Angular correlations between unidentified charged trigger ($t$) and associated ($a$) particles are measured by the ALICE experiment in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV for transverse momenta $0.25 < p_{T}^{t,\, a} < 15$ GeV/$c$, where $p_{T}^t > p_{T}^a$. The shapes of the pair correlation distributions are studied in a variety of collision centrality classes between 0 and 50% of the total hadronic cross section for particles in the pseudorapidity interval $|\eta| < 1.0$. Distributions in relative azimuth $\Delta\phi \equiv \phi^t - \phi^a$ are analyzed for $|\Delta\eta| \equiv |\eta^t - \eta^a| > 0.8$, and are referred to as "long-range correlations". Fourier components $V_{n\Delta} \equiv \langle \cos(n\Delta\phi)\rangle$ are extracted from the long-range azimuthal correlation functions. If particle pairs are correlated to one another through their individual correlation to a common symmetry plane, then the pair anisotropy $V_{n\Delta}(p_{T}^t, p_{T}^a)$ is fully described in terms of single-particle anisotropies $v_n (p_{T})$ as $V_{n\Delta}(p_{T}^t, p_{T}^a) = v_n(p_{T}^t) \, v_n(p_{T}^a)$. This expectation is tested for $1 \leq n \leq 5$ by applying a global fit of all $V_{n\Delta} (p_{T}^t, p_{T}^a)$ to obtain the best values $v_{n}\{GF\} (p_{T})$. It is found that for $2 \leq n \leq 5$, the fit agrees well with data up to $p_T^a \sim 3$-4 GeV/$c$, with a trend of increasing deviation as $p_{T}^t$ and $p_{T}^a$ are increased or as collisions become more peripheral. This suggests that no pair correlation harmonic can be described over the full $0.25 < p_{T} < 15$ GeV/$c$ range using a single $v_n(p_T)$ curve; such a description is however approximately possible for $2 \leq n \leq 5$ when $p_T^a < 4$ GeV/$c$. For the $n=1$ harmonic, however, a single $v_1(p_T$ curve is not obtained even within the reduced range $p_T^a < 4$ GeV/$c$.
Amplitudes of the VnDelta harmonics versus n for events with trigger particles having transverse momenta in the range 2-2.5 GeV and associated particles in the range 1.5-2.0 GeV for two centrality classes 0-2% and 2-10%. Note that in the paper the data are plotted multiplied by 100.
Amplitudes of the VnDelta harmonics versus n for events with trigger particles having transverse momenta in the range 2-2.5 GeV and associated particles in the range 1.5-2.0 GeV for three centrality classes 10-20%, 20-30% and 40-50%. Note that in the paper the data are plotted multiplied by 100.
Amplitudes of the VnDelta harmonics versus n for events with trigger particles having transverse momenta in the range 8-15 GeV and associated particles in the range 6-8 GeV for two centrality classes 40-50% and 0-20%. Note that in the paper the data are plotted multiplied by 100.
The ALICE experiment at the LHC has studied inclusive J/$\psi$ production at central and forward rapidities in pp collisions at $\sqrt{s} = 7$ TeV. In this Letter, we report on the first results obtained detecting the J/$\psi$ through its dilepton decay into $e^+e^-$ and $\mu^+\mu^-$ pairs in the rapidity range |y|<0.9 and 2.5<y<4, respectively, and with acceptance down to zero $p_{\rm T}$. In the dielectron channel the analysis was carried out on a data sample corresponding to an integrated luminosity $L_{\rm int}$ = 5.6 nb$^{-1}$ and the number of signal events is $N_{J/\psi}=352 \pm 32$ (stat.) $\pm$ 28 (syst.); the corresponding figures in the dimuon channel are $L_{\rm int}$ = 15.6 nb$^{-1}$ and $N_{J/\psi} = 1924 \pm 77$ (stat.) $\pm$ 144(syst.). The measured production cross sections are $\sigma_{J/\psi}$ (|y|<0.9) = 12.4 $\pm$ 1.1 (stat.) $\pm$ 1.8 (syst.) + 1.8 -2.7 (syst.pol.) $\mu$b and $\sigma_{J/\psi}$ (2.5<y<4) = 6.31 $\pm$ 0.25 (stat.) $\pm$ 0.76 (syst.) +0.95 -1.96 (syst.pol.) $\mu$b. The differential cross sections, in transverse momentum and rapidity, of the J/$\psi$ were also measured.
