Pp Data Research Articles

Perspectives for heavy-flavour measurements in ALICE with the upgraded Inner Tracking System

The ALICE detector at the LHC is specifically designed to investigate the properties of the hot and dense medium, consisting of deconfined quarks and gluons (QGP), created in high energy heavy-ion collisions. Heavy-flavour particles are well- suited probes to investigate the properties of such a medium, since they are mainly pro- duced in the initial phase and they subsequently experience the full evolution of the col- lision. In the ALICE experiment, the Inner Tracking System (ITS) plays an important role for heavy-flavour measurements. Interesting results have been obtained by analyz- ing pp, p-Pb and Pb-Pb data collected so far. The upgrade of the ITS, combined with the expected increase of LHC luminosity in Pb-Pb collisions, will allow the current per- formance for heavy flavour measurements to be significantly improved in particular in the low momentum region, and new measurements will become accessible (e.g. the Λc baryon in Pb-Pb collisions). The perspectives for heavy-flavour measurements expected after the second long shut-down (LS2) of LHC will be discussed.

3D simultaneous joint PP‐PS prestack seismic inversion at Schiehallion field, United Kingdom Continental Shelf

ABSTRACTA workflow for simultaneous joint PP‐PS prestack inversion of data from the Schiehallion field on the United Kingdom Continental Shelf is presented and discussed. The main challenge, describing reasonable PS to PP data registration before any prestack or joint PP‐PS inversion, was overcome thanks to a two‐stage process addressing the signal envelope, then working directly on the seismic data to estimate appropriate time‐variant time‐shift volumes. We evaluated the benefits of including PS along with PP prestack seismic data in a joint inversion process to improve the estimated elastic property quality and also to enable estimation of density compared with other prestack and post‐stack inversion approaches. While the estimated acoustic impedance exhibited a similar quality independent of the inversion used (PP post‐stack, PP prestack or joint PP‐PS prestack inversion) the shear impedance estimation was noticeably improved by the joint PP‐PS prestack inversion when compared to the PP prestack inversion. Finally, the density estimated from joint PP and PS prestack data demonstrated an overall good quality, even where not well‐controlled. The main outcome of this study was that despite several data‐related limitations, inverting jointly correctly processed PP and PS data sets brought extra value for reservoir delineation as opposed to PP‐only or post‐stack inversion.

Observation of sequential Υ suppression in PbPb collisions

The sequential suppression of the individual Υ states in PbPb collisions with respect to their yields in pp data has been measured. The PbPb and pp datasets used in these proceedings correspond to integrated luminosities of 150/μb and 230/nb, respectively, collected by the CMS experiment at the LHC at 2.76 TeV in 2011. The relative suppression of the excited Υ states has been measured with respect to the Υ(1S) ground state, expressed as a double ratio [Υ(nS)/Υ(1S)]pbPb/[Υ(nS)/Υ(1S)]pp. The absolute suppression of the Υ(nS) yields in PbPb relative to the yields in pp scaled by the number of nucleon-nucleon collisions, RAA, is measured as a function of the collision centrality. Integrated over centrality, the RAA values for Υ(1S), Υ(2S), and the upper limit of Υ(3S) RAA are reported in this proceeding, which demonstrate the sequential suppression of the Υ(nS) states in PbPb collisions at LHC energies.

Study of jet quenching using di-jet and photon-jet events in PbPb collisions at 2.76 TeV with CMS

The first measurement of the transverse momentum imbalance of isolated-photon-jet pairs and the modification of fragmentation function of the inclusive jets in relativistic heavy ion collisions are reported. The analysis uses data from PbPb collisions at a center-of-mass energy of 2.76 TeV per nucleon pair and corresponding to an integrated luminosity of 150 μb−1 recorded by the CMS experiment at the LHC in 2011. For events containing an isolated photon with transverse momentum pT > 60 GeV/c and an associated jet with pT > 30 GeV/c, the photon-jet pT imbalance is studied as a function of collision centrality and compared to pp data and PYTHIA calculations at the same center-of-mass energy. Using the pT of the isolated photon as an estimate of the energy of the associated parton at production, this measurement allows an unbiased characterization of the in-medium parton energy loss. In addition, further study on the modification of jet fragmentation function was studied using inclusive jets with pT > 100 GeV/c. Both show the gradual centrality dependence of jet energy loss and fragmentation function modification.

