Wei Li
· ProfessorRice University · Physics
Active 1991–2024
About
Wei Li is a Professor of Physics and Astronomy at Rice University and a Rice Academy Senior Fellow. His research interests include UPCs, collectivity, and MTD. He is involved in experimental nuclear and particle physics at colliders, focusing on the development and application of novel particle detectors. As a faculty member, he contributes to advancing the understanding of fundamental particles and their interactions through experimental investigations.
Research topics
- Physics
- Particle physics
- Nuclear physics
- Computer Science
- Quantum mechanics
- Optics
- Algorithm
- Artificial Intelligence
- Astrophysics
- Geology
- Mechanics
- Geography
- Mathematical analysis
- Astronomy
Selected publications
Dark sector searches with the CMS experiment
Physics Reports · 2024 · 22 citations
- Physics
- Particle physics
- Astrophysics
Astrophysical observations provide compelling evidence for gravitationally interacting dark matter in the universe that cannot be explained by the standard model of particle physics. The extraordinary amount of data from the CERN LHC presents a unique opportunity to shed light on the nature of dark matter at unprecedented collision energies. This Report comprehensively reviews the most recent searches with the CMS experiment for particles and interactions belonging to a dark sector and for dark-sector mediators. Models with invisible massive particles are probed by searches for signatures of missing transverse momentum recoiling against visible standard model particles. Searches for mediators are also conducted via fully visible final states. The results of these searches are compared with those obtained from direct-detection experiments. Searches for alternative scenarios predicting more complex dark sectors with multiple new particles and new forces are also presented. Many of these models include long-lived particles, which could manifest themselves with striking unconventional signatures with relatively small amounts of background. Searches for such particles are discussed and their impact on dark-sector scenarios is evaluated. Many results and interpretations have been newly obtained for this Report.
Model-independent search for pair production of new bosons decaying into muons in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV
arXiv (Cornell University) · 2024 · 2 citations
- Physics
- Particle physics
- Nuclear physics
A bstract The results of a model-independent search for the pair production of new bosons within a mass range of 0 . 21 < m < 60 GeV, are presented. This study utilizes events with a four-muon final state. We use two data sets, comprising 41 . 5 fb − 1 and 59 . 7 fb − 1 of proton-proton collisions at $$ \sqrt{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math> = 13 TeV, recorded in 2017 and 2018 by the CMS experiment at the CERN LHC. The study of the 2018 data set includes a search for displaced signatures of a new boson within the proper decay length range of 0 < cτ < 100 mm. Our results are combined with a previous CMS result, based on 35 . 9 fb − 1 of proton-proton collisions at $$ \sqrt{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math> = 13 TeV collected in 2016. No significant deviation from the expected background is observed. Results are presented in terms of a model-independent upper limit on the product of cross section, branching fraction, and acceptance. The findings are interpreted across various benchmark models, such as an axion-like particle model, a vector portal model, the next-to-minimal supersymmetric standard model, and a dark supersymmetric scenario, including those predicting a non-negligible proper decay length of the new boson. In all considered scenarios, substantial portions of the parameter space are excluded, expanding upon prior results.
Physical Review Letters · 2024 · 96 citations
- Physics
A search is reported for near-threshold structures in the J/ψJ/ψ invariant mass spectrum produced in proton-proton collisions at sqrt[s]=13 TeV from data collected by the CMS experiment, corresponding to an integrated luminosity of 135 fb^{-1}. Three structures are found, and a model with quantum interference among these structures provides a good description of the data. A new structure is observed with a local significance above 5 standard deviations at a mass of 6638_{-38}^{+43}(stat)_{-31}^{+16}(syst) MeV. Another structure with even higher significance is found at a mass of 6847_{-28}^{+44}(stat)_{-20}^{+48}(syst) MeV, which is consistent with the X(6900) resonance reported by the LHCb experiment and confirmed by the ATLAS experiment. Evidence for another new structure, with a local significance of 4.7 standard deviations, is found at a mass of 7134_{-25}^{+48}(stat)_{-15}^{+41}(syst) MeV. Results are also reported for a model without interference, which does not fit the data as well and shows mass shifts up to 150 MeV relative to the model with interference.
