Hadron Spectroscopy with Kaon Beam
Boris Grube
Institute for Hadronic Structure and Fundamental Symmetries Technische Universität München Garching, Germany
Workshop on Dilepton Productions with Meson and Antiproton Beams ECT*, Trento, 09. Nov 2017
E COMPASS
1 8 α
Hadrons and Strong Interaction
Binding of quarks and gluons into hadrons governed by low-energy (long-distance) regime of QCD Least understood aspect of QCD
Perturbation expansion in αs not applicable Revert to models or numerical simulation of QCD (lattice QCD) Details of binding related to hadron masses Only small fraction of proton mass explained by Higgs mechanism ⇒ most generated dynamically
Hadrons reflect workings of QCD at low energies Measurement of hadron spectra and hadron decays gives valuable input to theory and phenomenology
2 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Hadrons and Strong Interaction
Binding of quarks and gluons into 0.5 hadrons governed by low-energy July 2009 α s(Q) (long-distance) regime of QCD Deep Inelastic Scattering + – 0.4 e e Annihilation Least understood aspect of QCD Heavy Quarkonia
Perturbation expansion in αs not 0.3 applicable Revert to models or numerical simulation of QCD (lattice QCD) 0.2 Details of binding related to hadron masses 0.1 QCD α s (Μ Z ) = 0.1184 ± 0.0007 1 10 100 Only small fraction of proton mass Q [GeV] explained by Higgs mechanism ⇒ most generated dynamically
Hadrons reflect workings of QCD at low energies Measurement of hadron spectra and hadron decays gives valuable input to theory and phenomenology
2 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Hadrons and Strong Interaction
Binding of quarks and gluons into 0.5 hadrons governed by low-energy July 2009 α s(Q) (long-distance) regime of QCD Deep Inelastic Scattering + – 0.4 e e Annihilation Least understood aspect of QCD Heavy Quarkonia
Perturbation expansion in αs not 0.3 applicable Revert to models or numerical simulation of QCD (lattice QCD) 0.2 Details of binding related to hadron masses 0.1 QCD α s (Μ Z ) = 0.1184 ± 0.0007 1 10 100 Only small fraction of proton mass Q [GeV] explained by Higgs mechanism ⇒ most generated dynamically
Hadrons reflect workings of QCD at low energies Measurement of hadron spectra and hadron decays gives valuable input to theory and phenomenology
2 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Quark-Model Meson Nonets
Light-quark mesons
u, d, and s (anti)quarks ⇒ SU(3)flavor nonets
Ground-state nonets
Many more nonets for orbital and radial excitations
3 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Quark-Model Meson Nonets
Light-quark mesons
u, d, and s (anti)quarks ⇒ SU(3)flavor nonets
Ground-state nonets
Many more nonets for orbital and radial excitations
3 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Quark-Model Meson Nonets
Light-quark mesons
u, d, and s (anti)quarks ⇒ SU(3)flavor nonets
Ground-state nonets
Many more nonets for orbital and radial excitations
3 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Light-Meson Spectrum
“Light-meson frontier” Many states need confirmation in mass region m & 2 GeV/c2 Many wide states ⇒ overlap and mixing Identification of higher excitations becomes exceedingly difficult
Main focus of current COMPASS program [Courtesy K. Götzen, GSI]
4 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Light-Meson Spectrum
“Light-meson frontier” Many states need confirmation in mass region m & 2 GeV/c2 Many wide states ⇒ overlap and mixing Identification of higher excitations becomes exceedingly difficult
Main focus of current COMPASS program [Courtesy K. Götzen, GSI]
4 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Light-Meson Spectrum
“Light-meson frontier” Many states need confirmation in mass region m & 2 GeV/c2 Many wide states ⇒ overlap and mixing Identification of higher excitations becomes exceedingly difficult
Main focus of current COMPASS program [Courtesy K. Götzen, GSI]
4 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Light-Meson Spectrum
“Light-meson frontier” Many states need confirmation in mass region m & 2 GeV/c2 Many wide states ⇒ overlap and mixing Identification of higher excitations becomes exceedingly difficult
Main focus of current COMPASS program [Courtesy K. Götzen, GSI]
4 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Beyond the Constituent Quark Model
QCD permits additional color-neutral configurations Gell-Mann’s Totalitarian Principle for Quantum Mechanics: “Everything not forbidden is compulsory” M. Gell-Mann, Nuovo Cimento 4 (1956) 848
Physical mesons Linear superpositions of all allowed basis states “Configuration mixing” Amplitudes in principle determined by QCD interactions Disentanglement of contributions difficult
5 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Beyond the Constituent Quark Model
