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427 research outputs found

A Low-Cost Inertial Navigation System Onboard Balloons

Author: A. Folino
E. Medaglia
PALMERINI Giovanni Battista
T. Buccilli
P. Montefusco
A. Sestito
M. C. Oliva
Publication venue
Publication date: 01/01/2009
Field of study

The paper presents a navigation experiment, successfully flown onboard BEXUS 6 balloon mission on 8th October 2008 from ESRANGE Space Center in Kiruna. Northrop Grumman Italia (NG Italia) according to multi-year collaboration plan with University of Rome “La Sapienza” has provided support to the students’ team that proposed, designed and operated the LowCoINS (Low Cost Inertial Navigation System) experiment. LowCoINS has as the main component a low-cost three-axes inertial unit, integrating three accelerometers and three gyros, together with temperature sensors, three-axes magnetometer and a pressure sensor for augmentation purposes. Measurements from the sensors are both stored onboard and downlinked to a ground station making them available for a successive post-processing. Several tests have been exploited to verify the effectiveness of the choices operated in the design phase of the unit and its capability to withstand to all the environmental requirements. The data processing included the development and execution of different sensor fusion algorithm to obtain attitude, position and velocity data throughout the entire flight. An overview of the LowCoINS design philosophy, the extensive set of environmental test performed to validate the unit and a description of the algorithm used together with the results obtained are reported hereafter

Archivio della ricerca- Università di Roma La Sapienza

Measurement of the jet mass in highly boosted t(t)over-bar events from pp collisions at root s=8TeV

Author: Rumerio P.
Cooper S.I.
Henderson C.
Buccilli A.
CMS Collaboration
West C.
Publication venue
Publication date: 01/01/2017
Field of study

The first measurement of the jet mass

m_{jet}

of top quark jets produced in

t\overline{t}

events from pp collisions at

\sqrt{s}

=8TeV is reported for the jet with the largest transverse momentum

p_T

in highly boosted hadronic top quark decays. The data sample, collected with the CMS detector, corresponds to an integrated luminosity of 19.7 fb⁻¹. The measurement is performed in the lepton+jets channel in which the products of the semileptonic decay t→bW with W→ℓν where ℓ is an electron or muon, are used to select

t\overline{t}

events with large Lorentz boosts. The products of the fully hadronic decay t→bW with W→qq̅′ are reconstructed using a single Cambridge–Aachen jet with distance parameter R=1.2, and

p_T

>400 GeV. The

t\overline{t}

cross section as a function of

m_{jet}

is unfolded at the particle level and is used to test the modelling of highly boosted top quark production. The peak position of the mjet distribution is sensitive to the top quark mass

m_{t}

, and the data are used to extract a value of mt to assess this sensitivity

UA Institutional Repository (Univ. of Alabama)

Measurement of the top quark Yukawa coupling from t(t)over-bar kinematic distributions in the dilepton final state in proton-proton collisions at root s=13 TeV

Author: Rumerio P.
Cooper S.I.
Henderson C.
Buccilli A.
Gleyzer S.V.
Charaf O.
CMS Collaboration
West C.
Publication venue
Publication date: 01/01/2020
Field of study

A measurement of the Higgs boson Yukawa coupling to the top quark is presented using proton-proton collision data at

\sqrt{s}=13\text{}\text{}\mathrm{TeV}

, corresponding to an integrated luminosity of

137\text{}\text{}{\mathrm{fb}}^{-1}

, recorded with the CMS detector. The coupling strength with respect to the standard model value,

{Y}_{t}

, is determined from kinematic distributions in

t\overline{t}

final states containing

ee

\mu \mu

, or

e\mu

pairs. Variations of the Yukawa coupling strength lead to modified distributions for

t\overline{t}

production. In particular, the distributions of the mass of the

t\overline{t}

system and the rapidity difference of the top quark and antiquark are sensitive to the value of

