Lund University Publications
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Lund University Lund University Publications
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Enhanced Production of Λb0 Baryons in High-Multiplicity pp Collisions at s =13 TeV
https://lup.lub.lu.se/search/publication/4a81f8be-4e52-4703-a7ba-2f003d05344f
Aaij, R.
Ruiz-Vidal, Joan
Zunica, G.
2024
The production rate of Λb0 baryons relative to B0 mesons in pp collisions at a center-of-mass energy s=13 TeV is measured by the LHCb experiment. The ratio of Λb0 to B0 production cross sections shows a significant dependence on both the transverse momentum and the measured charged-particle multiplicity. At low multiplicity, the ratio measured at LHCb is consistent with the value measured in e+e- collisions, and increases by a factor of ∼2 with increasing multiplicity. At relatively low transverse momentum, the ratio of Λb0 to B0 cross sections is higher than what is measured in e+e- collisions, but converges with the e+e- ratio as the momentum increases. These results imply that the evolution of heavy b quarks into final-state hadrons is influenced by the density of the hadronic environment produced in the collision. Comparisons with several models and implications for the mechanisms enforcing quark confinement are discussed. © 2024 CERN.
https://lup.lub.lu.se/record/4a81f8be-4e52-4703-a7ba-2f003d05344f
http://dx.doi.org/10.1103/PhysRevLett.132.081901
scopus:85185840573
eng
Physical Review Letters; 132(8), no 081901 (2024)
ISSN: 1079-7114
Subatomic Physics
Hadrons
Momentum
Tellurium compounds
A-center
Center-of-mass energies
Centre-of-mass energies
Charged particle multiplicities
Final state
Hadronics
High multiplicity
Production cross section
Production rates
Transverse momenta
article
baryon
Charged particles
Enhanced Production of Λb0 Baryons in High-Multiplicity pp Collisions at s =13 TeV
contributiontojournal/article
info:eu-repo/semantics/article
text
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Helium identification with LHCb
https://lup.lub.lu.se/search/publication/84873b1e-9c4c-4013-b3e3-c26fe5247563
Aaij, R.
Ruiz-Vidal, Joan
Zunica, G.
2024
The identification of helium nuclei at LHCb is achieved using a method based on measurements of ionisation losses in the silicon sensors and timing measurements in the Outer Tracker drift tubes. The background from photon conversions is reduced using the RICH detectors and an isolation requirement. The method is developed using pp collision data at √s = 13 TeV recorded by the LHCb experiment in the years 2016 to 2018, corresponding to an integrated luminosity of 5.5 fb−1. A total of around 105 helium and antihelium candidates are identified with negligible background contamination. The helium identification efficiency is estimated to be approximately 50% with a corresponding background rejection rate of up to O(1012). These results demonstrate the feasibility of a rich programme of measurements of QCD and astrophysics interest involving light nuclei. © 2024 Institute of Physics. All rights reserved.
https://lup.lub.lu.se/record/84873b1e-9c4c-4013-b3e3-c26fe5247563
http://dx.doi.org/10.1088/1748-0221/19/02/P02010
scopus:85185549843
eng
Journal of Instrumentation; 19(2), no P02010 (2024)
ISSN: 1748-0221
Accelerator Physics and Instrumentation
Subatomic Physics
dE/dx detectors
Ion identification systems
Large detector systems for particle and astroparticle physics
Particle identification methods
Astrophysics
Tellurium compounds
Astroparticle physics
De/dx detector
Detector systems
Helium nuclei
Ion identification system
Ion identifications
Large detector system for particle and astroparticle physic
Large detectors
Measurements of
Particle Identification Method
Helium
Helium identification with LHCb
contributiontojournal/article
info:eu-repo/semantics/article
text
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Momentum scale calibration of the LHCb spectrometer
https://lup.lub.lu.se/search/publication/81f434b5-4bf3-43a7-8bd2-64138194de8c
Aaij, R.
Ruiz-Vidal, Joan
Zunica, G.
2024
For accurate determination of particle masses accurate knowledge of the momentum scale of the detectors is crucial. The procedure used to calibrate the momentum scale of the LHCb spectrometer is described and illustrated using the performance obtained with an integrated luminosity of 1.6 fb−1 collected during 2016 in pp running. The procedure uses large samples of J/ → +− and B+ → J/K+ decays and leads to a relative accuracy of 3 × 10−4 on the momentum scale. © 2024 Institute of Physics. All rights reserved.
https://lup.lub.lu.se/record/81f434b5-4bf3-43a7-8bd2-64138194de8c
http://dx.doi.org/10.1088/1748-0221/19/02/P02008
scopus:85185551130
eng
Journal of Instrumentation; 19(2), no P02008 (2024)
ISSN: 1748-0221
Subatomic Physics
Analysis
Particle tracking detectors
statistical methods
Spectrometers
Analyse
Integrated luminosity
Particle mass
Particle tracking
Particle tracking detector
Performance
Relative accuracy
Scale calibration
Tracking detectors
Momentum
Momentum scale calibration of the LHCb spectrometer
contributiontojournal/article
info:eu-repo/semantics/article
text
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Femtoscopic correlations of identical charged pions and kaons in pp collisions at s =13 TeV with event-shape selection
https://lup.lub.lu.se/search/publication/53357f36-bc89-46e6-b40c-2f701896d950
Acharya, S.
