Search For New Resonances Research Articles

Search for new resonances in events with one lepton and missing transverse momentum in pp collisions at s=13 TeV with the ATLAS detector

A search for $W^\prime$ bosons in events with one lepton (electron or muon) and missing transverse momentum is presented. The search uses 3.2 fb$^{-1}$ of $pp$ collision data collected at $\sqrt{s} = 13$ TeV by the ATLAS experiment at the LHC in 2015. The transverse mass distribution is examined and no significant excess of events above the level expected from Standard Model processes is observed. Upper limits on the $W^\prime$ boson cross-section times branching ratio to leptons are set as a function of the $W^\prime$ mass. Assuming a $W^\prime$ boson as predicted by the Sequential Standard Model, $W^\prime$ masses below 4.07 TeV are excluded at the 95% confidence level. This extends the limit set using LHC data at $\sqrt{s}=8$ TeV by around 800 GeV.

Higgs and flavour as doors to new physics

A natural solution to the hierarchy problem of the Fermi scale motivates signals of New Physics at current and near future experiments. After a critical synthesis of this general motivation, we concentrate our attention on the interplay between LHC searches for new resonances, and precision measurements of both Higgs couplings and flavour violating observables. We do so for i) the Higgs sectors of the NMSSM and MSSM, as paradigmatic examples of theories providing extra scalars, and for ii) CKM-like flavour symmetries, with a focus on U(2)^3. This article is mainly based on several papers by the author, but it also reviews other recent related results. Its goal is to provide a synthetic - yet comprehensive orientation on these subjects, at the dawn of several (ATLAS and CMS, LHCb, NA62 etc.) coming experimental results.

Search for new Resonances in Dielectron and Dimuon Mass Spectra at [formula omitted] with CMS

A search for new massive resonances decaying to a dielectron or a dimuon pair is presented. The search uses the full dataset corresponding to an integrated luminosity of about 20 fb−1 of pp collisions at a center-of-mass energy of 8 TeV, collected by the CMS experiment in 2012. In absence of a significant deviation from the standard model predictions, 95% confidence level limits are set on the ratio of cross section times branching ratio of a new resonance to the cross section times branching ratio of the Z boson. A sequential standard model ZSSM′ and a superstring-inspired Zψ′ of mass lighter than 2960 GeV and 2600 GeV, respectively, can be excluded at 95% confidence level.

Search for new resonances decaying via WZ to leptons in proton–proton collisions at [formula omitted

A search is performed in proton–proton collisions at s=8TeV for exotic particles decaying via WZ to fully leptonic final states with electrons, muons, and neutrinos. The data set corresponds to an integrated luminosity of 19.5 fb−1. No significant excess is observed above the expected standard model background. Upper bounds at 95% confidence level are set on the production cross section of a W′ boson as predicted by an extended gauge model, and on the W′WZ coupling. The expected and observed mass limits for a W′ boson, as predicted by this model, are 1.55 and 1.47 TeV, respectively. Stringent limits are also set in the context of low-scale technicolor models under a range of assumptions for the model parameters.

Search for new resonances in Wγ and Zγ final states in pp collisions at [formula omitted] with the ATLAS detector

This Letter presents a search for new resonances decaying to final states with a vector boson produced in association with a high transverse momentum photon, Vγ, with V=W(→ℓν) or Z(→ℓ+ℓ−), where ℓ=e or μ. The measurements use 20.3 fb−1 of proton–proton collision data at a center-of-mass energy of s=8 TeV recorded with the ATLAS detector. No deviations from the Standard Model expectations are found, and production cross section limits are set at 95% confidence level. Masses of the hypothetical aT and ωT states of a benchmark Low Scale Technicolor model are excluded in the ranges [275,960] GeV and [200,700]∪[750,890] GeV, respectively. Limits at 95% confidence level on the production cross section of a singlet scalar resonance decaying to Zγ final states have also been obtained for masses below 1180 GeV.

Search for massive resonances decaying into pairs of boosted bosons in semi-leptonic final states at s $$ \sqrt{s} $$ = 8 TeV

A search for new resonances decaying to WW, ZZ, or WZ is presented. Final states are considered in which one of the vector bosons decays leptonically and the other hadronically. Results are based on data corresponding to an integrated luminosity of 19.7 inverse femtobarns recorded in proton-proton collisions at sqrt(s) = 8 TeV with the CMS detector at the CERN LHC. Techniques aiming at identifying jet substructures are used to analyze signal events in which the hadronization products from the decay of highly boosted W or Z bosons are contained within a single reconstructed jet. Upper limits on the production of generic WW, ZZ, or WZ resonances are set as a function of the resonance mass and width. We increase the sensitivity of the analysis by statistically combining the results of this search with a complementary study of the all-hadronic final state. Upper limits at 95% confidence level are set on the bulk graviton production cross section in the range from 700 to 10 femtobarns for resonance masses between 600 and 2500 GeV, respectively. These limits on the bulk graviton model are the most stringent to date in the diboson final state.