Double differential J/PSI cross section from the di-electron channel as a function of transverse momentum, the first error is statistical, the first systematic error is the correlated one, the second is the non-correlated one. The last four columns are the errors considering. a +1 polarization in the Collins-Soper frame, a -1 polarization in the Collins-Soper frame, a +1 polarization in the Helicity frame and a -1 polarization in the Helicity frame, respectively.
Differential J/PSI cross section from the di-muon channel as a function of transverse momentum, the first error is statistical, the first systematic error is the correlated one, the second is the non-correlated one. The last four columns are the errors (in MUB/GEV) considering a +1 polarization in the Collins-Soper frame, a -1 polarization in the Collins-Soper frame, a +1 polarization in the Helicity frame and a -1 polarization in the Helicity frame, respectively.
Differential J/PSI cross section from the di-electron and di-muon channel as a function of rapidity, the first error is statistical, the first systematic error is the correlated one, the second is the non-correlated one. The last four columns are the errors (in MUB/GEV) considering. Data in the first point of this table updated from the erratum.
We report on the first measurement of the triangular $v_3$, quadrangular $v_4$, and pentagonal $v_5$ charged particle flow in Pb-Pb collisions at 2.76 TeV measured with the ALICE detector at the CERN Large Hadron Collider. We show that the triangular flow can be described in terms of the initial spatial anisotropy and its fluctuations, which provides strong constraints on its origin. In the most central events, where the elliptic flow $v_2$ and $v_3$ have similar magnitude, a double peaked structure in the two-particle azimuthal correlations is observed, which is often interpreted as a Mach cone response to fast partons. We show that this structure can be naturally explained from the measured anisotropic flow Fourier coefficients.
v2{SP} (red filled circles).
v3{SP} (blue filled squares).
v4{SP} (purprle stars).
A measurement of the angular correlations between beauty and anti-beauty hadrons (B B-bar) produced in pp collisions at a centre-of-mass energy of 7 TeV at the CERN LHC is presented, probing for the first time the region of small angular separation. The B hadrons are identified by the presence of displaced secondary vertices from their decays. The B hadron angular separation is reconstructed from the decay vertices and the primary-interaction vertex. The differential B B-bar production cross section, measured from a data sample collected by CMS and corresponding to an integrated luminosity of 3.1 inverse picobarns, shows that a sizable fraction of the B B-bar pairs are produced with small opening angles. These studies provide a test of QCD and further insight into the dynamics of b b-bar production.
Cross section as a function of DELTA(R) for leading jet transverse momentum > 56 GeV. . The (sys) error in the table is due to the limited MC statistics and is uncorrelated bin-to-bin. The other two systematic errors are correlated.
Cross section as a function of DELTA(R) for leading jet transverse momentum > 84 GeV. . The (sys) error in the table is due to the limited MC statistics and is uncorrelated bin-to-bin. The other two systematic errors are correlated.
Cross section as a function of DELTA(R) for leading jet transverse momentum > 120 GeV. . The (sys) error in the table is due to the limited MC statistics and is uncorrelated bin-to-bin. The other two systematic errors are correlated. Note that these two systematic errors are different for the final point.
The spectra of strange hadrons are measured in proton-proton collisions, recorded by the CMS experiment at the CERN LHC, at centre-of-mass energies of 0.9 and 7 TeV. The K^0_s, Lambda, and Xi^- particles and their antiparticles are reconstructed from their decay topologies and the production rates are measured as functions of rapidity and transverse momentum. The results are compared to other experiments and to predictions of the PYTHIA Monte Carlo program. The transverse momentum distributions are found to differ substantially from the PYTHIA results and the production rates exceed the predictions by up to a factor of three.
The rapidity production spectra per NSD event spectra for KS mesons at 0.9 and 7 TeV.
The transverse momentum production spectra per NSD event spectra for KS mesons at 0.9 and 7 TeV.
The rapidity production spectra per NSD event spectra for LAMBDA mesons at 0.9 and 7 TeV.
