Precision Measurement of the W Boson Mass at CDF Bodhitha - PowerPoint PPT Presentation

Precision Measurement of the W Boson Mass at CDF Bodhitha Jayatilaka Duke University Particle Physics Seminar University of Birmingham 10th October 2012

Motivation: a picture to start with • The standard model • Describes known particles and interactions • Does not (yet) verifiably describe • Spontaneous symmetry breaking of U(1) × SU(2) • Fermion masses • Does not describe gravity Birmingham Seminar, 10/10/12 2 Bo Jayatilaka

Motivation: a picture to start with • The standard model • Describes known particles and interactions • Does not (yet) verifiably describe • Spontaneous symmetry breaking of U(1) × SU(2) • Fermion masses • Does not describe gravity • Simple explanation: Higgs mechanism • Explains EWSB and fermion masses • Physical manifestation of Higgs boson Birmingham Seminar, 10/10/12 2 Bo Jayatilaka

Motivation: a picture to start with • The standard model • Describes known particles and interactions • Does not (yet) verifiably describe • Spontaneous symmetry breaking of U(1) × SU(2) • Fermion masses • Does not describe gravity • Simple explanation: Higgs mechanism • Explains EWSB and fermion masses • Physical manifestation of Higgs boson • Alternatively: ???? Birmingham Seminar, 10/10/12 2 Bo Jayatilaka

Cracking/checking the picture with colliders 1. Direct searches. e.g.: 3 (pb) 10 CMS Preliminary ∫ ) [pb] -1 L dt = 4.7 fb at s =7 TeV 0.3 -1 σ DØ Run II, L = 7.3 fb Observed Limit 95% CL Expected limits ± 0.25 µ 95% CL Observed limits ± Expected Limit Theory prediction LO µ B ( Theory prediction NLO 1 SD Expected ± 0.2 σ +/- 1 2 SD Expected ± σ +/- 2 × 10 σ Theoretical 0.15 0.1 0.05 δ ADD =2 0 -1 10 2 2.5 3 3.5 4 4.5 5 200 220 240 260 280 300 2 -1 M [TeV/c ] R [GeV] D 2. Precision measurements 10 5 Cross-section (pb) Z 10 4 e + e − → hadrons 10 3 W + W - 10 2 CESR DORIS PEP PETRA SLC TRISTAN KEKB PEP-II 10 LEP I LEP II 0 20 40 60 80 100 120 140 160 180 200 220 Centre-of-mass energy (GeV) Birmingham Seminar, 10/10/12 3 Bo Jayatilaka

What the W mass tells us • Electroweak sector of the standard model (SM) is constrained by G F = 1 . 16637(1) × 10 − 5 GeV − 2 α EM ( Q 2 = M 2 Z ) = 1 / 127 . 918(18) m Z = 91 . 1876(21) GeV /c 2 • These inputs give a prediction of m W πα em W = 1 − m 2 m 2 W = sin θ 2 W 2 G F sin 2 θ W (1 − ∆ r ) √ m 2 Z • Radiative corrections Δ r dominated by top and Higgs loops • Precision measurements of m W and m top constrain SM Higgs mass Where should the Higgs be? Birmingham Seminar, 10/10/12 4 Bo Jayatilaka

Measurements of M W 1.5 • State-of-the-art (Jan 2012) 80336 67 DELPHI ± • DØ M W =80401±43 MeV [1 fb -1 , e ] 80270 55 L3 ± PRL 103 :141801 (2009) 80416 53 OPAL ± • CDF M W =80413±48 MeV [200 pb -1 , e+µ ] 80440 51 ALEPH ± PRL 99: 151801 (2007) PRD 77: 112001 (2008) 80376 33 LEP2 ± • Combining with LEP ∆ M W = 23 MeV 80433 79 CDF I ± 80483 84 D0 I ± • Achieved: exceed precision of e + e - machine 80413 48 CDF II ± measurements with hadron collider 80401 43 D0 II ± 80420 31 Tevatron ± • Goal: match precision of all previous 80399 23 World Average (2009) ± measurements with single CDF measurement 0 80000 80100 80200 80300 80400 80500 80600 2 W boson mass (MeV/c ) Birmingham Seminar, 10/10/12 5 Bo Jayatilaka

The top quark mass Combination does not (yet) include Mass of the Top Quark 15 July 2011 (* preliminary) 0.6 log(L) = 0.5 � CDF-I dilepton 167.4 11.4 ( 10.3 4.9) ± ± ± � log(L) = 2.0 0.4 log(L) = 4.5 � Single best measurement DØ-I dilepton 168.4 12.8 ± ( ± 12.3 ± 3.6) 0.2 m top = 172.8±1.1 GeV [CDF] ) c CDF-II dilepton � 170.6 3.8 ( ± ( 2.2 3.1) ± ± JES � 0 DØ-II dilepton 174.0 ± 3.1 ( 1.8 2.5) ± ± -0.2 CDF-I lepton+jets 176.1 7.4 ± ( ± 5.1 ± 5.3) -1 CDF II Preliminary 8.7 fb -0.4 DØ-I lepton+jets 170.5 170.5 171 171 171.5 171.5 172 172 172.5 172.5 173 173 173.5 173.5 174 174 174.5 174.5 175 175 180.1 5.3 ± ( 3.9 3.6) ± ± 2 2 M M (GeV/c (GeV/c ) ) top top CDF-II lepton+jets 173.0 1.2 ± ( 0.6 1.1) ± ± Impressive results from LHC DØ-II lepton+jets 174.9 1.5 ( 0.8 1.2) ± ± ± CDF-I alljets 186.0 11.5 ± ( 10.0 5.7) ± ± CDF-II alljets * 172.5 2.1 ± ( 1.4 1.5) ± ± CDF-II track 166.9 9.5 ± ( ± 9.0 ± 2.9) CDF-II MET+Jets * 172.3 2.6 ± ( ± 1.8 ± 1.8) Tevatron combination * 173.2 0.9 ± ( 0.6 0.8) ± ± ( ± stat ± syst) CDF March’07 2 /dof = 8.3/11 (68.5%) � 12.4 ± 2.7 ( ± 1.5 ± 2.2) 0 150 160 170 180 190 200 2 m (GeV/c ) top • m top = 173.2 ± 0.9 GeV • Equivalent to ∆ m W = 6 MeV on m H fit • m W is limiting factor on m H prediction! Birmingham Seminar, 10/10/12 6 Bo Jayatilaka

