Physics Prospects at HL-LHC

Physics Prospects at HL-LHCAleandro NisatiINFN - RomaScuola di fisica di Otranto19 24 Settembre 2013 Present results by LHCLHC data sample: s = 7 and 8 TeV; L ~ 5 , 20 fb-1 Discovery of a Higgs boson with mass of about 125 GeVNO evidence of signal of NEW PHYSICS Beyond Standard Model, both from direct and indirect searchesImpressive success of Standard Model in describing the LHC dataVedi lezioni di Tiziano Camporesi (Higgs boson physics) e di Giacomo Polesello (BSM)

2Higgs bosonDistribution of the 4-lepton invariant mass obtained with the data recorded with the ATLAS detector3

Standard Model results4

Beyond Standard Model results5

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.SUSY Searches6

Exotics Searches7

The priorities for collider physics after July 4th 2012The 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 particleDetermination of the quantum numbers spin and parity, JP, and CP violationMeasurement of couplings to elementary fermions and bosonsMeasurement of the di-Higgs boson production Comparison of these physics properties with those predicted by Standard ModelSearch for possible partners (neutral and/or charged) of this bosonIs this particle a fundamental object, or it is composite?

8The priorities for collider physics after July 4th 2012The 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 d/dmVV (WW, WZ and ZZ)The hierarchy problem, that motivated new theories beyond SM, such as SUperSYmmetry, Extra-Dimensions, Technicolor models

9The priorities for collider physics after July 4thThis enriches the collider physics programme:

Analyse the 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,)10The European Strategy for Particle PhysicsThese 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.)

11The European Strategy for Particle PhysicsHigh Energy Frontier:Name beamscollidergeometrys, TeVluminosityOperation(years)HL-LHCppcircular143000 fb-12024-2030HE-LHCppcircular26-33100-300 fb-1/yearAfter 2035VHE-LHCppcircular40-100-After 2035LEP3e+ecircular0.24011034 cm-2s-1After 2024ILCe+elinear0.2501.0~11034 cm-2s-1~ 2030CLICe+elinear0.5003.02-61034 cm-2s-1After 2030TLEPe+ecircular0.24-0.35051034 cm-2s-1After 2035LHeCe(e+)pcircularO(100 fb-1)After 2022-collider?-collider+circular?Ill focus on examples of physics perspectives at the High Luminosity-LHC (HL-LHC)12Some proposals for future colliders13

LEP3TLEP/VHE-LHCCLICSee also: arxiv:1302.3318The LHC Upgrade planAbout 350 fb-1 are expected at the end of the LHC Programme300 fb-1 have been assumed as baseline in the studies made by ATLAS and CMS

Experimental challengesThe average number of proton-proton collisions per triggered events is about 140The trigger has to cope with the effects induced by the large pile-upThe inner detector has to be fast and with high granularity and redundancy, to cope with the effects from large occupancyThe detector has to be (even more) radiation hard14LHC roadmap to achieve full potentialPippa Wells, CERNJune 201315

What LHC will find during next runLHC physics programme: s = ~ 13 TeV; L ~ 300 fb-1

16LHC after 300 fb-1Will discover New PhysicsNo deviations from SMDirect evidence of NP productionDeviations from SM. An example: Higgs boson properties;Explore physics at the luminosity LHC upgradeStudy new accelerator facilities Event pileup at the LHCPresent ATLAS and CMS detectors have been designed for ~ 23 pp interactions / bunch-crossingAnd continue to do an excellent job with 35But cannot handle (an average of) 140 events of pileup

Z decay in a large pileup event Missing transverse energy resolution as a function of the number of the reconstructed vertices17Detector Upgrade18In a nutshell detector upgrades are planned so as to maintain or improve on the present performance as the instantaneous luminosity increasesA particular challenge is to refine the hardware (level-1) and software (high level) triggers to maintain sensitivity with many interactions per bunch crossing pileupOffline algorithms also need to be developed to maintain performance with pileupFocus 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

