We report the observation of transverse polarization-dependent azimuthal correlations in charged pion pair production with the STAR experiment in $p^\uparrow+p$ collisions at RHIC. These correlations directly probe quark transversity distributions. We measure signals in excess of five standard deviations at high transverse momenta, at high pseudorapidities eta>0.5, and for pair masses around the mass of the rho-meson. This is the first direct transversity measurement in p+p collisions. Comparing the results to data from lepton-nucleon scattering will test the universality of these spin-dependent quantities.
$p_T$ asymmetries, $\eta$ < 0, maximum opening angle of 0.2.
$<M_{inv}>$ asymmetries, $\eta$ < 0, maximum opening angle of 0.2.
$p_T$ asymmetries, $\eta$ > 0, maximum opening angle 0.2.
We search for evidence of physics beyond the Standard Model in the production of final states with multiple high transverse momentum jets, using 20.3 fb$^{-1}$ of proton-proton collision data recorded by the ATLAS detector at $\sqrt{s} = 8$ TeV. No excess of events beyond Standard Model expectations is observed, and upper limits on the visible cross-section for non-Standard Model production of multi-jet final states are set. Using a wide variety of models for black hole and string ball production and decay, the limit on the cross-section times acceptance is as low as 0.16 fb at the 95% CL for a minimum scalar sum of jet transverse momentum in the event of about 4.3 TeV. Using models for black hole and string ball production and decay, exclusion contours are determined as a function of the production mass threshold and the gravity scale. These limits can be interpreted in terms of lower-mass limits on black hole and string ball production that range from 4.6 to 6.2 TeV.
Number of data events (20.3 fb$^{-1}$), number of predicted events from the fit, statistical uncertainty on the fit, systematic uncertainty on the choice of control region, and on the choice of fit function versus inclusive $H_{\textrm{T}}^{\textrm{min}}$ lower bin edge for inclusive jet multiplicity $N_{\textrm{Jet}} \geq 3$. The total uncertainty is obtained by adding the three uncertainties linearly.
Number of data events (20.3 fb$^{-1}$), number of predicted events from the fit, statistical uncertainty on the fit, systematic uncertainty on the choice of control region, and on the choice of fit function versus inclusive $H_{\textrm{T}}^{\textrm{min}}$ lower bin edge for inclusive jet multiplicity $N_{\textrm{Jet}} \geq 4$. The total uncertainty is obtained by adding the three uncertainties linearly.
Number of data events (20.3 fb$^{-1}$), number of predicted events from the fit, statistical uncertainty on the fit, systematic uncertainty on the choice of control region, and on the choice of fit function versus inclusive $H_{\textrm{T}}^{\textrm{min}}$ lower bin edge for inclusive jet multiplicity $N_{\textrm{Jet}} \geq 5$. The total uncertainty is obtained by adding the three uncertainties linearly.
New results for the double spin asymmetry $A_1^{\rm p}$ and the proton longitudinal spin structure function $g_1^{\rm p}$ are presented. They were obtained by the COMPASS collaboration using polarised 200 GeV muons scattered off a longitudinally polarised NH$_3$ target. The data were collected in 2011 and complement those recorded in 2007 at 160\,GeV, in particular at lower values of $x$. They improve the statistical precision of $g_1^{\rm p}(x)$ by about a factor of two in the region $x\lesssim 0.02$. A next-to-leading order QCD fit to the $g_1$ world data is performed. It leads to a new determination of the quark spin contribution to the nucleon spin, $\Delta \Sigma$ ranging from 0.26 to 0.36, and to a re-evaluation of the first moment of $g_1^{\rm p}$. The uncertainty of $\Delta \Sigma$ is mostly due to the large uncertainty in the present determinations of the gluon helicity distribution. A new evaluation of the Bjorken sum rule based on the COMPASS results for the non-singlet structure function $g_1^{\rm NS}(x,Q^2)$ yields as ratio of the axial and vector coupling constants $|g_{\rm A}/g_{\rm V}| = 1.22 \pm 0.05~({\rm stat.}) \pm 0.10~({\rm syst.})$, which validates the sum rule to an accuracy of about 9\%.
Values of $A_1^{\rm p}$ and $g_1^{\rm p}$ for the 2011 COMPASS data at 200 GeV in ($x$, $Q^2$) bins.
Values of $A_1^{\rm p}$ and $g_1^{\rm p}$ for the 2011 COMPASS data at 200 GeV in $x$ bins averaged over $Q^2$.
Values of $A_1^{\rm p}$ for the 2007 COMPASS data at 160 GeV in ($x$, $Q^2$) bins.
