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

Measurement of exotic hadrons at LHCb

Outline:

 LHCb detector & data taking  Exotic mesons  Exotic baryons  LHCb upgrade  Summary

Pavel Krokovny

• n behalf of the LHCb Collaboration

Budker INP & Novosibirsk University

14-16 February KEK Flavour Factory KEK, Tsukuba

LHCb experiment

2

• Int. J. Mod. Phys. A30

(2015) 1530022

LHCb performance

 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

Acceptance: 2 < η < 5

3 1) Commun. 208 35 -42 2) Int. J. Mod. Phys. A 30 (2015) 153022

Most of results: Run1, 3 fb-1 Search of Xbbbb, 6.3 fb-1

10 fb-1 delivered!

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B+ → X(3872)K+ X(3872) → J/ψπ+π- Expected quark content [ccuu] Internal structure is still under discussion

Exotic hadrons

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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)]

Exotic Charminium-like states

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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

Searches for exotics

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Most of them are not narrow Need amplitude analysis Use Argand diagram to prove their resonance nature Decay quite fast Pentaquark lifetime ~10-23s 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

Study of the B+→J/ψφK+ decay

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First observed by CDF in J/ψφ system, then confirmed by CMS and D0 Exotic candidate, containing no u- or d-quarks World average: M = 4147.1 ± 2.4 MeV/c2 Γ = 15.7 ± 6.3 MeV

X(4140)

Study of the B+→J/ψφK+ decay

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First observed by CDF in J/ψφ system, then confirmed by CMS and D0 Exotic candidate, containing no u- or d-quarks World average: M = 4147.1 ± 2.4 MeV/c2 Γ = 15.7 ± 6.3 MeV

X(4140)

Seen by CDF: M = 4274.4+8.4

• 6.7± 1.9 MeV/c2

Γ = 32+22

• 15± 8 MeV

CMS: M = 4313.8±5.3±7.3 MeV/c2 Γ = 38+30

• 15±16 MeV

X(4274)

Study of the B+→J/ψφK+ decay

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First observed by CDF in J/ψφ system, NOT confirmed by Belle, BaBar and LHCb

X(4140)

Study of the B+→J/ψφK+ decay

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[PRL 118 (2017) 022003] [PRD 95 (2017) 012002]

First full amplitude analysis

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

Study of the B+→J/ψφK+ decay

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[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.

Study of the B+→J/ψφK+ decay

13

[PRL 118 (2017) 022003] [PRD 95 (2017) 012002]

Adding 4 X-states:

X(4160) and DD*S cusp may also contribute, but the statistics is too low for the moment. Adding more X-states or Z → J/ψK contributions does not improve the fit.

Study of the B+→J/ψφK+ decay

14

M = 4146.5 ± 4.5 +4.6

• 2.8 MeV/c2

Γ = 83 ± 21 +21

• 14 MeV – wider than world average

JPC = 1++ with 5.7σ Rules out 0++ or 2++ D*+D*- molecular models M = 4273.3 ± 8.3 +17.2

• 3.6 MeV/c2, Γ = 56.2 ± 10.9 +8.4
• 11.1 MeV

JPC = 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/c2, Γ = 92 ± 21+21
• 20 MeV

JPC = 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/c2, Г = 120 ± 31+32
• 33 MeV

JPC = 0++ with 4.5σ

X(4140) X(4274) X(4500) X(4700)

Study of the B+→J/ψK+p- decay

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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. [arXiv:1901.05745] Submitted to PRL

Study of the B+→J/ψK+p- decay

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The data reject the K*-only hypothesis with a large significance. The observation of exotic contributions in a model- independent way. [arXiv:1901.05745] Submitted to PRL M(J/ψπ−) versus M(K+π−) plane suggests structures near M(J/ψπ−)=4200 MeV/c2 and 4600 MeV/c2.

Search for beautiful tetraquarks

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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/c2 below ηbηb threshold → decay to Υl+l- (l = e, μ) Expected σ×Br(Υl+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/c2 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

Search for beautiful tetraquarks

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Events selected with cut-based selection. J/ψ veto for muons in m(μ+μ-) in [3050;3150] MeV/c2 Y(1S) yields after the selection (±2.5σ region): ~ 6×106 signal events for combined sample. No significant excess is seen in data Upper limits are set for Fiducial region pT < 30 GeV/c2 2.0 < y < 4.5

JHEP 10 (2018) 086

Search for beautiful tetraquarks

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Likelihood profile as a function of S is integrated to determine upper limits

JHEP 10 (2018) 086

Pentaquarks

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[PRL 115, 072001 (2015)]

