Browsing by Subject "PROTON"

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  • Mäntysaari, Heikki; Schenke, Björn (2020)
    We show how exclusive vector meson production off light ions can be used to probe the spatial distribution of small-x gluons in the deuteron and He-3 wave functions. In particular, we demonstrate how short-range repulsive nucleon-nucleon interactions affect the predicted coherent J/Psi production spectra. Fluctuations of the nucleon substructure are shown to have a significant effect on the incoherent cross section above vertical bar t vertical bar greater than or similar to 0.2 GeV2. By explicitly performing the Jalilian-Marian-Iancu-McLerran-Weigert-Leonidov-Kovner (JIMWLK) evolution, we predict the x dependence of coherent and incoherent cross sections in the electron-ion collider energy range. In addition to the increase of the average size of the nucleus with decreasing x, both the growth of the nucleons and subnucleonic hot spots are visible in the cross sections. The decreasing length scale of color charge fluctuations with decreasing x is also present, but may not be observable for vertical bar t vertical bar <1 GeV2, if subnucleonic spatial fluctuations are present.
  • Paukkunen, Hannu; Zurita, Pia (2016)
    New data coming from the LHC experiments have a potential to extend the current knowledge of parton distribution functions (PDFs). As a short cut to the cumbersome and time consuming task of performing a new PDF fit, re weighting methods have been proposed. In this talk, we introduce the so-called Hessian re-weighting, valid for PDF fits that carried out a Hessian error analysis, and compare it with the better-known Bayesian methods. We determine the existence of an agreement between the two approaches, and illustrate this using the inclusive jet production at the LHC.
  • d'Enterria, David; Eskola, Kari J.; Helenius, Ilkka; Paukkunen, Hannu (2014)
  • Annila, A. (2015)
    Spectrum of cosmic rays follows a broken power law over twelve orders of magnitude. Since ubiquitous power laws are manifestations of the principle of least action, we interpret the spectrum accordingly. Our analysis complies with understanding that low-energy particles originate mostly from rapidly receding sources throughout the cosmos. The flux peaks about proton rest energy whereafter it decreases because fewer and fewer receding sources are energetic enough to provide particles with high enough velocities to compensate for the recessional velocities. Above 10(15.6) eV the flux from the expanding Universe diminishes below the flux from the nearby nonexpanding part of the Universe. In this spectral feature, known as the "knee," we relate to a distance of about 1.3 Mpc where the gravitational potential tallies the energy density of free space. At higher energies particles decelerate in a dissipative manner to attain thermodynamic balance with the vacuum. At about 10(17.2) eV a distinct dissipative mechanism opens up for protons to slow down by electron-positron pair production. At about 10(19.6) eV a more effective mechanism opens up via pion production. All in all, the universal principle discloses that the broad spectrum of cosmic rays probes the structure of space from cosmic distances down to microscopic details.
  • Goharipour, Muhammad; Khanpour, Hamzeh; Guzey, Vadim (2018)
    We present GKG18-DPDFs, a next-to-leading order (NLO) QCD analysis of diffractive parton distribution functions (diffractive PDFs) and their uncertainties. This is the first global set of diffractive PDFs determined within the xFitter framework. This analysis is motivated by all available and most up-to-date data on inclusive diffractive deep inelastic scattering (diffractive DIS). Heavy quark contributions are considered within the framework of the Thorne-Roberts (TR) general mass variable flavor number scheme (GM-VFNS). We form a mutually consistent set of diffractive PDFs due to the inclusion of high-precision data from H1/ZEUS combined inclusive diffractive cross sections measurements. We study the impact of the H1/ZEUS combined data by producing a variety of determinations based on reduced data sets. We find that these data sets have a significant impact on the diffractive PDFs with some substantial reductions in uncertainties. The predictions based on the extracted diffractive PDFs are compared to the analyzed diffractive DIS data and with other determinations of the diffractive PDFs.