Vedi talk di L. RossiPhysics at HL-LHCOn 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-couplingsVector Boson Scattering SUSYExoticsSM: Vector Boson TGCs and top quark FCNCWorkshop ECFA HL-LHC Aix-les-Bains, October 1st-3rd 19Approaches adopted for physics perspectives estimationATLAS: 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 ratesCMS: 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

20Measurements of the 125 GeV boson21Mass & width are hard to improve beyond Run 2Direct measurement of width limited by resolutionDominant spin/parity will probably be established as 0+Investigate a CP-violating contributionAt LHC, we can only measure BR. Express a ratio to SM value.Ratios of partial widths can be made without further assumptionsInterpretation as coupling measurements is model dependent

125 GeV Higgs Couplings at the HL-LHCATLAS has performed projection studies to HL-LHC, assuming up to 3000 fb-1 of datafocused on the main channels already under study with LHC data, plus a few rare decay channels sensitive to top and muon couplingsZH,Hbb 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 studiesggFVBF HWHZHttHHHZZ*HWW*Hextrap.H22ATL-PHYS-PUB-2012-004ttH, H and H

One of the best channels to study Higgs boson couplings to fermionsVery rare: deviations from the expected rate would indicate new physicsLarge background from ZAnalysis included background modeling uncertaintiesMore than 6 sigma at L=3000 fb-1Important for H-top coupling measurementRequire multi-jet high-pT jetsAnalyse 1-lepton and 2- lepton eventsRequire very high luminosityS/B ~ 6A factor 2 better than 300 fb-123Higgs boson couplings in SM24

Higgs boson couplings in SM25

Partial widths are proportional to the coupling squareHiggs boson signal strengthMeasurements of the signal strength parameter mu for mH = 125GeV for the individual channels and for their combination. 26

if = i f = Higgs boson event productionk = analysis categoryi = production modef = decay final statenksignal = number of selected signal events by the k final stateL = integrated luminosityi,SM = production cross sectionBf,SM = finale state branching ratioi = production mode signal strength f = final state branching ratio strengthA = detector acceptance = reconstruction and selection efficiency27

Statistical procedureWrite the likelihood functionExample: do this for one channel/decay-final-state28

The Profile Likelihood ratio;here is the array of the various i entering the likelihood function() is the array of the nuisance parameters

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):

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example: the Higgs boson production in the WH channel with decay to ZZ:(WH) x BR(HZZ) = (WH)SM x BR(HZZ)SM x (k2W k2Z)/k2H H = i

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):

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example: the Higgs boson production in the WH channel with decay to ZZ:(WH) x BR(HZZ) = (WH)SM x BR(HZZ)SM x (k2W k2Z)/k2H H = iWarning! At LHC we dont measure the Higgs boson production cross section nor H !

31As a consequence, we have two ways to proceed:Make assumptions on H model dependent measurementsMake ratio of measurements, given that they are H independentWarning! At LHC we dont measure the Higgs boson production cross section nor H !Higgs Couplings32

Theoretical uncertainties33Theoretical predictions for known and new processes are criticalMissing higher order (QCD) radiative corrections are estimated by varying factorisation and renormalisation scales (0.5 ~ 2.0)Electroweak correctionsTreatment of heavy quarksPDF uncertainties (which also depend on the order of calculation available)mH=125 GeV @ 14 TeV: (pp(gg)H+X) scale +9 -12%, PDF 8.5%PDF uncertainties can be reduced by future precise experimental measurements at LHC, includingW, Z and differential distributions for lower x quarksHigh mass Drell-Yan measurements for higher x quarksInclusive jets, dijets for high x quarks and gluonsTop pair differential distributions for medium/large x gluonsSingle top for gluon and b-quarkDirect photons for small/medium x gluons

Higgs Couplings at the HL-LHC

Left: Expected measurement precision on the signal strength = (BR)=(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.34Higgs Couplings at the HL-LHC

