Exotic Hadron States at Lhcb Daria Savrina (ITEP & SINP MSU) on Behalf of the Lhcb Collaboration
Gatchina, Russia, August 6 – 10, 2018 Hadron Structure and QCD
Exotic hadron states at LHCb Daria Savrina (ITEP & SINP MSU) on behalf of the LHCb collaboration
Outline
Why exotic hadrons?
Exotic mesons study of the B+ → J/ψφK+ decay search for beautyfull tetraquarks
Exotic baryons 0 - search in Λb → J/ψpπ steps towards future studies search for b-flavoured pentaquarks
2/30 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 3/30 Exotic zoo „Charmonium-like“ states Not a very strict naming scheme X – neutral, first seen in B-mesons decays, positive parity Y – neutral, first seen in ee annihilation with initial state radiation, negative parity Z – charged (and their isospin partners) P – pentaquarks No clear pattern seen yet [S.Olsen,T.Skwarnicki, D.Zieminska, arXiv:1708.04012]
Lots of predictions within different theoretical models Meson Hadro- Quarkonium Tightly bound Diquark-onium tetraquarks molecules quarkonium adjoint meson q q q q q q q q q q q q q q q q q q q q
Would like not only to find new exotic hadrons, but also determine their quantum numbers 4/30 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 ~10-23s
Decays of b-hadrons Inclusive decays: good understanding of the initial state Relatively long lifetime Decays with charmonium provide a clear signature
Direct production B Access to high mass region ~ 1 cm
5/30 The LHCb experiment [JINST 3 (2008) S08005] LHC: Cross-sections in the LHCb acceptance:
σpp→bb = 72.0±0.3±6.8 µb @√s = 7TeV
σpp→bb =144 ±1 ±21 µb @√s =13TeV [Phys. Rev. Lett. 118, 052002 (2017)]
Access to all possible b-hadrons 0 0 0 B :Λ b:B s ~ 4:2:1 [JHEP08 (2014) 143]
Fully instrumented rapidity range 2 < η < 5: ~40% of b quarks produced hit the detector acceptance VELO: Decay time resolution ~45fs Impact parameter resolution: (15 +29/pT[GeV] ) μm Relative track momentum resolution: 0.5% at low momentum 1.0% at 200 GeV/c
Particle identification: Details are given in the talk by Vitaly Vorobyev Kaon ID ~95 % for ~ 5 % π→K mis-id probability Muon ID ~97 % for 1-3 % π→μ mis-id probability
Muon system: ~90% trigger efficiency for dimuon channels 6/30 The LHCb experiment
8fb-1 of data collected so far
Search for beautiful tetraquarks 6.3fb-1 of pp data
Most of the results in this talk: Run 1, 3fb-1 of pp data
7/30 Exotic mesons
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/c2 Γ = 15.7 ± 6.3 MeV/c2 [Phys. Rev. Lett. 102 (2009) 242002] [Phys. Lett. B734 (2014) 26]
CDF CDF
[Mod. Phys. Lett. A, Vol. 32, No. 26 (2017) 1750139] [Phys. Rev. D 89, 012004 (2014)] Not included in the average
CDF CDF
9/30 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/c2 Γ = 15.7 ± 6.3 MeV/c2 [Phys. Lett. B734 (2014) 26] Seen by CDF and CMS +8.4 2 X(4274) CDF: M = 4274.4 - 6.7 ± 1.9 MeV/c +22 2 Γ = 32.0 - 15 ± 8 MeV/c CMS:M = 4313.8 ± 5.3 ± 7.3 MeV/c2 +30 2 Γ = 38.0 - 15 ± 16 MeV/c
[Mod. Phys. Lett. A, Vol. 32, No. 26 (2017) 1750139]
CDF CDF
10/30 Study of the B+ → J/ψφK+ decay First observed by CDF in J/ψφ system, not confirmed by Belle, BaBar X(4140) and LHCb [Conf. Proc. C0908171 (2009) 299] Unpublished Belle [Phys. Rev. D85, 091103(R) (2012)]
0.37 fb-1
[Phys.Rev.Lett. 115 (2015) 23, 232001] BaBar
11/30 Study of the B+ → J/ψφK+ decay [PRL 118 (2017) 022003] Given more data the first full amplitude analysis of this [PRD 95 (2017) 012002] channel has been performed
6D amplitude analysis
1 mass: mφΚ
