DOCSLIB.ORG

Dilepton As a Possible Signature for the Baryon-Rich Quark-Gluon Plasma

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

PHYSICAL REVIE%' C VOLUME 41, NUMBER 2 FEBRUARY 1990 Dilepton as a possible signature for the baryon-rich quark-gluon plasma L. H. Xia, ' C. M. Ko, and C. T. Li Cyclotron Institute and Center for Theoretical Physics, Texas A&M University, College Station, Texas 77843 (Received 31 July 1989) In an expanding fireball model, we study dilepton production from high-energy heavy-ion col- lisions at the stopping regime. We find that the pion-pion annihilation gives the dominant contribu- tion to the dilepton yield at invariant masses between 2m„and 1 GeV. The total dilepton yield in this invariant mass region increases with the incident energy of the collision, but a saturation is seen once a baryon-rich quark-gluon plasma is formed in the initial stage. I. INTRODUCTION dilepton. It was suggested that the disappearance of the rho peak in the dilepton invariance mass spectrum might ' The ultimate goal of heavy-ion collisions at ultrarela- signal the formation of a quark-gluon plasma. ' De- tivistic energies is to create a deconfined quark-gluon tailed studies including the proper treatment of the ex- plasma. ' It is hoped that during the initial stage of the pansion dynamics, however, do not support such a possi- ' collision, a region of high-energy density will be produced bility. These studies are all concerned with the baryon so that a transition from the hadronic matter to the free quark-gluon plasma that might be produced in future quark-gluon plasma will take place. For future experi- RHIC energies. At the AGS, energies in the range of ments at the proposed relativistic heavy-ion collider about 15 GeV/nucleon, a dense hadronic matter will be (RHIC) a baryon free quark-gluon plasma is expected to formed if no quark-gluon plasma is created in the initial be created because of the increasing transparency of the stage. In the hadronic matter, dileptons can be produced nuclear matter with increasing collision energies. At from both pn bremsstrahlung and the m~ annihilation. present, the CERN experiments at both 60 GeV/nucleon For dense hadronic matter at high temperatures, it has and 200 GeV/nucleon indicate that the incident projec- been shown in Refs. 15 and 16 that the contribution from tile is not completely stopped by the target and a high- the stan annihilation is more significant than that from the ' energy density of many GeV/fm has been reached. The pn bremsstrahlung for dileptons of invariant masses in observation of the suppressed production of the J/4 par- the region of 2m to about 1 GeV, where m is the mass ticle has already stimulated great excitements as it might of pion. It is also found in Refs. 15-17 that the be a possible evidence for the formation of a quark-gluon modification of the pion dispersion relation by the dense plasma. However, it will not be considered as a nuclear matter because of the strong p-wave mN interac- definitive signature until a better understanding of the tion can lead to an enhanced production of dileptons at dissociation of J/4 by the hadronic particles is small invariant masses. This effect becomes more pro- achieved. For experiments carried out at the nounced as the density of the hadronic matter increases. Brookhaven National Laboratory Alternating Gradient On the other hand, if a baryon-rich quark-gluon plasma Synchrotron (AGS) at 14.5 GeV/nucleon, the analysis of is initially formed, then dileptons will be produced from the final transverse energy distribution indicates that the the qq annihilation. After the hadronization of the projectile is indeed completely stopped by the target and quark-gluon plasma, dileptons can also be produced from that a hadronic matter of density about five times the the hadronic matter via the pn bremsstrahlung and the normal nuclear matter density has been reached in the in- mm annihilation. Since the total entropy cannot decrease itial stage. Whether a baryon-rich quark-gluon plasma during the transition, the final hadronic matter will be at has been formed in such a collision is still uncertain. It a higher temperature and lower density than the initial ' has been argued in the past that the formation of a quark-gluon matter. If the quark-gluon plasma contrib- quark-gluon plasma may be signaled by an enhanced pro- utes mainly to dileptons with larger invariant masses, duction of kaons relative to that of pions. Data obtained then we expect a reduced production of dileptons with at the AGS indeed show an enhancement of a factor of 4 low invariant masses, compared