Searches for Rare Exclusive Higgs Boson Decays with ATLAS Rhys Owen 1 , 2 University of Birmingham 1 , Rutherford Appleton Laboratory 2 11th January 2017 Rhys Owen (University of Birmingham, RAL) Rare Exclusive Higgs Boson Decays 11th January 2017 1 / 26
Introduction ATLAS H → WW* Events / 10 GeV 800 -1 s =8 TeV, 20.3 fb Higgs Boson discovered at LHC -1 s =7 TeV, 4.5 fb (a) n ≤ 1 , e µ + ee/ µ µ 600 j Leading discovery channels all involve bosons Obs ± stat Bkg syst ± 400 Higgs weights / GeV WW Events/2.5 GeV 200 ATLAS Preliminary Data Misid 35 Data ATLAS Preliminary Background -1 s = 13 TeV, 13.3 fb 180 Higgs (m = 125 GeV) VV Signal + Background H → γ γ , m = 125.09 GeV 200 H ZZ* Signal H H ZZ* 4l Top → → 160 S/B weighted sum of 30 Z+jets, t t ∑ DY -1 event categories 13 TeV, 14.8 fb t t +V, VVV 140 Uncertainty 0 0 25 120 (b) Background-subtracted Events / 10 GeV 100 Obs - Bkg 150 20 80 Bkg ± syst Higgs 60 15 100 40 20 10 0 50 10 weights - bkg 5 5 0 0 0 ∑ − 80 90 100 110 120 130 140 150 160 170 5 110 120 130 140 150 160 m [GeV] 50 100 150 200 250 300 4l m [GeV] γ γ m [GeV] ATLAS-CONF-2016-079 ATLAS-CONF-2016-067 T Phys.Rev. D92 (2015) no.1, 012006 Rhys Owen (University of Birmingham, RAL) Rare Exclusive Higgs Boson Decays 11th January 2017 2 / 26
BEH Mechanism This mechanism underpins all of the Higgs Physics Introduces a new field into the standard model � φ + � φ = φ 0 Four new degrees of freedom ◮ 3 mix with the W ± , Z 0 giving them mass ◮ The fourth gives rise to the standard model Higgs boson This explains the link between the Higgs boson, the electroweak bosons and their masses but says nothing about fermions Rhys Owen (University of Birmingham, RAL) Rare Exclusive Higgs Boson Decays 11th January 2017 3 / 26
Fermion Masses L fermion = − y f · [ ¯ ψ L φψ R + ¯ ψ R ¯ φψ L ] L fermion = − y f v y f · ¯ · h ¯ √ ψψ − √ ψψ 2 2 � �� � � �� � mass term Yukawa coupling term This combination of the Higgs field and fermions gives: gauge invariant mass terms for the fermions Introduces a Yukawa coupling directly between the fermions and the Higgs boson But masses are not generated directly by the spontaneous symmetry breaking as for the bosons Rhys Owen (University of Birmingham, RAL) Rare Exclusive Higgs Boson Decays 11th January 2017 4 / 26
Existing Results H → ττ H → b ¯ top associated b production Events / bin 4 10 Weighted events after subtraction / 20.0 GeV Data ATLAS Data 2012 10 µ VH(bb) ( =1.0) ∫ Background ( =1.4) s = 8 TeV Ldt = 20.3 fb -1 µ Diboson Uncertainty ln(L) 0+1+2 lep., 2+3 jets, 2 tags Background ( =0) µ ATLAS Preliminary 5 3 Weighted by Higgs S/B 10 8 ∆ H (125) → τ τ ( µ =1.4) s =13 TeV, 13.2-13.3 fb -1 σ - 3 H (125) → τ τ ( µ =1) 4 → γ γ t t H(H ) 6 → τ τ t t H(H WW/ /ZZ) 2 10 → 3 t t H(H