Physics Prospects at HL-LHC

Aleandro Nisati

INFN - Roma

Scuola di fisica di Otranto

19 – 24 Settembre 2013

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Present results by LHC

• LHC data sample: √s = 7 and 8 TeV; L ~ 5 , 20 fb-

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1. Discovery of a Higgs boson with mass of about 125 GeV

2. 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

• Vedi lezioni di Tiziano Camporesi (Higgs boson physics) e di Giacomo Polesello (BSM)

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Higgs boson

• Distribution of the 4-lepton invariant mass obtained with the data recorded with the ATLAS detector

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Standard Model results

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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.

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SUSY Searches

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Exotics Searches

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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:1. Precision measurement of the mass of this new particle

2. Determination of the quantum numbers spin and parity, JP, and CP violation

3. Measurement of couplings to elementary fermions and bosons

4. Measurement of the di-Higgs boson production

5. Comparison of these physics properties with those predicted by Standard Model

6. Search for possible partners (neutral and/or charged) of this boson

7. Is this particle a fundamental object, or it is composite?

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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

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The priorities for collider physics after July 4th

• This enriches the collider physics programme:

8. 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;

9. 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.

10. 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,…)

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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.)

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The European Strategy for Particle Physics

• High Energy Frontier:Name beams collider

geometry√s, TeV luminosity Operation

(years)

HL-LHC pp circular 14 3000 fb-1 2024-2030

HE-LHC pp circular 26-33 100-300 fb-1/year After 2035

VHE-LHC pp circular 40-100 - After 2035

LEP3 e+e− circular 0.240 11034 cm-2s-1 After 2024

ILC e+e− linear 0.2501.0 ~11034 cm-2s-1 ~ 2030

CLIC e+e− linear 0.5003.0 2-61034 cm-2s-1 After 2030

TLEP e+e− circular 0.24-0.350 51034 cm-2s-1 After 2035

LHeC e−(e+)p circular O(100 fb-1) After 2022

γγ-collider γγ ?

μ-collider μ+μ− circular ?

I’ll focus on examples of physics perspectives at the High Luminosity-LHC (HL-LHC)

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Some proposals for future colliders

LEP3

TLEP/VHE-LHCCLIC

See also: arxiv:1302.3318

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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• The inner 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

LHC roadmap to achieve full potential

Pippa Wells, CERNJune 2013 15

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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

No deviations from SMDirect evidence of NP production

Deviations from SM. An example: Higgs boson properties;

Explore physics at the luminosity LHC upgrade Study new accelerator facilities

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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

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• But cannot handle (an average of) 140 events of pileup

Zμμ decay in a large pileup event

Missing transverse energy resolution as a function of the number of the reconstructed vertices

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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

Vedi talk di L. Rossi

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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

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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

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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

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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

• ZH,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 studies

ggF VBF H WH ZH ttH

Hγγ ✔ ✔ ✔ ✔ ✔

HZZ* ✔

HWW* ✔ ✔ ✔

Hττ extrap. ✔

Hμμ ✔ ✔

ATL-PHYS-PUB-2012-004

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ttH, Hγγ and Hμμ

• 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 Zμμ

• 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

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Higgs boson couplings in SM

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Higgs boson couplings in SM

Partial widths are proportional to the coupling square

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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

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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

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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

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• 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):

• example: the Higgs boson production in the WH channel with decay to ZZ:

σ(WH) x BR(HZZ) =

σ(WH)SM x BR(HZZ)SM x (k2W k2

Z)/k2H

ΓH = ΣΓi

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• 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):

• example: the Higgs boson production in the WH channel with decay to ZZ:

σ(WH) x BR(HZZ) =

σ(WH)SM x BR(HZZ)SM x (k2W k2

Z)/k2H

ΓH = ΣΓi

• Warning! At LHC we don’t measure the Higgs boson production cross section nor ΓH !

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• 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

• Warning! At LHC we don’t measure the Higgs boson production cross section nor ΓH !

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Higgs Couplings

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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 distributions for lower x quarks• High mass Drell-Yan measurements for higher x quarks• Inclusive jets, dijets for 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

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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.

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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).

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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

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Are the ATLAS and CMS results consistent?

(1) ATLAS uncertainty based on old result

(2) ATLAS uncertainty extrapolated with CMS approach

Channel Uncertainty on mu value with 300 fb-1 [%]

Experimental only Experimental + theory

ATLAS CMS ATLAS CMS

γγ 8 5 15 15

ZZ 9 8 16 11

WW (1) 26 9 29 14

ττ (2) 11 9 15 11

ττ 19 9 23 11

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Some proposals for future colliders

LEP3

TLEP/VHE-LHCCLIC

See also: arxiv:1302.3318

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125 GeV Higgs boson CP mixing

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Higgs boson CP mixing in HZZ4l• 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

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

Fro

m E

uro

pea

n S

trat

egy

PU

B N

ote

fa3 > 0.46 fa3 > 0.63

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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

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Higgs boson Self-CouplingA. 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

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Higgs Self-Coupling

• 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”:

1. HHbbWW2. HHbbγγ

ATL-PHYS-PUB-2012-004

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HHbbWW

• 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 107 ttbar events– S/B in agreement with estimates performed by other authors (M.J.

