View
8
Download
0
Category
Preview:
Citation preview
Strangeness photoproduction at extremely forwardangles at the BGO-OD experiment
Tom JudeOn behalf of the BGO-OD Collaboration
Physikalisches InstitutUniversity of Bonn
Supported by the DFG PN 50165297
28th June 2018
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 1 / 32
Strangeness photoproduction at extremely forward anglesat the BGO-OD experiment
The BGO-OD experiment at ELSA, Bonn
Motivation: Hadron structure - parallels in strange & charmed quarksectors?
Strangeness photoproduction - first results:
1 Λ(1405) & access to higher lying hyperons
2 Extreme forward cross sections for K+Λ & K+Σ0 photoproduction
3 K 0 photoproduction off proton & neutron (deuterium) targets
4 Future opportunities - Y-N interaction & hypernuclei studies
Summary
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 2 / 32
The Electron Stretcher Accelerator (ELSA)
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 3 / 32
The BGO-OD experiment at ELSA
BGO calorimeter (central region) & Forward Spectrometer combination
High momentum resolution, excellent charged & neutral particle ID
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 4 / 32
The BGO-OD experiment at ELSA
BGO calorimeter (central region) & Forward Spectrometer combination
High momentum resolution, excellent charged & neutral particle ID
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 4 / 32
The BGO-OD experiment at ELSA
BGO calorimeter (central region) & Forward Spectrometer combination
High momentum resolution, excellent charged & neutral particle ID
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 4 / 32
Motivation - Exotic phenomena in the charmed sector
Pentaquark candidates observed at LHCb -Pc(4450)+ & Pc(4380)+
R. Aaij et al, PRL 115, 072001 (2015)
Meson-baryon dynamically generated statesin the charmed sector - J.-J. Wu, R. Molina, E. Oset,
and B.S. Zou, Phys. Rev. Lett. 105, 232001 (2010)
Forsaken pentaquark particle spotted atCERN
Nature 523, 267 (2015)
X (3872) - a molecular D0D0∗ state?N.A. Tornqvist, Phys. Lett. B590, 209 (2004)
Close to D0D0∗ threshold, favouringDD∗ decay
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) discovery - most citedpaper from Belle, PRL91, 262001 (2003)
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 5 / 32
Motivation - Structure of the Λ(1405)
Between the πΣ & KN thresholds
Line shape (invariant mass)depends upon the πΣ decay mode
Distorted by interference of Isospin0 & 1 amplitudes J.C. Nacher et al., Nucl.
Phys. A 725, 181 (2003)
K. Moriya et al. (CLAS Collaboration) Phys. Rev. C 87,
035206 (2013)
Λ(1405) - dynamically generated bymeson-baryon interactions? J.C.
Nacher, E. Oset, H. Toki, A. Ramos, U.G. Meissner,
Nucl. Phys. A 725 (2003) 181
LQCD calculations: J.M.M Hall et al., Phys.
Rev. Lett. 114 (2015) 132002
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 6 / 32
Motivation - Cusp structure 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 dueto K∗0 subthresholdproduction rescatteringto 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 28th June 2018 7 / 32
Motivation - K 0 photoproduction off the neutron
A. Ramos and E. Oset, Phys. Lett. B 727, (2013) 287 Therole of vector-baryon channels andresonances in the γp → K 0Σ+ andγn→ K 0Σ0 reactions near the K∗Λthreshold
K 0Λ Complementary to K+Λ -relate hadronic coupling constants
Limited available data, K. Tsukada et al,
Phys. Rev. C 78, 014001 (2008)
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 8 / 32
Motivation - Parallels between charmed and strange sectors
Table and figures from H. Schmieden, private communication
c-sector s-sector
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 9 / 32
Motivation - Threshold dynamics
Figure from H. Schmieden, private communication
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 10 / 32
Λ∗ and Σ∗ spectra
Very limited succss with constituent quark models
Models including meson-baryon interactions as degrees of freedom - moresuccessful, 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.