{Y}_{t}

. The measurement yields a best fit value of

{{Y}_{t}=1.16}_{-0.35}^{+0.24}

, bounding

{Y}_{t}<1.54

at a 95% confidence level

UA Institutional Repository (Univ. of Alabama)

Measurement of the top quark Yukawa coupling from t(t)over-bar kinematic distributions in the lepton plus jets final state in proton-proton collisions at root s=13 TeV

Author: Rumerio P.
Cooper S.I.
Henderson C.
Buccilli A.
CMS Collaboration
West C.
Publication venue
Publication date: 01/01/2019
Field of study

Results are presented for an extraction of the top quark Yukawa coupling from top quark-antiquark

t\overline{t}

kinematic distributions in the lepton plus jets final state in proton-proton collisions, based on data collected by the CMS experiment at the LHC at

\sqrt{s}=13\text{}\text{}\mathrm{TeV}

, corresponding to an integrated luminosity of

35.8\text{}\text{}{\mathrm{fb}}^{-1}

. Corrections from weak boson exchange, including Higgs bosons, between the top quarks can produce large distortions of differential distributions near the energy threshold of

t\overline{t}

production. Therefore, precise measurements of these distributions are sensitive to the Yukawa coupling. Top quark events are reconstructed with at least three jets in the final state, and a novel technique is introduced to reconstruct the

t\overline{t}

system for events with one missing jet. This technique enhances the experimental sensitivity in the low invariant mass region,

{M}_{t\overline{t}}

. The data yields in

{M}_{t\overline{t}}

, the rapidity difference

|{y}_{t}-{y}_{\overline{t}}|

, and the number of reconstructed jets are compared with distributions representing different Yukawa couplings. These comparisons are used to measure the ratio of the top quark Yukawa coupling to its standard model predicted value to be

{1.07}_{-0.43}^{+0.34}

with an upper limit of 1.67 at the 95% confidence level

UA Institutional Repository (Univ. of Alabama)

Measurement of differential t(t)over-bar production cross sections using top quarks at large transverse momenta in pp collisions at root s=13 TeV

Author: Rumerio P.
Cooper S.I.
Henderson C.
Buccilli A.
Gleyzer S.V.
Charaf O.
CMS Collaboration
West C.
Publication venue
Publication date: 01/01/2021
Field of study

A measurement is reported of differential top quark pair

t\overline{t}

production cross sections, where top quarks are produced at large transverse momenta. The data collected with the CMS detector at the LHC are from

pp

collisions at a center-of-mass energy of

13\text{}\text{}\mathrm{TeV}

corresponding to an integrated luminosity of

35.9\text{}\text{}{\mathrm{fb}}^{-1}

. The measurement uses events where at least one top quark decays as

t\to Wb\to q{\overline{q}}^{\prime }b

and is reconstructed as a large-radius jet with transverse momentum in excess of 400 GeV. The second top quark is required to decay either in a similar way or leptonically, as inferred from a reconstructed electron or muon, a bottom quark jet, and missing transverse momentum due to the undetected neutrino. The cross section is extracted as a function of kinematic variables of individual top quarks or of the

t\overline{t}

system. The results are presented at the particle level, within a region of phase space close to that of the experimental acceptance, and at the parton level and are compared to various theoretical models. In both decay channels, the observed absolute cross sections are significantly lower than the predictions from theory, while the normalized differential measurements are well described

UA Institutional Repository (Univ. of Alabama)

Measurement of t(t)over-bar normalised multi-differential cross sections in pp collisions at root s=13 TeV, and simultaneous determination of the strong coupling strength, top quark pole mass, and parton distribution functions

Author: Rumerio P.
Cooper S.I.
Henderson C.
Buccilli A.
Charaf O.
CMS Collaboration
West C.
Publication venue
Publication date: 01/01/2020
Field of study

Normalised multi-differential cross sections for top quark pair (

\text{t}\overline{\text{t}}

) production are measured in proton-proton collisions at a centre-of-mass energy of 13