QCD permits additional color-neutral configurations Gell-Mann’s Totalitarian Principle for Quantum Mechanics: “Everything not forbidden is compulsory” M. Gell-Mann, Nuovo Cimento 4 (1956) 848
Physical mesons Linear superpositions of all allowed basis states “Configuration mixing” Amplitudes in principle determined by QCD interactions Disentanglement of contributions difficult
5 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Beyond the Constituent Quark Model
Best experimental evidence so far from heavy-quark sector + Tetraquark candidates Zc,b Pentaquark candidates Pc Charged |cci- and |bbi-like Heavy baryon + states Decay mode Pc → J/ψ + p ± ± E.g. Zc (3900) → J/ψ + π
Light-quark sector Model calculations suggest some states to be tetraquarks or hybrids No definite experimental evidence
6 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Beyond the Constituent Quark Model
Best experimental evidence so far from heavy-quark sector + Tetraquark candidates Zc,b Pentaquark candidates Pc Charged |cci- and |bbi-like Heavy baryon + states Decay mode Pc → J/ψ + p ± ± E.g. Zc (3900) → J/ψ + π
Light-quark sector Model calculations suggest some states to be tetraquarks or hybrids No definite experimental evidence
6 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Beyond the Constituent Quark Model
Best experimental evidence so far from heavy-quark sector + Tetraquark candidates Zc,b Pentaquark candidates Pc Charged |cci- and |bbi-like Heavy baryon + states Decay mode Pc → J/ψ + p ± ± E.g. Zc (3900) → J/ψ + π
Light-quark sector Model calculations suggest some states to be tetraquarks or hybrids No definite experimental evidence
6 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Light-Meson Spectrum from Lattice QCD 2 State-of-the-art calculation with mπ = 391 MeV/c Dudek et al., PRD 88 (2013) 094505
Essentially recovers quark-model pattern High towers of excited states Additional hybrid-meson super-multiplet
7 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Why kaon spectroscopy?
2 PDG 2016: 25 kaon states below 3.1GeV/c Only 12 kaon states in summary table, 13 need confirmation Many predicted quark-model states still missing Some hints for supernumerous states
0− 0+ 1− 1+ 2− 2+ 3− 3+ 4− 4+ 5−
2 ] 2 c /
Mass [GeV 1
K K∗ K∗ K K K∗ K∗ K K K∗ K∗ 0 1 2 2 3 3 4 4 5 [Courtesy S. Wallner, TUM]
8 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Why kaon spectroscopy?
Many kaon states need confirmation Little progress in the past Most PDG entries more than 30 years old Since 1990 only 4 kaon states added to PDG (only 1 to summary table)
Kaon spectrum crucial to understand light-meson spectrum
Identify supernumerous states by completing SU(3)flavor multiplets P + ∗ E.g. J = 0 multiplet with a0(980), K0 (800) [or κ], f0(500) [or σ], and f0(980) is hypothesized to be tetra-quark multiplet ∗ But K0 (800) still disputed Kaon spectrum required to analyse heavy-meson decays E.g. search for CP violation in multi-body decays ± 0 ± 0 0 + − e.g. B → D K with D → KS π π Dalitz-plot amplitude analysis requires accurate knowledge of 0 ± resonances in KS π subsystems
9 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Why kaon spectroscopy?
Many kaon states need confirmation Little progress in the past Most PDG entries more than 30 years old Since 1990 only 4 kaon states added to PDG (only 1 to summary table)
Kaon spectrum crucial to understand light-meson spectrum
Identify supernumerous states by completing SU(3)flavor multiplets P + ∗ E.g. J = 0 multiplet with a0(980), K0 (800) [or κ], f0(500) [or σ], and f0(980) is hypothesized to be tetra-quark multiplet ∗ But K0 (800) still disputed Kaon spectrum required to analyse heavy-meson decays E.g. search for CP violation in multi-body decays ± 0 ± 0 0 + − e.g. B → D K with D → KS π π Dalitz-plot amplitude analysis requires accurate knowledge of 0 ± resonances in KS π subsystems
9 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Why kaon spectroscopy?
Many kaon states need confirmation Little progress in the past Most PDG entries more than 30 years old Since 1990 only 4 kaon states added to PDG (only 1 to summary table)
Kaon spectrum crucial to understand light-meson spectrum
Identify supernumerous states by completing SU(3)flavor multiplets P + ∗ E.g. J = 0 multiplet with a0(980), K0 (800) [or κ], f0(500) [or σ], and f0(980) is hypothesized to be tetra-quark multiplet ∗ But K0 (800) still disputed Kaon spectrum required to analyse heavy-meson decays E.g. search for CP violation in multi-body decays ± 0 ± 0 0 + − e.g. B → D K with D → KS π π Dalitz-plot amplitude analysis requires accurate knowledge of 0 ± resonances in KS π subsystems
9 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam How to produce excited kaon states?
