In several searches for additional Higgs bosons at the LHC, in particular in a CMS search exploring decays to pairs of top quarks,
t
t
¯
, and in an ATLAS search studying tau leptons,
τ
+
τ
-
, local ...excesses of about
3
σ
standard deviations or above have been observed at a mass scale of approximately
400
GeV
. We investigate to what extent a possible signal in these channels could be accommodated in the Next-to-Two-Higgs-Doublet Model (N2HDM) or the Next-to Minimal Supersymmetric Standard Model (NMSSM). In a second step we analyze whether such a model could be compatible with both a signal at around
400
GeV
and
96
GeV
, where the latter possibility is motivated by observed excesses in searches for the
b
b
¯
final state at LEP and the di-photon final state at CMS. The analysis for the N2HDM reveals that the observed excesses at
400
GeV
in the
t
t
¯
and
τ
+
τ
-
channels point towards different regions of the parameter space, while one such excess and an additional Higgs boson at around
96
GeV
could simultaneously be accommodated. In the context of the NMSSM an experimental confirmation of a signal in the
t
t
¯
final state would favour the alignment-without-decoupling limit of the model, where the Higgs boson at
125
GeV
could be essentially indistinguishable from the Higgs boson of the standard model. In contrast, a signal in the
τ
+
τ
-
channel can only be accommodated outside of this limit, and parts of the investigated parameter space could be probed with Higgs signal-rate measurements at the (HL-)LHC.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The measurement of the luminosity recorded by the CMS detector installed at LHC interaction point 5, using proton–proton collisions at
s
=
13
TeV
in 2015 and 2016, is reported. The absolute ...luminosity scale is measured for individual bunch crossings using beam-separation scans (the van der Meer method), with a relative precision of 1.3 and 1.0% in 2015 and 2016, respectively. The dominant sources of uncertainty are related to residual differences between the measured beam positions and the ones provided by the operational settings of the LHC magnets, the factorizability of the proton bunch spatial density functions in the coordinates transverse to the beam direction, and the modeling of the effect of electromagnetic interactions among protons in the colliding bunches. When applying the van der Meer calibration to the entire run periods, the integrated luminosities when CMS was fully operational are 2.27 and 36.3
fb
-
1
in 2015 and 2016, with a relative precision of 1.6 and 1.2%, respectively. These are among the most precise luminosity measurements at bunched-beam hadron colliders.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Combined measurements of the production and decay rates of the Higgs boson, as well as its couplings to vector bosons and fermions, are presented. The analysis uses the LHC proton–proton collision ...data set recorded with the CMS detector in 2016 at
s
=
13
Te
, corresponding to an integrated luminosity of 35.9
fb
-
1
. The combination is based on analyses targeting the five main Higgs boson production mechanisms (gluon fusion, vector boson fusion, and associated production with a
W
or
Z
boson, or a top quark-antiquark pair) and the following decay modes:
H
→
γ
γ
,
Z
Z
,
W
W
,
τ
τ
,
b
b
, and
μ
μ
. Searches for invisible Higgs boson decays are also considered. The best-fit ratio of the signal yield to the standard model expectation is measured to be
μ
=
1.17
±
0.10
, assuming a Higgs boson mass of
125.09
Ge
. Additional results are given for various assumptions on the scaling behavior of the production and decay modes, including generic parametrizations based on ratios of cross sections and branching fractions or couplings. The results are compatible with the standard model predictions in all parametrizations considered. In addition, constraints are placed on various two Higgs doublet models.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A search for invisible decays of a Higgs boson is performed using proton-proton collision data collected with the CMS detector at the LHC in 2016 at a center-of-mass energy s=13TeV, corresponding to ...an integrated luminosity of 35.9fb−1. The search targets the production of a Higgs boson via vector boson fusion. The data are found to be in agreement with the background contributions from standard model processes. An observed (expected) upper limit of 0.33(0.25), at 95% confidence level, is placed on the branching fraction of the Higgs boson decay to invisible particles, assuming standard model production rates and a Higgs boson mass of 125.09 GeV. Results from a combination of this analysis and other direct searches for invisible decays of the Higgs boson, performed using data collected at s=7, 8, and 13 TeV, are presented. An observed (expected) upper limit of 0.19(0.15), at 95% confidence level, is set on the branching fraction of invisible decays of the Higgs boson. The combined limit represents the most stringent bound on the invisible branching fraction of the Higgs boson reported to date. This result is also interpreted in the context of Higgs-portal dark matter models, in which upper bounds are placed on the spin-independent dark-matter-nucleon scattering cross section.
A
bstract
A search is presented for physics beyond the standard model (SM) using electron or muon pairs with high invariant mass. A data set of proton-proton collisions collected by the CMS ...experiment at the LHC at
s
= 13 TeV from 2016 to 2018 corresponding to a total integrated luminosity of up to 140 fb
−
1
is analyzed. No significant deviation is observed with respect to the SM background expectations. Upper limits are presented on the ratio of the product of the production cross section and the branching fraction to dileptons of a new narrow resonance to that of the Z boson. These provide the most stringent lower limits to date on the masses for various spin-1 particles, spin-2 gravitons in the Randall-Sundrum model, as well as spin-1 mediators between the SM and dark matter particles. Lower limits on the ultraviolet cutoff parameter are set both for four-fermion contact interactions and for the Arkani-Hamed, Dimopoulos, and Dvali model with large extra dimensions. Lepton flavor universality is tested at the TeV scale for the first time by comparing the dimuon and dielectron mass spectra. No significant deviation from the SM expectation of unity is observed.
