We present a study of the average transverse momentum ($p_t$) fluctuations and $p_t$ correlations for charged particles produced in Cu+Cu collisions at midrapidity for $\sqrt{s_{NN}} =$ 62.4 and 200 GeV. These results are compared with those published for Au+Au collisions at the same energies, to explore the system size dependence. In addition to the collision energy and system size dependence, the $p_t$ correlation results have been studied as functions of the collision centralities, the ranges in $p_t$, the pseudorapidity $\eta$, and the azimuthal angle $\phi$. The square root of the measured $p_t$ correlations when scaled by mean $p_t$ is found to be independent of both colliding beam energy and system size studied. Transport-based model calculations are found to have a better quantitative agreement with the measurements compared to models which incorporate only jetlike correlations.
Event-by-event $\langle p_{t}\rangle$ distributions for data and mixed events in central Cu+Cu collisions at $\sqrt{s_{NN}}$ = 200 and 62.4 GeV.
Comparison of dynamical $\langle p_{t}\rangle$ fluctuations in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}$ = 62.4 and 200 GeV as a function of the number of participanting nucleons.
Comparison of dynamical $\langle p_{t}\rangle$ fluctuations in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}$ = 62.4 and 200 GeV as a function of the number of participanting nucleons.
A measurement of the cross-section for pp$ \rightarrow$Z$ \rightarrow$e$^+$e$^-$ is presented using data at $\sqrt{s}=7$ TeV corresponding to an integrated luminosity of 0.94 fb$^{-1}$. The process is measured within the kinematic acceptance $p_{\mathrm{T}}>20$GeV/$c$ and $2<\eta<4.5$ for the daughter electrons and dielectron invariant mass in the range 60-120 GeV/$c^2$. The cross-section is determined to be $$\sigma(pp \rightarrow Z \rightarrow e^+ e^- )=76.0\pm0.8\pm2.0\pm2.6{\rm pb}$$ where the first uncertainty is statistical, the second is systematic and the third is the uncertainty in the luminosity. The measurement is performed as a function of Z rapidity and as a function of an angular variable which is closely related to the Z transverse momentum. The results are compared with previous LHCb measurements and with theoretical predictions from QCD.
Cross-section of $pp \to Z \to e^+ e^-$ integrated over $Z$ rapidity. The first quoted uncertainty is statistical, the second is the experimental systematic uncertainty, the third is the luminosity uncertainty and the fourth uncertainty is due to FSR correction.
Differential cross-section of $pp \to Z \to e^+ e^-$ as function $Z$ rapidity. The first quoted uncertainty is statistical. The second and third uncertainties are the uncorrelated and correlated systematic uncertainties respectively. The fourth uncertainty is due to FSR correction.
Differential cross-section of $pp \to Z \to e^+ e^-$ as function of $\phi^*$ kinematic variable constructed from electron pair azimuthal angle and pseudorapidity and correlated to $Z$ tranverse momentum. The first quoted uncertainty is statistical. The second and third uncertainties are the uncorrelated and correlated systematic uncertainties respectively. The fourth uncertainty is due to FSR correction.
The energy flow created in pp collisions at is studied within the pseudorapidity range 1.9<η<4.9 with data collected by the LHCb experiment. The measurements are performed for inclusive minimum-bias interactions, hard scattering processes and events with an enhanced or suppressed diffractive contribution. The results are compared to predictions given by Pythia-based and cosmic-ray event generators, which provide different models of soft hadronic interactions.
Charged energy flow for inclusive mininum bias events, requiring at least one charged particle in the pseudorapidity range 1.9 < eta < 4.9.
Charged energy flow for hard scattering events, requiring at least one charged particle with transverse momentum > 3 GeV and in the pseudorapidity range 1.9 < eta < 4.9.
Charged energy flow for diffractive enriched events, requiring no charged particles in the pseudorapidity range -3.5 < eta < -1.5 and at least one charged particle in the pseudorapidity range 1.9 < eta < 4.9.
