! The Reaction γ p → { Λ Λ } p Revealed with GlueX Reinhard Schumacher Hao Li, Samuel Dai Carnegie Mellon University / GlueX Collaboration HYP2018 Conference, Portsmouth, VA June 26, 2018 Overview n Exploring baryon-baryon photoproDucEon n GlueX in Hall D at JLab n Experimental setup & analysis steps ! ! n DetecEng: (also ) γ p →{ΛΛ}p γ p →{pp}p n Phenomenology for the hyperon channel n All spectra shown toDay are very preliminary π − ! Λ p γ π + P Λ J = ? p p p 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 2 ! Itemized Goals re γ p → {ΛΛ}p n StuDy the reacEon mechanism: n Cross secEon measurements n Compare to pp n Beam spin asymmetry: Σ n Look for conEnuum resonances in anD pΛ ΛΛ “baryonium states” n Spin correlaons in creaon ΛΛ n Singlet fracEon n A CPT test (in principle) 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 3 Theory Status – one publication n Valery Lyubovitskij et al.* anD Priv. Comm. n Use: effecEve hADronic Lagrangian with 0 n vector/axial mesons Wv= ρ , ω anD WA= b1 , h1, + Reggeons n scalar mesons f0(1370), f0(1500), f0(1720) n Beam asymmetry anD cross secEons for: ! γ p →{pp}p ! γ p →{ΛΛ}p * T. Gutsche, S. Kuleshov, V. Lyubovitskij, I. Obukhovsky, Phys. Rev. D 96, 054024 (2017) 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 4 Theory Predictions ! γ p →{ΛΛ}p E = 9 GeV Σ γ Large beam asymmetry preDicteD - Cross secEon preDicteD dσ to be 1/10 as large as for pp dt pp case T. Gutsche, S. Kuleshov, V. Lyubovitskij, I. Obukhovsky, Phys. Rev. D 96, 054024 (2017) 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 5 GlueX Detector at JLab - • ~12 GeV e beam converteD to: 4 - 11.6 GeV photon beam Linear coherent peak 8-9 GeV (~40%) Four orientaons: 0°, 90°, 45°, 135° • Solenoidal magnet • Dri8 chambers • Start counter/Time of flight • ElectromagneBc Calorimeters 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 6 GlueX Experiment in Hall D / JLab • Physics-quality data runs in 2016, 2017, 2018, … (this talk) 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 7 Overall Kinematics How is the pair produced? - Orbital angular momentum? - Spin state: singlet or triplet? Λ - u-channel vs t-channel? nˆ - Need differential cross sections xˆ Θ - Need spin observables Λ yˆ - Σ beam spin asymmetry zˆ Λ - Cij hyperon spin correlations zˆʹ xˆʹ qˆ εˆ c.m. yˆ Θ ! ʹ ΛΛ γ xˆ proton yˆ proton zˆ 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 8 Kinematic Fitting n Vary measureD momenta within the permileD range to enforce exact momentum anD energy conservaon n Fit to 5 track GlueX events n Without constraining Λ masses anD fing to a single vertex n With Λ masses constraineD anD DetacheD verEces π − ! Λ p γ π + P Λ J = ? p p p 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 9 Kinematic Fit Confidence Level Kinemacally fit all 5-tracks events; Λ masses constraineD (or not) Keep events with C.L. > 0.01 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 10 − π pπ-←p Λ Invariant Mass Unconstrained ConvergeD KINFIT to 5 tracks, Aser 1% C.L. cut No PID cuts anD PID cuts Very clear signal! Λ Invariant Mass π-p Invariant Mass π-p (PloleD here using post-KINFIT variables) 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 11 + π p ← Λ Invariant Mass Unconstrained ConvergeD KINFIT to 5 tracks, Aser 1% C.L. cut No PID cuts anD PID cuts Very clear signal! Λ Invariant Mass π+p Invariant Mass π+p (PloleD here using post-KINFIT variables) 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 12 Photon Beam Energy Distribution GlueX linear beam polarizaon range ReacEon Threshold 4.9 GeV 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 13 Quiz: n How woulD you suppose that the LambDa parEcles are DistributeD in (γp) C.M. angle? π − n uniformly? ! Λ p γ n forwarD? π + P Λ J = ? p n backwarD? p p 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 14 Lambda Polar Angle in C.M. Dominantly at forwarD angles… …with a backwarD peak Cosine (LambDa Polar Angle in CM Frame) 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 15 AntiLambda Polar Angle in C.M. “All” at forwarD angles… …NO backwarD peak Cosine (AnE-LambDa Polar Angle in CM Frame) 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 16 Sign of Two Reaction Amplitudes Cosine (LambDa Polar Angle in CM Frame) Cosine (AnE-LambDa Polar Angle in CM Frame) 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 17 Proton