Search for exotic decays of the Higgs boson to a pair of pseudoscalars in the $\mu\mu$bb and $\tau\tau$bb final states

2024

• Physics
• Particle physics
• Nuclear physics

A search for exotic decays of the Higgs boson (H) with a mass of 125 GeV to a pair of light pseudoscalars $\mathrm{a}_1$ is performed in final states where one pseudoscalar decays to two b quarks and the other to a pair of muons or $\tau$ leptons. A data sample of proton-proton collisions at $\sqrt{s}$ = 13 TeV corresponding to an integrated luminosity of 138 fb$^{-1}$ recorded with the CMS detector is analyzed. No statistically significant excess is observed over the standard model backgrounds. Upper limits are set at 95% confidence level (CL) on the Higgs boson branching fraction to $\mu\mu$bb and to $\tau\tau$bb, via a pair of $\mathrm{a}_1$s. The limits depend on the pseudoscalar mass $m_{\mathrm{a}_1}$ and are observed to be in the range (0.17-3.3) $\times$ 10$^{-4}$ and (1.7-7.7) $\times$ 10$^{2}$ in the $\mu\mu$bb and $\tau\tau$bb final states, respectively. In the framework of models with two Higgs doublets and a complex scalar singlet (2HDM+S), the results of the two final states are combined to determine model-independent upper limits on the branching fraction $\mathcal{B}$(H $\to$ $\mathrm{a}_1\mathrm{a}_1$ $\to$ $\ell\ell$bb) at 95% CL, with $\ell$ being a muon or a $\tau$ lepton. For different types of 2HDM+S, upper bounds on the branching fraction $\mathcal{B}$(H $\to$ $\mathrm{a}_1\mathrm{a}_1$) are extracted from the combination of the two channels. In most of the Type II 2HDM+S parameter space, $\mathcal{B}($H $\to$ $\mathrm{a}_1\mathrm{a}_1$) values above 0.23 are excluded at 95% CL for $m_{\mathrm{a}_1}$ values between 15 and 60 GeV.

New Structures in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>J</mml:mi><mml:mo>/</mml:mo><mml:mi>ψ</mml:mi><mml:mi>J</mml:mi><mml:mo>/</mml:mo><mml:mi>ψ</mml:mi></mml:mrow></mml:math> Mass Spectrum in Proton-Proton Collisions at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msqrt><mml:mrow><mml:mi>s</mml:mi></mml:mrow></mml:msqrt><mml:mo>=</mml:mo><mml:mn>13</mml:mn><mml:mtext> </mml:mtext><mml:mtext> </mml:mtext><mml:mi>TeV</mml:mi></mml:mrow></mml:math>

Physical Review Letters · 2024 · 96 citations

• Physics

A search is reported for near-threshold structures in the J/ψJ/ψ invariant mass spectrum produced in proton-proton collisions at sqrt[s]=13 TeV from data collected by the CMS experiment, corresponding to an integrated luminosity of 135 fb^{-1}. Three structures are found, and a model with quantum interference among these structures provides a good description of the data. A new structure is observed with a local significance above 5 standard deviations at a mass of 6638_{-38}^{+43}(stat)_{-31}^{+16}(syst) MeV. Another structure with even higher significance is found at a mass of 6847_{-28}^{+44}(stat)_{-20}^{+48}(syst) MeV, which is consistent with the X(6900) resonance reported by the LHCb experiment and confirmed by the ATLAS experiment. Evidence for another new structure, with a local significance of 4.7 standard deviations, is found at a mass of 7134_{-25}^{+48}(stat)_{-15}^{+41}(syst) MeV. Results are also reported for a model without interference, which does not fit the data as well and shows mass shifts up to 150 MeV relative to the model with interference.

Measurement of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"><mml:msubsup><mml:mrow><mml:mtext>B</mml:mtext></mml:mrow><mml:mrow><mml:mtext>s</mml:mtext></mml:mrow><mml:mrow><mml:mn>0</mml:mn></mml:mrow></mml:msubsup><mml:mo stretchy="false">→</mml:mo><mml:msup><mml:mrow><mml:mi mathvariant="normal">μ</mml:mi></mml:mrow><mml:mrow><mml:mo linebreak="badbreak" linebreakstyle="after">+</mml:mo></mml:mrow></mml:msup><mml:msup><mml:mrow><mml:mi mathvariant="normal">μ</mml:mi></mml:mrow><mml:mrow><mml:mo linebreak="badbreak" linebreakstyle="after">−</mml:mo></mml:mrow></mml:msup></mml:math> decay properties and search for the B0 → μ+μ− decay in proton-proton collisions at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.svg"><mml:msqrt><mml:mrow><mml:mi>s</mml:mi></mml:mrow></mml:msqrt><mml:mo linebreak="goodbreak" linebreakstyle="after">=</mml:mo><mml:mn>13</mml:mn><mml:mspace width="0.2em"/><mml:mtext>TeV</mml:mtext></mml:math>