\phantom{\rule{0.166667em}{0ex}}\text{TeV}

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\phantom{\rule{0.166667em}{0ex}}{\text{fb}}^{-1}

. The double-differential

\text{t}\overline{\text{t}}

cross section is measured as a function of the kinematic properties of the top quark and of the

\text{t}\overline{\text{t}}

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

\text{t}\overline{\text{t}}

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}

and the top quark pole mass (

{m}_{\text{t}}^{\text{pole}}

) using several sets of parton distribution functions (PDFs). The measurement of

{m}_{\text{t}}^{\text{pole}}

exploits the sensitivity of the

\text{t}\overline{\text{t}}

invariant mass distribution to

{m}_{\text{t}}^{\text{pole}}

near the production threshold. Furthermore, a simultaneous fit of the PDFs,

{\alpha }_{S}

, and

{m}_{\text{t}}^{\text{pole}}

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}

and

{m}_{\text{t}}^{\text{pole}}

. The values

{\alpha }_{S}\left({m}_{\text{Z}}\right)=0.1135{}_{-0.0017}^{+0.0021}

and

{m}_{\text{t}}^{\text{pole}}=170.5±0.8\phantom{\rule{0.166667em}{0ex}}\text{GeV}

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

\text{t}\overline{\text{t}}

production threshold are neglected in these parameter extractions. A rough estimate of these effects indicates an expected correction of

{m}_{\text{t}}^{\text{pole}}

of the order of

+1\phantom{\rule{0.166667em}{0ex}}\text{GeV}

, which can be regarded as additional theoretical uncertainty in the current

{m}_{\text{t}}^{\text{pole}}

extraction

UA Institutional Repository (Univ. of Alabama)

Measurement of jet substructure observables in t(t)over-bar events from proton-proton collisions at root s=13 TeV

Author: Rumerio P.
Cooper S.I.
Henderson C.
Buccilli A.
CMS Collaboration
West C.
Publication venue
Publication date: 01/01/2018
Field of study

A measurement of jet substructure observables is presented using

t\overline{t}

events in the

\mathrm{lepton}+\text{jets}

channel from proton-proton collisions at

\sqrt{s}=13\text{}\text{}\mathrm{TeV}

recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of

35.9\text{}\text{}{\mathrm{fb}}^{-1}

. Multiple jet substructure observables are measured for jets identified as bottom, light-quark, and gluon jets, as well as for inclusive jets (no flavor information). The results are unfolded to the particle level and compared to next-to-leading-order predictions from powheg interfaced with the parton shower generators pythia 8 and herwig 7, as well as from sherpa 2 and Dire 2. A value of the strong coupling at the

Z

boson mass,

{\alpha }_{S}\left({m}_{Z}\right)=0.11{5}_{-0.013}^{+0.015}

, is extracted from the substructure data at leading-order plus leading-log accuracy

UA Institutional Repository (Univ. of Alabama)

Measurement of the top quark polarization and t(t)over-barspin correlations using dilepton final states in proton-proton collisions at root s=13 TeV

Author: Rumerio P.
Cooper S.I.
Henderson C.
Buccilli A.
Charaf O.
CMS Collaboration
West C.
Publication venue
Publication date: 01/01/2019
Field of study

Measurements of the top quark polarization and top quark pair

t\overline{t}

spin correlations are presented using events containing two oppositely charged leptons (

{e}^{+}{e}^{-}

{e}^{±}{\mu }^{\mp }

, or

{\mu }^{+}{\mu }^{-}

) produced in proton-proton collisions at a center-of-mass energy of 13 TeV. The data were recorded by the CMS experiment at the LHC in 2016 and correspond to an integrated luminosity of