C.M. angle Dominantly at backwarD angles… …with a forwarD peak 6-26-18 Cosine (Recoil Proton Polar Angle in CM Frame) HYP2018, R. A. Schumacher, Carnegie Mellon University 18 Consistent with two t-channel Amplitudes: n Nonstrange exchange: n recoiling proton goes backwarD in C.M. frame n π, ρ, Pomeron… n Strange exchange: n recoiling Λ goes backwarD in C.M. frame * n K, K exchange… 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 19 t-tmin Distribution ~ Cross Section Entries 3954 Entries 2397 2 2 χ / ndf 25.99 / 43 400 χ / ndf 78.5 / 40 Offset 0.6024 ± 0.2896 Offset 0.1663 ± 0.3392 600 N_0 690.9 ± 16.3 350 N_0 370 ± 10.8 b −3.534 ± 0.066 b −3.189 ± 0.076 500 300 pΛ 400 ΛΛ 250 200 300 150 200 100 100 50 0 0 0 0.5 1 1.5 2 2.5 3 0 0.5 1 1.5 2 2.5 3 -t' distribution for forward Λ -t' distribution for backward Λ - t’ of ΛΛ pairs (GeV2) - t’ of pΛ pairs (GeV2) DistribuEon for forwarD track pairing ΛΛ DistribuEon for forwarD track pairing pΛ -Does not resemble the moDel preDicEon! 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 20 Continuum Resonances n Baryon-(anE-)baryon interacEons n p p resonance searches came up empty… aer years of work at CERN & elsewhere n Look for resonant quasi-bounD states in invariant masses of Λ Λ anD pΛ n First-ever search for baryon-anE-baryon resonances in this reacEon 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 21 Looking for ΛΛΛΛ-onium ForwarD LambDa parEcles selecteD Entries 3954 600 One smooth DistribuEon 500 - BroADly consistent with t-DepenDence kinemacs Preliminary: not acceptance correcteD, - No stanD-out narrow structures seen 400 nor backgrounD subtracteD 300 200 100 0 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4 Invariant mass of ΛΛ for forward Λ Invariant Mass of ΛΛ (GeV) 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 22 Looking for p Λ -onium BackwarD LambDa parEcles selecteD Entries 2397 - Lower-stasEcs, with no stanD-out narrow structures seen 250 200 Preliminary: not acceptance correcteD, nor backgrounD subtracteD 150 100 50 0 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4 Invariant mass of pΛ for backward Λ Invariant Mass of pΛ (GeV) 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 23 (Possible) CPT Symmetry Test n Lifetimes for particle and anti-particle must be the same: τ Λ = τ Λ (by CPT) τ Λ = 263.2 ± 2.0 ps τ −τ / τ = −0.001± 0.009 (PDG) ( Λ Λ ) Λ 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 24 Reconstructed Lifetimes τ Λ −τ Λ / τ Λ = 0.03± 0.03 τ Λ = LifeEmes consistent, within uncertainEes 216.9 ± 3(.6 ps ) τ Λ = 224.1± 4.5ps Rest Frame LambDa LifeEme (ns) Rest Frame anE-LambDa LifeEme (ns) PRELIMINARY: GlueX neeDs about x10 events to be stasEcally compeEEve. It coulD happen… 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 25 Spin Correlations (in-progress work) n Beam spin asymmetry, Σ, coming (recall GlueX uses linear photon beam polarizaon...) n The LambDas can be proDuceD polarizeD 1 1 I(θ ) = 1−αP cos(θ ) I(θ ) = 1−αP cos(θ ) p 4π ( Λ p ) p 4π ( Λ p ) n Expect: PΛ = PΛ (by C) z axis α = −α (by CP) 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 26 Spin Correlations (in-progress work) ! ! n The LL spin correlaons: ΛΛ Cmn = σ m ⊗σ n n Observables: C C C C 0 (by P) Czx = Cxz (by C) xy = yx = zy = yz = n Singlet FracEon: 1 ! ! 1 S ≡ 1− σ •σ = 1+C −C +C F 4 ( Λ Λ ) 4 ( xx yy zz ) n SF = 0 - hyperons produced in spin triplet state n SF = 1 - hyperons produced in spin singlet state n SF = ¼ - stasEcal mixture of singlet & triplet 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 27 Spin Correlations n This is the leading edge of our work… n No results yet 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 28 Other Strangeness Physics at GlueX n Κ+Λ: beam asymmetry anD Λ polarizaon at GlueX energies n Λ(1520): beam asymmetry & anD higher-lying p K- states n Ξ’s: grounD state observeD anD eviDence for exciteD states n Κ/π Cerenkov separator (DIRC) being installeD 2018 6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 29 Summary / Conclusions n We see the reacEon! ΛΛ n InteresEng angular DistribuEons shown n EviDence for at least two exchange mechanisms n Acceptances have not been applieD yet: all very preliminary n Have ∼twice the stasEcs from 2018 run n Cross secEons & spin observables coming, compare & pp ΛΛ n We woulD welcome some theory support! 6-26-18 HYP2018, R.