with the case without the for K+/m. + ratio compared with that from the proton- formation of a quark-gluon plasma because of the low ha- proton and the proton-nucleus collisions. However, dronic matter density after its hadronization. In this theoretical studies show that a substantial enhancement case, it is of interest to measure the total yield of dilepton can be obtained by assuming either the formation of a with the invariant mass in the region of 2m to about 1 quark-gluon plasma or a dense hadronic matter in the ini- GeV as a function of the incident energy. The onset of a tial stage of the collision. ' " In view of the ambiguity baryon-rich quark-gluon plasma is thus signaled by the associated with these observables as signatures for the appearance of a plateau in this excitation function. quark-gluon plasma, the consideration of other observ- To substantiate this conjecture, we have carried out ables will be very useful. calculations for dilepton production based on the hydro- A very interesting suggestion in the past has been the dynamical description of heavy-ion collisions. In Sec. II, 41 572 1990The American Physical Society 41 DILEPTON AS A POSSIBLE SIGNATURE FOR THE BARYON-. 573 the nuclear phase diagram is introduced. The initial con- dg I k'dk (3b) dition of the fireball and its hydrodynamical expansion Q (k +P )/T 2~2 p e ' are described in Sec. III. The kinetic processes and the +1 hadronization model are discussed in Sec. IV. In Sec. V, dG P~ k dk G (3c) the elementary dilepton production processes are dis- 2 2 Jp k/T cussed. The results for dilepton production from high- energy heavy-ion collisions are presented in Sec. VI. Conclusions are given in Sec. VII. A brief report of this which lead to the total energy density in the quark-gluon work has already been published in Ref. 19. plasma e =eQ+e — q Q +eG+B II. NUCLEAR PHASE DIAGRAM 3p 30 T+3p T+ 2 +8 (4) Based on the quantum chromodynamics, it is generally believed that the nuclear matter exists in a deconfined where B is the bag constant. From the number and ener- phase of quarks and gluons when its density and tempera- gy densities, the pressure and entropy densities of the ture are high. The determination of the nuclear phase di- quark-gluon plasma are given by agram from the quantum chromodynamics however, a is, = — — diScult task. Instead, we shall use a simplified model to pq —,'(e 8) 8, construct the nuclear phase diagram. It is determined by 1 considering both the hadronic and the quark-gluon s =—(e+p 3p—n ). (6) matter as composed of noninteracting nonstrange parti- cles with the latter supplemented by a bag constant. This model of the nuclear phase diagram has been used previ- B. Equation of state for the hadronic phase ously in Refs. 20 and 21. As pointed out in these refer- ences, the inclusion of strange particles affects the phase For the hadronic matter, we include only nonstrange diagram only slightly. Since we shall look for qualitative stable hadrons (nucleon, pion, and eta) and their reso- signatures for the formation of a quark-gluon plasma, we nances (b,'s, N "s, p, and co) as in Refs. 20 and 21. In the believe that such a model will be suScient in the present case that their interactions can be neglected, the number work. For completeness, we describe briefly in the fol- density n;, the energy density e;, and the pressure p; of lowing the construction of the nuclear phase diagram in the ith particle are given by this simple model. d; „kdk n,. = ( — ) /T 2~2 p e e( p(. A. Equation of state for quark-gluon phase d, ek dk For the noninteracting quark-gluon matter consisting e;= — 2 p (, p)/ of the up and down quarks and the gluons, the quark e density the antiquark density and the den- nQ, nQ, gluon d, „e;'k dk sity can be written as nG 2 (E( )/T p e p( g (. k~dk — where e,. =(k +m; )'~ . In the above, + is for fermions Q 2 2 Jp (k P )/T e and —for bosons. The d; indicates the degeneracy, while dQ ~ k dk the chemical potential is denoted by p, . For baryons, we (lb) Q 2 (k+@ )/T have p; =b; pb, where b; is the baryon number and pb is 2 p e the baryon chemical potential. The total baryon number k 2dk and energy density, as well as the pressure of the hadron- nG = „=16((3)Tim. (1c) = = p e" — ic matter are then given by nb h g, b; n;, eh e;, and 2~ I 1 = g; ph g; p;, respectively. From these thermodynamical respectively. In the above, we have g(3}=1.20206, the quantities, the entropy density is quark degeneracy dQ = 12, the gluon degeneracy dG = 16, the chemical potential for the quark, and the tempera- 1 p ~h T(eh+Ph Pbnb, h } ture T.
Recommended publications
  • The Five Common Particles

