Strangeness photoproduction at the BGO-OD experiment Tom Jude, on - - PowerPoint PPT Presentation

▶
strangeness photoproduction at the bgo od experiment
SMART_READER_LITE
LIVE PREVIEW

Strangeness photoproduction at the BGO-OD experiment Tom Jude, on - - PowerPoint PPT Presentation

Mar 02, 2023 28 likes •638 views

Strangeness photoproduction at the BGO-OD experiment Tom Jude, on behalf of the BGO-OD collaboration Physikalisches Institut University of Bonn THEIA, 27th Nov 2019 Supported by the DFG PN 388979758 & 405882627 Tom Jude (University of

slide-1
SLIDE 1

Strangeness photoproduction at the BGO-OD experiment

Tom Jude, on behalf of the BGO-OD collaboration

Physikalisches Institut University of Bonn

THEIA, 27th Nov 2019 Supported by the DFG PN 388979758 & 405882627

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 1 / 35

slide-2
SLIDE 2

Strangeness photoproduction at the BGO-OD experiment

1

Introduction & motivation - parallels in strange & charmed quark sectors?

2

The BGO-OD experiment at ELSA, Bonn

3

Strangeness photoproduction - first results: K 0 photoproduction off proton & neutron (deuterium) targets Extreme forward cross sections for K +Y and excited hyperons Future opportunities with BGO-OD Supported by the DFG PN 50165297

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 2 / 35

slide-3
SLIDE 3
  • 1. Introduction - N∗ spectrum: CQM vs. experiment

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 3 / 35

slide-4
SLIDE 4
  • 1. Introduction - Status of N∗ spectroscopy

BnGa - E. Klempt, A. Sarantsev, U. Thoma, V. Nikonov

Wealth of data from ELSA, MAMI, GRAAL & CLAS facilities Much improved understanding of known resonances, but few new states observed hadronic structure & relevant degrees of freedom - 3 quark states only? Molecule-like states, meson-baryon degrees of freedom?

L.Ya. Glozman and D.O. Riska, Physics Reports 268 (1996) 263, C. Garcia-Recio et al., Phys. Lett. B 582 (2004) 49, M.F.M. Lutz, E.E. Kolomeitsev, Phys. Lett. B 585 (2004) 243.

How would this manifest in reaction mechanisms & excitation spectra?

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 4 / 35

slide-5
SLIDE 5
  • 1. Motivation - Exotic phenomena in the charmed sector

Pentaquark candidates observed at LHCb Pc(4450)+ & Pc(4380)+ at Σc ¯ D∗ threshold

  • R. Aaij et al, PRL 115, 072001 (2015)

Meson-baryon dynamically generated states in the charmed sector - J.-J. Wu, R. Molina, E. Oset,

and B.S. Zou, Phys. Rev. Lett. 105, 232001 (2010)

Forsaken pentaquark particle spotted at CERN

Nature 523, 267 (2015)

X(3872)→ π+π−J/ψ - most cited paper from Belle, PRL91, 262001 (2003) Very close to D0 ¯ D0∗ threshold

  • B. Aubert et al (BARBAR Collaboration), Phys. Rev.

D77 111101 (2008)

JPC verified: 1++ R. Aaij et al. (LHCb

Collaboration), PRL 110, 222001 (2013)

X(3872) - molecular D0 ¯ D0∗ state?

N.A. T¨

  • rnqvist, Phys. Lett. B590, 209 (2004)

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 5 / 35

slide-6
SLIDE 6
  • 1. Motivation - Similarities in the uds sector?

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 5 / 35

slide-7
SLIDE 7
  • 1. Motivation - Structure of the Λ(1405)

Well established since the 1960’s but peculiar features! Difficult to reconcile within a CQM Mass too low compared to N∗(1535) Large spin orbit splitting to Λ(1520) Lies between the πΣ & ¯ KN thresholds Line shape (invariant mass) depends upon the decay mode (→ π0Σ0, π+Σ−, π−Σ+) Distorted by interference of Isospin 0 & 1 amplitudes

  • K. Moriya et al. (CLAS) Phys. Rev. C 87, 035206 (2013)

Λ(1405) - dynamically generated by meson-baryon interactions?

J.C. Nacher, E. Oset, H. Toki, A. Ramos, U.G. Meissner, Nucl. Phys. A 725 (2003) 181

LQCD: J.M.M Hall et al., PRL 114 (2015) 132002 UχPT: R. Molina & M. D¨

  • ring, Phys. Rev. D 94,

056010 & 079901 (2016) Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 6 / 35

slide-8
SLIDE 8
  • 1. Motivation - Cusp in γp → K 0Σ+ cross section
  • R. Ewald et al.,Phys. Lett. B 713 (2012) 180 (CBELSA/TAPS Collaboration).

This data: Full squares, Previous CBELSA-TAPS data: open squares, Previous SAPHIR data: triangles (references therein)

Cusp-like structure due to K ∗0 subthreshold production rescattering to π0 & K 0? Grey points - K 0Σ+ + K ∗Σ+

  • M. Nanova et al., EPJ A35, 333 (2008)

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 7 / 35

slide-9
SLIDE 9
  • 1. Motivation - K 0 photoproduction
  • A. Ramos and E. Oset, Phys. Lett. B

727, (2013) 287 The role of vector-baryon channels &

resonances in the γp → K0Σ+ & γn → K0Σ0 reactions near the K∗Λ threshold

The same model that predicted Pc states as meson-baryon dynamically generated! Cusp - destructive interference of dynamically generated N∗ states Predict constructive interference & peak in γn → K 0Σ0 Off the proton: Off the neutron (bottom)

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 8 / 35

slide-10
SLIDE 10
  • 1. Motivation - Parallels between charmed & strange

sectors

Table from H. Schmieden, private communication (2018)

