Physics Prospects at HL-LHC

1. Physics Prospects at HL-LHC Aleandro Nisati INFN - Roma Scuola di fisica di Otranto 19 – 24 Settembre 2013

2. Present results by LHC • LHC data sample: √s = 7 and 8 TeV; L ~ 5 , 20 fb-1 • Discovery of a Higgs boson with mass of about 125 GeV • NO evidence of signal of NEW PHYSICS Beyond Standard Model, both from direct and indirect searches • Impressive success of Standard Model in describing the LHC data • Vedilezioni di TizianoCamporesi (Higgs boson physics) e di GiacomoPolesello (BSM)

3. Higgs boson • Distribution of the 4-lepton invariant mass obtained with the data recorded with the ATLAS detector

4. Standard Model results

5. Beyond Standard Model results Dielectron invariant mass (mee) distribution with statistical uncertainties after final selection, compared to the stacked sum of all expected backgrounds, with two selected Z′ signals overlaid. The SSM bin width is constant in log mee.

6. SUSY Searches

7. Exotics Searches

8. The priorities for collider physics after July 4th 2012 • The recently discovered new particle drives to a number of fundamental open points that are top priority for the physics programme for the LHC and future energy frontier accelerators: • Precision measurement of the mass of this new particle • Determination of the quantum numbers spin and parity, JP, and CP violation • Measurement of couplings to elementary fermions and bosons • Measurement of the di-Higgs boson production • Comparisonof these physics properties with those predicted by Standard Model • Search for possible partners (neutral and/or charged) of this boson • Is this particle a fundamental object, or it is composite?

9. The priorities for collider physics after July 4th 2012 • The investigations of the electroweak symmetry breaking cannot be limited to the study of the Higgs sector only: several points still to be addressed. Among these: • The dependence with energy of the Vector Boson Scattering cross section dσ/dmVV(WW, WZ and ZZ) • The hierarchy problem, that motivated new theories beyond SM, such as SUperSYmmetry, Extra-Dimensions, Technicolor models

10. The priorities for collider physics after July 4th • This enriches the collider physics programme: • Analysethe Vector Boson scattering cross section to study whether the cross-section regularization is operated by the Higgs boson (as predicted by SM) or by other processes associated to pyisics beyond SM; • Naturalness problem: continue the search for SUSY particles, in particular search for third generation squarks: to be effective, the mass of the stop quark cannot be too different from the one of the top quark; also continue the search for gauginos and for 1st and 2nd generation squarks; similarly for Extra-Dimensions. • Continue the search for heavy resonances decaying to photon, lepton or quark pairs, and for deviations from SM of physics distributions highly sensitive to New Physcs (di-jet angular distribution,…)

11. The European Strategy for Particle Physics • These themes have been widely discussed in the context of the Symposium on the European Strategy for Particle Physics, held on September 10 to 12, 2012. • Many proposals have been submitted (collider energy frontier physics, heavy flavour physics, neutrino and astroparticle physics, etc. etc.)

12. The European Strategy for Particle Physics • High Energy Frontier: • I’ll focus on examples of physics perspectivesat the High Luminosity-LHC (HL-LHC)

13. Some proposals for future colliders See also: arxiv:1302.3318 LEP3 TLEP/VHE-LHC CLIC

14. The LHC Upgrade plan • About 350 fb-1 are expected at the end of the LHC Programme • 300 fb-1 have been assumed as baseline in the studies made by ATLAS and CMS • Experimental challenges • The average number of proton-proton collisions per triggered events is about 140 • The trigger has to cope with the effects induced by the large pile-up • Theinner detector has to be fast and with high granularity and redundancy, to cope with the effects from large occupancy • The detector has to be (even more) radiation hard

15. LHC roadmap to achieve full potential Pippa Wells, CERN

16. What LHC will find during next run • LHC physics programme: √s = ~ 13 TeV; L ~ 300 fb-1 LHC after 300 fb-1 Will discover New Physics Direct evidence of NP production Deviations from SM. An example: Higgs boson properties; No deviations from SM • Explore physics at the luminosity LHC upgrade • Study new accelerator facilities

