The spectra of charged hadrons produced near mid-rapidity in d+Au, p+Au and n+Au collisions at 200 GeV center of mass energy per nucleon pair are presented as a function of transverse momentum and centrality. These measurements were performed using the PHOBOS detector at the Relativistic Heavy Ion Collider (RHIC). Nucleon-nucleus interactions were extracted from the d+Au data by identifying the deuteron spectators. The deuteron spectators were measured using two calorimeters; one that detected forward-going single neutrons and a newly installed calorimeter that detected forward-going single protons. The large suppression of high-pT hadron production in central Au+Au interactions relative to a naive superposition of p+pbar collisions has been interpreted as evidence of partonic energy loss in a dense medium. This interpretation is founded upon the absence of such suppression in the yield of d+Au collisions. It is shown that d+Au is indeed a valid reference system, as hadron production in d+Au agrees with a simple binary collision scaling of hadron production in p+Au. An ideal reference for Au+Au collisions is constructed using a weighted combination of p+Au and n+Au yields and is found to be similar to the d+Au reference. Further, hadron production in p+Au interactions is compared to that of n+Au interactions, in order to study the transport of charge from the initial state to mid-rapidity. No asymmetry between the positively and negatively charged hadron spectra of p+Au and n+Au interactions is observed for particles having an average pseudo-rapidity of 0.8. A study of the Cronin enhancement of hadrons produced in d+Au collisions using different centrality measures is also presented. A smooth evolution with centrality is observed, independent of the chosen centrality measure, when centrality is parameterized by the multiplicity density measured near mid-rapidity.
We present transverse momentum (p_T) spectra of charged hadrons measured in deuteron-gold and nucleon-gold collisions at \sqrts = 200 GeV for four centrality classes. Nucleon-gold collisions were selected by tagging events in which a spectator nucleon was observed in one of two forward rapidity detectors. The spectra and yields were investigated as a function of the number of binary nucleon-nucleon collisions, ν, suffered by deuteron nucleons. A comparison of charged particle yields to those in p+p collisions show that the yield per nucleon-nucleon collision saturates with νfor high momentum p…
The three-dimensional picture of quarks and gluons in the proton is set to be revealed through Deeply virtual Compton scattering while a critically important puzzle in the one-dimensional picture remains, namely, the origins of the EMC effect. Incoherent nuclear DVCS, i.e. DVCS on a nucleon inside a nucleus, can reveal the 3D partonic structure of the bound nucleon and shed a new light on the EMC effect. However, the Fermi motion of the struck nucleon, off-shell effects and final-state interactions (FSIs) complicate this parton level interpretation. We propose here a measurement of incoherent …
An attempt to extract critical exponents gamma, beta and tau from data on gold nuclei fragmentation due to interactions with nuclear emulsion at energies 4.0 A GeV and 10.6 A GeV is presented. Based on analysis of Campi's 2nd charge moments, two subsets of data at each energy are selected from the inclusive data, corresponding to 'liquid' and 'gas' phases. The extracted values of critical exponents from the selected data sets are in agreement with predictions of 'liquid-gas' model of phase transition.