Basu, S.
Christiansen, P.
Hansen, J.
Iversen, K.E.
Matonoha, O.
Nepeivoda, R.
Ohlson, A.
Silvermyr, D.
Staa, J.
Vislavicius, V.
Zurlo, N.
2024
Collective behavior has been observed in high-energy heavy-ion collisions for several decades. Collectivity is driven by the high particle multiplicities that are produced in these collisions. At the CERN Large Hadron Collider (LHC), features of collectivity have also been seen in high-multiplicity proton-proton collisions that can attain particle multiplicities comparable to peripheral Pb-Pb collisions. One of the possible signatures of collective behavior is the decrease of femtoscopic radii extracted from pion and kaon pairs emitted from high-multiplicity collisions with increasing pair transverse momentum. This decrease can be described in terms of an approximate transverse mass scaling. In the present work, femtoscopic analyses are carried out by the ALICE Collaboration on charged pion and kaon pairs produced in pp collisions at s=13TeV from the LHC to study possible collectivity in pp collisions. The event-shape analysis method based on transverse sphericity is used to select for spherical versus jetlike events, and the effects of this selection on the femtoscopic radii for both charged pion and kaon pairs are studied. This is the first time this selection method has been applied to charged kaon pairs. An approximate transverse-mass scaling of the radii is found in all multiplicity ranges studied when the difference in the Lorentz boost for pions and kaons is taken into account. This observation does not support the hypothesis of collective expansion of hot and dense matter that should only occur in high-multiplicity events. A possible alternate explanation of the present results is based on a scenario of common emission conditions for pions and kaons in pp collisions for the multiplicity ranges studied. © 2024 CERN.
https://lup.lub.lu.se/record/53357f36-bc89-46e6-b40c-2f701896d950
http://dx.doi.org/10.1103/PhysRevC.109.024915
scopus:85186217652
eng
Physical Review C; 109(2), no 024915 (2024)
ISSN: 2469-9985
Subatomic Physics
Femtoscopic correlations of identical charged pions and kaons in pp collisions at s =13 TeV with event-shape selection
contributiontojournal/article
info:eu-repo/semantics/article
text
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Measurements of inclusive J/ψ production at midrapidity and forward rapidity in Pb–Pb collisions at sNN = 5.02 TeV
https://lup.lub.lu.se/search/publication/819bd7db-ac65-4b24-86db-7c33f51b8a9f
Acharya, S.
Basu, S.
Christiansen, P.
Hansen, J.
Iversen, K.E.
Matonoha, O.
Nassirpour, A.F.
Ohlson, A.
Silvermyr, D.
Staa, J.
Vislavicius, V.
Zurlo, N.
2024
https://lup.lub.lu.se/record/819bd7db-ac65-4b24-86db-7c33f51b8a9f
http://dx.doi.org/10.1016/j.physletb.2024.138451
scopus:85185297531
eng
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics; 849, no 138451 (2024)
ISSN: 0370-2693
Subatomic Physics
Measurements of inclusive J/ψ production at midrapidity and forward rapidity in Pb–Pb collisions at sNN = 5.02 TeV
contributiontojournal/article
info:eu-repo/semantics/article
text
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Search for New Phenomena in Two-Body Invariant Mass Distributions Using Unsupervised Machine Learning for Anomaly Detection at √s = 13 TeV with the ATLAS Detector
https://lup.lub.lu.se/search/publication/f0f650f1-831f-4456-adac-b898d2580c3b
Aad, G.
Åkesson, T.P.A.
Corrigan, E.E.
Doglioni, C.
Geisen, J.
Hansen, E.
Hedberg, V.
Herde, Hannah
Konya, B.
Lytken, E.
Poettgen, R.
Simpson, N.D.
Smirnova, O.
Zwalinski, L.
2024
Searches for new resonances are performed using an unsupervised anomaly-detection technique. Events with at least one electron or muon are selected from 140 fb−1 of pp collisions at √s ¼ 13 TeV recorded by ATLAS at the Large Hadron Collider. The approach involves training an autoencoder on data, and subsequently defining anomalous regions based on the reconstruction loss of the decoder. Studies focus on nine invariant mass spectra that contain pairs of objects consisting of one light jet or b jet and either one lepton (e; μ), photon, or second light jet or b jet in the anomalous regions. No significant deviations from the background hypotheses are observed. Limits on contributions from generic Gaussian signals with various widths of the resonance mass are obtained for nine invariant masses in the anomalous regions. © 2024 CERN, for the ATLAS Collaboration.
