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Manqi Ruan Discussing & Support: Francois, Roman, Vincent,

Higgs mass measurement through μ channel of Higgs strahlungs process (e + e - HZ μμ H ). Manqi Ruan Discussing & Support: Francois, Roman, Vincent, Advisor: Z. ZHANG (LAL) & Y. GAO (Tsinghua)). Outline. Motivation & Software introduction Preselection cuts at generator level

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Manqi Ruan Discussing & Support: Francois, Roman, Vincent,

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  1. Higgs mass measurement through μ channel of Higgs strahlungs process (e+e-HZμμH) Manqi Ruan Discussing & Support: Francois, Roman, Vincent, Advisor: Z. ZHANG (LAL) & Y. GAO (Tsinghua)) SOCLE@Clermont

  2. Outline • Motivation & Software introduction • Preselection cuts at generator level • Higgs Mass & Xsection determination • Result for SM Higgs • Result if Higgs can decay invisibly • Summary SOCLE@Clermont

  3. Motivation: + - μ μ • Higgs strahlungs process: • Higgs Recoil Mass • X section measurement: coupling strength Higgs SM decay SOCLE@Clermont Higgs invisible decay

  4. Motivation: Xsec/fb Why Higgs strahlung: Only muon momentum information is needed in Higgs strahlung channel analysis A model independent (without any assumption on Higgs decay) analysis can be applied Any potentially model dependent cut will not be used here Hmass = 120 GeV Beam polarization will increase the signal cross section by 58%. (electron 80%, positron, 40%) ISR effect will reduce the cross section with sqrt(s)<300GeV while increase it a little at higher energy Sqrt(s) = 230GeV: Recall the analytic form of error on Higgs mass: δmh2 = sqrt{((4Ep1-mZ2)p1k(p1))2 + ((4Ep2-mZ2)p2k(p2))2 } ~ p2 ; Small sqrt(s) means better Higgs mass resolution! SOCLE@Clermont

  5. Software chain • Generator: whizard-1.50, pythia 6.4.13 ( with Guinea-Pig to simulate BS effect: Thanks to cecile!  ); • Full Simulation: Mokka-v06-04. with LDC01_sc detector conception (184 TPC layer), the accuracy of tracking system to 5E-5 at δ(1/P) on average • Reconstruction & Analysis: MarlinReco/Marlin, ROOT; • Fit: RooFit package SOCLE@Clermont

  6. X section of main BG Non-Polarized beam at 500 fb-1; ISR, BS actived SOCLE@Clermont

  7. Pre cuts introduction • If Higgs invisible decay, no pre cut • If N_track > 3, (SM Higgs decay), apply following pre cut (pions are included here for the PID have a chance ~1% to misidentify the a pion as a muon) • Energetic pion/muon (E1>15GeV ) • Exist another pion/muon (with energy E2), together with the most energetic pion/muon to form a invariant mass > 70 GeV • Dynamic cut: 2E1+E2<180&&2E1+3E2>200 • cos(θmumu)>-0.95 SOCLE@Clermont

  8. Higgs SM decay Huge SM background: (qq, WW, ZZ) Pre cut is needed before Process to Full Simulation! Current muon id efficiency ~ 93.6% purity ~ 99% (O.Martin, RDR) SOCLE@Clermont

  9. qq background • 3 Pre cuts to reduce the qq back ground • Energetic muons > 15GeV • Invariant mass of Muons > 70 GeV • cos(θmumu)> -0.95 • A few hundreds qq Events survive, far from signal region (115 -140GeV): qq back ground vanishes after pre cut selection SOCLE@Clermont

  10. Z decay ratio: ~3% to lepton pairs (each), ~20% to neutrino pairs, ~70% to qq W decay ratio: ~10% to lepton pairs (each), ~70% to qq ZZ & WW background ee μμττ vv qq ev μv τv qq ev μμ ττ νν qq ev μv τv qq WW ZZ Blue: background for Higgs invisible decay Gray: background for Higgs invisible decay through tau leptonic decay Light green: background for Higgs SM decay Red, pink and light blue: possible background for Higgs SM decay (pion be misidentified as muon & muon from bb, cc) Yellow and Dark Green: background for Higgs SM decay: H ττ SOCLE@Clermont

  11. Pre cuts effect on WW & ZZ background • Effect: 56k (of 7.9M) WW events & 11.3k (of 672k) ZZ events survive • Of the 56k WW events; • 220 events with 2 muon • 46.7k events with muon + pion • 10.55k events with 2 pions • With current PID~ 400 WW events remains after require both muons identified (reconstruction efficiency ~ 64%) • Of the 11.3k ZZ events; • 10.26k μμqq events (majority) • 410 ττqq events • 162 qqqq events • 1.06k 4-lepton events • 8.6k ZZ events remains after reconstruction with require both muons identified (reconstruction efficiency ~ 79%) SOCLE@Clermont

  12. S+B for Higgs SM decay. Br(SM)=100% SOCLE@Clermont

  13. Cuts Chain in Higgs SM decay Require both muon be identified will reduce our efficiency by ~17%, but also reduce greatly the back ground  a muon is more easily to be misidentified in forward region Cut applied on the reconstructed data is more strict than the pre cut at MC truth level SOCLE@Clermont

  14. S+B after cuts & Gaussian like background SOCLE@Clermont

  15. Fit 2 parameters with likelihood method : mH & Fraction mH = 119.999GeV ± 18.0 MeV Frac = 54.93%±1.4% (δσ ~ 0.19 fb) SOCLE@Clermont

