Alfredo Gurrola

Vector boson fusion processes at the Large Hadron Collider (LHC) provide a unique opportunity to search for new physics with electroweak couplings. A feasibility study for the search of supersymmetric dark matter in the final state of two vector boson fusion jets and large missing transverse energy is presented at 14 TeV. Prospects for determining the dark matter relic density are studied for the cases of wino and bino-Higgsino dark matter. The LHC could probe wino dark matter with mass up to approximately 600 GeV with a luminosity of $1000\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$.

We examine the stau-neutralino coannihilation (CA) mechanism of the early Universe. We use the minimal supergravity (mSUGRA) model and show that from measurements at the CERN Large Hadron Collider one can predict the dark matter relic density with an uncertainty of 6% with $30\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of data, which is comparable to the direct measurement by the Wilkinson Microwave Anisotropy Probe. This is done by measuring four mSUGRA parameters ${m}_{0}$, ${m}_{1/2}$, ${A}_{0}$, and $\mathrm{tan}\ensuremath{\beta}$ without requiring direct measurements of the top squark and bottom squark masses. We also provide precision measurements of the gaugino, squark, and lighter stau masses in this CA region without assuming gaugino universality.

A feasibility study is presented for the search of the lightest top squark in a compressed scenario, where its mass is approximately equal to the sum of the masses of the top quark and the lightest neutralino. The study is performed in the final state of two b-jets, one lepton, large missing energy, and two high-$E_{\rm T}$ jets with large separation in pseudo-rapidity, in opposite hemispheres, and with large dijet mass. The LHC could discover compressed top squarks with mass up to approximately 340 GeV (390 GeV) with an integrated luminosity of 1000 ifb (3000 ifb).

We perform a feasibility study to search for axion-like particles (ALPs) using vector boson fusion (VBF) processes at the LHC. We work in an effective field theory framework with cutoff scale $\Lambda$ and ALP mass $m_{a}$, and assume that ALPs couple to photons with strength $\propto 1/\Lambda$. Assuming proton-proton collisions at $\sqrt{s} = 13$ TeV, we present the total VBF ALP production cross sections, ALP decay widths and lifetimes, and relevant kinematic distributions as a function of $m_{a}$ and $\Lambda$. We consider the $a\to\gamma\gamma$ decay mode to show that the requirement of an energetic diphoton pair combined with two forward jets with large dijet mass and pseudorapidity separation can significantly reduce the Standard Model backgrounds, leading to a $5\sigma$ discovery reach for $10 \text{ MeV} \lesssim m_{a} \lesssim 1$ TeV with $\Lambda \lesssim 2$ TeV, assuming an integrated luminosity of 3000 fb$^{-1}$. In particular, this extends the LHC sensitivity to a previously unstudied region of the ALP parameter space.

This report summarizes the work of the Energy Frontier Top Quark working group of the 2013 Community Summer Study (Snowmass).

The observation of neutrino oscillations establishes that neutrinos have non-zero mass and provides one of the more compelling arguments for physics beyond the standard model (SM) of particle physics. We present a feasibility study to search for hypothetical Majorana neutrinos (N) with TeV scale masses, predicted by extensions of the SM to explain the small but non-zero SM neutrino mass, using vector boson fusion (VBF) processes at the 13 TeV LHC. In the context of the minimal Type-I seesaw mechanism (mTISM), the VBF production cross-section of a lepton (ℓ) and associated heavy Majorana neutrino (Nℓ) surpasses that of the Drell–Yan process at approximately mNℓ=1.4TeV. We consider second and third-generation heavy neutrino (Nμ or Nτ, where ℓ= muon (μ) or tau (τ) leptons) production through VBF processes, with subsequent Nμ and Nτ decays to a lepton and two jets, as benchmark cases to show the effectiveness of the VBF topology for Nℓ searches at the 13 TeV LHC. The requirement of a dilepton pair combined with four jets, two of which are identified as VBF jets with large separation in pseudorapidity and a TeV scale dijet mass, is effective at reducing the SM background. These criteria may provide expected exclusion bounds, at 95% confidence level, of mNℓ<1.7 (2.4) TeV, assuming 100 (1000) fb−1 of 13 TeV data from the LHC and mixing |VℓNℓ|2=1. The use of the VBF topology to search for mNℓ increases the discovery reach at the LHC, with expected significances greater than 5σ (3σ) for Nℓ masses up to 1.7 (2.05) TeV using 1000fb−1 of 13 TeV data from the LHC.

This is the third out of five chapters of the final report [1] of the Workshop on Physics at HL-LHC, and perspectives on HE-LHC [2]. It is devoted to the study of the potential, in the search for Beyond the Standard Model (BSM) physics, of the High Luminosity (HL) phase of the LHC, defined as $3~\mathrm{ab}^{-1}$ of data taken at a centre-of-mass energy of $14~\mathrm{TeV}$, and of a possible future upgrade, the High Energy (HE) LHC, defined as $15~\mathrm{ab}^{-1}$ of data at a centre-of-mass energy of $27~\mathrm{TeV}$. We consider a large variety of new physics models, both in a simplified model fashion and in a more model-dependent one. A long list of contributions from the theory and experimental (ATLAS, CMS, LHCb) communities have been collected and merged together to give a complete, wide, and consistent view of future prospects for BSM physics at the considered colliders. On top of the usual standard candles, such as supersymmetric simplified models and resonances, considered for the evaluation of future collider potentials, this report contains results on dark matter and dark sectors, long lived particles, leptoquarks, sterile neutrinos, axion-like particles, heavy scalars, vector-like quarks, and more. Particular attention is placed, especially in the study of the HL-LHC prospects, to the detector upgrades, the assessment of the future systematic uncertainties, and new experimental techniques. The general conclusion is that the HL-LHC, on top of allowing to extend the present LHC mass and coupling reach by $20-50\%$ on most new physics scenarios, will also be able to constrain, and potentially discover, new physics that is presently unconstrained. Moreover, compared to the HL-LHC, the reach in most observables will generally more than double at the HE-LHC, which may represent a good candidate future facility for a final test of TeV-scale new physics.

