Multidifferential study of identified charged hadron distributions in ZZ-tagged jets in proton-proton collisions at s=\sqrt{s}=13 TeV

Jet fragmentation functions are measured for the first time in proton-proton collisions for charged pions, kaons, and protons within jets recoiling against a $Z$ boson. The charged-hadron distributions are studied longitudinally and transversely to the jet direction for jets with transverse momentum 20 $< p_{\textrm{T}} < 100$ GeV and in the pseudorapidity range $2.5 < \eta < 4$. The data sample was collected with the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.64 fb$^{-1}$. Triple differential distributions as a function of the hadron longitudinal momentum fraction, hadron transverse momentum, and jet transverse momentum are also measured for the first time. This helps constrain transverse-momentum-dependent fragmentation functions. Differences in the shapes and magnitudes of the measured distributions for the different hadron species provide insights into the hadronization process for jets predominantly initiated by light quarks.Comment: All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-013.html (LHCb public pages

Study of the B−→Λc+Λˉc−K−B^{-} \to \Lambda_{c}^{+} \bar{\Lambda}_{c}^{-} K^{-} decay

The decay $B^{-} \to \Lambda_{c}^{+} \bar{\Lambda}_{c}^{-} K^{-}$ is studied in proton-proton collisions at a center-of-mass energy of $\sqrt{s}=13$ TeV using data corresponding to an integrated luminosity of 5 $\mathrm{fb}^{-1}$ collected by the LHCb experiment. In the $\Lambda_{c}^+ K^{-}$ system, the $\Xi_{c}(2930)^{0}$ state observed at the BaBar and Belle experiments is resolved into two narrower states, $\Xi_{c}(2923)^{0}$ and $\Xi_{c}(2939)^{0}$, whose masses and widths are measured to be $$m(\Xi_{c}(2923)^{0}) = 2924.5 \pm 0.4 \pm 1.1 \,\mathrm{MeV}, \\ m(\Xi_{c}(2939)^{0}) = 2938.5 \pm 0.9 \pm 2.3 \,\mathrm{MeV}, \\ \Gamma(\Xi_{c}(2923)^{0}) = \phantom{000}4.8 \pm 0.9 \pm 1.5 \,\mathrm{MeV},\\ \Gamma(\Xi_{c}(2939)^{0}) = \phantom{00}11.0 \pm 1.9 \pm 7.5 \,\mathrm{MeV},$$ where the first uncertainties are statistical and the second systematic. The results are consistent with a previous LHCb measurement using a prompt $\Lambda_{c}^{+} K^{-}$ sample. Evidence of a new $\Xi_{c}(2880)^{0}$ state is found with a local significance of $3.8\,\sigma$, whose mass and width are measured to be $2881.8 \pm 3.1 \pm 8.5\,\mathrm{MeV}$ and $12.4 \pm 5.3 \pm 5.8 \,\mathrm{MeV}$, respectively. In addition, evidence of a new decay mode $\Xi_{c}(2790)^{0} \to \Lambda_{c}^{+} K^{-}$ is found with a significance of $3.7\,\sigma$. The relative branching fraction of $B^{-} \to \Lambda_{c}^{+} \bar{\Lambda}_{c}^{-} K^{-}$ with respect to the $B^{-} \to D^{+} D^{-} K^{-}$ decay is measured to be $2.36 \pm 0.11 \pm 0.22 \pm 0.25$, where the first uncertainty is statistical, the second systematic and the third originates from the branching fractions of charm hadron decays.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-028.html (LHCb public pages

Measurement of the ratios of branching fractions R(D∗)\mathcal{R}(D^{*}) and R(D0)\mathcal{R}(D^{0})