b b ) t t H combination 4 σ 2 2 H → τ τ 10 ATLAS 2 1 -1 s = 8 TeV , 20.3 fb σ 1 1 -1 s = 7 TeV , 4.5 fb 0 0 − 0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 µ for m =125 GeV -4 -3 -2 -1 0 1 H t t H 50 100 150 200 250 ATLAS-CONF-2016-068 log (S / B) m [GeV] 10 bb JHEP 04 (2015) 117 JHEP 01 (2015) 069 There are several searches on-going with sensitivity to the Yukawa couplings The first direct evidence came from the observation of H → ττ (4 . 5(3 . 2) σ ) Most “Obvious” channels suffer from large backgrounds and other experimental challenges Rhys Owen (University of Birmingham, RAL) Rare Exclusive Higgs Boson Decays 11th January 2017 5 / 26
Higgs Boson → Q γ Meson Decay Photon Higgs Boson One promising channel is Higgs boson decays to a photon and a meson Gives direct access the Yukawa couplings A distinctive topology to trigger and select the events At the cost of a small SM branching ratio Channel SM Branching Ratio 3 × 10 − 2 BR ( H → c ¯ c ) 3 × 10 − 6 BR ( H → J /ψγ ) Rhys Owen (University of Birmingham, RAL) Rare Exclusive Higgs Boson Decays 11th January 2017 6 / 26
The ATLAS Experiment The ATLAS experiment is a general purpose detector based at the Large Hadron Collider. Rhys Owen (University of Birmingham, RAL) Rare Exclusive Higgs Boson Decays 11th January 2017 7 / 26
ATLAS Searches for Higgs Boson → J /ψγ I Phys. Rev. Lett. 114 (2015) 121801 Events/2 GeV Events / 0.02 GeV ATLAS Simulation 350 ATLAS Data 1 p µ ∫ 0.1 -1 H J/ s = 8 TeV L dt = 19.2 fb T → ψ γ 300 Fit Before selection ψ Loose Isol. Soft p J/ T 250 ψ γ 0.08 After selection J/ channel Background Barrel Categories σ ± 200 = 44 1 MeV 0.06 µ 2 p γ p T T 150 0.04 100 0.02 50 0 0 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 0 20 40 60 80 100 120 140 m [GeV] p [GeV] µ + µ - T Events / 4 GeV 24 Events / 4 GeV 25 22 ATLAS ATLAS 20 ∫ -1 ∫ -1 s =8 TeV Ldt = 19.2 fb s =8 TeV Ldt = 19.2 fb 20 Data Data 18 S+B Fit S+B Fit 16 Background Background -3 15 -3 14 H [B=10 ] H [B=10 ] -6 -6 Z [B=10 ] Z [B=10 ] 12 10 10 8 6 5 4 2 0 40 80 120 160 200 0 50 100 150 200 µ µ γ m [GeV] p [GeV] µ µ γ T h → J /ψγ First search for a decay of this type using √ s = 8 TeV Previously presented in this forum by Andrew Chisholm Rhys Owen (University of Birmingham, RAL) Rare Exclusive Higgs Boson Decays 11th January 2017 8 / 26
ATLAS Searches for Higgs Boson → Υ( nS ) γ Phys. Rev. Lett. 114 (2015) 121801 Events/2 GeV 0.12 Events / 0.1 GeV ATLAS ATLAS Simulation 80 Data µ 1 ∫ p -1 0.1 T H → ϒ (nS) γ s = 8 TeV L dt = 20.3 fb Fit 70 Before selection ϒ Loose Isol. Soft p (nS) T 60 ϒ γ 0.08 After selection (nS) channel Background Barrel Categories 50 σ = 108 ± 13 MeV 1S 0.06 p µ 2 40 p γ T T 30 0.04 20 0.02 10 0 0 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 