Measurements of azimuthal angle and transverse momentum ($p_\mathrm{T}$) correlations of isolated photons and associated jets are reported for pp and PbPb collisions at $\sqrt{s_{_{\mathrm{NN}}}} =$ 5.02 TeV. The data were recorded with the CMS detector at the CERN LHC. For events containing a leading isolated photon with $p_\mathrm{T}^\gamma >$ 40 GeV$/c$ and an associated jet with $p_\mathrm{T}^\text{jet} >$ 30 GeV$/c$, the photon+jet azimuthal correlation and $p_\mathrm{T}$ imbalance in PbPb collisions are studied as functions of collision centrality and $p_\mathrm{T}^\gamma$. The results are compared to pp reference data collected at the same collision energy and to predictions from several theoretical models for parton energy loss. No evidence of broadening of the photon+jet azimuthal correlations is observed, while the ratio $p_\mathrm{T}^\text{jet}/p_\mathrm{T}^\gamma$ decreases significantly for PbPb data relative to the pp reference. All models considered agree within uncertainties with the data. The number of associated jets per photon with $p_\mathrm{T}^\gamma >$ 80 GeV$/c$ is observed to be shifted towards lower $p_\mathrm{T}^\text{jet}$ values in central PbPb collisions compared to pp collisions.
Jet resolution parameters for pp and PbPb collisions in various centrality bins.
The azimuthal correlation of photons and jets in five $p_{\mathrm{T}}^{\gamma}$ intervals for 0-30% and 30-100% centrality PbPb collisions. The smeared pp data are included for comparison.
Distribution of $x_{\mathrm{j}\gamma} = p_{\mathrm{T}}^{\mathrm{jet}} / p_{\mathrm{T}}^{\gamma}$ in five $p_{\mathrm{T}}^{\gamma}$ intervals for 0-30% and 30-100% centrality PbPb collisions. The smeared pp data are included for comparison. Empty bins are denoted as 'empty' in the table.
We present measurements of two-particle angular correlations between high-transverse-momentum ($2<p_T<11$ GeV/$c$) $\pi^0$ observed at midrapidity ($|\eta|<0.35$) and particles produced either at forward ($3.1<\eta<3.9$) or backward ($-3.7<\eta<-3.1$) rapidity in $d$$+$Au and $p$$+$$p$ collisions at $\sqrt{s_{_{NN}}}=200$ GeV. The azimuthal angle correlations for particle pairs with this large rapidity gap in the Au-going direction exhibit a ridge-like structure that persists up to $p_T{\approx}6$ GeV/$c$ and which strongly depends on collision centrality, which is a similar characteristic to the hydrodynamical particle flow in A+A collisions. The ridge-like structure is absent in the $d$-going direction as well as in $p$$+$$p$ collisions, in the transverse-momentum range studied. The results indicate that the ridge-like structure is shifted in the Au-going direction toward more central collisions, similar to the charged-particle pseudorapidity distributions.
Fourier fit coefficients for CNT-MPCS (Au-going) correlations, as a function of collision system and $\pi^0$ $p_T$: (a) the negative of the dipole coefficient, $-c_1$; (b) the quadrupole coefficient $c_2$; (c) the ratio ${-c_2}/{c_1}$.
Fourier fit coefficients for CNT-MPCS (Au-going) correlations, as a function of collision system and $\pi^0$ $p_T$: Fractional systematic uncertainty on the quadrupole coefficient $c_2$ for $d$+Au.
Fourier fit coefficients for CNT-MPCS (Au-going) correlations, as a function of collision system and $\pi^0$ $p_T$: Fractional systematic uncertainty on the quadrupole coefficient $c_2$ for $p$+$p$.
