! 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 photoproducon n GlueX in Hall D at JLab

n Experimental setup & analysis steps ! ! n Detecng: (also ) γ p →{ΛΛ}p γ p →{pp}p n Phenomenology for the 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 reacon mechanism: n Cross secon measurements

n Compare to pp

n Beam spin asymmetry: Σ n Look for connuum resonances in and pΛ ΛΛ “baryonium states” n Spin correlaons in creaon ΛΛ n Singlet fracon 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: effecve hadronic Lagrangian with 0 n vector/axial Wv= ρ , ω and WA= b1 , h1, + Reggeons

n scalar mesons f0(1370), f0(1500), f0(1720) n Beam asymmetry and cross secons 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 secon 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 beam Linear coherent peak 8-9 GeV (~40%) Four orientaons: 0°, 90°, 45°, 135°

• Solenoidal magnet • Dri chambers • Start counter/Time of flight • Electromagnec 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 yˆ proton zˆ

6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 8 Kinematic Fitting

n Vary measured momenta within the permied 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 verces 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, Aer 1% C.L. cut No PID cuts and PID cuts

Very clear signal! Λ

Invariant Mass π-p Invariant Mass π-p

(Ploed 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, Aer 1% C.L. cut No PID cuts and PID cuts

Very clear signal! Λ

Invariant Mass π+p Invariant Mass π+p

(Ploed 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

Reacon Threshold 4.9 GeV

6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 13 Quiz:

n How would you suppose that the Lambda parcles 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 (An-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 (An-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, …

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)

Distribuon for forward track pairing ΛΛ Distribuon for forward track pairing pΛ

-does not resemble the model predicon!

6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 20 Continuum Resonances

n Baryon-(an-)baryon interacons 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-an-baryon resonances in this reacon

6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 21 Looking for ΛΛΛΛ-onium Forward Lambda parcles selected Entries 3954

600 One smooth distribuon

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 parcles selected Entries 2397

- Lower-stascs, 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 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 = Lifemes consistent, within uncertaines 216.9 ± 3(.6 ps ) τ Λ = 224.1± 4.5ps

Rest Frame Lambda Lifeme (ns) Rest Frame an-Lambda Lifeme (ns)

PRELIMINARY: GlueX needs about x10 events to be stascally compeve. 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 ( Λ p ) p ( Λ p ) 4π 4π 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 Fracon: 1 ! ! 1 S ≡ 1− σ •σ = 1+C −C +C F 4 ( Λ Λ ) 4 ( xx yy zz )

n SF = 0 - produced in spin triplet state

n SF = 1 - hyperons produced in spin singlet state

n SF = ¼ - stascal 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 reacon! ΛΛ n Interesng angular distribuons shown

n Evidence for at least two exchange mechanisms n Acceptances have not been applied yet: all very preliminary n Have ∼twice the stascs from 2018 run n Cross secons & spin observables coming, compare & pp ΛΛ n We would welcome some theory support!

6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 30 Supplemental Slides

6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 31 Spin Correlations

n The LLΛΛ spin correlations:

N k 3 1 ηk cosθm P ∑k=1 y = N α N η ∑k=1 k

Z axis N k k 9 1 ηk cosθm cosθn C ∑k=1 mn = N αα N η ∑k=1 k

6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 32 π − p ← Λ Invariant Mass Constrained

KINFIT to 5 tracks, Aer C.L. cut & No PID cuts dE/dx & ming cuts

Λ

Invariant Mass π-p Invariant Mass π-p

(Ploed here using pre-KINFIT variables; it’s really a delta funcon)

6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 33 π + p ← Λ Invariant Mass Constrained

KINFIT to 5 tracks, Aer C.L. cut & No PID cuts dE/dx & ming cuts

Λ

Invariant Mass π+p Invariant Mass π+p

(Ploed here using pre-KINFIT variables; it’s really a delta funcon)

6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 34 Theory Predictions ! γ p →{pp}p E = 9 GeV Σ γ Large beam asymmetry predicted

- Peak in Σ for Regge dσ model when trajectories cross zero

dt Regge

T. Gutsche, S. Kuleshov, V. Lyubovitskij, I. Obukhovsky, Phys. Rev. D 96, 054024 (2017)

6-26-18 HYP2018, R. A. Schumacher, Carnegie Mellon University 35