PHYS 5326 – Lecture #20 Wednesday, Apr. 25, 2007 Dr. Jae Yu •Higgs Search Strategy •Higgs Search Channels •Backgrounds to Higgs Searches •Requirement on Experiments for Higgs Searches Wednesday, Apr. 25, 2007 PHYS 5326, Spring 2007 Jae Yu 1 Hadron Collider SM Higgs Production s MH=130 GeV Wednesday, Apr. 25, 2007 PHYS 5326, Spring 2007 Jae Yu 2 Tevatron Run I Results • Run I limits are not very stringent Channel WH l nbb D (95% CL) <28 pb ZH nnbb ZH ll bb CDF(95% CL) Theory <27 pb 0.07 <8 pb 0.10 <7.5 pb 0.11 No real mass limit here… Wednesday, Apr. 25, 2007 PHYS 5326, Spring 2007 Jae Yu 3 Tevatron Run II Higgs Physics • s BR @ 2 TeV s (pb) for MH=100 GeV – Use associated H+W/Z production • H b`b gg H 1.17 qq,gg WH 0.31 qq,gg ZH 0.17 qq,gg H+2jets 0.12 All others <0.02 Backgrounds Wednesday, Apr. 25, 2007 WZ+ZZ 4.4 Wbb+Zbb 14 tt 7.5 tb+tq_tbq 3.4 QCD O(106) dijet O(105) 4jet W en 2800 PHYS 5326, Spring 2007 Jae Yu 4 MH=130 GeV For MH<130GeV • H b`b • H WW • H gg or t`t •Wednesday, H Apr.c`c 25, 2007 For MH>130GeV • H WW/ZZ • H b`b • H gg or t`t • H c`c PHYS 5326, Spring 2007 Jae Yu 5 H (h) b`b • Two b-quark jets in the final state • Look for signature of b-quark jets – b-quark jets contain B mesons – B-mesons have finite lifetime and decay in flight • Final state of interest – A displaced vertex from the primary vertex – Existence of secondary leptons from b-quark semileptonic decay Wednesday, Apr. 25, 2007 PHYS 5326, Spring 2007 Jae Yu 6 How does a displaced vertex look? 2” at Run II 1” at present b vertex Wednesday, Apr. 25, 2007 Beampipe PHYS 5326, Spring 2007 Jae Yu 7 H (h) WW • W’s decay immediately • Look for signature of W’s – W branching ratios • ~11% to leptonic final state (l+n) for each lepton • ~69% to quark and anti-quark final states • Final states of interest – One high PT lepton (e or ) + missing ET + two jets – Two opposite charge high PT leptons (ee, , or e) + Missing ET – Four jets Wednesday, Apr. 25, 2007 PHYS 5326, Spring 2007 Jae Yu 8 H (h) t`t t’s decay almost immediately • Look for signature of t’s – t branching ratios • ~17% to leptonic final state (e,+n+n) for each lepton • ~68% to hadrons (one or three charged hadrons) • Final states of interest – One medium PT lepton (e or ) + missing ET + one narrow jet – Two opposite charge medium PT leptons (ee, , or e) + Missing ET – Two narrow jets Wednesday, Apr. 25, 2007 PHYS 5326, Spring 2007 Jae Yu 9 For HW or HZ • Cross section is about 10% of ggH • Both H and W/Z decay immediately • Look for signature of vector bosons with H decay final states • W or Z final state characteristics – Decay to Leptons or quark jets • Final states of interest for HW – Higgs decay + One high PT lepton – Higgs decay + two light quark jets Wednesday, Apr. 25, 2007 PHYS 5326, Spring 2007 Jae Yu 10 HZ Final States • Z decay branching ratio – ~3% for each charged lepton pairs – ~20% two neutrino final states – ~70% quark, anti-quark final states • ~15% b`b final states • Final states of interest for HZ – Two high PT lepton + Higgs decay channels – Large Missing ET + Higgs decay channels – Four b-jet final states Wednesday, Apr. 25, 2007 PHYS 5326, Spring 2007 Jae Yu 11 Summary of Final States of Interest • W