Hadronic molecules - predict new Y ∗ states, eg Σ∗ (JP = 1/2−) close toΣ(1385): Jia-Jun Wu et al., Phys. Rev. D 80 (2009) 017503
K−p → Λπ+π−
26 PDG Σ∗ states - 16 are listed as existence poor to fair. C. Patrignani et al.
(Particle Data Group), Chin. Phys. C 40, 100001 (2016)Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 11 / 32
Experimental requirements
Charged particle identification at extremely forward angles - reactiondynamics at very low momentum exchange (t-channel)
High forward momentum resolution
Reconstruction of complicated, mixed charge final states - egK+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 neutralparticle reconstruction, CLAS charged particle reconstruction).
BGO-OD at the ELSA facility, Bonn (Germany)
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 12 / 32
Detector performance - central region
1st large data set taken in 2017. Neutral meson reconstruction (lH2 target):
invariant mass [MeV]γ20 100 200 300 400 500 600 700 800
[M
eV
]γ
mis
sin
g m
ass r
ecoili
ng fro
m 2
500
600
700
800
900
1000
1100
1200
1300
1400
1500
1
10
210
310
410
510
Neutral meson reconstruction in the BGO ball
invariant mass [MeV]γ2100 200 300 400 500 600 700
Counts
0
20
40
60
80
100
610×
= 10 MeVσ: mean = 135 MeV, 0π
= 20 MeVσ: mean = 557 MeV, η
(scaled x50)
Missing mass recoiling from the proton [MeV]0 200 400 600 800 1000 1200 1400
Counts
0
2000
4000
6000
8000
10000
12000=15.1 MeVσ η
=17.5 MeVσ ω
=18.6 MeVσ’ η
Momentum [MeV]500 1000 1500 2000 2500 3000
β
0
0.2
0.4
0.6
0.8
1
1.2
0
2000
4000
6000
8000
10000
12000
Charged particle identification in the forward spectrometer invariant mass [MeV]γ2
0 100 200 300 400 500 600 700 800
[M
eV
]γ
mis
sin
g m
ass r
ecoili
ng fro
m 2
500
600
700
800
900
1000
1100
1200
1300
1400
1500
1
10
210
310
410
510
Neutral meson reconstruction in the BGO ball
invariant mass [MeV]γ2100 200 300 400 500 600 700
Counts
0
20
40
60
80
100
610×
= 10 MeVσ: mean = 135 MeV, 0π
= 20 MeVσ: mean = 557 MeV, η
(scaled x50)
Missing mass recoiling from the proton [MeV]0 200 400 600 800 1000 1200 1400
Counts
0
2000
4000
6000
8000
10000
12000=15.1 MeVσ η
=17.5 MeVσ ω
=18.6 MeVσ’ η
Momentum [MeV]500 1000 1500 2000 2500 3000
β
0
0.2
0.4
0.6
0.8
1
1.2
0
2000
4000
6000
8000
10000
12000
Charged particle identification in the forward spectrometer
Demonstration (1 of many bench marks) - γp → ωp dσ/dΩ via the mixedcharge decay, ω → π0π+π− (G. Scheluchin)
[MeV]γE1200 1400 1600 1800 2000 2200 2400 2600 2800
b/s
r]µ
[Ω
/dσ
d
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
< 0.60CM
θ0.67 < cos
[MeV]γE1200 1400 1600 1800 2000 2200 2400 2600 2800
b/s
r]µ
[Ω
/dσ
d
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
< 0.33CM
θ0.44 < cos
)γ0π→ωCBELSA/TAPS (
)π+π0π→ωCLAS (
)π+π0π→ωBGOOD (
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 28th June 2018 13 / 32
Detector performance - forward spectrometer
Top - Particle identification in the Forward Spectrometer
Bottom - “Missing mass” from forward proton (raw counts)
p [MeV]500 1000 1500 2000 2500 3000
β
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1
10
210
310
410
Forward particle reconstructed mass [MeV]
0 200 400 600 800 1000 1200 14000
20
40
60
80
1003
10×
+e+π
+K
protons
Forward proton missing mass [MeV]
0 200 400 600 800 1000 1200 1400 1600 1800 2000
Counts
0
50
100
150
200
250
310×
η
ω
’ηφ
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 28th June 2018 14 / 32
Strangeness photoproduction at extremely forward anglesat the BGO-OD experiment
BGO-OD experiment at ELSA, Bonn
Motivation: Hadron structure - parallels in strange & charmed quarksectors?
