Talk QWG 2019 - agenda.infn.it

PERSPECTIVES OF HADRONSPECTROSCOPY AT LHCb

[ARXIV:1808.08865]

Marco PappagalloUniversity of Edinburgh

On behalf of the LHCb Collaboration

QWG 2019 – The 13th International Workshop on Heavy Quarkonium17 May 2019, Turin, Italy

2M. PappagalloQWG 2019

SPECTROSCOPY AT LHCb

PRL 114 (2015) 062004

PRL 109 (2012) 172003

Λb**

Ξb** Ξcc++

PRL 119 (2017) 112001

PRL 112 (2014) 222002PRD 92 (2015) 112009

Zc(4430)+

LHCb has largely contributed to populate the zoo of particles. Some of them have a clear “exotic” signature

STANDARD

EXOTIC

PRL 115 (2015) 072001arXiv:1904.03947

Pc(4450)+


SPECTROSCOPY AT LHCb

) [MeV]-K+cX(m3000 3100 3200 3300

Can

dida

tes /

(1 M

eV)

0

100

200

300

400 LHCb-K+cX

Full fitBackgroundFeed-downs

sidebands+cX

PRD 92 (2015) 011102PRL 110 (2013) 222001

PRL 118 (2017) 182001

Ωc**(?)

X(3872)PRL 114 (2015) 062004

PRL 109 (2012) 172003

PRL 119 (2017) 112001

Zc(4430)+

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

X(4140)

STANDARD

EXOTIC

…but many other states have uncertain nature. Goal of the upcoming years is to probe their conventional/exotic nature…and find new candidates of course

Λb**

Ξb** Ξcc++

PRL 112 222002 (2014)PRD 92 112009 (2015)

PRL 115 (2015) 072001arXiv:1904.03947

Pc(4450)+


LHCb GOING TO UPGRADE

Ø Main limitation that prevents exploiting higher luminosity with the present detector is the Level-0 (hardware) triggerü Level-0 output rate < 1 MHz (readout rate) requires raising thresholds

Ø This is particularly problematic for hadronic final statesØ Running at 2x1033 cm-2 s-1 with full software trigger, running at 40 MHz

Upgrade I ( Approved)

To be installed in Long Shutdown 4 of the LHC:Ø Subsystems redesigned to operate at a luminosity of 1-2 x 1034 cm-2 s-1

Ø Integrated luminosity of > 300 fb -1

Ø Extension of the experiment’s capabilities into selecting π0, η and low-momentumtracks

Upgrade II (Under approval)

Upgrade Ia Upgrade Ib Upgrade II

9


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

DOUBLY HEAVY BARYONS

Ø Observations of Ξcc+ and Ωcc+ expected with RUN II data or during the upcoming Upgrade I

Ø Upgrade II will be useful into studying their production and excited spectra: Ξ**cc and Ω**cc. Ωccc might be also observed

Ø Three weakly decaying C = 2 states are expected:Ø Ξcc isodoublet (ccu; ccd) and an Ωcc isosinglet (ccs), each with JP = 1/2+

Ø Ξcc++ observed in two different decay modes!

m(⌅++cc ) = 3621.24± 0.65(stat)± 0.31(syst) MeV

<latexit sha1_base64="+sIIFXinVS1FriMNqbSgWnpfPYg=">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</latexit>

⌧(⌅++cc ) = 0.256+0.024

�0.022(stat)± 0.014(syst) ps<latexit sha1_base64="ftQaOrZmJZ7oTXaOF6/PBZQbuW0=">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</latexit>

⌅++cc ! ⌅+

c ⇡+

<latexit sha1_base64="xUsPH5ZOjRTBztCthzvj46aCw6k=">AAACEXicdVDLSsNAFJ3UV62vqEs3g0UoBErSinVZdOOygn1Ak4bJdNIOnTyYmSgl9Bfc+CtuXCji1p07/8ZJG6GKHrhwOOde7r3HixkV0jQ/tcLK6tr6RnGztLW9s7un7x90RJRwTNo4YhHveUgQRkPSllQy0os5QYHHSNebXGZ+95ZwQaPwRk5j4gRoFFKfYiSV5OoVu0fdFOPZIDWMGbQ5HY0l4jy6g5mDBwaEdkwHhquXzao5B1widfOsYTaglStlkKPl6h/2MMJJQEKJGRKib5mxdFLEJcWMzEp2IkiM8ASNSF/REAVEOOn8oxk8UcoQ+hFXFUo4V5cnUhQIMQ081RkgORa/vUz8y+sn0j93UhrGiSQhXizyEwZlBLN44JBygiWbKoIwp+pWiMeIIyxViCUVwven8H/SqVWterV2fVpuXuRxFMEROAYVYIEGaIIr0AJtgME9eATP4EV70J60V+1t0VrQ8plD8APa+xcXAZyH</latexit>