We investigate the minimal supergravity signals at the Large Hadron Collider in the context of supercritical string cosmology (SSC). In this theory, the presence of a time dependent dilaton provides us with a smoothly evolving dark energy and modifies the dark matter allowed region of the minimal supergravity model with standard cosmology. Such a dilaton dilutes the supersymmetric dark matter density (of neutralinos) by a factor $\mathcal{O}(10)$ and consequently the regions with too much dark matter in the standard scenario are allowed in the SSC. The final states expected at the Large Hadron Collider in this scenario, unlike the standard scenario, consist of $Z$ bosons, Higgs bosons, and/or high energy taus. We show how to characterize these final states and determine the model parameters. Using these parameters, we determine the dark matter content and the neutralino-proton cross section. All these techniques can also be applied to determine model parameters in SSC models with different supersymmetry breaking scenarios.

New massive resonances are predicted in many extensions to the Standard Model (SM) of particle physics and constitutes one of the most promising searches for new physics at the LHC. We present a feasibility study to search for new heavy neutral gauge bosons using vector boson fusion (VBF) processes, which become especially important as the LHC probes higher collision energies. In particular, we consider the possibility that the discovery of a Z′ boson may have eluded searches at the LHC. The coupling of the Z′ boson to the SM quarks can be small, and thus the Z′ would not be discoverable by the searches conducted thus far. In the context of a simplified phenomenological approach, we consider the Z′→ττ and Z′→μμ decay modes to show that the requirement of a dilepton pair combined with two high pT forward jets with large separation in pseudorapidity and with large dijet mass is effective in reducing SM backgrounds. The expected exclusion bounds (at 95% confidence level) are m(Z′)<1.8TeV and m(Z′)<2.5TeV in the ττjfjf and μμjfjf channels, respectively, assuming 1000fb−1 of 13 TeV data from the LHC. The use of the VBF topology to search for massive neutral gauge bosons provides a discovery reach with expected significances greater than 5σ (3σ) for Z′ masses up to 1.4 (1.6) TeV and 2.0 (2.2) TeV in the ττjfjf and μμjfjf channels.

Dark matter that is electrically neutral but couples to the electromagnetic current through higher-dimensional operators constitutes an interesting class of models. We investigate this class of models at the Large Hadron Collider, focusing on the anapole moment operator in an effective field theory (EFT) framework, and utilizing the vector boson fusion (VBF) topology. Assuming proton-proton collisions at $\sqrt{s}=13\text{ }\text{ }\mathrm{TeV}$, we present the VBF anapole dark matter (ADM) cross sections and kinematic distributions as functions of the free parameters of the EFT, the cutoff scale $\mathrm{\ensuremath{\Lambda}}$ and the ADM mass ${m}_{\ensuremath{\chi}}$. We find that the distinctive VBF topology of two forward jets and large dijet pseudorapidity gap is effective at reducing SM backgrounds, leading to a $5\ensuremath{\sigma}$ discovery reach for all kinematically allowed ADM masses with $\mathrm{\ensuremath{\Lambda}}\ensuremath{\le}1.62$ (1.1) TeV, assuming an integrated luminosity of $3000\text{ }(100)\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$.

We present a feasibility study, to search for dark matter at the LHC, in events with one soft hadronically decaying tau lepton and missing transverse energy recoiling against a hard ${p}_{T}$ jet from initial state radiation. This methodology allows the search for supersymmetry in compressed mass spectra regions, where the mass difference between the lightest neutralino, ${\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{1}^{0}$, and the stau (the tau superpartner), $\stackrel{\texttildelow{}}{\ensuremath{\tau}}$, is small. Several theoretical models predict a direct connection between thermal bino dark matter and staus within this scenario. We show that compressed regions, not excluded by ATLAS nor CMS experiments, are opened up with the increase in experimental sensitivity reached with the proposed methodology. The requirement of a hard jet from initial state radiation combined with a soft tau lepton is effective in reducing Standard Model backgrounds, providing expected significances greater than $3\ensuremath{\sigma}$ for ${\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{1}^{\ifmmode\pm\else\textpm\fi{}}$ masses up to 300 GeV and $\stackrel{\texttildelow{}}{\ensuremath{\tau}}\ensuremath{-}{\stackrel{\texttildelow{}}{\ensuremath{\chi}}}_{1}^{0}$ mass gaps below 25 GeV with only $30\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of 13 TeV data from the LHC.

A bstract Searches for new low-mass matter and mediator particles have actively been pursued at fixed target experiments and at e + e − colliders. It is challenging at the CERN LHC, but they have been searched for in Higgs boson decays and in B meson decays by the ATLAS and CMS Collaborations, as well as in a low transverse momentum phenomena from forward scattering processes (e.g., FASER). We propose a search for a new scalar particle in association with a heavy vector-like quark. We consider the scenario in which the top quark ( t ) couples to a light scalar ϕ′ and a heavy vector-like top quark T . We examine single and pair production of T in pp collisions, resulting in a final state with a top quark that decays purely hadronically, a T which decays semileptonically ( T → W + b → ℓ ν b ), and a ϕ′ that is very boosted and decays to a pair of collimated photons which can be identified as a merged photon system. The proposed search is expected to achieve a discovery reach with signal significance greater than 5 σ (3 σ ) for m ( T ) as large as 1.8 (2) TeV and m ( ϕ′ ) as small as 1 MeV, assuming an integrated luminosity of 3000 fb − 1 . This search can expand the reach of T , and demonstrates that the LHC can probe low-mass, MeV-scale particles.