Charmed-sector Strange-sector Meson Baryons Meson Baryons State(s) X(3872) P∗

c (4380/4450)

f1(1285) N∗(2030/2080) π exchange transition D∗0 ¯ D0/D0 ¯ D∗0 Λ∗

c ¯

D + Σc ¯ D∗ K ∗ ¯ K/K ¯ K ∗ Λ∗ ¯ K + Σ ¯ K ∗ Quantum numbers JPC = 1++ JP = 3/2− JPC = 1++ JP = 3/2− 3-body threshold D0 ¯ D0π0 Σ+

c ¯

D0π0 K ¯ Kπ Σ ¯ Kπ0 Closed flavour thresh. J/ψω χc1p φf0(500) φp

c-sector s-sector

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 8 / 35

slide-11
SLIDE 11
  • 1. Motivation - Threshold dynamics

Figure from H. Schmieden, private communication (2018) Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 9 / 35

slide-12
SLIDE 12
  • 1. Motivation - Experimental requirements

Charged particle identification at extremely forward angles - reaction dynamics at very low momentum exchange (t-channel) High forward momentum resolution Reconstruction of complicated, mixed charge final states - eg K +Λ(1405) → K +(π0Σ0) → K +π0γpπ−

K N K Λ / Σ π K* γ K+ p K+ Λ(1405) γ

Unique & complementary to existing facilities (eg CBELSA-TAPS neutral particle reconstruction, CLAS charged particle reconstruction). BGO-OD at the ELSA facility, Bonn

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 10 / 35

slide-13
SLIDE 13

Strangeness photoproduction at the BGO-OD experiment

1

Introduction & motivation - parallels in strange & charmed quark sectors?

2

The BGO-OD experiment at ELSA, Bonn

3

Strangeness photoproduction - first results: K 0 photoproduction off proton & neutron (deuterium) targets Extreme forward cross sections for K +Y and excited hyperons Future opportunities with BGO-OD

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 10 / 35

slide-14
SLIDE 14
  • 2. The Electron Stretcher Accelerator (ELSA)

A 3 stage e− accelerator delivering continuous electron beams up to ∼ 3.2 GeV

  • pol. e

source (50 keV)

Mott polarimeter

skew quadrupoles tune jump quadrupole irradiation area PETRA cavities tune jump quadrupole extraction septa superconducting solenoid DESY cavity

  • electron
gun

injektion septa extraction septa half cell of stretcher ring

beam line for detector tests

synchrotron light diagnosis beam line

LINAC 2

(26 MeV)

0.5 GeV - 1.6 GeV hadron physics experiments

booster synchrotron

0.5 GeV - 3.2 GeV

stretcher ring

BGO-OD Crystal Barrel

Quadrupole Combined-Function Magnet Dipole (horizontal) Dipole (vertical) Radio Frequency Solenoid Sextupole Skew Quadrupole

0 m 5 m 10 m 15 m

M Q BPM Compton polarimeter

(for internal beam)

Figure adapted from W. Hillert et al., EPJ Web Conf. 134, 05002 (2017) Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 11 / 35

slide-15
SLIDE 15
  • 2. The BGO-OD experiment at ELSA

Spokespersons: H. Schmieden (Bonn) & P. Levi Sandri (Frascati)

The BGO-OD experimental setup at ELSA, S. Alef et al. Submitted to EPJA. arXiv:1910.11939v2 BGO calorimeter (central region) & Forward Spectrometer combination High momentum resolution, excellent charged & neutral particle ID

BGO ball Open Dipole magnet

flux monitoring e--beam goniometer T agger magnet T agger ARGUS beam dump MOMO SciFi2 forward spectrometer central detector T

  • F

driftchambers

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 12 / 35

slide-16
SLIDE 16
  • 2. The BGO-OD experiment at ELSA - Central region

Spokespersons: H. Schmieden (Bonn) & P. Levi Sandri (Frascati)

The BGO-OD experimental setup at ELSA, S. Alef et al. Submitted to EPJA. arXiv:1910.11939v2 BGO calorimeter (central region) Charged & neutral particle ID excellent time resolution (∼ 2 ns) per BGO crystal

Scintillator Barrel MWPC BGO SciRi MOMO MRPC SciFi

10.4° 24.7° twogammap_invmass_6 Entries 6.884315e+08 Mean 177.7 Std Dev 128.5

200 400 600 800 1000 ]

2

Two photon invariant mass [MeV/c

2

10

3

10

4

10

5

10

6

10

7

10

8

10 bin

2

Counts per 7 MeV/c

twogammap_invmass_6 Entries 6.884315e+08 Mean 177.7 Std Dev 128.5

twogammap_chargecut_invmass_6 Entries 1.16354e+08 Mean 137 Std Dev 85.63 twogammap_missmass_cut_invmass_6 Entries 3.037993e+07 Mean 158.3 Std Dev 100.6 twogammap_fitted_invmass_6 Entries 3.037735e+07 Mean 155 Std Dev 106.4 twogammap_fitted_cut_invmass_6 Entries 1.807174e+07 Mean 160.6 Std Dev 106.5

all combinatorics + charge cut + missing mass cut + kinematic fit + confidence level cut

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 13 / 35

slide-17
SLIDE 17
  • 2. The BGO-OD experiment at ELSA - Central region

Accurate neutral meson photoproduction cross sections γ flux well understood (∼ 3%) BGO-OD - both neutral & mixed charged identification! Well understood degree of linear polarisation

40 60 80 100 120 140 160 [deg]

CM π

θ 0.2 0.4 0.6 0.8

Σ = 1.45 GeV

γ

, E π p → p γ

BGO-OD GRAAL (O Bartalini et al. ’05) Photon beam energy [MeV] 500 1000 1500 2000 2500 b/sr] µ [ Ω /d σ d 0.5 1 1.5 2 2.5 3 3.5 4 4.5