17. Event pileup at the LHC • Present ATLAS and CMS detectors have been designed for <μ> ~ 23 pp interactions / bunch-crossing • And continue to do an excellent job with 35 Zμμ decay in a large pileup event Missing transverse energy resolution as a function of the number of the reconstructed vertices • But cannot handle (an average of) 140 events of pileup

18. Vedi talk di L. Rossi Detector Upgrade • In a nutshell – detector upgrades are planned so as to maintain or improve on the present performance as the instantaneous luminosity increases • A particular challenge is to refine the hardware (level-1) and software (high level) triggers to maintain sensitivity with many interactions per bunch crossing – “pileup” • Offline algorithms also need to be developed to maintain performance with pileup • Focus here on upgrades which change the performance. Inaddition, there is a continuoushuge effort in consolidation, eg. new cooling systems, improved electronics and power supplies, shielding additions... • Phase 0/I upgrades are betterdefined than Phase II

19. Physics at HL-LHC • On the basis of what discussed in the previous slides, ATLAS and CMS presented two documents for the Symposium in Cracow, subsequently updated in October 2012 for the Briefing Book, and for the Snowmass meeting in 2013. • These documents focused on: • Higgs couplings, confirm spin, CP and self-couplings • Vector Boson Scattering • SUSY • Exotics • SM: Vector Boson TGCs and top quark FCNC • Workshop ECFA HL-LHC Aix-les-Bains, October 1st-3rd

20. Approaches adopted for physics perspectives estimation • ATLAS: perform physics simulation with a fast procedure based on simple functions applied to physics objects (electrons, photons, muons, tau, jets, b-jets, missing transverse energy) to mimic the effects from energy (momentum) resolution; acceptance, identification and reconstruction efficiencies, b-tagging efficiencies, fake rates • CMS: the upgraded detector will compensate the effects from event pile-up; assume three different scenarios: • Scenario 1: all systematic uncertainties are kept unchanged wrt those in current data analyses • Scenario 2: the theoretical uncertainties are scaled by a factor of 1/2, while other systematic uncertainties are scaled √L; • Scenario 3: set theoretical uncertainties to zero, to demonstrate their interplay with the experimental uncertainties; • The truth will be most likely somewhere between Scenario 1 and 2

21. Measurements of the 125 GeV boson • Mass & width are hard to improve beyond Run 2 • Direct measurement of width limited by resolution • Dominant spin/parity will probably be established as 0+ • Investigate a CP-violating contribution • At LHC, we can only measure σ×BR. Express a ratio μ to SM value. • Ratios of partial widths can be made without further assumptions • Interpretation as coupling measurements is model dependent

22. 125 GeV Higgs Couplings at the HL-LHC • ATLAS has performed projection studies to HL-LHC, assuming up to 3000 fb-1 of data • focused on the main channels already under study with LHC data, plus a few rare decay channels sensitive to top and muon couplings ATL-PHYS-PUB-2012-004 • ZH,Hbb was studied, but S/B is bad and it it very difficult at present to estimate systematic uncertainties at L=5x1034 cm-2 s-1 not included in the available ES ATLAS studies

23. ttH, Hγγ and Hμμ • One of the best channels to study Higgs boson couplings to fermions • Very rare: deviations from the expected rate would indicate new physics • Large background from Zμμ • Analysis included background modeling uncertainties • More than 6 sigma at L=3000 fb-1 • Important for H-top coupling measurement • Require multi-jet high-pT jets • Analyse 1-lepton and 2- lepton events • Require very high luminosity • S/√B ~ 6 • A factor 2 better than 300 fb-1

24. Higgs boson couplings in SM

25. Higgs boson couplings in SM Partial widths are proportional to the coupling square

26. Higgs boson signal strength • Measurements of the signal strength parameter mu for mH= 125GeV for the individual channels and for their combination. μif = μi × μf= μ

