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Effective Field Theory Investigations of the “XYZ” Puzzle
Jorge Segovia
Physik-Department T30F
Technische Universitat Munchen, Germany
T30fTheoretische Teilchen- und Kernphysik
Main collaborators:
Nora Brambilla (Supervisor) and Antonio Vairo (Mentor)
Jorge Segovia ([email protected]) Effective Field Theory Investigations of the “XYZ” Puzzle 1/21
Nature (of matter) as we know it nowadays
Jorge Segovia ([email protected]) Effective Field Theory Investigations of the “XYZ” Puzzle 2/21
Matter is composed of smaller parts
The idea that matter consists of smaller parts and that there exists a limited numberof sorts of primary, smallest particles in nature has existed since time immemorial
☞ Old idea: (interesting but wrong)
☞ Modern idea: (interesting and right)
An atom itself is made up of three tiny kinds of particles called subatomic particles:Protons, neutrons and electrons
Jorge Segovia ([email protected]) Effective Field Theory Investigations of the “XYZ” Puzzle 3/21
The era of accelerators – 1950s and 1960s
Jorge Segovia ([email protected]) Effective Field Theory Investigations of the “XYZ” Puzzle 4/21
The subatomic zoo
Enrico Fermi to advise his student Leon Lederman: “Young man, if I could rememberthe names of these particles, I would have been a botanist.”
Jorge Segovia ([email protected]) Effective Field Theory Investigations of the “XYZ” Puzzle 5/21
Hadrons are not elementary particles
Protons and neutrons at the heart of theatomic nucleus (and generally hadrons) are notelementary particles.
The key evidence for their existence came froma series of inelastic electron-nucleon scatteringexperiments conducted between 1967 and 1973at the Stanford Linear Accelerator Center.
Quarks are recognized today as being amongthe elementary particles of which matter iscomposed.
We do not know what the future holds!
Jorge Segovia ([email protected]) Effective Field Theory Investigations of the “XYZ” Puzzle 6/21
The quark model (I)
☞ A classification scheme for hadrons in terms oftheir valence quarks and antiquarks:
☞ The quarks and antiquarks give rise the quantumnumbers of the hadrons:
d u s c b tQ - Electric charge -1/3 +2/3 -1/3 +2/3 -1/3 +2/3I - Isospin +1/2 +1/2 0 0 0 0Iz - Isospin z-component -1/2 +1/2 0 0 0 0S – strangeness 0 0 -1 0 0 0C – charm 0 0 0 +1 0 0B – Bottomness 0 0 0 0 -1 0T – Topness 0 0 0 0 0 +1
☞ Underlies “flavor SU(3)” symmetry
Murray Gell-Mann George Zweig
3 and 3 representations−−−−−−−−−−−−−−−−−→
Jorge Segovia ([email protected]) Effective Field Theory Investigations of the “XYZ” Puzzle 7/21
The quark model (II)
Successful classification scheme organizing the large number of conventional hadrons
Baryons Mesons
3 ⊗ 3 ⊗ 3 = 10S ⊕ 8M ⊕ 8M ⊕ 1A 3 ⊗ 3 = 8 ⊕ 1
Jorge Segovia ([email protected]) Effective Field Theory Investigations of the “XYZ” Puzzle 8/21
The heavy quarkonia before 2003
Charmonium and bottomonium states were discovered in the 1970s.Experimentally clear spectrum of narrow states below the open-flavor threshold
Eichten et al., Rev. Mod. Phys. 80, 1161 (2008)
Heavy quarkonia are bound states made of a heavy quark and its antiquark(cc charmonium and bb bottomonium).
They can be classified in terms of the quantum numbers of a nonrelativisticbound state → Reminds positronium [(e+e−)-bound state] in QED.
Heavy quarkonium is a very well established multiscale system which can serve asan ideal laboratory for testing all regimes of QCD.