Left: Expected measurement precision on the signal strength = (BR)=(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).35Higgs Couplings at the HL-LHCCoupling 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 better36

Are the ATLAS and CMS results consistent?37ATLAS uncertainty based on old resultATLAS uncertainty extrapolated with CMS approachChannelUncertainty on mu value with 300 fb-1 [%]Experimental only Experimental + theoryATLASCMSATLASCMS851515ZZ981611WW (1)2692914 (2)11915111992311Some proposals for future colliders38

LEP3TLEP/VHE-LHCCLICSee also: arxiv:1302.331839

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125 GeV Higgs boson CP mixing42Higgs boson CP mixing in HZZ4lExplore the ATLAS sensitivity to the CP-violating part of the HZZ scattering amplitude:

: polarisation vectors of the gauge bosons, form factors a1 and a2 refer to CP-even boson with mass MX, a3 to a CP-odd bosonThe presence of the two CP terms can lead to CP violationIn SM a1=1; a2=a3=0In this study we have set a1=1; a2=0, and varied a3

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

From European Strategy PUB Note43

fa3 > 0.46 fa3 > 0.63 HH production at HL-LHCThe 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 selfinteractions44

gluon-gluon fusion

Vector Boson Fusion

Higgs-strahlungHiggs boson Self-Coupling

A. Djouadi, et al., Eur. Phys. J. C10 (1999), 45HH (14 TeV) = 33.89 +18%-15% (QCD) 7% (PDF+S) 10% (EFT) fb +37.2 -29.8 fbA. Djouadi, et al., http://arxiv.org/abs/1212.558145Higgs Self-CouplingThe 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 robustFinal states with large enough production rates

Expected SM HH yields for proton-proton collisions at s = 14 TeV and L=3000 fb-1Two channels have been considered by ATLAS for the European Strategy:HHbbWWHHbb

46ATL-PHYS-PUB-2012-004HHbbWWBR ~ 25% 2.6 104 events in 3000 fb-1 at 14 TeV;This includes all W decay modesThe ttbar process represents a severe background for this final state;Study done considering one W decaying hadronically, the other leptonically (e,; 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 channelWe select q-gamma (t->qZ) decay. Limits at L=300 fb-1 are also shown. 60ConclusionsA data sample of 300 fb-1 at the LHC will allow to exclude strong deviations of the Higgs-like particle recently discovered from the Higgs boson predicted by Standard ModelA complete investigation on the physics properties of this new boson will require the search for rare decay final states, selfcoupling processes, CP violation effects, as well as the reduction of experimental (and theoretical) uncertainties High-Luminosity LHC with L=3000 fb-1 can provide the required statistics with an accuracy on the Higgs couplings in the range of 1-4%;HL-LHC extends the searches of LHC of BSM physics, and offers the required data to study the properties of new particles if found at the LHC61 and many other physics studies!62backup63Physics Prospects - introduction64Emphasis on prospects with LHC 300 fb-1 and HL-LHC 3000 fb-1 ATLAS has implemented functions to transform from generator level truth to reconstructed physics objects for HL-LHC Based on present detector with realistic/pessimistic assumptions on the effect of pileup of up to ~140 (for L=5 1034 cm-2s-1)eg. b-tagging performance from fully simulated ITk now shown to be better than that assumed for physics studies. CMS extrapolate from the present analyses with different scenariosExperimental systematic and theoretical uncertainties unchanged. (Statistical uncertainties scale with 1/L)Statistical and experimental systematic uncertainties scale with 1/L, theoretical uncertainties are reduced by a factor 2.Experimental errors unchanged, theoretical uncertainties zero

i.e. systematic uncertainties are always included, with different assumptions on possible detector/algorithm/theoretical improvementsbackup65

Higgs bosonDistribution of the 4-lepton invariant mass obtained with the data recorded with the CMS detector66