Prospects for Higgs Boson Measurements and Beyond Standard Model Physics at the High-Luminosity LHC with CMS

. The High-Luminosity Large Hadron Collider (HL-LHC) is a major upgrade of the LHC, expected to deliver an integrated luminosity of up to 3000 / fb over one decade. The very high instantaneous luminosity will lead to about 200 proton-proton collisions per bunch crossing (pileup) superimposed to each event of interest, therefore providing extremely challenging experimental conditions. The scientiﬁc goals of the HL-LHC physics program include precise measurement of the properties of the recently discovered standard model Higgs boson and searches for beyond the standard model physics (heavy vector bosons, SUSY, dark matter and exotic long-lived signatures, to name a few). In this contribution we will present the strategy of the CMS experiment to investigate the feasibility of such search and quantify the increase of sensitivity in the HL-LHC scenario.


Introduction
This paper presents physics studies and motivations that lead the development of the strategy of the future operation of the LHC collider with high luminosity (HL-LHC), also called LHC Phase-2.After the third long shutdown of the machine, that will take place around 2023, the instantaneous luminosity will be increased up to five times the design value, with 40 MHz operation (one bunch crossing every 25 ns) at a center of mass energy of 14 TeV.This yields challenging conditions for the CMS detector: up to 200 overlaying (pileup) events, high rates and high radiation levels, especially in the forward regions.An upgrade of the detectors is mandatory, in order to fully exploit the augmented luminosity and efficiently cope the new data taking conditions.It is foreseen that the total accumulated luminosity will reach 3000/fb of data, corresponding to ten times the data expected at the end of Phase-1.This environment offers great opportunities to shade some light on some unexplored or not fully explored physics searches.Test of the Standard Model can be performed with sufficient precision in the Higgs sector, by accurately measuring the couplings to fermions and bosons.Searches for the associated production of two Higgs boson and measurement of the trilinear Higgs boson coupling can be a unique opportunity to test the Higgs potential and is sensitive to the presence of new physics that can be explored in both resonant and non-resonant searches.The measurement of the differential cross-section of the Higgs boson is also an interesting test-bench of the Standard Model, providing that a percent precision can be reached.
The SM does not provide answers to the remaining questions.Those require new physics.In fact, the scalar nature of the particle, presents theoretical challenges.Radiative corrections to the Higgs should cause the mass to increase to very high values.New physics must appear at masses not too far from 1 TeV to cancel this growth.Deviations from perfect SM behavior because of its interaction with other forms of matter, including dark matter, could answer some very fundamental questions, such as the origin of the matter-antimatter asymmetry of the universe.The Supersymmetric (SUSY) particles, foreseen by the homonymous theory and still unobserved by date up to the TeV scale, could offer the advantage to cancel the the growth of the Higgs mass from radiative corrections.The rate of production and the characteristics of decays of SUSY particles depend on their mass spectrum, which is not predicted, so the search has to investigate many possibilities.SUSY also predicts several more Higgstype particles.Searches for these have also been undertaken but so far no additional Higgs bosons have been found.In what follows, the study of some selected benchmark physics processes, both in the Higgs sector and in the search for New Physics at the HL-LHC will be presented.
As mentioned above, a general upgrade of the detectors is crucial to maximize physics potential and maintain a good particle reconstruction in the harsh environment of HL-LHC.The planned upgrades of the CMS experiment in view of the HL-LHC phase will take place around 2023 and are fully described in [1], [2], [3], [4].

