A systematic study of the factorization of long-range azimuthal two-particle correlations into a product of single-particle anisotropies is presented as a function of pt and eta of both particles, and as a function of the particle multiplicity in PbPb and pPb collisions. The data were taken with the CMS detector for PbPb collisions at sqrt(s[NN]) = 2.76 TeV and pPb collisions at sqrt(s[NN]) = 5.02 TeV, covering a very wide range of multiplicity. Factorization is observed to be broken as a function of both particle pt and eta. When measured with particles of different pt, the magnitude of the factorization breakdown for the second Fourier harmonic reaches 20% for very central PbPb collisions but decreases rapidly as the multiplicity decreases. The data are consistent with viscous hydrodynamic predictions, which suggest that the effect of factorization breaking is mainly sensitive to the initial-state conditions rather than to the transport properties (e.g., shear viscosity) of the medium. The factorization breakdown is also computed with particles of different eta. The effect is found to be weakest for mid-central PbPb events but becomes larger for more central or peripheral PbPb collisions, and also for very high-multiplicity pPb collisions. The eta-dependent factorization data provide new insights to the longitudinal evolution of the medium formed in heavy ion collisions.
This article presents recent results of the Z boson production in the proton-lead collisions and the charmonium production in the ultra-peripheral lead-lead collisions at the LHC collected during 2013 to 2018 by the LHCb detector. The potential heavy ion programs in these topics are also discussed.
Measurements of azimuthal angular correlations are presented for high-multiplicity pPb collisions at $\sqrt{s_\mathrm{NN}}=$ 5.02 TeV and peripheral PbPb collisions at $\sqrt{s_\mathrm{NN}}=$ 2.76 TeV. The data used in this work were collected with the CMS detector at the CERN LHC. Fourier coefficients as functions of transverse momentum and pseudorapidity are studied using the scalar product method, 4-, 6-, and 8-particle cumulants, and the Lee-Yang zeros technique. The influence of event plane decorrelation is evaluated using the scalar product method and found to account for most of the obs…
Quantum statistical (Bose-Einstein) two-particle correlations are measured in pp collisions at $\sqrt{s}=$ 0.9, 2.76, and 7 TeV, as well as in pPb and peripheral PbPb collisions at nucleon-nucleon center-of-mass energies of 5.02 and 2.76 TeV, respectively, using the CMS detector at the LHC. Separate analyses are performed for same-sign unidentified charged particles as well as for same-sign pions and kaons identified via their energy loss in the silicon tracker. The characteristics of the one-, two-, and three-dimensional correlation functions are studied as functions of the pair average trans…
In this paper we present a comprehensive analysis of the exclusive heavy quark photoproduction in $pp$, $pPb$ and $PbPb$ collisions at LHC and FCC energies using the color dipole formalism and taking into account of nonlinear corrections to the QCD dynamics. We estimate the rapidity distributions and cross sections for the charm and bottom production considering three phenomenological models for the dipole-proton scattering amplitude that are able to describe the $ep$ HERA data. Our results indicate that a future experimental analysis of this process is feasible, which will allow us to improve…
Nuclear effects in photoproduction of heavy quarks and vector mesons in ultraperipheral PbPb and pPb collisions at the LHC
通过比较$c\bar{c}$和b-b（bar）在PbPb和pPb碰撞中的光生截面，可以得到对核遮蔽效应的敏感性.光生矢量介子对底层胶子的分布更为敏感。本文研究了在sqrt（s_NN）=5 TeV和sqrt（s_NN）=2.76 $ TeV, respectively. The potentials of using these processes for constraining nuclear gluon shadowing are explored. It is found that photoproduction of $ J/J条件下，在大型强子对撞机上进行的超周边pPb和PbPb碰撞中，重夸克光生和矢量介子光生的截面及其与快度的关系。特别是PbPb碰撞中的$ and $对胶子遮蔽表现出很好的敏感性。