0 20 40 60 80 100 120 140 m [GeV] p [GeV] µ + µ - T Events / 4 GeV Events / 4 GeV Events / 0.125 GeV ATLAS ATLAS 35 ATLAS 80 50 ∫ -1 ∫ -1 ∫ -1 s =8 TeV Ldt = 20.3 fb s =8 TeV Ldt = 20.3 fb s =8 TeV Ldt = 20.3 fb 70 30 Data Data Data S+B Fit S+B Fit S+B Fit 40 Combinatoric Combinatoric Combinatoric 60 ϒ ϒ 25 ϒ (nS) (nS) (nS) Z FSR Z FSR Z FSR 50 -3 -3 -3 H [B=10 ] H [B=10 ] H [B=10 ] 30 Z [B=10 -6 ] Z [B=10 -6 ] 20 Z [B=10 -6 ] 40 15 20 30 10 20 10 5 10 0 0 40 80 120 160 200 0 50 100 150 200 8 8.5 9 9.5 10 10.5 11 11.5 12 µ µ γ m [GeV] p [GeV] m [GeV] µ µ γ µ µ T h → Υ( nS ) γ Rhys Owen (University of Birmingham, RAL) Rare Exclusive Higgs Boson Decays 11th January 2017 9 / 26
ATLAS Searches for Higgs Boson → J /ψγ II 95% CLs upper limit on Branching Fraction . 10 − 2 √ s = 8 TeV 95% CL upper limit on Branching Fraction 20.3 fb − 1 ATLAS 20.3 fb − 1 20.3 fb − 1 20.3 fb − 1 19.2 fb − 1 Set limits on the Branching H / Z → Q γ ratio of the order 1 × 10 − 3 10 − 3 Observed Expected ( ± 1, 2 σ ) Compared with a predicted 20.3 fb − 1 SM branching ratio of 20.3 fb − 1 20.3 fb − 1 20.3 fb − 1 10 − 5 3 × 10 − 6 ( JHEP 1508 (2015) 012 ) 19.2 fb − 1 Any large deviation could be a sign of physics from 10 − 6 γ γ γ γ γ γ γ γ γ ) ) ) ) γ ) ) ) ) ψ S S S S S S S S 1 2 3 n ψ / / 1 2 3 n J ( ( ( ( J ( ( ( ( Υ Υ Υ Υ Υ Υ Υ Υ beyond the standard model. → → → → → → → → → → H Z H H H H Z Z Z Z H → J /ψγ H → Υ(1S) γ H → Υ(2S) γ H → Υ(3S) γ H → Υ(nS) γ Z → J /ψγ Z → Υ(1S) γ Z → Υ(2S) γ Z → Υ(3S) γ Z → Υ(nS) γ Phys. Rev. Lett. 114 (2015) 121801 Rhys Owen (University of Birmingham, RAL) Rare Exclusive Higgs Boson Decays 11th January 2017 10 / 26
ATLAS Searches for Higgs Boson → φγ γ γ/Z h h h γ γ The Latest Q γ search from ATLAS is for H → φγ Phys. Rev. Lett. 117, 111802 This is an analogous decay to the J /ψγ decay mode SM prediction B ( H → φγ ) = (2 . 3 ± 0 . 1) × 10 − 6 ( JHEP 1508 (2015) 012 ) The direct diagrams give access to the strange Yukawa coupling. Rhys Owen (University of Birmingham, RAL) Rare Exclusive Higgs Boson Decays 11th January 2017 11 / 26
Analysis Strategy Analysis performed using 2015 pp dataset 5 -1 ATLAS Preliminary fb s = 13 TeV Data is selected with a dedicated trigger LHC Delivered Total Integrated Luminosity 4 ATLAS Recorded All Good for Physics Backgrounds are modelled with a data Total Delivered: 4.2 fb -1 3 Total Recorded: 3.9 fb -1 driven model All G ood for Physics: 3.2 fb -1 2 SM signals are generated using the ATLAS simulation infrastructure. 1 These are combined in a Maximum 0 1/6 1/7 1/8 1/9 1/10 1/11 Likelihood fit to obtain CL s limits on the Day in 2015 Branching Ratio Rhys Owen (University of Birmingham, RAL) Rare Exclusive Higgs Boson Decays 11th January 2017 12 / 26
Recommend
More recommend
