1,715 research outputs found
Photo Thermal Effect Graphene Detector Featuring 105 Gbit s-1 NRZ and 120 Gbit s-1 PAM4 Direct Detection
The challenge of next generation datacom and telecom communication is to
increase the available bandwidth while reducing the size, cost and power
consumption of photonic integrated circuits. Silicon (Si) photonics has emerged
as a viable solution to reach these objectives. Graphene, a single-atom thick
layer of carbon5, has been recently proposed to be integrated with Si photonics
because of its very high mobility, fast carrier dynamics and ultra-broadband
optical properties. Here, we focus on graphene photodetectors for high speed
datacom and telecom applications. High speed graphene photodetectors have been
demonstrated so far, however the most are based on the photo-bolometric (PB) or
photo-conductive (PC) effect. These devices are characterized by large dark
current, in the order of milli-Amperes , which is an impairment in
photo-receivers design, Photo-thermo-electric (PTE) effect has been identified
as an alternative phenomenon for light detection. The main advantages of
PTE-based photodetectors are the optical power to voltage conversion, zero-bias
operation and ultra-fast response. Graphene PTE-based photodetectors have been
reported in literature, however high-speed optical signal detection has not
been shown. Here, we report on an optimized graphene PTE-based photodetector
with flat frequency response up to 65 GHz. Thanks to the optimized design we
demonstrate a system test leading to direct detection of 105 Gbit s-1
non-return to zero (NRZ) and 120 Gbit s-1 4-level pulse amplitude modulation
(PAM) optical signal
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Measurement of the Higgs boson width and evidence of its off-shell contributions to ZZ production
Since the discovery of the Higgs boson in 2012, detailed studies of its properties have been ongoing. Besides its mass, its widthârelated to its lifetimeâis an important parameter. One way to determine this quantity is to measure its off-shell production, where the Higgs boson mass is far away from its nominal value, and relating it to its on-shell production, where the mass is close to the nominal value. Here we report evidence for such off-shell contributions to the production cross-section of two Z bosons with data from the CMS experiment at the CERN Large Hadron Collider. We constrain the total rate of the off-shell Higgs boson contribution beyond the Z boson pair production threshold, relative to its standard model expectation, to the interval [0.0061, 2.0] at the 95% confidence level. The scenario with no off-shell contribution is excluded at a p-value of 0.0003 (3.6 standard deviations). We measure the width of the Higgs boson as ÎH=3.2â1.7+2.4MeV, in agreement with the standard model expectation of 4.1 MeV. In addition, we set constraints on anomalous Higgs boson couplings to W and Z boson pairs
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Luminosity determination using Z boson production at the CMS experiment
Data Availability Statement - This manuscript has no associated data or
the data will not be deposited. [Authorsâ comment: Release and preser
vation of data used by the CMS Collaboration as the basis for publi
cations is guidedbytheCMSpolicyasstatedinhttps://cms-docdb.cern.
ch/cgibin/PublicDocDB/RetrieveFile?docid=6032&filename=CMSD
ataPolicyV1.2.pdf&version=2. CMS data preservation,re-use and open
access policy.]The measurement of ZÂ boson production is presented as a method to determine the integrated luminosity of CMS data sets. The analysis uses protonâproton collision data, recorded by the CMS experiment at the CERN LHC in 2017 at a center-of-mass energy of 13 TeV . Events with ZÂ bosons decaying into a pair of muons are selected. The total number of ZÂ bosons produced in a fiducial volume is determined, together with the identification efficiencies and correlations from the same data set, in small intervals of 20 pb-1 of integrated luminosity, thus facilitating the efficiency and rate measurement as a function of time and instantaneous luminosity. Using the ratio of the efficiency-corrected numbers of ZÂ bosons, the precisely measured integrated luminosity of one data set is used to determine the luminosity of another. For the first time, a full quantitative uncertainty analysis of the use of Z bosons for the integrated luminosity measurement is performed. The uncertainty in the extrapolation between two data sets, recorded in 2017 at low and high instantaneous luminosity, is less than 0.5%. We show that the ZÂ boson rate measurement constitutes a precise method, complementary to traditional methods, with the potential to improve the measurement of the integrated luminosity.SCOAP
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Search for long-lived particles decaying to a pair of muons in proton-proton collisions at âs = 13 TeV
A preprint version of the article is available at arXiv:2205.08582v2 [hep-ex], https://arxiv.org/abs/2205.08582 . Comments: Replaced with the published version. Added the journal reference and the DOI. All the figures and tables, including additional supplementary figures and tables, can be found at https://cms-results.web.cern.ch/cms-results/public-results/publications/EXO-21-006 (CMS Public Pages).An inclusive search for long-lived exotic particles decaying to a pair of muons is presented. The search uses data collected by the CMS experiment at the CERN LHC in proton-proton collisions at s = 13 TeV in 2016 and 2018 and corresponding to an integrated luminosity of 97.6 fbâ1. The experimental signature is a pair of oppositely charged muons originating from a common secondary vertex spatially separated from the pp interaction point by distances ranging from several hundred ÎŒm to several meters. The results are interpreted in the frameworks of the hidden Abelian Higgs model, in which the Higgs boson decays to a pair of long-lived dark photons ZD, and of a simplified model, in which long-lived particles are produced in decays of an exotic heavy neutral scalar boson. For the hidden Abelian Higgs model with m(ZD) greater than 20 GeV and less than half the mass of the Higgs boson, they provide the best limits to date on the branching fraction of the Higgs boson to dark photons for cÏ(ZD) (varying with m(ZD)) between 0.03 and â0.5 mm, and above â0.5 m. Our results also yield the best constraints on long-lived particles with masses larger than 10 GeV produced in decays of an exotic scalar boson heavier than the Higgs boson and decaying to a pair of muons. [Figure not available: see fulltext.].SCOAP3