decay: – W qq channel very hard • depends on dijet mass resolution – W en, n, tn • Isolated lepton plus missing ET • Z decay – Z qq same as W – difficult – Z ee, (probably not tt) • Isolated lepton plus mass resolution • Higgs decay: – Look for b`b pairs • Impact parameter resolution • Silicon vertexing • Di-jet mass resolution Wednesday, Apr. 25, 2007 b-tagging is a MUST PHYS 5326, Spring 2007 Jae Yu 12 Higgs Backgrounds To WH • WH ln b`b backgrounds – Wb`b • Where the W decays leptonically • Cross section is 2.3nb*as2*mb-threshold factor for each lepton – WZ: • W decays leptonically while Z decays to b`b • Cross section is 2.3nb*aEW2*b final state branching ratio – t`t: Each t decays to W and b pairs. How would this become a background? – single t: How? • WH qq b`b overwhelmed by QCD background since it has four jets in the final state Wednesday, Apr. 25, 2007 PHYS 5326, Spring 2007 Jae Yu 13 Higgs Backgrounds to ZH • ZH l l b`b final state for signature – Zb`b • Z decays to two leptons • Cross section is 0.2nb*as2*mb-threshold factor for each lepton – ZZ • One Z decays to two leptons while the other decays to b`b • Cross section is 2*0.2nb*aEW*b branching ratio – t`t:How does this channel become background to ZH? Wednesday, Apr. 25, 2007 PHYS 5326, Spring 2007 Jae Yu 14 Higgs Backgrounds to ZH • ZH nn b`b – QCD:How would this become background to this process? – Zb`b: Z decays to neutrinos – ZZ: One Z decays to neutrinos while the other decays to b`b – t`t: How would this process become background? Wednesday, Apr. 25, 2007 PHYS 5326, Spring 2007 Jae Yu 15 Higgs Backgrounds to gg H WW* • WW final state is a generic, inherent and irreducible background • 2l+MET final state – ZZ: One Z decays to two leptons while the other to two neutrinos – Drell-Yan (q`qg*ll) – t`t: How this could be the background to this process? – WZ: Z decays to two leptons, while W decays to l+n where l is lost – tt: Both t’s decay leptonically Wednesday, Apr. 25, 2007 PHYS 5326, Spring 2007 Jae Yu 16 Higgs Backgrounds to gg H WW* • 1l+MET+2jets final state – WZ: W decays to l+n and Z decays to two jets – ZZ: One Z decays to two leptons (of which one is lost) while the other to two jets – t`t : How is this become a background to this process? – tW:How could this become a background to this process? Wednesday, Apr. 25, 2007 PHYS 5326, Spring 2007 Jae Yu 17 Summary of Higgs Physics Backgrounds • The best discovery channel is with HW and HZ • The background for mH < 130 GeV are – WH ln b`b backgrounds Wb`b, WZ, t`t, single t – WH qq b`b overwhelmed by QCD background since it has four jets in the final state – ZH l l b`b backgrounds Zb`b, ZZ, t`t – ZH nn b`b backgrounds QCD, Zb`b, ZZ, t`t • The background for mH > 130 GeV are – gg H WW* backgrounds Drell-Yan, WW, WZ, ZZ, tt, tW, tt Wednesday, Apr. 25, 2007 PHYS 5326, Spring 2007 Jae Yu 18 Tevatron Higgs Production s Wednesday, Apr. 25, 2007 PHYS 5326, Spring 2007 Jae Yu 19 TeVatron Run II Higgs S/N • H b`b – S/N drops as MH increases • Run out of events…. • Ultimately limits the experimental reach • H WW/ZZ (virtual) – Depends on di-jet mass resolution Better 1 fb-1 delivered Wednesday, Apr. 25, 2007 PHYS 5326, Spring 2007 Jae Yu 20