Strangeness photoproduction - first results:
1 Λ(1405) & access to higher lying hyperons
2 Extreme forward cross sections for K+Λ & K+Σ0 photoproduction
3 K 0 photoproduction off proton & neutron (deuterium) targets
4 Future opportunities - Y-N interaction & hypernuclei studies
Outlook and conclusions
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 15 / 32
Mass recoiling from K+ in the forward spectrometer
The study of Y ∗ states in an extremely low momentum transfer region
missing mass [MeV]+
K1100 1200 1300 1400 1500 1600
mis
sin
g m
ass [
Me
V]
0π
+K
900
950
1000
1050
1100
1150
1200
1250
1300
(1116)Λ
(1193)0Σ
(1405)Λ(1385)/Σ
n
γn+
Λ
0Σ
) missing mass0π+
Discriminating between states with (K
missing mass [MeV]+K1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
Co
un
ts
0
200
400
600
800
1000 (1116)Λ
(1193)0Σ (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)
Goal - Λ(1405) lineshape at low momentum transfer regionTom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 16 / 32
Λ(1405) over a broad kinematic range
G. ScheluchinComplements CLAS data - K. Moriya et al., Phys. Rev. C
88, 045201 (2013)
Triangle singularity can describe peak atW = 2110 MeV & cos θ = 0:
Full K+Λ(1405) & K+Λ(1520)reconstruction
K+Λ(1405)→ K+π0Σ0 → K+γγγπ−pE. Wang et al., Phys. Rev. C 95, 015205 (2017)
Preliminary
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 17 / 32
Strangeness photoproduction at extremely forward anglesat the BGO-OD experiment
BGO-OD experiment at ELSA, Bonn
Motivation: Hadron structure - parallels in strange & charmed quarksectors?
Strangeness photoproduction - first results:
1 Λ(1405) & access to higher lying hyperons
2 Extreme forward cross sections for K+Λ & K+Σ0 photoproduction
3 K 0 photoproduction off proton & neutron (deuterium) targets
4 Future opportunities - Y-N interaction & hypernuclei studies
Outlook and conclusions
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 18 / 32
K+Λ at forward angles - motivation
Not only Y ∗ states at forward angles important - ground state hyperonphotoproduction at low t virtually unconstrained by data!
Bydzovsky and D. Skoupil, arXiv:1211.2684v1 (2012) Proceedings of SNP12
Crucial constraint for hypernuclei electroproduction!- eg Saclay Leon model for p(e, e′K+)ΛT. Mizutani, C. Fayard, G.-H. Lamot & B. Saghai, Phys. Rev. C 58, 75 (1998)
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 19 / 32
K+Λ at forward angles - motivation
M. E. McCracken, et. al (CLAS Collaboration),
Phys. Rev. C 81, 025201 (2010)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
Unprecedented θK+
cm resolution (< 10)
PΛ - recoil Λ polarisation accessed by angular distribution of Λ→ π0n & π−p
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 20 / 32
Extracting K+Λ & K+Σ0 signal from background
W = 1600 - 1700 MeV
[MeV]+
Mass recoiling from K0 200 400 600 800 1000 1200 1400 1600 1800 2000
Counts
0
50
100
150
200
250
300
350
400
W = 1600 1700 MeV
[MeV]+
Mass recoiling from K0 200 400 600 800 1000 1200 1400 1600 1800 2000
Events
/ (
16 )
0
50
100
150
200
250
300
350
W = 1700 - 1800 MeV
[MeV]+
Mass recoiling from K0 200 400 600 800 1000 1200 1400 1600 1800 2000
Co
un
ts
0
100
200
300
400
500
600W = 1700 1800 MeV
[MeV]+
Mass recoiling from K0 200 400 600 800 1000 1200 1400 1600 1800 2000