Physics Letters B · 2023 · 75 citations

• Computer Science
• Physics
• Algorithm

Measurements are presented of the Bs0→μ+μ− branching fraction and effective lifetime, as well as results of a search for the B0→μ+μ− decay in proton-proton collisions at s=13TeV at the LHC. The analysis is based on data collected with the CMS detector in 2016–2018 corresponding to an integrated luminosity of 140fb−1. The branching fraction of the Bs0→μ+μ− decay and the effective Bs0 meson lifetime are the most precise single measurements to date. No evidence for the B0→μ+μ− decay has been found. All results are found to be consistent with the standard model predictions and previous measurements.

Performance of the CMS High Granularity Calorimeter prototype to charged pion beams of 20–300 GeV/c

Journal of Instrumentation · 2023 · 13 citations

• Computer Science
• Physics
• Nuclear physics

Abstract The upgrade of the CMS experiment for the high luminosity operation of the LHC comprises the replacement of the current endcap calorimeter by a high granularity sampling calorimeter (HGCAL). The electromagnetic section of the HGCAL is based on silicon sensors interspersed between lead and copper (or copper tungsten) absorbers. The hadronic section uses layers of stainless steel as an absorbing medium and silicon sensors as an active medium in the regions of high radiation exposure, and scintillator tiles directly read out by silicon photomultipliers in the remaining regions. As part of the development of the detector and its readout electronic components, a section of a silicon-based HGCAL prototype detector along with a section of the CALICE AHCAL prototype was exposed to muons, electrons and charged pions in beam test experiments at the H2 beamline at the CERN SPS in October 2018. The AHCAL uses the same technology as foreseen for the HGCAL but with much finer longitudinal segmentation. The performance of the calorimeters in terms of energy response and resolution, longitudinal and transverse shower profiles is studied using negatively charged pions, and is compared to GEANT4 predictions. This is the first report summarizing results of hadronic showers measured by the HGCAL prototype using beam test data.

Identification of hadronic tau lepton decays using a deep neural network

Journal of Instrumentation · 2022 · 51 citations

• Physics
• Particle physics
• Nuclear physics

A new algorithm is presented to discriminate reconstructed hadronic decays of tau leptons (τ h) that originate from genuine tau leptons in the CMS detector against τ h candidates that originate from quark or gluon jets, electrons, or muons. The algorithm inputs information from all reconstructed particles in the vicinity of a τ h candidate and employs a deep neural network with convolutional layers to efficiently process the inputs. This algorithm leads to a significantly improved performance compared with the previously used one. For example, the efficiency for a genuine τ h to pass the discriminator against jets increases by 10-30% for a given efficiency for quark and gluon jets. Furthermore, a more efficient τ h reconstruction is introduced that incorporates additional hadronic decay modes. The superior performance of the new algorithm to discriminate against jets, electrons, and muons and the improved τ h reconstruction method are validated with LHC proton-proton collision data at s = 13 TeV.

A portrait of the Higgs boson by the CMS experiment ten years after the discovery

Nature · 2022 · 320 citations

• Physics
• Particle physics
• Nuclear physics

In July 2012, the ATLAS and CMS collaborations at the CERN Large Hadron Collider announced the observation of a Higgs boson at a mass of around 125 gigaelectronvolts. Ten years later, and with the data corresponding to the production of a 30-times larger number of Higgs bosons, we have learnt much more about the properties of the Higgs boson. The CMS experiment has observed the Higgs boson in numerous fermionic and bosonic decay channels, established its spin-parity quantum numbers, determined its mass and measured its production cross-sections in various modes. Here the CMS Collaboration reports the most up-to-date combination of results on the properties of the Higgs boson, including the most stringent limit on the cross-section for the production of a pair of Higgs bosons, on the basis of data from proton-proton collisions at a centre-of-mass energy of 13 teraelectronvolts. Within the uncertainties, all these observations are compatible with the predictions of the standard model of elementary particle physics. Much evidence points to the fact that the standard model is a low-energy approximation of a more comprehensive theory. Several of the standard model issues originate in the sector of Higgs boson physics. An order of magnitude larger number of Higgs bosons, expected to be examined over the next 15 years, will help deepen our understanding of this crucial sector.

