What are hadrons made of Stephen L Olsen

What are hadrons made of? Stephen L. Olsen Seoul National University

Some Background

1963 “stable” hadrons meson resonances baryon resonances S L * N K* K w p m e r s” r o v “fla Two “classes” of hadrons “non-strange: ” n, p, p, r, … “strange: ” L, S, K, K*, … Y* K 2* D

1 st attempts at Classification With the discovery of new unstable particles (L, k) a new quantum number was invented: Þ strangeness Gell-Mann, Nakano, Nishijima realized that electric charge (Q) of all particles could be related to isospin (3 rd component), Baryon number (B) and Strangeness (S): Meson “octet” Q = I 3 +(S + B)/2= I 3 +Y/2 hypercharge (Y) = (S+B) all have same JP= Interesting patterns emerge when I 3 is plotted vs. Y Y I 3 4

Vector mesons also form an octet JP=1 - K*+ K*0 r- w r 0 r+ f K*- Y I 3 _ K*0

Baryons are in octets & decuplets ? 1 Y s g sin mi I 3 i 96 1 n

1961: Gell-Mann, Nishijima & Nee’man: “The Eightfold Way” The Eightfold Way appears in the Buddhist teaching: "This is the noble truth that leads to the cessation of pain. This is the noble eightfold way. "

Octets (and decuplets) are representations of the SU(3) Lie group: SU(2) group: Angular Momentum in QM SU(3) group: Generalization of SU(2) Gell-Mann Matrices Pauli Matrices Representations: … Spin=1/2 Spin=1 octets decuplets

SU(3) prediction for the W- mass Gell-Mann Okubo mass formula JP=3/2+ M=1232 Me. V D ≈ 153 Me. V M=1385 Me. V D ≈ 148 Me. V M=1533 Me. V ? M≈1533 + 150 M e. V = 16 83 Me. V

1965: W- discovery 1965: the W was discovered at the Brookhaven Lab in NY. USA with S=-3 & M = 1672 Me. V, very near the Gell-Mann-Okubo prediction

1964: triplet = the most fundamental representation of SU(3) B = 1/3 Y=+1 n-1/3 p-2/3 l-1/3 Fractional charges!! Y=+1/3 Y=0 Y=-2/3 Y=-1 Q =-1/3 Q =+2/3 Quarks Y=-2 Gell-Mann Aces Zwieg

Original Quark Model 1964 The model was proposed independently by Gell-Mann and Zweig Three fundamental building blocks 1960’s (p, n, l) Þ 1970’s (u, d, s) mesons are bound states of a of quark and anti-quark: Can make up "wave functions" by combining quarks: baryons are bound state of 3 quarks: proton = (uud), neutron = (udd), L= (uds) anti-baryons are bound states of 3 anti-quarks: Λ= (uds) 12

Make mesons from quark-antiquark __ uss _ ds d _ du_ _ sd _ dd _ uu u ss s u __ d ud _ su _

Ground state mesons (today) JP=0498 JP=1 - 494 892 896 K*+ K*0 135 548 139 776 783 r- r 0 w 776 r+ 776 f 958 1020 494 K*- 498 892 (p+, p 0, p-)=lightest _ K*0 896 (r+, r 0, r-)=lightest nr=0 S w av e

Adding 3 quarks 8 -tets & 10 -plets dud ddd sdd uud sudsud ssd ssu sss suu

Ground state Baryons 939 938 M=1232 Me. V 1115 1189 M=1385 Me. V 1197 1192 M=1533 Me. V 1315 1321 M=1672 Me. V JP=1/2+ es all S av -w JP=3/2+ all nr=0 S all s ve a -w all nr=0 16

Are quarks real objects? or just mathematical mnemonics? Are quarks actually real objects? " Gell-Mann asked. "My experimental friends are making a search for them in all sorts of places -- in high-energy cosmic ray reactions and elsewhere. A quark, being fractionally charged, cannot decay into anything but a fractionally charged object because of the conservation law of electric charge. Finally, you get to the lowest state that is fractionally charged, and it can't decay. So if real quarks exist, there is an absolutely stable quark. Therefore, if any were ever made, some are lying around the earth. " But since no one has yet found a quark, Gell-Mann concluded that we must face the likelihood that quarks are not real.

