1. Search for tetraquark states ▫$X_{c c \bar{s} \bar{s}}$▫ in ▫$D_s^+ D_s^+$▫ (▫$D_s^{\ast +} D_s^{\ast +}$▫) final states at BelleX. Y. Gao, Jyotirmoi Borah, Marko Bračko, Samo Korpar, Peter Križan, Rok Pestotnik, Tomaž Podobnik, Samo Stanič, Marko Starič, Luka Šantelj, Valentina Zhukova, 2022, izvirni znanstveni članek Opis: A search for double-heavy tetraquark state candidates Xccs¯s¯ decaying to Dþ s Dþ s and Dþ s Dþ s is presented for the first time using the data samples of 102 × 106 ϒð1SÞ and 158 × 106 ϒð2SÞ events, and the data samples at ffiffi ps ¼ 10.52, 10.58, and 10.867 GeV corresponding to integrated luminosities of 89.5, 711.0, and 121.4 fb−1, respectively, accumulated with the Belle detector at the KEKB asymmetric energy electron-positron collider. The invariant-mass spectra of the Dþ s Dþ s and Dþ s Dþ s are studied to search for possible resonances. No significant signals are observed, and the 90% confidence level upper limits on the product branching fractions [Bðϒð1S; 2SÞ → Xccs¯s¯ þ anythingÞ × BðXccs¯s¯ → Dþ s Dþ s ðDþ s Dþ s ÞÞ] in ϒð1S; 2SÞ inclusive decays and the product values of Born cross section and branching fraction [σðeþe− → Xccs¯s¯ þ anythingÞ × BðXccs¯s¯ → Dþ s Dþ s ðDþ s Dþ s ÞÞ] in eþe− collisions at pffiffis ¼ 10.52, 10.58, and 10.867 GeV under different assumptions of Xccs¯s¯ masses and widths are obtained.
Ključne besede: tetraquark states, final states at Belle
Objavljeno v DKUM: 15.04.2025; Ogledov: 0; Prenosov: 3
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2. LAPPD operation using ToFPETv2 PETSYS ASICAndrej Seljak, Marko Bračko, Rok Dolenec, Peter Križan, Andrej Lozar, Rok Pestotnik, Samo Korpar, 2023, objavljeni znanstveni prispevek na konferenci Opis: Single photon sensitive detectors used in high energy physics are, in some applica-tions, required to cover areas the size of several m2, and more specifically in very strong demand with an ever finer imaging and timing capability for Cherenkov Ring Imaging Detector (RICH) configurations. We are evaluating the Large Area Picosecond Photo-detector (LAPPD) produced by INCOM company, as a possible candidate for future RICH detector upgrades. In this work we perform tests on the second generation device, which is capacitively coupled to a custom designed anode back plane, consisting of various pixels and strips varying in size, that allows for connecting various readout systems such as standard laboratory equipment, as well as the TOFPET2 ASIC from PETsys company. Our aim is to evaluate what can be achieved by merging currently available technology, in order to find directions for future developments adapted for specific uses.
Ključne besede: data acquisition circuits, data acquisition concept, front-end electronics for detector readou, digital electronic circuits
Objavljeno v DKUM: 06.02.2024; Ogledov: 278; Prenosov: 25
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3. Search for ▫$Z^\prime \to \mu^+ \mu^-$▫ in the ▫$L_\mu - L_\tau$▫ gauge-symmetric model at BelleT. Czank, Karol Adamczyk, Jyoti Prakash Biswal, Marko Bračko, Boštjan Golob, Samo Korpar, Peter Križan, Manca Mrvar, Rok Pestotnik, Tomaž Podobnik, Samo Stanič, Marko Starič, Luka Šantelj, 2022, izvirni znanstveni članek Opis: We search for a new gauge boson Z′ that couples only to heavy leptons and their corresponding neutrinos in the process e+e−→Z′(→μ+μ−)μ+μ−, using a 643 fb−1 data sample collected by the Belle experiment at or near the Υ(1S,2S,3S,4S,5S) resonances at the KEKB collider. While previous searches for Z′ performed a data-based estimation of the initial state radiation effect, our search for the Z′ is the first to include effects due to initial state radiation in the signal simulated samples that were used in estimating the detection efficiency. No signal is observed in the Z′ mass range of 0.212–10 GeV/c2, and we set an upper limit on the coupling strength, g′, constraining the possible Z′ contribution to the anomalous magnetic dipole moment of the muon.