Jorge Segovia ([email protected]) Effective Field Theory Investigations of the “XYZ” Puzzle 9/21
The discovery of the X(3872)
In 2003, Belle observed an unexpected enhancement inthe π+π−J/ψ invariant mass spectrum while studyingB+ → K+π+π−J/ψ.
It was later confirmed by BaBar in B-decays and byboth CDF and D0 at Tevatron in prompt productionfrom pp collisions.
Its quantum numbers, mass, and decay patterns makeit an unlikely conventional charmonium candidate.
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eV
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/c
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Jorge Segovia ([email protected]) Effective Field Theory Investigations of the “XYZ” Puzzle 10/21
Many experiments around the world
The scientific community has witnessed an explosion of related experimental activity
BELLE@KEK (Japan) BABAR@SLAC (USA) CLEO@CORNELL (USA)
PANDA@GSI (Germany) BES@IHEP (China)
LHCb@CERN (Switzerland) GLUEX@JLAB (USA)
Jorge Segovia ([email protected]) Effective Field Theory Investigations of the “XYZ” Puzzle 11/21
The XYZ particles – A new particle zoo?
Jorge Segovia ([email protected]) Effective Field Theory Investigations of the “XYZ” Puzzle 12/21
Summary table of the XYZ particles
“Heavy quarkonium: progress, puzzles, and opportunities”
Brambilla et al., Eur. Phys. J. C71 (2011) 1534; pages: 181 citations: 822
Jorge Segovia ([email protected]) Effective Field Theory Investigations of the “XYZ” Puzzle 13/21
Exotic matter
The states that do not fit Quarkonium potential model are called Exotics
(Keep in mind that QCD allows new forms of matter beyond qqq and qq)
☞ Glueballs (only gluons)An hypothetical composite particle which consists solely ofgluon particles, without valence quarks.
☞ Hybrids (QQg)Exotic properties are due to gluonic excitations.
☞ Molecules (Qq − Qq)Shallow bound states of heavy mesons analogous to thedeuteron.
☞ Diquarkonium (Qq − Qq)The constituent quarks are assumed to be clustered intocolor triplet diquarks.
☞ Hadroquarkonium (QQ − qq)A compact core that is a color-singlet QQ surrounded bylight mesons.
Jorge Segovia ([email protected]) Effective Field Theory Investigations of the “XYZ” Puzzle 14/21
QCD’s Key feature
Quantum Electrodynamics (QED)
Theory of the electroweak interaction.
d.o.f: electrons and photons.
No Photon self-interactions.
Its consequences are extraordinary
Quantum Chromodynamics (QCD)
Theory of the strong interaction.
d.o.f.: quarks and gluons.
Gluon self-interactions.
Jorge Segovia ([email protected]) Effective Field Theory Investigations of the “XYZ” Puzzle 15/21
Non-perturbative QCD:Confinement and dynamical chiral symmetry breaking (I)
Hadrons, as bound states, are dominated by non-perturbative QCD dynamics
Explain how quarks and gluons bind together ⇒ Confinement
Origin of the 98% of the mass of the proton ⇒ DCSB
Emergent phenomena
ւ ց
Confinement DCSB
↓ ↓
Coloredparticles
have neverbeen seenisolated
Hadronsdo not
follow thechiral
symmetrypattern
Neither of these phenomena is apparent in QCD’s Lagrangian
however!
They play a dominant role in determining the characteristics of real-world QCD
Jorge Segovia ([email protected]) Effective Field Theory Investigations of the “XYZ” Puzzle 16/21
Non-perturbative QCD:Confinement and dynamical chiral symmetry breaking (II)
From a quantum field theoretical point of view: Emergent
phenomena are associated with dramatic, dynamically
driven changes in the analytic structure of QCD’s
propagators and vertices.
☞ Dressed-gluon propagator in Landau gauge:
i∆µν = −iPµν∆(q2), Pµν = gµν − qµqν/q2
An inflexion point at p2 > 0.
Breaks the axiom of reflexion positivity.
No physical observable related with.