⌅++cc ! ⇤+

c K�⇡+⇡+

<latexit sha1_base64="D5jb5FOP3qo80UmKcfOtGPZ/FiM=">AAACHnicdVDLSgMxFM34rPU16tJNsAhCscy0al0W3Qi6qGAf0JkOmUymDc08SDJKGfolbvwVNy4UEVzp35hOK1TRAwmHc+69yT1uzKiQhvGpzc0vLC4t51byq2vrG5v61nZTRAnHpIEjFvG2iwRhNCQNSSUj7ZgTFLiMtNzB+dhv3RIuaBTeyGFM7AD1QupTjKSSHP3YalMnxXjUTYvFEbQ47fUl4jy6g9aVGuMhB3eL8LJ7CK2YKpbdjl4wSkYGOEMqxknVqEJzqhTAFHVHf7e8CCcBCSVmSIiOacTSThGXFDMyyluJIDHCA9QjHUVDFBBhp9l6I7ivFA/6EVcnlDBTZztSFAgxDFxVGSDZF7+9sfiX10mkf2qnNIwTSUI8echPGJQRHGcFPcoJlmyoCMKcqr9C3EccYakSzasQvjeF/5NmuWRWSuXro0LtbBpHDuyCPXAATFAFNXAB6qABMLgHj+AZvGgP2pP2qr1NSue0ac8O+AHt4wsxb6E9</latexit>


WHAT ABOUT Ξbc?

(e.g.)N(⌅0bc ! J/ ⇤+

c K�; Run1) =N(B+

c ! J/ D(⇤)+s ; Run1)

⇥ �(pp ! ⌅bcX)

�(pp ! B+c X)

⇥ f⌅bc!⌅0bc

⇥ Br(⌅0bc ! J/ ⇤+

c K�)

Br(B+c ! J/ D(⇤)+

s )

⇥ ✏K�

' 3 candidates

Ø The Bc meson was discovered almost two decades ago In LHCb, ~5000 Bc àJ/ψπ in Run I

So, why have we not yet seen bcq baryons (Xbc)?Lower production rates, guess σ(Xbc) ~ (0.1 -0.5) � σ(Bc+)In J/ψ modes, (usually) get a charm baryon: yield reduced by BF(Xc) � εsel(Xc) Shorter lifetime (~0.15 – 0.4 ps range, compared to ~0.5 ps for Bc)

N(⌅0bc ! J/ ⇤+

c K�; Run 5) ' 6⇥ 102

Exclusive !bb are even more unlikely but see later for an alternative approach

[arXiv:1808.08865]


PROBING THE NATURE OF THEEXOTIC HADRONS

Ø Observation of several hadronic resonances with hidden charm or beauty(so called X, Y, Z states) in the last decade at LHC and B-factories

Ø They barely fit to standard quarkonium scenarios and “exotic”interpretations proposed: compact tetraquarks, molecules, cusps, …

Ø Most of them are quite broad and observed in 3-body decays of b-hadrons(e.g. B0 à Z(4430)- (à !(2S) "-) K+)

Upgrade II would allow to test further their nature by:Ø Probing the resonant characterØ Searching for isospin partnersØ Measurements of quantum numbers JP

Such goal relies on amplitude analysis techniques. Refinement of theoretical parametrization of hadronic amplitudes and advanced understanding of the light

spectroscopy are required in the meantime


PROBING THE NATURE OF THEEXOTIC HADRONS

Ø What about the narrow pentaquarks Pc+ recently

observed? (See Lucio’s talk for more details)https://agenda.infn.it/event/15632/contributions/89325/

Ø Determination of quantum numbers is verylikely but observation of isospin partners isdisfavored (Pc0 àJ/! n)

]2c) [MeV/-Kp1c

c(m5450 5500 5550 5600 5650 5700

)2 cEv

ents

/ ( 5

MeV

/

020406080

100120140160180200

LHCb

-Kp1c

c®0bL-Kp

2cc®0bL

PRL 119 (2017) 062001arXiv:1902.05588

However new insights might come by:Ø Studying Pc+ in different system (e.g. B0àJ/ ! p p ) or decay modes

(e.g. "b à #c1pK)Ø Measurements of production in prompt and from b-hadron decays

3 fb-1

arXiv:1904.03947

https://agenda.infn.it/event/15632/contributions/89325/


DOUBLY CHARMED TETRAQUARK: ccqq

Ø Doubly charmed particles are a straightforward consequence of the hiddencharmed exotic hadrons