35.9\text{}\text{}{\mathrm{fb}}^{-1}

. A set of parton-level normalized differential cross sections, sensitive to each of the independent coefficients of the spin-dependent parts of the

t\overline{t}

production density matrix, is measured for the first time at 13 TeV. The measured distributions and extracted coefficients are compared with standard model predictions from simulations at next-to-leading-order (NLO) accuracy in quantum chromodynamics (QCD), and from NLO QCD calculations including electroweak corrections. All measurements are found to be consistent with the expectations of the standard model. The normalized differential cross sections are used in fits to constrain the anomalous chromomagnetic and chromoelectric dipole moments of the top quark to

-0.24<{C}_{\mathrm{tG}}/{\Lambda }^{2}<0.07\text{}\text{}{\mathrm{TeV}}^{-2}

and

-0.33<{C}_{\mathrm{tG}}^{I}/{\Lambda }^{2}<0.20\text{}\text{}{\mathrm{TeV}}^{-2}

, respectively, at the 95% confidence level

UA Institutional Repository (Univ. of Alabama)

Measurement of the t(t)over-barb(b)over-bar production cross section in the all-jet final state in pp collisions at root s=13 TeV

Author: Rumerio P.
Cooper S.I.
Henderson C.
Buccilli A.
CMS Collaboration
West C.
Publication venue
Publication date: 01/01/2020
Field of study

A measurement of the production cross section of top quark pairs in association with two b jets (

t\stackrel{‾}{t}b\stackrel{‾}{b}

) is presented using data collected in proton-proton collisions at

\sqrt{s}=13\text{TeV}

by the CMS detector at the LHC corresponding to an integrated luminosity of

35.9{\text{fb}}^{-1}

. The cross section is measured in the all-jet decay channel of the top quark pair by selecting events containing at least eight jets, of which at least two are identified as originating from the hadronization of b quarks. A combination of multivariate analysis techniques is used to reduce the large background from multijet events not containing a top quark pair, and to help discriminate between jets originating from top quark decays and other additional jets. The cross section is determined for the total phase space to be

5.5±0.3\phantom{\rule{0.2em}{0ex}}{\text{(stat)}}_{-1.3}^{+1.6}\phantom{\rule{0.2em}{0ex}}\text{(syst)}\phantom{\rule{0.20em}{0ex}}\text{pb}

and also measured for two fiducial

t\stackrel{‾}{t}b\stackrel{‾}{b}

definitions. The measured cross sections are found to be larger than theoretical predictions by a factor of 1.5–2.4, corresponding to 1–2 standard deviations

UA Institutional Repository (Univ. of Alabama)

Search for electroweak production of a vector-like T quark using fully hadronic final states

Author: Rumerio P.
Cooper S.I.
Henderson C.
Buccilli A.
CMS Collaboration
West C.
Publication venue
Publication date: 01/01/2020
Field of study

A search is performed for electroweak production of a vector-like top quark partner T of charge 2/3 in association with a top or bottom quark, using proton-proton collision data at

\sqrt{s}

= 13 TeV collected by the CMS experiment at the LHC in 2016. The data sample corresponds to an integrated luminosity of 35.9 fb⁻¹. The search targets T quarks over a wide range of masses and fractional widths, decaying to a top quark and either a Higgs boson or a Z boson in fully hadronic final states. The search is performed using two experimentally distinct signatures that depend on whether or not each quark from the decays of the top quark, Higgs boson, or Z boson produces an individual resolved jet. Jet substructure, b tagging, and kinematic variables are used to identify the top quark and boson jets, and also to suppress the standard model backgrounds. The data are found to be consistent with the expected backgrounds. Upper limits at 95% confidence level are set on the cross sections for T quark-mediated production of tHQq, tZQq, and their sum, where Q is the associated top or bottom heavy quark and q is another associated quark. The limits are given for each search signature for various T quark widths up to 30% of the T quark mass, and are between 2 pb and 20 fb for T quark masses in the range 0.6–2.6 TeV. These results are significantly more sensitive than prior searches for electroweak single production of T → tH and represent the first constraints on T → tZ using hadronic decays of the Z boson with this production mode

UA Institutional Repository (Univ. of Alabama)