Eve
nts
/ (
16
)
0
100
200
300
400
500
600
W = 1800 - 1900 MeV
[MeV]+
Mass recoiling from K0 200 400 600 800 1000 1200 1400 1600 1800 2000
Counts
0
100
200
300
400
500
600
W = 1800 1900 MeV
[MeV]+
Mass recoiling from K0 200 400 600 800 1000 1200 1400 1600 1800 2000
Events
/ (
16 )
0
100
200
300
400
500
600
Fitting with RooFit https://root.cern.ch/roofit
Signal
Simulated K+Λ events
Simulated K+Σ0 events
Background from pair productionin the beam
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 21 / 32
Preliminary forward K+Σ0 differential cross sections
Test of systematics for forward K+ detection
Highest statistics data set (& only 75% of available data)
Work in progress - binning into fine polar angle intervals (30 centre of mass)
Photon beam energy [MeV]1100 1200 1300 1400 1500
b/s
r]µ
[Ω
/dσ
d
0
0.05
0.1
0.15
0.2
0.25 > 0.9+
K
CMθcos
BGOOD, preliminary
SAPHIR (Glander ’04)
BnGa PWA
CLAS (Bradford ’06)
CLAS (Dey ’10)
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 θCMK+ 0.85 to 0.95 interval
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 22 / 32
Preliminary forward K+Λ differential cross sections
Highest statistics data set - distinguish discrepancies in existing data
Ongoing analysis - statistical error to be reduced by 1/2
Photon beam energy [MeV]900 1000 1100 1200 1300 1400 1500
b/s
r]µ
[Ω
/dσ
d
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7 > 0.9CM+
Kθcos
BGOOD, preliminary
SAPHIR (Glander ’04)
CLAS (McCracken ’10)
CLAS (Bradford ’06)
BnGa PWA
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), CLAS data in cos θCMK+ 0.85 to 0.95 interval
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 23 / 32
Preliminary forward K+Λ differential cross sections
X-axis: Eγ , 900 - 1400 MeV. Y-axis: dσ/dΩ, 0 - 0.8 [µb/sr]
Unprecedented polar angle resolution
Ongoing analysis - statistical error to be reduced by 1/2
BnGa PWA
BGOOD, very preliminary
labelled inset+KCM
θ
900 1000 1100 1200 1300 14000
0.10.20.30.40.50.60.70.8
03.5
900 1000 1100 1200 1300 14000
0.10.20.30.40.50.60.70.8
06.5
Energy [MeV]γ900 1000 1100 1200 1300 1400
00.10.20.30.40.50.60.70.8
09.5
900 1000 1100 1200 1300 14000
0.10.20.30.40.50.60.70.8
012.5
900 1000 1100 1200 1300 14000
0.10.20.30.40.50.60.70.8
015.5
900 1000 1100 1200 1300 14000
0.10.20.30.40.50.60.70.8
018.5
900 1000 1100 1200 1300 14000
0.10.20.30.40.50.60.70.8
021.5
900 1000 1100 1200 1300 14000
0.10.20.30.40.50.60.70.8
024.5
Veryprelim
inary!!!!
Forward dσ/dΩ for K+Λ(1520), K+Σ−, & K+Σ−(1385) in preparationTom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 24 / 32
Strangeness photoproduction at extremely forward anglesat the BGO-OD experiment
BGO-OD experiment at ELSA, Bonn
Motivation: Hadron structure - parallels in strange & charmed quarksectors?
Strangeness photoproduction - first results:
1 Λ(1405) & access to higher lying hyperons
2 Extreme forward cross sections for K+Λ & K+Σ0 photoproduction
3 K 0 photoproduction off proton & neutron (deuterium) targets
4 Future opportunities - Y-N interaction & hypernuclei studies
Outlook and conclusions
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 25 / 32
Preliminary identification of K 0Σ+ with BGO-OD
Study the Cusp-like structure in the cross section. K∗0 subthresholdproduction rescattering to π0 & K 0?