Higgs Boson Signal Strength
The present status of the Higgs strength and couplings precision measurement performed by the CMS experiment is summarized in [5], where the the main decay channels of the Higgs bosons are exploited (WW, ZZ, γγ, µµ, ττ, bb).Using the 2016 CMS dataset (36/fb) 10-20% uncertainties are reached on the main parameters, and the signal strength relative to the standard model is close to unity [5].
The HL-LHC will be a Higgs factory: over 170 million Higgs bosons will be produced during the whole data taking period in 3000/fb.The increased size of this dataset will allow to achieve high precision measurements, down to the level of a few percents.The results summarized in this report are based on CMS public measurements performed using the 2015 and early 2016 proton-proton datasets, projected to larger datasets of 3000/fb assuming a center of mass energy of 13 TeV, thus using a smaller dataset with respect to the one used for extracting the measurement in [5].The projections on the Higgs coupling are presented under different scenarios assumed for the size of systematic uncertainties, which are expected to bracket a realistic extrapolation.The incorporation of the performance of the upgraded detectors and the effect of higher pileup conditions are included in both scenarios: • S1+ : All systematic uncertainties are kept constant with integrated luminosity.
• S2+ : Theoretical uncertainties scaled down by a factor 1/2, while experimental systematic uncertainties are scaled down by the square root of the integrated luminosity until they reach a defined lower limit based on estimates of the achievable accuracy with the upgraded detector.
The rates of Higgs boson production and decay into ZZ → 4l and γγ final states, parametrized using strength parameters µ (defined as the ratios between the observed rates and the expected ones in the SM) are showed in Fig. etrized uncertainties for the H ! gg signal strength relative to the ly and per production mode.Projections are given for 300 fb −1 (a) e scenarios described in the text.trized uncertainties for the H ! gg signal strength relative to the ly and per production mode.The inclusive signal strength is also : statistical uncertainties ("stat."),experimental systematic uncerretical systematic uncertainties ("theo.").Projections are given for der the scenarios described in the text.Figure 5: Projections for the differential fiducial cross section measurement of the Higgs boson transverse momentum at 300 fb −1 (a) and 3000 fb −1 (b).The theoretical uncertainty in the differential gluon fusion cross section, which does not affect the measurement, is taken at NLO and shown in magenta.The statistical uncertainty of the measurement ranges from 10 to 29% (4 to 9%) for 300 (3000) fb −1 .The last bin represents the integrated cross section for p T (H) >200 GeV and is scaled by 50 for presentation.
Figure 1.The projected 68% CL uncertainties in the Higgs boson signal strength for different production modes at 3000/fb, in the γγ (top plot) and ZZ → 4l (bottom plot) channels with S1(+) in green and S2(+) in red gluon fusion production mechanism) although systematics also important.One of the main goals of HL-LHC physics program is to bring uncertainty on the rate down to 5% level

Higgs differential cross-sections
Differential cross sections provide an interesting portal to a number of physical observables.The shape of the differential cross section distribution can be tested with respect to SM expectation: it has been shown in [6] that small variation of the Higgs boson couplings with fermions, introduced by BSM processes, can lead to significant shape distortions.The differential cross section as a function of the Higgs transverse momentum is sensitive to the modifications introduced by the of effective Higgs Yukawa couplings at low p T and to finite top mass effects at high p T .The present status of this measurement performed by CMS quotes a 30% to 40% uncertainties depending on the considered p T range [7].
The projection for the HL-LHC phase of the differential cross section measurement as a function of the transverse momentum of the Higgs boson is shown in Fig. 2 L uncertainties in the Higgs boson signal strength for different (a) and 3000 fb −1 (b), with S1(+) in green and S2(+) in red.
( differential fiducial cross section measurement of the Higgs bot 300 fb −1 (a) and 3000 fb −1 (b).The theoretical uncertainty in ross section, which does not affect the measurement, is taken at .The statistical uncertainty of the measurement ranges from 10 0) fb −1 .The last bin represents the integrated cross section for d by 50 for presentation.
Figure 2. Projections for the differential fiducial cross section measurement of the Higgs boson transverse momentum at 3000/fb.The theoretical uncertainty in the differential gluon fusion cross section, which does not affect the measurement, is taken at NLO and shown in magenta.The last bin represents the integrated cross section for p T ≥200 GeV and is scaled by 50 for presentation.
uncertainties in the total signal cross section are not relevant and the cross section is measured in a fiducial phase space closely matching the experimental acceptance.The statistical uncertainty of the measurements ranges from 4 to 9% depending on the p T bin.The las bin (p T ≥ 200 GeV) is still dominated by the statistical uncertainty even at 3000/fb [10].

