Measurement of exotic hadrons at LHCb Pavel Krokovny on behalf of - PowerPoint PPT Presentation

Measurement of exotic hadrons at LHCb Pavel Krokovny on behalf of the LHCb Collaboration Budker INP & Novosibirsk University Outline:  LHCb detector & data taking  Exotic mesons  Exotic baryons  LHCb upgrade  Summary 14-16 February KEK Flavour Factory KEK, Tsukuba

LHCb experiment Int. J. Mod. Phys. A30 (2015) 1530022 2

LHCb performance Acceptance: 2 < η < 5  Momentum resolution: 0.4 – 0.6% at 5 – 100 GeV  Muon ID efficiency: 97 % with 1-3 % π→μ mis-ID probability  Electron ID efficiency: 90% with 4% h→e mis-ID probability  Kaon ID efficiency: 95% with 5 % π→K mis-ID probability Search of Xbbbb, 6.3 fb -1 Most of results: Run1, 3 fb -1 1) Commun. 208 35 -42 2) Int. J. Mod. Phys. A 30 (2015) 153022 3

10 fb -1 delivered! 4

Exotic hadrons Exotic hadrons – everything beyond qq-meson and qqq-baryon scheme Could be various multiquark states, hadron molecules, glueballs, hybrids... First predicted in 1964 the original papers by M.Gell-Mann and G.Zweig [CERN-TH-412, Phys.Lett. 8 (1964) 214] First seen by Belle in 2003 [Phys. Rev. Lett. 91, 262001 (2003)] B + → X(3872)K + X(3872) → J/ψπ + π - Expected quark content [ccuu] Internal structure is still under discussion 5

Exotic Charminium-like states X – neutral, positive parity, first seen in B-mesons decays. Y – neutral, negative parity, first seen in e + e - annihilation with ISR. Z – charged (and their isospin partners) P – pentaquarks (No clear pattern seen yet) Lots of predictions within difgerent theoretical models Search for a new exotic hadrons and determine their properties 6

Searches for exotics Most of them are not narrow Need amplitude analysis Use Argand diagram to prove their resonance nature Decay quite fast Pentaquark lifetime ~10 -23 s Decays of b-hadrons Inclusive decays: good understanding of the initial state Relatively long lifetime Decays with charmonium provide a clear signature Direct production Access to high mass region 7

Study of the B + →J/ψφK + decay First observed by CDF in J/ψφ system, then confirmed by CMS and D0 X(4140) Exotic candidate, containing no u- or d-quarks World average: M = 4147.1 ± 2.4 MeV/c 2 Γ = 15.7 ± 6.3 MeV 8

Study of the B + →J/ψφK + decay First observed by CDF in J/ψφ system, then confirmed by CMS and D0 X(4140) Exotic candidate, containing no u- or d-quarks World average: M = 4147.1 ± 2.4 MeV/c 2 Γ = 15.7 ± 6.3 MeV Seen by X(4274) CDF: M = 4274.4 +8.4 -6.7 ± 1.9 MeV/c 2 Γ = 32 +22 -15 ± 8 MeV CMS: M = 4313.8±5.3±7.3 MeV/c 2 Γ = 38 +30 -15 ±16 MeV 9

Study of the B + →J/ψφK + decay First observed by CDF in J/ψφ system, NOT confirmed by Belle, BaBar and LHCb X(4140) 10

Study of the B + →J/ψφK + decay [PRL 118 (2017) 022003] First full amplitude analysis [PRD 95 (2017) 012002] 6D amplitude analysis: m(φΚ) 3 helicity angles: θΚ*,θJ/ψ,θφ 2 angles between decay planes: ΔφJ/ψ,Δφφ First fit with K* states only Then adding exotic states: X → J/ψφ Z → J/ψK 11

Study of the B + →J/ψφK + decay [PRL 118 (2017) 022003] [PRD 95 (2017) 012002] K* states decaying to Kφ are well established by now. Using theoretical predictions by Godfrey-Isgur. J/ψK and φK are well described by the model. 12

Study of the B + →J/ψφK + decay [PRL 118 (2017) 022003] Adding 4 X-states: [PRD 95 (2017) 012002] X(4160) and DD* S cusp may also contribute, but the statistics is too low for the moment. 13 Adding more X-states or Z → J/ψK contributions does not improve the fit.

Study of the B + →J/ψφK + decay M = 4146.5 ± 4.5 +4.6 -2.8 MeV/c 2 X(4140) Γ = 83 ± 21 +21 -14 MeV – wider than world average J PC = 1 ++ with 5.7σ Rules out 0 ++ or 2 ++ D* + D* - molecular models X(4274) M = 4273.3 ± 8.3 +17.2 -3.6 MeV/c 2 , Γ = 56.2 ± 10.9 +8.4 -11.1 MeV J PC = 1 ++ with 5.8σ Not a molecular bound state or cusp. Hybrid charmonium state would have 1 -+ . Tetraquarks? Lebed-Polosa: 1 ++ X(4140), but 0 -+ X(4274) [Phys. Rev. D93 (2016) 094024] Anisovich et al: only one 1 ++ state [Int. J. Mod. Phys. A30 (2015) 1550186] Stancu model: 1 ++ X(4140) and 1 ++ state slightly higher than X(4274) [J. Phys.G37 075017] M = 4506 ± 11 +12 -15 MeV/c 2 , Γ = 92 ± 21 +21 -20 MeV X(4500) J PC = 0 ++ with 4.0σ Wang et al predicted virtual 0 ++ D*+D*- state at 4.48 ± 0.17 GeV [Eur. Phys. J. C64 (2009) 373] M = 4704 ± 10 +14 -24 MeV/c 2 , Г = 120 ± 31 +32 -33 MeV X(4700) J PC = 0 ++ with 4.5σ 14

