Exotic hadron searches in photoproduction GHP2021 Astrid N. Hiller Blin [email protected] P C J A Phys. Rev. D100 (2019) 034010 1907.09393 [hep-ph] Phys. Rev. D102 (2020) 114010 2008.01001 [hep-ph] April 16, 2021 The family of exotics • Since 2003: discovery of many new unexpected resonance candidates in hadron colliders • E.g. mesons whose PC cannot be matched by content ( ) J qq¯ π1 Guo et al., 1912.07030 • XYZ states Brambilla et al., 1907.07583 Hosaka et al., 1603.09229 • Baryons with exotic flavor content, e.g. positive strangeness or negative charm • Pentaquarks, di-baryons, gluonium, quark-gluon hybrids, … 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 • Lepton beams provide efficient probes of the hadron spectrum, due to their point-like nature, free of kinematical effects from 3-body dynamics • Independent confirmation • Limited statistics so far at COMPASS and JLab (not yet seen in photoproduction): promising for searches with higher-luminosity in electron-ion colliders! A. N. Hiller Blin GHP2021 April 16th, 2021 2 XYZ photoproduction dynamics • t-channel exchanges assumed to give leading contributions • 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 • VMD assumed for determination of top couplings γ Q V efV α1⋯αj β1⋯βj ! < λ�λN′ |T |λγλN > = � �α ⋯α ;β ⋯β ℬ ! q ∑ λV=λγ,λ� 1 j 1 j λN λN′ q0 mV T V, ℰ k E j−M α(t)−M j −iπα(t) p p0 4 p(t) q(t) dμμ′(! θt) 1 1 + τ e s �j ⟶ − α′! Γ j − α(t) μμ′! (t) 2 ( ) ( s0 ) ξμμ(s, t) t − mℰ [ 2 ] ( s0 ) B N N 0 A. N. Hiller Blin GHP2021 April 16th, 2021 3 Z+ photoproduction: 1+- • Focus on the 3 narrow states with large branching fractions into pion and vector Exotic minimum quark content: • QQ¯q1q¯2 • Pion exchange and VMD • Sizeable cross sections especially at low energies 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 [GeV] https://github.com/dwinney/jpacPhoto W [GeV] γ p Albaladejo et al., 2008.01001 [hep-ph] γ p A. N. Hiller Blin GHP2021 April 16th, 2021 4 X and axial vector photoproduction • Focus on the famous X(3872), largely isospin violating, and similar non-exotic �c1 • � 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 GHP2021 April 16th, 2021 5 Y (hybrid?) and vector-meson photoproduction • Known to be well described by Pomeron exchange: we use fits from our previous works to LE (GlueX/SLAC) and HE (HERA/ZEUS); parameters assumed intrinsic to Pomeron ANHB et al., Phys. Rev. D 94 (2016) 034002 Winney et al., Phys. Rev. D 100 (2019) 034019 • Coupling ratio to usual J/� estimated from decay ratios into gg�: R ’ ≈ 0.55 (compatible with HERA/ZEUS ) � σψ′!/σψ ∼ 0.39 RY ≈ 1.5 (suggests affinity to gluons as expected for a hybrid Y) • Good candidates for EIC: diffractive production increases with energy! 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 W γp [GeV] W γp [GeV] A. N. Hiller Blin GHP2021 April 16th, 2021 6 LHCb 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 • K−p resonances (Λ: sud content) not sufficient to fit data Compact 5-quark state or weakly-bound (*) • D¯*Σc interpretations possible • Or possibly just kinematic effects A. N. Hiller Blin GHP2021 April 16th, 2021 7 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 GlueX data γ γ J/ψ J/ψ IP 1 Pc(4450) ′ ′ (nb) ppppσ ANHB et al., Phys. Rev. D 94 (2016) 034002 Winney et al., Phys. Rev. D 100 (2019) 034019 10−1 8.5 9.0 9.5 10.0 10.5 11.0 11.5 E γ (GeV) • Fits to GlueX data (no peak evidence) allowed for Pc branching fractions of 1-5% • If photoproduction experiments fail in finding signals, the scenario of LHCb signals being kinematic effects in the final-state is favoured A. N. Hiller Blin GHP2021 April 16th, 2021 8 Discriminatory power of polarization observables • Polarization observables more sensitive to broader or overlapping signals • With sensitivity studies provided by JPAC, Hall A LoI submitted: measuring A(K)LL LoI12-18-001 (PAC 46) C. Fanelli, L. Pentchev, B. Wojtsekhowski 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. Rev. D 100 (2019) 034019 https://github.com/dwinney/jpacPhoto dσ( ↑ ↑ ) − dσ( ↑ ↓ ) dσ⊥ − dσ∥ 0 0 20 40 60 80 A(K)LL = Σ = dσ( ↑ ↑ ) + dσ( ↑ ↓ ) dσ⊥ + dσ∥ θ • Beam asymmetries Σ can provide complementary information! A. N. Hiller Blin GHP2021 April 16th, 2021 9 Summary • X and Z states most promising close to threshold; diffractive states such as the Y are good candidates for the EIC • Pc searches require higher luminosity at low energies: polarization observables! Outlook: Albaladejo et al., SNOWMASS21-RF7_RF0-120 Albaladejo et al., SNOWMASS21-RF7_RF0-090 Albaladejo et al., SNOWMASS21-RF7_RF0-081 • Semi-inclusive reactions: though complicating the identification of final states, they have larger cross sections • Electroproduction: better experimental feasibility • Studies trivially extended to other XYZP once information about them is available A. N. Hiller Blin GHP2021 April 16th, 2021 10.