< 0.13

cms

θ p, -0.06 < π → p γ

BGO-OD (black points) Bonn-Gatchina PWA Photon beam energy [MeV] 500 1000 1500 2000 2500 b/sr] µ [ Ω /d σ d 0.2 0.4 0.6 0.8 1 1.2 1.4 (black points) γ γ → η BGO-OD, via

  • π

+

π π → η BGO-OD, via McNicoll et al. (Crystal Ball @ MAMI)

  • V. Crede et al. (CBELSA/TAPS)

< -0.1

cms

θ p, -0.3 < η → p γ

  • O. Bartalini et al., Eur. Phys. J. A26, 399 (2005)

Bn-Ga: A. V. Anisovich et al., Eur. Phys. J. A25, 427 (2005)

  • E. F. McNicoll et al., Phys. Rev. C82 035208 (2010)
  • V. Crede et al., Phys. Rev. C80, 055202 (2009)

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 14 / 35

slide-18
SLIDE 18
  • 2. BGO-OD - Forward region

Excellent charged particle identification & momentum reconstruction 1◦ < θLab < 12◦ ∆p/p ∼ 3 % ∆θlab ∼ 0.5◦

Y1 U1 V1 X1 Y2 U2 V2 X2 ToF3 ToF1 ToF2 MOMO SciFi2 Shift in X

x z 500 1000 1500 2000 2500 Reconstructed momentum [MeV/c] 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 β Reconstructed

1 10

2

10

3

10

4

10

200 400 600 800 1000 1200 1400 ]

2

Calculated particle mass [MeV/c 10

2

10

3

10

4

10

5

10 bin

2

Counts per 2 MeV/c

p

+

K

+

π

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 15 / 35

slide-19
SLIDE 19
  • 2. BGO-OD - Forward region

Accurate knowledge of detector & trigger efficiencies, momentum & β resolution Right: γp → ηp (proton in F.S) - excellent agreement with existing data

200 400 600 800 1000 1200 1400 ]

2

Proton missing mass [MeV/c 50 100 150 200 250 300 350 400

3

10 × bin

2

Counts per 24 MeV/c

Sum p π π p π π π p η p ρ ’p η p ω missing mass forward proton

BnGa: A. V. Anisovich et al., Eur. Phys. J. A25, 427 (2005)

  • E. F. McNicoll et al., Phys. Rev. C82 035208 (2010)
  • V. Crede et al., Phys. Rev. C80, 055202 (2009)

1600 1800 2000 W [MeV] 0.2 0.4 0.6 0.8 1 1.2 1.4 b/sr] µ [ Ω /d σ d < -0.9

cms

θ p, cos η → p γ BGO-OD (Black circles) McNicoll et al. (CB @ MAMI) Crede et al. (CBLSA/TAPS) Bonn-Gatchina PWA (a) 1 − 0.95 − 0.9 − 0.85 − 0.8 −

cms

θ cos 0.2 0.4 0.6 0.8 1 1.2 b/sr] µ [ Ω /d σ d W = 1577 MeV W = 1624 MeV W = 1647 MeV (b) Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 16 / 35

slide-20
SLIDE 20

Strangeness photoproduction at the BGO-OD experiment

1

Introduction

2

Motivation: Exotic hadron structure - parallels in strange & charmed quark sectors?

3

The BGO-OD experiment at ELSA, Bonn

4

Strangeness photoproduction - first results: K 0 photoproduction off proton & neutron (deuterium) targets Extreme forward cross sections for K +Y and excited hyperons Future opportunities with BGO-OD

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 16 / 35

slide-21
SLIDE 21
  • 3. First results - Identification of K 0Σ+ with BGO-OD

Cusp-like structure in the cross section. K ∗0 subthreshold production rescattering to π0 & K 0? Access γp → K 0Σ+ via different decay modes! K 0 decay vertex determination with MWPC (analysis underway)

  • A. Ramos & E. Oset, Phys. Lett. B 727, (2013) 287
  • B. -E Reitz PhD thesis work
  • S. Alef PhD thesis work

Preliminary

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 17 / 35

slide-22
SLIDE 22
  • 3. First results - γn(p) → K 0Σ0 using a deuterium target

Peak predicted - “smoking gun” for reaction mechanism!

  • A. Ramos and E. Oset, Phys. Lett. B 727, (2013) 287
  • K. Kohl PhD thesis analysis

γn(p) → K 0Σ0 at BGO-OD

K 0 → 2π0 in the BGO γ from Σ0 → γΛ: Σ0 − Λ mass difference (Σ0 rest frame)

200 300 400 500 600 700 800 )

2

invariant mass (MeV/c π Two 1000 2000 3000 4000 5000 6000 Counts

All events (x 0.1) Decay photon required

50 100 150 200 250 300 rest frame (MeV) Σ energy in γ Decay 500 1000 1500 2000 Counts

candidates Σ Real data, K candidates Σ

+

Real data, K Σ Simulated K

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 18 / 35

slide-23
SLIDE 23
  • 3. First results - γn(p) → K 0Σ0 using a deuterium target
  • K. Kohl PhD thesis analysis

Consistent with prediction from coherent interference of vector meson-baryon dynamically generated resonances

1000 1500 2000 2500 Photon beam energy (MeV) 0.05 0.1 0.15 0.2 0.25 b/sr) µ ( Ω /d σ d < 0.2

S

K CM

θ

  • 0.1 < cos

Predicted structure by A. Ramos & E. Oset (arbitrarily scaled) (Horizontal error bars indicate bin width)

Preliminary

Identification via K 0 → π+π−

B.E Reitz PhD thesis analysis Detached decay vertex ID using the MWPC (cτ ∼ 2.7 cm) Improve statistics & forward acceptance Statistics predicted to double with beam times early 2020

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 19 / 35

slide-24
SLIDE 24

Strangeness photoproduction at the BGO-OD experiment

1

Introduction

2

Motivation: Exotic hadron structure - parallels in strange & charmed quark sectors?