Ključne besede: Extensions of gauge sector, leptonic, semileptonic & radiative decays
Objavljeno v DKUM: 25.09.2023; Ogledov: 455; Prenosov: 37
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4. Measurement of two-particle correlations of hadrons in ▫$e^+ e^-$▫ collisions at BelleY.-C. Chen, Marko Bračko, Samo Korpar, Peter Križan, Tomaž Podobnik, Marko Starič, Luka Šantelj, 2022, izvirni znanstveni članek Opis: The measurement of two-particle angular correlation functions in high-multiplicity e+e− collisions at √s=10.52 GeV is reported. In this study, the 89.5 fb−1 of hadronic e+e− annihilation data collected by the Belle detector at KEKB are used. Two-particle angular correlation functions are measured in the full relative azimuthal angle (Δϕ) and three units of pseudorapidity (Δη), defined by either the electron beam axis or the event-shape thrust axis, and are studied as a function of charged-particle multiplicity. The measurement in the thrust axis analysis, with mostly outgoing quark pairs determining the reference axis, is sensitive to the region of additional soft gluon emissions. No significant anisotropic collective behavior is observed with either coordinate analyses. Near-side jet correlations appear to be absent in the thrust axis analysis. The measurements are compared to predictions from various event generators and are expected to provide new constraints to the phenomenological models in the low-energy regime.
Ključne besede: Particle & resonance production, Quark & gluon jets, Quark-gluon plasma
Objavljeno v DKUM: 24.08.2023; Ogledov: 396; Prenosov: 9
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5. Measurement of the branching fraction and ▫$CP$▫ asymmetry for ▫$B \to \bar{D}^0 \pi$▫ decaysT. Bloomfield, Jyoti Prakash Biswal, Marko Bračko, Samo Korpar, Peter Križan, Rok Pestotnik, Tomaž Podobnik, Marko Starič, Luka Šantelj, 2022, izvirni znanstveni članek Opis: We measure the branching fractions and CP asymmetries for the decays B⁰ → D¯ 0π⁰ and B⁺ → D¯ 0π⁺, using a data sample of 772 × 10⁶ BB¯ pairs collected at the ϒ(4S) resonance with the Belle detector at the KEKB e⁺e− collider. The branching fractions obtained and direct CP asym-metries are B(B⁰ → D¯ 0π⁰)=[2.70 0.06(stat) 0.10(syst)]×10−⁴, B(B⁺ → D¯ 0π⁺)=[4.53 0.02(stat) 0.15(syst)]×10−³, ACP(B⁰ → D¯ 0π⁰)= [+0.42 2.05(stat) 1.22(syst)]%, and ACP(B⁺ → D¯ 0π⁺) = [+0.19 0.36(stat) 0.57(syst)]%. The measurements of B are the most precise to date and are in good agreement with previous results, as is the measurement of ACP(B⁺ → D¯ 0π⁺). The measurement of ACP for B⁰ → D¯ 0π⁰ is the first for this mode, and the value is consistent with Standard Model expectations.
Ključne besede: branching fraction, hadronic decays, particle decays, mesons, CP violation, precision measurements
Objavljeno v DKUM: 17.08.2023; Ogledov: 364; Prenosov: 39
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6. Search for the decay ▫$B_s^0 \to \eta \eta$▫S. Bhuyan, Jyoti Prakash Biswal, Marko Bračko, Boštjan Golob, Samo Korpar, Peter Križan, Rok Pestotnik, Marko Starič, Luka Šantelj, 2022, izvirni znanstveni članek Opis: We report results from a search for the decay B0s→ηη using 121.4 fb−1 of data collected at the Υ(5S) resonance with the Belle detector at the KEKB asymmetric-energy e+e− collider. We do not observe any signal and set an upper limit on the branching fraction of 14.3×10−5 at 90% confidence level. This result represents a significant improvement over the previous most stringent limit.
Objavljeno v DKUM: 17.08.2023; Ogledov: 270; Prenosov: 33
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7. Vibracijski in rotacijski prehodi enostavnih molekul : magistrsko deloMatic Orel, 2022, magistrsko delo Opis: V magistrskem delu obravnavamo rotacijske in vibracijske prehode molekul. Molekulsko
dinamiko bomo opisali z analitiˇcnimi metodami, zato se bomo omejili na dovolj preproste
molekule z dobro definirano simetrijo. Pravilnost izraˇcunov bomo preverili z obiˇcajnimi
raˇcunalniˇskimi orodji, ki se v kemiji uporabljajo za prikaz in opis molekulske dinamike.