https://lup.lub.lu.se/record/f0f650f1-831f-4456-adac-b898d2580c3b
http://dx.doi.org/10.1103/PhysRevLett.132.081801
scopus:85186742137
eng
Physical Review Letters; 132(8), no 081801 (2024)
ISSN: 0031-9007
Subatomic Physics
Anomaly detection
Machine learning
Tellurium compounds
Anomalous regions
ATLAS detectors
Auto encoders
Invariant mass distribution
Large Hadron Collider
Large-hadron colliders
Region-based
Unsupervised anomaly detection
Unsupervised machine learning
Mass spectrometry
Search for New Phenomena in Two-Body Invariant Mass Distributions Using Unsupervised Machine Learning for Anomaly Detection at √s = 13 TeV with the ATLAS Detector
contributiontojournal/article
info:eu-repo/semantics/article
text
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Probing the CP nature of the top–Higgs Yukawa coupling in tt¯H and tH events with H→bb¯ decays using the ATLAS detector at the LHC
https://lup.lub.lu.se/search/publication/1eb12e70-d39e-40ce-bd85-55db21558153
Aad, G.
Åkesson, T.P.A.
Corrigan, E.E.
Doglioni, C.
Ekman, P.A.
Geisen, J.
Hedberg, V.
Jarlskog, G.
Konya, B.
Lytken, E.
Mankinen, K.H.
Marcon, C.
Mjörnmark, J.U.
Mullier, G.A.
Poettgen, R.
Simpson, N.D.
Skorda, E.
Smirnova, O.
Zwalinski, L.
2024
The CP properties of the coupling between the Higgs boson and the top quark are investigated using 139 fb−1 of proton–proton collision data recorded by the ATLAS experiment at the LHC at a centre-of-mass energy of s=13 TeV. The CP structure of the top quark–Higgs boson Yukawa coupling is probed in events with a Higgs boson decaying into a pair of b-quarks and produced in association with either a pair of top quarks, tt¯H, or a single top quark, tH. Events containing one or two electrons or muons are used for the measurement. Multivariate techniques are used to select regions enriched in tt¯H and tH events, where dedicated CP-sensitive observables are exploited. In an extension of the Standard Model (SM) with a CP-odd admixture in the top–Higgs Yukawa coupling, the mixing angle between CP-even and CP-odd couplings is measured to be α=11−73∘+52, compatible with the SM prediction corresponding to α=0. © 2024 The Author(s)
https://lup.lub.lu.se/record/1eb12e70-d39e-40ce-bd85-55db21558153
http://dx.doi.org/10.1016/j.physletb.2024.138469
scopus:85185283920
eng
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics; 849, no 138469 (2024)
ISSN: 0370-2693
Subatomic Physics
Probing the CP nature of the top–Higgs Yukawa coupling in tt¯H and tH events with H→bb¯ decays using the ATLAS detector at the LHC
contributiontojournal/article
info:eu-repo/semantics/article
text
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Electron and photon energy calibration with the ATLAS detector using LHC Run 2 data
https://lup.lub.lu.se/search/publication/e006cc7e-6f10-44c9-b531-0608ad773897
Aad, G
Åkesson, Torsten
Doglioni, Caterina
Ekman, Alexander
Hedberg, Vincent
Herde, Hannah
Konya, Balazs
Lytken, Else
Pöttgen, Ruth
Simpson, Nathan Daniel
Smirnova, Oxana
Zwalinski, L.
2024
This paper presents the electron and photon energy calibration obtained with the ATLAS detector using 140 fb−1 of LHC proton-proton collision data recorded at √s = 13 TeV between 2015 and 2018. Methods for the measurement of electron and photon energies are outlined, along with the current knowledge of the passive material in front of the ATLAS electromagnetic calorimeter. The energy calibration steps are discussed in detail, with emphasis on the improvements introduced in this paper. The absolute energy scale is set using a large sample of Z-boson decays into electron-positron pairs, and its residual dependence on the electron energy is used for the first time to further constrain systematic uncertainties. The achieved calibration uncertainties are typically 0.05% for electrons from resonant Z-boson decays, 0.4% at ET ∼ 10 GeV, and 0.3% at ET ∼ 1 TeV; for photons at ET ∼ 60 GeV, they are 0.2% on average. This is more than twice as precise as the previous calibration. The new energy calibration is validated using J/ → ee and radiative Z-boson decays. © 2024 Institute of Physics. All rights reserved.
https://lup.lub.lu.se/record/e006cc7e-6f10-44c9-b531-0608ad773897
http://dx.doi.org/10.1088/1748-0221/19/02/P02009
scopus:85185886671
eng
Journal of Instrumentation; 19(2), no P02009 (2024)
ISSN: 1748-0221
Subatomic Physics
calibration
Calorimeter methods; Pattern recognition
cluster finding
fitting methods; Performance of High Energy Physics Detectors
Bosons
Calorimeters
Electron energy levels
Electrons
Pattern recognition
Photons
Tellurium compounds
Calorimeter method;
Cluster finding
Electrons energy
Energy calibration
Fitting method
Fitting method;
High energy physics detector
Performance
Performance of high energy physic detector
Photon energy
Calibration
Electron and photon energy calibration with the ATLAS detector using LHC Run 2 data
contributiontojournal/article
info:eu-repo/semantics/article
text