27. Higgs boson event production • k = analysis category • i = production mode • f = decay final state • nksignal = number of selected signal events by the k final state • L = integrated luminosity • σi,SM= production cross section • Bf,SM= finale state branching ratio • μi = production mode signal strength • μf= final state branching ratio strength • A = detector acceptance • ε = reconstruction and selection efficiency

28. Statistical procedure • Write the likelihood function • Example: do this for one channel/decay-final-state • The Profile Likelihood ratio; • here μ is the array of the various μi entering the likelihood function • θ(μ) is the array of the nuisance parameters

29. the production rate of events in the various analysis categories can be expressed directly in terms of the Higgs boson couplings, starting from the expression, and using the coupling constants at the place of the partial widths (including production): ΓH = ΣΓi • example: the Higgs boson production in the WH channel with decay to ZZ: σ(WH) x BR(HZZ) = σ(WH)SM x BR(HZZ)SM x (k2W k2Z)/k2H

30. the production rate of events in the various analysis categories can be expressed directly in terms of the Higgs boson couplings, starting from the expression, and using the coupling constants at the place of the partial widths (including production): ΓH = ΣΓi • example: the Higgs boson production in the WH channel with decay to ZZ: σ(WH) x BR(HZZ) = σ(WH)SM x BR(HZZ)SM x (k2W k2Z)/k2H • Warning! At LHC we don’t measure the Higgs boson production cross section nor ΓH !

31. Warning! At LHC we don’t measure the Higgs boson production cross section nor ΓH ! • As a consequence, we have two ways to proceed: • Make assumptions on ΓH  model dependent measurements • Make ratio of measurements, given that they are ΓH independent

32. Higgs Couplings

33. Theoretical uncertainties • Theoretical predictions for known and new processes are critical • Missing higher order (QCD) radiative corrections are estimated by varying factorisation and renormalisation scales (0.5 ~ 2.0) • Electroweak corrections • Treatment of heavy quarks • PDF uncertainties (which also depend on the order of calculation available) • mH=125 GeV @ 14 TeV: σ(pp(gg)H+X) scale +9 -12%, PDF ±8.5% • PDF uncertainties can be reduced by future precise experimental measurements at LHC, including • W, Z σ and differential distributionsfor lower x quarks • High mass Drell-Yan measurements for higher x quarks • Inclusive jets, dijetsfor high x quarks and gluons • Top pair differential distributions for medium/large x gluons • Single top for gluon and b-quark • Direct photons for small/medium x gluons

34. Higgs Couplings at the HL-LHC Left: Expected measurement precision on the signal strength μ = (σ×BR)=(σ×BR)SM in all considered channels. Right: Expected measurement precisions on ratios of Higgs boson partial widths without theory assumptions on the particle content in Higgs loops or the total width.

35. Higgs Couplings at the HL-LHC Left: Expected measurement precision on the signal strength μ = (σ×BR)=(σ×BR)SM in all considered channels. Right: Expected measurement precisions on ratios of Higgs boson partial widths without theory assumptions on the particle content in Higgs loops or the total width. Expected precision for the determination of the coupling scale factors kV and kF. No additional BSM contributions are allowed in either loops or in the total width (numbers in brackets include current theory systematic uncertainties).

36. Higgs Couplings at the HL-LHC • Coupling CMS projection: In the first one (Scenario 1) all systematic uncertainties are kept unchanged. In the second one (Scenario 2) the theoretical uncertainties are scaled by a factor of 1/2, while other systematical uncertainties are scaled by the square root of the integrated luminosity. Couplings can be measured at the level of 5 % or better

37. Are the ATLAS and CMS results consistent? • ATLAS uncertainty based on old result • ATLAS uncertainty extrapolated with CMS approach