  16. Higgs Invisible decay Exotic Model beyond SM: SUSY ? Extra dimension ? Heavy neutrino ? … Main background e+e- WW, ZZ  μμvv Higgs Decay Br with a forth neutrino mH with mass = 50 GeV K.Belotsky hep-ph/0210153 (2002) SOCLE@Clermont

  17. S+B for Higgs invisible decay. Br(inv)=100% SOCLE@Clermont

  18. Cuts Chain in Higgs invisible decay SOCLE@Clermont

  19. S+B after cuts & Gaussian like background SOCLE@Clermont

  20. Fit 2 parameters with likelihood method : mH & Fraction δmH = 16.5 MeV δ(Frac) = 1.2% (δσ ~ 0.18 fb) SOCLE@Clermont

  21. For arbitrary Br(inv) Combination the result from Higgs invisible and visible decay ( Br(inv) + Br(visible) =100% ) Red, invisible part contribution Blue, visible part contribution Green, overall result δmH < 18 MeV σ ~ 6.6 fb δσ < 0.23 fb SOCLE@Clermont

  22. Summary • Accuracy of Higgs mass and cross section measurement through eeHZHμμwith Higgs SM decay and Higgs invisible decay assumption have been studied. • An accuracy of about 18MeV on Higgs mass measurement can be achieved at 500 fb-1 with non polarized beam. ( Details: δ(mH) = 13.6 MeV for Pure signal, δ(mH) = 16.5 MeV with Br(inv) = 100%, δ(mH) = 18 MeV with Br(SM) = 100% ). Overall reconstruction efficiency is 71.4% for SM Higgs decay case, and 86.8% for Higgs invisible decay • Cross section can be measured to an accuracy of 3% level • It is foreseen to improve a lot with beam polarization for it will not only reduce the WW background but also increase ~58% the cross section of Higgs strahlung channel (electron, 80%, positron, 40%). • To do: Generate samples with enough statistic to optimize the fit. Optimize the cuts to save signal efficiency. (Especially for Higgs SM decay, with using the jet information. ) SOCLE@Clermont

  23. Back Up Slides SOCLE@Clermont

  24. Fit Algorithm • Generate 2 samples with mH=119GeV and mH=121 GeV assumption (currently 10k statistic each). • Getting PDF f(119,m), f(121,m): smooth the Higgs recoil mass spectrum to a PDF function. • Assume the higgs mass is ma ( 119< ma <121); then the expected PDF f(ma,m) will be a linear combination of f(119,m-(ma-119)) and f(121,m+(121-ma)): (Shift the PDF(119) & PDF(121) to expected position and make a linear combination) f(ma) = 0.5*((ma -119)* f(121,m+(121-ma)) + (121-ma)* f(119,m-(ma-119)) ) • Use likelihood method to fit ma SOCLE@Clermont

  25. How the likelihood method works: Smoothed mH Spectrum with mH=121/119 assumption: Then shift to measured mH and together form an expected PDF at mH=120 (Green) Match the sample data nicely sample with 10k statistic each SOCLE@Clermont

  26. Red/Green/Blue: Smoothed mH Spectrum with mH=121/120/119 assumption and original Histogram (show in error bar); Yellow: expected PDF at mH=120, calculated from f(119) and f(121)  match to the sample (Green) nicely. 10k statistic for mH=121 & mH=119 cases; 6k statistic for mH=120 case. SOCLE@Clermont

  27. mH measurement with no background IO test at 500fb-1 Use toy MC provide by RooFit: Num of events per run is determined By a gaussian distribution Gaus(N, sqrt(N)). Totally 500 run Error on mH nicely agreed with Error on sample means distribution: IO test fine δmH = 13.7 MeV SOCLE@Clermont

  28. Fit 2 parameters with likelihood method : mH & Fraction δmH = 16.5 MeV δ(Frac) = 1.2% (δσ ~ 0.18 fb) mH measured: 119.966GeV±16.6MeV Total Event Num with 115<mH<140: 2871 events + 3202 background; Signal Fraction = 2871/(2871+3202) = 47.275% Measured Fraction = 47.0% ± 1.2% There is a displacement of about 2 sigma (34 MeV,) which could be eliminate using much meticulous samples (large statistic + detailed Higgs mass assumption) SOCLE@Clermont

  29. IO test with toy MC at 500fb-1. Br(invisible) = 100%. 1000 Samples δmH = 16.5 MeV Truth: 47.275%. Measured: 47.28%±1.2% δ(Frac) = 1.2% SOCLE@Clermont

  30. X Section measurement Br(inv)=100% • TotalEventNr*fraction=BranchingRatio*efficiency*luminosity*Xsection • Efficiency = 86.83%; luminosity = 500 fb-1 • Result: 6.613±0.181 fb. Accuracy at 2.7% level MCTruth: σ: 6.62 fb Br: 100% (invisible decay) SOCLE@Clermont

  31. Dynamical Pre Cut For SM Higgs decay 2*E1+E2<180 && 2*E1+3*E2>200 Effect: Signal Channel: 98.8% Back Ground WW: 25.4% ZZ: 31.9% WW Signal ZZ SOCLE@Clermont

  32. Effect of individual Cuts for Higgs invisible decay SOCLE@Clermont

  33. Cut on W mass resolve: (2<Ratio<4) 2<Ratio<4 SOCLE@Clermont

  34. SOCLE@Clermont

  35. Momentum resolution vary with energy: 10o, 15o, 20o, 30o ,40o, 60o, 80opolar angle: yellow curve is the Fast simulation result from M.Berggren 5*10-5 • Thanks to hengne’s work on the SIT radiation length, we have gain a factor of 5% improvement in the mu momentum resolution  SOCLE@Clermont

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