    The Five Common Particles

    The Five Common Particles The world around you consists of only three particles: protons, neutrons, and electrons. Protons and neutrons form the nuclei of atoms, and electrons glue everything together and create chemicals and materials. Along with the photon and the neutrino, these particles are essentially the only ones that exist in our solar system, because all the other subatomic particles have half-lives of typically 10-9 second or less, and vanish almost the instant they are created by nuclear reactions in the Sun, etc. Particles interact via the four fundamental forces of nature. Some basic properties of these forces are summarized below. (Other aspects of the fundamental forces are also discussed in the Summary of Particle Physics document on this web site.) Force Range Common Particles It Affects Conserved Quantity gravity infinite neutron, proton, electron, neutrino, photon mass-energy electromagnetic infinite proton, electron, photon charge -14 strong nuclear force ≈ 10 m neutron, proton baryon number -15 weak nuclear force ≈ 10 m neutron, proton, electron, neutrino lepton number Every particle in nature has specific values of all four of the conserved quantities associated with each force. The values for the five common particles are: Particle Rest Mass1 Charge2 Baryon # Lepton # proton 938.3 MeV/c2 +1 e +1 0 neutron 939.6 MeV/c2 0 +1 0 electron 0.511 MeV/c2 -1 e 0 +1 neutrino ≈ 1 eV/c2 0 0 +1 photon 0 eV/c2 0 0 0 1) MeV = mega-electron-volt = 106 eV. It is customary in particle physics to measure the mass of a particle in terms of how much energy it would represent if it were converted via E = mc2.
  • Higgs and Particle Production in Nucleus-Nucleus Collisions

    Higgs and Particle Production in Nucleus-Nucleus Collisions

    Higgs and Particle Production in Nucleus-Nucleus Collisions Zhe Liu Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Graduate School of Arts and Sciences Columbia University 2016 c 2015 Zhe Liu All Rights Reserved Abstract Higgs and Particle Production in Nucleus-Nucleus Collisions Zhe Liu We apply a diagrammatic approach to study Higgs boson, a color-neutral heavy particle, pro- duction in nucleus-nucleus collisions in the saturation framework without quantum evolution. We assume the strong coupling constant much smaller than one. Due to the heavy mass and colorless nature of Higgs particle, final state interactions are absent in our calculation. In order to treat the two nuclei dynamically symmetric, we use the Coulomb gauge which gives the appropriate light cone gauge for each nucleus. To further eliminate initial state interactions we choose specific prescriptions in the light cone propagators. We start the calculation from only two nucleons in each nucleus and then demonstrate how to generalize the calculation to higher orders diagrammatically. We simplify the diagrams by the Slavnov-Taylor-Ward identities. The resulting cross section is factorized into a product of two Weizsäcker-Williams gluon distributions of the two nuclei when the transverse momentum of the produced scalar particle is around the saturation momentum. To our knowledge this is the first process where an exact analytic formula has been formed for a physical process, involving momenta on the order of the saturation momentum, in nucleus-nucleus collisions in the quasi-classical approximation. Since we have performed the calculation in an unconventional gauge choice, we further confirm our results in Feynman gauge where the Weizsäcker-Williams gluon distribution is interpreted as a transverse momentum broadening of a hard gluons traversing a nuclear medium.
  • Baryon Number Fluctuation and the Quark-Gluon Plasma

    Baryon Number Fluctuation and the Quark-Gluon Plasma

    Baryon Number Fluctuation and the Quark-Gluon Plasma Z. W. Lin and C. M. Ko Because of the fractional baryon number Using the generating function at of quarks, baryon and antibaryon number equilibrium, fluctuations in the quark-gluon plasma is less than those in the hadronic matter, making them plausible signatures for the quark-gluon plasma expected to be formed in relativistic heavy ion with g(l) = ∑ Pn = 1 due to normalization of collisions. To illustrate this possibility, we have the multiplicity probability distribution, it is introduced a kinetic model that takes into straightforward to obtain all moments of the account both production and annihilation of equilibrium multiplicity distribution. In terms of quark-antiquark or baryon-antibaryon pairs [1]. the fundamental unit of baryon number bo in the In the case of only baryon-antibaryon matter, the mean baryon number per event is production from and annihilation to two mesons, given by i.e., m1m2 ↔ BB , we have the following master equation for the multiplicity distribution of BB pairs: while the squared baryon number fluctuation per baryon at equilibrium is given by In obtaining the last expressions in Eqs. (5) and In the above, Pn(ϑ) denotes the probability of ϑ 〈σ 〉 (6), we have kept only the leading term in E finding n pairs of BB at time ; G ≡ G v 〈σ 〉 corresponding to the grand canonical limit, and L ≡ L v are the momentum-averaged cross sections for baryon production and E 1, as baryons and antibaryons are abundantly produced in heavy ion collisions at annihilation, respectively; Nk represents the total number of particle species k; and V is the proper RHIC.
  • Fully Strange Tetraquark Sss¯S¯ Spectrum and Possible Experimental Evidence