Joint migration velocity analysis of PP- and PS-waves for VTI media

Combining PP-waves with mode-converted PS reflections in migration velocity analysis (MVA) can help build more accurate VTI (transversely isotropic with a vertical symmetry axis) velocity models. To avoid problems caused by the moveout asymmetry of PS-waves and take advantage of efficient MVA algorithms designed for pure modes, here we generate pure SS-reflections from PP and PS data using the [Formula: see text] method. Then the residual moveout in both PP and SS common-image gathers is minimized during iterative velocity updates. The model is divided into square cells, and the VTI parameters [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] are defined at each grid point. The objective function also includes the differences between the migrated depths of the same reflectors on the PP and SS sections. Synthetic examples confirm that 2D MVA of PP- and PS-waves may be able to resolve all four relevant parameters of VTI media if reflectors with at least two distinct dips are available. The algorithm is also successfully applied to a 2D line from 3D ocean-bottom seismic data acquired at Volve field in the North Sea. After the anisotropic velocity model has been estimated, accurate depth images can be obtained by migrating the recorded PP and PS data.

Full-waveform inversion of multicomponent data for horizontally layered VTI media

Although full-waveform inversion (FWI) has shown significant promise in reconstructing heterogeneous velocity fields, most existing methodologies are limited to acoustic models. We extend FWI to multicomponent (PP and PS) data from anisotropic media, with the current implementation limited to a stack of horizontal, homogeneous VTI (transversely isotropic with a vertical symmetry axis) layers. The algorithm is designed to estimate the interval vertical P- and S-wave velocities ([Formula: see text] and [Formula: see text]) and Thomsen parameters [Formula: see text] and [Formula: see text] from long-spread PP and PSV reflections. The forward-modeling operator is based on the anisotropic reflectivity technique, and the inversion is performed in the time domain using the gradient (Gauss-Newton) method. We employ nonhyperbolic semblance analysis and Dix-type equations to build the initial model. To identify the medium parameters constrained by the data, we perform eigenvalue/eigenvector decomposition of the approximate Hessian matrix for a VTI layer embedded between isotropic media. Analysis of the eigenvectors shows that the parameters [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] (density is assumed to be known) can be resolved not only by joint inversion of PP and PS data, but also with PP reflections alone. Although the inversion becomes more stable with increasing spreadlength-to-depth ([Formula: see text]) ratio, the parameters of the three-layer model are constrained even by PP data acquired on conventional spreads ([Formula: see text]). For multilayered VTI media, the sensitivity of the objective function to the interval parameters decreases with depth. Still, it is possible to resolve [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] for the deeper layers using PP-waves, if the ratio [Formula: see text] for the bottom of the layer reaches two. Mode-converted waves provide useful additional constraints for FWI, which become essential for smaller spreads. The insights gained here by examining horizontally layered models should help guide the inversion for heterogeneous TI media.

Measurement of isolated-photon+jet correlations in PbPb collisions at sNN=2.76 TeV with CMS

Abstract A measurement of the transverse momentum balance in isolated-photon+jet pairs in PbPb collisions is described. The analysis is performed using a dataset recorded by the CMS experiment at the LHC from PbPb collisions at s N N = 2.76 TeV , corresponding to an integrated luminosity of ∫ L d t = 150 μ b − 1 . For events containing an isolated photon with p T γ > 60 GeV / c and an associated jet with p T Jet > 30 GeV / c , the photon+jet transverse momentum balance is studied as a function of collision centrality and compared to pp data and PYTHIA calculations. Using the isolated photon as the probe of the partonic energy at production, this measurement allows an unbiased characterization of the in-medium parton energy loss. With increasing collision centrality, a significant decrease in the ratio p T Jet / p T γ relative to the pp reference is observed.

Diffraction at the LHC

We show that the diffractive pp (and p\bar{p}) data (on \sigma_tot, d\sigma_el/dt, proton dissociation into low-mass systems, \sigma^D(low M), and high-mass dissociation, d\sigma/d(\Delta\eta)) in a wide energy range from CERN-ISR to LHC energies, may be described in a two-channel eikonal model with only one `effective' pomeron. By allowing the pomeron coupling to the diffractive eigenstates to depend on the collider energy (as is expected theoretically) we are able to explain the low value of \sigma^D(low M) measured at the LHC. We calculate the survival probability, S^2, of a rapidity gap to survive `soft rescattering'. We emphasize that the values found for S^2 are particularly sensitive to the detailed structure of the diffractive eigenstates.

Measurements of jet shape in 2.76 TeV PbPb collisions with CMS

Abstract The fragmentation properties of inclusive jets produced in PbPb collisions at a center of mass energy of s N N = 2.76 TeV are characterized by measuring differential jet shapes. The jet shape is defined as the fractional jet transverse momentum carried by charged particles emitted at a distance r from the jet axis, with jets reconstructed using the anti- k T clustering algorithm. The jet shapes are measured for reconstructed jet p T , jet > 100 GeV / c and charged hardons with p T > 1 GeV / c . Different background subtraction methods are employed to remove the contribution from the underlying events. The results obtained for PbPb collisions as a function of collision centrality are compared to reference distributions from pp data collected at the same collision energy. For the most central collisions, the jet shapes are found to be modified at large distance from the jet axis.