The second- and third-order azimuthal anisotropy Fourier harmonics of charged particles produced in pPb collisions, at $\sqrt{s_\mathrm{NN}} =$ 8.16 TeV, are studied over a wide range of event multiplicities. Multiparticle correlations are used to isolate global properties stemming from the collision overlap geometry. The second-order "elliptic" harmonic moment is obtained with high precision through four-, six-, and eight-particle correlations and, for the first time, the third-order "triangular" harmonic moment is studied using four-particle correlations. A sample of peripheral PbPb collisio…
Charge-dependent azimuthal correlations of same- and opposite-sign pairs with respect to the second- and third-order event planes have been measured in pPb collisions at $\sqrt{s_\mathrm{NN}} =$ 8.16 TeV and PbPb collisions at 5.02 TeV with the CMS experiment at the LHC. The measurement is motivated by the search for the charge separation phenomenon predicted by the chiral magnetic effect (CME) in heavy ion collisions. Three- and two-particle azimuthal correlators are extracted as functions of the pseudorapidity difference, the transverse momentum ($p_\mathrm{t}$) difference, and the $p_\mathr…
The azimuthal anisotropy Fourier coefficients ($v_n$) in 8.16 TeV pPb data are extracted via long-range two-particle correlations as a function of event multiplicity and compared to corresponding results in pp and PbPb collisions. Using a four-particle cumulant technique, $v_n$ correlations are measured for the first time in pp and pPb collisions. The $v_2$ and $v_4$ coefficients are found to be positively correlated in all collision systems. For high multiplicity pPb collisions an anticorrelation of $v_2$ and $v_3$ is observed, with a similar correlation strength as in PbPb data at the same m…
For the first time a principle-component analysis is used to separate out different orthogonal modes of the two-particle correlation matrix from heavy ion collisions. The analysis uses data from sqrt(s[NN]) = 2.76 TeV PbPb and sqrt(s[NN]) = 5.02 TeV pPb collisions collected by the CMS experiment at the LHC. Two-particle azimuthal correlations have been extensively used to study hydrodynamic flow in heavy ion collisions. Recently it has been shown that the expected factorization of two-particle results into a product of the constituent single-particle anisotropies is broken. The new information…
Charge-dependent anisotropy Fourier coefficients ($v_n$) of particle azimuthal distributions are measured in pPb and PbPb collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} = $ 5.02 TeV with the CMS detector at the LHC. The normalized difference in the second-order anisotropy coefficients ($v_2$) between positively and negatively charged particles is found to depend linearly on the observed event charge asymmetry with comparable slopes for both pPb and PbPb collisions over a wide range of charged particle multiplicity. In PbPb, the third-order anisotropy coefficient, $v_3$, shows a similar l…
The study of charm production in heavy-ion collisions is considered an excellent probe for the properties of the hot and dense medium created in heavy-ion collisions. Measurements of D-meson nuclear modification can provide strong constraints into the mechanisms of in-medium energy loss and charm flow in the medium. The measurement of $D^0$ elliptic flow in pPb collisions helps us understand the strength of charm quarks coupling to significantly reduced systems which demonstrate hydrodynamic properties. In this paper, the measurements of the $D^0$ nuclear modification factor in PbPb collisions…
Inclusive heavy meson photoproduction in $pPb$ and $PbPb$ collisions
Federal University of Pelotas（佩洛塔斯联邦大学）；The Henryk Niewodniczański Institute of Nuclear Physics Polish Academy of Sciences (PAN)（波兰科学院亨利克·涅沃德尼茨基核物理研究所）
The production of axionlike particles (ALPs) with small masses in ultraperipheral $Pb - p$ and $Pb - Pb$ collisions at the LHC is investigated. The cross section and kinematical distributions associated to the diphoton final state produced in the $γγ\rightarrow a \rightarrow γγ$ subprocesses are estimated considering a realistic set of kinematical cuts. A detailed analysis of the backgrounds is performed and the expected sensitivity to the ALP production is derived. Our results demonstrate that a future experimental analysis of the exclusive diphoton production for the forward rapidities probe…
