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Exotic Hadron Photoproduction HADRON 2021 Exotic Hadron Photoproduction HADRON 2021 Astrid N. Hiller Blin [email protected] P C J A Phys. Rev. D94 (2016) 034002 1606.08912 [hep-ph] Phys. Rev. D100 (2019) 034010 1907.09393 [hep-ph] Phys. Rev. D102 (2020) 114010 2008.01001 [hep-ph] July 26, 2021 Spectroscopy of exotic states • Since 2003, a plethora of “exotic” resonance candidates has been measured: new challenges for quark model. Choi et al., PRL 91 (2003) 262001 Adolph et al., PLB 740 (2015) 303 Ablikim et al., PRL 118 (2017) 092001 Ablikim et al., PRL 110 (2013) 252001 Aaij et al., PRL 115 (2015) 072001 Aaij et al., PRL 122 (2019) 222001 • Even conventional quarkonium production is interesting: entangles perturbative (QQ¯ production) and non-perturbative (hadronization) regimes. • Hadron collisions (pp@LHC and pp¯@Tevatron) indispensable in advancing knowledge. • They suffer from kinematical effects from 3-body dynamics: might lead to model-dependent misinterpretation of signals. Guo et al., PPNP 112 (2020) 103757 • Resonances arise due to poles of non-perturbative dynamical nature due to the interaction strength between quarks and gluons and among hadrons. • Kinematical singularities are determined by masses and energies of reaction particles: while two-body branch points are more easily distinguishable from resonances, triangle singularities are close to pertinent thresholds and might be misidentified. Esposito et al., PR 668 (2017) 1 Hosaka et al., PTEP 2016 (2016) 062C01 Brambilla et al., PR 873(2020) 1 Brambilla et al., EPJC 71 (2011) 1534 A. N. Hiller Blin Hadron 2021 July 26, 2021 2 Distinguishing resonances • Triangle singularities are strongly sensitive to kinematic variables: peaks in invariant mass distribution should depend on choice of kinematical bin. • Quantum numbers constrained to S-wave pair of internal particles. • In electro- and photoproduction, we have beams of point-like particles: efficient, complementary measurements of the hadron spectrum and structure. • COMPASS, BES, Belle and Jefferson Lab have strongly furthered our understanding. • Limited statistics so far — we need higher luminosities at appropriate energies: well achievable in the electron-ion collider era! A. N. Hiller Blin Hadron 2021 July 26, 2021 3 The family of exotics • Mesons whose JPC cannot be matched by qq¯ content: hybrid smoking guns such as in ! system, charged quarkonium Z, … π1 η(′)π • Exotic charmonium/bottomonium - X and Y (vector) states: tetraquarks, hybrids, gluonium, … • Baryons with exotic flavor (positive strangeness, negative charm), hidden-charm(beauty) pentaquarks, … • Di-baryons, meson-baryon molecules (just below threshold and with sizable spatial extension), … q q q g q q q¯ g g q g q q q g g g g g g q q q g g g q • Need for confirmation and independent studies: promising for high-luminosity searches at JLab and electron-ion colliders! A. N. Hiller Blin Hadron 2021 July 26, 2021 4 Production formalism - phenomenological constraints Results: XYZ and pentaquarks What can the future of electron-ion colliders bring us? Production formalism - phenomenological constraints Results: XYZ and pentaquarks What can the future of electron-ion colliders bring us? Photoproduction dynamics • Description via t-channel exchanges. • Fixed spin near threshold: full s dependence; but asymptotically sj (exceeds unitarity bound). • Reggeization at high energies: tower of particles with increasing spin. • Couplings determined from known experimental branching fractions. • Vector-meson dominance (VMD) assumed for estimation of top couplings. γ Q Low energies High energies V j−M α(t)−M j −iπα(t) 4 p(t) q(t) dμμ′(! θt) 1 1 + τ e s q j ! q0 � ! ⟶ − α′ Γ(j − α(t)) μμ′ (t) 2 [ ] T ( s0 ) ξμμ(s, t) t − mℰ 2 ( s0 ) k E p p0 efV α1⋯αj β1⋯βj ! < λ�λN′ |T |λγλN > = � �α ⋯α ;β ⋯β ℬ ! ∑ λV=λγ,λ� 1 j 1 j λN λN′ mV B V, ℰ N N 0 A. N. Hiller Blin Hadron 2021 July 26, 2021 7 Production formalism - phenomenological constraints Results: XYZ and pentaquarks What can the future of electron-ion colliders bring us? Z+ states: 1+- Exotic minimum quark content: . • QQ¯q1q¯2 • Most are either broad or close to open-charm thresholds: we focus on narrow ones with large branching fractions into vector + π. • Three-body final state interactions and coupled channel effects: need for independent confirmation. BES III + Zc(3900) e+e− → J/ψπ+π− A. N. Hiller Blin Hadron 2021 July 26, 2021 9 Z+ photoproduction Sizable photoproduction cross sections expected especially at low energies. γ Q V q q0 T k