Putting it together 80.5 LEPEWWG (2011) 68% CL (excluding m , m & direct Higgs exclusion) top W < 127 GeV 68% CL (by area) m (2009), m W top 80.45 115 < m H As of July 2011: (GeV) 80.4 m H = 92 +34-26 GeV m H < 161 GeV @95% CL W < 1000 GeV m 80.35 600 < m H 80.3 155 160 165 170 175 180 185 190 195 m (GeV) top Birmingham Seminar, 10/10/12 7 Bo Jayatilaka

Since then... • ATLAS and CMS observe a boson with mass ~125-126 GeV • CDF and DØ see evidence of a boson decaying to bbar • Do precision measurements indicate a Higgs boson with this mass? Birmingham Seminar, 10/10/12 8 Bo Jayatilaka

Analysis strategy

The Tevatron at Fermilab D0 • 1.96 TeV ppbar collider p-pbar • Highest energy collider in the world ^ • Typical inst. lumi.: 3x10 32 cm -2 s -1 CDF • 2011 LHC: ~3x10 33 cm -2 s -1 • Bunch spacing: 396 ns • 2011 LHC: 50 ns • Ceased operations Sep 30, 2011 • ~12 fb -1 delivered to CDF and DØ • Analysis presented utilizes 2.2 fb -1 Birmingham Seminar, 10/10/12 10 Bo Jayatilaka

CDF II (2001-2011) Muon drift chambers m Central hadronic calorimeter End Wall 2.0 n = 1.0 Had. Cal. 0 3 0 Central EM calorimeter n = 1.0 1.4 Tesla Solenoid End Plug Hadron Calorimeter 1.5 End Plug EM Cal. 1.0 n = 2.0 Central Outer Tracker (COT) .5 n = 3.0 0 3 0 2.5 3.0 0 .5 1.0 1.5 2.0 m SVX Intermediate Silicon Layers Birmingham Seminar, 10/10/12 11 Bo Jayatilaka

Precision? • Start with clean , low-background events • i.e. , no taus, no hadronic decays • Lepton p T carries most information • Precision achieved: 0.01% • Hadronic recoil a ff ects inference of neutrino energy • Calibrate to ~0.5% • Reduce impact by requiring p T ( W ) << M W • Need: • Accurate theoretical model • Including boson p T model and QED radiation • Tunable fast simulation • Parameterized detector description for study of systematic e ff ects • Large data samples of well-measured states • Various dimuon resonances • Z boson Birmingham Seminar, 10/10/12 12 Bo Jayatilaka

Measurement strategy (broadly speaking) • Maximize internal constraints and cross-checks • Why? 1. Robustness : Constrain the same parameter multiple ways 2. Precision : After demonstrating 1), combine independent measurements Birmingham Seminar, 10/10/12 13 Bo Jayatilaka

Measurement strategy (more specifically) • Perform COT alignment with cosmic ray data • Calibrate track momentum scale using dimuon resonances ( J/ ψ , Υ ). • Cross-check with Z mass measurement and add as further calibration point • Calibrate calorimeter energy using E/p of W and Z decays • Cross-check with Z mass measurement • Calibrate hadronic recoil with Z decays to µ, e • Cross-check with W recoil distributions • Perform fits to e/µ p T , ν p T , and transverse mass � 2 p ⇤ T p � m T = T (1 − cos ∆ θ ⇤� ) 0.025 80 GeV • Binned maximum likelihood fit to templates from 0.02 81 GeV tuned simulation 0.015 0.01 • Combine all six fits to yield final answer 0.005 0 60 65 70 75 80 85 90 95 100 m (GeV) T Birmingham Seminar, 10/10/12 14 Bo Jayatilaka

Selecting W (and Z ) bosons at CDF Select e ν and µ ν decays with high- p T Production lepton trigger dominated by qq (~80%) Lepton candidates: Electron E T >30 GeV (track p T >18 GeV) or Muon p T >30 GeV W boson candidates: Analysis dataset: 2.2 fb -1 Z boson candidates: 1 lepton passing cuts 2 lepton passing cuts | u | < 15 GeV Candidate events: 66 < m ll < 116 GeV p Tv > 30 GeV W : 470126 ( e ), 624708 ( µ ) 60 < m T < 100 GeV Z : 16134 ( e ), 59738 ( µ ) Birmingham Seminar, 10/10/12 15 Bo Jayatilaka

Theoretical model