Projection on Double Higgs Boson Searches
The measurement of the Higgs boson self coupling is a fundamental test of the SM.In this context, a extremely small cross section is predicted for the main double Higgs bosons (HH) production mechanism, (gluon fusion) σ S M =33 fb at NNLO of the perturbative QCD expansion [8].Because of such small cross section, arising from the interference of the two loop induced processes involved at the tree level (associated double Higgs production and self coupling), LHC experiments are not yet sensitive to SM HH production with the current data.The best present upper limit based on in Run 2 dataset is given by ATLAS that excluded at 95% confidence level a signal strength µ ≥7 [12].However, BSM effects can strongly modify the HH production cross section and kinematics and be observed at the LHC and, at higher scale, at HL-LHC.
The direct production of new resonant states (called X in the following) decaying to HH, or resonant production, is predicted in many models such as scalars sectors extended with a doublet or a singlet, or extra dimension theories.Although different in motivation, they result in a similar experimental signature, but require experimentally the study of a broad m X range to be sensitive to a large variety of models.This results effectively in anomalous Higgs boson couplings that affect the non-resonant production, and may manifest with large modifications of both the cross section and the kinematic properties of the double Higgs boson final state.The exploration of many HH decay channels is crucial in this context to ensure a broad coverage of the possible BSM effects thanks to the complementarity of the different final states.
The extrapolations from Run II to HL-LHC luminosity are based on 2.3-2.7/fb of 2015 CMS dataset and shown in Fig. 3 [10], with the projections for the four final states currently under scrutiny by the CMS collaboration: HH → γγbb, HH → ττbb , HH → 4b as well as HH → VVbb , the latter looking at the llνν final state with l = e, µ and where b is a jet induced by a b-quak 1 .The most sensitive channel comes from the decay mode of HH → γγbb with 12 6 Double Higgs boson production Table 5: Projection of the sensitivity to the SM gg !HH production at 3000 fb −1 expected to be collected during the HL-LHC program.The projections are based on 13 TeV analysis performed with data collected in 2015.The median expected limit, Z-value and uncertainty in the signal modifier µ r = s HH /s SMHH are provided assuming S2 scenario on the systematic uncertainties and a scenario without systematic uncertainties shown to assess their impact (Stat.Only).For gg !HH !ggbb we use S2+ scenarios and we include the single Higgs contribution to the background.a significance of 1.47 standard deviations when only considering statistical uncertainty.The 1 The extrapolations presented in this document assume √ s = 13 TeV.However, the nominal center-of-mass energy at the HL-LHC is √ s=14 TeV with a predicted cross section of 39.51 fb, corresponding to an increase in cross section by 18%.Assuming a background scaling with the center of mass energies (14/13 ∼ 1.08), the projected results are expected to underperform by 1.18/ √ (1.08) ∼ 15% with respect to the HL-LHC energy conditions.
EPJ Web of Conferences 192, 00032 (2018) https://doi.org/10.1051/epjconf/201819200032QCD@Work 2018 scenario assumes uncertainty on the reconstructed b-tagged jet of 1% level and upgraded detector performance with an average of 200 pileup events.As shown, each of the channel alone is insufficient to observe the Higgs boson pair production.However, combining with these channels including other decay modes is promising.
In the HH → ττbb channel two complementary approaches have been pursued by extrapolating the projection using the full 2016 CMS dataset (36/fb) and running the full analysis on the signal and background Monte Carlo samples that incorporates the HL-LHC and Phase 2 CMS detector upgrades and operation conditions.Both the procedures are found to obtain compatible results, namely a cross section ratio σ HH /σ S M ∼1.6 [3].The distribution of the final discriminant used to extract the the results, the stransverse mass that is defined in [9], is showed in Fig. 4  earch for electroweakinos in the final states with two same-sign leptons metry is considered one of the most compelling theories of physics beyond the SM.large regions of parameter space characterized by the production of strongly inparticles with R-parity conserving decays have been excluded at 95% CL.On the ue to its low production cross section, the exploration of electroweak production of icles has just started at the LHC.The HL-LHC data, with an integrated luminosity 1 , will offer an unprecedented discovery potential for SUSY through searches for kinos.
the SUSY breaking scenarios, the supersymmetric partners of the gauge and Higgs expected to be lighter than a few hundreds of GeV based on naturalness and unifiuments.The higgsino(µ), bino(M1), and wino(M2) mass parameters typically satisfy n µ <M1<M2.As a result, the mass spectra are characterized by low-mass higginos-, e c  .Distribution of the stransverse mass, defined as the largest mass of the parent particle that is compatible with the kinematic constraints of the event.In the case of the bbττ decay, where the dominant background is tt production, the parent particle is interpreted as the top quark that decays into a bottom quark and a W boson.

Rare process
The measurement of the Yukawa couplings of the Higgs boson to fermions is one of the important studies to check the consistency with the SM and to search for possible deviations.
The H → µµ process can serve as a probe for coupling to fermion of second generation, provided that sufficient luminosity is collected to account for the small branching fraction (2.2×10 −4 in the SM) and reach a sizeable sensitivity.With the large datasets of the HL-LHC, searching for rare decays of the Higgs boson becomes accessible.Moreover this channel has been exploited as a benchmark for the CMS tracker upgrade.Thanks to the reduced material budget and improved spatial resolution of the upgraded tracker, about 65% better invariant mass resolution can be achieved.This leads to an uncertainty of 5% for couplings to muons and 10% for the cross section measurement with 3000/fb [2]. Figure 5 shows the dimuon invariant mass distribution of H → µµ decays for muons in the central region of the CMS detector as taken from simulated events that incorporates the CMS Phase II upgrade conditions.