    Fully Strange Tetraquark Sss¯S¯ Spectrum and Possible Experimental Evidence

    PHYSICAL REVIEW D 103, 016016 (2021) Fully strange tetraquark sss¯s¯ spectrum and possible experimental evidence † Feng-Xiao Liu ,1,2 Ming-Sheng Liu,1,2 Xian-Hui Zhong,1,2,* and Qiang Zhao3,4,2, 1Department of Physics, Hunan Normal University, and Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education, Changsha 410081, China 2Synergetic Innovation Center for Quantum Effects and Applications (SICQEA), Hunan Normal University, Changsha 410081, China 3Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China 4University of Chinese Academy of Sciences, Beijing 100049, China (Received 21 August 2020; accepted 5 January 2021; published 26 January 2021) In this work, we construct 36 tetraquark configurations for the 1S-, 1P-, and 2S-wave states, and make a prediction of the mass spectrum for the tetraquark sss¯s¯ system in the framework of a nonrelativistic potential quark model without the diquark-antidiquark approximation. The model parameters are well determined by our previous study of the strangeonium spectrum. We find that the resonances f0ð2200Þ and 2340 2218 2378 f2ð Þ may favor the assignments of ground states Tðsss¯s¯Þ0þþ ð Þ and Tðsss¯s¯Þ2þþ ð Þ, respectively, and the newly observed Xð2500Þ at BESIII may be a candidate of the lowest mass 1P-wave 0−þ state − 2481 0þþ 2440 Tðsss¯s¯Þ0 þ ð Þ. Signals for the other ground state Tðsss¯s¯Þ0þþ ð Þ may also have been observed in PC −− the ϕϕ invariant mass spectrum in J=ψ → γϕϕ at BESIII. The masses of the J ¼ 1 Tsss¯s¯ states are predicted to be in the range of ∼2.44–2.99 GeV, which indicates that the ϕð2170Þ resonance may not be a good candidate of the Tsss¯s¯ state.
  • Beyond the Standard Model Physics at CLIC

    Beyond the Standard Model Physics at CLIC

    RM3-TH/19-2 Beyond the Standard Model physics at CLIC Roberto Franceschini Università degli Studi Roma Tre and INFN Roma Tre, Via della Vasca Navale 84, I-00146 Roma, ITALY Abstract A summary of the recent results from CERN Yellow Report on the CLIC potential for new physics is presented, with emphasis on the di- rect search for new physics scenarios motivated by the open issues of the Standard Model. arXiv:1902.10125v1 [hep-ph] 25 Feb 2019 Talk presented at the International Workshop on Future Linear Colliders (LCWS2018), Arlington, Texas, 22-26 October 2018. C18-10-22. 1 Introduction The Compact Linear Collider (CLIC) [1,2,3,4] is a proposed future linear e+e− collider based on a novel two-beam accelerator scheme [5], which in recent years has reached several milestones and established the feasibility of accelerating structures necessary for a new large scale accelerator facility (see e.g. [6]). The project is foreseen to be carried out in stages which aim at precision studies of Standard Model particles such as the Higgs boson and the top quark and allow the exploration of new physics at the high energy frontier. The detailed staging of the project is presented in Ref. [7,8], where plans for the target luminosities at each energy are outlined. These targets can be adjusted easily in case of discoveries at the Large Hadron Collider or at earlier CLIC stages. In fact the collision energy, up to 3 TeV, can be set by a suitable choice of the length of the accelerator and the duration of the data taking can also be adjusted to follow hints that the LHC may provide in the years to come.
  • Baryon and Lepton Number Anomalies in the Standard Model