2015 – first observation of two resonances consistent with pentaquark states Pc(4380)+ 9σ significance M = 4380 ± 8 ± 29 MeV/c2 Г = 205 ± 18 ± 86 MeV Pc(4450)+ 12σ significance M = 4450 ± 2 ± 3 MeV/c2 Г = 39 ± 5 ± 19 MeV Possible JP 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)]

Study of the Λb→J/ψpπ decay

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Need confirmations in other decays

[PRL117, 082003 (2016)]

Similar strategy: 6D amplitude fit to the data Λb→J/ψpπ Cabbibo-suppressed analog of Λb→J/ψpK Expect N* states in m(pπ-) Expect Pc

+ in m(J/ψp)

Expect Zc(4200)- in m(J/ψπ-) [PRD90 (2014) 112009]

Study of the Λb→J/ψpπ decay

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Conventional states and non-resonant: Exotic states: Pc(4380)+, Pc(4450)+ with masses and widths fixed to the previously measured values JP fixed to the previously measured “best fit” (3/2-, 5/2+) Zc(4200)- with JP = 1+

[PRL117, 082003 (2016)]

Study of the Λb→J/ψpπ decay

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[PRL117, 082003 (2016)]

Combined statistical significance of three states is 3.1σ Individual significance of each contribution is low, if others are included Zc-only hypothesis (no pentaquarks) Zc significance 3.2σ Fit fraction increases almost twice, up to (17.2 ± 3.5)% Too large, given the fraction in the B0→J/ψK+π- ~2% [PRD90 (2014) 112009] Pc

+'s-only hypothesis (no Zc

• )

Combined significance of two pentaquarks is 3.3σ Fit fraction remains stable Measured ratios of branching fractions

Interpretations

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Tightly bound state? [PLB 749 289 (2015)] Hadronic molecule? [PRL 115 122001 (2015)] Rescattering effect? [PRD 92 071502 (2015)] χc1p → J/ψp Can explain the phase motionPc

+

won't be seen in the χc1p final state

Observation of Λb→χc1,2pK decays

25

[PRL 119, 062001 (2017)]

Search for Λb

0→χc1,2pK, χc1,2→J//ψγ

Normalize by Λb

0→ J/ψpK

Mass constrained fit to χc1 Λb

0→χc1pK: 453 ± 25 signal events

29σ significance Λb

0→χc2pK: 285 ± 23 signal events

17σ significance

2 first observations!

To few for the amplitude analysis yet Can measure the branching fractions:

Observation of Ξb → J/ψpK decay

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[PLB 772 (2017) 265-273] Decay similar to Λb

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 Λb

0 → J/ψΛ channel

Amplitude analysis expected using whole Run 2 dataset.

Search for weakly decaying b-flavoured pentaquarks

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[PRD97 (2018) 032010] The heavier the constituent quarks, the more tightly bound the pentaquark states [ Proc. Roy. Soc. Lond. A260 (1961) 127], [Phys. Lett. B590 (2004) 185] [Phys. Lett. B586 (2004) 337], [Phys. Lett. B331(1994) 362] No experimental searches have been published before

Subscript: dominant strong decay modes for the state, if its mass above the threshold Search mass windows: below the strong decay threshold Simultaneous search for four different states:

Search for weakly decaying b-flavoured pentaquarks

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[PRD97 (2018) 032010] No significant narrow structures are observed. Upper limits are set. Invariant mass distributions after the selection

Blinded analysis Event selection: Loose cut preselection Boosted-decision tree MC for BDT training and efficiencies calculations 4 different masses for P+ P+ lifetime set to 1.5 ps Phase-space assumption for P+ decays Total efficiencies 0.5-1.4% depending on the mode A narrow signal is expected with resolution

• f 5.2 – 6.0 MeV/c2

Search for weakly decaying b-flavoured pentaquarks

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[PRD97 (2018) 032010] 90% upper limits are set for the ratio using [Chin. Phys. C40 (2016) 011001] Fiducial region pT < 20 GeV/c2 2.0 < y < 4.5 Averaged between 7 and 8 TeV samples

LHCb upgrade

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LHCb upgrade

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LHCb upgrade

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LHCb upgrade II

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Major detector upgrade in LS4 (2030)

• Expression of Interest [CERN-LHCC-2017-003]
• Aim to run at 10 x Upgrade I luminosity and collect 300 fb-1
• Challenging conditions for flavour physics (number of visible interactions ~50)
• Physics case document: CERN-LHCC-2018-027
• LHCb may be the only large-scale flavour physics experiment to run in HL-LHC era

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Conclusion

LHCb has finished Run 2 data taking. 10 fb-1 has been collected. The exotic studies sector is rapidly developing. Many new states

confirmed/unconfirmed/waiting for confirmation. Still a large area for studies both from experimental and theoretical sides.