38. Some proposals for future colliders See also: arxiv:1302.3318 LEP3 TLEP/VHE-LHC CLIC

42. 125 GeV Higgs boson CP mixing

43. Higgs boson CP mixing in HZZ4l • Explore the ATLAS sensitivity to the CP-violating part of the HZZ scattering amplitude: • ε: polarisation vectors of the gauge bosons, form factors a1 and a2 refer to CP-even boson with mass MX, a3 to a CP-odd boson • The presence of the two CP terms can lead to CP violation • In SM a1=1; a2=a3=0 • In this study we have set a1=1; a2=0, and varied a3 From European Strategy PUB Note fa3 > 0.46 fa3 > 0.63 Expected significances in sigma to reject a CP-violating state in favour of 0+ hypothesis as a function of integrated luminosity for various strength of CP-violating contribution. Measurement of “large” form factors can be seen with ~100 fb-1. A similar conclusion can be drawn for the observation of anomalous form factor a2

44. HH production at HL-LHC • The only way to reconstruct the scalar potential of the Higgs doublet field , that is responsible for spontaneous electroweak symmetry breaking, it is necessary to measure the Higgs boson self–interactions gluon-gluon fusion Vector Boson Fusion Higgs-strahlung

45. Higgs boson Self-Coupling A. Djouadi, et al., Eur. Phys. J. C10 (1999), 45 σHH (14 TeV) = 33.89 +18%-15% (QCD) ±7% (PDF+αS) ±10% (EFT) fb +37.2 -29.8 fb A. Djouadi, et al., http://arxiv.org/abs/1212.5581

46. Higgs Self-Coupling ATL-PHYS-PUB-2012-004 • The “trouble” with a 125 GeV Higgs: it decays in many final states with similar “small” B.R. This is very good for couplings, but opens real challenges for HH final states, characterized by small production rates. • The selection of HH processes has to account for: • Final states experimentally clear and robust • Final states with large enough production rates Expected SM HH yields for proton-proton collisions at √s = 14 TeV and L=3000 fb-1 • Two channels have been considered by ATLAS for the “European Strategy”: • HHbbWW • HHbbγγ

47. HHbbWW • BR ~ 25%  2.6 × 104 events in 3000 fb-1 at 14 TeV; • This includes all W decay modes • The ttbar process represents a severe background for this final state; • Study done considering one W decaying hadronically, the other leptonically (e,μ; treated separately) • Select events with high lepton pT, large missing transverse energy, four high-pT jets, of which two b-tagged; • The result of the study shows how challenging is extract HH production from this channel • We select <~ 1000 signal events on top of 107ttbar events • S/B in agreement with estimates performed by other authors (M.J. Dolan et al., arXiv:1206.5001v2 [hep-ph])

48. HH  bbγγ • BR ~ 0.27% , σ × BR ~ 0.09 fb 260 HH events in 3000 fb-1 at 14 TeV; • bbγγ, ZH, Zbb, Hbb, ttbar are important backgrounds • Select events with high-pT photons, two jets b-tagged; reconstruct the invariant mass of the b-jets and of the photons and select events with mγγ and mbb = mZ within experimental mass resolution • Initial studies presented performed for the European Stratgey indicate that this channel is promising • Soon preliminary results at the ECFA HL-LHC Workshop

49. HH  bbττ • BR ~ 7.4% , σ × BR ~ 0.22 fb  7500 HH events in 3000 fb-1 at 14 TeV; • Ttbar is the most dangerous background; other backgrounds are bbττ, Zbb, Hbb • Some authors have submitted papers where extremely encouraging; recent analyses done by ATLAS and still on going, based on more realistic assumptions on tau and b-quark reconstruction, indicate how much challenging this channel is. • More work is still needed before making a statement on this final state.

50. Vector Boson Scattering • In the Standard Model, the Higgs boson preserves the unitarity of scattering amplitudes in longitudinal Vector Boson Scattering (VBS) • However new physics can contribute to the regularization of of the VBS cross-section or else enhancing it. • Example: in Technicolor models predict the appearance of resonances in the V-V invariant mass distribution •  the study of VBS properties at the LHC is a mandatory step to test the effects of the SM Higgs boson (if the existence will be confirmed) or from New Physics BSM.