Observation and spectroscopy of proton-unbound nucleus $^{21}$Al
D. Kostyleva, X. -D. Xu, I. Mukha, L. Acosta, M. Bajzek, E. Casarejos, A. A. Ciemny, D. Cortina-Gil, W. Dominik, J. A. Dueñas, J. M. Espino, A. Estradé, F. Fari… 展开作者
D. Kostyleva, X. -D. Xu, I. Mukha, L. Acosta, M. Bajzek, E. Casarejos, A. A. Ciemny, D. Cortina-Gil, W. Dominik, J. A. Dueñas, J. M. Espino, A. Estradé, F. Farinon, A. Fomichev, H. Geissel, J. Gómez-Camacho, A. Gorshkov, L. V. Grigorenko, Z. Janas, G. Kamiński, O. Kiselev, R. Knöbel, A. A. Korsheninnikov, S. Krupko, M. Kuich, N. Kurz, Yu. A. Litvinov, G. Marquinez-Durán, I. Martel, C. Mazzocchi, E. Yu. Nikolskii, C. Nociforo, A. K. Ordúz, M. Pfützner, S. Pietri, M. Pomorski, A. Prochazka, C. Rodríguez-Tajes, S. Rymzhanova, A. M. Sánchez-Benítez, C. Scheidenberger, H. Simon, B. Sitar, R. Slepnev, M. Stanoiu, P. Strmen, K. Sümmerer, I. Szarka, M. Takechi, Y. K. Tanaka, H. Weick, J. S. Winfield, P. J. Woods, M. V. Zhukov
We report on the observation of previously-unknown isotope $^{21}$Al, the first unbound aluminum isotope located beyond the proton dripline. The $^{21}$Al nucleus decays by one-proton (1p) emission, and its in-flight decays were detected by tracking trajectories of all decay products with micro-strip silicon detectors. The 1p-emission processes were studied by analyses of the measured angular correlations of decay products $^{20}$Mg+p. The 1p-decay energies of ground and low-lying excited states of $^{21}$Al, its mass excess and proton separation energy value $S_p$=$-1.1(1)$ MeV were determined.
The statistical event-by-event analysis of inelastic interactions of protons in emulsion at 800 GeV reveals the existence of group of events with Gaussian pseudorapidity distributions for produced particles, as suggested by hydrodynamic-tube model. Events belong to very central collisions of protons with heavy emulsion nuclei with probability of realization of less than 1% and with multiplicity of shower particles exceeding (2-3 times) the average multiplicity in proton-nucleus collisions in emulsion. The Bjorken's energy density for these events reaches 2.0 GeV per fm^3. The data are interpre…
System-size dependence of Lambda and Xi production in nucleus--nucleus collisions at 40A and 158A GeV measured at the CERN Super Proton Synchrotron
给出了40 A和158 A GeV中心选择Pb+Pb反应和158 A GeV近中心C+C和Si+Si反应中λ、反λ和Xi-产生的结果。横向质谱，快度谱，和依赖于系统大小的多重性进行了讨论。运输模型（UrQMD2.3和HSD）和核心电晕的方法进行比较。虽然λ和反λ的产生可以通过传输模型合理地描述，但这些模型与Xi-测量不一致。另一方面，核心电晕图片非常适合的系统尺寸依赖的λ和Xi-，而它同意不太好与反λ数据。
Available data on the polarization of the secondary proton (as a function of its momentum $K$) in the inelastic ({\it p, p$'$}) reactions with the $^{9}$Be, $^{12}$C, and $^{40}$Ca nuclei and differential cross section data (the momentum distributions) for the reactions at the initial proton energy 1 GeV and scattering angles $Θ$=21$^\circ$ and $Θ$=24.5$^\circ$ were analysed in a range of the high momenta $K$ close to the momentum corresponding to the proton elastic scattering off the investigated nucleus. A structure in the polarization and momentum distribution data at the high momenum $K$, …
Many properties of the atomic nucleus, such as vibrations, rotations and incompressibility, can be interpreted as due to a two component quantum liquid of protons and neutrons. Electron scattering measurements on stable nuclei demonstrate that their central densities are saturated, as for liquid drops. In exotic nuclei near the limits of mass and charge, with large imbalances in their proton and neutron numbers, the possibility of a depleted central density, or a 'bubble' structure, has been discussed in a recurrent manner since the 1970s. Here we report first experimental evidence that points…
Initial state geometry and the role of hydrodynamics in proton-proton, proton-nucleus and deuteron-nucleus collisions
我们将成功的重离子碰撞的Monte Carlo Glauber和IP-Mehma初态模型应用于质子-质子、质子-核和氘-核碰撞中产生的小得多的系统。我们观察到一个显着更大的灵敏度的初始状态的几何形状，在这些模型中的多粒子生产的细节相比，核-核碰撞。特别是，我们发现，在p+A碰撞中产生的系统的大小是非常相似的p+p碰撞中产生的，并预测可比的Hanbury-Brown-Twiss半径在两个系统中没有流动。模型中计算的偏心率差异较大，而生成的流量系数v_2和v_3之间的差异较小。对于大量的质子-铅碰撞的参与者，在IP-Plumma模型中产生的v_2值与质子-质子碰撞中获得的值相当。在较小尺寸的系统中，对流动的粘性修正在特征寿命上是大的。相反，粘性的贡献显着减少了较长的时空演化的重离子碰撞。