Two-particle correlations in relative azimuthal angle ($\Delta-\phi$) and pseudorapidity ($\Delta-\eta$) are measured in $\sqrt{s_{NN}}$ = 5.02 TeV p+Pb collisions using the ATLAS detector at the LHC. The measurements are performed using approximately 1 $\mu b^{-1}$ of data as a function of $p_T$ and the transverse energy ($\sum E_T^{Pb}$) summed over 3.1 < $\eta$ < 4.9 in the direction of the Pb beam. The correlation function, constructed from charged particles, exhibits a long-range (2<|$\Delta-\eta$|<5) near-side ($\Delta-\phi$ ~ 0) correlation that grows rapidly with increasing $\sum E_T^{Pb}$. A long-range away-side ($\Delta-\phi$ ~ pi) correlation, obtained by subtracting the expected contributions from recoiling dijets and other sources estimated using events with small $\sum E_T^{Pb}$, is found to match the near-side correlation in magnitude, shape (in $\Delta-\eta$ and $\Delta-\phi$) and $\sum E_T^{Pb}$ dependence. The resultant $\Delta-\phi$ correlation is approximately symmetric about $\pi$/2, and is consistent with a cos(2$\Delta-\phi$) modulation for all $\sum E_T^{Pb}$ ranges and particle $p_T$. The amplitude of this modulation is comparable in magnitude and $p_T$ dependence to similar modulations observed in heavy-ion collisions, suggestive of final-state collective effects in high multiplicity events.
Distribution of per-trigger yield, Y(DELTA(PHI)), in the peripheral and the central event activity classes and their differences, for 0.3 < pT(a) < 0.5 GeV and 0.5 < pT(b) < 4 GeV.
Distribution of per-trigger yield, Y(DELTA(PHI)), in the peripheral and the central event activity classes and their differences, for 0.5 < pT(a) < 1 GeV and 0.5 < pT(b) < 4 GeV.
Distribution of per-trigger yield, Y(DELTA(PHI)), in the peripheral and the central event activity classes and their differences, for 1 < pT(a) < 2 GeV and 0.5 < pT(b) < 4 GeV.
A measurement of the t t-bar production cross section in pp collisions at sqrt(s) = 7 TeV is presented. The results are based on data corresponding to an integrated luminosity of 2.3 inverse femtobarns collected by the CMS detector at the LHC. Selected events are required to have one isolated, high transverse momentum electron or muon, large missing transverse energy, and hadronic jets, at least one of which must be consistent with having originated from a b quark. The measured cross section is 158.1 +/- 2.1 (stat.) +/- 10.2 (syst.) +/- 3.5 (lum.) pb, in agreement with standard model predictions.
Measured cross section for t-tbar production for the combined result as well as the electron+jets and muon+jets channels separately.
Results of the fit to the combined electron + jets and muon + jets sample, and each channel individually. The contributions from the background processes are quoted as scale factors with respect to their theoretical predictions. The scale factors do not account for a full treatment of the systematic uncertainties and are strictly valid only in the context of the fit. For brevity, the QCD parameters are not shown.
Correlation matrix of the combined fit to the electron + jets plus muon + jets samples. Only non-QCD parameters are shown.
Measurements of inclusive jet and dijet production cross sections are presented. Data from LHC proton-proton collisions at $\sqrt{s}$ = 7 TeV, corresponding to 5.0 inverse femtobarns of integrated luminosity, have been collected with the CMS detector. Jets are reconstructed up to rapidity 2.5, transverse momentum 2 TeV, and dijet invariant mass 5 TeV, using the anti-k$_t$ clustering algorithm with distance parameter R = 0.7. The measured cross sections are corrected for detector effects and compared to perturbative QCD predictions at next-to-leading order, using five sets of parton distribution functions.
Inclusive Jet Cross Section for |rapidity| < 0.5 as a function of the jet transverse momentum. The (sys) error is the total systematic error, including the luminosity uncertainty of 2.2%.
Inclusive Jet Cross Section for |rapidity| 0.5 TO 1.0 as a function of the jet transverse momentum. The (sys) error is the total systematic error, including the luminosity uncertainty of 2.2%.
Inclusive Jet Cross Section for |rapidity| 1.0 TO 1.5 as a function of the jet transverse momentum. The (sys) error is the total systematic error, including the luminosity uncertainty of 2.2%.
The production of J/psi mesons is studied with the LHCb detector using data from pp collisions at sqrt(s)=2.76 TeV corresponding to an integrated luminosity of 71 nb^-1. The differential cross-section for inclusive J/psi production is measured as a function of its transverse momentum pT. The cross-section in the fiducial region 0<pT<12 GeV/c and rapidity 2.0<y<4.5 is measured to be 5.6 +/- 0.1(stat) +/- 0.4 (syst) mub, with the assumption of unpolarised J/psi production. The fraction of J/psi production from b-hadron decays is measured to be (7.1 +/- 0.6 (stat) +/- 0.7 (syst)) %.