☞ Dressed-quark propagator in Landau gauge:
S−1(p) = Z2(iγ·p+mbm)+Σ(p) =
(
Z (p2)
iγ · p + M(p2)
)
−1
Mass generated from the interaction of quarks withthe gluon-medium.
Light quarks acquire a HUGE constituent mass.
Responsible of i.e. the 98% of the mass of the protonand the large splitting between parity partners.
0 1 2 3
p [GeV]
0
0.1
0.2
0.3
0.4
M(p
) [G
eV
] m = 0 (Chiral limit)m = 30 MeVm = 70 MeV
effect of gluon cloudRapid acquisition of mass is
Jorge Segovia ([email protected]) Effective Field Theory Investigations of the “XYZ” Puzzle 17/21
Traditional tool: Phenomenological potential models
Solve the Schrodinger equation → Nonrelativistic dynamics.
Incorporate the basic properties of QCD:DCSB: Goldstone-boson exchanges between dressed constituent quarks.
The perturbative one-gluon fluctuations around the instanton vacuum.
A phenomenological confining potential of quarks and gluons.
☞ Advantages:
It is a simple and powerful computational method.
It gives an idea of the mechanism which drives theprocess under study.
It is very flexible allowing to develop new ideas inan easy way.
It shows the way to follow to more sophisticatedapproaches.
☞ Disadvantages:
It is not a theory.
It does not allow a systematic treatment because itis not clear how to improve the description.
It is a limited approach when you try to connect itto QCD.
Jorge Segovia ([email protected]) Effective Field Theory Investigations of the “XYZ” Puzzle 18/21
State-of-the-art tools: QCD on the Lattice
☞ Description:
Formulated on a grid of points in space and time.
Quarks placed on sites and gluons on the linksbetween sites.
The continuum theory is recovered by taking thelimit of vanishing lattice spacing.
☞ Advantages:
Allows nonperturbative calculations.
Direct connection with QCD.
Systematic and model independent treatment.
☞ Disadvantages:
Suffers from the fermion doubling problem.
For some observables, it is inconvenient to haveLattice-QCD formulated in Euclidean space-time.
Calculations are limited by the availability ofcomputational resources and the efficiency ofalgorithms.
Jorge Segovia ([email protected]) Effective Field Theory Investigations of the “XYZ” Puzzle 19/21
State-of-the-art tools: QCD on the continuum
Effective Field Theory allows us to perform a first principle computation of heavyquarkonium properties from QCD
→ Give model independent predictions with model independent errors
☞ Heavy quarkonium is a nonrelativistic system:
vc ∼ 0.55 vb ∼ 0.32 (vlight = 1.0)
☞ Heavy quarkonium is a multiscale system:
mQ ≫ p = mQv ≫ E = mQv2
☞ Scales are entangled in full QCD
☞ EFTs allows to deal only with scales we are interested in
Integrating out the mQ scale: QCD → NRQCD
Integrating out the mQv scale: NRQCD → pNRQCD
Jorge Segovia ([email protected]) Effective Field Theory Investigations of the “XYZ” Puzzle 20/21
Need of new Effective Field Theories
There is another scale in QCD: ΛQCD
☞ The matching of QCD to NRQCD
mQ ≫ ΛQCD → Perturbative matching.
☞ The matching of NRQCD to pNRQCD
E = mv2 & ΛQCD → Quarkonia deep below openflavor thresholds. Perturbative matching.
p = mv ∼ ΛQCD → Quarkonia mass of the order ofopen flavor thresholds. Nonperturbative matching.
☞ XYZ states have been found close or above threshold
Entanglement of the ΛQCD with p and E scales.
New dynamical degrees of freedom: gluonic excitationsand light quark-antiquark pairs.
Appearance of new scales.
Goal: Develop new EFTs able to deal with the new degrees of freedom and scales
“Combination of different EFTs (e.g. NRQCD + Large-Nc )”
Jorge Segovia ([email protected]) Effective Field Theory Investigations of the “XYZ” Puzzle 21/21