Preparation for LHCb Upgrade I proceeding well. Looking forward to new exciting exotic results!

35

Backup

Observation of five narrow Wc

0 states

36 PRL 118 (2017) 182001 Dataset: 1.0 fb-1 @ √s=7 TeV 2.0 fb-1 @ √s=8 TeV 0.3 fb-1 @ √s=13TeV

➢ Wc

0 family corresponds to css quark content

➢ Two ground states were known: Wc

0 JP=1+ and Wc 0(2770) JP=3/2+ [PLB 672 (2009) 1]

➢ Study spectrum of [Xc

+ → pK-p+]K+

➢ Spin-parity analysis is in progress

Wc

0 states properties

37 PRL 118 (2017) 182001

Four states have been confirmed by Belle [PRD 97 (2018) 051102]

Study of doubly charmed baryon Xcc

++

38 Dataset: 1.0 fb-1 @ √s=7 TeV 2.0 fb-1 @ √s=8 TeV 1.7 fb-1 @ √s=13TeV

➢ Using decay Xcc

++→Lc +K-p+p+

➢ DM = 1334.94 ± 0.72 ± 0.27 MeV/c2 ➢ M(Xcc

++)= 3621.40 ± 0.72 ± 0.27 ± 0.14 MeV/c2

PRL 119 (2017) 112001 PRL 121 (2018) 052002

Measurement of Xcc

++ lifetime

39 Dataset: 1.0 fb-1 @ √s=7 TeV 2.0 fb-1 @ √s=8 TeV 1.7 fb-1 @ √s=13TeV

➢ Decay time relative to Lb

0[Lc +p-p+p-]

➢ Decay time resolution is 63 (32) ps for Xcc

++ (Lb 0)

PRL 121 (2018) 052002

Confirmation of weak decay of Xcc

+ +

First observation of decay Xcc

++→ Xc +p-

40 Dataset: 1.0 fb-1 @ √s=7 TeV 2.0 fb-1 @ √s=8 TeV 1.7 fb-1 @ √s=13TeV PRL 121 (2018) 162002

Observation of Xb

• 41

Dataset: 1.0 fb-1 @ √s=7 TeV 2.0 fb-1 @ √s=8 TeV 1.5 fb-1 @ √s=13TeV

Hadronic channel Xb(6227)−→[Λb

0→Λc + p−]K−

M[Xb(6227)−] = 6226.9 ± 2.0 ± 0.3 ± 0.2 MeV/c2 Γ[Xb(6227)−] = 18.1 ± 5.4 ± 1.8 MeV

PRL 121 (2018) 072002

Observation of Xb

• 42

Dataset: 1.0 fb-1 @ √s=7 TeV 2.0 fb-1 @ √s=8 TeV 1.5 fb-1 @ √s=13TeV PRL 121 (2018) 072002

Semileptonic channels: Xb(6227)−→[Λb

0→Λc + m−X]K− and [Xb→Xc +m−X]p−

Larger samples (about 25s significance) but with missing mass. Relative production rates are

• reported. Consistent with strong decay of radially or orbitally excited state (1P Xb).

Measurement of Wc

0 lifetime

43 Dataset: 1.0 fb-1 @ √s=7 TeV 2.0 fb-1 @ √s=8 TeV

➢ Useful for testing higher order effects in heavy quark expansion (HQE) ➢ Using Ωc

0 →pK-π+π- decays obtained from Ωb

• → Ωc

0 m-nX

➢ B+→ D+ m-nX decays used as a normalization channel

PRL 121 (2018) 092003 PRL 121 (2018) 092003

Study Lb

0p± system

44 Dataset: 1.0 fb-1 @ √s=7 TeV 2.0 fb-1 @ √s=8 TeV

➢ Study of the Λb

0π± system using

Λb

0[→Λc +π-] baryons combined with a

prompt pion with pT(p) > 200 MeV/c

➢ Q = m(Λb

0π±)-m(Λb 0)-m(π±) < 200 MeV/c2

➢ Measurement of Σ± and Σ*± baryon

properties with ~5 times improved precision in comparison with CDF results

arXiv:1809.07752

Observation of two new resonances in Lb

0p±

45 Dataset: 1.0 fb-1 @ √s=7 TeV 2.0 fb-1 @ √s=8 TeV

➢ Extend study to region with Q < 600 MeV/c2 ➢ pT(p)> 1000 MeV/c used to suppress combinatorial background ➢ Peaks with local significance more than 12σ have been observed

arXiv:1809.07752

Search for X(5568)

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➢ Reported by D0: X(5568)→BSp+ with 4.8s significance. M=5568±3 MeV, G=22±7

MeV/c