Dolan et al., arXiv:1206.5001v2 [hep-ph])

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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

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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.

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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.

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Vector Boson Scattering• At LHC VBS are tagged with two forward high-pT jets on either

side, the remnants of the quarks that have emitted the W/Z bosons in the central rapidity region: WW+2jets, WZ+2jets, ZZ+2jets

• ATLAS has performed preliminary studies of the process pp ZZjj 4l+jj within the “Pade’” unitarization (IAM, Inverse Amplitude Method) and using the WHIZARD generator (it allows to generate weak boson scattering mediated by a new high-mass resonance in presence of a Higgs boson with 126 GeV mass)

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Vector Boson Scattering• At LHC VBS are tagged with two forward high-pT jets on either

side, the remnants of the quarks that have emitted the W/Z bosons in the central rapidity region: WW+2jets, WZ+2jets, ZZ+2jets

• ATLAS has performed preliminary studies of the process pp ZZjj 4l+jj within the “Pade’” unitarization (IAM, Inverse Amplitude Method) and using the WHIZARD generator (it allows to generate weak boson scattering mediated by a new high-mass resonance in presence of a Higgs boson with 126 GeV mass)

Summary of the expected sensitivity to anomalous VBS signal for a a few values of the mass of the resonance and of the coupling g.

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SUSY @ HL-LHC: the end of Naturalness?By G. Polesello

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SUSY Searches

• So far there has been no sign of Supersymmetry at LHC– However only < 10% of the LHC expected data have

been studied (and at √s=7 TeV)– 3rd generation squarks have low cross-sections

• If we find it:– We have a large set of new particles to study– Thus a SUSY discovery will mandate more luminosity

• If will not find it by 2020:– HL-LHC offers a 25% increase in mass reach– HL-LHC will explore a phase space no other machine

will probe for decades

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Searches for stop• Probably this will be

one of the most important points in SUSY for the immediate future: naturalness requires stop mass not larger than ~ 1 TeV

• Rates will be modest HL-LHC reprsents an ideal machine for this search

The 95% CL exclusion limits for 3000 fb-1 (dashed) and 5 sigma discovery reach (solid) for 300 fb-1 and 3000 fb-1 in the stop, neutralino_1 mass plane assuming:

Future Searches

• “Naturalness” dictates:– Stop < 700 GeV– Gluino < 1500 GeV

• Dedicated searches for direct stop/sbottom and

EW gaugino production will be a focus for therest of the 8 TeV run

• Can more complex models accommodate Naturalness?

by J. Hewett

Weak-scale Supersymmetry extremely well motivated: Don’t give up on Weak-scale SUSY until 14 TeV with 300 fb-1 !

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Electroweak production of neutralinos, and charginos

• LHC can also probe electroweak production of

charginos, neutralinos and sleptons.•

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Searches for squarks and gluinos• HL-LHC gives tight

limits:– ~ 3 TeV for squarks– ~ 2.5 TeV for gluinos

• This represents a 400 GeV rise in sensitivity with respect to the L=300 fb-1 case

The 95% CL exclusion limits (solid lines) and 5 sigma discovery reach (dashed lines) in a simplified squark--gluino model with massless neutralino with 300 fb-1 (blue lines) and 3000 fb-1 (red lines). The colour scale shows √s=14 TeV NLO production cross section calculated by Prospino 2.1.

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Exotics Searches• Searches for ttbar resonances or Z’ leptons can

exploit the physics potential offered by HL-LHC

• Main challenges:– Reconstruct highly boosted top decays– Ensure lepton measurement at very high pT

• Muon system alignment• Leakage from calorimeter (?)

Summary of the expected limits for gKK ttbar and Z’

Topcolorttbar searches in the lepton+jets(dilepton) channel and of Z’SSM ee and Z’SSM μμ searches in the Sequential Standard Model. All boson mass limits are quoted in TeV.

FCNC in top decays• Opportunity to search for rare processes

• BR(tbW)~1, BR(tsW)<0.18%, BR(tdW)<0.02%

• Approaching few 10-5 precision

Pippa Wells, CERNJune 2013 60

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Conclusions• A 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 Model

• A 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 LHC

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… and many other physics studies!

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Physics Prospects - introduction• Emphasis 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 scenarios

1. Experimental systematic and theoretical uncertainties unchanged. (Statistical uncertainties scale with 1/√L)

2. Statistical and experimental systematic uncertainties scale with 1/√L, theoretical uncertainties are reduced by a factor 2.

3. Experimental errors unchanged, theoretical uncertainties zero

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

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Higgs boson

• Distribution of the 4-lepton invariant mass obtained with the data recorded with the CMS detector