  • The ALICE collaboration; Acharya, S.; Adamova, D.; Kim, D. J.; Krizek, F.; Molander, Mikael Andreas; Novitzky, Norbert; Onnerstad, A.; Parkkila, J. E.; Rytkönen, Heidi Maria; Räsänen, Sami; Saarimäki, Oskari Antti Matti; Slupecki, M.; Trzaska, W. H. (2022)
  • Adam, J.; Brucken, E. J.; Chang, B.; Kim, D. J.; Litichevskyi, V.; Mieskolainen, M. M.; Orava, R.; Rak, J.; Räsänen, S. S.; Snellman, T. W.; Trzaska, W. H.; Viinikainen, J.; The ALICE collaboration (2017)
    Two-particle angular correlations were measured in pp collisions at root s = 7 TeV for pions, kaons, protons, and lambdas, for all particle/anti-particle combinations in the pair. Data for mesons exhibit an expected peak dominated by effects associated with mini-jets and are well reproduced by general purpose Monte Carlo generators. However, for baryon-baryon and anti-baryon-anti-baryon pairs, where both particles have the same baryon number, a near-side anti-correlation structure is observed instead of a peak. This effect is interpreted in the context of baryon production mechanisms in the fragmentation process. It currently presents a challenge to Monte Carlo models and its origin remains an open question.
  • The ALICE collaboration; Adamová, D.; Brucken, E.J.; Chang, B.; Kim, D.J.; Litichevskyi, V.; Mieskolainen, M.M.; Orava, R.; Rak, J.; Räsänen, S.S.; Saarinen, S.; Slupecki, M.; Snellman, T.W.; Trzaska, W.H.; Vargyas, M.; Viinikainen, J. (2018)
    We report measurements of the inclusive J/psi yield and average transverse momentum as a function of charged-particle pseudorapidity density dNch/d.in p-Pb collisions at root s(NN)= 5.02 TeVwith ALICE at the LHC. The observables are normalised to their corresponding averages in non-single diffractive events. An increase of the normalised J/psi yield with normalised dN(ch)/d(eta), measured at mid-rapidity, is observed at mid-rapidity and backward rapidity. At forward rapidity, a saturation of the relative yield is observed for high charged-particle multiplicities. The normalised average transverse momentum at forward and backward rapidities increases with multiplicity at low multiplicities and saturates beyond moderate multiplicities. In addition, the forward-to-backward nuclear modification factor ratio is also reported, showing an increasing suppression of J/psi production at forward rapidity with respect to backward rapidity for increasing charged-particle multiplicity. (C) 2017 The Author. Published by Elsevier B. V.
  • The ALICE collaboration; Acharya, S.; Adamova, D.; Kim, D. J.; Krizek, F.; Novitzky, Norbert; Onnerstad, B.S.; Parkkila, J. E.; Rak, Jan; Rytkönen, Heidi Maria; Räsänen, Sami; Saarimäki, Oskari Antti Matti; Slupecki, M.; Trzaska, W. H. (2021)
    Deuteron production in high-energy collisions is sensitive to the space-time evolution of the collision system, and is typically described by a coalescence mechanism. For the first time, we present results on jet-associated deuteron production in pp collisions at root s = 13 TeV, providing an opportunity to test the established picture for deuteron production in events with a hard scattering. Using a trigger particle with high transverse-momentum (p(T) > 5 GeV/c) as a proxy for the presence of a jet at midrapidity, we observe a measurable population of deuterons being produced around the jet proxy. The associated deuteron yield measured in a narrow angular range around the trigger particle differs by 2.4-4.8 standard deviations from the uncorrelated background. The data are described by PYTHIA model calculations featuring baryon coalescence. (C) 2021 The Author. Published by Elsevier B.V.
  • Singh, B. S. Nara; Cullen, D. M.; Taylor, M. J.; Srivastava, P. C.; Van Isacker, P.; Beeke, O.; Dodson, B.; Scholey, C.; O'Donell, D.; Jakobson, U.; Grahn, T.; Greenlees, P. T.; Jones, P. M.; Julin, R.; Khan, S.; Leino, M.; Leppänen, A-P.; Eeckhaudt, S.; Mäntyniemi, K.; Pakarinen, J.; Peura, P.; Rahkila, P.; Saren, J.; Sorri, J.; Uusitalo, J.; Venhart, M. (2018)
    Excited states above the 17(+) isomeric state in the proton-rich nucleus Tm-152 were established by employing the recoil-isomer tagging technique. Data were collected using the JUROGAM gamma-ray array and the GREAT spectrometer together with the recoil ion transport unit (RITU) gas-filled recoil separator and analyzed to identify the prompt and delayed gamma decays from the levels in Tm-152. Shell-model calculations, either in a large valence space or in a reduced model space with five protons in the pi 0h(11)(/2) orbital and one neutron in the nu 1 f(7/2) orbital, agree with the observed energies of the yrast levels up to angular momentum J = 21. The observation of near degeneracies in the energy spectrum can be attributed to specific components of the proton-neutron interaction. The isomeric decay of the 17(+) level is not reproduced in the shell-model calculations as it arises from a delicate balance between hindrance due to seniority selection rules and enhancement due to configuration mixing.
