scholarly journals Search for exotic decays of the Higgs boson into long-lived particles in pp collisions at $$ \sqrt{s} $$ = 13 TeV using displaced vertices in the ATLAS inner detector

2021 ◽  
Vol 2021 (11) ◽  
Author(s):  
◽  
G. Aad ◽  
B. Abbott ◽  
D. C. Abbott ◽  
A. Abed Abud ◽  
...  
Keyword(s):  
Higgs Boson ◽  
Standard Model ◽  
Branching Ratio ◽  
High Mass ◽  
Proton Collision ◽  
Proton Proton ◽  
Upper Limits ◽  
Stringent Constraint ◽  
Model Predictions ◽  
Proton Proton Collision

Abstract A novel search for exotic decays of the Higgs boson into pairs of long-lived neutral particles, each decaying into a bottom quark pair, is performed using 139 fb−1 of $$ \sqrt{s} $$ s = 13 TeV proton-proton collision data collected with the ATLAS detector at the LHC. Events consistent with the production of a Higgs boson in association with a leptonically decaying Z boson are analysed. Long-lived particle (LLP) decays are reconstructed from inner-detector tracks as displaced vertices with high mass and track multiplicity relative to Standard Model processes. The analysis selection requires the presence of at least two displaced vertices, effectively suppressing Standard Model backgrounds. The residual background contribution is estimated using a data-driven technique. No excess over Standard Model predictions is observed, and upper limits are set on the branching ratio of the Higgs boson to LLPs. Branching ratios above 10% are excluded at 95% confidence level for LLP mean proper lifetimes cτ as small as 4 mm and as large as 100 mm. For LLP masses below 40 GeV, these results represent the most stringent constraint in this lifetime regime.

scholarly journals Angular analysis of the rare decay $$ {B}_s^0 $$ → ϕμ+μ−

2021 ◽  
Vol 2021 (11) ◽  
Author(s):  
◽  
R. Aaij ◽  
A. S. W. Abdelmotteleb ◽  
C. Abellán Beteta ◽  
T. Ackernley ◽  
...  
Keyword(s):  
Standard Model ◽  
Invariant Mass ◽  
Rare Decay ◽  
Angular Distributions ◽  
Proton Collision ◽  
Centre Of Mass ◽  
Proton Proton ◽  
Angular Analysis ◽  
Model Predictions ◽  
Proton Proton Collision

Abstract An angular analysis of the rare decay $$ {B}_s^0 $$ B s 0 → ϕμ+μ− is presented, using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of 8.4 fb−1. The observables describing the angular distributions of the decay $$ {B}_s^0 $$ B s 0 → ϕμ+μ− are determined in regions of q2, the square of the dimuon invariant mass. The results are consistent with Standard Model predictions.

scholarly journals Search for top squarks in events with a Higgs or Z boson using 139 fb$$^{-1}$$ of pp collision data at $$\sqrt{s}=13$$ TeV with the ATLAS detector

2020 ◽  
Vol 80 (11) ◽  
Author(s):  
G. Aad ◽  
◽  
B. Abbott ◽  
D. C. Abbott ◽  
A. Abed Abud ◽  
...  
Keyword(s):  
Standard Model ◽  
Atlas Detector ◽  
Proton Collision ◽  
Top Squark ◽  
Proton Proton ◽  
Direct Production ◽  
Missing Transverse Momentum ◽  
The Standard Model ◽  
Model Predictions ◽  
Proton Proton Collision

AbstractThis paper presents a search for direct top squark pair production in events with missing transverse momentum plus either a pair of jets consistent with Standard Model Higgs boson decay into b-quarks or a same-flavour opposite-sign dilepton pair with an invariant mass consistent with a Z boson. The analysis is performed using the proton–proton collision data at $$\sqrt{s}=13$$ s = 13 TeV collected with the ATLAS detector during the LHC Run-2, corresponding to an integrated luminosity of 139 fb$$^{-1}$$ - 1 . No excess is observed in the data above the Standard Model predictions. The results are interpreted in simplified models featuring direct production of pairs of either the lighter top squark ($$\tilde{t}_1$$ t ~ 1 ) or the heavier top squark ($$\tilde{t}_2$$ t ~ 2 ), excluding at 95% confidence level $$\tilde{t}_1$$ t ~ 1 and $$\tilde{t}_2$$ t ~ 2 masses up to about 1220 and 875 GeV, respectively.

scholarly journals Measurements of the Higgs boson inclusive and differential fiducial cross sections in the 4$$\ell $$ decay channel at $$\sqrt{s}$$ = 13 TeV

2020 ◽  
Vol 80 (10) ◽  
Author(s):  
G. Aad ◽  
◽  
B. Abbott ◽  
D. C. Abbott ◽  
A. Abed Abud ◽  
...  
Keyword(s):  
Higgs Boson ◽  
Standard Model ◽  
Cross Sections ◽  
Decay Channel ◽  
Standard Model Prediction ◽  
Hadron Collider ◽  
Proton Collision ◽  
Proton Proton ◽  
The Standard Model ◽  
Proton Proton Collision