Search for a heavy Higgs boson decaying to a pair of W bosons in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV

Journal of High Energy Physics · 2020 · 56 citations

• Physics
• Particle physics
• Nuclear physics

A bstract A search for a heavy Higgs boson in the mass range from 0.2 to 3.0 TeV, decaying to a pair of W bosons, is presented. The analysis is based on 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 recorded by the CMS experiment at the LHC in 2016, corresponding to an integrated luminosity of 35.9 fb − 1 . The W boson pair decays are reconstructed in the 2ℓ2 ν and ℓ ν 2q final states (with ℓ = e or μ ). Both gluon fusion and vector boson fusion production of the signal are considered. Interference effects between the signal and background are also taken into account. The observed data are consistent with the standard model (SM) expectation. Combined upper limits at 95% confidence level on the product of the cross section and branching fraction exclude a heavy Higgs boson with SM-like couplings and decays up to 1870 GeV. Exclusion limits are also set in the context of a number of two-Higgs-doublet model formulations, further reducing the allowed parameter space for SM extensions.

Measurement of $$\hbox {t}{\bar{\hbox {t}}}$$ normalised multi-differential cross sections in $${\text {p}}{\text {p}} $$ collisions at $$\sqrt{s}=13\,{\text {TeV}} $$, and simultaneous determination of the strong coupling strength, top quark pole mass, and parton distribution functions

The European Physical Journal C · 2020 · 92 citations

• Physics
• Particle physics
• Nuclear physics

Abstract Normalised multi-differential cross sections for top quark pair ( $$\hbox {t}{\bar{\hbox {t}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>t</mml:mtext><mml:mover><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mrow><mml:mo>¯</mml:mo></mml:mrow></mml:mover></mml:mrow></mml:math> ) production are measured in proton-proton collisions at a centre-of-mass energy of 13 $$\,{\text {TeV}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mspace/><mml:mtext>TeV</mml:mtext></mml:mrow></mml:math> using events containing two oppositely charged leptons. The analysed data were recorded with the CMS detector in 2016 and correspond to an integrated luminosity of $$35.9{\,{\text {fb}}^{-1}} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>35.9</mml:mn><mml:mrow><mml:mspace/><mml:msup><mml:mrow><mml:mtext>fb</mml:mtext></mml:mrow><mml:mrow><mml:mo>-</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:mrow></mml:math> . The double-differential $$\hbox {t}{\bar{\hbox {t}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>t</mml:mtext><mml:mover><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mrow><mml:mo>¯</mml:mo></mml:mrow></mml:mover></mml:mrow></mml:math> cross section is measured as a function of the kinematic properties of the top quark and of the $$\hbox {t}{\bar{\hbox {t}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>t</mml:mtext><mml:mover><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mrow><mml:mo>¯</mml:mo></mml:mrow></mml:mover></mml:mrow></mml:math> system at parton level in the full phase space. A triple-differential measurement is performed as a function of the invariant mass and rapidity of the $$\hbox {t}{\bar{\hbox {t}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>t</mml:mtext><mml:mover><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mrow><mml:mo>¯</mml:mo></mml:mrow></mml:mover></mml:mrow></mml:math> system and the multiplicity of additional jets at particle level. The data are compared to predictions of Monte Carlo event generators that complement next-to-leading-order (NLO) quantum chromodynamics (QCD) calculations with parton showers. Together with a fixed-order NLO QCD calculation, the triple-differential measurement is used to extract values of the strong coupling strength $$\alpha _{S}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>α</mml:mi><mml:mi>S</mml:mi></mml:msub></mml:math> and the top quark pole mass ( $$m_{{\text {t}}}^{{\text {pole}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi>m</mml:mi><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mtext>pole</mml:mtext></mml:msubsup></mml:math> ) using several sets of parton distribution functions (PDFs). The measurement of $$m_{{\text {t}}}^{{\text {pole}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi>m</mml:mi><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mtext>pole</mml:mtext></mml:msubsup></mml:math> exploits the sensitivity of the $$\hbox {t}{\bar{\hbox {t}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>t</mml:mtext><mml:mover><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mrow><mml:mo>¯</mml:mo></mml:mrow></mml:mover></mml:mrow></mml:math> invariant mass distribution to $$m_{{\text {t}}}^{{\text {pole}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi>m</mml:mi><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mtext>pole</mml:mtext></mml:msubsup></mml:math> near the production threshold. Furthermore, a simultaneous fit of the PDFs, $$\alpha _{S}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>α</mml:mi><mml:mi>S</mml:mi></mml:msub></mml:math> , and $$m_{{\text {t}}}^{{\text {pole}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi>m</mml:mi><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mtext>pole</mml:mtext></mml:msubsup></mml:math> is performed at NLO, demonstrating that the new data have significant impact on the gluon PDF, and at the same time allow an accurate determination of $$\alpha _{S}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>α</mml:mi><mml:mi>S</mml:mi></mml:msub></mml:math> and $$m_{{\text {t}}}^{{\text {pole}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi>m</mml:mi><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mtext>pole</mml:mtext></mml:msubsup></mml:math> . The values $$\alpha _{S}(m_{{\text {Z}}}) = 0.1135{}^{+0.0021}_{-0.0017}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>α</mml:mi><mml:mi>S</mml:mi></mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mi>m</mml:mi><mml:mtext>Z</mml:mtext></mml:msub><mml:mo>)</mml:mo></mml:mrow><mml:mo>=</mml:mo><mml:mn>0.1135</mml:mn><mml:msubsup><mml:mrow/><mml:mrow><mml:mo>-</mml:mo><mml:mn>0.0017</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mn>0.0021</mml:mn></mml:mrow></mml:msubsup></mml:mrow></mml:math> and $$m_{{\text {t}}}^{{\text {pole}}} = 170.5 \pm 0.8 \,{\text {GeV}} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mi>m</mml:mi><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mtext>pole</mml:mtext></mml:msubsup><mml:mo>=</mml:mo><mml:mn>170.5</mml:mn><mml:mo>±</mml:mo><mml:mn>0.8</mml:mn><mml:mspace/><mml:mtext>GeV</mml:mtext></mml:mrow></mml:math> are extracted, which account for experimental and theoretical uncertainties, the latter being estimated from NLO scale variations. Possible effects from Coulomb and soft-gluon resummation near the $$\hbox {t}{\bar{\hbox {t}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>t</mml:mtext><mml:mover><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mrow><mml:mo>¯</mml:mo></mml:mrow></mml:mover></mml:mrow></mml:math> production threshold are neglected in these parameter extractions. A rough estimate of these effects indicates an expected correction of $$m_{{\text {t}}}^{{\text {pole}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi>m</mml:mi><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mtext>pole</mml:mtext></mml:msubsup></mml:math> of the order of $$+1 \,{\text {GeV}} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>+</mml:mo><mml:mn>1</mml:mn><mml:mspace/><mml:mtext>GeV</mml:mtext></mml:mrow></mml:math> , which can be regarded as additional theoretical uncertainty in the current $$m_{{\text {t}}}^{{\text {pole}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi>m</mml:mi><mml:mrow><mml:mtext>t</mml:mtext></mml:mrow><mml:mtext>pole</mml:mtext></mml:msubsup></mml:math> extraction.

