Search for SM Higgs with the ATlas detector 方亚泉 威士康辛大学麦迪逊分校 欧洲核子研究中心 Uni vers ity of Wiscons in, Madi son CERN yaquan fang@cern. ch 前沿物理工作月 北京-上海一武汉 August 29th, 2012
1 Search for SM Higgs with the ATLAS detector August 29th, 2012 方亚泉 威士康辛大学麦迪逊分校 欧洲核子研究中心 University of Wisconsin, Madison CERN yaquan.fang@cern.ch 前沿物理工作月 北京-上海-武汉
Outline LhC and atlas detector Standard Model, Higgs mechanism and its cross-section and branching ratio Show the most updated results of 2011+2012 N H→Y ●H→ZZ→4l ●H→→WW Combination of 2011+2012 ● Conclusion 2/2/2021
Outline LHC and ATLAS detector. Standard Model, Higgs Mechanism and its cross-section and branching ratio. Show the most updated results of 2011+2012 H→γγ H→ZZ→4l H→WW Combination of 2011+2012 Conclusion 2 2/2/2021
LHC Large Hadron Collider) CMS 4 Tev LHC ALICE Super protoN synchrotron: 450 Gev. SPS ATLAS proton synchrotron: 26 GeV PS u 100 meters underground, ring with radius 4.3 kilometers OFour experiment: ATLAS, CMS, ALICE, LHCb O CM energy: 2012,8TeV, 2011, 7TeV Ferney. Volto Higgs, "God Particle p(8 4 TeV 4 Tev 2012
LHC (Large Hadron Collider) 3 proton synchrotron : 26 GeV Super proton synchrotron : 450 GeV 4 TeV ❑ 100 meters underground, ring with radius 4.3 kilometers ❑Four experiment ：ATLAS，CMS, ALICE，LHCb ❑ CM energy : 2012，8 TeV, 2011, 7 TeV 4 TeV 4 TeV in 2012 Higgs, “God Particle
aTLAS detector Muon Detecto s Electromagnetic Calorimeters 回 Solenoid Forward Calor meters Barrel Toroid Had onic Calorimeters OLong: 44 meters, 12.5 meters in radius, -7000 tons (One Eiffel tower, 100 jet 747) u components built within 35 countries Muon Spectrometer, Hadronic Calorimeter Electromagnetic(EM) Calorimeter, Inner Detector, 2/2/2021
ATLAS detector 4 2/2/2021 ❑Long: 44 meters，12.5 meters in radius, ~7000 tons. (One Eiffel tower ,~100 jet 747). ❑ components built within 35 countries : Muon Spectrometer, Hadronic Calorimeter, Electromagnetic (EM) Calorimeter ，Inner Detector
The atlas collaboration 8000-scientists including 1ooggraduate students 188 countries versities and research labs ■國录■ tkat
The ATLAS Collaboration 3000 scientists including 1000 graduate students 38 countries 174 universities and research labs 5
Standard model Standard Model explains what and how the matter is built at the subatomic level It cannot tell who l am and where 日 Subatomic particle 1 am going to… 6 quarks: u, d, C, S, t, b THE STANDARD MODEL 3 leptons e, u, t and 3 neutrino Fermo Bosons uc t y THree fundamental forces to describe the charm interactions between particles ds bZ Electromagnetic(EM) force down bottom Weak W Strong VVV W boson neutrino neutrino neutrino aThree sets of mediators to mediate the forces: e At Y(EM) electron W/Z, Higgs(Weak) Higgs boson gluons(Strong) YEt to be confirmed Source: AS 口 NOT coVered Dark matter(energy) Neutrino oscillations and its non -zero mass Gravitons not included in the frame(GUT 2/2/2021
Standard Model 6 2/2/2021 Standard Model explains what and how the matter is built at the subatomic level : ❑ Subatomic particle : • 6 quarks : u, d, c, s, t, b • 3 leptons e, μ, t and 3 neutrino ❑Three fundamental forces to describe the interactions between particles : • Electromagnetic (EM) force • Weak • Strong ❑Three sets of mediators to mediate the forces : • g (EM). • W/Z, Higgs (Weak). • gluons (Strong). ❑ NOT covered: • Dark matter (energy). • Neutrino Oscillations and its non-zero mass. • Gravitons not included in the frame (GUT). It cannot tell who I am and where I am going to…
