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Ambrogi, F.

Publications and source records attributed to Ambrogi, F..

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Observation of B$^0_s$ mesons and measurement of the B$^0_s$/B$^+$ yield ratio in PbPb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV

The B$^0_s$ and B$^+$ production yields are measured in PbPb collisions at a center-of-mass energy per nucleon pair of 5.02 TeV. The data sample, collected with the CMS detector at the LHC, corresponds to an integrated luminosity of 1.7 nb$^{-1}$. The mesons are reconstructed in the exclusive decay channels B$^0_s$$\to$ J/$\psi(\mu^+\mu^-)\phi($K$^+$K$^-)$ and B$^+$$\to$ J/$\psi(\mu^+\mu^-)$K$^+$. The B$^0_s$ meson is observed with a statistical significance in excess of five standard deviations for the first time in nucleus-nucleus collisions. The measurements are performed as functions of the transverse momentum of the B mesons and of the PbPb collision centrality. The ratio of production yields of B$^0_s$ and B$^+$ is measured and compared to theoretical models that include quark recombination effects.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Measurement of prompt open-charm production cross sections in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV

The production cross sections for prompt open-charm mesons in proton-proton collisions at a center-of-mass energy of 13 TeV are reported. The measurement is performed using a data sample collected by the CMS experiment corresponding to an integrated luminosity of 29 nb-1. The differential production cross sections of the D *± , D ± , and D 0 $(\bar{D}^0)$ mesons are presented in ranges of transverse momentum and pseudorapidity 4 < pT < 100 GeV and |η| < 2.1, respectively. The results are compared to several theoretical calculations and to previous measurements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Search for long-lived particles using displaced jets in proton-proton collisions at $\sqrt{s}$ = 13 TeV

An inclusive search is presented for long-lived particles using displaced jets. The search uses a data sample collected with the CMS detector at the CERN LHC in 2017 and 2018, from proton-proton collisions at a center-of-mass energy of 13 TeV. The results of this search are combined with those of a previous search using a data sample collected with the CMS detector in 2016, yielding a total integrated luminosity of 132 fb - 1 . The analysis searches for the distinctive topology of displaced tracks and displaced vertices associated with a dijet system. For a simplified model, where pair-produced long-lived neutral particles decay into quark-antiquark pairs, pair production cross sections larger than 0.07 fb are excluded at 95% confidence level (C.L.) for long-lived particle masses larger than 500 GeV and mean proper decay lengths between 2 and 250 mm. For a model where the standard model-like Higgs boson decays to two long-lived scalar particles that each decays to a quark-antiquark pair, branching fractions larger than 1% are excluded at 95% C.L. for mean proper decay lengths between 1 mm and 340 mm. A group of supersymmetric models with pair-produced long-lived gluinos or top squarks decaying into various final-state topologies containing displaced jets is also tested. Gluino masses up to 2500 GeV and top squark masses up to 1600 GeV are excluded at 95% C.L. for mean proper decay lengths between 3 and 300 mm. The highest lower bounds on mass reach 2600 GeV for long-lived gluinos and 1800 GeV for long-lived top squarks. These are the most stringent limits to date on these models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Measurement of prompt ${\mathrm{D^0}}$ and ${\mathrm{\overline{D}}{}^0}$ meson azimuthal anisotropy and search for strong electric fields in PbPb collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV

The strong Coulomb field created in ultrarelativistic heavy ion collisions is expected to produce a rapidity-dependent difference ( Δv 2 ) in the second Fourier coefficient of the azimuthal distribution (elliptic flow, v 2 ) between D 0 ( $\bar{u}c$ ) and ${\mathrm{\overline{D}}{}^0}$ ( $u\bar{c}$ ) mesons. Motivated by the search for evidence of this field, the CMS detector at the LHC is used to perform the first measurement of Δv 2 . The rapidity-averaged value is found to be &lang;Δv2&rang;=0.001±0.001(stat)±0.003(syst) in PbPb collisions at $\sqrt{s_{NN}}$=5.02 TeV . In addition, the influence of the collision geometry is explored by measuring the D 0 and ${\mathrm{\overline{D}}{}^0}$ mesons v 2 and triangular flow coefficient ( v 3 ) as functions of rapidity, transverse momentum ( p T ), and event centrality (a measure of the overlap of the two Pb nuclei). A clear centrality dependence of prompt D 0 meson v 2 values is observed, while the v 3 is largely independent of centrality. These trends are consistent with expectations of flow driven by the initial-state geometry.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Measurement of differential t t ¯ production cross sections using top quarks at large transverse momenta in p p collisions at s = 13 TeV