Top-mode pseudo-Nambu-Goldstone bosons at the LHC

We discuss LHC phenomenologies of the Top-Mode Pseudos $(h^0_t,A^0_t)$, composite pseudo Nambu--Goldstone bosons predicted in the model recently proposed in a framework of the top quark condensation. The CP-even Top-Mode Pseudo, dubbed tHiggs ($h^0_t$), is identified with the 126 GeV Higgs boson at the LHC. We analyze the coupling properties of the tHiggs in comparison with the currently available data reported from LHC Run-I to find that the tHiggs can be consistent with the LHC Higgs boson. The mass formula relating masses of the Top-Mode Pseudos allows us to place an indirect limit on the mass of the CP-odd Top-Mode Pseudo ($A^0_t$) from the constraint on the tHiggs coupling strengths. The presence of the mass formula also significantly affects the coupling property of $A^0_t$, which ensures $A^0_t$ weakly coupled to the Standard Model particles. The direct limit on the mass of $A^0_t$ is placed by data on searches for new resonances in several channels at the LHC Run-I. We find the lower mass bound from both the indirect and direct limits, $m_{A^0_t} \gtrsim 560$ GeV. The discovery channel of $A^0_t$ in the upcoming LHC Run-II is also addressed.

The dark Z′ portal: direct, indirect and collider searches

We perform a detailed study of the dark Z' portal using a generic parametrization of the Z'-quarks couplings, both for light (8-15)GeV and heavy (130-1000)GeV dark matter scenarios. We present a comprehensive study of the collider phenomenology including jet clustering, hadronization, and detector artifacts, which allows us to derive accurate bounds from the search for new resonances in dijet events and from mono-jet events in the LHC 7TeV, LHC 8TeV, and Tevatron 1.96 TeV data. We also compute the dark matter relic abundance, the relevant scattering cross sections and pair-annihilation spectrum, and compare our results with the current PLANCK, Fermi-LAT and XENON100/LUX bounds. Lastly, we highlight the importance of complementary searches for dark matter, and outline the excluded versus still viable parameter space regions of the dark Z' portal.

Search for exotic resonances in diboson final states with the CMS detector at the LHC

The results of searches for new resonances decaying to a pair of massive vector bosons (WW, WZ, ZZ) are presented. All searches are performed using 5.0 fb−1 of proton-proton collisions, at TeV of center of mass energy, collected by the Compact Muon Solenoid detector at the Large Hadron Collider. No significant excess compared to the standard model background expectation is observed, and upper limits at 95% confidence level are set on the production cross section times the branching fraction of hypothetical particles decaying to a pair of vector bosons. The results are interpreted in the context of several benchmark models, such as the Randall-Sundrum gravitons, the Sequential Standard Model W′, and Technicolor. Graviton resonances in the Randall-Sundrum model with masses smaller than 940 GeV/c2, for coupling parameter k/m̄Pl = 0.05 are excluded. Bulk (ADPS) Randall-Sundrum gravitons with masses smaller than 610 GeV/c2 are excluded, for k/m̄Pl = 0.05. Sequential Standard Model W′ with masses smaller than 1143 GeV/c2 are excluded, as well as ρTC in the 167–687 GeV/c2 mass range, in Low Scale Technicolor models with M(πTC) = 3/4 M(ρTC) − 25 GeV/c2.

Recent charm physics results from BABAR

In this proceeding, recent charm physics results from the BABAR experiment are discussed. The studies include a Dalitz plot and partial-wave analysis of the decay Ds → K+ K− π+, a recent measurement of the leptonic decay constant fDs, the precision mass and width measurements of the Ds1(2535) meson, searches for new resonances in inclusive e+e− collisions, searches for flavor changing neutral currents, lepton-flavor and lepton-number violating decays, and searches for CP violation.

Charm spectroscopy in BaBar

The high luminosity of PEP-II in combination with the vertexing and particle identification capabilities of the BABAR detector offer unique opportunities for hadron spectroscopy. The recent results of the search for new resonances and the precise measurement of known open charm states are presented.

LEPTON PAIR PRODUCTION IN FIXED TARGET HADRON-HADRON COLLISIONS

In this paper the inclusive production of lepton pairs in hadron-hadron collisions is reviewed. Historically three motivations led to the study of lepton pairs: study of the hadronic structure via the continuum of lepton pairs, search for new resonances which decay into lepton pairs, and estimation of the production cross section of intermediate vector bosons. Nowadays the main issue is the test of QCD. This review will discuss the present status of the field with special emphasis on experimental aspects.

Search for new resonances and thresholds in inelastic electron scattering

We have extended the search for new resonances and thresholds in the hadronic final state ${X}^{+}$ in $ep\ensuremath{\rightarrow}{e}^{\ensuremath{'}}X$ for missing masses from 3 GeV to 5.5 GeV. At a level of roughly 5% of the cross sections we found no unexpected structure.

Pion Production in Antiproton-Proton Annihilations at3.3 and 3.7 BeVc

A study of antiproton-proton collisions at $3.3 \mathrm{and} 3.7 \frac{\mathrm{BeV}}{c}$ indicates that (41\ifmmode\pm\else\textpm\fi{}4)% of the total interaction cross section can be attributed to annihilation into pions. The average pion multiplicity is 6.5\ifmmode\pm\else\textpm\fi{}0.5. The positively charged pions and dipions tend to be emitted backward, while the negatively charged pions and dipions tend to be emitted forward in the center-of-mass system. Although there is a substantial amount of resonance production, especially of $\ensuremath{\rho}$ and of $\ensuremath{\omega}$ mesons, there is no clear evidence for double or associated resonance production in these final states. A search for new resonances as well as for some of the recently discovered mesons proved unsuccessful.