Search for new decays of the π²π² ππ baryon at the LHCb...
Transcript of Search for new decays of the π²π² ππ baryon at the LHCb...
The XXIV International WorkshopHigh Energy Physics and Quantum Field Theory
22 β 29 September, Sochi, Russia
Search for new decays of the π²π²ππππ baryon at the LHCb experiment
Pereima Dmitriion behalf of the LHCb collaboration
Institute for Theoretical and Experimental Physics, NRC Β«Kurchatov InstituteΒ», Moscow, Russia
This work is supported by grant of Russian Foundation for Basic Research β 19-32-90086
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Outline
β’The LHCb detector
β’New decays of the π²π²ππππ baryons:
β’Observation of the decay Ξb0 β Ξc+ pοΏ½pΟβ
β’Observation of the decays Ξb0 β J/ΟΞ and Ξb
0 β Ο(2S)Ξ
β’Observation of the Ξb0 β Ο 2S pΟβ decay
β’Observation of the Ξb0 β Οc1 3872 pKβ decay
β’Observation of the Ξb0 β ΞΞ³
β’Observation of a new Ξb0 resonances in the Ξb
0Ο+Οβ systems
β’Summary
See also other LHCb news in talks from: V. Shevchenko, V.Matiunin, E.Kurbatov and P. Krokovny
β [integrated lumi ~3fb-1, π π = 7, 8 TeV]
β [integrated lumi ~3fb-1 , π π = 7, 8 TeV]
β [integrated lumi ~5fb-1 , π π = 7, 8, 13 TeV]
β [integrated lumi ~5fb-1 , π π = 7, 8, 13 TeV]
β [integrated lumi ~1.7fb-1 , π π = 13 TeV]
β [integrated lumi ~9fb-1 , π π = 7, 8, 13 TeV]
The LHCb detector
Main subsystems:β’ VErtex LOcator VELO: for precise measurements of vertices
position, lifetime and impact parameter resolutions;β’ Tracking stations TT, T1-T3 and dipole magnet: provides
measurement of high momentum resolution of charged particlesβ’ Identification system (RICHβs, calorimeters): K/p/Ο separation,
trigger on high pT hadrons, ππΒ±,ππ energy reconstructionβ’ Muon system (M1 β M5): tracking stations for muon identification
p p
JINST 3 (2008) S08005Int. J. Mod. Phys. A 30 (2015) 1530022 Total integrated lumi ~9 fb-1
~40% of all produced πποΏ½Μ οΏ½π and πποΏ½Μ οΏ½π pairs are in acceptance
[see details in plenary talk from V. Shevchenko]
Allow to study all kinds of beauty baryons
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Analysis strategy
β’ Detached vertex method (keep only long-lived candidates)
β’ Further selection to suppress background: kinematics, particle identification, multivariateanalysis
Primary vertex (PV)
p p
Impactparameter
Secondary vertex
Β΅+
Β΅β
J/Ο
Οβ
p
Ξb0 β J/ΟΞ[β pΟβ]
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Observation of the decay π²π²ππππ β π²π²ππ+ π©π©οΏ½π©π©ππβ
Decay scheme of the signal channel:
Normalization channel:Ξb0 β Ξc+ Οβ
Motivation:Search for dibaryon ππc+ = cd ud ud with mass m(ππc+) < 4682 MeV/c2 could manifest Ξb
0 β οΏ½pππc+, where: 1) ππc+ β pΞ£c02) ππc+ β pπ«π«c0[β Ξc+ Οβ]
π«π«c0 is a possible pentaquark state Theory: Phys. Lett. B 750 (2015) 37.