    Baryon and Lepton Number Anomalies in the Standard Model

    Appendix A Baryon and Lepton Number Anomalies in the Standard Model A.1 Baryon Number Anomalies The introduction of a gauged baryon number leads to the inclusion of quantum anomalies in the theory, refer to Fig. 1.2. The anomalies, for the baryonic current, are given by the following, 2 For SU(3) U(1)B , ⎛ ⎞ 3 A (SU(3)2U(1) ) = Tr[λaλb B]=3 × ⎝ B − B ⎠ = 0. (A.1) 1 B 2 i i lef t right 2 For SU(2) U(1)B , 3 × 3 3 A (SU(2)2U(1) ) = Tr[τ aτ b B]= B = . (A.2) 2 B 2 Q 2 ( )2 ( ) For U 1 Y U 1 B , 3 A (U(1)2 U(1) ) = Tr[YYB]=3 × 3(2Y 2 B − Y 2 B − Y 2 B ) =− . (A.3) 3 Y B Q Q u u d d 2 ( )2 ( ) For U 1 BU 1 Y , A ( ( )2 ( ) ) = [ ]= × ( 2 − 2 − 2 ) = . 4 U 1 BU 1 Y Tr BBY 3 3 2BQYQ Bu Yu Bd Yd 0 (A.4) ( )3 For U 1 B , A ( ( )3 ) = [ ]= × ( 3 − 3 − 3) = . 5 U 1 B Tr BBB 3 3 2BQ Bu Bd 0 (A.5) © Springer International Publishing AG, part of Springer Nature 2018 133 N. D. Barrie, Cosmological Implications of Quantum Anomalies, Springer Theses, https://doi.org/10.1007/978-3-319-94715-0 134 Appendix A: Baryon and Lepton Number Anomalies in the Standard Model 2 Fig. A.1 1-Loop corrections to a SU(2) U(1)B , where the loop contains only left-handed quarks, ( )2 ( ) and b U 1 Y U 1 B where the loop contains only quarks For U(1)B , A6(U(1)B ) = Tr[B]=3 × 3(2BQ − Bu − Bd ) = 0, (A.6) where the factor of 3 × 3 is a result of there being three generations of quarks and three colours for each quark.
  • Arxiv:0810.4453V1 [Hep-Ph] 24 Oct 2008

    Arxiv:0810.4453V1 [Hep-Ph] 24 Oct 2008

    The Physics of Glueballs Vincent Mathieu Groupe de Physique Nucl´eaire Th´eorique, Universit´e de Mons-Hainaut, Acad´emie universitaire Wallonie-Bruxelles, Place du Parc 20, BE-7000 Mons, Belgium. [email protected] Nikolai Kochelev Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, Dubna, Moscow region, 141980 Russia. [email protected] Vicente Vento Departament de F´ısica Te`orica and Institut de F´ısica Corpuscular, Universitat de Val`encia-CSIC, E-46100 Burjassot (Valencia), Spain. [email protected] Glueballs are particles whose valence degrees of freedom are gluons and therefore in their descrip- tion the gauge field plays a dominant role. We review recent results in the physics of glueballs with the aim set on phenomenology and discuss the possibility of finding them in conventional hadronic experiments and in the Quark Gluon Plasma. In order to describe their properties we resort to a va- riety of theoretical treatments which include, lattice QCD, constituent models, AdS/QCD methods, and QCD sum rules. The review is supposed to be an informed guide to the literature. Therefore, we do not discuss in detail technical developments but refer the reader to the appropriate references. I. INTRODUCTION Quantum Chromodynamics (QCD) is the theory of the hadronic interactions. It is an elegant theory whose full non perturbative solution has escaped our knowledge since its formulation more than 30 years ago.[1] The theory is asymptotically free[2, 3] and confining.[4] A particularly good test of our understanding of the nonperturbative aspects of QCD is to study particles where the gauge field plays a more important dynamical role than in the standard hadrons.
  • Properties of Baryons in the Chiral Quark Model