We present the system size and flavour dependence of the chemical freeze-out temperature ($T_\mathrm{ch}$) at vanishing baryo-chemical potential calculated via thermal fits to experimental yields for several multiplicity classes in pp, pPb and PbPb collisions measured by ALICE. Using the Thermal-FIST Hadron Resonance Gas model package, we compare the quality of fits across various treatments of strangeness conservation under different freeze-out conditions as a function of the charged particle multiplicity density $\big \langle dN_\mathrm{ch}/dη\big \rangle$. Additionally, we examine how the a…
The almost hermetic coverage of the CMS detector is used to measure the distribution of transverse energy, $E_\mathrm{T}$, over 13.2 units of pseudorapidity, $η$, for pPb collisions at a center-of-mass energy per nucleon pair of $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV. The huge angular acceptance exploits the fact that the CASTOR calorimeter at $-6.6$ $<$ $η$ $<$ $-5.2$ is effectively present on both sides of the colliding system because of a switch in the proton-going and lead-going beam directions. This wide acceptance enables the study of correlations between well-separated angular regions and ma…
In a relativistic heavy ion collision, heavy flavor (charm and bottom) quarks are mostly created via hard processes at the early stage of the collisions. We present the latest results of the azimuthal anisotropy coefficients $v_{\text{n}}$ for prompt and nonprompt $\text{D}^{0}$ mesons in PbPb, pPb, and pp collisions from the CMS experiment. The studies are about collectivity phenomena in smaller systems (pp and pPb collisions), searches for the effects of very strong electromagnetic fields created in the initial stages of ultrarelativistic PbPb collisions, and charm quark energy loss in the q…
Modifications of the properties of jets in PbPb collisions, relative to those in pp collisions, are studied at a nucleon-nucleon center-of-mass energy of $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV via correlations of charged particles with the jet axis in relative pseudorapidity ($Δη$), relative azimuth ($Δϕ$), and relative angular distance from the jet axis $Δ\mathrm{r} = \sqrt{{(Δη)^{2}+(Δϕ)^{2}}}$. This analysis uses data collected with the CMS detector at the LHC, corresponding to integrated luminosities of 404 $μ$b$^{-1}$ and 27.4 pb$^{-1}$ for PbPb and pp collisions, respectively. Charged particl…
We study the two-photon production of the Higgs boson, $\rm γγ\to H$, at the Future Circular Collider (FCC) in ultraperipheral PbPb and pPb collisions at $\sqrt{s_{NN}} = 39$ and 63 TeV. Signal and background events are generated with MADGRAPH 5, including $γ$ fluxes from the proton and lead ions in the equivalent photon approximation, yielding $\rm σ(γγ\to H)$ = 1.75 nb and 1.5 pb in PbPb and pPb collisions respectively. We analyse the H$\,\to b\bar{b}$ decay channel including realistic reconstruction efficiencies for the final-state $b$-jets, showered and hadronized with PYTHIA 8, as well as…
The transverse energy ($E_\mathrm{T}^γ$) spectra of photons isolated from other particles are measured using proton-proton (pp) and lead-lead (PbPb) collisions at the LHC at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV with integrated luminosities of 27.4 pb$^{-1}$and 404 $μ$b$^{-1}$ for pp and PbPb data, respectively. The results are presented for photons with 25 $<$ $E_\mathrm{T}^γ$ $<$ 200 GeV in the pseudorapidity range $|η|$ $<$ 1.44, and for different centrality intervals for PbPb collisions. Photon production in PbPb collisions is consistent with that in pp collisions scaled by the number of binar…
Evidence for light-by-light (LbL) scattering, $γγ\toγγ$, in ultraperipheral PbPb collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV is reported. LbL scattering processes are selected in events with just two photons produced, with transverse energy $E_T^γ>2$ GeV, pseudorapidity $|η^γ|<2.4$; and diphoton invariant mass $m^{γγ}>5$ GeV, transverse momentum $p_{T}^{γγ}<1$ GeV, and acoplanarity $(1-Δϕ^{γγ}/π)<0.01$. After all selection criteria, 14 events are observed, compared to $11.1 \pm 1.1$ (theo) and $3.8 \pm 1.3$ (stat) events expected for signal and background processes respec…