Search for Supersymmetric particles
The present LHC has excluded large parts of the natural SUSY parameter space; limits for strong SUSY production are above 1 TeV and top and bottom squarks are already highly constrained.There are still many opportunities in the electroweak sector though which may be the dominating sector if squarks and gluinos are heavy.In most SUSY breaking scenarios the supersymmetric partners of the electroweak gauge bosons (EWK-inos) are expected to have a mass of the order 100 GeV based on naturalness.Given that EWK-inos are produced via https://doi.org/10.1051/epjconf/201819200032QCD@Work 2018 ariant mass distribution for H ! µ + µ − decays, for muons in the BB category.The Phase-2 detector achieves about 65% better invariant mass resolution, owing to the material budget and improved spatial resolution of the upgraded tracker.With this performance, the prospects for Higgs coupling measurements by CMS show an unof about 5% for couplings to muons [13], which corresponds to a 10% cross section ent.This sensitivity takes into account the improvement in di-muon invariant mass n brought by the tracker upgrade.Without it, the expected sensitivity is projected to Higgs couplings to muons and 16% for the cross section [79].

iggs boson pair production: HH ! bbbb
son pair production is the most direct way to study the scalar potential of the SM son and the nature of electroweak symmetry breaking.The observation of this process ortant objective of the HL-LHC program.Higgs pair production can occur through ar self-coupling or through a box diagram.In the SM the two processes interfere dely, resulting in a near minimal Higgs boson pair production cross section.If the Higgs linear self-coupling were zero the production cross section would be twice the SM n.The cross section for production of Higgs boson pairs via gluon fusion at a centrenergy of 14 TeV has been calculated at next-to-next-to-leading-order to be 40 fb [90].mount of integrated luminosity is required in order to observe this extremely rare Projections for the HL-LHC indicate that SM di-Higgs production can be observed by h a significance of 1.9 standard deviations by combining analyses in various channels a data set corresponding to an integrated luminosity of 3000 fb −1 [13].
ture with four b quarks in the final state (HH !bbbb) offers the highest branching The main challenge of this search is to distinguish the signal of four final state bottom at hadronize into jets (b jets) from the copious multijet background described by quanmodynamics (QCD).We address this challenge by suitable event selection criteria that edicated b jet identification techniques and a model of the multijet background that is in data control regions.Given the low cross section of the signal process, maintaining nal efficiency is a critical requirement.projections assume the same jet acceptance as for the Run 2 analysis, jet p T > 30 GeV y online selection) and jet |h| < 2.4 (driven by tracker acceptance).A b tagging alis then used to enrich the selected signal events and reject QCD background.The b tagging algorithm (Section 6.4.2) is exploited and at least four jets with a cMVAv2 EWK production the cross sections are small and HL-LHC has a large potential to increase sensitivity.
A brand-new CMS study for EWK-inos exploits the striking signature of same-sign leptons.It searches for mass degenerate χ0 4 , χ± 2 are then expected to decay into Higgsinos (which are taken to be the lightest SUSY particles) emitting same charge W bosons with a total branching ratio close to 25% (Fig. 6).

