Motivation Parton Level July 2016 Zhao-Huan Yu (Melbourne) 28 July 2016, Melbourne CoEPP lunch talk Based on Dolan, Spannowsky, Wang, ZHY, arXiv:1606.00019, PRD School of Physics, the University of Melbourne ARC Centre of Excellence for Particle Physics at the Terascale, Determining the Quantum Numbers of Conclusion Discrimination Detector Level 1 / 20 Simplifjed Models in t ¯ tX production at the LHC Zhao-Huan Yu ( 余钊焕 ) Quantum Numbers in t ¯ tX production at the LHC
Motivation : Fermi-LAT Galactic Centre excess matter (DM) annihilation into Standard Model (SM) particles Such a light resonance at the LHC forbidden Parton Level : decay into DM forbidden is likely to dominate LHC signature Easily hidden in Run 1 searches Promising in 13/14 TeV searches Zhao-Huan Yu (Melbourne) July 2016 [Cirelli et al. , 1407.2173] 2 / 20 Detector Level Motivation Conclusion Discrimination Galactic Centre excess of GeV difguse γ rays can be explained by dark DM annihilation into b ¯ b provides a particularly good fjt ⇒ a light mediator X coupled to DM and the 3rd generation quarks ? KRA, gNFW � Γ � 1.26 � 10 � 25 2 � dof � 1.44 � b Χ min 2 d � � dE Γ d � � GeV cm � 2 s � 1 sr � 1 � 4. 3. � �� �� � � Σ v � � cm 3 s � 1 � � 2. � � � � 1. �� �� � � 0. � �� � �� 10 6 � E Γ � � � 1. 10 0 10 1 10 2 10 � 26 E Γ � GeV � M DM � 37.8 GeV � Σ v � � 2.10 � 10 � 26 cm 3 s � 1 20 40 60 80 100 M DM � GeV � Quantum Numbers in t ¯ tX production at the LHC
Motivation Parton Level July 2016 Zhao-Huan Yu (Melbourne) Promising in 13/14 TeV searches Easily hidden in Run 1 searches the LHC matter (DM) annihilation into Standard Model (SM) particles Fermi-LAT Galactic Centre excess [Cirelli et al. , 1407.2173] 2 / 20 Discrimination Detector Level Conclusion Motivation Galactic Centre excess of GeV difguse γ rays can be explained by dark DM annihilation into b ¯ b provides a particularly good fjt ⇒ a light mediator X coupled to DM and the 3rd generation quarks ? KRA, gNFW � Γ � 1.26 � 10 � 25 Such a light ( ≲ 100 GeV ) resonance X at 2 � dof � 1.44 � b Χ min 2 d � � dE Γ d � � GeV cm � 2 s � 1 sr � 1 � 4. m X < 2 m t : X → t ¯ 3. � t forbidden �� �� � � Σ v � � cm 3 s � 1 � � 2. � � � � m X < 2 m DM : decay into DM forbidden 1. �� �� � � 0. � �� � �� X → b ¯ 10 6 � E Γ � b is likely to dominate � � 1. 10 0 10 1 10 2 10 � 26 E Γ � GeV � t b ¯ LHC signature pp → t ¯ tX → t ¯ b M DM � 37.8 GeV � Σ v � � 2.10 � 10 � 26 cm 3 s � 1 20 40 60 80 100 M DM � GeV � Quantum Numbers in t ¯ tX production at the LHC
Motivation Parton Level July 2016 Zhao-Huan Yu (Melbourne) and production cross section depends on The 3 / 20 Four simplifjed models with a new neutral resonance which is an eigenstate Detector Level Simplifjed Models Conclusion Discrimination If such a new light resonance X is discovered at the LHC, the fjrst priority will be the characterisation of its spin and CP quantum numbers of parity and charge conjugation are considered g q m q X = S ( J PC = 0 ++ ) : L S = − ∑ S ¯ qq v q = b , t g q m q X = A ( J PC = 0 − + ) : L P = − ∑ A ¯ qi γ 5 q v q = b , t V ( J PC = 1 −− ) : L V = − X = Z ′ µ ∑ g q Z ′ µ V ¯ q γ µ q q = b , t A ( J PC = 1 ++ ) : L AV = − X = Z ′ µ ∑ g q Z ′ µ A ¯ q γ µ γ 5 q q = b , t Quantum Numbers in t ¯ tX production at the LHC
Motivation Parton Level July 2016 Zhao-Huan Yu (Melbourne) Four simplifjed models with a new neutral resonance which is an eigenstate 3 / 20 Simplifjed Models Detector Level Discrimination Conclusion If such a new light resonance X is discovered at the LHC, the fjrst priority will be the characterisation of its spin and CP quantum numbers of parity and charge conjugation are considered − X production LHC, √ s g q m q = 14 TeV, tt X = S ( J PC = 0 ++ ) : L S = − ∑ S ¯ qq v Inclusive cross section (pb) q = b , t 10 1 g q m q X = A ( J PC = 0 − + ) : L P = − t − ∑ t Z A ¯ qi γ 5 q ′ A , g t = 0.2 v − t t S q = b , t , g t = 1 10 0 V ( J PC = 1 −− ) : L V = − − Z ′ X = Z ′ µ ∑ g q Z ′ µ tt V ¯ q γ µ q V , g t = 0.2 − A, g t = 1 tt q = b , t A ( J PC = 1 ++ ) : L AV = − X = Z ′ µ ∑ g q Z ′ µ A ¯ q γ µ γ 5 q 10 -1 20 40 60 80 100 120 140 160 180 200 q = b , t m X (GeV) The pp → t ¯ tX production cross section depends on g t and m X Quantum Numbers in t ¯ tX production at the LHC