The measurement of primary $\pi^{\pm}$, K$^{\pm}$, p and $\overline{p}$ production at mid-rapidity ($|y| <$ 0.5) in proton-proton collisions at $\sqrt{s} = 7$ TeV performed with ALICE (A Large Ion Collider Experiment) at the Large Hadron Collider (LHC) is reported. Particle identification is performed using the specific ionization energy loss and time-of-flight information, the ring-imaging Cherenkov technique and the kink-topology identification of weak decays of charged kaons. Transverse momentum spectra are measured from 0.1 up to 3 GeV/$c$ for pions, from 0.2 up to 6 GeV/$c$ for kaons and from 0.3 up to 6 GeV/$c$ for protons. The measured spectra and particle ratios are compared with QCD-inspired models, tuned to reproduce also the earlier measurements performed at the LHC. Furthermore, the integrated particle yields and ratios as well as the average transverse momenta are compared with results at lower collision energies.
Combined transverse momentum spectra of PI, K and P, sum of particles and antiparticles, measured at mid-rapidity in pp collisions at SQRT(S) = 7 TeV normalized to the number of inelastic collisions. Statistical and systematic uncertainties are reported. The uncertainty due to the normalization to inelastic collisions (+7-4 %) is not included.
Kaon/Pion ratio in pp collisions at SQRT(S) = 7 TeV.
Proton/Pion ratio in pp collisions at SQRT(S) = 7 TeV.
We have studied the transverse-momentum ($p_{\rm T}$) dependence of the inclusive J/$\psi$ production in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV, in three center-of-mass rapidity ($y_{\rm cms}$) regions, down to zero $p_{\rm T}$. Results in the forward and backward rapidity ranges ($2.03 < y_{\rm cms} < 3.53$ and $-4.46 <y_{\rm cms}< -2.96$) are obtained by studying the J/$\psi$ decay to $\mu^+\mu^-$, while the mid-rapidity region ($-1.37 < y_{\rm cms} < 0.43$) is investigated by measuring the ${\rm e}^+{\rm e}^-$ decay channel. The $p_{\rm T}$ dependence of the J/$\psi$ production cross section and nuclear modification factor are presented for each of the rapidity intervals, as well as the J/$\psi$ mean $p_{\rm T}$ values. Forward and mid-rapidity results show a suppression of the J/$\psi$ yield, with respect to pp collisions, which decreases with increasing $p_{\rm T}$. At backward rapidity no significant J/$\psi$ suppression is observed. Theoretical models including a combination of cold nuclear matter effects such as shadowing and partonic energy loss, are in fair agreement with the data, except at forward rapidity and low transverse momentum. The implications of the p-Pb results for the evaluation of cold nuclear matter effects on J/$\psi$ production in Pb-Pb collisions are also discussed.
$p_{\rm T}$-differential inclusive cross section ${\rm d}^2\sigma^{J/\psi}/{\rm d}y{\rm d}p_{T}$ in the backward rapidity range (-4.46<$y_{\rm cms}$<-2.96). The first uncertainty is statistical, the second one is the $p_{\rm T}$-uncorrelated systematic uncertainty, while the third is the $p_{\rm T}$-correlated one.
$p_{\rm T}$-differential inclusive cross section ${\rm d}^2\sigma^{J/\psi}/{\rm d}y{\rm d}p_{T}$ in the mid-rapidity range (-1.37<$y_{\rm cms}$<0.43). The first uncertainty is statistical, the second one is the $p_{\rm T}$-uncorrelated systematic uncertainty, while the third is the $p_{\rm T}$-correlated one.
$p_{\rm T}$-differential inclusive cross section ${\rm d}^2\sigma^{J/\psi}/{\rm d}y{\rm d}p_{T}$ in the forward rapidity range (2.03<$y_{\rm cms}$<3.53). The first uncertainty is statistical, the second one is the $p_{\rm T}$-uncorrelated systematic uncertainty, while the third is the $p_{\rm T}$-correlated one.
H1 and ZEUS have published single-differential cross sections for inclusive D^{*\pm}-meson production in deep-inelastic ep scattering at HERA from their respective final data sets. These cross sections are combined in the common visible phase-space region of photon virtuality Q2 > 5 GeV2, electron inelasticity 0.02 < y < 0.7 and the D^{*\pm} meson's transverse momentum pT (D^*) > 1.5 GeV and pseudorapidity |eta(D^*)| < 1.5. The combination procedure takes into account all correlations, yielding significantly reduced experimental uncertainties. Double-differential cross sections d2s /dQ2dy are combined with earlier D^{*\pm} data, extending the kinematic range down to Q2 > 1.5 GeV2. Perturbative next-to-leadingorder QCD predictions are compared to the results.
The combined differential $D^{*\pm}$-production cross section as a function of $p_T(D^{*})$, with its uncorrelated and correlated uncertainties.
The combined differential $D^{*\pm}$-production cross section as a function of $\eta(D^{*})$, with its uncorrelated and correlated uncertainties.
The combined differential $D^{*\pm}$-production cross section as a function of $z(D^{*})$, with its uncorrelated and correlated uncertainties.