  • McKay, D.; Paavilainen, T.; Gustavsson, B.; Kvammen, A.; Partamies, N. (2019)
    The development of a magnetospheric substorm may be classified into three phases: growth, expansion, and recovery. The growth phase is important as it includes processes that lead to the expansion. In a recent growth-phase study, a type of fast discrete auroral transient phenomena-referred to as Lumikot-were observed. The Lumikot are several kilometers across and move in the high-energy precipitation region, parallel to the main growth-phase arc, with both east-west and west-east directions of travel during the same event. Their apparent transverse movement and quasi-stable intensity make them distinct from cooccurring optical pulsating aurorae. Comparison to other studies show that they occur in the cosmic noise absorption region and it is likely that the Lumikot are colocated with high-energy particle populations on the boundary between the outer radiation belt and the plasmasheet.
  • Aidala, C.; Kim, D. J.; PHENIX Collaboration (2017)
    We present measurements of long-range angular correlations and the transverse momentum dependence of elliptic flow v(2) in high-multiplicity p + Au collisions at root S-NN = 200 GeV. A comparison of these results to previous measurements in high-multiplicity d + Au and He-3+Au collisions demonstrates a relation between v(2) and the initial collision eccentricity epsilon(2), suggesting that the observed momentum-space azimuthal anisotropies in these small systems have a collective origin and reflect the initial geometry. Good agreement is observed between the measured v(2) and hydrodynamic calculations for all systems, and an argument disfavoring theoretical explanations based on initial momentum-space domain correlations is presented. The set of measurements presented here allows us to leverage the distinct intrinsic geometry of each of these systems to distinguish between different theoretical descriptions of the long-range correlations observed in small collision systems.
  • The ALICE collaboration; Acharya, S.; Brücken, E. J.; Chang, B.; Hilden, T. E.; Kim, D. J.; Litichevskyi, V.; Mieskolainen, M. M.; Orava, R.; Parkkila, J. E.; Rak, J.; Räsänen, S. S.; Saarinen, S.; Slupecki, M.; Snellman, T. W.; Trzaska, W. H.; Vargyas, M.; Viinikainen, J. (2019)
    In this letter, the production of deuterons and anti-deuterons in pp collisions at root s = 7 TeV is studied as a function of the charged-particle multiplicity density at mid-rapidity with the ALICE detector at the LHC. Production yields are measured at mid-rapidity in five multiplicity classes and as a function of the deuteron transverse momentum (p(T)). The measurements are discussed in the context of hadron-coalescence models. The coalescence parameter B-2, extracted from the measured spectra of (anti-)deuteronsand primary (anti-)protons, exhibits no significant p(T)-dependence for p(T) < 3 GeV/c, in agreement with the expectations of a simple coalescence picture. At fixed transverse momentum per nucleon, the B-2 parameter is found to decrease smoothly from low multiplicity pp to Pb-Pb collisions, in qualitative agreement with more elaborate coalescence models. The measured mean transverse momentum of (anti-)deuterons in pp is not reproduced by the Blast-Wave model calculations that simultaneously describe pion, kaon and proton spectra, in contrast to central Pb-Pb collisions. The ratio between the p(T)-integrated yield of deuterons to protons, d/p, is found to increase with the charged-particle multiplicity, as observed in inelastic pp collisions at different centre-of-mass energies. The d/p ratios are reported in a wide range, from the lowest to the highest multiplicity values measured in pp collisions at the LHC. (C) 2019 The Author(s). Published by Elsevier B.V
  • The ALICE collaboration; Acharya, S.; Brücken, E. J.; Chang, B.; Hilden, T. E.; Kim, D. J.; Litichevskyi, V.; Mieskolainen, M. M.; Orava, R.; Parkkila, J. E.; Rak, J.; Räsänen, S. S.; Saarinen, S.; Slupecki, M.; Snellman, T. W.; Trzaska, W. H.; Vargyas, M.; Viinikainen, J. (2019)