3

The BGO-OD experiment at ELSA, Bonn

4

Strangeness photoproduction - first results: K 0 photoproduction off proton & neutron (deuterium) targets Extreme forward cross sections for K +Y and excited hyperons Future opportunities with BGO-OD

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 19 / 35

slide-25
SLIDE 25
  • 3. First results - Mass recoiling from forward K +

The study of Y ∗ states in an extremely low momentum transfer region

]

2

missing mass [MeV/c

+

K 1100 1200 1300 1400 1500 1600 missing mass [MeV] π

+

K 900 1000 1100 1200 1300

(1116) Λ (1193) Σ (1405) Λ (1385)/ Σ n γ n+ Λ Σ ) missing mass π

+

Discriminate states with (K ]

2

missing mass [MeV/c

+

K 1000 1200 1400 1600 1800 2000 Counts 200 400 600 800 1000

(1116) Λ (1193) Σ (1405) Λ (1385) Σ (1520) Λ momentum < 1 GeV

+

All events for K

Identify Y ∗ states from K +π0 recoiling mass

K +Λ → K +π0n (Missing neutron mass from K +π0 system) K +Λ(1405) → K +π0Σ0 (Missing Σ0 mass from K +π0 system) K +Σ(1385) → K +π0Λ (Missing Λ mass from K +π0 system)

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 20 / 35

slide-26
SLIDE 26
  • 3. First results - γp → K +(Λ(1405) → Σ0π0)
  • G. Scheluchin PhD thesis analysis

Line shape for Λ(1405) → Σ0π0 High statistics data with access to low momentum transfer (forward) region

CLAS: K. Moriya, R. A. Schumacher et al Phys. Rev. C 87, 035206 (2013) ANKE: I. Zychor et al, Phys. Lett. B 660, 167 (2008) Dashed line: J.C. Nacher et al. Phys.Lett. B455, 55 (1999) Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 21 / 35

slide-27
SLIDE 27
  • 3. First results - γp → K +(Λ(1405) → Σ0π0)
  • G. Scheluchin PhD thesis analysis

Differential cross section for Λ(1405) → Σ0π0 Two data sets - Full topology using all detectors (black points) High momentum resolution at forward angles (green points)

CLAS: K. Moriya, R. A. Schumacher et al Phys. Rev. C 87, 035206 (2013) Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 22 / 35

slide-28
SLIDE 28
  • 3. First results - γp → K +(Λ(1405) → Σ0π0)
  • G. Scheluchin PhD thesis analysis

Differential cross section vs √t for Λ(1405) → Σ0π0

CLAS: K. Moriya, R. A. Schumacher et al Phys. Rev. C 87, 035206 (2013) Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 23 / 35

slide-29
SLIDE 29
  • 3. First results - K +Λ at forward angles (motivation)

Not only Y ∗ states at forward angles important - photoproduction of ground state hyperons at low t virtually unconstrained by data!

  • D. Skoupil, P. Bydzovsky, Phys. Rev. C97, 025202 (2018) (& refs. therein)

MAMI - T. C. Jude et al., Phys. Lett. B 735, 112 (2014) CLAS 2005 - R. Bradford et al., Phys. Rev. C 73, 035202 (2006) CLAS 2010 - M. E. McCracken et al., Phys. Rev. C 81, 025201 (2010)

Isobar models

Effective meson-baryon Lagrangian Explicitly added resonances: > 20 for strangeness photoproduction!

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 24 / 35

slide-30
SLIDE 30
  • 3. First results - K +Λ at forward angles (motivation)

Crucial for hypernuclei electroproduction

eg, e− + 12C → K + + 12

ΛB at

very low Q2 (Λ remains within nucleus Fermi surface) Natural laboratories to probe the Y − N interaction! Essential for astrophysical phenomena & SUflavour(3) description of baryon interactions eg Saclay Leon model for p(e, e′K +)Λ

  • T. Mizutani, C. Fayard, G.-H. Lamot & B.

Saghai, Phys. Rev. C 58, 75 (1998)

  • D. Skoupil, P. Bydzovsky, Phys. Rev. C97, 025202 (2018)

At BGO-OD

Forward CM polar angle range approx. 3-260, 0.9 < cos θK +

cm < 1.0

θK +

cm resolution ∼ 1◦

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 25 / 35

slide-31
SLIDE 31
  • 3. First results - Forward K + Missing mass

50 100 150 200 250 Events / ( 8 )

Data (black) (red) Λ

+

Fitted simulated K (green) Σ

+

Fitted simulated K Total fit (blue) background (cyan)

+

π &

+

Fitted e

W = 1647 MeV W = 1669 MeV W = 1688 MeV

50 100 150 200 250 Events / ( 8 )

W = 1703 MeV W = 1718 MeV W = 1732 MeV

800 900 1000 1100 1200 1300 1400 ]

2

Missing mass [MeV/c

+

K 50 100 150 200 250 Events / ( 8 )

W = 1746 MeV

800 900 1000 1100 1200 1300 1400 ]

2

Missing mass [MeV/c

+

K

W = 1760 MeV

800 900 1000 1100 1200 1300 1400 ]

2

Missing mass [MeV/c

+

K

W = 1775 MeV

Distribution of e+ & π+ background determined by comparison to e− and π− Fitting routines using RooFit

https://root.cern.ch/roofit Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 26 / 35

slide-32
SLIDE 32
  • 3. First results - Forward K +: different selection cuts

Option 1: Standard analysis

+

Missing mass from forward K W = 1789 (beam energy 1236 MeV) mass

+

forward K σ 2 ± Select

600 800 1000 1200 1400 ]

2

Missing mass [MeV/c

+

K 400 600 800 1000 1200 missing mass [MeV] π

+

K

in the BGO γ γ → π + Identify Select events above red line

100 200 300 400 500 rest frame) [MeV] Σ energy ( γ 200 400 600 800 1000 1200 1400 Counts

