Precise measurements of the W mass at the Tevatron and indirect constraints on the Higgs mass. Rencontres de Moriond QCD and High Energy Interactions

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1 Precise measurements of the W mass at the evatron and indirect constraints on the Higgs mass Rafael Lopes de Sá for the CDF and DØ Collaborations March 11, 212 Rencontres de Moriond QCD and High Energy Interactions Precise measurement of the W-boson mass with the CDF II detector arxiv: Measurement of the W Boson Mass with the D Detector arxiv: R. Lopes de Sá (Stony Brook University) W Mass at the evatron March 212 1

2 Motivation Electroweak theory he W boson mass is not an input parameter, but can be calculated ( M W 1 M ) W 2 = πα (1 + r) MZ 2 2Gµ Loop Corrections t H r(m Z, M H, m t, α s,...) W + W + W W b Indirect dependence δm H = 13 GeV [ ] δm t = 1.8 GeV [ ] δ( α (5) HAD ) =.2 Current theoretical uncertainty δm W 6.2 MeV 1.8 MeV 3.6 MeV 4 MeV SM prediction known to complete 2-loop order (and some 3-loop parts) Phys.Rev.D69:536,24 R. Lopes de Sá (Stony Brook University) W Mass at the evatron March 212 2

3 Motivation Direct Measurements (before February 212) CDF Run /I ±.81 D Run I ±.83 CDF Run II ±.48 evatron ±.39 D Run II 8.42 ±.43 evatron ±.31 W boson mass (GeV) CMS excl. Atlas excl. evatron excl. LEP excl. 68% = M H = 127. M H LEP2 average ± World average ± m W (GeV) July References: SM prediction: Phys.Rev.D69:536,24 op Mass: 173.2±.9 GeV (arxiv: ) op quark mass (GeV) R. Lopes de Sá (Stony Brook University) W Mass at the evatron March 212 3

4 Motivation Global Electroweak Fit (before February 212) Precision EW Measurements (evatron, LEP and SLD data) W boson mass and width Z boson mass, total and partial width Z pole asymmetries and sin θ W Indirect measurement of the Higgs boson mass M H = GeV (EV EWWG and LEP EWWG July, 211) Does not include LHC direct exclusion. R. Lopes de Sá (Stony Brook University) W Mass at the evatron March 212 4

5 CDF Detector General purpose detector. For this analysis, the important subdetectors are: Central Drift Chamber immersed in a 1.4 solenoid. Provides accurate lepton momentum measurement and position measurement. Electromagnetic Calorimeter. Lead-aluminium-scintillator calorimeter. Provides shower energy measurement as well as position measurement via wire chamber embedded at the EM shower maximum. Central tracker single muon resolution: 3.2% (for p = 45 GeV ) R. Lopes de Sá (Stony Brook University) W Mass at the evatron March 212 5

6 DØ detector General purpose detector. For this analysis, the important subdetectors are: Central racker. Silicon and scintillating fiber trackers immersed in a 2 solenoid provide accurate position measurement. Electromagnetic Calorimeter. Highly segmented uranium-liquid argon calorimeter with good energy resolution and coverage. Electromagnetic calorimeter single electron energy resolution (with E = 45 GeV ): 3.33% at η =. Average over central cryostat with W eν angular spectrum: 4.16%. R. Lopes de Sá (Stony Brook University) W Mass at the evatron March 212 6

7 Measurement Strategy he evatron was a p p collider with 1.96 ev of energy. In a hadron collision, it is impossible to know the parton system initial longitudinal momentum and, therefore, to measure the longitudinal momentum of the neutrino from the W boson decay. he transverse momenta carry part of the mass information. Both CDF and DØ measurements use binned likelihood fits to extract the value of the W boson mass from the following kinematical distributions: ransverse mass m = 2 (p (l)p (ν) p (l) p (ν)) Lepton transverse momentum p (l) Neutrino transverse momentum p (ν) electron p W p e /E Underlying Event u Hadronic Recoil electr R. Lopes de Sá (Stony Brook University) W Mass at the evatron March itron