Very High-pT Triggered Dihadron Correlations in PbPb Collisions at 2.76 TeV with CMS

Measurements of dihadron correlations triggered by very high-pT particles in 2.76 TeV PbPb collisions are presented. The analysis explores the full 2011 PbPb data set corresponding to an integrated luminosity of 150μb−1 collected by CMS. Long-range correlations driven by single-particle azimuthal anisotropies (characterized by the Fourier harmonics, vn) are measured up to pT∼50 GeV/c. After subtracting the v2 – v4 harmonic components, the associated particle yields on the near and away side of the residual jet-like dihadron correlations are studied over a wide kinematic range in trigger and associated particle pT, as a function of collision centrality. By comparing to pp data at the same energy, a suppression of about 50% in the away-side associated yield is observed for pTassoc>3GeV/c. The yield is found to be significantly enhanced up to a factor of 3–4 on the away side at pTassoc∼0.5GeV/c. A moderate enhancement is suggested on the near side.

W and Z in heavy ion collisions with CMS

Abstract Electroweak W and Z boson measurements in PbPb collisions at nucleon–nucleon center of mass energy s = 2.76 TeV at the LHC using the CMS detector are presented. The W analysis is based on 2010 PbPb data corresponding to an integrated luminosity of 7.3 μ b − 1 and also on 2011 pp data corresponding to an integrated luminosity of 231 n b − 1 . The Z analysis is based on 2011 PbPb data with an integrated luminosity of 150 μ b − 1 . The dependence of W and Z production as a function of PbPb collision centrality is studied and shown to scale with the number of NN binary collisions. W + and W − yields in PbPb and pp collisions are in agreement once we take into account the proton and neutron composition in Pb nuclei. The muon charge asymmetry is measured as a function of pseudo-rapidity and is in agreement with next-to-leading order perturbative QCD calculations.

Study of jet quenching using photon-jet events in PbPb collisions at 2.76 TeV with CMS

Abstract The first measurement of the transverse momentum ( p T ) imbalance of isolated–photon + jet pairs in relativistic heavy ion collisions is reported. The analysis uses data from PbPb collisions at a centre-of-mass energy of 2.76 TeV per nucleon pair, corresponding to an integrated luminosity of 150 μ b − 1 recorded by the CMS experiment at the LHC in 2011. For events containing an isolated photon with transverse momentum p T > 60 GeV / c and an associated jet with p T > 30 GeV / c , the photon + jet p T imbalance is studied as a function of collision centrality and compared to pp data and pythia calculations at the same centre-of-mass energy. Using the p T of the isolated photon as an estimate of the energy of the scattered parton, this measurement allows an unbiased characterization of the in-medium parton energy loss.

Results on Jet Spectra and Structure from ALICE

Full jet reconstruction in ALICE uses the combined information from charged and neutral particles. Essentially all jet constituents can be measured with large efficiency down to very low transverse momenta (pT > 150 MeV/c). This has the advantage to introduce a minimum bias on the jet fragmentation, in particular for low jet momenta and in the presence of quenching. In this article, we present preliminary results from reconstruction of charged jets in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV. The inclusive charged jet spectrum, the jet nuclear modification factors (R_AA, R_CP), the ratio of spectra measured with different resolution parameters and hadron-jet correlations are discussed. For pp data at the same center of mass energy, the inclusive spectrum of fully reconstructed jets and its resolution parameter dependence are reported.

Jet fragmentation functions in PbPb and pp collisions at 2.76 TeV with CMS

Abstract The jet fragmentation function of inclusive jets with p T > 100 GeV/c in PbPb collisions is measured for reconstructed charged particles with p T > 1 GeV/c within the jet cone. A data sample of PbPb collisions collected in 2011 at a center-of-mass energy of s N N = 2.76 TeV corresponding to an integrated luminosity of 129 μ b − 1 is used. The results for PbPb collisions as a function of collision centrality are compared to reference distributions based on pp data collected at the same collision energy. A centrality-ordered modification of the fragmentation function is revealed. For the most central collisions a significant rise of the PbPb/pp fragmentation function ratio for the softest fragmentation products with p T 3 GeV/c is observed.

Using converted-wave seismic data for lithology discrimination in a complex fluvial setting: Tenerife oil field, Middle Magdalena Valley, Colombia

The Middle Magdalena Basin is an actively producing region in Colombia, which in recent years has been chosen for development by means of water and steam flooding. However, complex stratigraphy has challenged the development of a detailed reservoir static model. The Tenerife 3C-3D experimental survey was conducted in 2009 as an integrated application (from acquisition design to interpretation) of multicomponent technology to differentiate lithology (sand and clay) in a Colombian field. The Tenerife 3C-3D survey was twice as expensive as conventional surveys in the same region, so a requirement was to evaluate its added value. The acquisition design resulted in a 22.3 km2 survey with a trace density of 480,000 traces/km2. After careful processing, the PP and PS data were jointly inverted for elastic properties. Even though density is the best discriminator for clay volume in this area, it was not possible to obtain a reliable estimate. Density log data were unavailable for all Tenerife wells, and shear sonic was available for only one well. However, it was possible to derive sand and shale probability volumes using the output elastic attributes from PP and PS joint inversion.

