PoS(ICHEP2020)498 Λ https://pos.sissa.it/ ∗ 0, [email protected] Speaker ∗ Dept. of Physics and Astronomy, Uppsala University, BoxE-mail: 516, 75120 Uppsala, Sweden Polarised and entangled hyperons provideQCD a and powerful to diagnostic search for tool physics toexperiment beyond the study in Standard non-perturbative China Model offer at unique theunder possibilities precision particle-antiparticle-symmetric frontier. to conditions. study The strange BESIII Recent hyperon-antihyperon resultssurement final include of states the the time-like first structure complete of mea- anyhyperon. baryon, as Both well analyses as exploit a the precise self-analysingpolarization CP weak symmetry and decay test of entanglement for hyperons, the of giving the accessinformation hyperon-antihyperon of to pair. production spin and Using decay of a ahyperons. similar number approach, of These single- new proceedings and present multi-strange a asof summary well ongoing as of studies charmed the where most new results recent are findings expected and in give the a near glimpse future. Copyright owned by the author(s) under the terms of the Creative Commons 0 © Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). Karin Schönning for the BESIII collaboration 40th International Conference on High EnergyJuly physics 28 - - ICHEP2020 August 6, 2020 Prague, Czech Republic (virtual meeting) Polarised and entangled hyperon-antihyperon pairs in BESIII PoS(ICHEP2020)498 , ± ) (1) the , the and/or " i.e. 3900 ( . hyperons W 2 / , . V GeV [11]. The 770 . 3 = B √ at 1 − Karin Schönning for the BESIII s 2 and a pseudoscalar meson −  cm  \ the polarisation. Sequentially decaying 33 % 10 cos baryon % annihilations can provide new insights on two 2 1 . − U 4 2 + + 4 1 ) ∝  [13]. into a spin \ ¯ @ ( . ¯  @ @@ hyperon 2 1 , provide information on the additional decay parameters Ω and collider optimised for a luminosity of − Ξ 4 + 4 is the decay asymmetry parameter [10] and e.g. elastic or deep inelastic scattering), ii) excite it (spectroscopy) or iii) replace one of the . U e.g. Ground-state hyperons have an advantage compared to nucleons: their spin properties are . In this sense, hyperons reveal more information about themselves than nucleons as we will . q BES III detector covers 93%chamber of for the tracking, ii) full an solid electromagnetic angle calorimeterof and for electrons, energy has positrons measurement five and and components: identification photons,deflection iii) i) of a a particle time-of-flight multiwire trajectories, system, and iv) drift v) aBESIII a is super-conducting famous muon magnet for detection for the discovery system. of For thewith first more a confirmed details, minimum charged see charmonium quark state, Ref. content the [12]. of demonstrate in this presentation. Furthermore,and entangled by hyperon-antihyperon going pairs even from deeper we will show how polarised where hyperons, angular distribution of the daughter baryon is given by of the most challenging problemsand the in matter-antimatter asymmetry contemporary of physics: the Universe.being non-perturbative New applied techniques strong at have been the interactions developed BEijing and Spectrometer are will (BESIII) report experiment in on China. the most In recent thesestudies at proceedings, results we BESIII. and summarise the future prospects for hyperon-antihyperon 2. The BESIII experiment The BES III detector isdouble-ring an integrated part of the BEPC-II (Beijing Electron Positron Collider), a experimentally accessible through their weak,two-body decay parity of violating a decay. spin For instance, in the weak, Polarised and entangled hyperon-antihyperon pairscollaboration in BESIII 1. Introduction The Standard Model of particle physicsmental has particles proven immensely and successful their in short-rangeit describing interactions. comes the to funda- However, describing its one usefulnessnucleon. of has the limitations Describing most when fundamental abundantand building properties blocks abundance such of [8] as our remain the visible objectsnon-perturbative spin Universe, nature of of [1,2], the vital strong structure interaction discussions makes [3,4], quantitative andimpossible predictions size to research. from perform first5–7] [ analytically. principles Instead, This approaches are isphenomenological required models, largely such or because as effective Lattice the field QCD; theories, researchnected areas to where experimental the data. progress isnucleon One very way itself. tightly