Event-by-event fluctuations in the elliptic-flow coefficient $v_2$ are studied in PbPb collisions at $\sqrt{s_{_\text{NN}}} = 5.02$ TeV using the CMS detector at the CERN LHC. Elliptic-flow probability distributions ${p}(v_2)$ for charged particles with transverse momentum 0.3$< p_\mathrm{T} <$3.0 GeV and pseudorapidity $| \eta | <$ 1.0 are determined for different collision centrality classes. The moments of the ${p}(v_2)$ distributions are used to calculate the $v_{2}$ coefficients based on cumulant orders 2, 4, 6, and 8. A rank ordering of the higher-order cumulant results and nonzero standardized skewness values obtained for the ${p}(v_2)$ distributions indicate non-Gaussian initial-state fluctuation behavior. Bessel-Gaussian and elliptic power fits to the flow distributions are studied to characterize the initial-state spatial anisotropy.
Unfolded elliptic flow probability density (p(v_2)) for 15-20\% collision centralities
Unfolded elliptic flow probability density (p(v_2)) for 30-35\% collision centralities
Unfolded elliptic flow probability density (p(v_2)) for 55-60\% collision centralities
A search for heavy resonances decaying to a pair of Z bosons is performed using data collected with the CMS detector at the LHC. Events are selected by requiring two oppositely charged leptons (electrons or muons), consistent with the decay of a Z boson, and large missing transverse momentum, which is interpreted as arising from the decay of a second Z boson to two neutrinos. The analysis uses data from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The hypothesis of a spin-2 bulk graviton (X) decaying to a pair of Z bosons is examined for 600 $\le m_\mathrm{X} \le$ 2500 GeV and upper limits at 95% confidence level are set on the product of the production cross section and branching fraction of X $\to$ ZZ ranging from 100 to 4 fb. For bulk graviton models characterized by a curvature scale parameter $\tilde{k} =$ 0.5 in the extra dimension, the region $m_\mathrm{X} < $ 800 GeV is excluded, providing the most stringent limit reported to date. Variations of the model considering the possibility of a wide resonance produced exclusively via gluon-gluon fusion or $\mathrm{q}\overline{\mathrm{q}}$ annihilation are also examined.
The $p_T^Z$ distributions for electron channel comparing the data and background model with systematic uncertainty.
The $p_T^Z$ distributions for muon channel comparing the data and background model with systematic uncertainty.
The $p_T ^{miss}$ distributions for electron channel comparing the data and background model with systematic uncertainty.
A search for new physics is presented in final states with two oppositely charged leptons (electrons or muons), jets identified as originating from b quarks, and missing transverse momentum ($p_\mathrm{T}^\text{miss}$). The search uses proton-proton collision data at $\sqrt{s}=$ 13 TeV amounting to 35.9 fb$^{-1}$ of integrated luminosity collected using the CMS detector in 2016. Hypothetical signal events are efficiently separated from the dominant $\mathrm{t}\overline{\mathrm{t}}$ background with requirements on $p_\mathrm{T}^\text{miss}$ and transverse mass variables. No significant deviation is observed from the expected background. Exclusion limits are set in the context of simplified supersymmetric models with pair-produced top squarks. For top squarks, decaying exclusively to a top quark and a neutralino, exclusion limits are placed at 95% confidence level on the mass of the lightest top squark up to 800 GeV and on the lightest neutralino up to 360 GeV. These results, combined with searches in the single-lepton and all-jet final states, raise the exclusion limits up to 1050 GeV for the lightest top squark and up to 500 GeV for the lightest neutralino. For top squarks undergoing a cascade decay through charginos and sleptons, the mass limits reach up to 1300 GeV for top squarks and up to 800 GeV for the lightest neutralino. The results are also interpreted in a simplified model with a dark matter (DM) particle coupled to the top quark through a scalar or pseudoscalar mediator. For light DM, mediator masses up to 100 (50) GeV are excluded for scalar (pseudoscalar) mediators. The result for the scalar mediator achieves some of the most stringent limits to date in this model.
Figure 2 (left). Distribution of $M_{T2}(ll)$ in simulation after preselection and requiring $M_{T2}(ll) > 100$ GeV.
Figure 2 (center). Distribution of $M_{T2}(blbl)$ in simulation after preselection and requiring $M_{T2}(ll) > 100$ GeV.
