Putting the dip in diphoton Sophie Renner DAMTP, Cambridge (soon - PowerPoint PPT Presentation

Putting the dip in diphoton Sophie Renner DAMTP, Cambridge (soon Mainz) Based on “Exploring Peaks and Valleys in the Diphoton Spectrum” (1607.06074) with Nathaniel Craig and Dave Sutherland Sophie Renner DAMTP, Cambridge (soon Mainz) Putting the dip in diphoton 1 / 15

Outline • There was a bump in diphotons • Fits were done to find the preferred “mass”, “width” and “cross-section” of a possible resonance • But how might resonance-continuum interference affect these numbers? • And can we use interference effects to deduce the most likely “spin”? • Obviously we now know that the bump was just a statistical fluctuation of the background • Can we learn anything for if and when it happens again (and for real)? • Can we dip-hunt as well as bump hunt? Sophie Renner DAMTP, Cambridge (soon Mainz) Putting the dip in diphoton 2 / 15

The diphoton bump: ATLAS and CMS fits to 2015 data CMS: • Best fit with 13 TeV data ∼ 760 GeV • Preference for a narrow width • 2.85 σ local significance ( < 1 σ global) ATLAS: • Best fit with 13 TeV data ∼ 750 GeV • Preference for a ∼ 45 GeV width • 3.6 σ local significance (2 σ global) Sophie Renner DAMTP, Cambridge (soon Mainz) Putting the dip in diphoton 3 / 15

Particle explanations • Spin 0 (scalar or pseudoscalar) or spin 2 • qq initiated or gg initiated • wide or narrow Effective Lagrangians: − 1 Λ g φ G µν G µν − 1 Λ γ φ F µν F µν − c q φ qq ; L 0 ++ ⊃ − 1 G µν − 1 Λ g φ G µν ˜ Λ γ φ F µν ˜ F µν − ic q φ q γ 5 q ; L 0 − + ⊃ � − 1 λ + 1 λ + 1 4 g µν F 2 − G µλ G ν 4 g µν G 2 − F µλ F ν L 2 ++ ⊃ Λ T φ µν +1 � 2 iq ( γ µ ∂ ν + γ ν ∂ µ ) q − ig µν q ✁ ∂ q . Sophie Renner DAMTP, Cambridge (soon Mainz) Putting the dip in diphoton 4 / 15

Signal-background interference • Calculate interference for each scenario using helicity amplitudes A P = √ s − M 2 + i Γ ˆ ˆ s • A , M , Γ all free parameters √ At √ s = 13 TeV and s = 750 GeV, the background is mostly q ¯ ˆ q initiated contributions = ⇒ interference effects will be largest in q ¯ q initiated signals Lots of previous work on interference ef- fects in Higgs to gamma gamma (eg. hep- ph/0302233, 1208.1533), but the very narrow width of the Higgs means effects are small Other papers focus on effects of interference in the interpretation of the 750GeV excess, using benchmark models (eg 1601.00006, 1605.00542) Sophie Renner DAMTP, Cambridge (soon Mainz) Putting the dip in diphoton 5 / 15

Bumps with interference No phase: s = 13 TeV s = 13 TeV gg → γγ , u u → γγ , d σ / dm [ fb / GeV ] d σ / dm [ fb / GeV ] 0.04 0.14 BG BG BG + S 0.12 BG + S 0.03 BG + PS BG + T 0.10 BG + T 0.02 0.08 0.06 0.01 0.04 m γγ [ GeV ] m γγ [ GeV ] 700 800 900 700 800 900 Spin 2 qq initiated with phases: d σ / dm [ fb / GeV ] 0.16 0.14 No int. ϕ = 0 0.12 ϕ = 90 o In the EFT no phases are possible in couplings 0.10 ϕ = 180 o due to hermiticity of effective lagrangian 0.08 0.06 0.04 m γγ [ GeV ] 700 800 900 Using M = 750 GeV, Γ = 40GeV Sophie Renner DAMTP, Cambridge (soon Mainz) Putting the dip in diphoton 6 / 15

Fits with interference: spin 2 qq -initiated - 2 ln ( L / L 0 ) ; - 2 ln L 0 = - 1472364. - 2 ln ( L / L 0 ) ; - 2 ln L 0 = - 1472372. Combined8 + 13 Combined8 + 13 70 70 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 6000 4000 4000 4000 4000 4000 4000 4000 4000 4000 60 60 8000 8000 8000 8000 8000 6000 6000 4000 4000 4000 4000 4000 4000 6000 4000 4000 4000 4000 4000 4000 20 20 50 8000 8000 8000 8000 8000 6000 4000 4000 4000 4000 50 4000 4000 4000 6000 4000 4000 4000 4000 4000 4000 15 15 Γ / GeV Γ / GeV 40 40 8000 8000 8000 8000 8000 4000 4000 4000 4000 6000 4000 4000 4000 6000 4000 4000 4000 4000 4000 4000 10 10 30 30 8000 8000 8000 8000 6000 6000 6000 6000 6000 6000 4000 4000 4000 4000 4000 4000 4000 4000 6000 6000 5 5 20 20 8000 8000 8000 8000 6000 6000 6000 6000 6000 6000 6000 6000 6000 6000 6000 6000 6000 6000 6000 6000 0 0 10 10 8000 8000 8000 6000 6000 6000 6000 8000 8000 8000 8000 6000 6000 6000 6000 6000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 700 720 740 760 780 700 720 740 760 780 M / GeV M / GeV With interference Without interference Big change: due to • Dominance of qq initiated background (large interfering background = ⇒ large interference effects) Sophie Renner DAMTP, Cambridge (soon Mainz) Putting the dip in diphoton 7 / 15