forward con- is Another, to complementarychange further way to to refine it understand and and the intensify see the nucleonwith how studies better it of is reacts. the to For make instance,building a we small blocks. can i) In scatter thein on following, the it we nucleon (structure focus with and on heavier spin iii)provide strange studies and a or new replace charm angle quarks one on [9]. or the nucleon several The and of properties on the of non-perturbative light the QCD. quarks resulting PoS(ICHEP2020)498 ) ¯ + ). . . an 0 . ¯ ?c sys > ( via → 2 → @ 02 ( − ¯ . Λ 4 reaction at 0 , + − 4 ¯ Λ . ) ± ?c Λ 2 + . potential models Λ time-like e.g. → → stat ¯ Λ ( charmonium states. ∗ Λ Λ W , ) or 14 ¯ 0 . Λ 0 state is unpolarised [14]. e.g. → Λ < ± − 2 − 4 → 4 @ [8]. This, however, requires typically results in large data 96 ( + + . ∗ 4 ) 4 0 W Karin Schönning for the BESIII [19]. These results have already ( ) 2 . and the charmed = ( → − Ψ − ' sys Ω ( 4 + or o space-like 4 6 Ψ Baryogenesis / ) ± . hyperon in the Λ stat hyperon, but also for other octet hyperons such as 3 ( Λ o 12 . This phase is a quantifies the interference between the ± , was measured to be o ΔΦ " 37  . Hence, the experimentally accessible polarisation of hyperons / . The EMFFs are either c  2 @  ΔΦ = = 550 exclusively reconstructed ' isodoublet, as well as the decuplet ≈ Ξ , the space-like and time-like EMFFs should converge to the same value, meaning that colliders, hyperon-antihyperon pairs can be produced either electromagnetically, − | → ∞ isotriplet and the 4 2 The next step is to study the energy dependence of the phase. BESIII has collected an The BESIII experiment has recently performed the first complete measurement of the time-like + must be an integer multiple of Σ @ 4 | 3.2 Hyperon decays One of the most puzzling, unresolvedof conundrums so of modern much science more is matter whyantimatter than the asymmetry antimatter. Universe consists must Unless have this a was dynamical fine-tuned in origin, the Big Bang, this matter- the unprecedented sample of off-resonancepossibilities not data only between for further 2.0 studies of GeV the and 4.7 GeV that open up new 2.396 GeV. An sample of [20], vector dominance [21] and dispersion theory [22]. structure of any baryon, through a study of the The space-like EMFFs arestudied related in to elastic charge- lepton-hadron and scattering.unstable magnetisation However, hadrons the densities space-like such of region the as isprocesses, hadron hyperons. difficult provide a to and viable study option. are Instead, for The the space-likerelations and time-like [18]. the time-like region, It region are is probed related interestingcan by in dispersion to be note complex that with whereas aproduction space-like relative amplitudes EMFFs phase and therefore are induces a real, polarising the effectas on time-like the produced ones hyperons. However, ΔΦ makes it possible to studydirect measurements the in onset the of space-like region. the scale of the space-like/time-like convergence without events was analysed using the formalismthe outlined magnetic in form factors, Ref. [16]. The ratio between the electricsparked and progress in the theory community, with interpretations in terms of and the phase was found to be intermediate virtual photon, orIn from both the cases, decay interferencepolarised of between with a different respect vector production to resonance Electromagnetic amplitudes the production production result gives plane, in access even to hyperonsproduction if the that through the inner are charmonium initial structure resonances of such the as produced hyperon, whereas Polarised and entangled hyperon-antihyperon pairscollaboration in BESIII 3. Recent results In samples which enables precision studiesentangled hyperon-antihyperon of pairs decay and parameters. their subsequenttime-like decays The can hadronic joint be and parameterised electromagnetic angular in form distributions factors terms of and of decay asymmetry parameters3.1 [15–17]. Hyperon structure Hadron structure can be quantified bythe electromagnetic momentum form transfer factors squared (EMFFs), analytic functions of PoS(ICHEP2020)498 + Ψ c (2) / 0 Σ and/or , (syst.), 10 decays, B . . Finally, 10 W Ψ 0 ? , 004 / . c (syst.) [23]. . + 0 V Σ , ± 007 . . U that was closer to, 0 is to the first order and Λ ± + an interplay between U (stat.) c %  Λ [26]. pairs from via ) was extracted for the first 009 ¯ (stat.) Λ ( . 2 0 Λ (  % ±  012 Ψ Karin Schönning for the BESIII . 