Decays τ leptons, charmed mesons, and charmonium states ⇒ limited mass reach B meson decays ⇒ description of large Dalitz plots difficult
Production experiments E.g. diffractive production using high-energy kaon beam on stationary target Large cross section Not very selective: all kaon states can appear as intermediate state X
10 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam How to produce excited kaon states?
Decays τ leptons, charmed mesons, and charmonium states ⇒ limited mass reach B meson decays ⇒ description of large Dalitz plots difficult
Production experiments E.g. diffractive production using high-energy kaon beam on stationary target Large cross section Not very selective: all kaon states can appear as intermediate state X
´ ´ h1 Kbeam X . hn P, R
target recoil
10 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam The COMPASS Experiment at the CERN SPS Experimental Setup C. Adolph, NIMA 779 (2015) 69 Fixed-target experiment Two-stage spectrometer Large acceptance over wide kinematic range Electromagnetic and hadronic calorimeters Beam and final-state particle ID (CEDARs, RICH)
11 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam The COMPASS Experiment at the CERN SPS Experimental Setup C. Adolph, NIMA 779 (2015) 69 Fixed-target experiment Two-stage spectrometer Large acceptance over wide kinematic range Electromagnetic and hadronic calorimeters Beam and final-state particle ID (CEDARs, RICH)
Hadron spectroscopy 2008, 2009 190 GeV/c secondary hadron beam − h beam: 97 % π−, 2 % K−, 1 % p
ℓH2 target
11 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Example: Analysis of K−π+π− Final State
´ ´ ´ K Kbeam X π+ π´ P
ptarget precoil
Diffractive production of excited kaon states X− that decay into K−π+π− Beam-particle ID via Cherenkov detectors (CEDARs) Ca. 50× more π− than K− in beam Final-state PID via RICH detector Distinguish K− from π− over wide momentum range
12 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Example: Analysis of K−π+π− Final State
´ ´ h h1 beam + h2 ´ h3 P
ptarget precoil
Diffractive production of excited kaon states X− that decay into K−π+π− Beam-particle ID via Cherenkov detectors (CEDARs) Ca. 50× more π− than K− in beam Final-state PID via RICH detector Distinguish K− from π− over wide momentum range
12 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Example: Analysis of K−π+π− Final State
´ ´ h h1 beam + h2 ´ h3 P
ptarget precoil
Diffractive production of excited kaon states X− that decay into K−π+π− Beam-particle ID via Cherenkov detectors (CEDARs) Ca. 50× more π− than K− in beam Final-state PID via RICH detector Distinguish K− from π− over wide momentum range
12 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Example: Analysis of K−π+π− Final State
´ ´ h h1 beam + h2 ´ h3 P
ptarget precoil
Diffractive production of excited kaon states X− that decay into K−π+π− Beam-particle ID via Cherenkov detectors (CEDARs) Ca. 50× more π− than K− in beam Final-state PID via RICH detector Distinguish K− from π− over wide momentum range
12 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Example: Analysis of K−π+π− Final State Data sample
´ ´ ´ K Kbeam X π+ π´ P Ó t1
ptarget precoil