Abstract Leptoquarks ( $$\textrm{LQ}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mtext>LQ</mml:mtext> </mml:math> s) are hypothetical particles that appear in various extensions of the Standard Model (SM), that can explain observed differences between SM theory predictions and experimental results. The production of these particles has been widely studied at various experiments, most recently at the Large Hadron Collider (LHC), and stringent bounds have been placed on their masses and couplings, assuming the simplest beyond-SM (BSM) hypotheses. However, the limits are significantly weaker for $$\textrm{LQ}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mtext>LQ</mml:mtext> </mml:math> models with family non-universal couplings containing enhanced couplings to third-generation fermions. We present a new study on the production of a $$\textrm{LQ}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mtext>LQ</mml:mtext> </mml:math> at the LHC, with preferential couplings to third-generation fermions, considering proton-proton collisions at $$\sqrt{s} = 13 \, \textrm{TeV}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> <mml:mo>=</mml:mo> <mml:mn>13</mml:mn> <mml:mspace /> <mml:mtext>TeV</mml:mtext> </mml:mrow> </mml:math> and $$\sqrt{s} = 13.6 \, \textrm{TeV}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> <mml:mo>=</mml:mo> <mml:mn>13.6</mml:mn> <mml:mspace /> <mml:mtext>TeV</mml:mtext> </mml:mrow> </mml:math> . Such a hypothesis is well motivated theoretically and it can explain the recent anomalies in the precision measurements of $$\textrm{B}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mtext>B</mml:mtext> </mml:math> -meson decay rates, specifically the $$R_{D^{(*)}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>R</mml:mi> <mml:msup> <mml:mi>D</mml:mi> <mml:mrow> <mml:mo>(</mml:mo> <mml:mrow /> <mml:mo>∗</mml:mo> <mml:mo>)</mml:mo> </mml:mrow> </mml:msup> </mml:msub> </mml:math> ratios. Under a simplified model where the $$\textrm{LQ}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mtext>LQ</mml:mtext> </mml:math> masses and couplings are free parameters, we focus on cases where the $$\textrm{LQ}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mtext>LQ</mml:mtext> </mml:math> decays to a $$\tau $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>τ</mml:mi> </mml:math> lepton and a $$\textrm{b}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mtext>b</mml:mtext> </mml:math> quark, and study how the results are affected by different assumptions about chiral currents and interference effects with other BSM processes with the same final states, such as diagrams with a heavy vector boson, $$\textrm{Z}^{\prime }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mtext>Z</mml:mtext> <mml:mo>′</mml:mo> </mml:msup> </mml:math> . The analysis is performed using machine learning techniques, resulting in an increased discovery reach at the LHC, allowing us to probe new physics phase space which addresses the $$\textrm{B}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mtext>B</mml:mtext> </mml:math> -meson anomalies, for $$\textrm{LQ}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mtext>LQ</mml:mtext> </mml:math> masses up to $$5.00\, \textrm{TeV}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>5.00</mml:mn> <mml:mspace /> <mml:mtext>TeV</mml:mtext> </mml:mrow> </mml:math> , for the high luminosity LHC scenario.

A measurement of the Higgs boson Yukawa coupling to the top quark is presented using proton-proton collision data at $\sqrt{s} =$ 13 TeV, corresponding to an integrated luminosity of 137 fb$^{-1}$, recorded with the CMS detector. The coupling strength with respect to the standard model value, $Y_\mathrm{t}$, is determined from kinematic distributions in $\mathrm{t\bar{t}}$ final states containing ee, $μμ$, or e$μ$ pairs. Variations of the Yukawa coupling strength lead to modified distributions for $\mathrm{t\bar{t}}$ production. In particular, the distributions of the mass of the $\mathrm{t\bar{t}}$ system and the rapidity difference of the top quark and antiquark are sensitive to the value of $Y_\mathrm{t}$. The measurement yields a best fit value of $Y_\mathrm{t} =$ 1.16 $^{+0.24}_{-0.35}$, bounding $Y_\mathrm{t}$ $\lt$ 1.54 at a 95% confidence level.

A feasibility study is presented for the search of the lightest bottom squark (sbottom) in a compressed scenario, where its mass difference from the lightest neutralino is 5 GeV. Two separate studies are performed: $(1)$ final state containing two VBF-like tagging jets, missing transverse energy, and zero or one $b$-tagged jet; and $(2)$ final state consisting of initial state radiation (ISR) jet, missing transverse energy, and at least one $b$-tagged jet. An analysis of the shape of the missing transverse energy distribution for signal and background is performed in each case, leading to significant improvement over a cut and count analysis, especially after incorporating the consideration of systematics and pileup. The shape analysis in the VBF-like tagging jet study leads to a $3\sigma$ exclusion potential of sbottoms with mass up to $530 \, (462)$ GeV for an integrated luminosity of $300$ fb$^{-1}$ at 14 TeV, with $5\%$ systematics and PU $= 0 \, (50)$.