Differential cross-section $d\sigma/dp_T$ at $\sqrt{s}$ = 2.76 TeV for inclusive $J/\psi$ production in bins of $p_T$. The rapidity range covered is $2.0 < y < 4.5$. The first uncertainty is statistical and the second is systematic.
The jet fragmentation function is measured with direct photon-hadron correlations in p+p and Au+Au collisions at sqrt(s_NN)=200 GeV. The p_T of the photon is an excellent approximation to the initial p_T of the jet and the ratio z_T=p_T^h/p_T^\gamma is used as a proxy for the jet fragmentation function. A statistical subtraction is used to extract the direct photon-hadron yields in Au+Au collisions while a photon isolation cut is applied in p+p. I_ AA, the ratio of jet fragment yield in Au+Au to that in p+p, indicates modification of the jet fragmentation function. Suppression, most likely due to energy loss in the medium, is seen at high z_T. The fragment yield at low z_T is enhanced at large angles. Such a trend is expected from redistribution of the lost energy into increased production of low-momentum particles.
Direct photon-hadron pair per-trigger yields vs Delta-phi (Au+Au and p+p)
Integrated per-trigger yields and I_AA vs xi
Integrated per-trigger yields and I_AA vs xi
The measurement of J/{psi} azimuthal anisotropy is presented as a function of transverse momentum for different centralities in Au+Au collisions at {sqrt{s_{NN}}} = 200 GeV. The measured J/{psi} elliptic flow is consistent with zero within errors for transverse momentum between 2 and 10 GeV/c. Our measurement suggests that J/{psi} with relatively large transverse momentum are not dominantly produced by coalescence from thermalized charm quarks, when comparing to model calculations.
J/Psi azimuthal anisotropy v2 vs pT measured via the dielectron channel in 0-10%, 10-40%, and 40-80% central Au+Au collisions at 200 GeV. The brackets represent systematic errors. The boxes show the estimated maximum possible range of v2 if the nonflow influence is corrected. The mean pT in each bin for v2 calculation is drawn, but is shifted a little for some centralities so that all points can be seen clearly.
J/Psi azimuthal anisotropy v2 vs pT measured via the dielectron channel in 0-80% central Au+Au collisions at 200 GeV. The brackets represent systematic errors. The boxes show the estimated maximum possible range of v2 if the nonflow influence is corrected.
Jet-medium interactions are studied via a multi-hadron correlation technique (called "2+1"), where a pair of back-to-back hadron triggers with large transverse momentum is used as a proxy for a di-jet. This work extends the previous analysis for nearly-symmetric trigger pairs with the highest momentum threshold of trigger hadron of 5 GeV/$c$ with the new calorimeter-based triggers with energy thresholds of up to 10 GeV and above. The distributions of associated hadrons are studied in terms of correlation shapes and per-trigger yields on each trigger side. In contrast with di-hadron correlation results with single triggers, the associated hadron distributions for back-to-back triggers from central Au+Au data at $\sqrt{s_{NN}}$=200 GeV show no strong modifications compared to d+Au data at the same energy. An imbalance in the total transverse momentum between hadrons attributed to the near-side and away-side of jet-like peaks is observed. The relative imbalance in the Au+Au measurement with respect to d+Au reference is found to increase with the asymmetry of the trigger pair, consistent with expectation from medium-induced energy loss effects. In addition, this relative total transverse momentum imbalance is found to decrease for softer associated hadrons. Such evolution indicates the energy missing at higher associated momenta is converted into softer hadrons.
Projections of 2-D correlation functions on $\Delta \phi$ (a) (with $|\Delta \eta|$ < 1.0) and $\Delta \eta$ (b) (with $|\Delta \phi|$ < 0.7) for the hadrons associated with their respective triggers (T1 for near-side, T2 for away–side) are shown for d+Au (circles) and central 0-20% Au+Au (squares).
Projections of 2-D correlation functions on $\Delta \phi$ (a) (with $|\Delta \eta|$ < 1.0) and $\Delta \eta$ (b) (with $|\Delta \phi|$ < 0.7) for the hadrons associated with their respective triggers (T1 for near-side, T2 for away–side) are shown for d+Au (circles) and central 0-20% Au+Au (squares).
Projections of 2-D correlation functions on $\Delta \phi$ (a) (with $|\Delta \eta|$ < 1.0) and $\Delta \eta$ (b) (with $|\Delta \phi|$ < 0.7) for the hadrons associated with their respective triggers (T1 for near-side, T2 for away–side) are shown for d+Au (circles) and central 0-20% Au+Au (squares).
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