https://github.com/dwinney/jpacPhoto E Albaladejo et al., Phys. Rev. D 102 (2020) 114010 p p0 B N N 0 102 J PAC 1 J PAC + Z c(3900) 10 Z (10610)+ b −1 + 10 Z b'(10650) [nb] [nb] Z n) Z n) −2 → 1 → 10 p p γ γ ( ( σ σ + 10−3 Z c(3900) −1 + 10 Z b(10610) + Z b'(10650) 10−4 5 10 15 20 20 30 40 50 60 70 W γ p [GeV] W γ p [GeV] A. N. Hiller Blin Hadron 2021 July 26, 2021 10 X(3872): 1++ We focus on the famous X(3872), strongly isospin violating: narrow state with large branching into low-lying charmonium (loosely bound molecule). Belle A. N. Hiller Blin Hadron 2021 July 26, 2021 11 X(3872) photoproduction • � and � exchanges give main contributions. • Extremely suppressed cross sections at high energies: threshold most promising. 1 J PAC J PAC 102 −1 10 χ (1P) c1 X (3872) 10 [nb] [nb] 10−2 X p) X p) 1 → → −3 p p 10 γ γ ( ( σ 10−1 σ χ (1P) c1 10−4 X (3872) 10−2 10−5 4.5 5 5.5 6 6.5 7 20 30 40 50 60 W γ p [GeV] W γ p [GeV] A. N. Hiller Blin Hadron 2021 July 26, 2021 12 X(6900): 0++? • The new di-J/ψ X(6900) is assumed to be a scalar here. • Couplings for J/ψ exchange too small for detection: for ω exchange with assumed 1% branching fraction still sizable cross sections (OZI suppressed but possible as in known ψ(3770) → ϕ η). • Extremely suppressed cross sections at HE: threshold (LE) most promising. J PAC 10 X (6900) with BR(X → ψ ω) = 1% [nb] 1 X p) → p γ ( σ 10−1 10−2 8 10 12 14 W γp [GeV] A. N. Hiller Blin Hadron 2021 July 26, 2021 13 Y photoproduction: 1-- • Well studied experimentally because they can be produced in e+e− annihilation: BES III, Belle, BaBar, CLEO. • Probably not conventional charmonium: decay mostly into hidden-charm states, instead of open; overpopulate predictions of vector charmonium spectrum. • Could be hybrids, tetraquarks, hadronic molecules, … BES III Y(4260), Y(4360) A. N. Hiller Blin Hadron 2021 July 26, 2021 14 Y: perhaps the most promising EIC candidates • Known to be well described by diffractive Pomeron (� ∼ 2-gluon 0++) exchange: fits to GlueX/SLAC and HERA/ZEUS. • Top-coupling (γ → V�) ratio to J/� estimated from decay ratios into gg�: RY ≈ 1.5 suggests affinity to gluons as expected for a hybrid Y. ANHB et al., Phys. Rev. D 94 (2016) 034002 • Diffractive production increases with energy! Winney et al., Phys. Rev. D 100 (2019) 034019 20 200 PAC PAC J / ψ J J / ψ J ψ(2S) ψ(2S) 15 Y (4260) 150 Y (4260) [nb] [nb] Y p) 10 Y p) 100 → → p p γ γ ( ( σ σ 5 50 0 0 4 6 8 10 40 60 80 100 Note: W γp [GeV] W γp [GeV] Charge asymmetries in open charm production promise increased sensitivity to small Odderon 0+- contributions. A. N. Hiller Blin Hadron 2021 July 26, 2021 15 LHCb pentaquark discovery • 2015: exotic-like structures in J/ψ p channel found. LHCb collaboration, PRL 115 (2015) 072001; PRL 122 (2019) 222001 c b J/ψ c¯ Λ s − b u u¯ K d u u p d Pc ≡ cc¯uud • Possible interpretations: compact 5-quark state; Weakly-bound (*): mass consistent with predictions; • D¯*Σc would be strongly isospin breaking (J/ψ p vs J/ψ Δ) and require discovery of more multiplet members; • Or possibly just kinematic effects: LHCb showed that this kind of fits only is good if all exchanged resonances have narrow width (not so realistic). A. N. Hiller Blin Hadron 2021 July 26, 2021 16 Pentaquarks in J / ψ photoproduction • Confirmation of resonant nature vs kinematic effects. • Peak close to threshold: low background. • Non-resonant contribution — Pomeron exchange; Resonant amplitude — Breit-Wigner ansatz and VMD assumption. γ γ J/ψ J/ψ IP Pc(4450) ′ pppp′ ANHB et al., Phys. Rev. D 94 (2016) 034002 Winney et al., Phys. Rev. D 100 (2019) 034019 • Fits to GlueX data (no peak evidence) allowed for Pc branching fractions of 1-5%: model dependent, thus ruling out some models. • If photoproduction experiments fail in finding signals (Hall A/C update coming soon), the scenario of LHCb signals being kinematic effects in the final-state is favoured. A. N. Hiller Blin Hadron 2021 July 26, 2021 17 Discriminatory power of polarization observables • Polarization observables more sensitive to broader or overlapping signals. • Helpful information for determining quantum numbers. LoI12-18-001 (PAC 46) C. Fanelli, L. Pentchev, B. Wojtsekhowski • With sensitivity studies provided by JPAC, Hall A LoI submitted: measuring A(K)LL. 0.8 0.2 PAC KLL ALL J W = 4.45 GeV- - - {3/2-,3/2 ,3/2 } {3/2 ,5/2+,5/2+} 0.1 - - + {3/2-,3/2 ,5/2 -} 0.6 {3/2 ,5/2+,3/2 } Background 0 Σ 0.4 -0.1 Pc 3/2- Pc 3/2+ Pc 5/2+ Pc 5/2- bkg only -0.2 8.5 9 9.5 10 10.5 11 11.5 12 0.2 Preliminary Eγ [GeV] Winney et al., Phys.
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