Λ γ → Σ from γ + Identify rest frame: Σ in

γ

P = 77 MeV

Λ

  • m

Σ

= m

γ

E Real data Σ

+

Simulated K

800 900 1000 1100 1200 1300 1400 ]

2

Missing mass [MeV/c

+

K 20 40 60 80 100 120 140 160 Events / ( 8 ) 800 900 1000 1100 1200 1300 1400 ]

2

Missing mass [MeV/c

+

K 10 20 30 40 50 60 Events / ( 8 ) 800 900 1000 1100 1200 1300 1400 ]

2

Missing mass [MeV/c

+

K 10 20 30 40 50 60 70 80 Events / ( 8 ) Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 27 / 35

slide-33
SLIDE 33
  • 3. First results - Forward K +: different selection cuts

Option 2: π0 analysis (identify Λ → π0n)

+

Missing mass from forward K W = 1789 (beam energy 1236 MeV) mass

+

forward K σ 2 ± Select

600 800 1000 1200 1400 ]

2

Missing mass [MeV/c

+

K 400 600 800 1000 1200 missing mass [MeV] π

+

K

in the BGO γ γ → π + Identify Select events above red line

100 200 300 400 500 rest frame) [MeV] Σ energy ( γ 200 400 600 800 1000 1200 1400 Counts

Λ γ → Σ from γ + Identify rest frame: Σ in

γ

P = 77 MeV

Λ

  • m

Σ

= m

γ

E Real data Σ

+

Simulated K

800 900 1000 1100 1200 1300 1400 ]

2

Missing mass [MeV/c

+

K 20 40 60 80 100 120 140 160 Events / ( 8 ) 800 900 1000 1100 1200 1300 1400 ]

2

Missing mass [MeV/c

+

K 10 20 30 40 50 60 Events / ( 8 ) 800 900 1000 1100 1200 1300 1400 ]

2

Missing mass [MeV/c

+

K 10 20 30 40 50 60 70 80 Events / ( 8 ) Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 27 / 35

slide-34
SLIDE 34
  • 3. First results - Forward K +: different selection cuts

Option 3: Σ0 decay analysis (identify Σ0 → γΛ)

+

Missing mass from forward K W = 1789 (beam energy 1236 MeV) mass

+

forward K σ 2 ± Select

600 800 1000 1200 1400 ]

2

Missing mass [MeV/c

+

K 400 600 800 1000 1200 missing mass [MeV] π

+

K

in the BGO γ γ → π + Identify Select events above red line

100 200 300 400 500 rest frame) [MeV] Σ energy ( γ 200 400 600 800 1000 1200 1400 Counts

Λ γ → Σ from γ + Identify rest frame: Σ in

γ

P = 77 MeV

Λ

  • m

Σ

= m

γ

E Real data Σ

+

Simulated K

800 900 1000 1100 1200 1300 1400 ]

2

Missing mass [MeV/c

+

K 20 40 60 80 100 120 140 160 Events / ( 8 ) 800 900 1000 1100 1200 1300 1400 ]

2

Missing mass [MeV/c

+

K 10 20 30 40 50 60 Events / ( 8 ) 800 900 1000 1100 1200 1300 1400 ]

2

Missing mass [MeV/c

+

K 10 20 30 40 50 60 70 80 Events / ( 8 ) Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 27 / 35

slide-35
SLIDE 35
  • 3. First results - Forward K +Λ differential cross sections

Paper in preparation. In discussion with Dalibor Skoupil (NPI CAS), Terry Mart (Uni. Indonesia), Andrey Sarantsev (Uni. Bonn)

BGO-OD systematic errors - Total (grey), “scaling” blue, “fitting” red

900 1000 1100 1200 1300 1400 Photon Beam Energy (MeV) 0.1 0.2 0.3 0.4 0.5 0.6 b/sr) µ ( Ω /d σ d Λ

+

K → p γ > 0.9

+

K CM

θ cos BGO-OD CLAS (McCracken ’10) CLAS (Bradford ’06) SAPHIR (Glander ’04)

Preliminary

  • R. Bradford et al., Phys. Rev. C73, 035202 (2006), M.E.McCracken et al., Phys.Rev. C81, 025201 (2010), K.H. Glander et al.,
  • Eur. Phys. J. A19, 251 (2004), Bonn-Gatchina PWA: Eur.Phys.J. A50 74 (2014) CLAS 0.85 < cos θCM

K+ < 0.95.

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 28 / 35

slide-36
SLIDE 36
  • 3. First results - Forward K +Λ differential cross sections

Angular resolution ∼ 0.015 in cos θK +

CM

1000 1200 1400 Photon Beam Energy (MeV) 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 b/sr) µ ( Ω /d σ d

< 0.92 θ 0.90 < cos

1000 1200 1400 Photon Beam Energy (MeV) 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 b/sr) µ ( Ω /d σ d

< 0.94 θ 0.92 < cos

1000 1200 1400 Photon Beam Energy (MeV) 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 b/sr) µ ( Ω /d σ d

< 0.96 θ 0.94 < cos

900 1000 1100 1200 1300 1400 Photon Beam Energy (MeV) 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 b/sr) µ ( Ω /d σ d

< 0.98 θ 0.96 < cos

900 1000 1100 1200 1300 1400 Photon Beam Energy (MeV) 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 b/sr) µ ( Ω /d σ d

< 1.00 θ 0.98 < cos

Preliminary

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 29 / 35

slide-37
SLIDE 37
  • 3. First results - Forward K +Λ recoil polarisation

First ever data set at extreme forward angles! Access via the self-analysing weak decay

  • f the Λ

Up-down asymmetry between Λ decay & the reaction plane Λ → π0n identified in the BGO PΛ = 2 α Nup − Ndown Nup + Ndown α = 0.642 (Λ decay parameter)

W [MeV] 1650 1700 1750 1800 1850 1900

Λ

P 1 − 0.8 − 0.6 − 0.4 − 0.2 − 0.2 0.4 0.6 0.8 1 BGO-OD, preliminary CLAS (McCracken ’10) GRAAL (Lleres ’07) BnGa PWA < 1.0

+

K CM

θ , 0.9 < cos Λ

+

K → p γ

Preliminary

M.E.McCracken et al. (CLAS), Phys.Rev. C81, 025201 (2010).