8 Event Selection CDF analysis Analyzed 2.2 fb 1. Uses W eν and W µν decay channels. Central leptons η < 1 with 3 < p < 55 GeV Missing transverse energy 3 < /E < 55 GeV ransverse mass 6 < m < 1 GeV Hadronic recoil momentum u < 15 GeV DØ analysis Analyzed 4.3 fb 1 (1 fb 1 analyzed before) Uses W eν decay channel. Central electrons η < 1.5 with p > 25 GeV Missing transverse energy /E > 25 GeV ransverse mass 5 < m < 2 GeV Hadronic recoil momentum u < 15 GeV W eν candidates W µν candidates otal CDF 2.2 fb 1 47, , 78 1, 94, 834 DØ 4.3 fb 1 1, 677, 394 1, 677, 394 (+1 fb 1 ) 2, 177, 224 R. Lopes de Sá (Stony Brook University) W Mass at the evatron March 212 8

9 Calibration Strategies Full GEAN detector simulations are not fast nor accurate enough to describe the kinematical distributions used to measure the W boson mass. Both CDF and DØ develop parametrized fast simulations of the detector response to W lν events. he parametrizations are calibrated with data, using very different strategies. CDF strategy Detailed model of lepton interactions at the central tracker. Precise alignment using cosmic rays. Momentum scale calibrated using J/ψ µµ, Υ µµ and Z µµ mass fits. Use calibrated momentum scale and E/p distribution in W eν events to calibrate the calorimeter energy scale. DØ strategy Detailed model of the calorimeter response to electrons and photons. Detailed model of the underlying energy flow. Detailed model of efficiencies. Calibrate the calorimeter energy scale using the dielectron invariant mass and angular distribution in Z ee decays (electron energy scale α and energy offset β). R. Lopes de Sá (Stony Brook University) W Mass at the evatron March 212 9

10 Calibration Results -.1 CDF II -1 L dt 2.2 fb CDF II L dt fb p/p events /.1 2 χ 2 /dof = 18 / J/ψ µµ data (stat. only) Υ µµ data (stat. only) Z µµ data (stat. only) combined p/p (stat. syst.) for W µν events µ <1/p > (GeV -1 ) E/p (W eν) Offset, β (GeV) D Run II, 4.3 fb L< <L< <L<2.2 L> Scale, α (L in 1 32 cm 2 s 1 ) DØ tests the calibration method doing a closure test with GEAN simulation treated as data. he results are consistent with the input value of M W within statistical uncertainty ( 6 MeV ) for a sample equivalent to 24 fb 1! CDF momentum scale and DØ energy scale precision:.1% (!!!) R. Lopes de Sá (Stony Brook University) W Mass at the evatron March 212 1

11 Z Mass Fits A very strict test of the calibration procedure CDF II preliminary L dt fb events /.5 GeV 4 2 M Z = (9118 ± 12 stat ) MeV χ 2 /dof = 3 / 3 All values consistent with the precisely measured value at LEP. M Z = ± 2 MeV (GeV) m µµ M Z(µµ) = 9118±12(stat)±1(syst) MeV events /.5 GeV 1 5 M Z CDF II preliminary = (9123 ± 3 stat ) MeV χ 2 /dof = 42 / 38 L dt fb Events/.25 GeV D Run II, 4.3 fb Fit Region χ 2 /d.o.f. = 153/159 Data Fast MC (GeV) m ee M Z(ee) = 9123 ± 3(stat) ± 14(syst) MeV χ m ee, GeV M Z(ee) = ± 17(stat) MeV 4-1 D Run II, 4.3 fb R. Lopes de Sá (Stony Brook University) W Mass at the evatron 2 March

12 Systematic uncertainties Comparison of systematic uncertainties in the m (l, ν) measurement (values in MeV) Source CDF m (µ, ν) CDF m (e, ν) DØ m (e, ν) Experimental Statistical power of the calibration sample. Lepton Energy Scale Lepton Energy Resolution Lepton Energy Non-Linearity 4 Lepton Energy Loss 4 Recoil Energy Scale 5 5 Recoil Energy Resolution 7 7 Lepton Removal 2 3 Recoil Model 5 Efficiency Model 1 Background W production and decay model Not statistically driven. PDF QED Boson p R. Lopes de Sá (Stony Brook University) W Mass at the evatron March