Fits with interference: spin 2 gg -initiated - 2 ln ( L / L 0 ) ; - 2 ln L 0 = - 1472376. - 2 ln ( L / L 0 ) ; - 2 ln L 0 = - 1472376. Combined8 + 13 Combined8 + 13 70 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 70 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 60 60 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 25 25 20 50 20 50 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 15 Γ / GeV 15 Γ / GeV 40 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 40 4000 4000 4000 4000 4000 4000 4000 4000 4000 4000 10 10 30 30 4000 4000 4000 4000 4000 4000 4000 4000 6000 6000 4000 4000 4000 4000 4000 4000 4000 4000 4000 6000 5 5 20 20 6000 6000 6000 4000 4000 6000 6000 6000 6000 6000 6000 6000 4000 4000 4000 4000 6000 6000 6000 6000 0 0 10 8000 8000 6000 6000 6000 6000 6000 8000 8000 8000 10 6000 6000 6000 6000 6000 6000 6000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 700 720 740 760 780 700 720 740 760 780 M / GeV M / GeV With interference Without interference Some change: due to • Relative suppression of gg - initiated background Sophie Renner DAMTP, Cambridge (soon Mainz) Putting the dip in diphoton 8 / 15

Fits with interference: spin 0 qq - initiated - 2 ln ( L / L 0 ) ; - 2 ln L 0 = - 1472375. - 2 ln ( L / L 0 ) ; - 2 ln L 0 = - 1472375. Combined8 + 13 Combined8 + 13 70 70 00000 100000 100000 100000 100000 100000 100000 100000 100000 15000 00000 100000 100000 100000 100000 100000 100000 100000 100000 15000 40 40 60 50000 150000 150000 100000 100000 150000 150000 150000 150000 15000 60 50000 150000 150000 100000 100000 150000 150000 150000 150000 15000 50 30 50 30 50000 150000 150000 150000 150000 150000 150000 150000 150000 15000 50000 150000 150000 150000 150000 150000 150000 150000 150000 15000 Γ / GeV Γ / GeV 40 40 00000 150000 150000 150000 150000 150000 150000 200000 200000 20000 00000 150000 150000 150000 150000 150000 150000 200000 200000 20000 20 20 30 50000 250000 200000 200000 200000 200000 200000 200000 250000 25000 30 50000 250000 200000 200000 200000 200000 200000 250000 250000 25000 10 10 20 20 50000 250000 250000 250000 250000 250000 250000 250000 250000 25000 50000 250000 250000 250000 250000 250000 250000 250000 250000 25000 0 0 10 50000 250000 250000 250000 250000 250000 250000 250000 250000 25000 10 50000 250000 250000 250000 250000 250000 250000 200000 250000 25000 50000 250000 250000 250000 250000 250000 250000 250000 250000 25000 50000 250000 250000 250000 250000 150000 250000 250000 250000 25000 700 720 740 760 780 700 720 740 760 780 M / GeV M / GeV With interference Without interference No change: due to • No interference at LO Sophie Renner DAMTP, Cambridge (soon Mainz) Putting the dip in diphoton 9 / 15

Fits with interference: spin 0 gg - initiated: - 2 ln ( L / L 0 ) ; - 2 ln L 0 = - 1472380. - 2 ln ( L / L 0 ) ; - 2 ln L 0 = - 1472380. Combined8 + 13 Combined8 + 13 70 10000 10000 10000 10000 10000 10000 10000 10000 10000 1000 70 10000 10000 10000 10000 10000 10000 10000 10000 10000 1000 60 60 10000 10000 10000 10000 10000 10000 10000 10000 10000 1500 10000 10000 10000 10000 10000 10000 10000 10000 10000 1000 25 25 50 50 10000 10000 10000 10000 10000 10000 10000 10000 15000 1500 10000 10000 10000 10000 10000 10000 10000 10000 15000 1500 20 20 Γ / GeV Γ / GeV 15 40 15000 15000 15000 10000 15000 15000 15000 15000 15000 1500 40 15000 15000 15000 10000 10000 15000 15000 15000 15000 1500 15 10 10 30 30 15000 15000 15000 15000 15000 15000 15000 15000 15000 1500 15000 15000 15000 15000 15000 15000 15000 15000 15000 1500 5 5 20 20 15000 15000 15000 15000 15000 15000 15000 15000 20000 2000 20000 15000 15000 15000 15000 15000 15000 15000 20000 2000 0 0 10 30000 20000 20000 20000 20000 20000 20000 20000 20000 3000 10 20000 20000 20000 20000 20000 20000 20000 20000 20000 3000 30000 30000 30000 30000 30000 30000 30000 30000 30000 3000 30000 30000 30000 30000 30000 30000 30000 30000 30000 3000 700 720 740 760 780 700 720 740 760 780 M / GeV M / GeV With interference Without interference V little change change: due to • PDF suppression of gg background compared to qq Sophie Renner DAMTP, Cambridge (soon Mainz) Putting the dip in diphoton 10 / 15