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Search for CP violating top quark couplings in pp collisions at âs = 13 TeV
A preprint version of the article is available at arXiv:2205.07434v2 [hep-ex], https://arxiv.org/abs/2205.07434. It has not been certified by peer review.Results are presented from a search for CP violation in top quark pair production, using proton-proton collisions at a center-of-mass energy of 13 TeV. The data used for this analysis consist of final states with two charged leptons collected by the CMS experiment, and correspond to an integrated luminosity of 35.9 fbâ1. The search uses two observables, O1 and O3, which are Lorentz scalars. The observable O1 is constructed from the four-momenta of the charged leptons and the reconstructed top quarks, while O3 consists of the four-momenta of the charged leptons and the b quarks originating from the top quarks. Asymmetries in these observables are sensitive to CP violation, and their measurement is used to determine the chromoelectric dipole moment of the top quark. The results are consistent with the expectation from the standard model. [Figure not available: see fulltext.].SCOAP
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Search for nonresonant Higgs boson pair production in the four leptons plus two b jets final state in proton-proton collisions at = 13 TeV
A preprint version of the article is available at arXiv:2206.10657v2 [hep-ex], https://arxiv.org/abs/2206.10657 . Comments: Replaced with the published version. Added the journal reference and the DOI. All the figures and tables can be found at this http URL (CMS Public Pages). Report number: CMS-HIG-20-004, CERN-EP-2022-114.The first search for nonresonant production of Higgs boson pairs (HH) with one H decaying into four leptons and the other into a pair of b quarks is presented, using proton-proton collisions recorded at a center-of-mass energy of s = 13 TeV by the CMS experiment. The analyzed data correspond to an integrated luminosity of 138 fbâ1. A 95% confidence level upper limit of 32.4 is set on the signal strength modifier ÎŒ, defined as the ratio of the observed HH production rate in the HHâ ZZâb b ÂŻ â 4 âb b ÂŻ decay channel to the standard model (SM) expectation. Possible modifications of the H trilinear coupling λ HHH with respect to the SM value are investigated. The coupling modifier Îșλ, defined as λ HHH divided by its SM prediction, is constrained to be within the observed (expected) range â8.8 (â9.8) < Îșλ < 13.4 (15.0) at 95% confidence level. [Figure not available: see fulltext.].SCOAP3
MUSiC: a model-unspecific search for new physics in protonâproton collisions at âs=13TeV
Results of the Model Unspecific Search in CMS (MUSiC), using protonâproton collision data recorded at the LHC at a centre-of-mass energy of 13TeV, corresponding to an integrated luminosity of 35.9fb-1, are presented. The MUSiC analysis searches for anomalies that could be signatures of physics beyond the standard model. The analysis is based on the comparison of observed data with the standard model prediction, as determined from simulation, in several hundred final states and multiple kinematic distributions. Events containing at least one electron or muon are classified based on their final state topology, and an automated search algorithm surveys the observed data for deviations from the prediction. The sensitivity of the search is validated using multiple methods. No significant deviations from the predictions have been observed. For a wide range of final state topologies, agreement is found between the data and the standard model simulation. This analysis complements dedicated search analyses by significantly expanding the range of final states covered using a model independent approach with the largest data set to date to probe phase space regions beyond the reach of previous general searches
Combined searches for the production of supersymmetric top quark partners in protonâproton collisions at âs=13Te
A combination of searches for top squark pair production using protonâproton collision data at a center-of-mass energy of 13TeV at the CERN LHC, corresponding to an integrated luminosity of 137fb collected by the CMS experiment, is presented. Signatures with at least 2 jets and large missing transverse momentum are categorized into events with 0, 1, or 2 leptons. New results for regions of parameter space where the kinematical properties of top squark pair production and top quark pair production are very similar are presented. Depending on the model, the combined result excludes a top squark mass up to 1325GeV for a massless neutralino, and a neutralino mass up to 700GeV for a top squark mass of 1150GeV. Top squarks with masses from 145 to 295GeV, for neutralino masses from 0 to 100GeV, with a mass difference between the top squark and the neutralino in a window of 30GeV around the mass of the top quark, are excluded for the first time with CMS data. The results of theses searches are also interpreted in an alternative signal model of dark matter production via a spin-0 mediator in association with a top quark pair. Upper limits are set on the cross section for mediator particle masses of up to 420GeV
Search for low-mass dilepton resonances in Higgs boson decays to four-lepton final states in protonâproton collisions at âs=13TeV
A search for low-mass dilepton resonances in Higgs boson decays is conducted in the four-lepton final state.
The decay is assumed to proceed via a pair of beyond the standard model particles, or one such particle and a Z boson. The
search uses protonâproton collision data collected with the
CMS detector at the CERN LHC, corresponding to an integrated luminosity of 137 fbâ1, at a center-of-mass energy
âs = 13 TeV. No significant deviation from the standard
model expectation is observed. Upper limits at 95% confidence level are set on model-independent Higgs boson decay
branching fractions. Additionally, limits on dark photon and
axion-like particle production, based on two specific models,
are reported
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