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BESIII Physics and Future Tau-Charm Factories BESIII physics and future tau-charm factories Xiaorong Zhou (on behalf of BESIII Collaboration) University of Science and Technology of China Snowmass2020: Rare Processes and Precision Frontier Townhall Meeting 2020.10.2 1 The Standard Model The standard model of particle physics is a well-tested theoretical framework, However, the SM has a number of issues need further investigation: The nature of quark confinement Matter-antimatter asymmetry of the Universe Gravity, dark matter, neutrino masses, numbers of flavors, etc. 19 free parameters of the SM QCD coupling strength 2 Physics in tau-Charm Region • Light hadron spectroscopy • Hadron form factors • XYZ particles • Y(2175) resonance • Gluonic and exotic states • Physics with D mesons • Mutltiquark states with s quark, • Process of LFV and CPV • fD and fDs • MLLA/LPHD and QCD sum • Rare and forbidden decays • D0-D0 mixing rule predictions • Physics with lepton • Charm baryons The interplay of perturbative and nonperturbative dynamics Unique features: Rich of resonances, Threshold characteristics, Quantum correlation 3 BEPCII: a 흉-charm factory Storage ring Electromagnetic Muon Counter Calorimeter ~240 m RPC CsI(Tl): L=28 cm Barrel: 9 layers Barrel 휎퐸=2.5% Endcap: 8 layers Endcap 휎 =5.0% σspatial: 1.48 cm Linac ~200 m 퐸 BESIII detector Ecm= 2.0-4.6 GeV (2.0-4.9 GeV since 2019) Time Of Flight Energy spread: 훥퐸 ≈ 5 × 10−4 Main Drift Chamber Plastic scintillator Small cell, 43 layer Peak luminosity in continuously operation 휎푇(barrel): 80 ps 33 −2 −1 휎푥푦=130 휇m @E = 3.77 GeV: ~0.8× 10 cm s 휎 (endcap): 110 ps cm dE/dx~6% 푇 (update to 65 ps 휎 /푝= 0.5% at 1 GeV 4 푝 with MRPC) BESIII Collaboration 15 countries, 74 institutions ~500 members 5 Data samples collected at BESIII Data sets collected so far include, ➢ ퟏퟎ × ퟏퟎퟗ 푱/흍 events ➢ 0.5 × 109 휓′ events ➢ Scan data [2.0, 3.08] GeV; [3.735, 4.600] GeV, 130 energy points, about 2.0 fb-1 ➢ Large data sets for XYZ study above 4.0 GeV about 17 fb-1 Unique data sets at open charm thresholds 4.6-4.7 4.3 6 BESIII physics highlights ✓ Best precision of tau mass measurement (∆푚휏 = 0.18 MeV) ✓ Charmonium and XYZ spectroscopy: Zc(3900), X(3872), Y(4260)… ✓ Light hadron & searches of exotics: X(1835), glueball… ✓ Precision charm physics: CKM, decay constant, form factors, LFU, Λ푐 decays ✓ Probe EM structure of baryons: GE, GM of proton, neutron, hyperons ✓ Hyperon-anti-hyperon pairs from J/휓 and 휓′ decays: asymmetry parameters, CP violation, polarizations ✓ … Until end of June >300 publications 7 Charmonium (Like) spectroscopy Excellent platform to explore the QCD Fruitful results in past decade, a new territory to study exotic hadrons Y(3940) Z(3900) X(3872) Y(4008) Z(4020) X(3940) Y(4260) Z(4050) X(4160) Y(4360) Z(4200) X(4350) Y(4660) Z(4250) Z(4430) Tasks : Precisely measurement the transition Search for the missing states Understand the nature of unknown states