×103 COMPASS 2008 negative hadron beam - - 140 K p → K π+ π- p From 2008 data taking Events recoil not acceptance corrected campaign 120 270 000 events 100 0.07 < t′ < 0.7 (GeV/c)2 80 Exclusivity ensured by 60 preliminary measuring recoil proton 40 Also suppresses target 20
excitations 0 160 165 170 175 180 185 190 195 200 - Energy(K π+ π-)[GeV]
13 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Example: Analysis of K−π+π− Final State Invariant Mass of π−π+ Subsystem − − + − + − COMPASS: π π π COMPASS: K π π ×106 )
3 2
c ρ(770) ×10 COMPASS 2008 negative hadron beam ] - - + - 2 K p → K π π p recoil 12 ρ(770) not acceptance corrected
10 1 8 Entries / (5 MeV/ 6 f 0(980) f (980) 0.5 0 Events / 20 [MeV/c / Events preliminary 4 f (1270) f 2(1270) 2 2 ρ (1690) 3 0 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0.5 1 1.5 2 2 M ( + -)[GeV/c ] 2 π π mπ −π + [GeV/c ] COMPASS, PRD 95 (2017) 032004
mπ−π+ spectrum contains states already known from analysis of diffractively produced π−π−π+
14 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Example: Analysis of K−π+π− Final State Invariant Mass of K−π+ Subsystem WA03 (CERN) COMPASS 3 ×10 COMPASS 2008 negative hadron beam ] - - + - 2 K p → K π π p recoil 30 K*(892) not acceptance corrected 25 20 15
Events / 20 [MeV/c / Events 10 preliminary K*2(1430) 5 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 - M (K π+)[GeV/c2]
ACCMOR, NPB 187 (1981) 1
∗ ∗ Clear K (892) and K2 (1430) signals Data set slightly larger than that of most precise previous experiment
15 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Example: Analysis of K−π+π− Final State Invariant Mass of K−π+π− System COMPASS WA03 (CERN) < ′ < 2 0.07 < t′ < 0.7 (GeV/c)2 0 t 0.7 (GeV/c)
3 ×10 COMPASS 2008 negative hadron beam ] - - + - 2 K p → K π π p 3.5 recoil not acceptance corrected K1(1270) K1(1400) 3
2.5 K2(1770) 2 1.5
Events / 10 [MeV/c / Events preliminary 1 0.5 0 0.5 1 1.5 2 2.5 - M (K π+ π-)[GeV/c2] ACCMOR, NPB 187 (1981) 1
Various potential resonance signals Need partial-wave analysis (PWA) to disentangle contributions from various JP quantum numbers
16 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Example: Analysis of K−π+π− Final State Partial-Wave Analysis
X´ ´ P ǫ ´ ´ Kbeam [J M ] K π [L] + + P ξ π π π´ K´
ptarget precoil
PWA model similar to WA03 6 “isobars” − + π π subsystem: ξ = f0(500), ρ(770), and f2(1270) − + ∗ ∗ ∗ K π subsystem: ξ = K0 (800), K (892), and K2 (1430) 19 “waves” = combinations of X− JP and decay modes
17 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam × ] COMPASS- - K → K π-π+ 0.07 GeV /c < t’ < 0.7 GeV /c + +K*(892)[21]π−
Intensity / 0.02 [GeV/c / Intensity preliminary
- Mass of (K π-π+) [GeV/c ]
Example: Analysis of K−π+π− Final State Results of Partial-Wave Analysis ×103 ] 2 COMPASS- - 2008 30 K p → K π-π+p 0.07 GeV2/c2 < t’ < 0.7 GeV2/c2 25 1+0+K*(892)[01]π− 20 1+ → K∗(892)+ π− in S-wave 15 Clear signals from K1(1270) 10 Intensity / 0.02 [GeV/c / Intensity preliminary and K1(1400) 5
0 1 1.2 1.4 1.6 1.8 2 - Mass of (K π-π+) [GeV/c2]
2+ → K∗(892)+ π− in D-wave ∗ Clear signal from K2 (1430) ∗ K2 (1980)?
18 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Example: Analysis of K−π+π− Final State Results of Partial-Wave Analysis ×103 ] 2 COMPASS- - 2008 30 K p → K π-π+p 0.07 GeV2/c2 < t’ < 0.7 GeV2/c2 25 1+0+K*(892)[01]π− 20 1+ → K∗(892)+ π− in S-wave 15 Clear signals from K1(1270) 10 Intensity / 0.02 [GeV/c / Intensity preliminary and K1(1400) 5