Dijet angular distributions are measured over a wide range of dijet invariant masses in pp collisions at sqrt(s) = 7 TeV, at the CERN LHC. The event sample, recorded with the CMS detector, corresponds to an integrated luminosity of 36 inverse picobarns. The data are found to be in good agreement with the predictions of perturbative QCD, and yield no evidence of quark compositeness. With a modified frequentist approach, a lower limit on the contact interaction scale for left-handed quarks of Lambda = 5.6 TeV (6.7 TeV) for destructive (constructive) interference is obtained at the 95% confidence level.
Normalized dijet angular distribution for the dijet mass range > 2200 GeV.
Normalized dijet angular distribution for the dijet mass range 1800 to 2200 GeV.
Normalized dijet angular distribution for the dijet mass range 1400 to 1800 GeV.
Hadronic event shapes have been measured in proton-proton collisions at sqrt(s)=7 TeV, with a data sample collected with the CMS detector at the LHC. The sample corresponds to an integrated luminosity of 3.2 inverse picobarns. Event-shape distributions, corrected for detector response, are compared with five models of QCD multijet production.
Distribution of the logarithm of the central transverse thrust for events with jet transverse momentum > 30 GeV, jet |pseudorapidity| < 1.3 and leading the jet transverse momentum from 90 to 125 GeV/c,.
Distribution of the logarithm of the central thrust minor for events with jet transverse momentum > 30 GeV, jet |pseudorapidity| < 1.3 and leading the jet transverse momentum from 90 to 125 GeV/c,.
Distribution of the logarithm of the central transverse thrust for events with jet transverse momentum > 30 GeV, jet |pseudorapidity| < 1.3 and leading the jet transverse momentum from 125 to 200 GeV/c,.
Measurements of the total and differential cross sections with respect to transverse momentum and rapidity for B+ mesons produced in pp collisions at sqrt(s) = 7 TeV are presented. The data correspond to an integrated luminosity of 5.8 inverse picobarns collected by the CMS experiment operating at the LHC. The exclusive decay B+ to J/psi K+, with the J/psi decaying to an oppositely charged muon pair, is used to detect B+ mesons and to measure the production cross section as a function of the transverse momentum and rapidity of the B. The total cross section for p_t(B) > 5 GeV and |y(B)| < 2.4 is measured to be 28.1 +/- 2.4 +/- 2.0 +/- 3.1 microbarns, where the first uncertainty is statistical, the second is systematic, and the last is from the luminosity measurement.
Total integrated cross section in the given kinematic range. The (sys) error includes the uncertainty in the branching fraction.
Measured differential cross section as a function of the transverse momentum of the B+ particle.
Measured differential cross section as a function of the rapidity of the B+ particle.
A measurement of the b-hadron production cross section in proton-proton collisions at sqrt(s)=7 TeV is presented. The dataset, corresponding to 85 inverse nanobarns, was recorded with the CMS experiment at the LHC using a low-threshold single-muon trigger. Events are selected by the presence of a muon with transverse momentum greater than 6 GeV with respect to the beam direction and pseudorapidity less than 2.1. The transverse momentum of the muon with respect to the closest jet discriminates events containing b hadrons from background. The inclusive b-hadron production cross section is presented as a function of muon transverse momentum and pseudorapidity. The measured total cross section in the kinematic acceptance is sigma(pp to b+X to mu + X') =1.32 +/- 0.01 (stat) +/- 0.30 (syst) +/- 0.15 (lumi) microbarns.
Total inclusive cross section in the visible kinematic range.
Muon transverse momentum differential distibution.
Muon pseudorapidity differential distibution.
Measurements of dijet azimuthal decorrelations in pp collisions at sqrt(s) = 7 TeV using the CMS detector at the CERN LHC are presented. The analysis is based on an inclusive dijet event sample corresponding to an integrated luminosity of 2.9 inverse picobarns. The results are compared to predictions from perturbative QCD calculations and various Monte Carlo event generators. The dijet azimuthal distributions are found to be sensitive to initial-state gluon radiation.
Normalized Delta_Phi distributions for events with a maximum jet pT between 80 and 110 GeV.
Normalized Delta_Phi distributions for events with a maximum jet pT between 110 and 140 GeV.
Normalized Delta_Phi distributions for events with a maximum jet pT between 140 and 200 GeV.
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