We propose to measure tagged deep inelastic scattering from light nuclei (deuterium and $^4$He) by detecting the low energy nuclear spectator recoil (p, $^3$H and $^3$He) in addition to the scattered electron. The proposed experiment will provide stringent tests leading to clear differentiation between the many models describing the EMC effect, by accessing the bound nucleon virtuality through its initial momentum at the point of interaction. Indeed, conventional nuclear physics explanations of the EMC effect mainly based on Fermi motion and binding effects yield very different predictions tha…
Forward calorimetry in the PHOBOS detector has been used to study charged hadron production in d+Au, p+Au and n+Au collisions at sqrt(s_nn) = 200 GeV. The forward proton calorimeter detectors are described and a procedure for determining collision centrality with these detectors is detailed. The deposition of energy by deuteron spectator nucleons in the forward calorimeters is used to identify p+Au and n+Au collisions in the data. A weighted combination of the yield of p+Au and n+Au is constructed to build a reference for Au+Au collisions that better matches the isospin composition of the gold…
We present work in a model used to describe semi-inclusive deep inelastic scattering off the deuteron. The model uses the virtual nucleon approximation to describe the interaction of the photon with the bound neutron and the generalized eikonal approximation is applied to calculate the final-state interaction diagram. Comparison with data taken at Jefferson Lab shows good agreement in the covered range of kinematics and points at a largely suppressed off-shell rescattering amplitude. The $W$ and $Q^2$ dependences of the total cross section and slope factor of the interaction of DIS products, $…
The modification of jet shapes in PbPb collisions, relative to those in pp collisions, is studied for jets associated with an isolated photon. The data were collected with the CMS detector at the LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Jet shapes are constructed from charged particles with track transverse momenta ($p_\mathrm{T}$) above 1 GeV/c in annuli around the axes of jets with $p^\mathrm{jet}_\mathrm{T}$ $>$ 30 GeV/c associated with an isolated photon with $p^γ_\mathrm{T}$ $>$ 60 GeV/c. The jet shape distributions are consistent between peripheral PbPb and pp collisio…
Electroweak bosons produced in conjunction with jets in high-energy collider experiments is one of the principle final-state channels that can be used to test the accuracy of perturbative Quantum Chromodynamics calculations and to assess the potential to uncover new physics through comparison between data and theory. In this paper we present results for the $Z^0/γ^*$+jet production cross sections at the LHC at leading and next-to-leading orders. In proton-proton reactions we elucidate up to ${\cal O}(G_Fα_s^2)$ the constraints that jet tagging via the $Z^0/γ^*$ decay dileptons provides on the …
Hyperon production off the proton in the $K^0 Σ^+$ channel has been studied at the tagged photon beam facility at the ELSA electron accelerator in Bonn. This experiment was part of a series of neutral meson production experiments on various targets. For this purpose, the Crystal Barrel and TAPS photon spectrometers have been combined to provide a $4 π$ detector for multi-neutral-particle final states. A high-quality excitation function, recoil polarizations, and angular distributions from threshold up to 2.3 GeV center-of-mass energy were obtained. The results are compared with predictions of …
The yield of charged particles opposite to a $Z$ boson with large transverse momentum ($p_{T}$) is measured in 260 pb$^{-1}$ of $pp$ and 1.7 nb$^{-1}$ of Pb+Pb collision data at 5.02 TeV per nucleon pair recorded with the ATLAS detector at the Large Hadron Collider. The $Z$ boson tag is used to select hard-scattered partons with specific kinematics, and to observe how their showers are modified as they propagate through the quark-gluon plasma created in Pb+Pb collisions. Compared with $pp$ collisions, charged-particle yields in Pb+Pb collisions show significant modifications as a function of c…
The PHENIX experiment has measured single electron spectra at RHIC in proton-proton (p-p), deuteron-gold (d-Au), and gold-gold (Au-Au) collisions at an available energy per nucleon-nucleon pair of sqrt{s_NN} = 200 GeV. Contributions from photonic sources, i.e. Dalitz decays of light mesons and photon conversions, are subtracted from the inclusive spectra. The remaining non-photonic single electron spectra are dominated by semileptonic decays of particles carrying heavy flavor. Implications of these systematic measurements for heavy flavor production in cold and hot nuclear systems are discusse…
We obtain leading- and next-to-leading order predictions of chiral perturbation theory for several prominent moments of nucleon structure functions. These free-parameter free results turn out to be in overall agreement with the available empirical information on nearly all of the considered moments, in the region of low-momentum transfer ($Q^2 < 0.3$ GeV$^2$). Especially surprising is the situation for the spin polarizability $δ_{LT}$, which thus far was not reproducible in chiral perturbation theory for proton and neutron simultaneously. This problem, known as the "$δ_{LT}$ puzzle," is not se…
Ultra-peripheral heavy ion collisions involve long range electromagnetic interactions at impact parameters larger than twice the nuclear radius, where the strong nucleon-nuecleon interactions are uneffective. We present recent results from the STAR collaboration on these ultra-peripheral interactions likes incoherent rho0 production in deuteron-gold collisions and interferometry in gold-gold collisions