Impact of extended coverage of the muon detector upgrade 301
would be characterized by almost mass degenerate e c 0 1 , e c 0 2 , c± 1 (higgsinos-like), followed by a heavier bino-like c0 3 , and by wino-like c± 2 and c0 4 .The latter states have masses roughly twice as large as that of the c0 3 .The associated production cross sections of the charginos and neutralinos depend on the nature of the particle (whether it is a mixed or pure state) but they are nevertheless expected to be smaller than a few picobarns.Such processes can only be studied with the high luminosity of Phase-2 operation.Among all electroweak pair production processes, the e c 0 1 e c 0 2 exhibits the highest cross section for the spectra described above.However, since the e c 0 1 , e c 0 2 , c± 1 are almost mass degenerate in the higgsino scenario, the final states are characterized by the presence of very low p T standard model particles making the search experimentally challenging.As documented in [144], the next largest visible cross section is that of the winolike c± 2 and c0 4 .The search for wino pair production of c± 2 and c0 4 , depicted in Fig. 8.8 (left), can be carried out using a novel signature with two W bosons of the same electrical charge, large missing transverse energy (MET), and modest jet activity.This background-free final state has an excellent potential offering sensitivities to winos up to the TeV scale.
Requiring two similarly charged leptons ensures a nearly background-free signal.One of the dominant backgrounds is due to SM WZ production where only two leptons with the same electrical charge are reconstructed and the third lepton is lost (a "lost lepton" background).Efficient suppression of this background is essential for the sensitivity to this process.The fraction of correctly identified background events increases with the pseudorapidity coverage of the detector.The analysis is performed using DELPHES [130] and a scenario with an average of 200 pileup events.To study the impact of the upgraded muon detectors, events with two muons of equal charge within |h| < 1.6 are selected and the generator-level h of the third non-reconstructed muon is shown in Fig. 8.8 (right).It is apparent that the extended coverage up to 2.8 in h allows a more efficient veto of WZ! µµµ decays.If the coverage is extended from |h| < 1.6 to |h| < 2.8, the WZ background in the selected mode decreases by a factor four.If the coverage can be exploited for |h| < 2.4 the background decreases by only a factor two, relative to the background for |h| < 1.6.In this forward region, additional hits are beneficial to reconstructing muons in the high pileup environment.
As an illustration, we compute the impact of extending |h| from 2.4 to 2.8, because of ME0, on the upper limit on the production cross-section of pair produced c± 2 , c0 4 decaying into a final Given the small mass difference, the W bosons are soft, thus decaying into leptons with very low p T that are quite challanging to detect both at the trigger and offline reconstruction level.The full analysis has been performed using the fast simulation tool Delphes [13], that accounts for the performance of the upgraded CMS detector on the reconstructed final state objects.Main benefits come from the upgraded high-granularity calorimeters that improved the missing energy measurement and the extended Muon system acceptance, that yields factor 3 reduction of the irreducible WZ background.Two Higgisno mass scenarios considered: • m( χ1 ) = 150 GeV is representative of the region of the parameter space outside the reach of the Run 2 • m( χ1 ) =250 GeV is outside the sensitivity reach of the same search when extrapolated to the HL-LHC The spectrum of the transverse mass of the lepton candidate (built by combining the lepton p T and missing energy), is shown in Fig. 7 top panel.Wino-like mass degenerate χ0 4 , χ± 2 are excluded at 95% CL up to 900 GeV in the tested mass scenarios as shown in Fig. 7 (bottom panel).

Exotic Searches
It may happen that the only hints of new physics are rather exotic signatures that cannot be detected with conventional analyses New physics could manifest itself with a non-standard  Background processes containing misidentified leptons are determined from Delphes as well.However, only non-prompt leptons from heavy flavor decays are included in Delphes.For the misidentified leptons from light flavor quarks, gluons, conversions, the yields from Delphes have to be increased by 25% [85].
The search sensitivity is then calculated using a modified frequentist approach with the CL S criterion and asymptotic results for the test statistic [86,87].The systematic uncertainty in the prompt (misidentified, signal) yields are assumed to be 20% (50%, 20%) based on the estimates computed in the corresponding search carried out in Run 2 collision data [85].
The upper limit on the production cross-section of pair produced e c ± 2 , e c 0 4 decaying into a final state with two same charge W boson with a branching ratio of 25% is shown in ).The value e c 0 1 =150 GeV is representative of the region of the parameter space outside the reach of the Run 2 search for the direct production of higgsinos in the final states with two same flavor opposite sign leptons [88], while e c 0 1 =250 GeV is outside the sensitivity reach of the same search when extrapolated to the HL-LHC.As expected the sensitivity depends on the value of e c 0 1 mildly at large e c ± 2 , e c 0 4 mass values, while the dependence is more significant when e c ± 2 , e c 0 4 mass approaches e c 0 1 .Wino-like mass degenerate e c ± 2 , e c 0 4 are excluded at 95% CL for masses up to 900 GeV in the µ=150 and 250 GeV scenarios.This demonstrates that the HL-LHC has the potential to probe most of the natural SUSY parameter space with electroweak naturalness measure DEW 30 [89].