Access γp → K 0Σ+ via different decay modes at BGO-OD
Reduction of background & improved momentum resolution acheivable withthe MWPC (analysis underway)
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 26 / 32
Test beam time data (Deuterium target), 2 days
Peak predicted from coherent interference of dynamically generated resonancesA. Ramos and E. Oset, Phys. Lett. B 727, (2013) 287
K 0 → 2π0 reconstructed in theBGO
Total neutral particles < 6
Total charged particles < 3
K 0 → 2π0 reconstructed in theBGO
Proton in the Forwardspectrometer & select missing π0
mass from Σ+ → pπ0
Total neutral particles < 6
Total charged particles < 3
invariant mass [MeV]0π2
300 400 500 600 700 800 900
Counts
0
500
1000
1500
2000
2500
3000
Mean = 508 MeV
Height = 380
= 26 MeVσ
= 23753σ 2±Integral over
in the BGO, Missing mass between 1000 1200 MeV0π(a) 2
invariant mass [MeV]0π2
300 400 500 600 700 800 900
Counts
0
20
40
60
80
100
120
Mean = 512 MeV
Height = 296
= 18 MeVσ
= 5787σ 2±Integral over
and proton, Missing mass between 1000 1200 MeV0π(b) 2
Preliminary
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 27 / 32
Strangeness photoproduction at extremely forward anglesat the BGO-OD experiment
BGO-OD experiment at ELSA, Bonn
Motivation: Hadron structure - parallels in strange & charmed quarksectors?
Strangeness photoproduction - first results:
1 Λ(1405) & access to higher lying hyperons
2 Extreme forward cross sections for K+Λ & K+Σ0 photoproduction
3 K 0 photoproduction off proton & neutron (deuterium) targets
4 Future opportunities - Y-N interaction & hypernuclei studies
Outlook and conclusions
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 28 / 32
Future opportunities: Hypernuclei production
Hypernuclei photoproduction, egγ +12 C → K+ +12
Λ B - natural laboratoryto probe the Y − N interaction
Forward K+, coherent production, leavingthe Λ within the Fermi surface of theresidual 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, differentialcross sections...
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 29 / 32
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]0πCalculated measured 300− 200− 100− 0 100 200 300
Counts
0
100
200
300
400
500
600
700
800
900 = 297 MeVγE
angles0πAll 0
< 400πθ
events0π1. Search for coherent
Photon energy [MeV]2 4 6 8 10
Counts
0
100
200
300
400
500
600
700
800
900Exponential + Gaussian fn.
4.5 MeV≈Mean
0.6 MeV≈ σ
2. Search for additional decay photon
[deg]α0 50 100 150
Counts
0
1
2
3
4
5
) fitα(22sin
angular distr.γ3. Verification decay
Not efficiency corrected
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 30 / 32
Future opportunities: Y-N studies with deuterium targets
Data being taken this very moment!
Final state interactions forγd → 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. Glockle, Phys. Rev.
C74 (2006) 034002
Cross section & pol. obs. sensitive toYN interactions at these cusps!
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 31 / 32
Summary
Hadrons - molecular-like structure?
BGO-OD - strangenessphotoproduction - extreme forwardangles
Low momentum transfer region
1st preliminary results - K+Y atforward angles
Λ(1405), K 0 off protons & neutrons -analyses ongoing
Deuterium target - data being takennow!
Y-N interaction study opportunities -deuterium, hypernuclei...
missing mass [MeV]+
K1100 1200 1300 1400 1500 1600
mis
sin
g m
ass [
Me
V]
0π
+K
900
950
1000
1050
1100
1150
1200
1250
1300
(1116)Λ
(1193)0Σ
(1405)Λ(1385)/Σ
n
γn+
Λ
0Σ
) missing mass0π+
Discriminating between states with (K
missing mass [MeV]+K1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