Journal of High Energy Physics · 2023 · 69 citations
- Physics
- Particle physics
- Nuclear physics
A bstract Three searches are presented for signatures of physics beyond the standard model (SM) in ττ final states in proton-proton collisions at the LHC, using a data sample collected with the CMS detector at $$ \sqrt{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math> = 13 TeV, corresponding to an integrated luminosity of 138 fb − 1 . Upper limits at 95% confidence level (CL) are set on the products of the branching fraction for the decay into τ leptons and the cross sections for the production of a new boson ϕ , in addition to the H(125) boson, via gluon fusion (gg ϕ ) or in association with b quarks, ranging from $$ \mathcal{O} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>O</mml:mi> </mml:math> (10 pb) for a mass of 60 GeV to 0.3 fb for a mass of 3.5 TeV each. The data reveal two excesses for gg ϕ production with local p -values equivalent to about three standard deviations at m ϕ = 0 . 1 and 1.2 TeV. In a search for t -channel exchange of a vector leptoquark U 1 , 95% CL upper limits are set on the dimensionless U 1 leptoquark coupling to quarks and τ leptons ranging from 1 for a mass of 1 TeV to 6 for a mass of 5 TeV, depending on the scenario. In the interpretations of the $$ {M}_{\textrm{h}}^{125} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>M</mml:mi> <mml:mi>h</mml:mi> <mml:mn>125</mml:mn> </mml:msubsup> </mml:math> and $$ {M}_{\textrm{h},\textrm{EFT}}^{125} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>M</mml:mi> <mml:mrow> <mml:mi>h</mml:mi> <mml:mo>,</mml:mo> <mml:mi>EFT</mml:mi> </mml:mrow> <mml:mn>125</mml:mn> </mml:msubsup> </mml:math> minimal supersymmetric SM benchmark scenarios, additional Higgs bosons with masses below 350 GeV are excluded at 95% CL.
Physics Letters B · 2023 · 75 citations
- Computer Science
- Physics
- Algorithm
Measurements are presented of the Bs0→μ+μ− branching fraction and effective lifetime, as well as results of a search for the B0→μ+μ− decay in proton-proton collisions at s=13TeV at the LHC. The analysis is based on data collected with the CMS detector in 2016–2018 corresponding to an integrated luminosity of 140fb−1. The branching fraction of the Bs0→μ+μ− decay and the effective Bs0 meson lifetime are the most precise single measurements to date. No evidence for the B0→μ+μ− decay has been found. All results are found to be consistent with the standard model predictions and previous measurements.
Identification of hadronic tau lepton decays using a deep neural network
Journal of Instrumentation · 2022 · 51 citations
- Physics
- Particle physics
- Nuclear physics
A new algorithm is presented to discriminate reconstructed hadronic decays of tau leptons (τ h) that originate from genuine tau leptons in the CMS detector against τ h candidates that originate from quark or gluon jets, electrons, or muons. The algorithm inputs information from all reconstructed particles in the vicinity of a τ h candidate and employs a deep neural network with convolutional layers to efficiently process the inputs. This algorithm leads to a significantly improved performance compared with the previously used one. For example, the efficiency for a genuine τ h to pass the discriminator against jets increases by 10-30% for a given efficiency for quark and gluon jets. Furthermore, a more efficient τ h reconstruction is introduced that incorporates additional hadronic decay modes. The superior performance of the new algorithm to discriminate against jets, electrons, and muons and the improved τ h reconstruction method are validated with LHC proton-proton collision data at s = 13 TeV.
A portrait of the Higgs boson by the CMS experiment ten years after the discovery
Nature · 2022 · 320 citations
- Physics
- Particle physics
- Nuclear physics
In July 2012, the ATLAS and CMS collaborations at the CERN Large Hadron Collider announced the observation of a Higgs boson at a mass of around 125 gigaelectronvolts. Ten years later, and with the data corresponding to the production of a 30-times larger number of Higgs bosons, we have learnt much more about the properties of the Higgs boson. The CMS experiment has observed the Higgs boson in numerous fermionic and bosonic decay channels, established its spin-parity quantum numbers, determined its mass and measured its production cross-sections in various modes. Here the CMS Collaboration reports the most up-to-date combination of results on the properties of the Higgs boson, including the most stringent limit on the cross-section for the production of a pair of Higgs bosons, on the basis of data from proton-proton collisions at a centre-of-mass energy of 13 teraelectronvolts. Within the uncertainties, all these observations are compatible with the predictions of the standard model of elementary particle physics. Much evidence points to the fact that the standard model is a low-energy approximation of a more comprehensive theory. Several of the standard model issues originate in the sector of Higgs boson physics. An order of magnitude larger number of Higgs bosons, expected to be examined over the next 15 years, will help deepen our understanding of this crucial sector.