Phenomenological MSSM interpretation of the CMS 2011 7 TeV 5 fb−1results

We interpret within the phenomenological MSSM (pMSSM) results obtained by CMS using a pp data set collected in 2011 at 7 TeV, corresponding to an integrated luminosity of 5 fb 1 . The pMSSM is a 19-parameter realization of the MSSM defined at the SUSY scale, that captures most of the features of the general R-parity conserving weak-scale MSSM. A global Bayesian analysis is performed that yields posterior probability densities of model parameters, masses and observables. We provide conclusions that are more generic, and therefore more robust, than those derived in more constrained setups, including simplified models and models that impose particular SUSY breaking schemes, such as the CMSSM. Our results also comprise implications for the MSSM Higgs sector, as well as for dark matter searches. Furthermore, we discuss which scenarios currently escape detection despite a high production cross section. Our study thus gives a coherent global picture of how the current CMS searches constrain SUSY in general.

Jets and Vector Bosons in Heavy Ion Collisions

This paper reviews experimental results on jets and electroweak boson (photon,Wand Z) production in heavy-ion collisions, from the CMS and ATLAS detectors, using data collected during 2011 PbPb run and pp data collected at an equivalent energy. By comparing the two collision systems, the energy loss of the partons propagating through the medium produced in PbPb collisions can be studied. Its characterization is done using dijet events and isolated photon-jet pairs. Since the electroweak gauge bosons do not participate in the strong interaction, and are thus unmodified by the nuclear medium, they serve as clean probes of the initial state in the collision.

Observation of SequentialΥSuppression in PbPb Collisions

The suppression of the individual Υ(nS) states in PbPb collisions with respect to their yields in pp data has been measured. The PbPb and pp data sets used in the analysis correspond to integrated luminosities of 150 μb(-1) and 230 nb(-1), respectively, collected in 2011 by the CMS experiment at the LHC, at a center-of-mass energy per nucleon pair of 2.76 TeV. The Υ(nS) yields are measured from the dimuon invariant mass spectra. The suppression of the Υ(nS) yields in PbPb relative to the yields in pp, scaled by the number of nucleon-nucleon collisions, R(AA), is measured as a function of the collision centrality. Integrated over centrality, the R(AA) values are 0.56±0.08(stat)±0.07(syst), 0.12±0.04(stat)±0.02(syst), and lower than 0.10 (at 95% confidence level), for the Υ(1S), Υ(2S), and Υ(3S) states, respectively. The results demonstrate the sequential suppression of the Υ(nS) states in PbPb collisions at LHC energies.

Dijet imbalance in 2.76 TeV PbPb collisions in CMS

We present the measurement of dijet production in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV that is studied with the CMS detector at the LHC. We use data corresponding to an integrated luminosity of 150 μb−1. Jets are reconstructed using the anti-kT algorithm on particle flow objects. The dijet momentum balance and angular correlations are studied as a function of collision centrality and leading jet momentum. For the most peripheral PbPb collisions, good agreement of the dijet momentum balance distributions with pp data and reference calculations at the same collision energy is found. However, more central collisions show a strong imbalance of leading and subleading jet transverse momenta, confirming the previous observations made using a smaller dataset. The extended jet transverse momentum range significantly increases the discriminatory power of the measurement for different models of parton energy loss in hot QCD matter.

Studies of jet quenching using isolated-photon + jet correlations in PbPb and pp collisions at [formula omitted

Results from the first study of isolated-photon+jet correlations in relativistic heavy ion collisions are reported. The analysis uses data from PbPb collisions at a centre-of-mass energy of 2.76 TeV per nucleon pair corresponding to an integrated luminosity of 150 μb−1 recorded by the CMS experiment at the LHC. For events containing an isolated photon with transverse momentum pTγ>60 GeV/c and an associated jet with pTJet>30 GeV/c, the photon+jet pT imbalance is studied as a function of collision centrality and compared to pp data and pythia calculations at the same collision energy. Using the pTγ of the isolated photon as an estimate of the momentum of the associated parton at production, this measurement allows an unbiased characterisation of the in-medium parton energy loss. For more central PbPb collisions, a significant decrease in the ratio pTJet/pTγ relative to that in the pythia reference is observed. Furthermore, significantly more pTγ>60 GeV/c photons in PbPb are observed not to have an associated pTJet>30 GeV/c jet, compared to the reference. However, no significant broadening of the photon+jet azimuthal correlation is observed.