We study the transverse momentum ( $p_T$ ) differential anisotropic flow and flow fluctuation in Pb+Pb collisions at $\sqrt{s_{_{NN}}}$ =5.02 TeV at the LHC. A (3+1)-dimensional CLVisc hydrodynamics framework with fluctuating TRENTO (or AMPT) initial conditions is utilized to simulate the space-time evolution of the quark-gluon plasma (QGP) medium. The effects of shear viscosity and the sub-nucleon structure on anisotropic flow and flow fluctuation are analyzed. Our result shows that shear viscosity tends to suppress both flow coefficients ( ${v_2\{2}\}$ , ${v_2\{4\}}$ , and ${\langle v_2\rangle}$ ) and flow fluctuation ( ${\sigma_{v_2}}$ ) owing to its smearing effect on local density fluctuation. The flow coefficients appear to be insensitive to the sub-nucleon structure, whereas the flow fluctuation ${\sigma_{v_2}}$ tends to be suppressed by the sub-nucleon structure in central collisions but enhanced in peripheral collisions. After taking into account the sub-nucleon structure effect, our numerical result can qualitatively describe the relative flow fluctuations ( ${v_2\{4\}/v_2\{2\}}$ , $F({v_2})$ ) measured by the ALICE Collaboration at the LHC. We further investigate the effects of shear viscosity, sub-nucleon structure, and initial condition model on the flow angle and flow magnitude decorrelations ( ${A_2^f}$ , ${M_2^f}$ ) using the four-particle correlation method. We find that the flow decorrelation effect is typically stronger in central collisions than in peripheral collisions. The flow angle decorrelation is found to be insensitive to the shear viscosity and sub-nucleon structure, whereas the flow magnitude decorrelation shows quite different behaviors when using the TRENTO and AMPT initial condition models. Our study sheds light on the anisotropic flow, transport properties, and initial structure of the QGP created in high-energy nuclear collisions.

China

Germany

Jie Zhu

Canada

Xiang-Yu Wu

Guang-You Qin

Anisotropic flow, flow fluctuation, and flow decorrelation in relativistic heavy-ion collisions: the roles of sub-nucleon structure and shear viscosity * Supported in part by the Natural Science Foundation of China (12225503, 11890710, 11890711, 11935007). Zhu Jie is supported in part by the China Scholarship Council (202306770009). Wu Xiang-Yu is supported in part by the National Science Foundation within the framework of the JETSCAPE collaboration (OAC-2004571) and in part by the Natural Sciences and Engineering Research Council of Canada. Some of the calculations were performed in the Nuclear Science Computing Center at Central China Normal University (NSC$^{3}$), Wuhan, Hubei, China.

The large gap between a galactic dark matter subhalo’s velocity and its own gravitational binding velocity creates the situation that small subhalos can be evaporated before dark matter thermalize with baryons due to the low binding velocity. In case dark matter acquires an electromagnetic dipole moment, the survival of low-mass subhalos requires stringent limits on the photon-mediated soft scattering. The current stringent direct detection limits indicate for a small dipole moment, which lets DM decouple early and allows small subhalos to form. We calculate the DM kinetic decoupling temperature in the Early Universe and evaluate the smallest protohalo mass. In the late Universe, low-mass subhalos can be evaporated via soft collision by ionized gas and accelerated cosmic rays. We calculate the subhalos evaporation rate and show that subhalos lighter than  $$10^{-5}M_{\odot }$$  <math> <mrow> <msup> <mn>10</mn> <mrow> <mo>-</mo> <mn>5</mn> </mrow> </msup> <msub> <mi>M</mi> <mo>⊙</mo> </msub> </mrow> </math>   in the gaseous inner galactic region are subject to evaporation via dark matter’s effective electric and magnetic dipole moments below current direct detection limits, which potentially affects the low-mass subhalos distribution in the galactic center.

Xiao-jun Bi

Yu Gao

Mingjie Jin

Yugen Lin

Qian-Fei Xiang

Soft scattering evaporation of dark matter subhalos by inner galactic gases

New physics could be explored through loop effects using the precision measurements at the Circular Electron Positron Collider (CEPC) owing to its clean collision environment and high luminosity. In this paper, we focus on two dark matter models that involve additional electroweak fermionic multiplets. We calculate their one-loop corrections in five processes, i.e.,   $ e^+e^- \to \mu^+\mu^-, \; Zh, \; W^+W^-, \; ZZ $  , and   $ e^+e^- \to \mu^+\mu^-, \; Zh, \; W^+W^-, \; ZZ $  , and investigate the corresponding signatures at the CEPC with the projected sensitivity. We observe that the detectable parameter regions of these processes are complementary. The combined analysis shows that the mass of dark matter   $ e^+e^- \to \mu^+\mu^-, \; Zh, \; W^+W^-, \; ZZ $   in these two models can be probed up to   $ e^+e^- \to \mu^+\mu^-, \; Zh, \; W^+W^-, \; ZZ $   and   $ e^+e^- \to \mu^+\mu^-, \; Zh, \; W^+W^-, \; ZZ $   GeV, respectively, at a 95% confidence level.