Background: Eclipse effect of the neutron and proton in a deuteron target is essential to correctly describe high-energy deuteron scattering. The nucleus-deuteron scattering needs information not only on the nucleus-proton but also the nucleus-neutron interaction, for which no direct measurement of the nucleus-neutron cross sections is available for unstable nuclei. Purpose: We systematically evaluated the total reaction cross sections by a deuteron target to explore the feasibility of extracting the nucleus-neutron interaction from measurable cross sections. Methods: High-energy nucleus-deute…
We show that the incoherent elastic scattering of partons, as present in a multi-phase transport model (AMPT), with a modest parton-parton cross-section of $σ=1.5 - 3$ mb, naturally explains the long-range two-particle azimuthal correlation as observed in proton-proton and proton-nucleus collisions at the Large Hadron Collider.
In proton-nucleus and nucleus-nucleus collision experiments, one determines the centrality of a collision according to the multiplicity or energy deposited in a detector. This serves as a proxy for the true collision centrality, as defined by the impact parameter. We show that the probability distribution of impact parameter in a given bin of experiment-defined centrality can be reconstructed without assuming any specific model for the collision dynamics, in both proton-nucleus and nucleus-nucleus systems. The reconstruction is reliable up to about 10\% centrality, and is more accurate for nuc…
The PHENIX experiment at BNL-RHIC recently reported the single transverse spin asymmetry $A_N$ for forward neutrons measured in polarized proton-nucleus collisions at $\sqrt{s_{NN}} = 200\,$GeV; $A_N$ in proton-aluminum and proton-gold collisions are -0.015 and 0.18, respectively, which are clearly different from $A_N=-0.08$ in proton-proton collisions. In this paper, we propose large $A_N$ for forward neutrons in ultraperipheral polarized proton-nucleus collisions as an explanation of the PHENIX measurements. The proposed model is demonstrated using two Monte Carlo simulations organized as fo…
We perform the first study on asymmetric longitudinal decorrelations of elliptic, triangular and quadrangular flows in proton-nucleus collisions at the LHC and RHIC energies. To measure the longitudinal flow decorrelations for asymmetric collision systems, we propose a new set of rapidity-asymmetric flow decorrelation functions. Our event-by-event hydrodynamic calculations show that the flow decorrelations in proton-going direction are larger than those in nucleus-going direction. We also find that proton-nucleus collisions at RHIC have larger longitudinal flow decorrelation effects than those…
We find a new method to deduce nuclear radii from proton-nucleus elastic scattering data. In this method a nucleus is viewed as a ``black'' sphere. A diffraction pattern of protons by this sphere is equivalent to that of the Fraunhofer diffraction by a circular hole of the same radius embedded in a screen. We determine the black sphere radius in such a way as to reproduce the empirical value of the angle of the observed first diffraction peak. It is useful to identify this radius multiplied by $\sqrt{3/5}$ with the root-mean-square matter radius of the target nucleus. For most of stable isotop…
Rapidity-dependent transverse momentum spectra of negatively charged pions measured at different rapidities in proton-proton collisions at the Super Proton Synchrotron (SPS) at various energies within its Beam Energy Scan (BES) program are investigated by using one- and two-component standard distributions where the chemical potential and spin property of particles are implemented. The rapidity spectra are described by a double-Gaussian distribution. At the stage of kinetic freeze-out, the event patterns are structured by the scatter plots in the three-dimensional subspaces of velocity, moment…
Role of diproton correlation in two-proton emission decay of the $^6$Be nucleus
讨论了双质子关联在富质子核$^6$ Be基态双质子发射中的作用。假设$α+ p + p$组态为三体结构，我们发展了一种含时方法，将双质子发射描述为三体亚稳态的时间演化。利用这种方法，可以通过监测双粒子密度分布随时间的变化，直观地讨论双质子发射的动力学过程。与模型的哈密顿量，很好地再现实验的两个质子衰变宽度，我们表明，强关联的双质子发射是一个主导过程中的早期阶段的两个质子发射。当双质子关联不存在时，双质子发射与双质子发射竞争，衰变宽度被低估。这些结果表明，双质子发射衰变提供了一个很好的机会，探测质子滴线以外的丰质子核的双质子关联。
A new method is proposed to deduce the neutron radii of neutron-rich nuclei. This method requires measuring the reaction cross sections of both the neutron-rich nucleus and its stable isotope at the same energy on a proton target. Using this method and the available experimental data of $^{12,22}$C + $p$ and $^{9,14}$Be + $p$ at 40$A$ MeV, the neutron radii of $^{22}$C and $^{14}$Be have been deduced for the first time.