Co
un
ts
0
200
400
600
800
1000 (1116)Λ
(1193)0Σ (1405)Λ
(1385)Σ
(1520)Λ
momentum < 1 GeV+
All events for K
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 32 / 32
Extra slides
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 32 / 32
Previous γp → K 0Σ+ measurements
The 1st beam asymmetry measurementR. Ewald et.al, PLB 738 (2014) 268(CBELSA/TAPS Collaboration)
1
0.5
0
0.5
1
= 0.8K
cmθcos
1200 1400 1600 1800 2000 22001
0.5
0
0.5
1
= 0.4K
cmθcos
1500 20001
0.5
0
0.5
1
= +0.4cm
Kθcos
1200 1400 1600 1800 2000 22001
0.8
0.6
0.4
0.2
0
0.2
0.4
0.6
0.8
1
= 0.0K
cmθcos
1500 20001
0.8
0.6
0.4
0.2
0
0.2
0.4
0.6
0.8
1
= +0.8cm
Kθcos
γΣ
Photon beam energy [MeV]
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 32 / 32
K 0 photoproduction off the neutron
T. Mart, Phys. Rev. C 83, 048203 (2011)
Complimentary to γp → K+Λ measurements: relate hadronic couplingconstant - predictions of n(γ,K 0)Λ cross section
gK+Λp= gK 0Λn
gK+Σ0p
= −gK 0Σ0n
gV ,TK∗+Λp
= gV ,TK∗0Λn
BGO-OD - 1st differential cross section measurement to Eγ = 3 GeV &polarisation observables
Higher statistics - K 0 identification via both main decay modesTom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 32 / 32
Separating K 0Λ and K 0Σ0 final states
Simulated data to demonstrate separation of channels
Identify the decay: Σ0 → Λγ
energy in Hyperon rest frame [MeV]γ0 20 40 60 80 100 120 140 160 180 200
Co
un
ts
0
50
100
150
200
250
300 0Σ0
Simulated K
Λ0
Simulated K
(d)
invariant mass [MeV]0π2300 350 400 450 500 550 600
[M
eV
]0
πM
issin
g m
ass r
eco
ilin
g f
rom
2
800
900
1000
1100
1200
1300
1400
1500
1600Λ
0 + K0Σ
0(a) Simulated K
[MeV]0
Missing mass recoiling from K800 900 1000 1100 1200 1300 1400 1500 1600
Co
un
ts
0
100
200
300
400
500
600
700
800
WithDecay_Lambda
Entries 2119Mean 1141RMS 112.7
NDEntries 31903Mean 1194
RMS 144.1
0(b) Missing mass recoiling from K
All data
γEvents with decay
γEvents with no decay
energy in Hyperon rest frame [MeV]γ0 20 40 60 80 100 120 140 160 180 200
[M
eV
]γ
0π
Mis
sin
g m
ass r
eco
ilin
g f
rom
2
800
900
1000
1100
1200
1300
1400Λ
0 + K0Σ
0(c) Simulated K
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 32 / 32
Tagger timing
Cluster Time [ns]600− 400− 200− 0 200 400 600
Co
un
ts
0
20
40
60
80
100
120
1403
10×
Cluster Time [ns]10− 8− 6− 4− 2− 0 2 4 6 8 10
Co
un
ts
0
20
40
60
80
100
120
1403
10×
RF bunch structure
from ELSA
~ 160 psσ
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 32 / 32
K 0 photoproduction off the neutron
No K 0 t-channel exchange (but still K∗) - s channel resonances moreprominent
Complementary to K+Λ - relate hadronic coupling constants
K. Tsukada et al, Phys. Rev. C 78, 014001 (2008)
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 32 / 32
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 28th June 2018 32 / 32
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+νµK+ → π+π0
µ
3ns18ns
16ns
19nsBGOcrystal
Incident sub−clusterDecay sub−cluster
νµ
Κ
+
+
Decay cluster energy [MeV]0 50 100 150 200 250 300 350 400
Co
un
ts
0
500
1000
1500
2000
2500
3000Simulated data
Real data
Decay time [ns]0 10 20 30 40 50 60 70 80 90 100
Co
un
ts
0
1000
2000
3000
4000
5000
6000
Fitted lifetime ~ 11 ns
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 32 / 32
Identifying the Σ0 → Λγ decay (Γ = 100%)
Boost all neutral particles in theBGO into missing hyperon restframe
If K+Σ0:
γ energy (Σ0 rest frame) =MΣ0 −MΛ = 77 MeV
Efficiency scale eventswith/without ID to separatemissing mass spectrum
Photon detection in the BGO toseparate different K+Y ∗ states!