    Comprehensive results on the production of unidentified charged particles, pi(+/-), K-+/-, K-s(0), K*(892)(0), p, (p) over bar, phi(1020), Lambda, (Lambda) over bar, Xi(-) , (Xi) over bar (+), Omega(-), and (Omega) over bar (+) hadrons in proton-proton (pp) collisions at root s = 7 TeV at midrapidity (vertical bar y vertical bar < 0.5) as a function of charged-particle multiplicity density are presented. In order to avoid autocorrelation biases, the actual transverse momentum (p(T)) spectra of the particles under study and the event activity are measured in different rapidity windows. In the highest multiplicity class, the charged-particle density reaches about 3.5 times the value measured in inelastic collisions. While the yield of protons normalized to pions remains approximately constant as a function of multiplicity, the corresponding ratios of strange hadrons to pions show a significant enhancement that increases with increasing strangeness content. Furthermore, all identified particleto-pion ratios are shown to depend solely on charged-particle multiplicity density, regardless of system type and collision energy. The evolution of the spectral shapes with multiplicity and hadron mass shows patterns that are similar to those observed in p-Pb and Pb-Pb collisions at Large Hadron Collider energies. The obtained p(T), distributions and yields are compared to expectations from QCD-based pp event generators as well as to predictions from thermal and hydrodynamic models. These comparisons indicate that traces of a collective, equilibrated system are already present in high-multiplicity pp collisions.
  • Aschenauer, E. C.; Fazio, S.; Lamont, M. A. C.; Paukkunen, H.; Zurita, P. (2017)
    The quantitative knowledge of heavy nuclei's partonic structure is currently limited to rather large values of momentum fraction x-robust experimental constraints below x similar to 10(-2) at low resolution scale Q(2) are particularly scarce. This is in sharp contrast to the free proton's structure which has been probed in Deep Inelastic Scattering (DIS) measurements down to x similar to 10(-5) at perturbative resolution scales. The construction of an electron-ion collider (EIC) with a possibility to operate with a wide variety of nuclei, will allow one to explore the low-x region in much greater detail. In the present paper we simulate the extraction of the nuclear structure functions from measurements of inclusive and charm reduced cross sections at an EIC. The potential constraints are studied by analyzing simulated data directly in a next-toleading order global fit of nuclear Parton Distribution Functions based on the recent EPPS16 analysis. A special emphasis is placed on studying the impact an EIC would have on extracting the nuclear gluon parton distribution function, the partonic component most prone to nonlinear effects at low Q(2). In comparison to the current knowledge, we find that the gluon parton distribution function can be measured at an EIC with significantly reduced uncertainties.
  • Wijsen, N.; Aran, A.; Scolini, C.; Lario, D.; Afanasiev, A.; Vainio, R.; Sanahuja, B.; Pomoell, J.; Poedts, S. (2022)
    Aims. We model the energetic storm particle (ESP) event of 14 July 2012 using the energetic particle acceleration and transport model named 'PArticle Radiation Asset Directed at Interplanetary Space Exploration' (PARADISE), together with the solar wind and coronal mass ejection (CME) model named 'EUropean Heliospheric FORcasting Information Asset' (EUHFORIA). The simulation results illustrate both the capabilities and limitations of the utilised models. We show that the models capture some essential structural features of the ESP event; however, for some aspects the simulations and observations diverge. We describe and, to some extent, assess the sources of errors in the modelling chain of EUHFORIA and PARADISE and discuss how they may be mitigated in the future. Methods. The PARADISE model computes energetic particle distributions in the heliosphere by solving the focused transport equation in a stochastic manner. This is done using a background solar wind configuration generated by the ideal magnetohydrodynamic module of EUHFORIA. The CME generating the ESP event is simulated by using the spheromak model of EUHFORIA, which approximates the CME's flux rope as a linear force-free spheroidal magnetic field. In addition, a tool was developed to trace CME-driven shock waves in the EUHFORIA simulation domain. This tool is used in PARADISE to (i) inject 50 keV protons continuously at the CME-driven shock and (ii) include a foreshock and a sheath region, in which the energetic particle parallel mean free path, lambda(parallel to), decreases towards the shock wave. The value of lambda(parallel to) at the shock wave is estimated from in situ observations of the ESP event. Results. For energies below similar to 1 MeV, the simulation results agree well with both the upstream and downstream components of the ESP event observed by the Advanced Composition Explorer. This suggests that these low-energy protons are mainly the result of interplanetary particle acceleration. In the downstream region, the sharp drop in the energetic particle intensities is reproduced at the entry into the following magnetic cloud, illustrating the importance of a magnetised CME model.