0 1 1.2 1.4 1.6 1.8 2 - Mass of (K π-π+) [GeV/c2] ×103 ] 2 7 COMPASS- - 2008 K p → K π-π+p 6 0.07 GeV2/c2 < t’ < 0.7 GeV2/c2 2+1+K*(892)[21]π− 5 2+ → K∗(892)+ π− in D-wave 4 ∗ 3 Clear signal from K2 (1430)
Intensity / 0.02 [GeV/c / Intensity 2 preliminary ∗ K2 (1980)? 1 0 1 1.2 1.4 1.6 1.8 2 - Mass of (K π-π+) [GeV/c2]
18 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Example: Analysis of K−π+π− Final State Results of Partial-Wave Analysis ×103 ] 2 4.5 COMPASS- - 2008 K p → K π-π+p 4 0.07 GeV2/c2 < t’ < 0.7 GeV2/c2 3.5 2−0+K (1430)[02] − 2 π − ∗ − 3 2 → K2 (1430)+ π in S-wave 2.5 Possible signals from K (1770) 2 2 1.5 and K2(1820) Intensity / 0.02 [GeV/c / Intensity preliminary 1 0.5 K2(1580) and K2(2250)? 0 1 1.2 1.4 1.6 1.8 2 2.2 2.4 - Mass of (K π-π+) [GeV/c2] Work in progress: improving analysis Improved beam PID + data sample from 2009 run ⇒ ca. 8 × 105 K−π+π− events ⇒ world’s largest data set (4× WA03) Improved PWA model ⇒ clearer resonance signals Resonance-model fit ⇒ extraction of K−π+π− resonances and their parameters
19 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Example: Analysis of K−π+π− Final State Results of Partial-Wave Analysis ×103 ] 2 4.5 COMPASS- - 2008 K p → K π-π+p 4 0.07 GeV2/c2 < t’ < 0.7 GeV2/c2 3.5 2−0+K (1430)[02] − 2 π − ∗ − 3 2 → K2 (1430)+ π in S-wave 2.5 Possible signals from K (1770) 2 2 1.5 and K2(1820) Intensity / 0.02 [GeV/c / Intensity preliminary 1 0.5 K2(1580) and K2(2250)? 0 1 1.2 1.4 1.6 1.8 2 2.2 2.4 - Mass of (K π-π+) [GeV/c2] Work in progress: improving analysis Improved beam PID + data sample from 2009 run ⇒ ca. 8 × 105 K−π+π− events ⇒ world’s largest data set (4× WA03) Improved PWA model ⇒ clearer resonance signals Resonance-model fit ⇒ extraction of K−π+π− resonances and their parameters
19 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Example: Analysis of K−π+π− Final State Results of Partial-Wave Analysis ×103 ] 2 4.5 COMPASS- - 2008 K p → K π-π+p 4 0.07 GeV2/c2 < t’ < 0.7 GeV2/c2 3.5 2−0+K (1430)[02] − 2 π − ∗ − 3 2 → K2 (1430)+ π in S-wave 2.5 Possible signals from K (1770) 2 2 1.5 and K2(1820) Intensity / 0.02 [GeV/c / Intensity preliminary 1 0.5 K2(1580) and K2(2250)? 0 1 1.2 1.4 1.6 1.8 2 2.2 2.4 - Mass of (K π-π+) [GeV/c2] Work in progress: improving analysis Improved beam PID + data sample from 2009 run ⇒ ca. 8 × 105 K−π+π− events ⇒ world’s largest data set (4× WA03) Improved PWA model ⇒ clearer resonance signals Resonance-model fit ⇒ extraction of K−π+π− resonances and their parameters
19 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Example: Analysis of K−π+π− Final State Results of Partial-Wave Analysis ×103 ] 2 4.5 COMPASS- - 2008 K p → K π-π+p 4 0.07 GeV2/c2 < t’ < 0.7 GeV2/c2 3.5 2−0+K (1430)[02] − 2 π − ∗ − 3 2 → K2 (1430)+ π in S-wave 2.5 Possible signals from K (1770) 2 2 1.5 and K2(1820) Intensity / 0.02 [GeV/c / Intensity preliminary 1 0.5 K2(1580) and K2(2250)? 0 1 1.2 1.4 1.6 1.8 2 2.2 2.4 - Mass of (K π-π+) [GeV/c2]
Further final states accessible by COMPASS Isospin partner channel K−π0π0 K−K+K− − 0 0 − − (′) − K π , KSπ , K η , K ω ...