In this paper a role of many-nucleon dynamics in formation of the compound $^{5}{\rm Li}$ nucleus in the scattering of protons off $α$-particles at the proton incident energies up to 20 MeV is investigated. We propose a bremsstrahlung model allowing to extract information about probabilities of formation of such nucleus on the basis of analysis of experimental cross-sections of the bremsstrahlung photons. In order to realize this approach, the model includes elements of microscopic theory and also probabilities of formation of the short-lived compound nucleus. Results of calculations of the br…
The rapidity dependence of elliptic, $v_2$, and triangular, $v_3$, flow coefficients in proton-nucleus (p+A) collisions is predicted in hydrodynamics and in a multi-phase transport model (AMPT). We find that $v_n$ ($n=2,3$) on a nucleus side is significantly larger than on a proton side and the ratio between the two, $v_n^{\rm Pb}/v_n^{\rm p}$, weekly depends on the transverse momentum of produced particles.
Centrality, as a geometrical property of the collision, is crucial for the physical interpretation of nucleus-nucleus and proton-nucleus experimental data. However, it cannot be directly accessed in event-by-event data analysis. Common methods for centrality estimation in A-A and p-A collisions usually rely on a single detector (either on the signal in zero-degree calorimeters or on the multiplicity in some semi-central rapidity range). In the present work, we made an attempt to develop an approach for centrality determination that is based on machine-learning techniques and utilizes informati…
We present an analysis of $Ξ^-$ baryon production in subthreshold proton--nucleus ($p+A$) collisions in the framework of a BUU type transport model. We propose a new mechanism for $Ξ$ production in the collision of a secondary $Λ$ or $Σ$ hyperon and a nucleon from the target nucleus. We find that the $Ξ^-$ multiplicity in $p+A$ collisions is sensitive to the angular distribution of hyperon production in the primary $N+N$ collision. Using reasonable assumptions on the unknown elementary cross sections we are able to reproduce the $Ξ^-$ multiplicity and the $Ξ^-/(Λ+Σ^0)$ ratio obtained in the HA…
A new approach is presented to determine the proton-nucleus interactions from the analysis of the accompanying photon bremsstrahlung. We study the scattering of $p + ^{208}{\rm Pb}$ at the proton incident energies of 140 and 145~MeV, and the scattering of $p + ^{12}{\rm C}$, $p + ^{58}{\rm Ni}$, $p + ^{107}{\rm Ag}$ and $p + ^{197}{\rm Au}$ at the proton incident energy of 190~MeV. The model determines contributions of the coherent emission (formed by an interaction between the scattering proton and nucleus as a whole without the internal many-nucleon structure), incoherent emission (formed by…
The transverse momentum spectra of charged particles produced in proton(deuteron)-nucleus and nucleus-nucleus collisions at high energies are analyzed by the Hagedorn thermal model and the standard distribution in terms of multi-component. The experimental data measured in central and peripheral gold-gold (Au-Au) and deuteron-gold ($d$-Au) collisions by the PHENIX Collaboration at the Relativistic Heavy Ion Collider (RHIC), as well as in central and peripheral lead-lead (Pb-Pb) and proton-lead ($p$-Pb) collisions by the ALICE Collaboration at the Large Hadron Collider (LHC) are fitted by the t…
High energy proton-nucleus (pA) collisions provide an important constraint on the study of the chiral magnetic effect in QCD matter. Naively, in pA collisions one expects no correlation between the orientation of event plane as reconstructed from the azimuthal distribution of produced hadrons and the orientation of magnetic field. If this is the case, any charge-dependent hadron correlations can only result from the background. Nevertheless, in this paper we point out that in high multiplicity pA collisions a correlation between the magnetic field and the event plane can appear. This is becaus…