Lin-Qing Gao

Xiao-Jun Bi

Italy

Jin-Wei Wang

Peng-Fei Yin

Exploring fermionic multiplet dark matter through precision measurements at the CEPC  

Direct detection experiments tend to lose sensitivity in searches for sub-MeV light dark matter candidates due to the threshold of recoil energy. However, such light dark matter particles could be accelerated by energetic cosmic rays, such that they could be detected with existing detectors. We derive constraints on the scattering of a boosted light dark matter particle and electron from the XENON100/1T experiment. We illustrate that the energy dependence of the cross section plays a crucial role in improving both the detection sensitivity and also the complementarity of direct detection and other experiments.

Qing-Hong Cao

Ran Ding

Searching for sub-MeV boosted dark matter from xenon electron direct detection  

The sensitivity of the direct detection of dark matter (DM) approaches the so-called neutrino floor, below which it is difficult to disentangle the DM candidate from the neutrino background. In this work, we consider the scenario that no DM signals are reported in various DM direct detection experiments and explore whether collider searches could probe DM below the neutrino floor. We adopt several simplified models in which the DM candidate couples to electroweak gauge bosons or leptons in the standard model only through high-dimensional operators. After including the RGE running effect, we investigate the constraints of direct detection, indirect detection, and collider searches. The collider search can probe light DM below the neutrino floor. Particularly, for the effective interaction of 
					, current data from the mono-photon channel at the 13 TeV LHC has already covered the entire parameter space of the neutrino floor.
				

An-Kang Wei

Dark matter search at colliders and neutrino floor Supported in part by the National Science Foundation of China (11725520, 11675002, 11635001) and in part by the China Postdoctoral Science Foundation (8206300015)

The exclusive photoproduction of vector mesons (
					 and 
					) is investigated by considering the next-to-leading order corrections in the framework of the color glass condensate. We compare the next-to-leading order modified dipole amplitude with the HERA data, finding a good agreement. Our studies show that the 
					 from the leading order, running coupling, and collinearly improved next-to-leading order dipole amplitudes are 2.159, 1.097, and 0.932 for the elastic cross-section, and 2.056, 1.449, and 1.357 for the differential cross-section, respectively. The results indicate that the higher-order corrections contribute significantly to the vector meson productions, and the description of the experimental data is dramatically improved once the higher order corrections are included. We extend the next-to-leading order exclusive vector meson production model to LHC energies using the same parameters obtained from HERA. We find that our model provides a rather good description of the 
					 and 
					 data in proton-proton collisions at 7 TeV and 13 TeV in LHCb experiments.
				

Yanbing Cai

Wenchang Xiang

Mengliang Wang

Daicui Zhou

Exclusive photoproduction of vector meson at next-to-leading order from color glass condensate Supported by the National Natural Science Foundation of China (11765005, 11947119, 11305040, 11847152, 11775097), the Fund of Science and Technology Department of Guizhou Province ([2018]1023, [2019]5653), the Education Department of Guizhou Province (KY[2017]004), Qian Kehe Platform Talents ([2017]5736-027), the National key research and development program of China (2018YFE0104700, CCNU18ZDPY04), and the 2018 scientific research startup foundation for the introduced talent of Guizhou University of Finance and Economics (2018YJ60)

We propose a <math><mrow><mi>U</mi><mo>(</mo><mn>1</mn><msup><mrow><mo>)</mo></mrow><mrow><mo>′</mo></mrow></msup></mrow></math> model inspired by <math><msub><mi>E</mi><mn>6</mn></msub></math>, which has an isospin-violation dark matter. With extra an two pairs of vectorlike quarks, we can assign the proper <math><mi>U</mi><mo>(</mo><mn>1</mn><msup><mo>)</mo><mo>′</mo></msup></math> charges for the first two-generation quark doublets and explain why the first two-generation quarks are lighter than the third generation. By choosing a proper linear combination of two extra <math><mi>U</mi><mo>(</mo><mn>1</mn><mo>)</mo></math> gauge symmetries in <math><msub><mi>E</mi><mn>6</mn></msub></math>, it is natural to realize the ratio <math><msub><mi>f</mi><mi>n</mi></msub><mo>/</mo><msub><mi>f</mi><mi>p</mi></msub><mo>=</mo><mo>−</mo><mn>0.7</mn></math> so as to maximally relax the constraints from the xenon based direct detection experiments. We study the sensitivities of the dark matter direct and indirect detection experiments and identify the parameter spaces that can give the observed relic density. We also study the sensitivities of the future colliders with a center mass energy <math><msqrt><mi>s</mi></msqrt><mo>=</mo><mrow><mn>33</mn><mo>/</mo><mn>50</mn></mrow><mo>/</mo><mn>100</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> and compare the different detection methods. We show that in some parameter spaces, the future colliders can give much stronger limits.