Search for FCNC in t!qg events
In the SM, flavor-changing neutral currents occur only at loop level and are highly suppressed by the Glashow-Iliopoulos-Maiani (GIM) mechanism [90].In the top sector, the predicted branching fractions for the t!u+g and t!c+g decays are approximately 10 −16 and 10 −14 , respectively [91].However, in many extensions of the SM, such as supersymmetry or multiple Higgs boson doublet models, the GIM suppression can be relaxed leading to an enhance-11.2.CMS physics channel results 317 450 500 550 600 650 700 750 800 850 900 950  The most stringent constraints on the B(t!q+g) are set by the CMS experiment through singletop quark production in association with a photon.The 95% CL upper limit on the branching fractions are B(t!u+g) < 0.016% and B(t!c+g) < 0.182% [94].
In this section, the sensitivity of the upgraded CMS detector to tqg FCNC transitions is estimated for integrated luminosities of 300 and 3000 fb −1 using single top quark production via q!tg, with q being a u or c quark.This analysis focuses on subsequent SM decays of the top quark, i.e. top quark decays into a W boson and a bottom quark, followed by the decay of the W boson to a muon or electron and a neutrino.
The final-state signature of these events is the presence of a single muon or electron, large missing transverse momentum, a b jet, and an isolated high energetic photon, with a broad h spectrum.The photon properties themselves provide good separation with respect to the dominant background processes from W+jets, and single-top or top quark pair production in association with photons.
The signal is generated with MADGRAPH 5, while the background processes are generated with POWHEG (t t, single top), MADGRAPH (W+jets), and aMCatNLO (single top + photon).
For parton showering and hadronization the matrix-element calculations are interfaced with PYTHIA 8. Except for the associated production of a single top quark with one or two additional photons, all samples employ a full simulation of the upgraded CMS detector.For the latter sample, the detector response is simulated using Delphes [81].For illustrative purposes, the signal samples are normalized to a 1 pb production cross section.For the background processes, next-to-leading order or next-to-next-to leading order cross section predictions are used where available.
Events are selected requiring the presence of exactly one muon or electron that passes high pu- signature, requiring dedicated trigger and reconstruction algorithms and specific detector features.One example are slow moving particles, also known as Heavy Stable Charged Particles (HSCP) foreseen by Split SUSY scenarios.These particles feature very high mass and small velocity.One way to detect such particle is their anomalous energy loss (dE/dx) [11] provided they are triggered.Muons from the decay of slow moving particles can already be identified at the trigger level based on the difference in arrival time with respect to relativistic SM particles.The muons from such decays are delayed w.r.t. to the time-zero bunch crossing (BX) and will spill over in neighbouring BXs.Fig. 8 (left) illustrates such a time difference as seen by CMS RPC chambers instrumenting the barrel and the forward muon system.The ns time resolution of the upgraded muon trigger allows to detect slowly moving charged particles by their hits.This will significantly extend the trigger capability to very slow particles with beta ≤0.5 (red) compared to present conditions, as displayed in Fig. 8   .16:RPC hit time measurement distribution for muons from Z !µµ events and for semi-stable t's with m⇡1600 GeV, produced in pp !t t processes.