New massive spin-2 particles are predicted in theoretical extensions to the Standard Model (SM) attempting to solve the hierarchy problem. Such theories postulate that gravity is diluted compared to the other fundamental forces because it can propagate in extra spatial dimensions. While such theoretical models are of high experimental interest because they predict massive spin-2 particles ($Y_{2}$) potentially detectable by collider experiments, searches at the Large Hadron Collider (LHC) have thus far produced no significant evidence for their existence. This work considers a hypothetical physics scenario where low coupling strengths between the $Y_{2}$ and quarks/gluons is the underlying reason behind the null $Y_{2}$ search results at the LHC, which have mainly relied on Drell-Yan and gluon-gluon fusion production mechanisms. The focus of this paper is a feasibility study to search for $Y_{2}$ particles using vector boson fusion (VBF) processes at the LHC. In the context of an effective field theory approach with varying couplings $\kappa_{V}$ between $Y_{2}$ and the weak bosons of the SM, we consider the $Y_{2}\to\gamma\gamma$ decay mode to show that the requirement of a diphoton pair combined with two high $p_{T}$ forward jets with large dijet mass and with large separation in pseudorapidity can significantly reduce the SM backgrounds. Assuming proton-proton collisions at $\sqrt{s} = 13$ TeV, we present the total VBF production cross sections, $Y_{2}$ decay widths, and $Y_{2}\to\gamma\gamma$ branching ratios as a function of $m(Y_{2})$, considering universal and non-universal couplings to the SM particles. The unitarity-violating phase space is described. The proposed VBF $Y_{2}\to\gamma\gamma$ search is expected to achieve a discovery reach with signal significance greater than 5$\sigma$ for $Y_{2}$ masses up to 4.4 TeV and $\kappa_{V}$ couplings down to 0.5.

A new physics scenario shows that four-fermion operators of Nambu-Jona-Lasinio (NJL) type have a strong-coupling UV fixed point, where composite fermions $F$ (bosons $\Pi$) form as bound states of three (two) SM elementary fermions and they couple to their constituents via effective contact interactions at the composite scale $\Lambda \approx {\cal O} $(TeV). We present a phenomenological study to investigate such composite particles at the LHC by computing the production cross sections and decay widths of composite fermions in the context of the relevant experiments at the LHC with $pp$ collisions at $\sqrt{s}={\rm 13}$ TeV and $\sqrt{s}={\rm 14}$ TeV. Systematically examining all the different composite particles $F$ and the signatures with which they can manifest, we found a vast spectrum of composite particles $F$ that has not yet been explored at the LHC. Recasting the recent CMS results of the resonant channel $pp\rightarrow e^+F \rightarrow e^+e^- q\bar{q}'$, we find that the composite fermion mass $m_F$ below 4.25 TeV is excluded for $\Lambda$/$m_F$ = 1. We further highlight the region of parameter space where this specific composite particle $F$ can appear using 3 ab$^{-1}$, expected by the High-Luminosity LHC, computing 3 and 5 $\sigma$ contour plots of its statistical significance.

The production of heavy mass resonances has been widely studied theoretically and experimentally. Several extensions of the standard model (SM) of particle physics, naturally give rise to a new resonance, with neutral electric charge, commonly referred to as the $\textrm{Z}^{\prime}$ boson. The nature, mass, couplings, and associated quantum numbers of this hypothetical particle are yet to be determined. We present a feasibility study on the production of a vector like $\textrm{Z}^{\prime}$ boson at the LHC, with preferential couplings to third generation fermions, considering proton-proton collisions at $\sqrt{s} = 13$ $\mathrm{TeV}$ and 14 TeV. We work under two simplified phenomenological frameworks where the $\mathrm{Z}^{\prime}$ masses and couplings to the SM particles are free parameters, and consider final states of the $\textrm{Z}^{\prime}$ decaying to a pair of $\mathrm{b}$ quarks. The analysis is performed using machine learning techniques in order to maximize the experimental sensitivity. The proposed search methodology can be a key mode for discovery, complementary to the existing search strategies considered in literature, and extends the LHC sensitivity to the $\mathrm{Z}^{\prime}$ parameter space.

A search for exclusive two-photon production via photon exchange in proton-proton collisions, pp $\to$ p$γγ$p with intact protons, is presented. The data correspond to an integrated luminosity of 9.4 fb$^{-1}$ collected in 2016 using the CMS and TOTEM detectors at a center-of-mass energy of 13 TeV at the LHC. Events are selected with a diphoton invariant mass above 350 GeV and with both protons intact in the final state, to reduce backgrounds from strong interactions. The events of interest are those where the invariant mass and rapidity calculated from the momentum losses of the forward-moving protons matches the mass and rapidity of the central, two-photon system. No events are found that satisfy this condition. Interpreting this result in an effective dimension-8 extension of the standard model, the first limits are set on the two anomalous four-photon coupling parameters. If the other parameter is constrained to its standard model value, the limits at 95% CL are $\lvertζ_1\rvert$ $\lt$ 2.9 $\times$ 10$^{-13}$ GeV$^{-4}$ and $\lvertζ_2\rvert$ $\lt$ 6.0 $\times$ 10$^{-13}$ GeV$^{-4}$.

