Coherent diffractive photoproduction of $ρ^{0}$ mesons on gold nuclei at RHIC
STAR Collaboration, L. Adamczyk, J. K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, N. N. Ajitanand, I. Alekseev, D. M. Anderson, R. Aoyama, A. Aparin, D.… 展开作者
STAR Collaboration, L. Adamczyk, J. K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, N. N. Ajitanand, I. Alekseev, D. M. Anderson, R. Aoyama, A. Aparin, D. Arkhipkin, E. C. Aschenauer, M. U. Ashraf, A. Attri, G. S. Averichev, X. Bai, V. Bairathi, A. Behera, R. Bellwied, A. Bhasin, A. K. Bhati, P. Bhattarai, J. Bielcik, J. Bielcikova, L. C. Bland, I. G. Bordyuzhin, J. Bouchet, J. D. Brandenburg, A. V. Brandin, D. Brown, I. Bunzarov, J. Butterworth, H. Caines, M. Calderón de la Barca Sánchez, J. M. Campbell, D. Cebra, I. Chakaberia, P. Chaloupka, Z. Chang, N. Chankova-Bunzarova, A. Chatterjee, S. Chattopadhyay, X. Chen, X. Chen, J. H. Chen, J. Cheng, M. Cherney, W. Christie, G. Contin, H. J. Crawford, S. Das, L. C. De Silva, R. R. Debbe, T. G. Dedovich, J. Deng, A. A. Derevschikov, L. Didenko, C. Dilks, X. Dong, J. L. Drachenberg, J. E. Draper, L. E. Dunkelberger, J. C. Dunlop, L. G. Efimov, N. Elsey, J. Engelage, G. Eppley, R. Esha, S. Esumi, O. Evdokimov, J. Ewigleben, O. Eyser, R. Fatemi, S. Fazio, P. Federic, P. Federicova, J. Fedorisin, Z. Feng, P. Filip, E. Finch, Y. Fisyak, C. E. Flores, J. Fujita, L. Fulek, C. A. Gagliardi, D. Garand, F. Geurts, A. Gibson, M. Girard, D. Grosnick, D. S. Gunarathne, Y. Guo, A. Gupta, S. Gupta, W. Guryn, A. I. Hamad, A. Hamed, A. Harlenderova, J. W. Harris, L. He, S. Heppelmann, S. Heppelmann, A. Hirsch, G. W. Hoffmann, S. Horvat, B. Huang, T. Huang, H. Z. Huang, X. Huang, T. J. Humanic, P. Huo, G. Igo, W. W. Jacobs, A. Jentsch, J. Jia, K. Jiang, S. Jowzaee, E. G. Judd, S. Kabana, D. Kalinkin, K. Kang, K. Kauder, H. W. Ke, D. Keane, A. Kechechyan, Z. Khan, D. P. Kikoła, I. Kisel, A. Kisiel, S. R. Klein, L. Kochenda, M. Kocmanek, T. Kollegger, L. K. Kosarzewski, A. F. Kraishan, P. Kravtsov, K. Krueger, N. Kulathunga, L. Kumar, J. Kvapil, J. H. Kwasizur, R. Lacey, J. M. Landgraf, K. D. Landry, J. Lauret, A. Lebedev, R. Lednicky, J. H. Lee, W. Li, X. Li, C. Li, Y. Li, J. Lidrych, T. Lin, M. A. Lisa, Y. Liu, F. Liu, H. Liu, P. Liu, T. Ljubicic, W. J. Llope, M. Lomnitz, R. S. Longacre, S. Luo, X. Luo, G. L. Ma, Y. G. Ma, L. Ma, R. Ma, N. Magdy, R. Majka, D. Mallick, S. Margetis, C. Markert, H. S. Matis, K. Meehan, J. C. Mei, Z. W. Miller, N. G. Minaev, S. Mioduszewski, D. Mishra, S. Mizuno, B. Mohanty, M. M. Mondal, D. A. Morozov, M. K. Mustafa, Md. Nasim, T. K. Nayak, J. M. Nelson, M. Nie, G. Nigmatkulov, T. Niida, L. V. Nogach, T. Nonaka, S. B. Nurushev, G. Odyniec, A. Ogawa, K. Oh, V. A. Okorokov, D. Olvitt, B. S. Page, R. Pak, Y. Pandit, Y. Panebratsev, B. Pawlik, H. Pei, C. Perkins, P. Pile, J. Pluta, K. Poniatowska, J. Porter, M. Posik, A. M. Poskanzer, N. K. Pruthi, M. Przybycien, J. Putschke, H. Qiu, A. Quintero, S. Ramachandran, R. L. Ray, R. Reed, M. J. Rehbein, H. G. Ritter, J. B. Roberts, O. V. Rogachevskiy, J. L. Romero, J. D. Roth, L. Ruan, J. Rusnak, O. Rusnakova, N. R. Sahoo, P. K. Sahu, S. Salur, J. Sandweiss, M. Saur, J. Schambach, A. M. Schmah, W. B. Schmidke, N. Schmitz, B. R. Schweid, J. Seger, M. Sergeeva, P. Seyboth, N. Shah, E. Shahaliev, P. V. Shanmuganathan, M. Shao, A. Sharma, M. K. Sharma, W. Q. Shen, Z. Shi, S. S. Shi, Q. Y. Shou, E. P. Sichtermann, R. Sikora, M. Simko, S. Singha, M. J. Skoby, N. Smirnov, D. Smirnov, W. Solyst, L. Song, P. Sorensen, H. M. Spinka, B. Srivastava, T. D. S. Stanislaus, M. Strikhanov, B. Stringfellow, T. Sugiura, M. Sumbera, B. Summa, Y. Sun, X. M. Sun, X. Sun, B. Surrow, D. N. Svirida, A. H. Tang, Z. Tang, A. Taranenko, T. Tarnowsky, A. Tawfik, J. Thäder, J. H. Thomas, A. R. Timmins, D. Tlusty, T. Todoroki, M. Tokarev, S. Trentalange, R. E. Tribble, P. Tribedy, S. K. Tripathy, B. A. Trzeciak, O. D. Tsai, T. Ullrich, D. G. Underwood, I. Upsal, G. Van Buren, G. van Nieuwenhuizen, A. N. Vasiliev, F. Videbæk, S. Vokal, S. A. Voloshin, A. Vossen, G. Wang, Y. Wang, F. Wang, Y. Wang, J. C. Webb, G. Webb, L. Wen, G. D. Westfall, H. Wieman, S. W. Wissink, R. Witt, Y. Wu, Z. G. Xiao, W. Xie, G. Xie, J. Xu, N. Xu, Q. H. Xu, Y. F. Xu, Z. Xu, Y. Yang, Q. Yang, C. Yang, S. Yang, Z. Ye, Z. Ye, L. Yi, K. Yip, I. -K. Yoo, N. Yu, H. Zbroszczyk, W. Zha, Z. Zhang, X. P. Zhang, J. B. Zhang, S. Zhang, J. Zhang, Y. Zhang, J. Zhang, S. Zhang, J. Zhao, C. Zhong, L. Zhou, C. Zhou, X. Zhu, Z. Zhu, M. Zyzak
The STAR Collaboration reports on the photoproduction of $π^+π^-$ pairs in gold-gold collisions at a center-of-mass energy of 200 GeV/nucleon-pair. These pion pairs are produced when a nearly-real photon emitted by one ion scatters from the other ion.
We fit the $π^+π^-$ invariant mass spectrum with a combination of $ρ$ and $ω$ resonances and a direct $π^+π^-$ continuum. This is the first observation of the $ω$ in ultra-peripheral collisions, and the first measurement of $ρ-ω$ interference at energies where photoproduction is dominated by Pomeron exchange. The $ω$ amplitude is consistent with the measured $γp\rightarrow ωp$ cross section, a classical Glauber calculation and the $ω\rightarrowπ^+π^-$ branching ratio. The $ω$ phase angle is similar to that observed at much lower energies, showing that the $ρ-ω$ phase difference does not depend significantly on photon energy.
The $ρ^0$ differential cross section $dσ/dt$ exhibits a clear diffraction pattern, compatible with scattering from a gold nucleus, with 2 minima visible. The positions of the diffractive minima agree better with the predictions of a quantum Glauber calculation that does not include nuclear shadowing than with a calculation that does include shadowing.
We discuss the prospects of diffractive dijet photoproduction at the EIC to distinguish different fits of diffractive proton PDFs, different schemes of factorization breaking, to determine diffractive nuclear PDFs and pion PDFs from leading neutron production.
Feasibility studies of an observation of the exclusive diffractive bremsstrahlung at RHIC at $\sqrt{s} = 200$~GeV and at $\sqrt{s} = 500$~GeV are reported. A simplified approach to the photon and the scattered proton energy reconstruction is used. Influence of possible backgrounds is discussed.
In the framework of collinear factorization and next-to-leading order (NLO) perturbative QCD, we make predictions for inclusive and diffractive dijet photoproduction in electron-proton and electron-nucleus scattering in the EIC kinematics. We establish kinematic ranges in the ${\bar p}_T$, ${\bar η}$, $x_A^{\rm obs}$ and $x_γ^{\rm obs}$ variables, quantify sensitivity to small-$x$ nuclear PDFs, and analyze various scenarios of factorization breaking in the case of diffractive scattering.
