2. Contents Timelike Formfactors of Hyperons HADES Upgrade
PANDA Phase-0 in HADES
Double Strange Hyperon Spectroscopy
PANDA Phase-1
Summary

3. Radiative Hyperon Decays
Decays to real and virtual photons sensitive to baryon structure:
SLg : test of CP violation
Hyperon Lee not measured at all: strong effects of vector mesons expected

4. Radiative Hyperon Decays
Timelike (GM(q2), GE(q2)) complementary to Spacelike
Low energy TL complementary to high energy TL (e.g. BES-III, CLEO)
𝐵𝐵→M 𝑒+𝑒−
𝐵1 →𝐵2𝑒+𝑒−

5. Timelike Hyperon Formfactors
Timelike region recently measured in e+e- annihilation
Measured |GM|2 a factor 10 larger than VMD
Larger values for L than S indicate strong effects of (ud) quark correlations (S,I=0 for Λ) (S,I=1 for Σ)
But, FF Analysis on resonance peak . . .
K. Seth EPJ Web Conf. 95 (2015) 03033

6. Using HADES to Measure Y*Lee
Proposed reaction: p p(A) Y (any hyperon) X e+e- X (BR~10-5))
High intensity AND energy proton beams (T = 4.5 GeV)
Measured BR (Λγ) are large! (comparable to Δ→Nγ)
Hyperon states are narrow
HADES has excellent Λ and e+e- capabilities
Upgrade challenges:
Increase DAQ rate
Improve g, e+e- efficiency (ECAL, RICH)
Improve L efficiency (STS, FTOF)

7. HADES Upgrade

8. Forward Tracker (STS1/2+TOF)
Reactions with low Q, and also the baryon from hyperon decay are strongly forward peaked ( Tracker + TOF Upgrade) Pions (and electrons) from Hyperon decay are emitted with a large polar angle ( HADES)

9. PANDA Phase 0 with HADES STS1/2
PANDA pre-series and prototype detectors for STS1/2
HADES measures the dileptons & mesons
PANDA Straw Trackers for the baryon (Q<7˚) STS1: 640 tubes (use later as FT3/4) STS2: 900 tubes (use later as FT5/6) (4 double layers each)
76 cm

10. PANDA Phase 0 Experiments with HADES
STS1 Jülich
STS2 Cracow/Orsay
FE and TRB Jülich
Mechanics Orsay
HV-System Cracow/GSI
Gas-system Cracow/Jülich
Software/Simul. Cracow/Jülich/Uppsala
Construction in (on schedule)
Installation in 2018
Operation

11. Physics Reach for L(1520) p+(p/C) pKL(1520)  pK Lee
Λ(1520)→Λe+e-(3/2-→1/2-) transition
Max. SIS18 energy
108 /s
= 40 mb (assumed)
~ 500 evts/day reconstructed
plus further increase due to upgraded RICH

12. Physics Program
Plan: 30 days of proton beam at close to max. SIS18 energy
Improve BR for S*0→Λg and S*+→S+g
Establish BR for S*-→S-g and S*0→S0g
Angular distributions of S0→Λg and S*0→Λg for a limit on P, CP violation (statistics??)
Branching Ratio of S0(S*0)→Λe+e-
Form Factors (most sensitive to magnetic) q2<(260) MeV2
BR and FF for Λ(1520)→Λe+e-
Explore double strange - (1321) production (complementary to PANDA with pbar-p)

13. Multi-Strangeness Baryon Spectroscopy
With PANDA

14. Quark Model for Ξ & Ω Ξ: many states predicted below 3 GeV
compare 1/2+ and 1/2- excitation Ω:
several states predicted between 2 and 3 GeV
compare 3/2+ and 3/2- excitation Ξ
U. Löring et al., EPJA 10 (2001) 447 Ω
s.a.: M. Pervin, W. Roberts, PRC 77 (2008)