The identity of Dark Matter (DM) is one of the relevant topics in particle physics today. The R-parity conserving Minimal Supersymmetric Standard Model (MSSM), which naturally provides a DM candidate in the form of the lightest neutralino (χ̃10), is used as a benchmark scenario to show that a measurement of the DM relic density, Ωχ̃10h2, can be achieved from measurements at the CERN Large Hadron Collider. Focus is placed on compressed mass spectra regions, where the mass difference Δm between the χ̃10 and the supersymmetric partner of the tau lepton (τ̃1) is small and where the τ̃1-χ̃10 coannihilation (CA) mechanism of the early Universe plays an important role. The technique for measuring Ωχ̃10h2 relies on two proposed searches for compressed Supersymmetry (SUSY): (1) production via Vector Boson Fusion (VBF) processes; and (2) production with associated energetic jets from initial state radiation (ISR). These approaches allow for the determination of the relic abundance at the LHC for any model where CA is an important DM reduction mechanism in the early Universe. Thus, it is possible to confirm that the DM we observe today corresponds to χ̃10's created in the early Universe. We show that from measurements in the VBF and ISR SUSY searches at the LHC, the mass gap Δm and the dark matter relic density can be measured with an uncertainty of 4.5% and 25%, respectively, assuming 13 TeV proton–proton data from the high-luminosity LHC. The precise measurement of a small Δm value would also confirm the existence of τ̃1-χ̃10 CA.

Leptoquarks (LQs) are hypothetical particles that appear in various extensions of the Standard Model (SM) that can explain observed differences between SM theory predictions and experimental results. The production of these particles has been widely studied at various experiments, most recently at the Large Hadron Collider (LHC), and stringent bounds have been placed on their masses and couplings, assuming the simplest beyond-SM (BSM) hypotheses. However, the limits are significantly weaker for LQ models with family non-universal couplings containing enhanced couplings to third-generation fermions. We present a new study on the production of a LQ at the LHC, with preferential couplings to third-generation fermions, considering proton-proton collisions at $\sqrt{s} = 13$ $\mathrm{TeV}$ and $\sqrt{s} = 13.6$ $\mathrm{TeV}$. Such a hypothesis is well motivated theoretically and it can explain the recent anomalies in the precision measurements of $\mathrm{B}$-meson decay rates, specifically the $R_{D^{(*)}}$ ratios. Under a simplified model where the LQ masses and couplings are free parameters, we focus on cases where the LQ decays to a $\tau$ lepton and a $\mathrm{b}$ quark, and study how the results are affected by different assumptions about chiral currents and interference effects with other BSM processes with the same final states, such as diagrams with a heavy vector boson, $\mathrm{Z}^{'}$. The analysis is performed using machine learning techniques, resulting in an increased discovery reach at the LHC, allowing us to probe new physics phase space which addresses the $\mathrm{B}$-meson anomalies, for $\mathrm{LQ}$ masses up to 5.00 $\mathrm{TeV}$, for the high luminosity LHC scenario.

We present a detailed study concerning a new physics scenario involving four fermion operators of the Nambu-Jona-Lasinio type characterized by a strong-coupling ultraviolet fixed point where composite particles are formed as bound states of elementary fermions at the scale $\Lambda ={\cal O}(\text{TeV})$. After implementing the model in the Universal FeynRules Output format, we focus on the phenomenology of the scalar leptoquarks at the LHC and the High-Luminosity option. Leptoquark particles have undergone extensive scrutiny in the literature and experimental searches, primarily relying on pair production and, more recently, incorporating single, t-channel, and lepton-induced processes. This study marks, for the first time, the examination of these production modes at varying jet multiplicities. Novel mechanisms emerge, enhancing the total production cross-section, especially for leptoquarks couplings to higher fermion generations. A global strategy is devised to capture all final state particles produced in association with leptoquarks or originating from their decay, which we termed ``exclusive'', in an analogy to the nomenclature used in nuclear reactions. The assessment of the significance in current and future LHC runs, focusing on the case of leptoquark coupling to a muon - $\textit{c}$ quark pair, reveals superior sensitivity compared to ongoing searches. Given this heightened discovery potential, we advocate the incorporation of exclusive leptoquark searches in future investigations at the LHC.

We examine the stau-neutralino coannihilation (CA) mechanism of the early universe. We use the minimal supergravity (mSUGRA) model and show that from measurements at the Large Hadron Collider one can predict the dark matter relic density with an uncertainty of 6% with 30 fb-1 of data, which is comparable to the direct measurement by Wilkinson Microwave Anisotropy Probe. This is done by measuring four mSUGRA parameters m0, m1/2, A0 and tan(beta) without requiring direct measurements of the top squark and bottom squark masses. We also provide precision measurements of the gaugino, squark, and lighter stau masses in this CA region without assuming gaugino universality.

A search for long-lived particles (LLPs) produced in association with a Z boson is presented. The study is performed using data from proton-proton collisions with a center-of-mass energy of 13 TeV recorded by the CMS experiment during 2016-2018, corresponding to an integrated luminosity of 117 fb$^{-1}$. The LLPs are assumed to decay to a pair of standard model quarks that are identified as displaced jets within the CMS tracker system. Triggers and selections based on Z boson decays to electron or muon pairs improve the sensitivity to light LLPs (down to 15 GeV). This search provides sensitivity to beyond the standard model scenarios which predict LLPs produced in association with a Z boson. In particular, the results are interpreted in the context of exotic decays of the Higgs boson to a pair of scalar LLPs (H $\to$ SS). The Higgs boson decay branching fraction is constrained to values less than 6% for proper decay lengths of 10-100 mm and for LLP masses between 40 and 55 GeV. In the case of low-mass ($\approx$15 GeV) scalar particles that subsequently decay to a pair of b quarks, the search is sensitive to branching fractions $\mathcal{B}$(H $\to$ SS) $\lt$ 20% for proper decay lengths of 10-50 mm. The use of associated production with a Z boson increases the sensitivity to low-mass LLPs of this analysis with respect to gluon fusion searches. In the case of 15 GeV scalar LLPs, the improvement corresponds to a factor of 2 at a proper decay length of 30 mm.