The strong electromagnetic fields carried by relativistic highly charged ions make heavy-ion colliders attractive places to study photonuclear interactions and two-photon interactions. At RHIC, three experiments have studied coherent photoproduction of $ρ^0$, 4$π$, $J/ψ$, $e^+e^-$ pairs, and $e^+e^-$ pairs where the electron is bound to one of the incident nuclei. These results show that photoproduction studies are possible, and demonstrate some of the unique possibilities due to the symmetric final states and the ion targets. The LHC will reach photon-nucleon energies many times higher than a…
We calculate the cross section of inclusive dijet photoproduction in ultraperipheral collisions (UPCs) of heavy ions at the CERN Large Hadron Collider using next-to-leading order perturbative QCD and demonstrate that it provides a good description of the ATLAS data. We study the role of this data in constraining nuclear parton distribution functions (nPDFs) using the Bayesian reweighting technique and find that it can reduce current uncertainties of nPDFs at small $x$ by a factor of 2. We also make predictions for diffractive dijet photoproduction in UPCs and examine its potential to shed ligh…
We present a first, detailed study of diffractive dijet photoproduction at the recently approved electron-ion collider (EIC) at BNL. Apart from establishing the kinematic reaches for various beam types, energies and kinematic cuts, we make precise predictions at next-to-leading order (NLO) of QCD in the most important kinematic variables. We show that the EIC will provide new and more precise information on the diffractive parton density functions (PDFs) in the pomeron than previously obtained at HERA, illuminate the still disputed mechanism of global vs.\ only resolved-photon factorization br…
We make predictions for the cross sections of diffractive dijet photoproduction in $pp$, $pA$ and $AA$ ultraperipheral collisions (UPCs) at the LHC during Runs 1 and 2 using next-to-leading perturbative QCD. We find that the resulting cross sections are sufficiently large and, compared to lepton-proton scattering at HERA, have an enhanced sensitivity to small observed momentum fractions in the diffractive exchange, commonly denoted $z_{P}^{\rm jets}$, and an unprecedented reach in the invariant mass of the photon-nucleon system $W$. We examine two competing schemes of diffractive QCD factoriza…
In this work we investigate the photoproduction of radially excited vector mesons off nuclei in heavy ion relativistic collisions. In particular, we analyze the exclusive photoproduction of psi(2S) off nuclei, evaluating the coherent and the incoherent contributions to that process. The theoretical framework used in the present analysis is the light-cone dipole formalism and predictions are done for PbPb collisions at the CERN-LHC energy of 2.76 TeV. The theoretical uncertainties are analyzed and comparison is also done to the recent ALICE Collaboration data for the psi(1S) state photoproducti…
We present the inclusive and identified particle (pion, proton and their antiparticle) production in Single Diffraction Dissociation and Central Diffraction processes with the STAR detector at RHIC. The forward-scattered proton(s) are tagged in the STAR Roman Pot system while the charged particle tracks are reconstructed in the STAR Time Projection Chamber. Ionization energy loss and time of flight of charged particles are used for particle identification. In addition, the proton-antiproton production asymmetry as a function of rapidity is measured and used to study the baryon number transfer …
In this work we study the diffractive photoproduction of $J/Ψ$ in proton-proton, proton - nucleus and nucleus - nucleus collisions at LHC energies using the color dipole formalism and different models for the forward dipole - target scattering amplitude. Our goal is to estimate the theoretical uncertainty present in the current predictions in the literature. Our results are compared with the experimental data and predictions for higher energies are presented.
We present predictions for the J/psi and rho meson production in the heavy ion ultraperipheral collisions (UPC) for the current energy 2.76 TeV at the LHC. Both total cross sections and cross sections with the neutron emission from one or both nuclei are presented. We also analyse the RHIC rho meson photoproduction data and emphasize importance of these data to test the current model for nucleus break up in UPC.