Figure 2 (right). Distribution of $p_{T}^{miss}$ in simulation after preselection and requiring $M_{T2}(ll) > 100$ GeV.
A search for new physics in events with a Z boson produced in association with large missing transverse momentum at the LHC is presented. The search is based on the 2016 data sample of proton-proton collisions recorded with the CMS experiment at $\sqrt{s} = $ 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The results of this search are interpreted in terms of a simplified model of dark matter production via spin-0 or spin-1 mediators, a scenario with a standard-model-like Higgs boson produced in association with the Z boson and decaying invisibly, a model of unparticle production, and a model with large extra spatial dimensions. No significant deviations from the background expectations are found, and limits are set on relevant model parameters, significantly extending the results previously achieved in this channel.
Expected event yields in each $p_{\mathrm{T}}^{\mathrm{miss}}$ bin for the sum of background processes in the signal region (SR). The background yields and their corresponding uncertainties are obtained after performing a fit to data. Two sets of background yields are reported: one from a background-only fit to data in both the SR and the control regions (CRs), and one from a fit to data in all CRs, but excluding data in the SR. The observed numbers of events in each bin are also included. The last bin includes overflow.
Limit on the signal strength of the DM signal in a simplified model with a vector mediator.
Limit on the signal strength of the DM signal in a simplified model with an axial-vector mediator.
A search for supersymmetry is presented based on proton-proton collision events containing identified hadronically decaying top quarks, no leptons, and an imbalance $p_\mathrm{T}^\text{miss}$ in transverse momentum. The data were collected with the CMS detector at the CERN LHC at a center-of-mass energy of 13 TeV, and correspond to an integrated luminosity of 35.9 fb$^{-1}$. Search regions are defined in terms of the multiplicity of bottom quark jet and top quark candidates, the $p_\mathrm{T}^\text{miss}$, the scalar sum of jet transverse momenta, and the $m_{\mathrm{T2}}$ mass variable. No statistically significant excess of events is observed relative to the expectation from the standard model. Lower limits on the masses of supersymmetric particles are determined at 95% confidence level in the context of simplified models with top quark production. For a model with direct top squark pair production followed by the decay of each top squark to a top quark and a neutralino, top squark masses up to 1020 GeV and neutralino masses up to 430 GeV are excluded. For a model with pair production of gluinos followed by the decay of each gluino to a top quark-antiquark pair and a neutralino, gluino masses up to 2040 GeV and neutralino masses up to 1150 GeV are excluded. These limits extend previous results.
Figure 8. The 95% CL upper limit on the production cross section of the T2tt simplified model as a function of the top squark and LSP masses. No interpretation is provided for signal models for which |mStop−mLSP−mTop|≤ 25 GeV and mStop≤ 275 GeV because signal events are essentially indistinguishable from SM ttbar events in this region, rendering the signal event acceptance difficult to model.
Figure 8. Observed exclusion region at 95% CL assuming 100% branching fraction.
Figure 8. Expected exclusion region at 95% CL assuming 100% branching fraction.
The transversity distribution, which describes transversely polarized quarks in transversely polarized nucleons, is a fundamental component of the spin structure of the nucleon, and is only loosely constrained by global fits to existing semi-inclusive deep inelastic scattering (SIDIS) data. In transversely polarized $p^\uparrow+p$ collisions it can be accessed using transverse polarization dependent fragmentation functions which give rise to azimuthal correlations between the polarization of the struck parton and the final state scalar mesons. This letter reports on spin dependent di-hadron correlations measured by the STAR experiment. The new dataset corresponds to 25 pb$^{-1}$ integrated luminosity of $p^\uparrow+p$ collisions at $\sqrt{s}=500$ GeV, an increase of more than a factor of ten compared to our previous measurement at $\sqrt{s}=200$ GeV. Non-zero asymmetries sensitive to transversity are observed at a $Q^2$ of several hundred GeV and are found to be consistent with the former measurement and a model calculation. %we observe consistent with the former measurement are observed.} We expect that these data will enable an extraction of transversity with comparable precision to current SIDIS datasets but at much higher momentum transfers where subleading effects are suppressed.