0 : CP violation would result in a . 750 ± and . from two-body hyperon decays have U (syst.). In addition, it was found that 0 Ψ / 006 % . 010 .  . 0 ¯ ¯ . . 0 was studied for the decay modes measurement was utilized in the analysis of U U ± 2 + ¯ Λ + + decays, it is important to understand why the Λ Λ U . . were determined. A new, large-scale data taking Λ so far: 4 U U 0 → (stat.) c =  % + was found to be Ψ  Σ / Λ 037 % . However, the joint angular distribution of single-tagged . U 2  − 0 ¯ and Λ ± 2 + + Λ c changes sign between decays. The decay asymmetry 004 Λ . ) ) with previous measurements based on the proton polarimeter , 0 ) with, the BESIII result [25]. Since many measurements in various ( + ΔΦ f hyperon spin observables, spectroscopy, decay parameters of heavier 2 f c ( 3 0 12 Ψ Σ even in the presence of CP violating processes. Sequentially decaying ≈ e.g. ≈ , isodoublet, offer a way to directly measure and separate strong and weak hyperons provide a test for strong CP violation [30]. The formalism for Λ  % and Ξ 0 U  Σ or the charmed Ψ / + ¯ Ω − and found to be is derived in Ref. [31, 32] and is being applied in an ongoing study with BESIII. + Ω of the modes 0 Σ ¯ 2 + Σ 0 Λ W Σ to CP violation. On the one hand, strong CP conserving processes could dilute or hide CP pairs, employing the formalism outlined in Refs. [17, 29]. Furthermore, electromagnetic pairs from → A recent work by BESIII, exploiting polarised and entangled The technique applied in the BESIII So far, all existing measurements of the asymmetry Presently, the data samples at BESIII do not allow for exclusive reconstruction of pairs of and +  % − − ¯ ¯ . In Ref. [33], the decay asymmetry parameter  Ξ 2 + Σ 4 − + Λ . + V q 4 More importantly, the decay asymmetry in strong disagreement ( technique [24]. This triggered a re-analysisthough of still not CLAS consistent data ( that resultedfields in depend an directly different techniques yield different results. A recently collected world-record sample of hyperons and beams of polarised protons from Polarised and entangled hyperon-antihyperon pairscollaboration in BESIII processes that violate conservation ofand fundamental parity (CP). quantum In numbers short, such CPpatterns. as symmetry implies charge In that conjugation two-body particles decays of and entangled antiparticles hyperonscan have and the be antihyperons, same differences decay defined in decay in patterns terms of the decay asymmetry parameter provided the most precise measurement of the hadronic form factor phase non-zero value of the asymmetry events from BESIII can help resolving thissystematic issue effects. since it allows for a more precise determination of time for the violating components from weak or BSM processes. On the other hand, Σ strong and weak (or possibly even beyondof SM) interactions, it is difficult to quantify the sensitivity a product of strong andresult weak phase in differences a, [27 vanishing 28 ].hyperons, Hence, such a as very the small strong phase would phase differences. This isΞ being utilized in andecays ongoing of BESIII polarised study of polarised and entangled been found to be consistent with zero. However, since hyperons decay triple-strange for the first time. In addition, the precision was improved for the modes sequential decays of these hyperons provide information on the decay parameters campaign in the region 4.6-4.7 GeVhyperon offers and increased antihyperon decay precision asymmetries. and potentially also a separation of PoS(ICHEP2020)498 → (3) Ψ / ∗ helicity could be W ) 2 → / 3 , 59 (2015). − d 4 ( + 82 3 hyperon has been 4 Λ events from BESIII, has Ψ / baryons can be produced po- 2 3 10 Karin Schönning for the BESIII 10 0 ` A A 1 = hyperon, where the main contributions come 15 ` Õ pairs. The formalism for the − v u t 1 2 Ω cannot, makes baryon-antibaryon pair production 5 = 1 2 , 142002 (2017). ) 2 , 655 (2013). / , 042001 (2020). 3 119 d 85 ( 124 3 , 112001 (2007). , Issue 6457, 1007-1012 (2019). 99 365 (2010) 213; C. E. Carlson, Prog. Part. Nucl. Phys. baryon pairs is described by four complex form factors, or 3 2 data sample collected by BESIII, the helicity amplitudes as well as the 466 Phys. Rev. Lett. ) Rev. Mod. Phys. Science hyperon has not yet been determined in a model-independent way [24]. Phys. Rev. Lett. − were reconstructed. In addition, the degree of polarisation 3686 et al., Ω ( Nature Ω et al., et al., Ψ et al., q that are non-zero for an unpolarised initial state. Applying the aforementioned et al.,