19 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Why do we need even larger data sets? − − − + Example: π + p → π π π + precoil COMPASS, PRD 95 (2017) 032004
´ ´ ´ πbeam X π π+ π´ P
ptarget precoil
50 × 106 π−π−π+ events ⇒ approx. 10× world data
20 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Why do we need even larger data sets? − − − + Example: π + p → π π π + precoil COMPASS, PRD 95 (2017) 032004
´ ´ ´ πbeam X π π+ π´ P
ptarget precoil
50 × 106 π−π−π+ events ⇒ approx. 10× world data
×106 ) 2
c a (1320) 0.4 2
a1(1260)
0.3
Events / (5 MeV/ (1670) 0.2 π 2
0.1
0 0.5 1 1.5 2 2.5 2 m3π [GeV/c ] 20 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Why do we need even larger data sets? − − − + Example: π + p → π π π + precoil COMPASS, PRD 95 (2017) 032004
´ ´ ´ πbeam X π
+ 1 ξ π P Ó t ´ π
ptarget precoil
50 × 106 π−π−π+ events ⇒ approx. 10× world data
×106 ×106 ) ) 2 2
c a (1320) c ρ(770) 0.4 2
a1(1260)
0.3 1 Events / (5 MeV/ (1670) Entries / (5 MeV/ 0.2 π 2 f (980) 0.5 0 f (1270) 0.1 2 ρ (1690) 3 0 0 0.5 1 1.5 2 2.5 0.5 1 1.5 2 2 2 m3π [GeV/c ] mπ −π + [GeV/c ] 20 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Why do we need even larger data sets? − − − + Example: π + p → π π π + precoil
PWA in narrow bins of four-momentum transfer squared t′ Resolve t′ dependence of partial-wave amplitudes Improved separation between resonant and nonresonant components in resonance-model fits First extraction of t′ spectra of resonances from such an analysis ⇒ can study production mechanism(s)
− − − + − − − + 3 −p − − +p π p → π π π p (COMPASS 2008) π p → π π π p (COMPASS 2008) ×10 π → π π π (COMPASS 2008) ] ]
2 +− + 2 +− + )
− 0 0 f (980) π S − 0 0 f (980) π S 2 +− + ) 7 0 ) 0
c 0 0 f (980) π S c 10 c 0 π(1800) non-resonant 140 0.100 < t' < 1.000 (GeV/c)2 b = 8.72 (GeV/c)-2 b = 27.50 (GeV/c)-2
Mass-independent fit (GeV/ (GeV/ [ [ 106 120 Mass-dependent fit 106 resonant 100 non-resonant Intensity Intensity 105 80 105 Intensity / (20 MeV/ 60 104 Preliminary Preliminary
40 104 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 100 100 20 Preliminary [deg] 0 [deg] 0 Prod. −100 Prod. −100 φ∆ φ∆ 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 2 t' [(GeV/c)2] t' [(GeV/c)2] m3π [GeV/c ]
21 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Why do we need even larger data sets? − − − + Example: π + p → π π π + precoil
×103 ) 2 25 ++ +
c 1 0 f (980) π P 0 0.1 < t' < 1.0 (GeV/c)2 20 (1) Model curve Improved sensitivity for small (2) a1(1420) resonance signals (3) Non-resonant term 15 E.g. surprising find: (2) resonance-like a1(1420) signal in peculiar decay Intensity / (20 MeV/ 10 mode (1) Only 0.3 % of total 5 intensity (3) 0 1 1.2 1.4 1.6 1.8 2 2.2 2 m3π [GeV/c ]
COMPASS, PRL 115 (2015) 082001
22 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam − + = + − + −
Why do we need even larger data sets? − − − + Example: π + p → π π π + precoil
Novel analysis technique 6 “freed-isobar” PWA 5 X´ ´ PC ǫ ´ πbeam [J M ] π 4 [L] + P ξ π 3 π´ Intensity 2 ptarget precoil Conventional PWA requires complete 1 knowledge of isobar amplitude 0 Novel approach: replace fixed 0.5 1.0 1.5 2.0 m − + c2 parametrization by step-like function π π [GeV/ ] Isobar amplitude determined from data ⇒ reduced model dependence E.g. amplitude of π−π+ subsystem with JPC = 0++ ⇒ f0(500) (?), f0(980), f0(1500)
23 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam − + = + − + −
Why do we need even larger data sets? − − − + Example: π + p → π π π + precoil 0 +− 0+ [ ππ ] π S 0 ++ Novel analysis technique ] 2
1/2 600 0.194 < t' < 0.326 (GeV/c) )
) 2 2 1.78 < m < 1.82 GeV/c
“freed-isobar” PWA c 3π 0.925 X´ 400 ´ PC ǫ ´ πbeam [J M ] π [L] 200 0.965 1.420 Events/(GeV/
+ ( π [
ξ ) P ´ 1.620 π T 0 1.075 Im( 1.540 ptarget precoil −200 Conventional PWA requires complete 0.995 −600 −400 −200 0 200 knowledge of isobar amplitude Re(T) [(Events/(GeV/c2))1/2] Novel approach: replace fixed COMPASS, PRD 95 (2017) 032004 parametrization by step-like function Isobar amplitude determined from data ⇒ reduced model dependence E.g. amplitude of π−π+ subsystem with JPC = 0++ ⇒ f0(500) (?), f0(980), f0(1500)
23 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Why do we need even larger data sets? − − − + Example: π + p → π π π + precoil 0 +− 0+ [ ππ ] π S 0 ++ Novel analysis technique ] 2
1/2 600 0.194 < t' < 0.326 (GeV/c) )
) 2 2 1.78 < m < 1.82 GeV/c
“freed-isobar” PWA c 3π 0.925 X´ 400 ´ PC ǫ ´ πbeam [J M ] π [L] 200 0.965 1.420 Events/(GeV/
+ ( π [
ξ ) P ´ 1.620 π T 0 1.075 Im( 1.540 ptarget precoil −200 Conventional PWA requires complete 0.995 −600 −400 −200 0 200 knowledge of isobar amplitude Re(T) [(Events/(GeV/c2))1/2] Novel approach: replace fixed COMPASS, PRD 95 (2017) 032004 parametrization by step-like function Would allow to study Isobar amplitude determined from K−π+ subsystem with data ⇒ reduced model dependence JP = 0+ in K−π+π− E.g. amplitude of π−π+ subsystem with JPC = 0++ Requires huge data ⇒ f0(500) (?), f0(980), f0(1500) samples
23 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam How to get more data?