Namen magisterskega dela je bilo preveriti, do kam lahko pridemo z analitiˇcnim pristopom
pri obravnavi infrardeˇce spektroskopije manjˇsih molekul z enostavnimi simetrijami.
Izkazalo se je, da je to izredno zahteven postopek, kateri zahteva tako znanje kemije kot
tudi teorije grup. V tem delu smo predstavili ter uporabili nastavke za izraˇcun najpomembnej
ˇsih parametrov, kateri vplivajo na intenzitete v infrardeˇcem spektru, t.j. spinska
statistiˇcna uteˇz za dane irreducibilne specije spinske valovne funkcije ter energije rotacij
oz. vibracij ˇzeljene molekule. S pomoˇcjo ter dveh parametrov smo pri dani temperaturi
zapisali Boltzmannovo enaˇcbo infrardeˇcega spektra ter s prikazali odsek le-tega. Primera
vode ter CHF3 sta bila skrbno izbrana zaradi razliˇcnih simetrijskih lastnosti (asimetriˇcni
vs. simetriˇcni rotor, 2 protona vs. 3 protoni itd.) ter zaradi relativne enostavnosti
izraˇcunov. V zakljuˇcku smo predstavili ˇse dodatne aspekte analitiˇcne analize, katerim bi
se lahko posluˇzili t.j. spremembe simetrije molekule ob substituciji tipa atoma, teˇzave z
relativistiˇcnim nadaljevanjem ter karakterizacija elektronske valovne funkcije preko LCAO
ansazt-a.
Ključne besede: Molekulska dinamika, vibracije in rotacije molekul, molekulska simetrija, infrardeˇca spektroskopija, resonanˇcne frekvence, raˇcunski program Gaussian
Objavljeno v DKUM: 20.05.2022; Ogledov: 749; Prenosov: 70
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8. Primerjava izračunanih in numeričnih rezultatov pri obravnavi molekule vodika : diplomsko delo univerzitetnega študijskega programa I. stopnjeTibor Mlakar, 2019, diplomsko delo Opis: V mnogih vejah teoretične kemije kot fizike zastavljene sisteme proučujemo z reševanjem Schrödingerjeve enačbe. Rešitvam te enačbe pravimo valovne funkcije, s katerimi lahko določimo vse bistvene parametre nekega sistema. Oblika členov Schrödingerjeve enačbe se spreminja skupaj z izbiro sistema, načeloma kompleksnejši kot je proučevani sistem zahtevnejše je reševanje omenjene enačbe.
V diplomskem delu smo iskali rešitve Schrödingerjeve enačbe za najenostavnejši analitično rešljiv sistem - molekulo vodikovega iona (H2+). Analitične rešitve smo poiskali v okviru teorije molekulskih orbital (MO), ki smo jih opisali z linearno kombinacijo atomskih orbital (“linear combination of atomic orbitals” - LCAO). Rešitve istega problema smo iskali tudi numerično, z računskim programom Gaussian, pri čemer smo za računanje uporabili tako semi-empirične kot ab initio metode. Rezultate vseh izračunov smo primerjali z eksperimentalno izmerjenimi vrednostmi. V drugem delu diplomske naloge smo analitično iskali rešitve Schrödingerjeve enačbe za nekoliko večji sistem – molekulo vodika (H2). Zaradi pomankanja znanja novega sistema ni bilo možno obravnavati do konca.
Ugotovili smo, da enostaven analitični račun vodi do vrednosti za ravnovesno razdaljo in vezavno energijo, ki se v okviru 30-40% ujemata z eksperimentalnimi podatki. Pri numeričnih metodah se je izkazalo, da posamezne ab initio metode privedejo do podobnih rezultatov, prav tako tudi posamezne semi-empirične metode. Ugotovili smo, da je ujemanje rezultatov za ravnovesno razdaljo pri vseh numeričnih metodah znotraj 10% od eksprimentalnih vrednosti. Pri energijah je ujemanje nekoliko slabše, so pa dobljene vrednosti še vedno v okviru 20% proč od eksperimentalnih rezultatov. Edina izjema sta bili obe semi-empirični metodi, ki sta za izračunano energijo sistema dali popolnoma neprimerne rezultate.