13 CDF Results Method (2.2 fb 1 ) M W (MeV) Method (2.2 fb 1 ) M W (MeV) m (µ, ν) 8379 ± 16(stat) m (e, ν) 848 ± 19(stat) p (µ) 8348 ± 18(stat) p (e) 8393 ± 21(stat) /E (µ, ν) 846 ± 22(stat) /E (e, ν) 8431 ± 25(stat) Combination (2.2 fb 1 ) 8387 ± 19 MeV (syst + stat) R. Lopes de Sá (Stony Brook University) W Mass at the evatron March

14 DØ Results Events/.5 GeV χ 5 1 D Run II, 4.3 fb Fit Region χ 2 /dof = 37.4/49 DAA FAS MC W >τν Z >ee MJ m, GeV D Run II, 4.3 fb m, GeV Events/.5 GeV χ 1 D Run II, 4.3 fb Fit Region χ 2 /dof = 26.7/31 DAA FAS MC W >τν Z >ee MJ e 6 p, GeV D Run II, 4.3 fb p e 6 GeV, Method (4.3 fb 1 ) M W (MeV) m (e, ν) 8371 ± 13(stat) p (e) 8343 ± 14(stat) /E (e, ν) 8355 ± 15(stat) Combination m p (4.3 fb 1 ) 8367 ± 26(syst + stat) Combination (5.3 fb 1 ) 8375 ± 23(syst + stat) R. Lopes de Sá (Stony Brook University) W Mass at the evatron March

15 Comparing Results CDF (2.2/fb) ME(e,nu) CDF (2.2/fb) p(e) CDF (2.2/fb) m(e,nu) CDF (2.2/fb) ME(mu,nu) CDF (2.2/fb) p(mu) CDF (2.2/fb) m(mu,nu) D (4.3/fb) ME(e,nu) D (4.3/fb) p(e) CDF 2.2/fb combination (stat+syts) D 4.3/fb combination (stat+syts) 1 D (4.3/fb) m(e,nu) D ME not included in the combination Fitted W boson mass (MeV) Very consistent results obtained with completely different calibration strategies! (uncertainties from individual measurements are only statistical) R. Lopes de Sá (Stony Brook University) W Mass at the evatron March

16 Single Experiment Uncertainty evatron Single Experiment Uncertainties W Mass uncertainty (MeV) DZero (e) CDF (e + mu) Integrated Luminosity (pb ) 4 Both experiments are getting close to the model and theoretical plateau. Some work need to be done in this front as well! R. Lopes de Sá (Stony Brook University) W Mass at the evatron March

17 heoretical and modeling issues Ideas and developments to improve the model and theoretical uncertainties in the W mass measurement Use a wider lepton η acceptance to be less sensitive to PDF uncertainties. It has been done before at the evatron (DØ RunI). Phys.Rev.D62:926,2 Use evatron W lepton charge asymmetry to constrain the u/d PDF instead of low energy experiments. Available: C1W PDF set. Phys.Rev.D82:7424,21 Explore lepton longitudinal momentum to extract the W mass. Concrete example: JHEP 118:23,211 Study QED uncertianties in the measurement using NLO QCD EW generators. wo recent implementations in the POWHEG framework. arxiv: , arxiv: Asymmetry Asymmetry DØ, L=.75 fb e E >25 GeV ν E >25 GeV CEQ6.6 central value MRS4NLO central value CEQ6.6 uncertainty band η e (a) DØ, L=.75 fb e 25<E <35 GeV ν E >25 GeV CEQ6.6 central value MRS4NLO central value CEQ6.6 uncertainty band η e R. Lopes de Sá (Stony Brook University) W Mass at the evatron March

18 Higgs Constraints (Preliminary) New World Average CDF Run I ±.81 D Run I ±.83 D Run II (prel.) ±.23 CDF II (prel.) ±.19 evatron 212 (prel.) ±.17 W boson mass (GeV) CMS excl. Atlas excl. evatron excl. LEP excl. 68% = M H = 127. M H LEP2 average ± World average (prel.) ± m W (GeV) Winter References: SM prediction: Phys.Rev.D69:536,24 op Mass: 173.2±.9 GeV (arxiv: ) op quark mass (GeV) R. Lopes de Sá (Stony Brook University) W Mass at the evatron March