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time of flight can be computed in each RPC station with respect to a number of BX hypotheses.Should there be a common velocity solution, derived from Eq. (7.1), with b < 0.6, a trigger is formed.For b > 0.6, the delays are small and can be handled by the Phase-1 trigger.The performance of this algorithm has been studied in CMS full simulation.All the detector effects (electronics jitter, signal time propagation along strips) are taken into account.A particle speed measurement resolution is shown in Fig. 7.18 (right) for the case of 25 ns signal sampling time (Phase-1) and 1.56 ns sampling time provided with the upgraded RPC Link Board System.An important class of Gauge Mediated SUSY breaking models predict long-lived particles that would potentially lead to displaced signatures.For particles of a few hundred GeV https://doi.org/10.1051/epjconf/201819200032QCD@Work 2018 mass, impact parameters can reach up to approximately one meter (or longer) for sufficiently large lifetimes In this context, an interesting benchmark channel studied in the context of the CMS Phase II upgrade is the search for the supersymmetric partners of the muons (s-muons) that can be the co-NLSP (i.e. they are the next to lightest LSP) and almost degenerate in mass.This search has low sensitivity in the present LHC runs, given the extremely small cross section, around 10 −2 fb for 1 TeV s-muon masses but became accessible in the HL-LHC scenario.The search sensitivity depends on the s-muons decay lengths: larger displacement (driven by M limits on q q ! e µe µ for various mass hypotheses and ct = e decay length for M = 200 GeV (right).In both panels, the ecific model is represented by the blue solid line.For different therwise modified parameters, the cross sections may be 100 dash-dotted line.Green (yellow) shaded bands show the one the expected 95% CL limits.Phase-2 results with an average ted luminosity of 3000 fb −1 are compared to results obtained ws the sensitivity without the DSA algorithm, which reduces factor three. sion limits for the gauge-mediated SUSY breaking model with the predicted cross section as well as for a factor 100 larger s are shown as functions of smuon mass in Fig. 8.13 (left) and The sensitivity depends on ct because shorter decay lengths nd. Figure 8.12 (right) shows the resulting physics sensitiviection for HL-LHC, normalized to 3000 fb −1 , for the dedicated s and for the standard reconstruction.Also shown is the exhase-1.Systematic uncertainties for the Phase-1 scenario are s: for HL-LHC they are guided by the assumptions of reduced rly, only the HL-LHC will allow this process to be studied.A he production cross section as a function of smuon mass and ig.8.14.The expected exclusion limit is around 200 GeV for r the same mass, a discovery sensitivity of 3s significance can the importance of keeping lepton trigger thresholds at a few Figure 9.The 95% CL upper limits of qq → μ μ with μ to a muon and a gravitino as a function of the decay length for s-muon mass of 200 GeV.The theoretical cross section for the specific model is represented by the blue solid line.For different SUSY breaking scales, tan β or otherwise modified parameters, the cross sections may be 100 times larger, reflected by the blue dash-dotted line.Green (yellow) shaded bands show the one (two) sigma range of variation of the expected 95% CL limits.Phase II results with an average 200 pileup events and an integrated luminosity of 3000/fb are compared to results obtained with 300/fb.The black line shows the sensitivity without the muon reconstruction algorithm dedicated to the displaced muon and mainly relying on the muon system chambers.Using the standard muon reconstruction algorithms reduces the reconstruction efficiency by a factor three. longer s-muon lifetimes) allow to test a phase space region that is free from the SM background.In the proposed benchmark channel, the s-muon decay to a SM muon and a gravitino (whose signature in the detector is the missing energy) with lifetimes which can be very long such that the displacement is of the order of meter.Muon triggering and reconstruction can be performed by the muon system in stand-alone, without the tracker.Discovery sensitivity of 3σ significance can be reached with 3000b of data (Fig. 9), providing full trigger and offline reconstruction efficiency even in the pile-up 200 environment.

Conclusions
In the middle of 2026, LHC will reach a peak instantaneous luminosity of 7.5×10 34 cm−2s−1.The HL-LHC will be the first Higgs factory, opening up the possibility to perform high precision measurement thanks to the to large amounts of events that is planned to collect, corresponding to an integrated luminosity of 3000/fb, more than 10 times larger than data by the end of Run 3. Thanks to the high statistics, rare processes in the Higgs sector will become accessible as well as the possibility to study the any possible deviation from the Standard Model.Towards the high precision era, a key role will be thus played by the theoretical and experimental systematics.The large Phase 2 dataset will enrich the potential to test physics beyond the SM, providing that the CMS experiment will be able to cope the challenging operation conditions.An extensive detector upgrade program has been planned and will start around 2023.Long-term exploration of Higgs sector and New Physics searches at HL-LHC will have crucial impact on our understanding of nature.There is a coordinated effort by ATLAS, CMS and theorists to update and combine results which will be documented in a

Figure 8 :
Figure 8: (a) Projection of the sensitivity to the SM gg !production at 3000 fb −1 , based on 13 TeV preliminary analyses performed with data collected in 2015.The uncertainty in the signal modifier µ = s/s SM is provided assuming different scenarios on the systematic uncertainties.(b) Projection of the sensitivity to the SM HH !ttbb production as function of the collected luminosity, based on the 13 TeV preliminary analysis [17] performed with data collected in 2015, under different assumptions on the systematic uncertainties.

Figure 3 .
Figure 3. Projection of the sensitivity to the SM gg → HH production at 3000/fb, based on 13 TeV preliminary analyses performed with data collected in 2015.The uncertainty in the signal modifier µ = σ/σ S M is provided assuming different scenarios on the systematic uncertainties.

± 1 ,
heavier bino-like e c 0 3 along with mass-degenerate wino-like e c ± mass difference between the low mass the e c 0 is just a few GeV leading to signatures with very low p SM particles and

Figure 4
Figure4.Distribution of the stransverse mass, defined as the largest mass of the parent particle that is compatible with the kinematic constraints of the event.In the case of the bbττ decay, where the dominant background is tt production, the parent particle is interpreted as the top quark that decays into a bottom quark and a W boson.
di-muon invariant mass distribution for H ! µ + µ − decays for muons in the gion, simulated with the Phase-2 detector.