Study of the B + →J/ψK + p - decay [arXiv:1901.05745] Submitted to PRL The M(K + π − ) spectrum is divided into fine bins. In each M(K + π − ) bin, the three-dimensional angular distribution is described by structures induced only by K* resonances, w/o assumptions about the K + π − system. 15

Study of the B + →J/ψK + p - decay [arXiv:1901.05745] Submitted to PRL The data reject the K*-only hypothesis with a large significance. The observation of exotic contributions in a model- independent way. M(J/ψπ − ) versus M(K + π − ) plane suggests structures near M(J/ψπ − )=4200 MeV/c 2 and 4600 MeV/c 2 . 16

Search for beautiful tetraquarks JHEP 10 (2018) 086 No hadron containing more than two heavy quarks has been observed so far Xbbbb Theoretical predictions Mass within [18.4; 18.8] GeV/c 2 below η b η b threshold → decay to Υ l + l - (l = e, μ) Expected σ×Br( Υ l + l - ) ~1fb at the LHC energies Lattice QCD calculations do not find any evidence of this state Search for Xbbbb → Y(1S)μ + μ - with Y(1S) → μ + μ - Wide 4μ invariant mass range [17.5; 20.0] GeV/c 2 Use Run I and Run II data: 1.0 fb-1 @ 7 TeV 2.0 fb-1 @ 8 TeV 3.3 fb-1 @ 13 TeV 17

Search for beautiful tetraquarks Events selected with cut-based selection. J/ψ veto for muons in m(μ + μ - ) in [3050;3150] MeV/c 2 Y(1S) yields after the selection (±2.5σ region): ~ 6×10 6 signal events for combined sample. No significant excess is seen in data Upper limits are set for Fiducial region p T < 30 GeV/c2 2.0 < y < 4.5 JHEP 10 (2018) 086 18

Search for beautiful tetraquarks JHEP 10 (2018) 086 Likelihood profile as a function of S is integrated to determine upper limits 19

Pentaquarks [PRL 115, 072001 (2015)] 2015 – first observation of two resonances consistent with pentaquark states P c (4380) + 9σ significance M = 4380 ± 8 ± 29 MeV/c 2 Г = 205 ± 18 ± 86 MeV P c (4450) + 12σ significance M = 4450 ± 2 ± 3 MeV/c 2 Г = 39 ± 5 ± 19 MeV Possible J P combinations: Best fit (3/2 - , 5/2 + ) Satisfactory fits (3/2 + , 5/2 + ) or (5/2 + , 3/2 + ) Check their resonance nature with Argand diagram Cross-check with the help of model-independend analysis – supports the observation [PRL 117, 082002 (2016)] 20

Study of the Λ b →J/ψpπ decay [PRL117, 082003 (2016)] Need confirmations in other decays Similar strategy: 6D amplitude fit to the data Λ b →J/ψpπ Cabbibo-suppressed analog of Λ b →J/ψpK Expect N* states in m(pπ - ) Expect P c + in m(J/ψp) Expect Z c (4200) - in m(J/ψπ - ) [PRD90 (2014) 112009] 21

Study of the Λ b →J/ψpπ decay Conventional states and non-resonant: Exotic states: P c (4380) + , P c (4450) + with masses and widths fixed to the previously measured values J P fixed to the previously measured “best fit” (3/2 - , 5/2 + ) Z c (4200) - with J P = 1 + 22 [PRL117, 082003 (2016)]

Study of the Λ b →J/ψpπ decay [PRL117, 082003 (2016)] Combined statistical significance of three states is 3.1σ Individual significance of each contribution is low, if others are included Z c -only hypothesis (no pentaquarks) Z c significance 3.2σ Fit fraction increases almost twice, up to (17.2 ± 3.5)% Too large, given the fraction in the B 0 →J/ψK + π - ~2% [PRD90 (2014) 112009] P c + 's-only hypothesis (no Z c - ) Combined significance of two pentaquarks is 3.3σ Fit fraction remains stable Measured ratios of branching fractions 23

Interpretations Tightly bound state? [PLB 749 289 (2015)] Hadronic molecule? [PRL 115 122001 (2015)] Rescattering effect? [PRD 92 071502 (2015)] χ c1 p → J/ψp Can explain the phase motionP c + won't be seen in the χ c1 p final state 24

Observation of Λb→χ c1,2 pK decays [PRL 119, 062001 (2017)] Search for Λ b 0 →χ c1,2 pK, χ c1,2 →J//ψγ Normalize by Λ b 0 → J/ψpK 2 first observations! Mass constrained fit to χ c1 Λ b 0 →χ c1 pK: 453 ± 25 signal events 29σ significance Λ b 0 →χ c2 pK: 285 ± 23 signal events 17σ significance To few for the amplitude analysis yet Can measure the branching fractions: 25

Observation of Ξ b → J/ψpK decay [PLB 772 (2017) 265-273] Decay similar to Λ b 0 → J/ψpK Search for a hidden-charm pentaquark with open strangeness: [sccud] Total signal yield ~300 events Signal significance 21σ Branching fraction is measured through normalization by Λ b 0 → J/ψΛ channel Amplitude analysis expected using whole Run 2 dataset. 26