15. Most Promising: Study Ξ Resonances
very little known  rather high cross section
find missing resonances
determine branching to various decay modes:
Ξ𝜋, Ξ 𝜋 + 𝜋 − , Ξ 𝜋 0 𝜋 0 , Λ 𝐾 − , Σ 𝐾 , Ξ𝜂, Ξ𝜂𝜋, Ξ 𝜂 ′ , Ξ𝜔, Ξ𝜙, …
determine JP quantum numbers if possible
strategy:
select 𝑝 momentum to produce a specific resonance close to threshold

16. Ξ + Λ 𝐾 − final state: 𝑀 2 Λ 𝐾 − vs. 𝑀 2 Ξ + ΛdM
Ξ + Λ 𝐾 − final state: 𝑀 2 Λ 𝐾 − vs. 𝑀 2 Ξ + Λ
(bef. 4C kin. fit)
σM(Ξ+) = 3.2 MeV
frec ~ 2.5%, fbckg ~ 0.210-7 _
André Zambanini, Dissertation Univ. Bochum (2015)

17. _
pp  Ξ+Ξ(1820)-  Ξ+ΛK-
Ξ + Λ 𝐾 − final state: 𝑀 2 Ξ + 𝐾 − vs 𝑀 2 Λ 𝐾 −
Generated
Reconstructed
σM(Ξ+) = 4.0 MeV
frec = 2.1% (updated)
background suppression under study _
Jenny Pütz, Talk at FAIRNESS 2016

18. PANDA is a Factory for (Excited) Hyperons !
hyperon-antihyperon cross sections:
𝜎 𝑝 𝑝→ Λ Λ, Λ Σ, Σ Σ ≅10…100 𝜇b measured
𝜎 𝑝 𝑝→ Ξ Ξ ≅2 𝜇b measured
𝜎 𝑝 𝑝→ Ω Ω ≅2…100 nb predicted
production rates at phase 1&2 luminosity 11031 s-1cm-2 :
up to 108 Λ per day, ~107 Σ per day (charge state dep.)
up to 2106 Ξ per day
~3104 Ω per day (assuming σ = 30 nb)
at comparative energy above threshold, we expect the same order of magnitude for excited states

19. Ξ* / Ω* Studies within PANDA Physics Program
Initial phase with lower Lumi
Λ & Σ spectroscopy in parallel
long runs to measure the X(3872) width in energy scan:
in parallel, trigger for Ξ* and Ω* (peak finding)
Mmax(Ξ*)  2.55 GeV (Mmax(Ω*)  2.20 GeV)
later: long runs for threshold scan of DsDs(2317)
Mmax(Ω*)  2.61 GeV
Dedicated runs for JP determination of specific states!

20. Summary HADES – upgrade (Leptons and decay mesons)
PANDA – Phase (decay baryon)
On schedule for renewed SIS operation during 2nd half of 2018
Hyperon transition form factors at HADES
Excited Double Strange Hyperons at PANDA

23. Competitiveness LHCb large number of Ξ and Ω observed
spectroscopy in the light quark sector, JP determination?
neutrals in final state difficult
Belle 2
small Υ and 𝐵 branching to baryon-antibaryon final states
GlueX, CLAS-12
small production cross section, no state seen above Ξ 1530
J-PARC
𝐾 − beam, but so far focussed on missing mass experiments
PANDA is the best experiment for hyperon spectroscopy !

24. Baryon Spectroscopy Production of multi-strangeness baryons
(unexplored, new territory, „Strangeness-Factory“)
Octet X states: no partner of most N* states
Decuplet X and W states: no partner of D* states
PDG note on X resonances: “… nothing of significance on X resonances has been added since our 1988 edition.”
What are the relevant degrees of freedom?
ms~100 MeV mQCD~200 MeV
Test of QCD at the transition
Which are the relevant degrees of freedom?
m S ≈100 MeV ~ Λ QCD ≈200 MeV
Test of QCD at the transition
Paola Gianotti