A measurement of inclusive four-jet production in proton-proton collisions at a center-of-mass energy of 13\TeV is presented. The transverse momenta of jets within $\lvert\eta\rvert \lt$ 4.7 reach down to 35, 30, 25, and 20 GeV for the first-, second-, third-, and fourth-leading jet, respectively. Differential cross sections are measured as functions of the jet transverse momentum, jet pseudorapidity, and several other observables that describe the angular correlations between the jets. The measured distributions show sensitivity to different aspects of the underlying event, parton shower, and matrix element calculations. In particular, the interplay between angular correlations caused by parton shower and double-parton scattering contributions is shown to be important. The double-parton scattering contribution is extracted by means of a template fit to the data, using distributions for single-parton scattering obtained from Monte Carlo event generators and a double-parton scattering distribution constructed from inclusive single-jet events in data. The effective double-parton scattering cross section is calculated and discussed in view of previous measurements and of its dependence on the models used to describe the single-parton scattering background.

A bstract The identity of Dark Matter (DM) is one of the most active topics in particle physics today. Supersymmetry (SUSY) is an extension of the standard model (SM) that could describe the particle nature of DM in the form of the lightest neutralino in R-parity conserving models. We focus on SUSY models that solve the hierarchy problem with small fine tuning, and where the lightest SUSY particles $$ \left({\tilde{\upchi}}_1^0,{\tilde{\upchi}}_1^{\pm },{\tilde{\upchi}}_2^0\right) $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:msubsup> <mml:mover> <mml:mi>χ</mml:mi> <mml:mo>˜</mml:mo> </mml:mover> <mml:mn>1</mml:mn> <mml:mn>0</mml:mn> </mml:msubsup> <mml:msubsup> <mml:mover> <mml:mi>χ</mml:mi> <mml:mo>˜</mml:mo> </mml:mover> <mml:mn>1</mml:mn> <mml:mo>±</mml:mo> </mml:msubsup> <mml:msubsup> <mml:mover> <mml:mi>χ</mml:mi> <mml:mo>˜</mml:mo> </mml:mover> <mml:mn>2</mml:mn> <mml:mn>0</mml:mn> </mml:msubsup> </mml:mfenced> </mml:math> are a triplet of higgsino-like states, such that the mass difference $$ \Delta m\left({\tilde{\upchi}}_2^0,{\tilde{\upchi}}_1^0\right) $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Δ</mml:mi> <mml:mi>m</mml:mi> <mml:mfenced> <mml:msubsup> <mml:mover> <mml:mi>χ</mml:mi> <mml:mo>˜</mml:mo> </mml:mover> <mml:mn>2</mml:mn> <mml:mn>0</mml:mn> </mml:msubsup> <mml:msubsup> <mml:mover> <mml:mi>χ</mml:mi> <mml:mo>˜</mml:mo> </mml:mover> <mml:mn>1</mml:mn> <mml:mn>0</mml:mn> </mml:msubsup> </mml:mfenced> </mml:math> is 0.5–50 GeV. We perform a feasibility study to assess the long-term discovery potential for these compressed SUSY models with higgsino-like states, using vector boson fusion (VBF) processes in the context of proton-proton collisions at $$ \sqrt{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math> = 13 TeV, at the CERN Large Hadron Collider. Assuming an integrated luminosity of 3000 fb − 1 , we find that stringent VBF requirements, combined with large missing momentum and one or two low- p T leptons, is effective at reducing the major SM backgrounds, leading to a 5 σ (3 σ ) discovery reach for $$ m\left({\tilde{\upchi}}_2^0\right) $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>m</mml:mi> <mml:mfenced> <mml:msubsup> <mml:mover> <mml:mi>χ</mml:mi> <mml:mo>˜</mml:mo> </mml:mover> <mml:mn>2</mml:mn> <mml:mn>0</mml:mn> </mml:msubsup> </mml:mfenced> </mml:math> &lt; 180 (260) GeV, and a projected 95% confidence level exclusion region that covers $$ m\left({\tilde{\upchi}}_2^0\right) $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>m</mml:mi> <mml:mfenced> <mml:msubsup> <mml:mover> <mml:mi>χ</mml:mi> <mml:mo>˜</mml:mo> </mml:mover> <mml:mn>2</mml:mn> <mml:mn>0</mml:mn> </mml:msubsup> </mml:mfenced> </mml:math> up to 385 GeV, parameter space that is currently unconstrained by other experiments.

Searches for new low-mass matter and mediator particles have actively been pursued at fixed target experiments and at $e^+e^-$ colliders. It is challenging at the CERN LHC, but they have been searched for in Higgs boson decays and in $B$ meson decays by the ATLAS and CMS Collaborations, as well as in a low transverse momentum phenomena from forward scattering processes (e.g., FASER). We propose a search for a new scalar particle in association with a heavy vector-like quark. We consider the scenario in which the top quark ($t$) couples to a light scalar $ϕ^\prime$ and a heavy vector-like top quark $T$. We examine single and pair production of $T$ in $pp$ collisions, resulting in a final state with a top quark that decays purely hadronically, a $T$ which decays semileptonically ($T$ $\rightarrow$ $W$ + $b$ $\rightarrow$ $\ell$ $ν$ $b$), and a $ϕ^\prime$ that is very boosted and decays to a pair of collimated photons which can be identified as a merged photon system. The proposed search is expected to achieve a discovery reach with signal significance greater than 5$σ$ (3$σ$) for $m(T)$ as large as 1.8 (2) TeV and $m(ϕ^\prime)$ as small as 1 MeV, assuming an integrated luminosity of 3000 fb$^{-1}$. This search can expand the reach of $T$, and demonstrates that the LHC can probe low-mass, MeV-scale particles.