3 helicity angles: θΚ*,θJ/ψ,θφ 2 angles between decay planes: Δφ ,Δφ Signal: 4289 ± 51 J/ψ φ Only 23% background First fit with under K* hypothesis only
Second fit including exotic states: X → J/ψφ Z → J/ψK 2σ
12/30 Study of the B+ → J/ψφK+ decay [PRL 118 (2017) 022003] [PRD 95 (2017) 012002]
Not many K* states decaying to Kφ are well established by now Use theoretical predictions by Godfrey-Isgur
K* contributions only p-value below 10-7
[Phys. Rev. D 32 (1985) 189]
Forbidden
J/ψK and φK are well described by the model 13/30 Study of the B+ → J/ψφK+ decay [PRL 118 (2017) 022003] After inclusion of 4 additional X-states [PRD 95 (2017) 012002]
p-value 22%
Χ(4140) X(4700) 8.4σ 5.6σ
X(4274) X(4500) 6.0σ 6.1σ X(4160) and DD* cusp may also contribute, but the statistics is too low for the moment s [Phys. Rev. D97, 014017 (2018)] Adding more X-states or Z → J/ψK contributions does not improve the fit any more 14/30 Study of the B+ → J/ψφK+ decay [PRL 118 (2017) 022003] +4.6 2 M = 4146.5 ± 4.5 - 2.8 MeV/c [PRD 95 (2017) 012002] +21 2 Χ(4140) Γ = 83 ± 21 -14 MeV/c – wider than world average JPC = 1++ with 5.7σ ++ ++ + - Rules out 0 or 2 D* sD* s molecular models
+17.2 2 m = 4273.3 ± 8.3 - 3.6 MeV/c +8.4 2 X(4274) Γ = 56.2 ± 10.9 - 11.1 MeV/c 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]
+12 2 M = 4506 ± 11- 15 MeV/c +21 2 X(4500) Γ = 92 ± 21- 20 MeV/c JPC = 0++ with 4.0σ ++ + - Wang et al predicted virtual 0 D* sD* s state at 4.48 ± 0.17 GeV [Eur. Phys. J. C64 (2009) 373] +14 2 M = 4704 ± 10 - 24 MeV/c +42 2 X(4700) Г = 120 ± 31 - 33 MeV/c JPC = 0++ with 4.5σ 15/30 Search for beautiful tetraquarks
[arXiv:1806.09707, submitted to JHEP] No hadron containing more than 2 heavy quarks has been observed so far
Xbbbb Theoretical predictions Mass within [18.4; 18.8] GeV/c2 + - Typically below ηbηb threshold → could 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 At LHCb + - Search for Xbbbb → Y(1S)μ μ with Y(1S) → μ+μ- Y(1S) ±2.5σ In normalization to 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 pp collisions 2.0 fb-1 @ 8 TeV pp collisions
3.3 fb-1 @ 13 TeV pp collisions and combined sample 16/30 Search for beautiful tetraquarks
[arXiv:1806.09707, submitted to JHEP]
Events selected with cut-based selection J/ψ veto for muons in m(μμ) 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 ηbηb threshold Y(1S)Y(1S) threshold Background-only fit In normalization to Limits setting region
[JHEP 11 (2015) 103] [arXiv:1804.09214] Fiducial region 2 pT < 30 GeV/c 2.0 < y < 4.5 Search for beautiful tetraquarks
[arXiv:1806.09707, submitted to JHEP] Likelihood profile as a function of S is integrated to determine upper limits
Scan over 101 values of Xbbbb mass
Theoretical expectation of σ×Br(Υl+l-) is ~1fb 18/30 Exotic baryons
Pentaquarks 2015 – first observation of resonances consistent with pentaquark states [Phys. Rev. Lett. 115, 072001 (2015)]
+ Pc(4380) @ 9σ significance M = 4380 ± 8 ± 29 MeV/c2 Г = 205 ± 18 ± 86 MeV/c2
+ Pc(4450) @ 12σ significance M = 4450 ± 2 ± 3 MeV/c2 Г = 39 ± 5 ± 19 MeV/c2
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
[Phys. Rev. Lett. 117, 082002 (2016)] 20/30 Study of the Λb → J/ψpπ decay Need confirmations in other decays [Phys. Rev. Lett. 117, 082003 (2016)] Similar strategy: 6D amplitude fit to the data
Λb → J/ψpπ Cabbibo-suppressed - d π analog of Λb → J/ψpK Expect N* states in m(pπ) + d Expect P c in m(J/ψp) N* - Expect Zc(4200) in m(J/ψπ) [PRD90 (2014) 112009]
1885 ± 50 signal events
21/30 Study of the Λb → J/ψpπ decay Conventional states and non-resonant [Phys. Rev. Lett. 117, 082003 (2016)] background:
m(pπ) > 1.8 GeV
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+) - P + Zc(4200) with J = 1 22/30 Study of the Λb → J/ψpπ decay
[Phys. Rev. Lett. 117, 082003 (2016)] Combined statistical significance of 3 states 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] + - P c's-only hypothesis (no Zc ) Combined significance of two pentaquarks is 3.3σ Fit fraction remains stable
RK/π ~0.07-0.08 Measure the ratio of branching fractions + [Cheng et al. PRD 92, 096009 (2015)] Br(Λb → Pc(4380) K) +0.016 + = 0.050 ± 0.016 - 0.014 ± 0.025 Br(Λb → Pc(4380) π) Rules out: Br(Λ → P (4450)+K) b c +0.016 +0.011 RK/π ~0.58 ± 0.05 + = 0.033 - 0.014 - 0.010 ± 0.009 Br(Λb → Pc(4450) π)
[Hsiao, Phys. Lett. B 751, 572 (2015)] 23/30 Interpretations Need to have interpretations
Tightly bound state? [PLB 749 289 (2015)]
Hadronic molecule? [PRL 115 122001 (2015)]
Rescattering effect?
χc1p → J/ψp Can explain the phase motion + P c won't be seen in the χc1p final state [PRD 92 071502 (2015)]
24/30 Λb → χc1,2pK decays
[Phys. Rev. Lett. 119, 062001 (2017)]
0 Search for 2 decays together: Λ b → χc1,2pK 0 Normalize by Λ b → J/ψpK
2 first observations! χc1,2 → J//ψγ decays reconstructed
Mass constrained to χc1 mode
χc2 mode shifted to lower mass values
0 Λ b → χc1pK: 453 ± 25 signal events 29σ significance
0 Λ b → χc2pK: 285 ± 23 signal events 17σ significance To few for the amplitude analysis yet Can measure the branching fractions:
25/30 Ξb → J/ψpK decay Need to see other pentaquarks [Phys. Lett. B 772 (2017) 265-273]
Decay similar to Λb → J/ψpK Just replace u-quark with s-quark One may expect appearence of a hidden-charm pentaquark with open strangeness: [sccud]
Total signal yield ~300 events Signal significance 21σ
First Branching fraction is measured through
observation! normalization by Λb → J/ψΛ channel
By the end of Run 2 there should be enough data for an amplitude analysis 26/30 Search for weakly decaying b-flavoured pentaquarks [Phys. Rev. D97 (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 Simultaneous search for four different states: + Case IV implicitly includes corresponding P 0 decay B sp
Subscript: dominant strong decay modes for Search mass windows: below the the state, if its mass above the threshold strong decay threshold
→ μ+μ- → μ+μ-
→ K+K-
27/30 Search for weakly decaying b-flavoured pentaquarks [Phys. Rev. D97 (2018) 032010] Blinded analysis Invariant mass distributions after the selection Event selection: I II Loose cut-based preselection Boosted-decision tree (BDT)
Simulation used for BDT training and efficiencies calculations 4 different masses for each P+ P+ lifetime set to 1.5 ps III IV Phase-space assumption for P+ decays
Total efficiencies 0.45-1.4% depending on the mode
A narrow signal is expected with resolution of 5.2 – 6.0 MeV/c2
No significant narrow structures are observed. Upper limits are set.
28/30 Search for weakly decaying b-flavoured pentaquarks [Phys. Rev. D97 (2018) 032010] 90% upper limits are set for the ratio
where
[Chin. Phys. C40 (2016) 011001] I II Fiducial region 2 pT < 20 GeV/c 2.0 < y < 4.5
Averaged between III IV 7 and 8 TeV samples
29/30 Conclusions 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
More future prospects are covered in the talk by Viacheslav Matiunin 0 - Observation of the decay Λb → ψ(2S)pπ 0 + - Observation of the decay Λb → Λc ppπ
The LHCb Run 2 data is being analysed Many prospects and ideas
Looking forward to new exciting exotic results!
30/30