The ratios of branching fractions $\mathcal{R}(D^{*})\equiv\mathcal{B}(\bar{B}\to D^{*}\tau^{-}\bar{\nu}_{\tau})/\mathcal{B}(\bar{B}\to D^{*}\mu^{-}\bar{\nu}_{\mu})$ and $\mathcal{R}(D^{0})\equiv\mathcal{B}(B^{-}\to D^{0}\tau^{-}\bar{\nu}_{\tau})/\mathcal{B}(B^{-}\to D^{0}\mu^{-}\bar{\nu}_{\mu})$ are measured, assuming isospin symmetry, using a sample of proton-proton collision data corresponding to 3.0 fb${ }^{-1}$ of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode $\tau^{-}\to\mu^{-}\nu_{\tau}\bar{\nu}_{\mu}$. The measured values are $\mathcal{R}(D^{*})=0.281\pm0.018\pm0.024$ and $\mathcal{R}(D^{0})=0.441\pm0.060\pm0.066$, where the first uncertainty is statistical and the second is systematic. The correlation between these measurements is $\rho=-0.43$. Results are consistent with the current average of these quantities and are at a combined 1.9 standard deviations from the predictions based on lepton flavor universality in the Standard Model.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-039.html (LHCb public pages

Exotic diboson searches in the ℓνqq\ell\nu qq final state using proton-proton collisions data at s=13 TeV\sqrt{s} = 13\ TeV collected with the ATLAS detector.

Analyses searching for diboson resonances are very powerful tools to investigate many beyond the Standard Model scenarios such as extension of the Higgs sector, Heavy Vector triplets ($W^{'}$ and $Z^{'}$) or excited states of Gravitons. These searches exploit the many decay channels of the two bosons allowing to select topologies with varied signal to background ratios and statistics. Among these searches the one looking for $WW$/$WZ$ in the semileptonic final state finds a compromise between the high signal statistics allowed by the high branching ratio of the hadronic decay of the gauge boson while profiting of the good trigger and analysis signature of the lepton, decay product of the second gauge boson. The $WW$/$WZ$ search for TeV scale resonances in the $\ell\nu qq$ channel with 36.1~\ifb of data collected with the ATLAS detector at \sqrt{s} = 13 \TeV will be detailed. No significant excess is observed in data with respect to the Standard Model backgrounds. Limits on the production cross section are set for various benchmark scenarios

Ricerca di risonanze di-bosoniche nello stato finale semi-leptonico (lvqq) in collisioni protone-protone a s=13\sqrt{s}= 13 TeV collezionate con il rivelatore ATLAS.

With the discovery of the Higgs boson by the ATLAS and CMS experiments at the LHC at CERN in 2012, the Standard Model is now complete, yet unanswered questions are still present. In example the Standard Model does not explain the hierarchy between the weak and Planck scales, nor it includes a dark matter candidate, nor it explain the origin of barion asymmetry. For this reason, one of the goals of particle physics research is to find new hints of physics beyond the Standard Model that could answer some of these questions. Analyses searching for di-boson resonances are a very powerful tool to investigate many beyond the Standard Model scenarios such as extension of the Higgs sector, Heavy Vector triplets (W' and Z' ) or excited states of Gravitons. These searches exploit many decay channels of the two bosons allowing to select topologies with varied signal to background ratios and statistics. This thesis describes the search for new resonances decaying to a pair of massive vector bosons (X → WW, W Z) in a 36.1 fb −1 data sample of proton-proton collisions produced at a centre-of-mass energy of √s = 13TeV collected with the ATLAS detector. The final state is reconstructed through the semi-leptonic decays lνqq (l = e, μ) of the two vector bosons

Exotic diboson searches in the ℓνqq\ell\nu qq final state using data at s=13 TeV\sqrt{s}=13\, TeV collected with the ATLAS detector