25. X(1820) High signal rates and high background rejection for excited
double strange baryons

26. PANDA is a Factory for (Excited) Hyperons !_
PANDA is a Factory for (Excited) Hyperons !
hyperon-antihyperon cross sections:
𝜎 𝑝 𝑝→ Λ Λ, Λ Σ, Σ Σ ≅10…100 𝜇b measured
𝜎 𝑝 𝑝→ Ξ Ξ ≅2 𝜇b measured
𝜎 𝑝 𝑝→ Ω Ω ≅2…100 nb predicted
production rates at phase 1&2 luminosity 11031 s-1cm-2 :
up to 108 Λ per day, ~107 Σ per day (charge state dep.)
up to 2106 Ξ per day
~3104 Ω per day (assuming σ = 30 nb)
at comparative energy above threshold, we expect the same order of magnitude for excited states

27. Open Questions Missing resonances Wrong masses, wrong sequence
Relevant degrees of freedom?
3-quark?
quark-diquark?
meson-baryon dynamics
from RPP 2014 / QM: S. Capstick, W. Roberts

28. Strange Partners Approximate SU(3) flavor symmetry
N* & Δ states have partners in the strange sector
focus on Ξ and Ω
Ξ: as many states as N* & Δ together (1)
Ω: as many states as Δ
scrutinize our understanding of the baryon excitation pattern
(1) in case of SU(3) symmetry !

29. Status of Ξ* Resonances: RPP 2014
Chin. Phys. C 38 (2014) ?
Ξ(1820):
Teodoro78 favors J = 3/2, but cannot make a parity discrimination. Biagi 87c is consistent with J = 3/2 and favors negative parity for this J value.

30. SU(6) x O(3) Classification
RPP 2014: Chin. Phys. C 38 (2014)
„Assignments for …
Ξ(1820) and Ξ(2030), are merely
educated guesses.“
Ξ(1690), Ξ(1950):
T. Melde et al., PRD 77 (2008)
decuplet: no Ξ*, no Ω*
“… nothing of significance on X resonances has been added since our edition.” ?

31. J = 3/2
J = 5/2
Data on Ξ* States: Ξ(1530)
The only reasonably well studied Ξ resonance:
Ξ(1530) - decuplet g.s JP = 3/2+
Г = 9…10 MeV
decay: ~100% Ξπ
BaBar measured the Ξ(1530)0 spin J = 3/2 in Λc+  Ξ- π+ K+
favor JP = 1/2- for Ξ(1690)
Compare to Δ!!
BaBar: B. Aubert et al., PRD 78 (2008)

32. Early Physics: Expected Rates for Strange Baryons
initial phase: 𝐿≅ cm −2 s −1 instead of 𝐿≅ 2∙ cm −2 s −1
nevertheless the Ξ Ξ production rate will be 𝑅 Ξ Ξ ≅10/s≅ /d
for Ω Ω production we expect 𝑅 Ω Ω ≅0.3/s≅ 3∙10 4 /d
for excited states the cross section should be of the same order of magnitude as for the ground state for given 𝑠 − 𝑠 thr
the detected rate depends on the specific decay mode (branching & reconstruction efficiency)
e.g. 𝑝 𝑝→ Ξ + Ξ ∗− → Ξ + Ξ − 𝜋 0 → Λ 𝜋 + Λ 𝜋 − 𝜋 0 → 𝑝 𝜋 + 𝜋 + 𝑝 𝜋 − 𝜋 − 𝜋 assume 𝑏=0.5∙ =0.2 and 𝜖= 5%  𝑅 𝑑𝑒𝑡 ≅ /d

33. Recent Simulation & Analysis
MC simulations & analyses:
André Zambanini, PhD thesis U Bochum 2015
4.1 GeV/c pp  Ξ(1690)-Ξ+  K-ΛΞ+
Jennifer Pütz, PhD thesis on Ξ spectroscopy
4.6 GeV/c pp  Ξ(1820)-Ξ+  K-ΛΞ+ & c.c _