Physical review. C · 2021 · 106 citations
- Physics
- Particle physics
- Nuclear physics
Global hyperon polarization, ${\overline{P}}_{\mathrm{H}}$, in $\mathrm{Au}+\mathrm{Au}$ collisions over a large range of collision energy, $\sqrt{{s}_{\mathrm{NN}}}$, was recently measured and successfully reproduced by hydrodynamic and transport models with intense fluid vorticity of the quark-gluon plasma. While na\"{\i}ve extrapolation of data trends suggests a large ${\overline{P}}_{\mathrm{H}}$ as the collision energy is reduced, the behavior of ${\overline{P}}_{\mathrm{H}}$ at small $\sqrt{{s}_{\mathrm{NN}}}<7.7$ GeV is unknown. Operating the STAR experiment in fixed-target mode, we measured the polarization of $\mathrm{\ensuremath{\Lambda}}$ hyperons along the direction of global angular momentum in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{{s}_{\mathrm{NN}}}=3$ GeV. The observation of substantial polarization of $4.91\ifmmode\pm\else\textpm\fi{}0.81(\mathrm{stat}.)\ifmmode\pm\else\textpm\fi{}0.15(\mathrm{syst}.)%$ in these collisions may require a reexamination of the viscosity of any fluid created in the collision, of the thermalization timescale of rotational modes, and of hadronic mechanisms to produce global polarization.
Physical review. C · 2020 · 109 citations
- Physics
- Particle physics
- Nuclear physics
Strange hadrons are an excellent probe for identifying the phase boundary and onset of deconfinement in the QCD phase diagram. The STAR Collaboration has performed precision measurements of the abundances and transverse-momentum distributions for 8 species of strange mesons and baryons, as functions of centrality during a Au+Au beam-energy scan at RHIC. The results point to a possible change in strange-hadron production dynamics for $\sqrt{{s}_{N\phantom{\rule{0}{0ex}}N}}<20$ GeV. The results significantly improve the experimental knowledge in the energy range where key features of the QCD phase diagram are nowadays being studied.
A deep neural network to search for new long-lived particles decaying to jets
Machine Learning Science and Technology · 2020 · 54 citations
- Artificial Intelligence
- Computer Science
- Physics
A tagging algorithm to identify jets that are significantly displaced from the proton-proton (pp) collision region in the CMS detector at the LHC is presented. Displaced jets can arise from the decays of long-lived particles (LLPs), which are predicted by several theoretical extensions of the standard model. The tagger is a multiclass classifier based on a deep neural network, which is parameterised according to the proper decay length c 0 of the LLP. A novel scheme is defined to reliably label jets from LLP decays for supervised learning. Samples of pp collision data, recorded by the CMS detector at a centre-of-mass energy of 13 TeV, and simulated events are used to train the neural network. Domain adaptation by backward propagation is performed to improve the simulation modelling of the jet class probability distributions observed in pp collision data. The potential performance of the tagger is demonstrated with a search for long-lived gluinos, a manifestation of split supersymmetric models. The tagger provides a rejection factor of 10 000 for jets from standard model processes, while maintaining an LLP jet tagging efficiency of 30%-80% for gluinos with 1 mmc 0 10 m. The expected coverage of the parameter space for split supersymmetry is presented.
Frequent coauthors
- 1454 shared
M. Titov
Institut de Recherche sur les Lois Fondamentales de l'Univers
- 1444 shared
G. Hamel de Monchenault
Université Paris-Saclay
- 1401 shared
A. Rosowsky
Institut de Recherche sur les Lois Fondamentales de l'Univers
- 1379 shared
M. Besançon
CEA Paris-Saclay
- 1260 shared
M. Lethuillier
Institute of Nuclear Physics of Lyon
- 1166 shared
S. Perriès
Institute of Nuclear Physics of Lyon
- 1134 shared
F. Couderc
Commissariat à l'Énergie Atomique et aux Énergies Alternatives
- 1123 shared
F. Beaudette
Laboratoire Leprince-Ringuet
Labs
Li LabPI
Education
- 2009
PhD, Physics
Massachusetts Institute of Technology
Awards & honors
- Early Career Award from the U.S. Department of Energy
- Sloan Research Fellowship
- Presidential Early Career Award for Scientists and Engineers…
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