19 (Preliminary) Global Electroweak Fit March 212 m Limit = 152 GeV heory uncertainty α (5) had =.275± ±.1 incl. low Q 2 data χ LEP LHC excluded excluded m H [GeV] New (preliminary) indirect Higgs mass determination M H = GeV (was MH = GeV before) R. Lopes de Sá (Stony Brook University) W Mass at the evatron March

20 Conclusions CDF and DØ measured the W mass with precision at least as good as the world average before. he CDF measurement is now the single most precise measurement of the W mass. CDF and DØ measurements in excellent agreement. Model and theory uncertainties begin to play an important role. CDF analyzed 2.2 fb 1. DØ analyzed 4.3 fb 1 of integrated luminosity collected at high instantaneous luminosity runs of the evatron. he measurements at CDF and DØ can reduce the world average uncertainty down to 1 MeV when all the rest of the data is analyzed. he W mass will play an ever increasing role in the determination of the consistency of the Standard Model. R. Lopes de Sá (Stony Brook University) W Mass at the evatron March 212 2

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22 Backup Slides R. Lopes de Sá (Stony Brook University) W Mass at the evatron March

23 CDF Systematic Uncertainties Source Uncertainty (MeV) Experimental Statistical power of the calibration sample. Lepton Energy Scale 7 Lepton Energy Resolution 2 Recoil Energy Scale 4 Recoil Energy Resolution 4 Lepton Removal 2 Background 3 Experimental otal 1 W production and decay model Not statistically driven. PDF 1 QED 4 Boson p 5 W model otal 12 otal Systematic Uncertainty 15 W Statistics 12 otal Uncertainty 19 R. Lopes de Sá (Stony Brook University) W Mass at the evatron March

24 DØ Systematic Uncertainties Source m MeV p e MeV /E MeV Experimental Z statistics driven! Electron Energy Scale Electron Energy Resolution Electron Energy Nonlinearity W and Z Electron energy loss differences Recoil Model Electron Efficiencies Backgrounds Experimental otal W production and decay model Not dependent on Z statistics! PDF QED Boson p W model otal otal Systematic Uncertainty W Statistics otal Uncertainty R. Lopes de Sá (Stony Brook University) W Mass at the evatron March

25 Recoil Model Z Z Hard recoil: Parametrized from Z ll events. Soft recoil: Data min-bias (CDF) or min-bias + zero-bias (DØ) events. Lepton removal: Hadronic energy reconstructed as lepton. Out-of-cone FSR: Photons reconstructed as recoil. CDF and DØ: Final tune with Z ll momentum imbalance. 5 Mean (GeV) imb η Width (GeV) imb η D Run II, 4.3 fb Data PMCS ee p (GeV) D Run II, 4.3 fb Data PMCS ee p (GeV) χ χ D Run II, 4.3 fb ee p (GeV) D Run II, 4.3 fb ee p (GeV) e + p ee ŷ ˆη p ee ˆη (GeV) + u η η.65p CDF II preliminary L dt χ fb -1 / DoF = 15.6 / 9 ) (GeV) + u η η σ (.65p CDF II preliminary χ 2 L dt / DoF = 15.9 / fb e ˆx -2 4 ˆξ u ˆη u p (Z ee) (GeV) p (Z ee) (GeV) R. Lopes de Sá (Stony Brook University) W Mass at the evatron March

26 DØ Consistency Check Instantaneous Luminosity L < 2 2 < L < 4 m p 4 < L < 6 ME L > Blinded W mass (GeV) Z mass (GeV) (Blinded W mass) / (Z mass) R. Lopes de Sá (Stony Brook University) W Mass at the evatron March

27 DØ Consistency Check ime Early Run IIb1 Late Run IIb1 m p Early Run IIb2 ME Late Run IIb Blinded W mass (GeV) Z mass (GeV) (Blinded W mass) / (Z mass) R. Lopes de Sá (Stony Brook University) W Mass at the evatron March

28 DØ Consistency Check u < GeV u m p ME > GeV u Blinded W mass (GeV) R. Lopes de Sá (Stony Brook University) W Mass at the evatron March

29 DØ Consistency Check Recoil u < 1 GeV u m p ME < 2 GeV u Blinded W mass (GeV) Z mass (GeV) (Blinded W mass) / (Z mass) R. Lopes de Sá (Stony Brook University) W Mass at the evatron March