We consider a simplified model where a W' boson is added to the standard model with negligible couplings to quarks, but generic couplings to leptons and electroweak bosons. We study the implications of such a model for LHC searches. Consequently, we propose an LHC search through the vector boson fusion topology which would have sensitivity for such a new particle with the current proton-proton collisions's energy and available luminosity.

The production of heavy mass resonances has been widely studied theoretically and experimentally. Several extensions of the standard model (SM) of particle physics, naturally give rise to a new resonance, with neutral electric charge, commonly referred to as the $\textrm{Z}^{\prime}$ boson. The nature, mass, couplings, and associated quantum numbers of this hypothetical particle are yet to be determined. We present a feasibility study on the production of a vector like $\textrm{Z}^{\prime}$ boson at the LHC, with preferential couplings to third generation fermions, considering proton-proton collisions at $\sqrt{s} = 13$ $\mathrm{TeV}$ and 14 TeV. We work under two simplified phenomenological frameworks where the $\mathrm{Z}^{\prime}$ masses and couplings to the SM particles are free parameters, and consider final states of the $\textrm{Z}^{\prime}$ decaying to a pair of $\mathrm{b}$ quarks. The analysis is performed using machine learning techniques in order to maximize the experimental sensitivity. The proposed search methodology can be a key mode for discovery, complementary to the existing search strategies considered in literature, and extends the LHC sensitivity to the $\mathrm{Z}^{\prime}$ parameter space.

The identity of Dark Matter (DM) is one of the most captivating topics in particle physics today. The R-parity conserving Minimal Supersymmetric Standard Model (MSSM), which naturally provides a DM candidate in the form of the lightest neutralino ($\tilde{\chi}_{1}^{0}$), is used as a benchmark scenario to show that a measurement of $\Omega_{\tilde{\chi}_{1}^{0}}h^{2}$ can be achieved from measurements at the CERN Large Hadron Collider. Focus is placed on compressed mass spectra regions, where the mass difference between the $\tilde{\chi}_{1}^{0}$ and the $\tilde{\tau}_{1}$ is small and where the $\tilde{\tau}_{1}$-$\tilde{\chi}_{1}^{0}$ coannihilation (CA) mechanism of the early Universe plays an important role. The technique for measuring $\Omega_{\tilde{\chi}_{1}^{0}}h^{2}$ relies on two proposed searches for compressed Supersymmetry (SUSY): 1) production via Vector Boson Fusion (VBF) processes; and 2) production with associated energetic jets from initial state radiation (ISR). These approaches allow for the determination of the relic abundance at the LHC for any model where CA is an important DM reduction mechanism in the early Universe. Thus, it is possible to confirm that the DM we observe today were $\tilde{\chi}_{1}^{0}$'s created in the early Universe. We show that from measurements in the VBF and ISR SUSY searches at the LHC, the dark matter relic density can be measured with an uncertainty of 25\% with 3000 fb$^{-1}$ of 13 TeV proton-proton data.

A new physics scenario shows that four-fermion operators have a strong-coupling UV fixed point, where composite fermions $F$ (bosons $\Pi$) form as bound states of three (two) SM elementary fermions and they couple to their constituents via effective contact interactions at the composite scale $\Lambda \approx {\cal O} $(TeV). We present a phenomenological study to investigate such composite particles at the LHC. Using these contact interactions, we compute the production cross sections and decay widths of composite fermions in the context of the relevant experiments at LHC with $pp$ collisions at $\sqrt{s}=13$ TeV and $\sqrt{s}=14$ TeV. In particular, we focus on the resonant channel $pp\rightarrow e^+F \rightarrow e^+e^- qq'$, whose cross section has been recently limited by the CMS Collaboration. By a simple recasting of this result, we obtain a constraint on the model parameters such that composite fermions of mass $m_F$ below 4.25 TeV are excluded for $\Lambda$ = $m_F$. We further compute 5$\sigma$ contour plots of the statistical significance and highlight the region of parameter space where $F$ can manifest using 3 ab$^{-1}$, expected by the High-Luminosity LHC. It turns out that there is a large portion of the parameter space where $F$ can be discovered and that deserve a dedicated investigation. In addition, we also study the composite boson state $\Pi_0$ with the estimation of branching ratios into two quarks (two jets) ${\cal B}(\Pi_0\rightarrow qq')$ and into two boosted gauge bosons ${\cal B}(\Pi_0\rightarrow \tilde G \tilde G')$, from which we obtain the branching ratios of composite-fermion decay into an electron and two boosted gauge bosons ${\cal B}(F\rightarrow e\tilde G\tilde G')$. Moreover we briefly discuss the possible final states of four jets or one jet with two gauge bosons in LHC $pp$ collision.

