Joe Davies Imperial College London Supervisors: Dr Nick Wardle, Prof Gavin Davies Joe Davies Feb 2018 1 / 22 Probing BSM physics using H → γγ at CMS BSM physics using H → γγ at CMS
Table of Contents 1 Introduction The Higgs boson The CMS detector Higgs decay 2 The analysis Analysis aim and strategy Reconstruction of the Higgs mass Simplifjed template cross sections BSM Higgs and future studies Joe Davies Feb 2018 2 / 22 BSM physics using H → γγ at CMS
Table of Contents 1 Introduction The Higgs boson The CMS detector Higgs decay 2 The analysis Analysis aim and strategy Reconstruction of the Higgs mass Simplifjed template cross sections BSM Higgs and future studies Joe Davies Feb 2018 3 / 22 BSM physics using H → γγ at CMS
The Higgs boson scalar “Higgs” fjeld: Feb 2018 Joe Davies Figure 2: The Higgs potential[2] Figure 1: The Standard Model particles[1] – Predicts neutral scalar particle of Lagrangian – Ground state break symmetry – Non zero VEV Solution: introduce a complex Neutral scalar particle of mass point-like weak interaction was – But experiments suggested be massless gauge invariant, needed – To keep Lagrangian locally Why was it proposed? 4 / 22 ∼ 125 GeV photon and weak bosons to BSM physics using H → γγ at CMS
The CMS detector One of the two general-purpose LHC detectors Joe Davies Feb 2018 5 / 22 BSM physics using H → γγ at CMS
The CMS detector One of the two general-purpose LHC detectors Joe Davies Feb 2018 5 / 22 BSM physics using H → γγ at CMS
The CMS detector Figure 3: Cross-sectional view of the CMS detector[3]. Particle fmow algorithm used in global event reconstruction [4]. Joe Davies Feb 2018 5 / 22 BSM physics using H → γγ at CMS
Higgs decay Which channel to use? Feb 2018 Joe Davies Figure 5: Higgs decaying to two photons. t t t 6 / 22 H of Higgs mass [8]. Figure 4: Higgs branching ratios as a function Key channel in discovery[6, 7] Hard to distinguish against backgrounds – only recently discovered [5] b would have best sensitivity Might think that b ¯ Diphoton channel has a low BR ( < 1%) but clean signature in ECAL γ ¯ γ BSM physics using H → γγ at CMS
Higgs decay Which channel to use? b would have best sensitivity Hard to distinguish against backgrounds – only recently discovered [5] Key channel in discovery[6, 7] Figure 4: Higgs branching ratios as a function of Higgs mass [8]. Joe Davies Feb 2018 6 / 22 Might think that b ¯ Diphoton channel has a low BR ( < 1%) but clean signature in ECAL BSM physics using H → γγ at CMS
Table of Contents 1 Introduction The Higgs boson The CMS detector Higgs decay 2 The analysis Analysis aim and strategy Reconstruction of the Higgs mass Simplifjed template cross sections BSM Higgs and future studies Joe Davies Feb 2018 7 / 22 BSM physics using H → γγ at CMS
Analysis aim and strategy Aim To probe to what extent the Higgs boson behaves as the SM predicts How do we do this? Or measure cross sections for difgerent categories of Higgs production and decay (STXS) – How do we obtain them? Joe Davies Feb 2018 8 / 22 – Measure the signal strength modifjer, µ , defjned as: µ = Observed rate of H → γγ SM rate of H → γγ – Any deviations from µ = 1 may indicate BSM physics BSM physics using H → γγ at CMS
Reconstruction of Higgs mass signal Identify candidate photons Feb 2018 Joe Davies category binned in histogram for each Accepted signal candidates shower shape, isolation, – Takes inputs such as multivariate classifjer: From conservation of 4-momentum: from background pairs using a identifjcation (BDT) – Dependent on vertex Opening angle: ECAL – Dependent on resolution of Photon energy measurements: (1) 9 / 22 � m γγ = 2 E 1 E 2 ( 1 − cos θ ) and pseudorapidity. BSM physics using H → γγ at CMS Figure 6: m γγ for combined categories[9]
Simplifjed template cross sections (I) Figure 7: Event fmow chart for STXS[10]. Feb 2018 Joe Davies inclusive measurements – Higher sensitivity than – Reduced theory uncertainty Why do this? simultaneous likelihood fjt 10 / 22 number of jets, etc. topology of fjnal state e.g. p T , kinematic features and event Stage 1 : further split by mechanisms for difgerent Higgs production Stage 0 : construct categories Event categorisation in STXS → Extract µ or cross sections by BSM physics using H → γγ at CMS
Simplifjed template cross sections (II) Some distributions for example categories[9]: Figure 8: VH subcategory Figure 10: ggH subcategory t H subcategory Joe Davies Feb 2018 11 / 22 Figure 11: t ¯ BSM physics using H → γγ at CMS