The first study of W boson production in pPb collisions is presented, for bosons decaying to a muon or electron, and a neutrino. The measurements are based on a data sample corresponding to an integrated luminosity of 34.6 inverse nanobarns at a nucleon-nucleon centre-of-mass energy of sqrt(s[NN]) = 5.02 TeV, collected by the CMS experiment. The W boson differential cross sections, lepton charge asymmetry, and forward-backward asymmetries are measured for leptons of transverse momentum exceeding 25 GeV, and as a function of the lepton pseudorapidity in the abs(eta[lab]) < 2.4 range. Deviations from the expectations based on currently available parton distribution functions are observed, showing the need for including W boson data in nuclear parton distribution global fits.
Lepton charge asymmetry, $(N_{\ell}^+ - N_{\ell}^-)/(N_{\ell}^+ + N_{\ell}^-)$ as a function of the lepton pseudorapidity.
Production cross section for $\textrm{pPb} \to W^+ + X \to \ell \nu + X$ for positively (top) and negatively (bottom) charged leptons of $p_T$ larger than 25 GeV$/c$, in nanobarns, as a function of the lepton pseudorapidity. Values are given first for muons and electrons separately, then combined. The global normalization uncertainty of 3.5\% is not included in the listed uncertainties.
Production cross section for $\textrm{pPb} \to W^- + X \to \ell \nu + X$ for positively (top) and negatively (bottom) charged leptons of $p_T$ larger than 25 GeV$/c$, in nanobarns, as a function of the lepton pseudorapidity. Values are given first for muons and electrons separately, then combined. The global normalization uncertainty of 3.5\% is not included in the listed uncertainties.
Measurements of the ZZ production cross sections in proton-proton collisions at center-of-mass energies of 7 and 8 TeV are presented. Candidate events for the leptonic decay mode ZZ to 2 l 2 nu, where l denotes an electron or a muon, are reconstructed and selected from data corresponding to an integrated luminosity of 5.1 (19.6) inverse femtobarns at 7 (8) TeV collected with the CMS experiment. The measured cross sections, sigma(pp to ZZ) = 5.1 -1.4 +1.5 (stat) -1.1 +1.4 (syst) +/- 0.1 (lumi) pb at 7 TeV, and 7.2 -0.8 +0.8 (stat.) -1.5 +1.9 (syst) +/- 0.2 (lumi) pb at 8 TeV, are in good agreement with the standard model predictions with next-to-leading-order accuracy. The selected data are analyzed to search for anomalous triple gauge couplings involving the ZZ final state. In the absence of any deviation from the standard model predictions, limits are set on the relevant parameters. These limits are then combined with the previously published CMS results for ZZ in 4 l final states, yielding the most stringent constraints on the anomalous couplings.
pp->ZZ->2l2nu reduced-MET distribution in the 7 TeV dataset. Uncertainties are statistical. Last bin includes overflow events.
pp->ZZ->2l2nu reduced-MET distribution in the 8 TeV dataset. Uncertainties are statistical. Last bin includes overflow events.
pp->ZZ->2l2nu dilepton pT distribution in the 7 TeV dataset. Uncertainties are statistical. Last bin includes overflow events.
A search is presented for narrow diboson resonances decaying to $WW$ or $WZ$ in the final state where one $W$ boson decays leptonically (to an electron or a muon plus a neutrino) and the other $W/Z$ boson decays hadronically. The analysis is performed using an integrated luminosity of 20.3 fb$^{-1}$ of $pp$ collisions at $\sqrt{s}$ = 8 TeV collected by the ATLAS detector at the LHC. No evidence for resonant diboson production is observed, and resonance masses below 700 GeV and 1490 GeV are excluded at 95% confidence level for the spin-2 Randall-Sundrum bulk graviton $G^*$ with coupling constant of 1.0 and the extended gauge model $W'$ boson respectively.
Reconstructed mass distribution in the low-pt resolved region (LRR).
Reconstructed mass distribution in the high-pt resolved region (HRR).
Reconstructed mass distribution in the merged region (MR).
This Letter presents a search for a heavy neutral particle decaying into an opposite-sign different-flavor dilepton pair, $e^\pm \mu^\mp$, $e^\pm \tau^\mp$, or $\mu^\pm \tau^\mp$ using 20.3 fb$^{-1}$ of $pp$ collision data at $\sqrt{s} = 8$ TeV collected by the ATLAS detector at the LHC. The numbers of observed candidate events are compatible with the Standard Model expectations. Limits are set on the cross section of new phenomena in two scenarios: the production of $\tilde{\nu}_{\tau}$ in $R$-parity-violating supersymmetric models and the production of a lepton-flavor-violating $Z'$ vector boson.
Observed and predicted $e\mu$ invariant mass distributions.
The expected invariant mass distribution of signal Z'@0.75TeV and $\tilde{\nu}_{\tau}$@1TeV. The arbitrary choice of couplings are: $\lambda_{311}^{'}=0.11$ and $\lambda_{i3k}=0.07$ for $\tilde{\nu}_{\tau}$, $Q_{ll^{'}}=1$ for Z' .
Observed and predicted $e\tau$ invariant mass distributions.
Forum