Search for the new exotic states Godfrey & Isgur, PRD 32, 189 (1985) 8 The XYZ states PRL 122, 202001 (2019) PRL 118, 092001 (2017) PRL 110, 252001 (2013) Y(4260) Zc(3900) X(3872) • XYZ states are studied extensively at BESIII with high efficiency & low background • Relations between XYZ states are building • Various models are proposed to understand their structure(tetraquark, molecule, hybrid…) • More efforts are needed to understand their properties 9 More details can be found in Ryan’s talk in RF7 Systematic study of glueball at BESIII Charmonium decays provides an ideal hunting ground for light glueballs ➢ “Glue-rich” process ➢ Clean high statistics data samples from e+e- production 10 ퟎ ퟎ PWA of 푱/흍 → 휸휼휼/휸푲풔 푲풔 푱/흍 → 휸휼휼 ퟎ ퟎ 푱/흍 → 휸푲풔 푲풔 BESIII’s results favor f (1710) as scalar glueball, 0 11 more experimental measurements are needed. Anomalous line shape of η′π+π- near p풑ഥ mass threshold 225 Million J/psi 1.3 Billion J/psi 12 Charm physics CKM matrix elements are fundamental SM parameters that describe the mixing of quark fields due to weak interaction. d' V V V d ud us ub s' = VcdVcsVcb s b' VtdVtsVtb b Purely Leptonic: Leptonic and semileptonic decays of charmed 0 + + + hadrons (D , D ,Ds , 휦풄 ) provide ideal testbeds to explore weak and strong interactions 1. |Vcs(d)|: better test on CKM matrix unitarity Semi-Leptonic: 2. (Semi-)leptonic D(s) decays allow for LFU tests K(휋) 3. fD(s)+,f+ (0): test of LQCD 13 D(s) (Semi-)Leptonic decay 2.93 fb-1 data @3.773 GeV PRD 89, 051104 (2014) PRL 123, 211802 (2019) PRL 121, 171803 (2019) + + 푫 → 흁 흂 푫+ → 흉+흂 푫ퟎ(+) → 흅−(ퟎ)흁+흂 0.48 fb-1 data @4.01 GeV 3.19 fb-1 data @4.178 GeV PRL 122, 011804 (2019) PRD 94, 072004 (2016) PRL 122, 071802 (2019) ퟎ − + + + + + 푫 → 푲 흁 흂흁 푫풔 → 풍 흂 푫풔 → 흁 흂 14 Determination of 3 angle The cleanest way to extract γ is from B→DK decays: + 0 + A(B → D K ) i( B +3 ) rBe A(B+ → D0 K + ) − Interference between tree-level decays; theoretically clean − current uncertainty σ(γ) ~5⁰ − however, theoretical relative error ~10-7 (very small!) Information of D decay strong phase is needed − Best way is to employ quantum coherence of DD production at threshold 15 More details can be found in Xiaorui’s talk in RF1 Precision measurements of 휦풄 decay + − -1 With the unique data near 휦풄 횲ഥ풄 threshold (567 pb @ 4.6 GeV), lots of 16 improved measurements have been achieved for 휦풄 decays at BESIII Nucleon electromagnetic form factors • Fundamental properties of the nucleon ➢ Connected to charge, magnetization distribution ➢ Crucial testing ground for models of the nucleon internal structure • Can be measured from space-like processes (eN) (precision 1%) or time-like process (precision 10%-30% before BESIII) Annihilation:Time-Like Unphysical B region e+ pp ® e+e-p 0 Scattering p p B e- FFs are real FFs are complex_ Space-Like region 0 q2 17 Nucleon electromagnetic form factors 688 pb-1 data @2.0-3.08 GeV PRL 124, 042001 (2020) ✓ Both ISR and scan approach Proton are used to obtain proton