AbstractInclusive and differential fiducial cross sections of the Higgs boson are measured in the $$H \rightarrow ZZ^{*} \rightarrow 4\ell $$ H → Z Z ∗ → 4 ℓ ($$\ell = e,\mu $$ ℓ = e , μ ) decay channel. The results are based on proton−proton collision data produced at the Large Hadron Collider at a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector from 2015 to 2018, equivalent to an integrated luminosity of 139 $$\hbox {fb}^{-1}$$ fb - 1 . The inclusive fiducial cross section for the $$H \rightarrow ZZ^{*} \rightarrow 4\ell $$ H → Z Z ∗ → 4 ℓ process is measured to be $$\sigma _\mathrm {fid} = 3.28 \pm 0.32$$ σ fid = 3.28 ± 0.32  fb, in agreement with the Standard Model prediction of $$\sigma _\mathrm {fid, SM} = 3.41 \pm 0.18 $$ σ fid , SM = 3.41 ± 0.18  fb. Differential fiducial cross sections are measured for a variety of observables which are sensitive to the production and decay of the Higgs boson. All measurements are in agreement with the Standard Model predictions. The results are used to constrain anomalous Higgs boson interactions with Standard Model particles.

Review of combined measurements of Higgs boson production and decay using up to 80 fb−1 of proton–proton collision data at s = 13 TeV collected with the ATLAS experiment

2020 ◽  
pp. 2030023
Author(s):  
Hongtao Yang
Keyword(s):  
Higgs Boson ◽  
Standard Model ◽  
Vector Boson ◽  
Proton Collision ◽  
Boson Production ◽  
Proton Proton ◽  
Associated Production ◽  
The Standard Model ◽  
Proton Proton Collision ◽  
Combined Measurements

The combined measurements of Higgs boson production and decay are performed based on up to 80 fb[Formula: see text] of proton–proton collision data collected at [Formula: see text] = 13 TeV by the ATLAS detector. The overall signal strength, defined as measured signal yield divided by the Standard Model prediction, is [Formula: see text]. The inclusive and differential cross-sections of gluon–gluon fusion, vector-boson fusion, associated production with vector boson, and associated production with top quarks processes are also measured. The measurements are interpreted with leading-order motivated coupling strength modifiers. No significant deviations from the Standard Model predictions are observed.

scholarly journals Search for π0 decays to invisible particles

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
E. Cortina Gil ◽  
◽  
A. Kleimenova ◽  
E. Minucci ◽  
S. Padolski ◽  
...  
Keyword(s):  
Higgs Boson ◽  
Standard Model ◽  
Confidence Level ◽  
Branching Ratio ◽  
Standard Model Higgs Boson ◽  
Scalar Mixing ◽  
Upper Limit ◽  
Upper Limits ◽  
The Standard Model ◽  
Model Independent

Abstract The NA62 experiment at the CERN SPS reports a study of a sample of 4 × 109 tagged π0 mesons from K+ → π+π0(γ), searching for the decay of the π0 to invisible particles. No signal is observed in excess of the expected background fluctuations. An upper limit of 4.4 × 10−9 is set on the branching ratio at 90% confidence level, improving on previous results by a factor of 60. This result can also be interpreted as a model- independent upper limit on the branching ratio for the decay K+ → π+X, where X is a particle escaping detection with mass in the range 0.110–0.155 GeV/c2 and rest lifetime greater than 100 ps. Model-dependent upper limits are obtained assuming X to be an axion-like particle with dominant fermion couplings or a dark scalar mixing with the Standard Model Higgs boson.

scholarly journals Search for decays of the 125 GeV Higgs boson into a Z boson and a ρ or ϕ meson

2020 ◽  
Vol 2020 (11) ◽  
Author(s):  
A. M. Sirunyan ◽  
◽  
A. Tumasyan ◽  
W. Adam ◽  
F. Ambrogi ◽  
...  
Keyword(s):  
Higgs Boson ◽  
Z Boson ◽  
Branching Fractions ◽  
Proton Collision ◽  
Data Set ◽  
Proton Proton ◽  
Decay Channels ◽  
Decay Products ◽  
Upper Limits ◽  
Z Boson Decays

Abstract Decays of the 125 GeV Higgs boson into a Z boson and a ρ0(770) or ϕ(1020) meson are searched for using proton-proton collision data collected by the CMS experiment at the LHC at $$ \sqrt{s} $$ s = 13 TeV. The analysed data set corresponds to an integrated luminosity of 137 fb−1. Events are selected in which the Z boson decays into a pair of electrons or a pair of muons, and the ρ and ϕ mesons decay into pairs of pions and kaons, respectively. No significant excess above the background model is observed. As different polarization states are possible for the decay products of the Z boson and ρ or ϕ mesons, affecting the signal acceptance, scenarios in which the decays are longitudinally or transversely polarized are considered. Upper limits at the 95% confidence level on the Higgs boson branching fractions into Zρ and Zϕ are determined to be 1.04–1.31% and 0.31–0.40%, respectively, where the ranges reflect the considered polarization scenarios; these values are 740–940 and 730–950 times larger than the respective standard model expectations. These results constitute the first experimental limits on the two decay channels.