Ø If discovered, they would be almost full-proof states made of 4 quarks

Tetraquark Loosely bound molecules

[A. Esposito et al.: PRD 88 (2013) 054029]

Between them, the doubly charged states play an important role into understanding their nature: indeed in a loosely bound molecule, Coulomb

repulsion would induce a fall-apart decay on very short time scales


DOUBLY CHARMED TETRAQUARK: ccqq

Ø If their masses are above the DD thresholds, pure tetraquark modelspredict (narrow) states with quantum numbers JP = 0+, 1+ and 2+

Ø 0+ and 1+ states expected to be the lightest and most likely to be formed(and observed)

JP = 1+ JP = 0+

Natural widths as predicted by a pure tetraquark model

4000 4100 4200 4300 4400

1

2

5

10

20

50

M!!s!!" #MeV$

"!! s!!"#Me

V$

PV

PV!VV

PVPV!VV

Good ! state

3900 4000 4100 4200 4300 4400

1

2

5

10

20

50

M!!s!!" #MeV$

"!! s!!"#Me

V$

PP

PP!VV

PP

PP!VVBad ! state

m(D*Ds) m(D*D*s) m(DDs) m(D*D*s)

[A. Esposito et al.: PRD 88 (2013) 054029]


DOUBLY CHARMED TETRAQUARK INPROMPT PRODUCTION

Narrow states could be easily spotted in the prompt production

Associated production of D+D+ and D+Ds+ (0.3 fb-1) [JHEP 06 (2012) 141]

N(D+D+; Run5) ' 750k candidatesN(D+D+

s ; Run5) ' 150k candidates

1.82 1.84 1.86 1.88 1.9

1.821.84

1.861.88

1.90

10

20

1.82 1.84 1.86 1.88 1.9

1.9

1.95

2

0

5

10

m(Kππ) [GeV] m(Kππ) [GeV]m(Kππ) [GeV]

m(KKπ) [GeV]

Ds+D+

D+ D+

arXiv:1808.08865


DOUBLY CHARMED TETRAQUARKIN Bc DECAYS

Ø If the states are broad-ish à Search for them in Bc decays where the quantum numbers can be also measured

Ø The Bc meson is the lightest state in the standard model that can decay to two same-flavour charmed hadrons:

N = 28.9 � 5.6 (3 fb-1)

N(B+c ! D0D0D+

s ; Run5) ' 102 candidates

Clear signature. Expected to be background free.Three pseudoscalars in the final state

T +s (ccus) ! D0D+

s

PRD 87 ( 2013) 112012

arXiv:1808.08865


MULTIPLETS OF PENTAQUARKS

[E. Santopinto et al.: PRD 96 (2017) 014014]

300 candidates of Ξb

- àJ/ψΛK- (3 fb-1)

LHCb: PLB 772 (2017) 265

N(⌅�b ! J/ ⇤K�; Run5) ' 6⇥ 104

As for other hadrons, multiplets of pentaquarks should exist. The observedPc+ should be states with quark content uudcc. We could look for strangepentaquark Pcs

0àJ/ψΛ in Ξb decays.

arXiv:1808.08865


INCLUSIVE SEARCH FOR DOUBLY BEAUTYHADRONS (!bb, "bb, Xbbqq, etc…)

Yields and shape can return insights on the cross-section, mass and lifetime Theoretical inputs required to probe the composition of the bb-hadron mixture

Ø Exclusive approaches not promising (e.g. ): • Curse of BFs: 2 x (b à c) x (c à s) x efficiency

Ø What about an inclusive approach? E.g. Displaced charm hadrons used to measure inclusive #(pp→bbX)

PLB 694 (2010) 209Weakly decaying double beauty hadrons are the only

possible source of displaced Bc- mesons

Prompt charm

b à c

Bc-

T. Gershon, A. PoluektovJHEP 01 (2019) 019

Xbbud ! B�D+⇡�<latexit sha1_base64="eCdT4XsqxMKevCrN5wLgvwZ5jus=">AAACDnicdVBLSwMxGMzWV62vVY9egqUgSMu2FeuxVA8eK9gHdLdLNpttQ7MPkqxQlv4CL/4VLx4U8erZm//GdLtCFR0IGWa+j2TGiRgV0jA+tdzK6tr6Rn6zsLW9s7un7x90RRhzTDo4ZCHvO0gQRgPSkVQy0o84Qb7DSM+ZXM793h3hgobBrZxGxPLRKKAexUgqydZLfTtxHNNBHMYwvdwZNGUIW8MyvBqeQjOiw7KtF42KkQIukbpx3jAasJopRZChbesfphvi2CeBxAwJMagakbQSxCXFjMwKZixIhPAEjchA0QD5RFhJGmcGS0pxoRdydQIJU3V5I0G+EFPfUZM+kmPx25uLf3mDWHoXVkKDKJYkwIuHvJhBFXfeDXQpJ1iyqSIIc6r+CvEYcYSlarCgSvhOCv8n3VqlWq/Ubs6KzVZWRx4cgWNwAqqgAZrgGrRBB2BwDx7BM3jRHrQn7VV7W4zmtGznEPyA9v4F8HyaHw==</latexit>


