HL-LHC and challenges for CEPC Electroweak Physics

Transcription

1 HL-LHC and challenges for CEPC Electroweak Physics Paolo Azzurri INFN Pisa CEPC Workshop November 7 th 2017 IHEP Beijing

2 outline global EW fit status status and perspeckves of W mass, width, decay couplings Z pole A, sin 2 θ W, couplings, α QED EW gauge self couplings Beijing 07/11/17 P. Azzurri - LHC & CEPC : EW Physics 2

3 EW fit status arxiv: m W is the loose end of the EW fit Beijing 07/11/17 P. Azzurri - LHC & CEPC : EW Physics 3

4 EW fit Beijing 07/11/17 P. Azzurri - LHC & CEPC : EW Physics 4

5 W boson mass : LHC Run1 ATLAS: arxiv: with TeV fit to: p T l and m T Lepton p T affected by pt(w) uncertainkes (PDF/QCD) Missing E T affected by detector resolukon effects m T compromise between TH and EXP Beijing 07/11/17 P. Azzurri - LHC & CEPC : EW Physics 5

6 ATLAS: arxiv: with TeV W mass LHC Run1 stability per channels, ficed distribukons and kinemakc ranges Beijing 07/11/17 P. Azzurri - LHC & CEPC : EW Physics 6

7 W mass at Run2-3 &HL-LHC will go down! improve e,μ energy calibrakon W pt spectrum higher order correckons improve PDF uncertainty ~ XX MeV? Beijing 07/11/17 P. Azzurri - LHC & CEPC : EW Physics 7

8 W boson mass : e + e - full m W reco with kinemakc fit. main ingredients : E CM jet/lepton angles (jet boost ) Number of events per GeV/c WW qq ZZ ALEPH µνqq channel Number of events per GeV/c WW qq ZZ ALEPH eνqq channel Number of events per GeV/c WW qq ZZ ALEPH 4q channel C Mass (GeV/c 2 ) 2C Mass (GeV/c 2 ) 5C Mass (GeV/c 2 ) ALEPH Eur.Phys.J.C47:309 (2006) : 683 /pb ~10k WW events ignoring low energy par-cles in the qqqq channel m W = 80440±43(stat.)±24(syst.)±9(FSI)±9(LEP) MeV Γ W = 2140 ±90(stat.) ±45(syst.) ±46(FSI) ± 7(LEP) MeV Beijing 07/11/17 P. Azzurri - LHC & CEPC : EW Physics 8

9 mass of the W boson : e + e - CEPC 5/ab@240GeV è 80M W-pairs: LEP2 x 2000 è Δm W (stat)= 0.5 MeV è Δm W (syst) X MeV? Is ΔE beam ~ 1MeV at E CM =240 GeV possible? With Zγ events? ΔE beam lepton and jet uncertainkes from (Z) calibrakon data Beijing 07/11/17 P. Azzurri - LHC & CEPC : EW Physics 9

10 mass of the W boson : e + e - threshold m W = σ 1 ( E) " Δm W = dσ % $ ' # dm W & 1 Δσ LEP2 : 4x10/pb ~4x30 events è m W = 80.40±0.21 GeV " Δm W (stat) = dσ % $ ' # dm W & 1 σ L 1 ε p σ WW (pb) LEP PRELIMINARY YFSWW and RacoonWW Max stat sensibvity at s~2m W +400MeV /02/ s (GeV) CEPC: X/ab è Δm W (stat)= 1 MeV / X Δmw 1 MeV would require ΔE(beam)<1 MeV (10-5 ) Δε/ε, ΔL/L < 10-3 Δσ B <2 U (~10-2 ) Beijing 07/11/17 P. Azzurri - LHC & CEPC : EW Physics 10

11 mass & width of the W boson : e + e - Measure σww in two energy points E 1, E 2 with a frackon f of lumi in E 1 è extract both m W & Γ W m W, Γ W (MeV) 6 5 8/ab GeV GeV 7 FCCee dσ WW /dγ W =0 at E CM ~162.3 GeV ( m W, Γ W ) correlation luminosity fraction with E 1 =157.1 GeV E 2 =162.3 GeV f=0.4 Δm W =0.62 ΔΓ W =1.5 Δm W =0.56 (MeV) [FCC ee] èδα S (3 π/2)δγ/γ Beijing 07/11/17 P. Azzurri - LHC & CEPC : EW Physics 11

12 W decay BR Winter LEP Preliminary W Leptonic Branching Ratios 23/02/2005 ALEPH ± 0.29 DELPHI ± 0.34 L ± 0.32 OPAL ± 0.35 LEP W eν ± 0.17 ALEPH ± 0.26 DELPHI ± 0.27 L ± 0.31 OPAL ± 0.35 LEP W µν ± 0.15 ALEPH ± 0.38 DELPHI ± 0.43 L ± 0.45 OPAL ± 0.48 LEP W τν ± 0.22 χ 2 /ndf = 6.3 / 9 LEP W lν ± Br(W lν) [%] χ 2 /ndf = 15.4 / 11 Lept universality test at 2% level tau BR ~2.7 σ larger than e/mu è level Winter LEP Preliminary W Hadronic Branching Ratio 23/02/2005 ALEPH ± 0.40 DELPHI ± 0.48 L ± 0.52 OPAL ± 0.61 LEP ± Br(W hadrons) [%] χ 2 /ndf = 15.4 / 11 q/ l universality at 0.6% è 10-4 level 5/ab@240GeV è 80M W-pairs è ΔBR(qq) (stat) =[1] 10-4 (rel) è Δα S (9 π/2)δbr 10-3 è ΔBR(e/μ/τv)(stat)=[4]10-4 (rel) will need very good control of lepton id i.e. cross contaminakons in signal channels ( τàe,μ in the e,μ channels and v.v. ) Flavor tagging would allow to measure coupling to c & b-quarks (Vcs, Vcb,.. ) Beijing 07/11/17 P. Azzurri - LHC & CEPC : EW Physics 12

