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Gavin Salam, CERN PSI Summer School Exothiggs, Zuoz, August 2016

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Gavin Salam, CERN PSI Summer School Exothiggs, Zuoz, August 2016 INGREDIENTS FOR ACCURATE COLLIDER PHYSICS Gavin Salam, CERN PSI Summer School Exothiggs, Zuoz, August 2016 1 LHC – TWO ROLES – A DISCOVERY MACHINE AND A PRECISION MACHINE Today ➤ 20 fb-1 at 8 TeV ➤ 13 fb-1 at 13 TeV Future ➤ 2018: 100 fb-1 @ 13 TeV ATLAS: general purpose CMS: general purpose ➤ 2023: 300 fb-1 @ 1? TeV ➤ 2035: 3000 fb-1 @ 14 TeV Interconnection between 1 fb-1 = 1014 collisions two “dipoles” (bending ALICE: heavy-ion physicsmagnets) in the LHCb: LHC B-physics tunnel. Increase in luminosity brings +TOTEM,LHCf discovery reach and precision LHC – TWO ROLES – A DISCOVERY MACHINE AND A PRECISION MACHINE Post/pre-dictionsZ’ exclusion for sequential reach Z' v.exclusion lumi reach 8 GPSreference & Weiler (ATLAS) 14 TeV 7 cern.ch/collider-reachextrapolations 2035 [preliminary plot] ATLAS / CDF 6 CMS / D0 2023 13 TeV 5 2018 4 mid 2016 end 2012 Z' reach [TeV] 3 8 TeV ATLAS: general purpose CMS: general purpose 7 TeV 2 − 1.96 TeV, pp 1 Interconnection between 0 two “dipoles” (bending 0.01 0.1 1 10 100 1000 10000 ALICE: heavy-ion physicsmagnets) in the LHCb: LHC B-physics -1 tunnel. integrated lumi [fb ] Increase in luminosity brings +TOTEM,LHCf discovery reach and precision LHC – TWO ROLES – A DISCOVERY MACHINE AND A PRECISION MACHINE Higgs couplings ATLAS and CMS H → γγ 3 LHC Run 1 f VBF+VH H → ZZ µ H → WW H → ττ 2 H → bb 1 ATLAS: general purpose CMS: general purpose 0 −1 68% CL Best fit SM expected Interconnection between two “dipoles” (bending 0 1 2 3 ALICE: heavy-ion physics LHCb: B-physics µf magnets) in the LHC ggF+ttH tunnel. f f Figure 14: Negative log-likelihood contours at 68% CL in the (µggF+ttH, µVBF+VH) plane for the combination of ATLAS and CMS, as obtained from the ten-parameter fit described in the text for each of the five decay channels H ZZ, H WW, H γγ, H ⌧⌧, and H bb. The best fit values obtained for each of the five decay ! ! ! ! ! channels are also shown, together with the SM expectation. mass measurementsIncrease in the di↵erent in channels. luminosity Several BSM models predict, brings for example, a superposition of states with indistinguishable mass values [121–124], possibly with di↵erent coupling structures to the +TOTEM,LHCf SM particles.discovery With such an assumption, reach it may be possible and to distinguish precision between single and multiple states by measuring the cross sections of individual production processes independently for each decay mode, as described in Section 4.1.1. Several methods have been proposed to assess the compatibility of the data with a single state [125, 126]. A test for the possible presence of overlapping Higgs boson states is performed, based on a profile likelihood ratio suggested in Ref. [127]. This test accounts both for missing measurements, such as the H bb decay mode in the ggF and VBF production processes, ! and for uncertainties in the measurements, including their correlations. 35 LONG-TERM HIGGS PRECISION? ����� ���������� ������������� �� ��� ���� ��� ��� ������� �� ����� NAIVELY EXTRAPOLATE��� ����� 7+8 TEV RESULTS (based on lumi and σ) official HL-LHC ����� ���������� ������������� �� ��� ���� ��� ��� ������� forecasts ����������� ����������� today’s ��� ����� �� ����� TH syst ��� ��������� ����������� �� CMS naively extrapolate 7/8 TeV results��� (based on lumi and 50% TH syst. ATLAS �� �� no TH syst. ��������� � Extrapolation suggests that ��������� � � we get value from full lumi only if we aim for O(1%) ������������ � µγγ or better precision ��� � �� �� ��� ��� ���� ���� �� ���� �� ����� ��� ��� � 3 σ ������������ � µγγ ) ��� �� �� ��� ��� ���� ���� ���� �� ����� ��� ������ Naive extrapolation suggests LHC has long-term potential to do Higgs physics at 1% accuracy 5 Phenomenology: lecture 1 (9/101) Recall of SM (EW part) Higgs mechanism THE HIGGS SECTOR Higgs fields: complex scalar doublet The theory is old (1960s-70s). V( ) + φ φ µ φ = , H =(D φ)†(Dµφ) V (φ) But the particle and it’s theory are φ0 L − unlike anything we’ve seen in nature. ! " Potential has form ➤ A fundamental scalar φ, i.e. spin 0 2 2 (all other particles are spin 1 or 1/2) V (φ)= µ φ†φ + λ(φ†φ) − 2 † † 2 ➤ + Α potential V(φ) ~ -μ (φφ ) + λ(φφ ) , 0 |φ | which leads to a Vacuum Ex- which until now was limited to being |φ | pectation Value (VEV): φ = 4 2 | | theorists’ “toy model” (φ ) µ /2λ = v/√2. SU(2) symmetry of configurations with#φ = v/√2. Choose gauge ➤ ”Yukawa” interactions responsible for | | transformation (unitary gauge) to map fermion masses, y i φ ¯ , with couplings (y ) spanning 5 orders of magnitude 0 i φ → (v + H)/√2 ! " 6 Phenomenology: lecture 1 (9/101) Recall of SM (EW part) Higgs mechanism THE HIGGS SECTOR Higgs fields: complex scalar doublet The theory is old (1960s-70s). V( ) + φ φ µ φ = , H =(D φ)†(Dµφ) V (φ) But the particle and it’s theory are φ0 L − unlike anything we’ve seen in nature. ! " Potential has form ➤ A fundamental scalar φ, i.e. spin 0 2 2 (all other particles are spin 1 or 1/2) V (φ)= µ φ†φ + λ(φ†φ) − 2 † † 2 ➤ + Α potential V(φ) ~ -μ (φφ ) + λ(φφ ) , 0 |φ | which leads to a Vacuum Ex- which until now was limited to being |φ | pectation Value (VEV): φ = 4 2 | | theorists’ “toy model” (φ ) µ /2λ = v/√2. SU(2)Higgs symmetry sector of configurationsneeds with#φ = v/√2. Choose gauge ➤ ”Yukawa” interactions responsible for | | transformationstress-testing (unitary gauge) to map fermion masses, y i φ ¯ , with couplings (y ) spanning 5 orders of magnitude 0 i φ Is Higgs fundamental or composite?