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Significance of Strangeness Conservation/Violation Studies at BESIII

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Significance of Strangeness Conservation/Violation Studies at BESIII Proceedings of the Pakistan Academy of Sciences: Pakistan Academy of Sciences A. Physical and Computational Sciences 55 (2): 1–11 (2018) Copyright © Pakistan Academy of Sciences ISSN: 2518-4245 (print), 2518-4253 (online) Review Article Significance of Strangeness Conservation/Violation Studies at BESIII Aneela Amin1 , Khadija Saeed1, Farzana Younas1, and Ghalib ul Islam2 ∗ 1Centre for High Energy Physics, University of the Punjab, Lahore (54590), Pakistan 2Department of Physics, The University of Lahore, Lahore (53700), Pakistan Abstract Strangeness violation and conservation have been studied in Charmonia and its higher state decays. The data of some prominent decay modes has been collected from BESIII laboratory from the years 2009 to date. The strangeness violating decays play an important role in the study of weak interactions. On the other hand, strangeness conserving decays describe the strong interactions. An overview of strangeness conserving decays and strangeness violating decays has been given and the decay modes are presented in tabular form. The study reveals that associated production occurs only in strangeness conserving decays rather than strangeness violating decays. Experimental and theoretical results are presented in order to arrange phenomenological developments and queries may search new domains in Experimental High Energy Physics, and will explore new prospects of strangeness, a basic quantum number of hadrons and its associated production. Keywords: Strangeness, Charmonia, Strangeness conserving decays, Strangeness violating decays, Standard model 1. INTRODUCTION described the interactions among these particles known as Standard Model. According to The study of particles and the interaction between Standard Model, three types of interactions exist them shows that quarks and leptons are the basic among these particles i.e. electromagnetic, strong constituents of matter [1]. These quarks exist in and weak interaction [4-5]. bound states. There are six type of quarks, named as, up , down , strange , charm , In this paper, all those decay processes have bottom , top quark. Similarly, there are six been studied in which strangeness exists. These type of leptons , electron , muon and tau processes involve strange baryons and strange alongwith their neutrinos electron neutrinos , mesons and the list of these strange mesons and muon neutrino and tau neutrino [2]. baryons are listed in Table 1 and Table 2 respectively. The data involving strangeness has According to the quark model, these quarks been collected from BESIII Laboratory for the are combined together to form hadrons. Hadrons period 2009 to 2017. It was observed that some are strongly interacting particles and are divided decay processes are those in which law of into two categories, named as, Baryons and conservation of strangeness holds. This fact is Mesons [3]. In 1960, these particles are arranged according to the theory of Standard Model. On the in Eightfold way-classification according to their other hand, some strangeness violating reactions quantum numbers. Baryons consist of three quarks have also been observed in BESIII, which show or three anti-quarks. Mesons consist of a quark that evidences for the strangeness violations are and anti-quark. The baryons and mesons are increasing day by day. Such kind of decays, arranged into octets and decuplets according to showing weak interactions are discussed and their spin, charge and strange quantum numbers. highlighted in many decay modes in BESIII and This classification of baryon and meson is shown their branching fractions have also been reported. in the Fig. 1 to Fig. 4. An important property of strangeness, called associated production, has also been introduced In 1970, a new theory was predicted which which is very prominent in the strangeness ———————————————— Received, December 2017; Accepted, June 2018 * Corresponding Author: Aneela Amin; [email protected] 2 Aneela Amin et al conserving decays of Charmonia. The decays modes showing associated production are listed in the Table 3(a) to 3(d). These decay modes are governed by strong interactions only [2]. Here is the baryon with mass The data consisting of strangeness conserving [6] . Since baryon is very unstable decays and strangeness violating decays along particle, so it decays further into some other with their branching fractions have been arranged particles as shown in the following reaction; in the Table 3(a) to 3(d) and Table 4(a) to 4(e). 