The first observation of top quark production in proton-nucleus collisions is reported using proton-lead data collected by the CMS experiment at the CERN LHC at a nucleon-nucleon center-of-mass energy of sqrt(s[NN]) = 8.16 TeV. The measurement is performed using events with exactly one isolated electron or muon and at least four jets. The data sample corresponds to an integrated luminosity of 174 inverse nanobarns. The significance of the tt-bar signal against the background-only hypothesis is above five standard deviations. The measured cross section is sigma[tt-bar] = 45 +/- 8 nb, consistent…
The study of multiparticle correlations and collectivity in the hot and dense matter created in collisions of heavy-ions as well as those of smaller systems such as proton--heavy-ion collisions has progressed to the point where detailed knowledge of the three-dimensional structure of the proton is needed to confront experimental data. We discuss results from a simple proof-of-principle initial state parton model which reproduces many features of the data on proton--heavy-ion collisions that are often ascribed to hydrodynamic flow. We outline how this model can be further improved with particul…
The observation of long-range collective correlations for particles emitted in high-multiplicity pp and pPb collisions has opened up new opportunities of investigating novel high-density QCD phenomena in small colliding systems. We review experimental results related to the studies of collective phenomena in small systems from RHIC and the LHC over the past several years. Latest development in theoretical interpretations motivated by different frameworks are also reviewed, and confronted with the experimental data. Perspectives on possible future directions are discussed, with the aim of furth…
I give a brief overview of the recent theoretical progress in the study of quarkonium production in proton-nucleus collisions in view of the recent LHC and RHIC results. A special emphasis is put on the excited states such as the psi', Upsilon(2S) and Upsilon(3S).
We apply a Color Glass Condensate+Non-Relativistic QCD (CGC+NRQCD) framework to compute $J/ψ$ production in deuteron-nucleus collisions at RHIC and proton-nucleus collisions at the LHC. Our results match smoothly at high $p_\perp$ to a next-to-leading order perturbative QCD + NRQCD computation. Excellent agreement is obtained for $p_\perp$ spectra at RHIC and LHC for central and forward rapidities, as well as for the normalized ratio $R_{pA}$ of these results to spectra in proton-proton collisions. In particular, we observe that the $R_{pA}$ data is strongly bounded by our computations of the …
An experimental overview of the energy dependence of strangeness production is presented. The strange hadrons are considered a good probe to study the QCD matter created in relativistic nucleus-nucleus collisions. The heavy-ion experiments at SPS, RHIC, and LHC have recorded a wealth of data in proton-proton, proton-nucleus and nucleus-nucleus collisions at several beam energies. In this proceeding, I discuss the invariant yield and azimuthal anisotropy measurement of strange hadrons in nucleus-nucleus collisions at SPS, RHIC, and LHC.
Studying experimental data obtained at ITEP [1] on neutron production in interactions of protons with various nuclei in the energy range from 747 MeV up to 8.1 GeV, we have found that slow neutron spectra have scaling and asymptotic properties [2]. The spectra weakly depend on the collision energy at momenta of projectile protons larger than 5 - 6 GeV/c. These properties are taken into account in the Geant4 Fritiof (FTF) model. The improved FTF model describes as well as the Geant4 Bertini model the experimental data on neutron production by 1.2 GeV and 1.6 GeV protons on targets (Fe, Pb) [3] …
The cross section for the nuclear diffractive dissociation in proton-lead collisions at the LHC is estimated. Based on the current theoretical uncertainties for the single (target) diffactive cross section in hadron-hadron reactions one obtains sigma_SD(5.02 TeV) = 19.67 \pm 5.41 mb and sigma_SD(8.8 TeV) = 18.76 \pm 5.77 mb, respectively. The invariant mass M_X for the reaction pPb -> pX is also analyzed. Discussion is performed on the main theoretical uncertainties associated to the calculations.