Motivation for Higgs Mechanism Gauge symmetry agrangian is invariant under local phase transformation QED local gauge invariance -massless photon field A, U(1) QCD: local gauge invariance =8 massless vector gluon fields G. SU(3) o Weak interaction: massive/Z instead of massless(1983 o A solution: spontaneous breaking of a local gauge symmetry(introduce mass without breaking gauge invariance)(1960s) Or ignore the experiment factor that massive W/z quarks mediators have been discovered LEPTONS
Motivation for Higgs Mechanism 7 Gauge Symmetry Lagrangian is invariant under local phase transformation QED : local gauge invariance → massless photon field Aμ QCD: local gauge invariance → 8 massless vector gluon fields Weak interaction: massive W/Z instead of massless (1983). A solution: spontaneous breaking of a local gauge symmetry (introduce mass without breaking gauge invariance) (1960s). Or ignore the experiment factor that massive W/Z mediators have been discovered. a G U(1) SU(3)
Higgs Mechanism Peter Higgs in 2008 at CERN w非创M correct and promising L=(4+ie4)(a-ieA)db-2Φ-x(Φ (Where u20) We substitute o and A with (v+h( )e0(x)/y →)A.+ L=(Oh)2-h2+e2n22 ah+=elah +ve24h--F FAn+ So a vector gauge boson Au and massive scalar h(higgs particle)are produced Similarly, for SU(2), three massive gauge fields(W=, Z)and one massive scalar H are produced Higgs particle The last particle in SM that hasn't been shown experimentally 8
Higgs Mechanism 8 L ieA ieA F F 4 1 ( ) ( ) ( ) * 2 * 2 * 2 = + − − − − We substitute Φ and Aμ with : → + → + ev A A v h x e i x v 1 ( ( )) 2 1 ( )/ ... 4 1 2 1 4 1 2 1 ( ) 2 ' 1 2 2 2 2 2 2 3 4 2 2 2 2 2 = − + − − + + − + v L h v h e v A v h h e A h v e A h F v F V(f) f So a vector gauge boson A and massive scalar h (higgs particle) are produced Similarly, for SU(2), three massive gauge fields (W± ,Z) and one massive scalar H are produced (Where μ 20) Higgs particle : The last particle in SM that hasn’t been shown experimentally. correct and promising ? Peter Higgs in 2008 at CERN
SM Higgs Production and decay for LHC ggFusion: dominant Vector Boson Fusion Associated(small cross-sections) (VBF): Second largest WZ 鱼QQ变负 10 \s=7 TeV \S=tEv 10E WW→rvqa 工 WW→rv NLO EWY zz→rq 10 l=e,μ wH→Fvb 10 zH→rbb 100 200 300400500 100 200 300400500 M,Gevo Higgs boson mass(GeV/c) O Most sensitive channels are: <130 GeV YY: 125-300 GeV: ZZ*4I 300-600GeV:ZZ→,125-180Gev:WW*→lvv H-Tt, H- bb are significantly affected by QCD backgrounds. Try associated/BF mode 9
SM Higgs Production and decay for LHC 9 Vector Boson Fusion (VBF): Second largest Associated (small cross-sections) ggFusion : dominant 9 ❑ Most sensitive channels are : <130 GeV: γγ; 125-300 GeV: ZZ*→4l; 300-600 GeV: ZZ→llvv, 125-180 GeV: WW*→lvlv. ❑ H→tt, H→ are significantly affected by QCD backgrounds. Try associated/VBF mode bb
Previous limits from lep and tevatron Tevatron Run II Preliminary, =5.9fb LEP Exclusion Tevatron 10 Exclusion Expected Observed o Expec SM=l - Tevatron Exclusion Jly19.2010 100110120130140150160170180190200 (Ge V/c aBefore LHC's 2011 results, some Higgs mass regions have been excluded by TEVATRON July, 2010) and LEP OLEP: excludes <114.4 GeV UTEVaTRoN excludes 158-175 GeV 2/2/2021
Previous limits from LEP and TEVATRON 10 2/2/2021 ❑Before LHC’s 2011 results, some Higgs mass regions have been excluded by TEVATRON (July, 2010) and LEP. ❑LEP : excludes <114.4 GeV. ❑TEVATRON : excludes 158-175 GeV