    Properties of Baryons in the Chiral Quark Model

    Properties of Baryons in the Chiral Quark Model Tommy Ohlsson Teknologie licentiatavhandling Kungliga Tekniska Hogskolan¨ Stockholm 1997 Properties of Baryons in the Chiral Quark Model Tommy Ohlsson Licentiate Dissertation Theoretical Physics Department of Physics Royal Institute of Technology Stockholm, Sweden 1997 Typeset in LATEX Akademisk avhandling f¨or teknologie licentiatexamen (TeknL) inom ¨amnesomr˚adet teoretisk fysik. Scientific thesis for the degree of Licentiate of Engineering (Lic Eng) in the subject area of Theoretical Physics. TRITA-FYS-8026 ISSN 0280-316X ISRN KTH/FYS/TEO/R--97/9--SE ISBN 91-7170-211-3 c Tommy Ohlsson 1997 Printed in Sweden by KTH H¨ogskoletryckeriet, Stockholm 1997 Properties of Baryons in the Chiral Quark Model Tommy Ohlsson Teoretisk fysik, Institutionen f¨or fysik, Kungliga Tekniska H¨ogskolan SE-100 44 Stockholm SWEDEN E-mail: [email protected] Abstract In this thesis, several properties of baryons are studied using the chiral quark model. The chiral quark model is a theory which can be used to describe low energy phenomena of baryons. In Paper 1, the chiral quark model is studied using wave functions with configuration mixing. This study is motivated by the fact that the chiral quark model cannot otherwise break the Coleman–Glashow sum-rule for the magnetic moments of the octet baryons, which is experimentally broken by about ten standard deviations. Configuration mixing with quark-diquark components is also able to reproduce the octet baryon magnetic moments very accurately. In Paper 2, the chiral quark model is used to calculate the decuplet baryon ++ magnetic moments. The values for the magnetic moments of the ∆ and Ω− are in good agreement with the experimental results.
  • Observation of Global Hyperon Polarization in Ultrarelativistic Heavy-Ion Collisions

    Observation of Global Hyperon Polarization in Ultrarelativistic Heavy-Ion Collisions

    Available online at www.sciencedirect.com Nuclear Physics A 967 (2017) 760–763 www.elsevier.com/locate/nuclphysa Observation of Global Hyperon Polarization in Ultrarelativistic Heavy-Ion Collisions Isaac Upsal for the STAR Collaboration1 Ohio State University, 191 W. Woodruff Ave., Columbus, OH 43210 Abstract Collisions between heavy nuclei at ultra-relativistic energies form a color-deconfined state of matter known as the quark-gluon plasma. This state is well described by hydrodynamics, and non-central collisions are expected to produce a fluid characterized by strong vorticity in the presence of strong external magnetic fields. The STAR Collaboration at Brookhaven National Laboratory’s√ Relativistic Heavy Ion Collider (RHIC) has measured collisions between gold nuclei at center of mass energies sNN = 7.7 − 200 GeV. We report the first observation of globally polarized Λ and Λ hyperons, aligned with the angular momentum of the colliding system. These measurements provide important information on partonic spin-orbit coupling, the vorticity of the quark-gluon plasma, and the magnetic field generated in the collision. 1. Introduction Collisions of nuclei at ultra-relativistic energies create a system of deconfined colored quarks and glu- ons, called the quark-gluon plasma (QGP). The large angular momentum (∼104−5) present in non-central collisions may produce a polarized QGP, in which quarks are polarized through spin-orbit coupling in QCD [1, 2, 3]. The polarization would be transmitted to hadrons in the final state and could be detectable through global hyperon polarization. Global hyperon polarization refers to the phenomenon in which the spin of Λ (and Λ) hyperons is corre- lated with the net angular momentum of the QGP which is perpendicular to the reaction plane, spanned by pbeam and b, where b is the impact parameter vector of the collision and pbeam is the beam momentum.
  • Charm and Strange Quark Contributions to the Proton Structure