Simplifjed template cross sections (II) Some distributions for example categories[9]: Figure 9: VH subcategory Figure 10: ggH subcategory t H subcategory Joe Davies Feb 2018 11 / 22 Figure 12: t ¯ BSM physics using H → γγ at CMS
BSM Higgs and future studies From the fjt, we can extract observed cross sections compare to some Feb 2018 Joe Davies Low statistics channels will benefjt from full run 1 and run 2 data sets p-value BSM contexts e.g. using EFT Or re-interpret in difgerent compare to the SM... For example, we could prediction factorised into model Theory uncertainty is Figure 13: Stage 0 of the STXS framework[9] model (STXC stage 0) 12 / 22 → quantify agreement with ( ∼ 150fb − 1 ) BSM physics using H → γγ at CMS
Summary To conclude: We are now in the era of precision Higgs measurements Current results are compatible with the Higgs being SM-like these with the full run 1 and 2 data sets Joe Davies Feb 2018 13 / 22 Some categories still limited by statistics → Aim to improve BSM physics using H → γγ at CMS
Thank you Joe Davies Feb 2018 14 / 22 BSM physics using H → γγ at CMS
Back up slides Joe Davies Feb 2018 15 / 22 BSM physics using H → γγ at CMS
Invariant mass distributions Figure 14: Diphoton invariant mass distributions for difgerent production categories, forming the initial stages of the simplifjed template cross section framework[9]. Joe Davies Feb 2018 16 / 22 BSM physics using H → γγ at CMS
Traditional signal strength Can obtain a “traditional” signal strength: ratio of rates for each mode. Current best CMS result[9]: Joe Davies Feb 2018 17 / 22 µ = 1 . 18 + 0 . 17 − 0 . 14 = 1 . 18 + 0 . 12 − 0 . 11 ( stat ) + 0 . 09 − 0 . 07 ( syst ) + 0 . 07 − 0 . 06 ( theo ) BSM physics using H → γγ at CMS
Traditional signal strength Can obtain a “traditional” signal strength: ratio of rates for each mode. Current best CMS result[9]: Joe Davies Feb 2018 17 / 22 µ = 1 . 18 + 0 . 17 − 0 . 14 = 1 . 18 + 0 . 12 − 0 . 11 ( stat ) + 0 . 09 − 0 . 07 ( syst ) + 0 . 07 − 0 . 06 ( theo ) BSM physics using H → γγ at CMS
Higgs production at the LHC Four main LHC production modes Vector boson fusion (VBF) Production in association with: – a weak boson (VH) t H) Gluon-gluon fusion (ggH) Figure 15: Higgs production cross sections as a Joe Davies Feb 2018 18 / 22 – a top-antitop pair (t ¯ function of Higgs mass, at √ s = 13 TeV[8] BSM physics using H → γγ at CMS
BDTs Figure 16: Photon BDT that separates background from signal[9]. Joe Davies Feb 2018 19 / 22 BSM physics using H → γγ at CMS
Bibliography I Standard Model of Elementary Particles . [Accessed: 20 March Feb 2018 Joe Davies 10.1088/1748-0221/8/09/P09009 . arXiv: 1306.2016 [hep-ex] . In: JINST 8 (2013). [JINST8,9009(2013)], P09009. doi : Serguei Chatrchyan et al. “Energy Calibration and Resolution of the Effjcient Digital Modulation”. In: (Apr. 2010). Tracker Optical Links and Future Upgrade Using Bandwidth Stefanos Dris, C Foudas, and J Troska. “Performance of the CMS [hep-ph] . John Ellis, Mary K. Gaillard, and Dimitri V. Nanopoulos. “A Standard_Model_of_Elementary_Particles.svg . 2017]. url : https://commons.wikimedia.org/wiki/File: 20 / 22 Historical Profjle of the Higgs Boson”. In: (2012). arXiv: 1201.6045 CMS Electromagnetic Calorimeter in pp Collisions at √ s = 7 TeV”. BSM physics using H → γγ at CMS
Bibliography II A. M. Sirunyan et al. “Observation of Higgs boson decay to bottom Feb 2018 Joe Davies 10.23731/CYRM-2017-002 . arXiv: 1610.07922 [hep-ph] . Deciphering the Nature of the Higgs Sector”. In: (2016). doi : D. de Florian et al. “Handbook of LHC Higgs Cross Sections: 4. 10.1016/j.physletb.2012.08.020 . arXiv: 1207.7214 [hep-ex] . the Standard Model Higgs boson with the ATLAS detector at the Georges Aad et al. “Observation of a new particle in the search for 10.1016/j.physletb.2012.08.021 . arXiv: 1207.7235 [hep-ex] . B716 (2012), pp. 30–61. doi : Serguei Chatrchyan et al. “Observation of a new boson at a mass of [hep-ex] . 10.1103/PhysRevLett.121.121801 . arXiv: 1808.08242 21 / 22 quarks”. In: Phys. Rev. Lett. 121.12 (2018), p. 121801. doi : 125 GeV with the CMS experiment at the LHC”. In: Phys. Lett. LHC”. In: Phys. Lett. B716 (2012), pp. 1–29. doi : BSM physics using H → γγ at CMS
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