Analyses searching for diboson resonances are very powerful tools to investigate many beyond the Standard Model (BSM) scenarios such as extension of the Higgs sector, Heavy Vector triplets (W’ and Z’) or excited states of Gravitons. These searches exploit the many decay channels of the two bosons allowing to select topologies with varied signal to background ratios and statistics. Among these searches the search for WW/WZ in the semileptonic final state finds a compromise between the high signal statistics allowed by the high branching ratio of the hadronic decay of the gauge boson while profiting of the good trigger and analysis signature of the lepton, decay product of the second gauge boson. The WW/WZ search for TeV scale resonances in the ℓνqq channel will be detailed, explaining the current boson-tagging techniques and the signal categorization used to improve sensitivity. The limit presently set in the various scenarios using 2015-2016 dataset will be reported

ATLAS Searches for VH, HH, VV, V+gamma/gammagamma Resonances

The discovery of a Higgs boson at the Large Hadron Collider (LHC) motivates searches for physics beyond the Standard Model (SM) in channels involving coupling to the Higgs boson. A search for a massive resonance decaying into a standard model Higgs boson (h) and a W or Z boson or two a standard model Higgs bosons is performed. Final states with different number of leptons or photons and where in many cases at least one Higgs decays into a b-quark pair are studied using different jet reconstruction techniques which are complementary in their acceptance for low and high mass transverse momentum. This talk summarizes ATLAS searches for diboson resonances including at least one h boson in the final state and searches for resonant and non-resonant di-Higgs production with LHC Run 2 data

First performance measurements of the Fast Tracker Real Time Processor at ATLAS

Real time track reconstruction at hadron colliders is one of the most powerful tools to select interesting events from the huge background while mitigating the effect of pile-up. The Fast Tracker, an upgrade to the current ATLAS trigger system, will feed the High Level Trigger with high quality tracks reconstructed over the entire detector at 100 kHz rate. This is accomplished by dividing the detector into 64 η−ϕ towers. Each tower is processed by a dedicated asynchronous, data-driven pipeline. The combinatorial challenge inherent to tracking is solved with the use of Associative Memory ASICs that compare inner detector hits to millions of pre-calculated patterns simultaneously. The tracking problem within matched patterns is further simplified by using pre-computed linearized fitting constants and leveraging fast digital signal processing in modern commercial FPGAs. Half of the system has been produced and integration in ATLAS is proceeding to demonstrate functionality with real data with a partial detector coverage. We show the first results on system performance studies. Tracks were reconstructed and validated with Fast Tracker functional simulation. The system integration in the ATLAS experiment is progressing through 2018 to reach stable track processing. These studies will continue by evaluating the Fast Tracker tracking resolution and latency on real data. Those measurements will allow optimization of the system improving its performance. We report results of this first important experience with data in preparation of the full Fast Tracker operational conditions in 2021

Integration and Commissioning of the Fast TracKer system

The Fast TracKer (FTK) system is a track reconstruction processor able to perform full event tracking synchronously with the ATLAS Level 1 trigger acceptance rate. The high quality tracks produced by the system will be used by the High Level Trigger algorithms to improve the iden- tification of physics objects such as b-jets and taus, as well as to help mitigating the effects of pile-up. The combinatorial challenge of global track fitting requires the use of a custom designed track processor. The idea behind the Fast TracKer system is to simulate all possible tracks before an ATLAS data taking run. During the actual data-taking, the hits coming from the detector are compared with the hits expected from the simulated tracks. This comparison or ‘pattern match- ing’ is then followed by a two step linearized track fit. This task is executed by a system of seven custom electronics board types that will process data from the Inner Detector at the 100 kHz rate of the Level 1 trigger. Currently, the FTK system is under installation and commissioning into the ATLAS Data Acquisition System. The status of the system integration is presented and a review of the first data collected by the FTK system is shown

ATLAS Searches for VV, VH and HH Resonances

The unprecedented datasets of Run 2 LHC are scanned for new particles decaying to pairs of bosons, VV, VH or HH, where V represents W or H. Final states with different number of leptons and where the Higgs decays into a b-quark pair are studied using different jet reconstruction techniques which are complementary in their acceptance for low and high mass transverse momentum. The new particle may be produced from quark or gluon fusion, or through vector boson fusion. This talk summarizes the latest ATLAS searches in this are