Using next-to-leading order (NLO) perturbative QCD, we calculate the diffractive contribution to inclusive dijet photoproduction in Pb-Pb ultraperipheral collisions (UPCs) at the LHC and find that it does not exceed $5-10$% in small-$x_A$ bins in the ATLAS kinematics at $\sqrt{s_{NN}}=5.02$ TeV. Its smallness is a result of the restricted kinematics ($p_{T1} > 20$ GeV and $x_A > 0.001$), the large nuclear suppression of nuclear diffractive parton distribution functions predicted in the leading twist model of nuclear shadowing, and additional suppression due to QCD factorization breaking in dif…
We have discussed single and central diffractive production of $c \bar c$ pairs in the Ingelman-Schlein model. In these calculations we have included diffractive parton distributions obtained by the H1 collaboration at HERA and absorption effects neglected in some early calculations in the literature. The absorption effects which are responsible for the naive Regge factorization breaking cause that the cross section for diffractive processes is much smaller than that for the fully inclusive case, but could be measured at RHIC and LHC by imposing special condition on rapidity gaps. We discuss a…
We present a next-to-leading order QCD calculation of inclusive dijet photoproduction in ultraperipheral Pb-Pb collisions at the LHC and show that the results agree very well with various kinematic distributions measured by the ATLAS collaboration. The effect of including these data in nCTEQ or EPPS16 nuclear parton density functions (nPDFs) is then studied using the Bayesian reweighting technique. For an assumed total error of 5\% on the final data, its inclusion would lead to a significant reduction of the nPDF uncertainties of up to a factor of two at small values of the parton momentum fra…
The vector meson production in coherent hadron-hadron interactions at LHC energies is studied assuming that the color singlet $t$-channel exchange carries large momentum transfer. We consider the non-forward solution of the BFKL equation at high energy and large momentum transfer and estimate the rapidity distribution and total cross section for the process $h_1 h_2 \to h_1 J/ΨX$, where $h_i$ can be a proton or a nucleus. We predict large rates, which implies that the experimental identification can be feasible at the LHC.
A new effort to explore the diffractive regime in polarized $p+p$ collisions in a broad high energy range ($\sqrt{s}$ = 200 - 500 GeV) has been initiated with the STAR detector at RHIC. Staged implementation of multiple Roman Pot stations for tagging the forward proton in the diffractive processes will enable searches for the centrally produced for the possible gluon bound state via double Pomeron exchange process and the theoretically expected Odderon state in QCD by studying spin-dependent elastic scattering in a wide $t$-range with polarized $p+p$.
We argue that with an increase of the collision energy, elastic photoproduction of $ρ$ mesons on nuclei becomes affected by the significant cross section of photon inelastic diffraction into large masses, which results in the sizable inelastic nuclear shadowing correction to $σ_{γA \to ρA}$ and the reduced effective $ρ$-nucleon cross section. We take these effects into account by combining the vector meson dominance model, which we upgrade to include the contribution of high-mass fluctuations of the photon according to QCD constraints, and the Gribov-Glauber approximation for nuclear shadowing…
Experimental evidence from coherent diffractive proton scattering has been reported for two narrow baryonic resonances which decay predominantly to strange particles. These states, with masses close to 2.0 GeV would, if confirmed, be candidates for hidden strangeness states with unusual internal structure. In this paper we examine the literature on strangeness photoproduction, to seek additional evidence for or against these states. We find that one state is not confirmed, while for the other state there is some mild supporting evidence favoring its existence. New experiments are called for, a…
Photoproduction of $ϕ$-meson on protons was studied by means of linearly polarized photons at forward angles in the low-energy region from threshold to $E_γ$= 2.37 GeV. The differential cross sections at $t = -|t|_{min}$ do not increase smoothly as $E_γ$ increases, but show a local maximum at around 2.0 GeV. The angular distributions demonstrate that $ϕ$-mesons are photo-produced predominantly by helicity-conserving processes, and the local maximum is not likely due to unnatural-parity processes.
We argue that hadron production in coherent diffraction of proton on a heavy nucleus provides a very sensitive probe of the low-x QCD dynamics. This process probes the BFKL dynamics in proton and the non-linear gluon evolution in nucleus. We calculate the diffractive hadron production cross sections in the RHIC and LHC kinematic regions. To study the nuclear effects we introduce the diffractive nuclear modification factor. We show that unlike the nuclear modification factor for inclusive hadron production that has a very interesting dynamics at RHIC but is expected to be almost completely satu…
The strong electromagnetic fields of short duration associated with relativistic heavy ions make a heavy-ion collider a unique tool to study two-photon and photonuclear collisions. In this talk, we introduce the principles of photoproduction at hadron colliders, review recent results from RHIC on meson and e$^+$e$^-$ production. At RHIC, STAR has studied exclusive $ρ^{0}$ vector meson production and $ρ^{0}$ production accompanied by electromagnetic dissociation of both nuclei in collisions of AuAu at 62, 130 and 200 GeV. Recent results suggest the validity of the Glauber calculations for the v…
Transversity generalized parton distributions (GPDs) can be probed in diffractive electro- and photoproduction of two vector mesons on a hadron in kinematics where the two vector mesons are separated by a large rapidity gap. We report on calculations for this process in the case of coherent $ρ^0-ω$ meson production on a deuteron target. Our cross section results show that an electron-ion collider with deuteron beams and forward detectors could probe deuteron transversity GPDs.