Current parameters of h− beam Composition: 97 % π−, 2 % K−, 1 % p Intensity: 5 × 106 s−1 for approximately 10 s every 45 s Intensity of kaon component: 105 s−1
Main limiting factor: low kaon fraction in beam Need to increase intensity of kaons by at least factor 10
Possible solution RF-separated beam at M2 beam line
24 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam How to get more data?
Current parameters of h− beam Composition: 97 % π−, 2 % K−, 1 % p Intensity: 5 × 106 s−1 for approximately 10 s every 45 s Intensity of kaon component: 105 s−1
Main limiting factor: low kaon fraction in beam Need to increase intensity of kaons by at least factor 10
Possible solution RF-separated beam at M2 beam line
24 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam How to get more data?
Current parameters of h− beam Composition: 97 % π−, 2 % K−, 1 % p Intensity: 5 × 106 s−1 for approximately 10 s every 45 s Intensity of kaon component: 105 s−1
Main limiting factor: low kaon fraction in beam Need to increase intensity of kaons by at least factor 10
Possible solution RF-separated beam at M2 beam line
24 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam RF-separated Kaon Beam [See J. Bernhard’s talk on Tue]
Possible beam parameters Beam momentum . 100 GeV/c Not an issue: diffractive production depends only weakly on energy Kaon intensity 3.7 × 106 s−1 More than factor 35 increase w.r.t. conventional beam line Would correspond to 10 to 20 × 106 K−π+π− events assuming same acceptance as current experimental setup ⇒ would be ≈ 10× world data More detailed studies needed to determine beam parameters more precisely Requires major investment
25 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam RF-separated Kaon Beam [See J. Bernhard’s talk on Tue]
Possible beam parameters Beam momentum . 100 GeV/c Not an issue: diffractive production depends only weakly on energy Kaon intensity 3.7 × 106 s−1 More than factor 35 increase w.r.t. conventional beam line Would correspond to 10 to 20 × 106 K−π+π− events assuming same acceptance as current experimental setup ⇒ would be ≈ 10× world data More detailed studies needed to determine beam parameters more precisely Requires major investment
25 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Requirements for experimental Setup
Beam PID [See J. Bernhard’s talk on Tue] Upgrade of CEDAR detectors ⇒ improve rate capability and thermal stability Requires precise measurement of beam inclination with resolution < 40 µrad ⇒ silicon beam telescope
Spectrometer As uniform acceptance as possible High-precision tracking over broad kinematic range Precise measurement of vertex position Detection of target recoil particle Ensures exclusivity of measured events
26 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Requirements for experimental Setup
Beam PID [See J. Bernhard’s talk on Tue] Upgrade of CEDAR detectors ⇒ improve rate capability and thermal stability Requires precise measurement of beam inclination with resolution < 40 µrad ⇒ silicon beam telescope
Spectrometer As uniform acceptance as possible High-precision tracking over broad kinematic range Precise measurement of vertex position Detection of target recoil particle Ensures exclusivity of measured events
26 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Requirements for experimental Setup
Final-state PID Existing RICH kaon ID covers only 10 < p < 50 GeV/c More than 50 % of kaons in K−π+π− outside of acceptance
Lower beam momentum ⇒ more events in RICH acceptance Goal: extend kaon ID to increase acceptance
27 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Requirements for experimental Setup
Final-state PID Existing RICH kaon ID covers only 10 < p < 50 GeV/c More than 50 % of kaons in K−π+π− outside of acceptance
Lower beam momentum ⇒ more events in RICH acceptance Goal: extend kaon ID to increase acceptance
27 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Requirements for experimental Setup
Electromagnetic calorimeters Efficient detection of photons over broad kinematic range is essential Gives access to interesting final states: K−π0π0, K−ω, K−η(′),...
Work in progress Detailed studies of experimental setup once beam energy is fixed
28 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Requirements for experimental Setup
Electromagnetic calorimeters Efficient detection of photons over broad kinematic range is essential Gives access to interesting final states: K−π0π0, K−ω, K−η(′),...