EMFFs ✓ Scan approach is applied on neutron EMFFs ✓ Significantly improved precision of nucleon EMFFs Preliminary Preliminary in timelike (comparable to Proton spacelike) ✓ Observed oscillation of Neutron neutron with a relative phase shift around ퟗퟎ° to Neutron proton 18 Threshold effects of baryons • The Born cross section for 풆+풆− → 휸∗ → 푩푩ഥ, can be expressed in terms of electromagnetic form factor 푮푬 and 푮푴 ∶ ퟐ ퟒ흅휶 푪휷 ퟐ ퟏ ퟐ 흈 ഥ 풒 = [|푮 풒 | + |푮 (풒)| ] 푩푩 ퟑ풒ퟐ 푴 ퟐ흉 푬 흅휶 ퟏ • The Coulomb factor C= 흅휶 for a charged 푩푩ഥ pair, and equals 휷 ퟏ−풆풙풑 (− ) 휷 to 1 for a neutral 푩푩ഥ pair ퟐ ퟑ 풎 ퟐ 흅 휶 ퟐ ퟐ 풑 ퟐ 흈푩푩ഥ ퟒ풎푩 = ퟐ |푮| = ퟖퟒퟖ|푮| ( ) 퐩퐛 ퟑ풎푩 풎푩 Non-zero cross sections at threshold are observed in various baryon pair + − production: 풑풑ഥ, 풏풏ഥ, 휦휦ഥ, 휦풄 휦ഥ풄 … 19 Polarization of 횲 hyperons and CPV ~7s upward Nature Phys. 15, 631-634 (2019) shift from all BESIII results with 1.3 billion 푱/흍 previous measurements 2% level sensitivity for CPV test SM prediction:10-4~10-5 Highest sensitivity test of CPV in baryon sector! More results with 10 billion 푱/흍 and other hyperons are coming. 20 More details can be found in Andrzej’s talk in RF1 Physics programs for future data taking at BESIII BESIII white paper: Chin. Phys. C 44, 040001 (2020) Upgrades of detector: -1 Wishlist comprises about 40 fb : ✓ Endcap TOF upgrade (2015) ➢ Inner most part of the drift chamber • 10~17 fb-1 on 휓(3770) ➢ Super Conduct magnet • 6 fb-1 at 4.18 GeV →Ds meson • Scan at the highest energy? Gain luminosity with “Topup” injection • Continue XYZ scan -1 • Large Zc samples: 5 fb each at 4.23, 4.42 GeV • High-statistics data samples around 2.2, 2.4 GeV • 3 billion 휓′ • ... BESIII detector is in good status, inner detector upgrade in progress, will continue data taking for another 5-10 years 21 Future tau charm factory • Limited by length of storage ring, BEPCII has no space and potential for major upgrade • Physics study limited by the statistics, collision energy • There is strong competition/synergy between 푐 − 휏 and 퐵 factories • BelleII • LHCb Started in 2019 Upgrade now 50 ab-1 in total 50/300 fb-1 (Run 3/4) Future tau charm factory proposed in China and Russia 22 Super tau-Charm Facility in China • Peaking luminosity >0.5×1035 cm-2s-1 at 4 GeV • Potential to increase luminosity and realize beam polarization • Energy range Ecm = 2-7 GeV • A nature extension and a viable option for China accelerator project in the post BEPCII/BESIII era Expected data with 1ab-1 CME No. of Events 3.097 3 T J/휓 3.686 500 B 휓’ 3.77 3.6 B D0 2.8 B D+ 4.04 0.2 B Ds 1 B Y(4260) 4.23 100 M Zc 5 M X(3872) 3.6 M tau 4.63 0.5 M Λ푐 >5 fine scan 23 More details can be found in Haiping’s talk in RF7 Super Charm-Tau Factory in Russia + - • Symmetric e e collider, energy region Ecm=2-6 GeV • Luminosity 1035 cm-2s-1 @ 4GeV • Crab waist beam collision, longitudinal e- polarization Circumference 478.092 m 2휃 60 mrad ∗ ∗ 훽푥/훽푦 50 mm / 0.5 mm 퐹푅퐹 349.9 MHz 퐸beam (GeV) ퟏ ퟏ.
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