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 32 / 32
K+Λ Recoil Polarisation at forward angles
Up-down asymmetry between decay proton/neutron direction in Λ restframe & normal to the reaction plane
Λ→ π0n identified in the BGO
PΛ =2
α
Nup − Ndown
Nup + Ndown, α = 0.642 (Λ decay parameter)
W [MeV]1600 1650 1700 1750 1800 1850 1900 1950 2000
ΛP
1−
0.5−
0
0.5
1 = 0.95, Preliminary)+
KθBGOOD (cos
= 0.9)CM+
KθCLAS (cos
= 0.85)CM+
KθGRAAL (cos
BonnGatchina PWA
“Dilution” - spatialresolutions/particle miss ID
Energy [MeV]γ
900 1000 1100 1200 1300 1400 1500
Effic
iency o
f corr
ect asym
metr
y0.7
0.75
0.8
0.85
0.9
0.95
1
1.05
1.1
~ 0.89∈
Simulated data event by event comparison
M.E.McCracken et al. (CLAS), Phys.Rev. C81, 025201 (2010). A. Lleres et al. (GRAAL), Eur. Phys. J. A 31, 79 (2007)
Can now identify Λ→ pπ− for greater statisticsTom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 32 / 32
d∗(2380) dibaryon, Γ ≈ 70 MeV, JP = 3+
Decay branching ratios determinedM. Bashkanov, H. Clement, T. Skorodko, Eur. Phys. J. A 51, 87 (2015)
Hexaquark/molecule/dominated by diquark components?Md∗ = M∆∆ − 80 MeV
P. Adlarson et al., (WASA-at-COSY Collaboration), PRL 106,
242302 (2011)
γd → pπ0π0
solid (dashed) lines - Conventional background (with d∗(2380)contribution),M. Egorov and A. Fix, Nucl. Phys. A933, 104(2015)M. Guenther, Master thesis, Basel (2015), T Ishikawa et al.,Phys. Lett B 772, 398 (2017)
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 32 / 32
High statistics new dataset
Missing mass [MeV]+
K0 200 400 600 800 1000 1200 1400 1600 1800 2000
Counts
0
200
400
600
800
1000
1200
1400
Signal
Entries 28098Mean 961.2RMS 236.9
April 2017 beam time
< 1300 MeVγ914 < E
eventsΛ+
8200 K
0π events with Λ
+3500 K
Missing mass [MeV]+
K0 200 400 600 800 1000 1200 1400 1600 1800 2000
Counts
0
50
100
150
200
250
300
350
400
450Signal
Entries 8626Mean 916.8RMS 262.9
July 2015 beam time
< 1300 MeVγ914 < E
eventsΛ+
2450 K
0π events with Λ
+1000 K
30 bins in θK+
CM , 6-7 bins in angle
25 bins in energy
∼ 10% statistical error - consistent with PAC proposal (& higher than otherdatasets at more backward angles)
Small bug found in track-tagger correlations, will increase yield by ∼ 1.5
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 32 / 32
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) Momentumconservation & K+
“missing mass” cut
(b) Kinematic fit &confidence level cut
(c) Neural network tosuppress background
Reconstructed invariant mass [MeV]1100 1200 1300 1400 15000
10000
20000
30000
40000
50000
(a) All combinations
Real data0
Σ+
Simulated K
Reconstructed invariant mass [MeV]1100 1200 1300 1400 15000
10000
20000
30000
40000
50000
(b) With a kinematic fit
confidence level > 1%
Reconstructed invariant mass [MeV]1100 1200 1300 1400 15000
10000
20000
30000
40000
50000
(c) Kinematic fit & neural network
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 32 / 32
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/s
r]µ
[Ω
/dσ
d
1− 0.5− 0 0.5 1
0.2
0.4
15 MeV±=1690s
1− 0.5− 0 0.5
0.2
0.4
15 MeV±=1810s
1− 0.5− 0 0.5
0.2
0.4
15 MeV±=1930s
1− 0.5− 0 0.5
0.2
0.425 MeV±=2080s
1− 0.5− 0 0.5 1
0.2
0.4
15 MeV±=1720s
1− 0.5− 0 0.5
0.2
0.4
15 MeV±=1840s
1− 0.5− 0 0.5
0.2
0.4
15 MeV±=1960s
0.5− 0 0.5
0.2
0.425 MeV±=2130s
1− 0.5− 0 0.5 1
0.2
0.4
15 MeV±=1750s
1− 0.5− 0 0.5
0.2
0.4
15 MeV±=1870s
1− 0.5− 0 0.5
0.2
0.4
15 MeV±=1990s
1− 0.5− 0 0.5
0.2
0.4100 MeV±=2255s
− −
0.2
0.4
0.2
0.4
15 MeV±=1780s
−