The identity of Dark Matter (DM) is one of the most captivating topics in particle physics today. The R-parity conserving Minimal Supersymmetric Standard Model (MSSM), which naturally provides a DM candidate in the form of the lightest neutralino ($\tilde{\chi}_{1}^{0}$), is used as a benchmark scenario to show that a measurement of $\Omega_{\tilde{\chi}_{1}^{0}}h^{2}$ can be achieved from measurements at the CERN Large Hadron Collider. Focus is placed on compressed mass spectra regions, where the mass difference between the $\tilde{\chi}_{1}^{0}$ and the $\tilde{\tau}_{1}$ is small and where the $\tilde{\tau}_{1}$-$\tilde{\chi}_{1}^{0}$ coannihilation (CA) mechanism of the early Universe plays an important role. The technique for measuring $\Omega_{\tilde{\chi}_{1}^{0}}h^{2}$ relies on two proposed searches for compressed Supersymmetry (SUSY): 1) production via Vector Boson Fusion (VBF) processes; and 2) production with associated energetic jets from initial state radiation (ISR). These approaches allow for the determination of the relic abundance at the LHC for any model where CA is an important DM reduction mechanism in the early Universe. Thus, it is possible to confirm that the DM we observe today were $\tilde{\chi}_{1}^{0}$'s created in the early Universe. We show that from measurements in the VBF and ISR SUSY searches at the LHC, the dark matter relic density can be measured with an uncertainty of 25\% with 3000 fb$^{-1}$ of 13 TeV proton-proton data.

A measurement of the top quark mass is performed using a data sample enriched with single top quark events produced in the $t$ channel. The study is based on proton-proton collision data, corresponding to an integrated luminosity of 35.9 fb$^{-1}$, recorded at $\sqrt{s}$ = 13 TeV by the CMS experiment at the LHC in 2016.Candidate events are selected by requiring an isolated high-momentum lepton (muon or electron) and exactly two jets, of which one is identified as originating from a bottom quark. Multivariate discriminants are designed to separate the signal from the background. Optimized thresholds are placed on the discriminant outputs to obtain an event sample with high signal purity. The top quark mass is found to be 172.13$^{+0.76}_{-0.77}$ GeV, where the uncertainty includes both the statistical and systematic components, reaching sub-GeV precision for the first time in this event topology. The masses of the top quark and antiquark are also determined separately using the lepton charge in the final state, from which the mass ratio and difference are determined to be 0.9952$^{+0.0079}_{-0.0104}$ and 0.83$^{+1.79}_{-1.35}$ GeV, respectively. The results are consistent with $CPT$ invariance.

Measurements of the inclusive and differential fiducial cross sections of the Higgs boson are presented, using the $\tau$ lepton decay channel. The differential cross sections are measured as functions of the Higgs boson transverse momentum, jet multiplicity, and transverse momentum of the leading jet in the event if any. The analysis is performed using proton-proton data collected with the CMS detector at the LHC at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 138 fb$^{-1}$. These are the first differential measurements of the Higgs boson cross section in the final state of two $\tau$ leptons, and they constitute a significant improvement over measurements in other final states in events with a large jet multiplicity or with a Lorentz-boosted Higgs boson.

The associated production of a W and a Z boson is studied in final states with multiple leptons produced in proton-proton (pp) collisions at a centre-of-mass energy of 13 TeV using 137 fb$^{-1}$ of data collected with the CMS detector at the LHC. A measurement of the total inclusive production cross section yields $\sigma_{\text{tot}}$(pp $\to$ WZ) = 50.6 $\pm$ 0.8 (stat) $\pm$ 1.5 (syst) $\pm$ 1.1 (lum) $\pm$ 0.5 (thy) pb. Measurements of the fiducial and differential cross sections for several key observables are also performed in all the final-state lepton flavour and charge compositions with a total of three charged leptons, which can be electrons or muons. All results are compared with theoretical predictions computed up to next-to-next-to-leading order in quantum chromodynamics plus next-to-leading order in electroweak theory and for various sets of parton distribution functions. The results include direct measurements of the charge asymmetry and the W and Z vector boson polarization. The first observation of longitudinally polarized W bosons in WZ production is reported. Anomalous gauge couplings are searched for, leading to new constraints on beyond-the-standard-model contributions to the WZ triple gauge coupling.

The CMS experiment at the LHC has measured the differential cross sections of Z bosons decaying to pairs of leptons, as functions of transverse momentum and rapidity, in lead-lead collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The measured Z boson elliptic azimuthal anisotropy coefficient is compatible with zero, showing that Z bosons do not experience significant final-state interactions in the medium produced in the collision. Yields of Z bosons are compared to Glauber model predictions and are found to deviate from these expectations in peripheral collisions, indicating the presence of initial collision geometry and centrality selection effects. The precision of the measurement allows, for the first time, for a data-driven determination of the nucleon-nucleon integrated luminosity as a function of lead-lead centrality, thereby eliminating the need for its estimation based on a Glauber model.

Measurements of differential and double-differential cross sections of top quark pair ($\text{t}\overline{\text{t}}$) production are presented in the lepton+jets channels with a single electron or muon and jets in the final state. The analysis combines for the first time signatures of top quarks with low transverse momentum $p_\text{T}$, where the top quark decay products can be identified as separated jets and isolated leptons, and with high $p_\text{T}$, where the decay products are collimated and overlap. The measurements are based on proton-proton collision data at $\sqrt{s} = $ 13 TeV collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 137 fb$^{-1}$. The cross sections are presented at the parton and particle levels, where the latter minimizes extrapolations based on theoretical assumptions. Most of the measured differential cross sections are well described by standard model predictions with the exception of some double-differential distributions. The inclusive $\text{t}\overline{\text{t}}$ production cross section is measured to be $\sigma_{\text{t}\overline{\text{t}}} = $ 791 $\pm$ 25 pb, which constitutes the most precise measurement in the lepton+jets channel to date.