13 CMS: PAS SMP : LHC : A FB and sin 2 θ eff Beijing 07/11/17 P. Azzurri - LHC & CEPC : EW Physics 13

14 CMS: PAS SMP ATLAS: JHEP 1509 (2015) 49 LHCb:JHEP 1511 (2015) 190 TeV LHC : A FB and sin 2 θ eff LEP+SLD skll ~3 Kmes becer LHCb high rapidity yields less A FB dilukon Beijing 07/11/17 P. Azzurri - LHC & CEPC : EW Physics 14

15 CMS PAS FTR HL- LHC : A FB and sin 2 θ eff reach LEP+SLD precision with 1/ab (maybe improve with 3/ab) Beijing 07/11/17 P. Azzurri - LHC & CEPC : EW Physics 15

16 CEPC Z pole precision Z decays : LEP1 x conknuous E CM calibrakon (resonant depolarizakon) Z mass and width : 500 KeV (syst) pre CDR IHEP-CEPC-DR Beijing 07/11/17 P. Azzurri - LHC & CEPC : EW Physics 16

17 @LEP acceptance effects at 10-4 OK for cross seckons at 10-3 level. Main effects were due to track losses, angle mis-measurements and knowledge of exploit a stakskcal uncertainty at some 10-5 Example from ALEPH, EPJC 14 (2000) 1 Z pole detectors inner edge (relevant boundary) was known at the level of up to 20 μm The beam displacement (verbcal and horizontal) becomes ineffeckve by choosing two fiducial regions (loose and Bght) and alternabng them in the two can use similar methods for cross secbons measurements (e.g. different and alternakng forward and backward fiducial regions), but skll need to idenkfy and know well the relevant boundaries (~5μm level) Beijing 07/11/17 P. Azzurri - LHC & CEPC : EW Physics 17

18 couplings and R b couplings measurements require asymmetry and width rakos AFB(b) = σ F σ B σ tot = 3 4 A ea b (LEP) g g Vf Af R b = Γ( Z bb ) Γ had A b = AFB pol (b) = ± (SLC) Rb = ± (LEP +SLC) ( g Af ) 2 + ( g Vf ) 2 R b Very sensikve to rad. vertex correckons due to new parkcles Important to sort out LEP b-couplings issue Measurement exploits the presence of two b hadrons and b-tagging. Independent from b-tagging efficiency, but not from hemisphere correlabons Higher b-tagging performance (vertex detectors) helps in reducing the correlakon CorrelaKons sources should be idenkfied and studied with data (done at LEP) ΔR b 5 (5-20) 10-5 stat (syst) ΔR c 10 (50) 10-5 stat (syst) Beijing 07/11/17 P. Azzurri - LHC & CEPC : EW Physics 18

19 Direct measurement of α QED (m Z2 ) Patrick Janot: arxiv:1512:05544, JHEP 2016(2) 1 e + µ + EW high precision will require higher order perturbakve calculakons : a bojleneck will be represented by the hadronic contribukons to the vacuum polarizakon Direct measurement with the forward-backward asymmetry - e γ, Z µ - OpKmal centre-of-mass energies s - = 87.9 GeV and s + = 94.3 GeV Two measurements with possible cancellakon of some correlated syst effects Type Source Uncertainty E beam calibration E beam spread < 10 7 Experimental Acceptance and efficiency negl. Charge inversion negl. Backgrounds negl. m Z and Z Parametric sin 2 W G F QED (ISR, FSR, IFI) < 10 6 Theoretical Missing EW higher orders few 10 4 New physics in the running 0.0 Total Systematics (except missing EW higher orders) Statistics Beijing 07/11/17 P. Azzurri - LHC & CEPC : EW Physics 19

20 W/Z/γ couplings LEP2/TeV/LHC gauge cancellakons Run1 LHC ~ LEP2 HL LHC ~ Run1 x /ab@240 ~ LEP2 x Beijing 07/11/17 P. Azzurri - LHC & CEPC : EW Physics 20

21 summary EW physics at the LHC is a challenging business most promising advances with Run2-3 and HL will come in the context of VBF and VBS processes ( & quarkc couplings) improvements on diboson & TGC limits should be at hand hard work on systs can deliver W mass and sin 2 ϑ with some improvement over current precision CEPC would deliver game changing precision for EW parameters possible x improvement factors to LEP1 & 2 precision W mass and width to ~1 MeV (make a visit to the threshold if possible) Z pole physics also very worth to be exploited Beijing 07/11/17 P. Azzurri - LHC & CEPC : EW Physics 21