Work in progress Detailed studies of experimental setup once beam energy is fixed
28 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Kaon Spectroscopy: Competition
Decays of τ leptons or heavy mesons Mainly BESIII, Belle II, LHCb Current data samples typically factor 10 smaller than existing COMPASS data set Mass ranges limited COMPASS: K−π+π− 3 ×10 COMPASS 2008 negative hadron beam ] - - + - 0 + − 2 K p → K π π p recoil Belle: B → J/ψK π K*(892) not acceptance corrected
30 2 220 200 25 180 160 140 20 120 100 80 15 60 Entries / 10 MeV/c 10 / Entries 40 Events / 20 [MeV/c / Events 10 preliminary 20 0 K*2(1430) 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 + 5 M(K π-) (GeV/c2)
0 Belle, PRD 83 (2011) 032005 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 - M (K π+)[GeV/c2]
29 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Kaon Spectroscopy: Competition
Decays of τ leptons or heavy mesons Mainly BESIII, Belle II, LHCb Current data samples typically factor 10 smaller than existing COMPASS data set Mass ranges limited COMPASS: K−π+π− 3 ×10 COMPASS 2008 negative hadron beam + + + − ] - - + - 2 K p → K π π p Belle: B → J/ψK π π 3.5 recoil not acceptance corrected K1(1270) K1(1400) 2 600 3 500
2.5 K2(1770) 400 2 300 200 1.5
Entries / 25.0 MeV/c 25.0 / Entries 100 Events / 10 [MeV/c / Events preliminary 1 0 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 0.5 M(K ππ ) (GeV/c2)
0 Belle, PRD 83 (2011) 032005 0.5 1 1.5 2 2.5 - M (K π+ π-)[GeV/c2]
29 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Kaon Spectroscopy: Competition
Photoproduction GlueX Phase IV proposal (Jlab) 100 × 106 KKππ events 30 × 106 KKπ events Excited kaons appear in subsystems Could be extracted using freed-isobar method More complicated compared to direct production Possible distortions due to rescattering effects More difficult to find new states
30 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Kaon Spectroscopy — Competition
Kaon beam experiments J-PARC Separated p and K− beams with 2 to 10 GeV/c and 107 K− per spill Low energy ⇒ separation between beam and target excitations difficult Various Regge-exchanges contribute ⇒ more complicated production process Experimental setup with high-precision tracking and calorimetry needed ⇒ not yet planned Neutral kaon beam at GlueX (Jlab) 0 4 −1 KL beam with 0.3 to 10 GeV/c and 10 s intensity Main focus on hyperon spectroscopy
31 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Kaon Spectroscopy — Competition
Kaon beam experiments J-PARC Separated p and K− beams with 2 to 10 GeV/c and 107 K− per spill Low energy ⇒ separation between beam and target excitations difficult Various Regge-exchanges contribute ⇒ more complicated production process Experimental setup with high-precision tracking and calorimetry needed ⇒ not yet planned Neutral kaon beam at GlueX (Jlab) 0 4 −1 KL beam with 0.3 to 10 GeV/c and 10 s intensity Main focus on hyperon spectroscopy
31 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Conclusions
Kaon spectroscopy Many kaon states require further confirmation or more precise measurement of their paramaters COMPASS has already acquired the world’s largest data sample − − + − 5 for K + p → K π π + precoil (8 × 10 events)
Future program Goal: collect 10 to 20 × 106 K−π+π− events using high-intensity RF-separated kaon beam Would exceed any existing data sample by at least factor 10 High physics potential: rewrite PDG for kaon states above 1.5 GeV/c2 (like LASS and WA03 did 30 year ago) Precision study of Kπ S-wave Requires experimental setup with uniform acceptance over wide kinematic range (including PID and calorimeters) No direct competitors
32 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam Conclusions
Kaon spectroscopy Many kaon states require further confirmation or more precise measurement of their paramaters COMPASS has already acquired the world’s largest data sample − − + − 5 for K + p → K π π + precoil (8 × 10 events)
Future program Goal: collect 10 to 20 × 106 K−π+π− events using high-intensity RF-separated kaon beam Would exceed any existing data sample by at least factor 10 High physics potential: rewrite PDG for kaon states above 1.5 GeV/c2 (like LASS and WA03 did 30 year ago) Precision study of Kπ S-wave Requires experimental setup with uniform acceptance over wide kinematic range (including PID and calorimeters) No direct competitors
32 Boris Grube, TU München Hadron Spectroscopy with Kaon Beam