  • A. Lleres et al. (GRAAL), Eur. Phys. J. A 31, 79 (2007)

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 30 / 35

slide-38
SLIDE 38
  • 3. First results - Forward K +Σ0 differential cross sections

Cusp-like structure at W = 1900 MeV (Eγ ∼ 1450 MeV)? BGO-OD systematic errors - Total (grey), “scaling” blue, “fitting” red

1100 1200 1300 1400 1500 1600 Photon Beam Energy (MeV) 0.05 0.1 0.15 0.2 0.25 0.3 b/sr) µ ( Ω /d σ d BGO-OD CLAS (Dey ’10) SAPHIR (Glander ’04) CLAS (Bradford ’06) Σ

+

K → p γ > 0.9

+

K CM

θ cos

Preliminary

  • R. Bradford et al., Phys. Rev. C73, 035202 (2006), B.Dey et al., Phys.Rev. C82, 025202 (2010),

K.H. Glander et al., Eur. Phys. J. A19, 251 (2004), CLAS data in cos θCM

K+ 0.85 to 0.95 interval

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 31 / 35

slide-39
SLIDE 39
  • 3. First results - Forward K +Σ0 differential cross sections

Cusp-like structure at W = 1900 MeV (Eγ ∼ 1450 MeV)?

1000 1200 1400 1600 Photon Beam Energy (MeV) 0.05 0.1 0.15 0.2 0.25 0.3 b/sr) µ ( Ω /d σ d

< 0.92 θ 0.90 < cos

1000 1200 1400 1600 Photon Beam Energy (MeV) 0.05 0.1 0.15 0.2 0.25 0.3 b/sr) µ ( Ω /d σ d

< 0.94 θ 0.92 < cos

1000 1200 1400 1600 Photon Beam Energy (MeV) 0.05 0.1 0.15 0.2 0.25 0.3 b/sr) µ ( Ω /d σ d

< 0.96 θ 0.94 < cos

1000 1200 1400 1600 Photon Beam Energy (MeV) 0.05 0.1 0.15 0.2 0.25 0.3 b/sr) µ ( Ω /d σ d

< 0.98 θ 0.96 < cos

1000 1200 1400 1600 Photon Beam Energy (MeV) 0.05 0.1 0.15 0.2 0.25 0.3 b/sr) µ ( Ω /d σ d

< 1.00 θ 0.98 < cos

Preliminary

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 32 / 35

slide-40
SLIDE 40
  • 3. First results - Forward K +Σ0 differential cross sections

“Cusp” appears more pronounced at most forward angles!

1100 1200 1300 1400 1500 1600 Photon beam energy (MeV) 0.05 0.1 0.15 0.2 0.25 0.3 b/sr) µ ( Ω /d σ d < 0.94

CM

θ 0.92 < cos < 1.00

CM

θ 0.98 < cos W = 1900 MeV

Preliminary

Threshold effects at low momentum transfer?

At W ∼ 1900 MeV, close to several thresholds: K +Λ(1405) p f0(980) pη′

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 33 / 35

slide-41
SLIDE 41

Strangeness photoproduction at the BGO-OD experiment

1

Introduction

2

Motivation: Exotic hadron structure - parallels in strange & charmed quark sectors?

3

The BGO-OD experiment at ELSA, Bonn

4

Strangeness photoproduction - first results: K 0 photoproduction off proton & neutron (deuterium) targets Extreme forward cross sections for K +Y and excited hyperons Future opportunities with BGO-OD

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 33 / 35

slide-42
SLIDE 42
  • 4. Future opportunities in strangeness photoproduction

γp → K +Λ(1520) - “Cusp” seen in forward cross section at LEPS

  • H. Kohri et al. (LEPS), Phys. Rev. Lett. 104,

172001 (2010)

Λ(1520) at BGO-OD:

1350 1400 1450 1500 1550 1600 1650 1700 ]

2

Missing mass [MeV/c

+

K 20 40 60 80 100 120 140 160 180 200 220 Events / ( 8 )

Background Data (black points) (1520) Λ

+

Simulated K Total fit

missing mass example at W = 2100 MeV

+

K

Preliminary

New projects in K ∗Y photoproduction Deuterium target: γn → K +Σ− & γn → K +Σ−(1385) (limited data at forward angles 1st analysis at BGO-OD:

]

2

Missing mass [MeV/c

+

K 800 1000 1200 1400 1600 1800 2000 Counts 200 400 600 800 1000 1200 Liquid hydrogen target (analysis shown) Liquid deuterium target (preanalysis underway)

Preliminary

K + identification in the BGO Rugby Ball via time delayed weak decay!

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 34 / 35

slide-43
SLIDE 43
  • 4. Future opportunities in strangeness photoproduction

Study the Λ − n interaction - Very little data available! Final state interactions for γd → K +Λ + (n) KN, YN & pion mediated θK < 300 - FSI dominated by Y-N Models of YN forces - cusps at ΣN & YN thresholds

  • K. Miyagawa, T. Mart, C. Bennhold, W. Gl¨
  • ckle, Phys. Rev.

