1 9 Me. V (also at LHC) CDF RUN II PRELIMINARY Removed muon towers C. Hays, Duke University, TEV 4 LHC

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

CDF Run 2 Backgrounds Muons CDF RUN II PRELIMINARY Electrons W= + 20 Me. V W ~ 5 Me. V with 4 fb-1 C. Hays, Duke University, TEV 4 LHC (also at LHC)

Milestones CDF RUN II PRELIMINARY * Improve understanding of passive material (E/p tail) * Improve COT alignment * Understand W/Z differences in recoil model * W p. T constrained with Z p. T * Detailed understanding of upsilon/Z systematics * PDF constrained with W charge asymmetry * Include 2 -photon FSR C. Hays, Duke University, TEV 4 LHC

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? p. TW uncertainty could be larger than m. T measurement DØ Run 1 Experience (82 pb-1) C. Hays, Duke University, TEV 4 LHC

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 p. TW parameters (need input from Z p. T measurement) Potential Improvements at the LHC Can large Z statistics get recoil model below 10 Me. V uncertainty? Can PDF uncertainty get below 10 Me. V? C. Hays, Duke University, TEV 4 LHC