First! Ξb0 decay with three baryons in the final state
Observation of the decay π²π²ππππ β π²π²ππ+ π©π©οΏ½π©π©ππβ
The mass spectra of the Ξc+ pΟβ final state is also inspected for possible dibaryon resonances, but no evidence of peaking structures is seen. 6
Normalization Ξb0 β Ξc+ ΟβSignal Ξb
0 β Ξc+ pοΏ½pΟβ (NEW!)
s = 7, 8 TeVN = 926 Β± 43
s = 7, 8 TeVN = (167.00 Β± 0.50)Γ 103
LHCb: Phys. Lett. B 784 (2018) 101
NΞ£cβ0 = 104 Β± 17NΞ£c0 = 59 Β± 10
Contributions from Ξ£c(2455)0and Ξ£c(2520)0 resonances are observed:
Relative branching fraction ratio:
Dominant systematics: modelling of hadron interaction with the detector material
Observation of the decays π²π²ππππ β ππ/πππ²π² and π²π²ππ
ππ β ππ(ππππ)π²π²
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Motivation:Ratios of branching fractions of b-hadrons decays into [cοΏ½c]+X provide useful information on the productionof charmonia in b-hadron decays. These ratios can be used to test factorization of amplitudes.
Previous ATLAS measurements:ATLAS: Phys. Lett. B 751 (2015) 63
differs by 2.8Ο from a theoretical prediction:
Theory: Phys. Rev. D 88 (2013) 114018Theory: Phys. Rev. D 92 (2015) 114008
A measurement with improved precision helps to better understand this possible discrepancy
In both channels Ξ hyperon is reconstructed using pΟβ final state. The ratio of branching fractions isdetermined separately for long- and downstream-track candidates and then combined into weightedaverage value.
Observation of the decays π²π²ππππ β ππ/πππ²π² and π²π²ππ
ππ β ππ(ππππ)π²π²
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Weighted average value of branching fraction ratio:
N = (280 Β± 18) Γ 103
N = (223 Β± 13) Γ 103 N = (3320 Β± 50) Γ 103
N = (3980 Β± 80) Γ 103
The measurement is compatible within 1Ο with ATLAS result and has a better precision. It confirms the discrepancy with the covariant quark model theory predictions
LHCb: JHEP 03 (2019) 126
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Observation of the π²π²ππππ β ππ ππππ π©π©ππβ decay
Motivation:The decay Ξb
0 β Ο 2S pΟβ decay is of particular interest due to possible contributions from exotic states inboth the Ο 2S p and Ο 2S Οβsystems, similar to the Pc(4380)+ and Pc(4450)+ pentaquark states and tothe charmonium-like state Zc(4430)β, respectively.
LHCb: JHEP 08 (2018) 131
NEW!
N = 121 Β± 13SΟ > 9Ο
N = 806 Β± 29
Branching fraction ratio Absolute branching fraction
no evident peaking structure in the Ο 2S p and Ο 2S Οβsystems
Observation of the π²π²ππππ β ππππππ ππππππππ π©π©ππβ decay
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The Οc1(3872) state (a.k.a X(3872)) was discovered by the Belle collaboration at KEK in 2003 andsubsequently confirmed by several other experiments (BaBar, CDF, D0, LHCb, ATLAS, CMS).
BΒ± β Οc1(3872)KΒ±, Οc1(3872) β J/ΟΟ+ΟβBelle: Phys. Rev. Lett. 91 (2003) 262001
Belle
Quantum numbers JPC = 1++, mass M(ππππππ(ππππππππ)) = 3871.69 Β± 0.17 MeV/c2 [PDG] and dipion mass spectrumare measured. Despite significant experimental information the nature of the state is still uncertain.
Possible interpretations: ππππππ ππππ charomonium state, tetraquark, β¦ and their mixtures. The LHCb studiesof radiative Οc1(3872)β Ο(2S)Ξ³ decays provide constraints to the interpretations of this state.
LHCb: Nucl. Phys. B (2014) 886
Motivation:Several decays of the Ξb
0 baryon to charmonium have been observed. This analysis is the first observation of the Οc1(3872) state in beauty baryon decays.
Observation of the π²π²ππππ β ππππππ ππππππππ π©π©ππβ decay
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Signal Ξb0 β Οc1 3872 pKβ, Οc1(3872) β J/ΟΟ+Οβ(NEW!)