BELLE II AND LHCb AT WORK

Complementarity of the two experiments essential in exploring spectroscopyØ LHCb: larger production cross-sections, more performant for decay mode

involving charged particles (e.g. X(3872)àJ/!"", …), unique in many sectors: Bs(**), Bc(**), Ξbc(**)

Ø Belle II: smaller background, more suitable for decay modes with neutrals in the final state (e.g. X(3872)àJ/! # and its isospin/C-odd partners, …)

300 fb-150 fb-1

50 ab-1

arXiv:1808.08865


SUMMARY

The large data set collected in the HL-LHC era, together with an upgraded detector, will boost sensitivity in searches for heavy states with

small production cross sections and/or small decay rates

Ξcc++

X(3872)

��to be continued) [MeV]-K+cX(m

3000 3100 3200 3300

Can

dida

tes /

(1 M

eV)

0

100

200

300

400 LHCb-K+cX

Full fitBackgroundFeed-downs

sidebands+cX

Ωc**

Predictions are always complicated…even more when concerning unknown states!

Pc+


BACK UP


SEARCH FOR A STABLE 1++ bbud TETRAQUARK

XbbudD+

B-u

bd

b

cd

bu

du

! -

Ø Inclusive reconstructive efficiencies for B mesons are low at LHCb due to low branching fractions into low multiplicity final states

Ø Not promising even for Upgrade II!

Ø It would have observable lifetime, this combinatorial background would be under control

Ø Unfortunately bbq baryons have not been observed yet, reflecting low prompt production rates expected for both b quarks to end up in the same hadron, and difficulty in reconstruction of two subsequent weak decays of b quark


IMPACT OF CALORIMETER UPGRADE

]2c) [MeV/-Kp1c

c(m5450 5500 5550 5600 5650 5700

)2 cEv

ents

/ ( 5

MeV

/

020406080

100120140160180200

LHCb

-Kp1c

c®0bL-Kp

2cc®0bL

Ø Measurement of B(X(3872)àψ(2S) γ)/B(X(3872)àJ/ψ γ) [Nucl.Phys.B886 (2014) 665]

Ø Search for pentaquarks decaying to χc1p where χc1àJ/ψ γ[LHCb: PRL 119 (2017) 062001]

BR(X(3872) ! (2S)�)

BR(X(3872) ! J/ �)= 2.46± 0.64± 0.29 Pure molecule scenario

disfavored

Ø Increased calorimeter resolutionØ Reduction in background by a fast timing

calorimeter informationØ Increased sensitivity to low pT photon and π0

See Preema Pais’s Talk on Wednesday


IMPACT OF CALORIMETER UPGRADE

X(3872) (JPC = 1++) X(3872) (JPC = 1+-)C-odd partner

(tetraquark/molecule)

~

J/ψ ηIsospin partner

(tetraquark/molecule)

X(3872)�

J/ψ π±π0

Xb

ϒ(1S)ωπ+π-π0

Neutrals will be crucial into probing further the X(3872) meson


IMPACT OF VELO UPGRADE

Removal of RF foilØ Improved vertex resolutionØ Higher signal efficiency with large

background rejectionØ Increased track efficiencyØ Reduction in ghost rates

Ø Better performance into detecting low momentum tracks will contributeinto studying/observing excited states decaying through dipion transitions(e.g. Bc* à Bc π π)

Ø Better reconstruction efficiency for multibody B decays, such as BàDDKaiming to the search for charmonium-like states

Ø Improved vertex resolution è Higher efficiency into selecting short-livedparticles: Bc, Ξcc, Ωcc, Ξbc, Ωccc

LHCb Simulation

LHCb Simulation


LIGHT BARYON SPECTROSCOPY

Ø The poor knowledge of the light sector (Λ*, N*, etc…) has had a large impact on the amplitude analyses aiming to the search for the pentaquarks

Ø LHCb can contribute to study the spectroscopy of the light sector as well

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Talk QWG 2019 - agenda.infn.it