2. Strangeness Baryon number is conserved in this reaction, Strangeness „S‟ [6] is a quantity associated with all therefore should decay via strong interaction hadrons. Strangeness is basically an additive and its life time should be of the order quantum number. Like baryon number, lepton of . But it has been observed that number, this quantum number is assigned to all its decay time is of the order of hadrons named as strangeness quantum number. It which is approximately equal to the life time of became necessary to introduce this quantum weak decays. So baryon deca ys via weak number for the study of properties of particles. interaction and it shows strange behavior [6]. The reasons for introducing this quantity are few reactions which are quite different in nature from A similar strange behavior has been observed the other decay processes. For example, in the in the decay of kaon meson. This reaction is also following reaction, a proton and pion interacts given below; very strongly to produce a baryon. Figure 1. The spin ½ baryons arranged in baryon octet Figure 2. The spin 3⁄2 baryons arranged in baryon decu- [4-5] plets [4-5]. Figure 3. The meson nonet with spin 0 [4-5] Figure 4. The meson nonet with spin 1 [4-5] Study of Strangeness at BESIII 3 This decay has baryon number . So it the section below. must be carried out via strong interaction. But this does not happen. Its life time is again observed to 3. Associated Production and its Significance be rather than which shows In 1952, Abraham Pais observed some neutral that it is a weak decay. Again, this is the Strange 0 particles (V ‟s) produced in cloud chamber with Behavior [6]. Strangeness [6] leads to a new -27 2 conservation law. This law is known as Law of larger cross section (~ 10 cm ) and these particles decayed through smaller cross section (~ Conservation of Strangeness. -40 2 10 cm ) [6]. This phenomenon happened in strange particles as strange particles are produced Strangeness values could be 0, 1, -1. The -23 abundantly having life time of 10 seconds but strangeness quantum number violates in those -10 reactions which do not decay via strong interaction their decay time is relatively slow about 10 but this quantum number is conserved in strong seconds. This shows that their production interactions. The results of three reactions mechanism is different from their disintegration indicating the strangeness conservation and mechanism. So one can say that strong force strangeness violation as under; governs the production of strange particles whereas weak force is responsible for their decay. So if a strange particle is produced in strong (decays via strong interaction) interaction, they are always produced in pairs of particles of opposite strangeness so as to conserve (decays via weak intercation) the total strangeness. This phenomenon is called (decays via weak interaction) Associated Production [6]. It has been observed from the above three Some strange mesons have been listed in the reactions that law of strangeness is violated in the Table 1 along with their quark contents and processes which decay through weak interactions strangeness, . Similarly, some strange and it is conserved in strong decays [6]. The baryons having strangeness are conservation of strangeness via strong interaction listed in the Table 2 [7]. In next section, a brief is discussed in terms of associated production in description of BESIII experimental setup is given. Table 1. List of Strange Mesons with [7] Mesons Quark Contents Strangeness ̅ ̅ ̅ ( ⃰ ) ̅ ̅ ( ̅ ̅) ⁄ √ ( ⃰ ) ( ̅ ̅) ⁄ √ Charmed+ Strange Mesons Quark Content ̅ s Strangeness ̅ ̅ ̅ Bottom +Strange Mesons Quark Content ̅ s Strangeness ̅ ̅ ̅ ̅ ̅ 4 Aneela Amin et al 4. BESIII Experimental Setup (GDML). BOSS provides many services to meet the requirement of analysis such as navigation and This paper is about the theoretical study of reconstruction of MC tracks. This Data processing strangeness conservations and violation of and physics analysis software system has three Charmonia, based on the data collected from main functions i.e. Simulation, Reconstruction and BESIII detector. BESIII detector uses the BESIII Calibration. BESIII detector simulation is based offline software system (BOSS), CLHEP libraries upon GEANT4 package which gives information and Root software to study the charmonium about the detector, particle tracking and their spectroscopy [8-9]. interaction with the detector [9]. The upgraded version of BES is BESIII that 6. CHARMONIUM SPECTROSCOPY consists of BEPCII collider and BESIII detector. BESIII detector is specifically used to In 1974, the discovery of charmonium meson study the Tau-Charm P hysics within energy range at BNL (Brookhaven National Laboratory) and of 2 to 5 GeV. BESIII detector became SLAC (Stanford Linear Accelerator Center) has operational from 2009 [8]. BESIII detector has opened up a new horizon in the field of research. four main components named as Main Drift After that, some other states of charmonium were Chamber (MDC), Electromagnetic Calorimeter discovered at some higher energies named as , (EMC), Time of Flight System (TOF) and Muon , , , and states. The decays of Chamber System (MUC). These parts of detector these charmonium and its higher states were detect various particles and their specific mainly studied at BES (Beijing Electron properties such as their momentum, energy, Spectrometer) Lab [8-10]. energy losses, position and time etc. within certain energy range of Charmonia. For more detail, for The charmonium and its higher energy states example, MDC used to measure the momentum being discussed here, contain charm quark as one and energy loss information of charged particles.
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