→ (v + H)/√2 If fundamental, is it “minimal”?! " 4 Is it really φ ? Are Yukawa couplings responsible for all fermion masses? 6 up) interactions are modelled by overlaying minimum-bias interactions generated using Pythia8. Further detail of all MC generators and cross sections used is given in Ref. [19]. 4 Event selection This section describes the reconstruction-level definition of the signal region. The definition of physics objects reconstructed in the detector follows that of Ref. [19] exactly and is summarised here. All objects are defined with respect to a primary interaction vertex, which is required to have at least three associated tracks with pT 400 MeV. If more than one such vertex is present, the one with the largest value of 2 ≥ (pT), where the sum is over all tracks associated with that vertex, is selected as the primary vertex. P 4.1 Object reconstruction and identification Electron candidates are built from clusters of energy depositions in the EM calorimeter with an associ- ated well-reconstructed track. They are required to have ET > 10 GeV, where the transverse energy ET is defined as E sin(✓). Electrons reconstructed with ⌘ < 2.47 are used, excluding 1.37 < ⌘ < 1.52, which A three-level trigger system reduces the event rate| to| about 400 Hz [21]. The Level-1| trigger| is imple- corresponds to the transition region between the barrel and the endcap calorimeters. Additional identi- mented in hardware and uses a subset of detector information to reduce the event rate to a design value fication criteria are applied to reject background, using the calorimeter shower shape, the quality of the of at most 75 kHz. The two subsequent trigger levels, collectively referred to as the High-Level Trigger match between the track and the cluster, and the amount of transition radiation emitted in the ID [46–48]. (HLT), are implemented in software. ForATLAS electrons H → withWW* 10 GeV ANALYSIS< ET < 25[1604.02997] GeV, a likelihood-based electron selection at the “very tight” oper- ating point is used for its improved background rejection. For ET > 25 GeV, a more efficient “medium” selection is used because background is less of a concern. The efficiency of these requirements varies 3strongly Signal as a and function background of ET, starting models from 65–70% for ET < 25 GeV, jumping to about 80% with the change in identification criteria at ET = 25 GeV, and then steadily increasing as a function of ET [47]. The ggF and VBF production modes for H WW are modelled at next-to-leading order (NLO) in the Muon candidates are selected from tracks! reconstructed⇤ in the ID matched to tracks reconstructed in strong coupling ↵ with the Powheg MC generator [22–25], interfaced with Pythia8[26] (version 8.165) the muon spectrometer.S Tracks in both detectors are required to have a minimum number of hits to for the parton shower, hadronisation, and underlying event. The CT10 [27] PDF set is used and the para- ensure robust reconstruction. Muons are required to have ⌘ < 2.5 and p > 10 GeV. The reconstruction meters of the Pythia8 generator controlling the modelling| of| the parton showerT and the underlying event efficiency is between 96% and 98%, and stable as a function of p [49]. are those corresponding to the AU2 set [28]. The Higgs boson massT set in the generation is 125.0 GeV, whichAdditional is close criteria to the are measured applied to value. electrons The and Powheg muonsggF to reducemodel takes backgrounds into account from finitenon-prompt quark massesleptons andand a electromagnetic running-width Breit–Wigner signatures produced distribution by hadronic that includes activity. electroweak Lepton isolation corrections is atdefined NLO [ using29]. To track- im- provebased the and modelling calorimeter-based of the Higgs quantities. boson p AllT distribution, isolation variables a reweighting used are scheme normalised is applied relative to reproduce to the trans- the predictionverse momentum of the next-to-next-to-leading-order of the lepton, and are optimised (NNLO) for the andH next-to-next-to-leading-logarithmWW e⌫µ⌫ analysis, resulting in (NNLL) stricter ! ⇤! dynamic-scalecriteria for better calculation background given rejection by the HR ates lower2.1 programp and looser [30].
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