Ključne besede: Schrödingerjeva enačba, molekula vodikovega iona, teorija molekulskih orbital, računski program Gaussian, ravnovesna razdalja, energija sistema
Objavljeno v DKUM: 11.09.2019; Ogledov: 1394; Prenosov: 217
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9. Measurement of branching fractions for $B \to J/\psi \eta K$ decays and search for a narrow resonance in the $J/\psi \eta$ final stateT. Iwashita, Marko Bračko, Boštjan Golob, Jure Klučar, Samo Korpar, Peter Križan, Rok Pestotnik, Marko Petrič, Marko Starič, Luka Šantelj, Anže Zupanc, 2014, izvirni znanstveni članek Opis: We report an observation of the $B^{\pm } \to J/\psi \eta K^{\pm }$ and $B^0 \to J/\psi \eta K^0_S$ decays using $772\times 10^{6}B\overline {B}$ pairs collected at the $\Upsilon (4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We obtain the branching fractions ${\mathcal B}(B^{\pm }\rightarrow J/\psi \eta K^{\pm })=(1.27\pm 0.11(\hbox {stat.})\pm 0.11(\hbox {syst.}))\times 10^{-4}$ and ${\mathcal B}(B^0\to J/\psi \eta K^0_S)=(5.22 \pm 0.78 (\hbox {stat.}) \pm 0.49 (\hbox {syst.}))\times 10^{-5}$. We search for a new narrow charmonium(-like) state $X$ in the $ J/\psi \eta$ mass spectrum and find no significant excess. We set upper limits on the product of branching fractions, ${\mathcal B}(B^\pm \to XK^\pm){\mathcal B}(X \to J/\psi \eta)$, at $3872\,\hbox {MeV}\,c^{-2}$ where a $C$-odd partner of $X(3872)$ may exist, at $\psi (4040)$ and $\psi (4160)$ assuming their known mass and width, and over a range from 3.8 to $4.8\,\hbox {GeV}\,c^{-2}$. The obtained upper limits at 90% confidence level for $X^{C\hbox {-}{\rm odd}}(3872)$, $\psi (4040)$, and $\psi (4160)$ are $3.8\times 10^{-6}$, $15.5\times 10^{-6}$, and $7.4\times 10^{-6}$, respectively.
Ključne besede: C07, C21, particle properties, lepton collider experiments, experimental particle physics
Objavljeno v DKUM: 21.07.2017; Ogledov: 1540; Prenosov: 240
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10. High-statistics study of $K^0_S K^0_S$ pair production in two-photon collisionsS. Uehara, Marko Bračko, Boštjan Golob, Jure Klučar, Samo Korpar, Peter Križan, Rok Pestotnik, Marko Petrič, Marko Starič, Luka Šantelj, Anže Zupanc, 2013, izvirni znanstveni članek Opis: We report a high-statistics measurement of the differential cross section of the process $\gamma \gamma \to K^0_S K^0_S$ in the range $1.05\,{\mathrm {GeV}} \leq W \leq 4.00$ , where W is the center-of-mass energy of the colliding photons, using 972 $^{-1}$ of data collected with the Belle detector at the KEKB asymmetric-energy e+e− collider operated at and near the $\Upsilon$-resonance region. The differential cross section is fitted by parameterized S-, $D_0$, $D_2$-, $G_0$-, and $G_2$-wave amplitudes. In the $D_2$ wave, the $f_2$(1270), $a_2$(1320), and $f′_2$(1525) are dominant and a resonance, the $f_2$(2200), is also present. The $f_0$(1710) and possibly the $f_0$(2500) are seen in the S wave. The mass, total width, and product of the two-photon partial decay width and decay branching fraction to the $K \bar {K}$ state $\Gamma _{\gamma \gamma }\mathcal {B}(K \bar {K})$ are extracted for the $f′_2$(1525), $f_0$(1710), $f_2$(2200), and $f_0$(2500). The destructive interference between the $f_2$(1270) and $a_2$(1320) is confirmed by measuring their relative phase. The parameters of the charmonium states $\chi _{c0}$ and $\chi _{c2}$ are updated. Possible contributions from the $\chi _{c0}(2P)$ and $\chi _{c2}(2P)$ states are discussed. A new upper limit for the branching fraction of the P- and CP-violating decay channel $\eta _c \to K^0_S K^0_S$ is reported. The detailed behavior of the cross section is updated and compared with QCD-based calculations.
Ključne besede: C00, C05, C07, C21, quantum chromodynamics, quark model, particle properties, lepton collider experiments, experimental particle physics
Objavljeno v DKUM: 21.07.2017; Ogledov: 1578; Prenosov: 249
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