P-P PHYSICS AT LHC. W and Z produc1on. Data and MC comparison. Lecture 4

Transcription

1 P-P PHYSICS A LHC W and Z producon. Data and MC comparison Lecture 4

2 RIGGER URN ON rigger Efficiency CMS preliminary, nb 8 67 y < 0.5 s = 7 ev MinBias Jet6u Jet5u Jet0u Anti-k R=0.5 JP p (GeV) 60

3 ROAD O DISCOVERY OF EWK SYMMERY BREAKING 6

4 Production Cross Section, σ [pb] ELECROWEAK DISCOVERY A LHC July 05 CMS Preliminary 5 4 n jet(s) n jet(s) 7 ev CMS measurement (L 8 ev CMS measurement (L 7 ev heory prediction 8 ev heory prediction CMS 95%CL limit 5.0 fb ) 9.6 fb ) =n jet(s) W Z Wγ Zγ WW WZ ZZ All results at: hp://cern.ch/go/pnj7 EW qqw EW γγ qqz WW W lν, Z ll, l=e,µ EW γ ssww WV -ch tw ts-ch γ W Z ggh VBF qqh VH H h. σ H in exp. σ 6

5 W/Z RELAED MEASUREMENS Inclusive cross section measurements status of theoretical calculations impact of Parton Distribution Functions (PDF) Differential cross sections (dσ/dη, dσ/dp ) V+jets measurement Z boson properties Couplings between Z boson and fermions Asymmetries induced by couplings Angular coefficients Weak mixing angle W Boson properties Charge asymmetries W polarization W mass W width Diboson production: Wγ, Zγ, WW, WZ, ZZ 6

6 W/Z PRODUCION u parton 4 parton W + d W Cross section and spectrum of W and Z in hadron collisions is measured with small uncertainties Benchmark for Standard Model physics One of very first validation measurements at LHC data/mc comparison provides powerful validation of calculations Provides luminosity monitor at LHC at high luminosity similar to use of Bhabha at LEP! 64

7 W/Z CROSS SECION [ ] dˆσ dm = ˆσ 0 N Q qδ(ŝ M ), ˆσ 0 = 4πα M he mass of the lepton pair. In the centr ˆσ(q q e + e )= 4πα ŝ N Q q dσ dm dy = ˆσ [ 0 Ns k Q k(q k (x,m ) q k (x,m )+[ ]) ] ˆσ q q W = π GF M W V qq δ(ŝ M W ), ˆσ q q Z = π GF M Z(v q + a q)δ(ŝ M Z) 65

8 W/Z RAE Production: q W/Z l g q/qbar q W/Z qbar l / DY production at LO rate evatron: rate LHC: (Z rate ~ / W rate) Signature: relatively high p, isolated leptons (trigger) missing E due to neutrino in W decay pileup / Underlying Event / jets at NLO 66

9 W CANDIDAES 67

10 Z E E CANDIDAE 68

11 INCLUSIVE W ANALYSIS Measurement of the W and Z/ production cross sections in proton-... High p leptons select isolated leptons: reduce probability of hadrons faking leptons 5 4 L dt = 5 nb Data 0 ( W eν W τ ν Z ee s = 7 ev ) 4 Data 0 ( W µν W τν Z µµ s = 7 ev) L dt = nb Large missing transverse energy m m Main W backgrounds from tau decays leptons with correct charge in final state missing energy from neutrinos (a) 5 (b) Data 0 ( s = 7 ev ) Data 0 ( s = 7 ev) Fig. : Distributions of the transverse mass, W eνm 4, of the electron-e W µν 4 miss system (a) and muon-e L dt = 5 nb W τ ν miss system (b) without an E L dt = nb miss requirement. he data are compared to Monte-Carlo simulation, broken down into the signal W τν and various Z µµ background components. Z ee L dt = 5 nb Data 0 ( W eν W τ ν Z ee s = 7 ev ) E miss 4 Data 0 ( W µν W τν Z µµ s = 7 ev) (b) L dt = nb miss E 69

12 W sample: p spectrum of leptons after requirements on missing energy and transverse mass Z sample almost background free Recall: no other sources of high energy leptons in Standard Model Only background due to New Particles which typically are expected to have small cross section! :-) Entries /.5 GeV INCLUSIVE 60 W/Z ANALYSIS Data 0 ( s = 7 ev ) 00 0 Data 0 ( s = 7 ev) 80 W eν W µν 40 L dt = 5 nb L dt = nb 60 W τ ν W τν Z µµ 0 Z ee L dt = 5 nb 80 L dt = nb p W p W (a) 40 (b) Fig. 6: Distributions 0 of the transverse momentum p of the W 0candidates in the electron channel (a) and m channel (b) after final selection. he requirements of E miss > 5 0GeV and m > 40 GeV are applied. he data compared to Monte-Carlo simulation, broken down into the signal and various background components. p Entries /.5 GeV 80 Data 0 ( s = 7 ev ) W eν W τ ν Z ee E Fig. 5: Distributions of the electron cluster E (a) and muon p (b) of the W candidates after final selection. h requirements of E miss > 5 GeV and m > 40 GeV are applied. he Data 0 ( s=7 ev) data are compared to Monte-Carlo simulatio Z µµ broken down into the signal and various Data 0 background ( s= 7 ev) components. L dt=6 nb L dt = nb Z ee Z τ τ W eν Requirement Number of candidates Z ee Z µµ rigger wo leptons (ee or µµ with E (p ) >0 GeV) 8 44 Muon isolation: p ID /p < Opposite charge ee or µµ pair: < m < 6 GeV able 0 : 0 Number of Z 60 ee 70 and 80 Z 90 0 µµ candidates 0 in data, 0 remaining after 60each 70major requirement. 0 0 E p able summarises the number of Z candidates remaining after each major requirement has bee (a) (b) 70 Entries /.5 Ge Entries /.5 GeV 00 Data 0 ( s = 7 ev) W µν (b) W µν W τν Z µµ