C74 (2006) 034002 Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 34 / 35

slide-44
SLIDE 44

Summary

Molecular-like structure in the light quark system? Parallels between heavy charm and uds systems? BGO-OD - strangeness photoproduction at extremely forward angles & low momentum transfer K 0Σ0 photoproduction - preliminary results consistent with dynamically generated meson-baryon resonance contributions γp → K +Λ(1405) → Σ0π0 - lineshapes & differential cross sections K +Y photoproduction at forward angles - cusp in γp → K +Σ0 at W ∼ 1900 MeV

BGO ball Open Dipole magnet

flux monitoring e--beam goniometer T agger magnet T agger ARGUS beam dump MOMO SciFi2 forward spectrometer central detector T

  • F

driftchambers

]

2

missing mass [MeV/c

+

K 1000 1200 1400 1600 1800 2000 Counts 200 400 600 800 1000

(1116) Λ (1193) Σ (1405) Λ (1385) Σ (1520) Λ momentum < 1 GeV

+

All events for K Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 35 / 35

slide-45
SLIDE 45

Extra slides

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 35 / 35

slide-46
SLIDE 46

Tagger timing

Cluster Time [ns] 600 − 400 − 200 − 200 400 600 Counts 20 40 60 80 100 120 140

3

10 ×

Cluster Time [ns] 10 − 8 − 6 − 4 − 2 − 2 4 6 8 10

Counts 20 40 60 80 100 120 140

3

10 ×

RF bunch structure from ELSA ~ 160 ps σ

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 35 / 35

slide-47
SLIDE 47

Incident photon beam parameters

Energy tagged γ beam ≤ 3 GeV, 250 ps time resolution Current ≤2 nA, 10 nA upgrade planned Circularly and linearly polarised γ beams available

Coherent bremsstrahlung using a diamond radiator

30% polarisation at 1.8 GeV with an incident electron energy of 3.2 GeV

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 35 / 35

slide-48
SLIDE 48

K + identification in the BGO

Time delayed, K + weak decay within the crystals of the BGO ball

T.C Jude, D.I. Glazier, D.P. Watts, et al, PLB, 735 (2014) 112

Lifetime 12 ns, 2 main decay modes:

K + → µ+νµ K + → π+π0

µ

3ns 18ns 16ns 19ns BGO crystal Incident sub−cluster Decay sub−cluster

ν

µ

Κ

+ + Decay cluster energy [MeV] 50 100 150 200 250 300 350 400 Counts 500 1000 1500 2000 2500 3000

Simulated data Real data

Decay time [ns] 10 20 30 40 50 60 70 80 90 100 Counts 1000 2000 3000 4000 5000 6000

Fitted lifetime ~ 11 ns

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 35 / 35

slide-49
SLIDE 49

Identifying the Σ0 → Λγ decay (Γ = 100%)

Boost all neutral particles in the BGO into missing hyperon rest frame If K +Σ0: γ energy (Σ0 rest frame) = MΣ0 − MΛ = 77 MeV Efficiency scale events with/without ID to separate missing mass spectrum Photon detection in the BGO to separate different K +Y ∗ states!

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 35 / 35

slide-50
SLIDE 50

γp → K +Σ0 with no initial particle Identification

Preliminary analysis , 25 days data, (G. Scheluchin, PhD thesis work) K + & Λ → pπ− over large acceptance region (10 < θ < 1550) Σ0 decay photon in the BGO (Σ0 → Λγ) Technique used for higher lying Y* states (eg Λ(1405) → π0Σ0)

Reconstructing the Σ0 invariant mass

(a) Momentum conservation & K + “missing mass” cut (b) Kinematic fit & confidence level cut (c) Neural network to suppress background

Reconstructed invariant mass [MeV] 1100 1200 1300 1400 1500 10000 20000 30000 40000 50000

(a) All combinations Real data Σ

+

Simulated K

Reconstructed invariant mass [MeV] 1100 1200 1300 1400 1500 10000 20000 30000 40000 50000

(b) With a kinematic fit

confidence level > 1%

Reconstructed invariant mass [MeV] 1100 1200 1300 1400 1500 10000 20000 30000 40000 50000

(c) Kinematic fit & neural network Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 35 / 35

slide-51
SLIDE 51

γp → K +Σ0 with no initial particle Identification

BGO-OD (preliminary), CLAS: B. Dey, et al., Phys. Rev. C82 025202 (2010) SAPHIR: K.-H. Glander et al., Eur. Phys. J. A19 251 (2004), LEPS: M. Sumihama et al., Phys. Rev. C73 035214 (2006)

b/sr] µ [ Ω /d σ d

0.2 0.4

15 MeV ± =1690 s

0.2 0.4

15 MeV ± =1810 s

0.2 0.4

15 MeV ± =1930 s

1 − 0.5 − 0.5 0.2 0.4

25 MeV ± =2080 s

0.2 0.4

15 MeV ± =1720 s

0.2 0.4

15 MeV ± =1840 s

0.2 0.4

15 MeV ± =1960 s

0.5 − 0.5 0.2 0.4

25 MeV ± =2130 s

0.2 0.4

15 MeV ± =1750 s

0.2 0.4

15 MeV ± =1870 s

0.2 0.4

15 MeV ± =1990 s

1 − 0.5 − 0.5 0.2 0.4

100 MeV ± =2255 s

0.2 0.4

15 MeV ± =1780 s

0.2 0.4

15 MeV ± =1900 s

0.2 0.4

25 MeV ± =2030 s LEPS 2006 CLAS 2010 SAPHIR 2003 BGO-OD 2016

+

K cm

θ cos

Preliminary

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 35 / 35

slide-52
SLIDE 52

Preliminary identification of K 0Σ+ with BGO-OD

Analysis by S. Alef

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 35 / 35

slide-53
SLIDE 53

Future opportunities: Hypernuclei production

Hypernuclei photoproduction, eg γ +12 C → K + +12

Λ B - natural laboratory

to probe the Y − N interaction Forward K +, coherent production, leaving the Λ within the Fermi surface of the residual nuclei

  • P. Achenbach, arXiv:1101.4395 (2008)

Opportunities for first real photon beam photoproduction?