A measurement is reported of differential top quark pair (${t\bar{t}}$) 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 TeV corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The measurement uses events where at least one top quark decays as t$ \to $Wb $ \to q\bar{q}'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 a 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 ${t\bar{t}}$ 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.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Correlations of azimuthal anisotropy Fourier harmonics with subevent cumulants in p Pb collisions at s N N = 8.16 TeV

Event-by-event long-range correlations of azimuthal anisotropy Fourier coefficients ($v_n$) in 8.16 TeV p Pb data, collected by the CMS experiment at the CERN Large Hadron Collider, are extracted using a subevent four-particle cumulant technique applied to very low multiplicity events. Each combination of four charged particles is selected from either two, three, or four distinct subevent regions of a pseudorapidity range from -2.4 to 2.4 of the CMS tracker, and with transverse momentum between 0.3 and 3.0 GeV. Using the subevent cumulant technique, correlations between $v_n$ of different orders are measured as functions of particle multiplicity and compared to the standard cumulant method without subevents over a wide event multiplicity range. At high multiplicities, the $v_2$ and $v_3$ coefficients exhibit an anticorrelation; this behavior is observed consistently using various methods. The $v_2$ and $v_4$ correlation strength is found to depend on the number of subevents used in the calculation. As the event multiplicity decreases, the results from different subevent methods diverge because of different contributions of noncollective or few-particle correlations. Correlations extracted with the four-subevent method exhibit a tendency to diminish monotonically toward the lowest multiplicity region (about 20 charged tracks) investigated. These findings extend previous studies to a significantly lower event multiplicity range and establish the evidence for the onset of long-range collective multiparticle correlations in small system collisions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Reconstruction of signal amplitudes in the CMS electromagnetic calorimeter in the presence of overlapping proton-proton interactions

A template fitting technique for reconstructing the amplitude of signals produced by the lead tungstate crystals of the CMS electromagnetic calorimeter is described. This novel approach is designed to suppress the contribution to the signal of the increased number of out-of-time interactions per beam crossing following the reduction of the accelerator bunch spacing from 50 to 25 ns at the start of Run 2 of the LHC. Execution of the algorithm is sufficiently fast for it to be employed in the CMS high-level trigger. It is also used in the offline event reconstruction. Results obtained from simulations and from Run 2 collision data (2015–2018) demonstrate a substantial improvement in the energy resolution of the calorimeter over a range of energies extending from a few GeV to several tens of GeV.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Measurements of $t\overline tH$ Production and the CP Structure of the Yukawa Interaction between the Higgs Boson and Top Quark in the Diphoton Decay Channel

The first observation of the t t ¯ H process in a single Higgs boson decay channel with the full reconstruction of the final state ( H → γ γ ) is presented, with a significance of 6.6 standard deviations ( σ ). The C P structure of Higgs boson couplings to fermions is measured, resulting in an exclusion of the pure C P -odd structure of the top Yukawa coupling at 3.2 σ . The measurements are based on a sample of proton-proton collisions at a center-of-mass energy s = 13 TeV collected by the CMS detector at the LHC, corresponding to an integrated luminosity of 137 fb – 1 . The cross section times branching fraction of the t t ¯ H process is measured to be σ t t ¯ H B γ γ = 1.56 – 0.32 + 0.34 fb , which is compatible with the standard model prediction of 1.13 – 0.11 + 0.08 fb . The fractional contribution of the C P -odd component is measured to be f C P H t t = 0.00 ± 0.33 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