Measurements of fragmentation functions for jets associated with an isolated photon are presented for the first time in pp and PbPb collisions. The analysis uses data collected with the CMS detector at the CERN LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Fragmentation functions are obtained for jets with p$_\mathrm{T}^\text{jet} >$ 30 GeV in events containing an isolated photon with p$_\mathrm{T}^γ>$ 60 GeV, using charged tracks with transverse momentum p$_\mathrm{T}^\text{trk} >$ 1 GeV in a cone around the jet axis. The association with an isolated photon constrains the initia…
The study of nucleon resonances in electromagnetic meson production with the CLAS detector is discussed. The electromagnetic interaction is complementary to pion scattering in the exploration of the nucleon excitation spectrum. Higher mass states often decouple from the $Nπ$ channel and are not seen in $πN \to πN$. Photoproduction of mesons, such as $KΛ$, $ωp$ and $η^\prime p$ may be more sensitive to many of these states. The CLAS detector, combined with the use of energy-tagged polarized photons and polarized electrons, as well as polarized targets and the measurement of recoil polarization,…
We review recent progress in studies of nuclear final-state interactions in deep inelastic scattering (DIS) off the lightest nuclei tagged by a recoil nucleon. These processes hold a lot of potential for resolving the outstanding issues related to the dynamics of hadronization in QCD. Within the minimal Fock component framework, valid at large Bjorken $x$, the main features of the theoretical approach based on the virtual nucleon approximation are elaborated. In this approach, the strong final-state interaction of the DIS products with the nuclear fragments is described by an effective eikonal…
The rho-0 has been photoproduced using tagged photon energies in the 700-1120 MeV region on 2H, 3He and 12C by utilizing the Fermi momentum of the bound nucleons to produce the rho-0. These energies lie mostly below the production threshold on the free proton. Large mass modifications are indicated from the analysis, together with large polarizations of the produced rho-0 mesons with helicity zero, unlike the case of coherent rho-0 production on nuclei.
The energy and nuclear mass dependences of the total hadronic cross section in the energy range 0.5-2.6 GeV have been measured at Bonn using the SAPHIR tagged photon beam. The measurement, performed on C, Al, Cu, Sn and Pb, provides the first photoabsorption data in the region 1.2-1.7 GeV. The results show a significant reduction of the photoabsorption strength on the bound nucleon compared to the free nucleon case in the whole energy region. Above 1.2 GeV this reduction decreases with the nuclear density and can be interpreted as a signature of a low energy onset of the shadowing effect.
This paper presents results on event-by-event elliptic flow fluctuations in Au+Au collisions at sqrt(s_NN)=200Gev, where the contribution from non-flow correlations has been subtracted. An analysis method is introduced to measure non-flow correlations, relying on the assumption that non-flow correlations are most prominent at short ranges (Delta eta < 2). Assuming that non-flow correlations are of the order that is observed in p+p collisions for long range correlations (Delta eta > 2), relative elliptic flow fluctuations of approximately 30-40% are observed. These results are consistent with p…
Charged-particle fragmentation functions for jets azimuthally balanced by a high-transverse-momentum, prompt, isolated photon are measured in $25$ pb$^{-1}$ of $pp$ and $0.49$ nb$^{-1}$ of Pb+Pb collision data at $5.02$ TeV per nucleon pair recorded with the ATLAS detector at the Large Hadron Collider. The measurements are compared to predictions of Monte Carlo generators and to measurements of inclusively selected jets. In $pp$ collisions, a different jet fragmentation function in photon-tagged events from that in inclusive jet events arises from the difference in fragmentation between light …
The cross sections of 110 radioactive nuclide with mass numbers 22 < A < 198 amu from the interaction of 2.2 GeV/nucleon deuterons from the Nuclotron of the Laboratory of High Energies (LHE), Joint Institute for Nuclear Research (JINR) at Dubna with a 197Au target are investigated using induced activity method. The results including charge and mass distributions are parameterized in terms of 3-parameter equation in order to complete the real isobaric distribution. Using data from charge distribution total mass-yield distribution was obtained. The analysis of the mass-yield distribution allows …
Results from the PHENIX Collaboration on the production of deuterons and anti-deuterons in collisions between gold nuclei at a nucleon-nucleon center-of-mass energy of sqrt(s) = 200 GeV are presented.
We fit the single-particle $p_t$ spectra of identified pions, kaons, and (anti)protons from central collisions of gold or lead nuclei at energies between 7.7 and 2760~GeV per nucleon pair. Blast wave model with included resonance production and with an assumption of partial chemical equilibrium is used and the fits are performed with the help of a Gaussian emulator process. A kinetic freeze-out temperature is found about 100~MeV for the lowest collision energies and 80~MeV at the LHC. The average transverse expansion velocity grows with increasing $\sqrt{s_{NN}}$ from 0.45 to 0.65. Due to part…