In conversation with P. Achenbach & J. Pochodzalla, 2018

Mesic decay (Λ → πN) identification in BGO - favour light nuclei Identify specific states, eg γ +12 C → π0 +12 C ∗ → π0 +12 C + γ′ (4.4 MeV) Can use “sensitive” targets that are spoiled by intense e− beams (eg Li) Hypernuclei lifetime measurements, angular K + distributions, differential cross sections...

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 35 / 35

slide-54
SLIDE 54

Future opportunities: Hypernuclei production

Coherent pion production (“non-strange” example)

Method similar to C.M. Tarbert, D.P. Watts et. al (A2 Collaboration) Phys Rev. Lett. 100 (2008) 13 γ +12 C → π0 +12 C ∗ → π0 +12 C + γ′ (4.4 MeV) E2 transition, Jπ : 2+ → 0+, sin2(2α) distr. between nuclear recoil & γ’ ∼ 2 hours of commissing data with BGO-OD:

energy [MeV] π Calculated - measured 300 − 200 − 100 − 100 200 300 Counts 100 200 300 400 500 600 700 800 900

= 297 MeV

γ

E angles π All < 40

π

θ events π

  • 1. Search for coherent

Photon energy [MeV] 2 4 6 8 10 Counts 100 200 300 400 500 600 700 800 900

Exponential + Gaussian fn. 4.5 MeV ≈ Mean 0.6 MeV ≈ σ

  • 2. Search for additional decay photon

[deg] α 50 100 150

Counts

1 2 3 4 5

) fit α (2

2

sin angular distr. γ

  • 3. Verification - decay

Not efficiency corrected Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 35 / 35

slide-55
SLIDE 55
  • 4. First results - Selecting forward K + at BGO-OD

Mass calculated from momentum and β Select events ±2σ for a given K + momentum, pK +

]

2

Calculated mass [MeV/c 300 350 400 450 500 550 600 650 700 Counts

10 20 30 40 50 60 70

= 500 - 600 MeV/c

+

K

p

Real data Simulated data

]

2

Calculated mass [MeV/c 300 350 400 450 500 550 600 650 700 Counts 20 40 60 80 100

= 600 - 700 MeV/c

+

K

p

]

2

Calculated mass [MeV/c 300 350 400 450 500 550 600 650 700

Counts 20 40 60 80 100

= 700 - 800 MeV/c

+

K

p

]

2

Calculated mass [MeV/c 300 350 400 450 500 550 600 650 700 Counts

20 40 60 80 100 120 140

= 800 - 900 MeV/c

+

K

p Low mass shoulder from background

+

& e

+

π

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 35 / 35

slide-56
SLIDE 56

The BGO-OD collaboration

A special thanks to group members!

  • S. Alef, A. Bella, D. Hammann, J. Hannappel, K. Kohl, F. Messi, B. Reitz,
  • G. Scheluchin, H. Schmieden, T. Zimmermann & present Masters & Bachelor

students: J. Groß, C. Tillmanns, S Heider & J. Glowacz A special thanks to the ELSA technical staff and previous BGO-OD technical coordinators (D. Elsner)!

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 35 / 35

slide-57
SLIDE 57
  • 4. First results - Forward K +Λ

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 35 / 35

slide-58
SLIDE 58
  • 4. First results - Forward K +Σ0

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 35 / 35

slide-59
SLIDE 59
  • 2. BGO-OD Detector performance - central region

Neutral meson reconstruction in the BGO - π0 → γγ & η → γγ

]

2

invariant mass [MeV/c γ 2 100 200 300 400 500 600 700 800 ]

2

[MeV/c γ Mass recoiling from 2 600 800 1000 1200 1400

1 10

2

10

3

10

4

10

5

10

invariant mass [MeV] γ 2 100 200 300 400 500 600 700 Counts 20 40 60 80 100

6

10 × = 10 MeV σ : mean = 135 MeV, π = 20 MeV σ : mean = 557 MeV, η (scaled x50)

Demonstration - γp → ωp dσ/dΩ via ω → π0π+π− (G. Scheluchin PhD thesis)

[MeV]

γ

E 1200 1400 1600 1800 2000 2200 2400 2600 2800 b/sr] µ [ Ω /d σ d 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

< -0.60

CM

θ

  • 0.67 < cos

[MeV]

γ

E 1200 1400 1600 1800 2000 2200 2400 2600 2800 b/sr] µ [ Ω /d σ d 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

< -0.33

CM

θ

  • 0.44 < cos

) γ π → ω CB-ELSA/TAPS ( )

  • π

+

π π → ω CLAS ( )

  • π

+

π π → ω BGO-OD (

Preliminary

  • F. Dietz et al.

(CB-ELSA/TAPS),

  • Eur. Phys. J. A

51, 6 (2015)

  • M. Williams et al.

(CLAS), Phys.

  • Rev. C 80, 065208

(2009) Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 35 / 35

slide-60
SLIDE 60

Beam asymmetry for γp → η′p near threshold - motivation

Previous GRAAL data:

  • A. Fantini, R. Di Salvo, P. Levi Sandri

Strong variation in γp → η′p beam asymmetry near threshold Suggested evidence of narrow resonance at W=1903 MeV, JP = 1/2−, Γ ∼ 2.1 MeV

η and η′ Photoproduction on the Nucleon with the Isobar Model EtaMAID2018, L. Tiator et al., arXiv:1807.04525 (2018)

Near threshold the recoil proton is always in our forward spectrometer!

Forward proton missing mass [MeV] 900 920 940 960 980 1000 1020 1040 1060 Counts 14000 16000 18000 20000 22000 24000 26000

’ η φ Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 35 / 35

slide-61
SLIDE 61

Beam asymmetry for γp → η′p near threshold - motivation

  • S. Alef PhD thesis analysis - 18:00, parallel session B Tuesday

Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD THEIA, 27th Nov 2019 35 / 35