Search for physics beyond the standard model in multilepton final states in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV

Journal of High Energy Physics · 2020 · 46 citations

• Physics
• Particle physics
• Nuclear physics

A bstract A search for physics beyond the standard model in events with at least three charged leptons (electrons or muons) is presented. The data sample corresponds to an integrated luminosity of 137 fb − 1 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, collected with the CMS detector at the LHC in 2016–2018. The two targeted signal processes are pair production of type-III seesaw heavy fermions and production of a light scalar or pseudoscalar boson in association with a pair of top quarks. The heavy fermions may be manifested as an excess of events with large values of leptonic transverse momenta or missing transverse momentum. The light scalars or pseudoscalars may create a localized excess in the dilepton mass spectra. The results exclude heavy fermions of the type-III seesaw model for masses below 880 GeV at 95% confidence level in the scenario of equal branching fractions to each lepton flavor. This is the most restrictive limit on the flavor-democratic scenario of the type-III seesaw model to date. Assuming a Yukawa coupling of unit strength to top quarks, branching fractions of new scalar (pseudoscalar) bosons to dielectrons or dimuons above 0.004 (0.03) and 0.04 (0.03) are excluded at 95% confidence level for masses in the range 15–75 and 108–340 GeV, respectively. These are the first limits in these channels on an extension of the standard model with scalar or pseudoscalar particles.

A measurement of the Higgs boson mass in the diphoton decay channel

Physics Letters B · 2020 · 165 citations

• Physics
• Particle physics
• Nuclear physics

A measurement of the mass of the Higgs boson in the diphoton decay channel is presented. This analysis is based on 35.9 fb -1 of proton-proton collision data collected during the 2016 LHC running period, with the CMS detector at a centre-of-mass energy of 13 TeV. A refined detector calibration and new analysis techniques have been used to improve the precision of this measurement. The Higgs boson mass is measured to be m H = 125.78 0.26 GeV. This is combined with a measurement of m H already performed in the H ZZ 4 decay channel using the same data set, giving m H = 125.46 0.16 GeV. This result, when further combined with an earlier measurement of m H using data collected in 2011 and 2012 with the CMS detector, gives a value for the Higgs boson mass of m H = 125.38 0.14 GeV. This is currently the most precise measurement of the mass of the Higgs boson.