  • Walt, Marina; Helenius, Ilkka; Vogelsang, Werner (2019)
    We present new sets of nuclear parton distribution functions (nPDFs) at next-to-leading order and next-to-next-to-leading order. Our analyses are based on deeply inelastic scattering data with charged-lepton and neutrino beams on nuclear targets. In addition, a set of proton baseline PDFs is fitted within the same framework with the same theoretical assumptions. The results of this global QCD analysis are compared to existing nPDF sets and to the fitted cross sections. Also, the uncertainties resulting from the limited constraining power of the included experimental data are presented. The published work is based on an open-source tool, xFitter, which has been modified to be applicable also for a nuclear PDF analysis. The required extensions of the code are discussed as well.
  • The ALICE collaboration; Acharya, S.; Brucken, E. J.; Chang, B.; Kim, D. J.; Litichevskyi, V.; Mieskolainen, M. M.; Orava, R.; Rak, J.; Räsänen, S. S.; Saarinen, S.; Slupecki, M.; Snellman, T. W.; Trzaska, W. H.; Vargyas, M.; Viinikainen, J. (2018)
    A measurement of beauty hadron production at mid-rapidity in proton-lead collisions at a nucleon-nucleon centre-of-mass energy root s(NN) = 5.02 TeV is presented. The semi-inclusive decay channel of beauty hadrons into J/psi is considered, where the J/psi mesons are reconstructed in the dielectron decay channel at mid-rapidity down to transverse momenta of 1.3 GeV/c. The bb production cross section at mid-rapidity, d sigma(bb)/dy, and the total cross section extrapolated over full phase space, sigma(bb), are obtained. This measurement is combined with results on inclusive J/psi production to determine the prompt J/psi cross sections. The results in p-Pb collisions are then scaled to expectations from pp collisions at the same centre-of-mass energy to derive the nuclear modification factor R-pPb, and compared to models to study possible nuclear modifications of the production induced by cold nuclear matter effects. RpPb is found to be smaller than unity at low pT for both J/psi coming from beauty hadron decays and prompt J/psi.
  • Kern, R.; Zidarova, R.; Pietralla, N.; Rainovski, G.; Stegmann, R.; Blazhev, A.; Boukhari, A.; Cederkall, J.; Cubiss, J. G.; Djongolov, M.; Fransen, C.; Gaffney, L. P.; Gladnishki, K.; Giannopoulos, E.; Hess, H.; Jolie, J.; Karayonchev, V.; Kaya, L.; Keatings, J. M.; Kocheva, D.; Kroell, Th; Möller, O.; O'Neill, G. G.; Pakarinen, J.; Reiter, P.; Rosiak, D.; Scheck, M.; Snäll, J.; Söderström, P.-A.; Spagnoletti, P.; Stoyanova, M.; Thiel, S.; Vogt, A.; Warr, N.; Welker, A.; Werner, M.; Wiederhold, J.; De Witte, H. (2020)
    A projectile Coulomb-excitation experiment was performed at the radioactive-ion beam facility HIE-ISOLDE at CERN to obtain E2 and M1 transition matrix elements of Nd-140 using the multistep Coulomb-excitation code GOSIA. The absolute M1 strengths, B(M1; 2(2)(-) -> 2(1)(+)) = 0.033(8)mu(2)(N), B(M1 ; 2(3)(+) -> 2(1)(+)) = 0.26(-0.10)(+0.11)mu(2)(N), and B(M1; 2(4)+ -> 2(1)(+)) <0.04 mu(2)(N) identify the 2(3)(+) state as the main fragment of the one-quadrupole-phonon proton-neutron mixed-symmetry state of Nd-140. The degree of F-spin mixing in Nd-140 was quantified with the determination of the mixing matrix element VF-mix <7(-7)(-13) keV.