    Charm and Strange Quark Contributions to the Proton Structure

    Report series ISSN 0284 - 2769 of SE9900247 THE SVEDBERG LABORATORY and \ DEPARTMENT OF RADIATION SCIENCES UPPSALA UNIVERSITY Box 533, S-75121 Uppsala, Sweden http://www.tsl.uu.se/ TSL/ISV-99-0204 February 1999 Charm and Strange Quark Contributions to the Proton Structure Kristel Torokoff1 Dept. of Radiation Sciences, Uppsala University, Box 535, S-751 21 Uppsala, Sweden Abstract: The possibility to have charm and strange quarks as quantum mechanical fluc- tuations in the proton wave function is investigated based on a model for non-perturbative QCD dynamics. Both hadron and parton basis are examined. A scheme for energy fluctu- ations is constructed and compared with explicit energy-momentum conservation. Resulting momentum distributions for charniand_strange quarks in the proton are derived at the start- ing scale Qo f°r the perturbative QCD evolution. Kinematical constraints are found to be important when comparing to the "intrinsic charm" model. Master of Science Thesis Linkoping University Supervisor: Gunnar Ingelman, Uppsala University 1 kuldsepp@tsl .uu.se 30-37 Contents 1 Introduction 1 2 Standard Model 3 2.1 Introductory QCD 4 2.2 Light-cone variables 5 3 Experiments 7 3.1 The HERA machine 7 3.2 Deep Inelastic Scattering 8 4 Theory 11 4.1 The Parton model 11 4.2 The structure functions 12 4.3 Perturbative QCD corrections 13 4.4 The DGLAP equations 14 5 The Edin-Ingelman Model 15 6 Heavy Quarks in the Proton Wave Function 19 6.1 Extrinsic charm 19 6.2 Intrinsic charm 20 6.3 Hadronisation 22 6.4 The El-model applied to heavy quarks
  • Discovery of Gluon

    Discovery of Gluon

    Discovery of the Gluon Physics 290E Seminar, Spring 2020 Outline – Knowledge known at the time – Theory behind the discovery of the gluon – Key predicted interactions – Jet properties – Relevant experiments – Analysis techniques – Experimental results – Current research pertaining to gluons – Conclusion Knowledge known at the time The year is 1978, During this time, particle physics was arguable a mature subject. 5 of the 6 quarks were discovered by this point (the bottom quark being the most recent), and the only gauge boson that was known was the photon. There was also a theory of the strong interaction, quantum chromodynamics, that had been developed up to this point by Yang, Mills, Gell-Mann, Fritzsch, Leutwyler, and others. Trying to understand the structure of hadrons. Gluons can self-interact! Theory behind the discovery Analogous to QED, the strong interaction between quarks and gluons with a gauge group of SU(3) symmetry is known as quantum chromodynamics (QCD). Where the force mediating particle is the gluon. In QCD, we have some quite particular features such as asymptotic freedom and confinement. 4 α Short range:V (r) = − s QCD 3 r 4 α Long range: V (r) = − s + kr QCD 3 r (Between a quark and antiquark) Quantum fluctuations cause the bare color charge to be screened causes coupling strength to vary. Features are important for an understanding of jet formation. Theory behind the discovery John Ellis postulated the search for the gluon through bremsstrahlung radiation in electron- proton annihilation processes in 1976. Such a process will produce jets of hadrons: e−e+ qq¯g Furthermore, Mary Gaillard, Graham Ross, and John Ellis wrote a paper (“Search for Gluons in e+e- Annihilation.”) that described that the PETRA collider at DESY and the PEP collider at SLAC should be able to observe this process.
  • Observation of Structure in the J/Ψ-Pair Mass Spectrum

    Observation of Structure in the J/Ψ-Pair Mass Spectrum

    EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN) CERN-EP-2020-115 LHCb-PAPER-2020-011 CERN-EP-2020-115June 30, 2020 22 June 2020 Observation of structure in the J= -pair mass spectrum LHCb collaborationy Abstract p Using proton-proton collision data at centre-of-mass energies of s = 7, 8 and 13 TeV recorded by the LHCb experiment at the Large Hadron Collider, corresponding to an integrated luminosity of 9 fb−1, the invariant mass spectrum of J= pairs is studied. A narrow structure around 6:9 GeV/c2 matching the lineshape of a resonance and a broad structure just above twice the J= mass are observed. The deviation of the data from nonresonant J= -pair production is above five standard deviations in the mass region between 6:2 and 7:4 GeV/c2, covering predicted masses of states composed of four charm quarks. The mass and natural width of the narrow X(6900) structure are measured assuming a Breit{Wigner lineshape. Submitted to Science Bulletin c 2020 CERN for the benefit of the LHCb collaboration. CC BY 4.0 licence. yAuthors are listed at the end of this paper. ii 1 1 Introduction 2 The strong interaction is one of the fundamental forces of nature and it governs the 3 dynamics of quarks and gluons. According to quantum chromodynamics (QCD), the 4 theory describing the strong interaction, quarks are confined into hadrons, in agreement 5 with experimental observations. The quark model [1,2] classifies hadrons into conventional 6 mesons (qq) and baryons (qqq or qqq), and also allows for the existence of exotic hadrons 7 such as tetraquarks (qqqq) and pentaquarks (qqqqq).