0.2
0.4
0.2
0.4
15 MeV±=1900s
1− 0.5− 0 0.5
0.2
0.4
0.2
0.4
25 MeV±=2030s
LEPS 2006
CLAS 2010
SAPHIR 2003
BGOOD 2016
+Kcmθcos
Preliminary
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 32 / 32
Preliminary identification of K 0Σ+ with BGO-OD
Analysis by S. Alef
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 32 / 32
Previous γp → K 0Σ+ measurements
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)
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 32 / 32
Access to rare Y ∗ decays
missing mass [MeV]+
K1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
mis
sin
g m
ass [M
eV
]η
+K
400
600
800
1000
1200
1400
) missing massη+
Discriminating between states with (K
missing mass [MeV]+
K1100 1200 1300 1400 1500 1600
mis
sin
g m
ass [M
eV
]γ
+K
1000
1100
1200
1300
1400
1500
1600
1700
0Σ
Λ
) missing massγ+
Discriminating between states with (K
Λ(1405)→ Λγ
ΓγΛ indication of compositeness:
T. Sekihara, S. Kumano, Phys. Rev C89, 025202 (2014)
K+η recoiling mass
eg, Λ(1670)1/2+ (PDG ****)Width 25 - 50 MeVΓΛη = 10− 25% (never observed)
Many poorly known Σ∗ and Λ∗ states
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 32 / 32
Motivation - Λ hyperons in a constituent quark model
Parity ordering of 3 lowest states agrees with CQM model, but Λ(1405)mass too low (compared to N∗(1535))
Y* spectrum - limited success with constituent quark models
Models including meson-baryon interactions as degrees of freedom - moresuccessful, 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.
U. Loring, B. Ch. Metsch, H. R. Petry, Eur. Phys. J A 10, 395 (2001)
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 32 / 32
High statistics new dataset
Unprecedented angular resolution - 30 bins in θK+
CM
Fit to background: e+e− from the beam, misidentifed π+ at higher energy
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 32 / 32
Preliminary forward K+Λ differential cross sections
X-axis: θCMK+ , 0 - 300. Y-axis: dσ/dΩ, 0 - 0.8 [µb/sr]
Magenta line - BnGa PWA, Beam energy labelled inset
π0 identification required - x4 stats anticipated without this
+K
θ
0 5 10 15 20 25 300
0.10.20.30.40.50.60.70.8
937 MeV
[deg]+
Kθ
0 5 10 15 20 25 300
0.10.20.30.40.50.60.70.8
976 MeV
0 5 10 15 20 25 300
0.10.20.30.40.50.60.70.8
1016 MeV
0 5 10 15 20 25 300
0.10.20.30.40.50.60.70.8
1049 MeV
0 5 10 15 20 25 300
0.10.20.30.40.50.60.70.8
1076 MeV
0 5 10 15 20 25 300
0.10.20.30.40.50.60.70.8
1103 MeV
0 5 10 15 20 25 300
0.10.20.30.40.50.60.70.8
1129 MeV
0 5 10 15 20 25 300
0.10.20.30.40.50.60.70.8
1156 MeV
0 5 10 15 20 25 300
0.10.20.30.40.50.60.70.8
1183 MeV
0 5 10 15 20 25 300
0.10.20.30.40.50.60.70.8
1210 MeV
0 5 10 15 20 25 300
0.10.20.30.40.50.60.70.8
1237 MeV
0 5 10 15 20 25 300
0.10.20.30.40.50.60.70.8
1263 MeV
0 5 10 15 20 25 300
0.10.20.30.40.50.60.70.8
1290 MeV
+K
θ
0 5 10 15 20 25 300
0.10.20.30.40.50.60.70.8
1317 MeV
0 5 10 15 20 25 300
0.10.20.30.40.50.60.70.8
1344 MeV
0 5 10 15 20 25 300
0.10.20.30.40.50.60.70.8
1370 MeV
Preliminary
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 32 / 32
Future opportunities in K+Y studies: Y-N interaction
Forward kinematics ideal for BGO-OD
Increase OD magnetic field to improvemomentum resolution
Difficult measurement but veryimportant and not possible anywhereelse!
Right hand side plots:K. Miyagawa, T. Mart, C. Bennhold, W. Glockle, Phys. Rev. C74
(2006) 034002
Tom Jude (University of Bonn) Strangeness photoproduction at BGO-OD 28th June 2018 32 / 32
Recommended