Figure 5 .
Figure 5.The di-muon invariant mass distribution for H → µµ decays for muons in the central region, simulated with the Phase-2 detector.

Figure 8 . 8 :
Figure 8.8: Left: Example signal process which yields two same-sign leptons and large MET in the final state.Right: Distribution of generator-level h of unreconstructed muons in WZ background events after selection of exactly two same-sign signal muons with |h| < 1.6.The event numbers are for 3000 fb −1 .

Figure 6 .
Figure 6.Example signal process which yields two same-sign leptons and large missing energy in the final state.

Figure 11
Figure 11.31:Distribution of the m T,min in candidate events satisfying the baseline signal region selection.In the case of the signal the first number refers to the e c ± 2 , e c 0 4 mass while the second to the value of the e c 0 1 mass.
Fig. 11.32 for the two µ scenarios (where µ ⇠ m e

Figure 11
Figure 11.32:Upper limit on the production cross-section of pair produced e c ± 2 , e c 0 4 decaying into a final state with two same charge W boson with a branching ratio of 25% for two assumptions on the e c 0 1 mass.ment of several orders of magnitude in branching fractions that could be observed at the HL-LHC [92, 93].

Figure 7 .
Figure 7. Top panel: the discriminating variable mT,min reconstructed from the leptons and missing transverse energy.The seven bins would allow an extraction of the signal from the background.Botton panel: exclusion limit in case of no observation of a signal.

Figure 7
Figure 7.16: RPC hit time measurement distribution for muons from Z !µµ events and for semi-stable t's with m⇡1600 GeV, produced in pp !t t processes.

. 1 )
where d is the distance between the IP and the point where an HSCP crosses an RPC.For RE4/1 chambers and b = v/c = 0.2, the delay time is > 6 BXs = 150 ns.BX=+1 d, RPC hit Distance to the Vertex [cm] time delay [ns] Muon produced at BX= 0 hit Muon produced at BX=+1 hit HSCP produced at BX=0 hit 12

Figure 7 .
Figure 7.18: (Left) Resolution of a particle speed measurement at L1 trigger level with Phase-1 and upgraded RPC Link Board System.(Right) The efficiency as a function of b of the standard L1 muon trigger without any p T threshold, and the RPC-HSCP Phase-2 trigger with 1.56 ns sampling time.

Figure 8 .
Figure 8. Left: measured time for a particle to traverse CMS with respect to the transit time of a particle traveling at the speed of light.Muons from the decay of Z bosons are relativistic (β = 1) and HSCPs are slower.Right: the efficiency as a function of b of the standard L1 muon trigger without any pT threshold, and the RPC-HSCP Phase-2 trigger with 1.56 ns sampling time

Chapter 8 .
Physics performanceby the timing of the hits in the upper leg.Cosmic ray muons d therefore pass the upper barrel sectors in reverse direction cosmic ray muons in the endcaps is negligible.Given the cess, it is essential to reduce the background efficiently.The the impact parameter significance d 0 /s(d 0 ) ≥ 10.Given the uld move in roughly opposite directions and MET should be the two gravitinos.After this selection the signal efficiency nearly independent of the smuon mass, and 10 −5 -10 −4 for In scenarios S2 and ematics uncertainties are dominated by luminosity, reduced to 1.5%, 1.The extrapolations show that all the couplings precisions are statistically limited, so theoretical and and experimental systematics will play a central role in the future measurements.Further improvements are expected by incorporating features of recent Run 2 analyses (e.g.ttH) and the full Run 2 dataset.The benefit given by the increased dataset is clearly shown in the Higgs to top quarks coupling (accessible via ponents: statistical uncertainties ("stat."),experimental systematic theoretical systematic uncertainties ("theo.").

. The theoretical 4 H ! ZZ
normalized to the full Phase 2 expected luminosity.Similar studies are ongoing in the other channels.Stransverse mass distribution for t h t h events in the two b-tagged jets category..6:Final expected limit, presented as ratio over the SM double Higgs production.tegory 95%CL on s HH /s SM 95%CL on s ggHH /s SM 95%CL on s VBF /s on value is expected for the SM double Higgs boson production in the bbtt chans in good agreement with previous projections obtained by rescaling lower energies statistics results.Further improvements on these results can be obtained by includtegory with one b-tagged jet and the semileptonic final states, which can potentially close to the SM sensitivity.