scholarly journals Search for heavy neutral leptons in $$W^+\rightarrow \mu ^{+}\mu ^{\pm }\, \text {jet}$$ decays

2021 ◽  
Vol 81 (3) ◽  
Author(s):  
R. Aaij ◽  
◽  
C. Abellán Beteta ◽  
T. Ackernley ◽  
B. Adeva ◽  
...  
Keyword(s):  
Mass Range ◽  
Lepton Number ◽  
Heavy Neutrino ◽  
Proton Collision ◽  
Final State ◽  
Data Set ◽  
Proton Proton ◽  
Upper Limits ◽  
The Standard Model ◽  
Proton Proton Collision

AbstractA search is performed for heavy neutrinos in the decay of a W boson into two muons and a jet. The data set corresponds to an integrated luminosity of approximately $$3.0\, \text {fb} ^{-1} $$ 3.0 fb - 1 of proton–proton collision data at centre-of-mass energies of 7 and $$8\, \text {TeV} $$ 8 TeV collected with the LHCb experiment. Both same-sign and opposite-sign muons in the final state are considered. Data are found to be consistent with the expected background. Upper limits on the coupling of a heavy neutrino with the Standard Model neutrino are set at $$95\%$$ 95 % confidence level in the heavy-neutrino mass range from 5 to $$50\, \text {GeV/}c^2 $$ 50 GeV/ c 2 . These are of the order of $$10^{-3}$$ 10 - 3 for lepton-number-conserving decays and of the order of $$10^{-4}$$ 10 - 4 for lepton-number-violating heavy-neutrino decays.

scholarly journals Exploration of Extended Higgs Sectors with Run-2 Proton–Proton Collision Data at the LHC

Symmetry ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 2144
Author(s):  
Arnaud Ferrari ◽  
Nikolaos Rompotis
Keyword(s):  
Standard Model ◽  
Higgs Sector ◽  
Scalar Fields ◽  
Higgs Bosons ◽  
Proton Collision ◽  
Complex Scalar ◽  
Proton Proton ◽  
The Standard Model ◽  
Extended Higgs Sectors ◽  
Proton Proton Collision

One doublet of complex scalar fields is the minimal content of the Higgs sector in order to achieve spontaneous electroweak symmetry breaking and, in turn, to generate the masses of fundamental particles in the Standard Model. However, several theories beyond the Standard Model predict a nonminimal Higgs sector and introduce additional singlets, doublets or even higher-order weak isospin representations, thereby yielding additional Higgs bosons. With its high proton–proton collision energy (13 TeV during Run-2), the Large Hadron Collider opens a new window towards the exploration of extended Higgs sectors. This review article summarises the current state-of-the-art experimental results recently obtained in searches for new neutral and charged Higgs bosons with a partial or full Run-2 dataset.

scholarly journals Higgs boson production cross-section measurements and their EFT interpretation in the $$4\ell $$ decay channel at $$\sqrt{s}=$$13 TeV with the ATLAS detector

2020 ◽  
Vol 80 (10) ◽  
Author(s):  
G. Aad ◽  
◽  
B. Abbott ◽  
D. C. Abbott ◽  
A. Abed Abud ◽  
...  
Keyword(s):  
Higgs Boson ◽  
Standard Model ◽  
Cross Section ◽  
Decay Channel ◽  
Branching Ratio ◽  
Proton Collision ◽  
Boson Production ◽  
Theory Approach ◽  
Higgs Boson Production ◽  
The Standard Model

AbstractHiggs boson properties are studied in the four-lepton decay channel (where lepton = e, $$\mu $$ μ ) using 139 $$\hbox {fb}^{-1}$$ fb - 1 of proton–proton collision data recorded at $$\sqrt{s}=$$ s = 13 TeV by the ATLAS experiment at the Large Hadron Collider. The inclusive cross-section times branching ratio for $$H\rightarrow ZZ^*$$ H → Z Z ∗ decay is measured to be $$1.34 \pm 0.12$$ 1.34 ± 0.12  pb for a Higgs boson with absolute rapidity below 2.5, in good agreement with the Standard Model prediction of $$1.33 \pm 0.08$$ 1.33 ± 0.08  pb. Cross-sections times branching ratio are measured for the main Higgs boson production modes in several exclusive phase-space regions. The measurements are interpreted in terms of coupling modifiers and of the tensor structure of Higgs boson interactions using an effective field theory approach. Exclusion limits are set on the CP-even and CP-odd ‘beyond the Standard Model’ couplings of the Higgs boson to vector bosons, gluons and top quarks.

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