Tianjun Li

Qi-Shu Yan

Xianhui Zhang

Han Zhou

Isospin-violating dark matter in a <math><mrow><mi>U</mi><mo>(</mo><mn>1</mn><msup><mrow><mo>)</mo></mrow><mrow><mo>′</mo></mrow></msup></mrow></math> model inspired by <math><msub><mi>E</mi><mn>6</mn></msub></math>

Instead of the usual dijet decay, the coloron may mainly decay into its own “Higgs bosons”, which subsequently decay into many jets. This is a general feature of the renormalizable coloron model, where the corresponding “Higgs bosons” are a color-octet Θ and a color-singlet ϕ  I . In this paper, we perform a detailed collider study for the signature of  <math><mi>pp</mi><mo>→</mo><msup><mi>G</mi><mo>′</mo></msup><mo>→</mo><mfenced><mrow><mi>Θ</mi><mspace width="0.25em"></mspace><mo>→</mo><mi>gg</mi></mrow></mfenced><mfenced><mrow><msub><mi>ϕ</mi><mi>I</mi></msub><mo>→</mo><mi>g</mi><mi>g</mi><mi>q</mi><mover><mi>q</mi><mo>¯</mo></mover></mrow></mfenced></math> $$ pp\to {G}^{\prime}\to \left(\varTheta\ \to gg\right)\left({\phi}_I\to ggq\overline{q}\right) $$ with the coloron G ′ as a six-jet resonance. For a light ϕ  I  below around 0.5 TeV, it may be boosted and behave as a four-prong fat jet. We also develop a jet-substructure-based search strategy to cover this boosted ϕ  I  case. Independent of whether ϕ  I  is boosted or not, the 13 TeV LHC with 100 fb−1 has great discovery potential for a coloron with the mass sensitivity up to 5 TeV.

United States

Yang Bai

Sida Lu

Hexapod coloron at the LHC

We study natural supersymmetry in the generalized minimal supergravity (GmSUGRA). For the parameter space with low energy, electroweak fine-tuning measures less than 50, we are left with only the <math><mrow><mi>Z</mi></mrow></math>-pole, Higgs-pole, and Higgsino LSP scenarios for dark matter (DM). We perform the focused scans for such parameter space and find that it satisfies various phenomenological constraints and is compatible with the current direct detection bound on neutralino DM reported by the LUX experiment. Such parameter space also has solutions with correct DM relic density besides the solutions with DM relic density smaller or larger than <math><mrow><mn>5</mn><mi>σ</mi></mrow></math> WMAP9 bounds. We present five benchmark points as examples. In these benchmark points, the gluino and the first two generations of squarks are heavier than 2 TeV, stop <math><msub><mover><mi>t</mi><mo>˜</mo></mover><mrow><mn>1</mn><mo>,</mo><mn>2</mn></mrow></msub></math> are in the mass range [1, 2] TeV, while sleptons are lighter than 1 TeV. Some part of the parameter space can explain the muon anomalous magnetic moment within <math><mrow><mn>3</mn><mi>σ</mi></mrow></math> as well. We also perform the collider study of such solutions by implementing and comparing with relevant studies done by the ATLAS and CMS Collaborations. We find that the points with Higgsino dominant <math><msubsup><mover><mi>χ</mi><mo>˜</mo></mover><mn>2</mn><mn>0</mn></msubsup><mo>/</mo><msubsup><mover><mi>χ</mi><mo>˜</mo></mover><mn>1</mn><mo>±</mo></msubsup></math> mass up to 300 GeV are excluded in <math><mi>Z</mi></math>-pole scenario while for Higgs-pole scenario, the points with <math><msubsup><mover><mi>χ</mi><mo>˜</mo></mover><mn>2</mn><mn>0</mn></msubsup></math> mass up to 460 GeV are excluded. We also notice that the Higgsino LSP points in our present scans are beyond the reach of present LHC searches. Next, we show that for both the <math><mi>Z</mi></math>-pole and Higgs-pole scenarios, the points with electroweak fine-tuning measures around 20 do still survive.

Waqas Ahmed

Jia-Shu Niu

Pakistan

Shabbar Raza

Status of natural supersymmetry from the generalized minimal supergravity in light of the current LHC run-2 and LUX data

We study the impact of fermionic dark matter (DM) on projected Higgs precision measurements at the Circular Electron Positron Collider (CEPC), including the one-loop effects on the <math><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo>→</mo><mi>Z</mi><mi>h</mi></math> cross section and the Higgs boson diphoton decay, as well as the tree-level effects on the Higgs boson invisible decay. As illuminating examples, we discuss two UV-complete DM models, whose dark sector contains electroweak multiplets that interact with the Higgs boson via Yukawa couplings. The CEPC sensitivity to these models and current constraints from DM detection and collider experiments are investigated. We find that there exist some parameter regions where the Higgs measurements at the CEPC will be complementary to current DM searches.

Australia

Zhao-Huan Yu

Exploring fermionic dark matter via Higgs boson precision measurements at the Circular Electron Positron Collider