Squared 4-momentum transfer $Q^2$ vs x coverage of STAR .
$A_{UT}$ as a function of $\eta$ for $<p_{T}>$ = 13 GeV/c and $<M_{inv}>$ = 1 GeV/($c^2$) (Upper panel of the fig. 3). Kinematic variables $<x>$, $<z>$ as a function of $\eta$ for $<p_{T}>$ = 13 GeV/c and $<M_{inv}>$ = 1 GeV/($c^2$) (Lower panel of the fig. 3). In addition to statistical uncertainties, systematic uncertainties originating from PID and trigger bias systematic uncertainties are also mentioned for $A_{UT}$.
$A_{UT}$ as a function of $<M_{inv}>$ for pT bin $<p_{T}>$ = 4 GeV/c for $\eta > 0$ and $\eta < 0$. In addition to statistical uncertainties, systematic uncertainties originating from PID and trigger bias systematic uncertainties are also mentioned.
We present measurements of the transverse-momentum dependence of elliptic flow $v_2$ for identified pions and (anti)protons at midrapidity ($|\eta|<0.35$), in 0%--5% central $p$$+$Au and $^3$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV. When taken together with previously published measurements in $d$$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV, the results cover a broad range of small-collision-system multiplicities and intrinsic initial geometries. We observe a clear mass-dependent splitting of $v_2(p_{T})$ in $d$$+$Au and $^3$He$+$Au collisions, just as in large nucleus-nucleus ($A$$+$$A$) collisions, and a smaller splitting in $p$$+$Au collisions. Both hydrodynamic and transport model calculations successfully describe the data at low $p_T$ ($< 1.5$ GeV/$c$), but fail to describe various features at higher $p_T$. In all systems, the $v_2$ values follow an approximate quark-number scaling as a function of the hadron transverse kinetic energy per constituent quark($KE_T/n_q$), which was also seen previously in $A$$+$$A$ collisions.
Values of $v_2$($p_T$) for kaons in central 0-5% $p$+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
Values of $v_2$($p_T$) for kaons in central 0-5% $^3$He+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV.
Transverse momentum dependence of $v_2$ for identified pions and protons within $|\eta|$ < 0.35 in 0-5% central $p$+Au collisions.
The pseudorapidity distributions of charged hadrons in proton-lead collisions at nucleon-nucleon center-of-mass energies $\sqrt{s_{_\mathrm{NN}}} =$ 5.02 and 8.16 TeV are presented. The measurements are based on data samples collected by the CMS experiment at the LHC. The number of primary charged hadrons produced in non-single-diffractive proton-lead collisions is determined in the pseudorapidity range $|\eta_\mathrm{lab}| <$ 2.4. The charged-hadron multiplicity distributions are compared to the predictions from theoretical calculations and Monte Carlo event generators. In the center-of-mass pseudorapidity range $|\eta_\mathrm{cm}| < 0.5$, the average charged-hadron multiplicity densities $<\mathrm{d}N_{\mathrm{ch}}/\mathrm{d}\eta_{\mathrm{cm}}>$$\vert_{|\eta_{\mathrm{cm}}| < 0.5}$ are 17.31 $\pm$ 0.01 (stat) $\pm$ 0.59 (syst) and 20.10 $\pm$ 0.01 (stat) $\pm$ 0.85 (syst) at $\sqrt{s_{_\mathrm{NN}}} =$ 5.02 and 8.16 TeV, respectively. The particle densities per participant nucleon are compared to similar measurements in proton-proton, proton-nucleus, and nucleus-nucleus collisions.
Distributions of the pseudorapidity density of charged hadrons in the region $|\eta_{\mathrm{lab}}|<2.4$ in non-single-diffractive pPb collisions at $\sqrt{s_{_{\mathrm{NN}}}} = 5.02$ (open squares) and 8.16 TeV (full squares). The systematic uncertainties are correlated between the two beam energies. The proton beam goes in the positive $|\eta_{\mathrm{lab}}|$ direction.