N = 55 Β± 11SΟ = 7.2Ο
Normalization Ξb0 β Ο(2S)pKβ,Ο(2S) β J/ΟΟ+Οβ
N = 610 Β± 30
Relative branching fraction ratio:
Result is compatible with similar studies in B-meson decays
LHCb: JHEP 09 (2019) 028
Observation of the π²π²ππππ β π²π²ππ
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Signal: Ξb0 β Ξ[β pΟβ]Ξ³
N = 65 Β± 13SΟ = 5.6Ο
Normalization: B0 β Kβ0[β K+Οβ]Ξ³
N = 32670 Β± 290
Measured branching fraction is found to be:
In agreement with theoretical predictions: Theory: Eur. Phys. J. C 59 (2009) 861Theory: JHEP 12 (2011) 067
Motivation:1) The decay Ξb
0 β Ξ[β pΟβ]Ξ³ proceeds via the b β sΞ³ flavor-changing neutral-current transition. Thisprocess is sensitive to new particles, which can modify decay properties.
2) First observation of the radiative b-baryon decay
LHCb: Phys. Rev. Lett. 123 (2019) 031801
Observation of a new π²π²ππππ resonances in the π²π²ππ
ππππ+ππβ systems
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LHCb: Phys. Rev. Lett. 109 (2012) 172003 CDF: Phys. Rev. D 88 (2013) 071101(R)
CDF
Analysis strategy:β’ Adding Ο+Οβ pair to the reconstructed Ξb
0 to probe excitationsβ’ Ξb
0 candidates are reconstructed in π²π²ππππ β π²π²ππ+ ππβ and π²π²ππππ β ππ/πππ©π©ππβ
β’ Check structures near (above) 6.1 GeV/c2
β’ Investigate substructure of decays: X β Ξb0 Ο+Οβ
Ξ£b(β)
Motivation:The spectrum of excited states decaying to the Ξb
0Ο+Οβ final state has already been studied by the LHCbexperiment with the discovery of two narrow states, denoted Ξb
0 (5912) and Ξb0 (5920) (Confirmed by CDF).
In addition to the already observed doublet of first orbital excitations, more states in the mass region near6.1 GeV/c2 (or above) are expected.
Observation of a new π²π²ππππ resonances in the π²π²ππ
ππππ+ππβ systems
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LHCb: arXiv:1907.13598Two NEW narrow states π²π²ππππ (6146) and π²π²ππππ (6152) are found:
N (Ξb0 (6146)) = 67 Β± 40N (Ξb0 (6152)) = 357 Β± 52
N (Ξb0 (6146)) = 460 Β± 92N (Ξb0 (6152)) = 305 Β± 70
N (Ξb0 (6146)) = 624 Β± 136N (Ξb0 (6152)) = 510 Β± 109
β
M(Ξb0 (6146)) = 6146.17 Β± 0.33 Β± 0.22 Β± 0.16 MeV/c2
Π(Ξb0 (6146)) = 2.9 Β± 1.3 Β± 0.3 MeV
M(Ξb0 (6152)) = 6151.51 Β± 0.26 Β± 0.22 Β± 0.16 MeV/c2
Π(Ξb0 (6152)) = 2.1 Β± 0.8 Β± 0.3 MeV
The measured masses and widths of these new excited states suggesttheir possible interpretation as a doublet of Ξb
0 (1D) states and areconsistent with predictions.Theory: Phys. Rev. D 34 (1986) 2809, Phys. Rev. Lett. 66 (1991) 1130, Eur. Phys. J. A (2015) 51: 82
Summary
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β’ Using data collected by the LHCb experiment during Run 1 (2011 - 2012) and Run 2 (2015 - 2018) numberof new decays of the Ξb
0 baryons were observed:
β’ Ξb0 β Ξc+ pοΏ½pΟβ, Ξb
0 β J/ΟΞ, Ξb0 β Ο(2S)Ξ, Ξb
0 β Ο 2S pΟβ, Ξb0 β Οc1 3872 pKβ and Ξb
0 β ΞΞ³
β’ The existence of the Οc1 3872 state in beauty baryon decays was confirmed
β’ First observation of radiative b-baryon decay was done
β’ New Ξb0 resonances Ξb
0 (6146) and Ξb0 (6152) were observed in the Ξb
0Ο+Οβ systems
β’ Looking forward for new results!
The LHCb experiment provides a significant contribution to the knowledge of b-baryon spectroscopy
Stay tuned with the news from LHCb!
Thank you for attention!
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Backup #1
π²π²ππππ baryon quantum transitions