Motivation Parton Level July 2016 Zhao-Huan Yu (Melbourne) discriminating variables Helpful for exploring other spin and parity Able to nearly fully reconstruct the two tops the missing transverse momentum is the only source of The neutrino Larger backgrounds Semi-leptonic top decay channel [Buckley & Gonçalves, 1407.2173, PRL] 4 / 20 Discrimination Detector Level Spin and Parity Discrimination Conclusion Di-leptonic top decay channel pp → t ¯ tX → b ℓν + b ℓν + bb The azimuthal angle between the leptons ∆ ϕ ℓℓ encodes the spin correlation information of the top pair, which is related to the ttX coupling structure Previous studies showed that ∆ ϕ ℓℓ is useful for discriminating S ( 0 ++ ) from A ( 0 − + ) + 0 t t d σ 0.04 - [fb] 0 t t d ∆ φ t t b b ll 0.035 0.03 0.025 0.02 0.015 0.01 BDRS R=1.2 P > 200 GeV TJ 0.5 1 1.5 / 2 2.5 3 σ σ - + 1.5 0 t t 0 t t 1 0.5 0 1 2 3 ∆ φ ll Quantum Numbers in t ¯ tX production at the LHC
Motivation Parton Level July 2016 Zhao-Huan Yu (Melbourne) discriminating variables Helpful for exploring other spin and parity Able to nearly fully reconstruct the two tops Larger backgrounds Semi-leptonic top decay channel [Buckley & Gonçalves, 1407.2173, PRL] 4 / 20 Conclusion Spin and Parity Discrimination Discrimination Detector Level Di-leptonic top decay channel pp → t ¯ tX → b ℓν + b ℓν + bb The azimuthal angle between the leptons ∆ ϕ ℓℓ encodes the spin correlation information of the top pair, which is related to the ttX coupling structure Previous studies showed that ∆ ϕ ℓℓ is useful for discriminating S ( 0 ++ ) from A ( 0 − + ) + 0 t t d σ 0.04 - [fb] 0 t t d ∆ φ t t b b ll 0.035 pp → t ¯ tX → b j j + b ℓν + bb 0.03 0.025 0.02 The neutrino ν is the only source of 0.015 the missing transverse momentum / p T 0.01 BDRS R=1.2 P > 200 GeV ⇓ TJ 0.5 1 1.5 / 2 2.5 3 σ σ - + 1.5 0 t t 0 t t 1 ⇓ 0.5 0 1 2 3 ∆ φ ll Quantum Numbers in t ¯ tX production at the LHC
Motivation Parton Level July 2016 Zhao-Huan Yu (Melbourne) MadGraph : parton-level simulation samples for the 14 TeV LHC FeynRules : implementation of the simplifjed models 5 / 20 Detector Level Discrimination Parton-Level Simulation Conclusion ⇓ UFO format Normalised distributions of p T, X and m t ¯ t for m X = 50 GeV : similar in shape; difgerent peak positions; t ¯ tS is the softest; t ¯ tA is the hardest − X production, m X = 50 GeV − X production, m X = 50 GeV LHC, √ s LHC, √ s = 14 TeV, tt = 14 TeV, tt 0.012 0.006 − S − S tt tt − A − A tt tt 0.010 0.005 1/ σ d σ /dp T,X (GeV -1 ) − Z ′ − Z ′ tt − (GeV -1 ) tt V V − Z ′ − Z ′ tt tt A A 0.008 0.004 1/ σ d σ /dm tt 0.006 0.003 0.004 0.002 0.002 0.001 0.000 0.000 0 100 200 300 400 500 300 400 500 600 700 800 900 1000 p T,X (GeV) m tt − (GeV) Quantum Numbers in t ¯ tX production at the LHC
Motivation Parton Level July 2016 Zhao-Huan Yu (Melbourne) Other signals: a double-peak structure : a broad plateau around CM frame Boost to the CM frame Boost Lab frame 6 / 20 Discrimination Detector Level Variable Conclusion Centre-of-Mass (CM) Frame: the θ CM t Distributions of θ t (the angle between t and the beamline) in the lab frame show no difgerence − X production, m X = 50 GeV LHC, √ s = 14 TeV, tt 0.70 − S − Z ′ tt tt V 0.60 − A − Z ′ tt tt A 0.50 1/ σ d σ /d θ t 0.40 0.30 0.20 0.10 0.0 0.5 1.0 1.5 2.0 2.5 3.0 θ t Quantum Numbers in t ¯ tX production at the LHC
Motivation Lab frame July 2016 Zhao-Huan Yu (Melbourne) Parton Level Boost 6 / 20 Variable Discrimination Detector Level Conclusion Centre-of-Mass (CM) Frame: the θ CM t Distributions of θ t (the angle between t and the Normal X beamline) in the lab frame show no difgerence Θ CM Beamline Boost to the t ¯ tX CM frame ⇒ θ CM t θ CM t ¯ ▶ t ¯ t t tS : a broad plateau around π/ 2 ▶ Other signals: a double-peak structure t ¯ tX CM frame − X production, m X = 50 GeV − X production, m X = 50 GeV LHC, √ s LHC, √ s = 14 TeV, tt = 14 TeV, tt 0.70 0.50 − S − Z ′ 0.45 tt tt V 0.60 − A − Z ′ tt tt 0.40 A 0.35 0.50 CM 1/ σ d σ /d θ t 1/ σ d σ /d θ t 0.30 0.40 0.25 0.20 0.30 0.15 − Z ′ − S 0.10 tt tt 0.20 V − A − Z ′ tt tt 0.05 A 0.10 0.00 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 CM θ t θ t t ¯ tX CM frame Quantum Numbers in t ¯ tX production at the LHC
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