Observation of t t ¯ H Production Erö, J.; Flechl, M.; Schieck, J. ...
Physical review letters,
06/2018, Letnik:
120, Številka:
23
Journal Article
Recenzirano
Odprti dostop
Here, the observation of Higgs boson production in association with a top quark-antiquark pair is reported, based on a combined analysis of proton-proton collision data at center-of-mass energies of ...√s=7, 8, and 13 TeV, corresponding to integrated luminosities of up to 5.1, 19.7, and 35.9 fb-1, respectively. The data were collected with the CMS detector at the CERN LHC. The results of statistically independent searches for Higgs bosons produced in conjunction with a top quark-antiquark pair and decaying to pairs of W bosons, Z bosons, photons, τ leptons, or bottom quark jets are combined to maximize sensitivity. An excess of events is observed, with a significance of 5.2 standard deviations, over the expectation from the background-only hypothesis. The corresponding expected significance from the standard model for a Higgs boson mass of 125.09 GeV is 4.2 standard deviations. The combined best fit signal strength normalized to the standard model prediction is1.26+0.31–0.26.
Studies of on-shell and off-shell Higgs boson production in the four-lepton final state are presented, using data from the CMS experiment at the LHC that correspond to an integrated luminosity of ...80.2 fb−1 at a center-of-mass energy of 13 TeV. Joint constraints are set on the Higgs boson total width and parameters that express its anomalous couplings to two electroweak vector bosons. These results are combined with those obtained from the data collected at center-of-mass energies of 7 and 8 TeV, corresponding to integrated luminosities of 5.1 and 19.7 fb−1, respectively. Kinematic information from the decay particles and the associated jets are combined using matrix element techniques to identify the production mechanism and to increase sensitivity to the Higgs boson couplings in both production and decay. The constraints on anomalous HVV couplings are found to be consistent with the standard model expectation in both the on-shell and off-shell regions. Under the assumption of a coupling structure similar to that in the standard model, the Higgs boson width is constrained to be ... MeV while the expected constraint based on simulation is ... MeV. The constraints on the width remain similar with the inclusion of the tested anomalous HVV interactions. (ProQuest: ... denotes formulae omitted.)
Evidence for the light-by-light scattering process, γγ→γγ, in ultraperipheral PbPb collisions at a centre-of-mass energy per nucleon pair of 5.02TeV is reported. The analysis is conducted using a ...data sample corresponding to an integrated luminosity of 390μb−1 recorded by the CMS experiment at the LHC. Light-by-light scattering processes are selected in events with two photons exclusively produced, each with transverse energy ETγ>2GeV, pseudorapidity |ηγ|<2.4, diphoton invariant mass mγγ>5GeV, diphoton transverse momentum pTγγ<1GeV, and diphoton acoplanarity below 0.01. After all selection criteria are applied, 14 events are observed, compared to expectations of 9.0±0.9(theo) events for the signal and 4.0±1.2(stat) for the background processes. The excess observed in data relative to the background-only expectation corresponds to a significance of 3.7 standard deviations, and has properties consistent with those expected for the light-by-light scattering signal. The measured fiducial light-by-light scattering cross section, σfid(γγ→γγ)=120±46(stat)±28(syst)±12(theo)nb, is consistent with the standard model prediction. The mγγ distribution is used to set new exclusion limits on the production of pseudoscalar axion-like particles, via the ▪ process, in the mass range ▪.
A search for narrow, low-mass, scalar, and pseudoscalar resonances decaying to bottom quark-antiquark pairs is presented. The search is based on events recorded in √ s = 13 TeV proton-proton ...collisions with the CMS detector at the LHC, collected in 2016, and corresponding to an integrated luminosity of 35.9 fb−1 . The search selects events in which the resonance would be produced with high transverse momentum because of the presence of initial- or final-state radiation. In such events, the decay products of the resonance would be reconstructed as a single large-radius jet with high mass and two-prong substructure. A potential signal would be identified as a narrow excess in the jet invariant mass spectrum. No evidence for such a resonance is observed within the mass range from 50 to 350 GeV, and upper limits at 95% confidence level are set on the product of the cross section and branching fraction to a bottom quark-antiquark pair. These constitute the first constraints from the LHC on exotic bottom quark-antiquark resonances with masses below 325 GeV.
A measurement of the Higgs boson mass is presented based on the combined data samples of the ATLAS and CMS experiments at the CERN LHC in the H arrow right gamma gamma and H arrow right ZZ arrow ...right 4scriptl decay channels. The results are obtained from a simultaneous fit to the reconstructed invariant mass peaks in the two channels and for the two experiments. The measured masses from the individual channels and the two experiments are found to be consistent among themselves. The combined measured mass of the Higgs boson is mH=125.09+ or -0.21 (stat)+ or -0.11 (syst) GeV.
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