1974: discovery of J/ and ’ stot(e+e- hadrons) J/ ’ c c e S- v wa nr=0 M=3. 097 Ge. V c e S av -w c nr=1 M=3. 686 Ge. V J/ & ’ interpreted as charmed-quark anticharmed-quark mesons

Charmonium mesons formed from c- and c-quarks c r c c-quarks are heavy: mc ~ 1. 5 Ge. V velocities small: v/c~1/4 non-relativistic, undergraduate-level QM applies

What is V(r)? c V(r) ~0. 1 fm r c “Cornell” Potential ~1 pe o l s fm / V Ge linear “confining” long distance component r 2 parameters: slope & intercept 1/r “coulombic” short distance component

_ Charmonium (cc) spectrum ’ J/ Positronium (e+e-)spectrum

J/ ’ Run the accelerator here

P-wave Charmonium states e+ e- ’ g X ’ ’ Crystal Ball expt: Phys. Rev. D 34: 711, 1986. Eg “smoking gun” evidence that quarks are real spin=1/2 objects J/

What are hadrons made of? • Hadrons are made of quarks – Three quarks baryons – quark-antiquark meson • The discovery of the charmonium states convinced everyone that quarks are real • Google hits for “quarks” = 1, 760, 000

The Nobel Prize in Physics 1969 "for his contributions and discoveries concerning the classification of elementary particles and their interactions" This classification of the elementary particles and their interaction discovered by Gell-Mann has turned out to applicable to all strongly interacting particles found later and these are practically all particles discovered after 1953. His discovery is therefore fundamental in elementary particle physics.

End of story? ? ! ! !! t s fa The o end? o N s t

Problem with the quark model: Violation of the spin-statistics theorem? s-1/3 W-=three s-quarks in the same quantum state

The strong interaction “charge” of each quark comes in 3 different varieties Y. Nambu M. -Y. Han Ws-1/3 1 2 s-1/3 3 the 3 s-1/3 quarks in the W- have different strong charges & evade Pauli

Attractive configurations Baryons: eijk eiejek i≠ j≠k i j k Mesons: dij ei ej i j same as the rules for combining colors to get white: add 3 primary colors --or-- add color+complementary color quarks: eiejek color charges antiquarks: ei ej ek anticolor charges eijk eiejek dij ei ej “Quantum Chromo Dynamics” QCD

Are there other, “exotic” color-singlet spectroscopies? Other possible “white” combinations of quarks & gluons: Pentaquark: e. g. an S=+1 baryon u d_ u d s 5 -quark state H-dibaryon: s u ds tightly bound 6 -quark state Glueballs: gluon-gluon color singlet states Tetraquark mesons _ u _c c u _ qq-gluon hybrid mesons c _ c

Pentaquarks & the H-dibaryon

quark + quark antiquark? du dd d u s du ud d = 3 3 = 6 3 uu us su s _ ds u ds sd s _ 3 diquark antitriplet us = dd ud sd 6 ss ss uu su

Pentaquarks? Exotics D. Diakonov, V. Petrov, and M. Polyakov, Z. Phys. A 359 (1997) 305. __ R. Jaffe & F. Wilczek PRL 91, 232003 (2003) 10 du ds _ 3 antitriplet _ s du _ 3 us ds us antitriplet _ u _ 3 N 0 S- = _ u antitriplet -- S 0 S+ 0 ---- S=-1 + - S=-2 N 0 S- N+ S 0 L See also: Y. S. Oh & H. C. Kim PRD 70, 094022 (2004) ---- S=0 N+ - _ 8 ----- S=+1 Q+ 0 0 ---- S=0 S+ -- S=-1 ------ S=-2 Prediction: M( - -) ≈ 1750~1850 Me. V - - - p - very clean!! | 0 p. L

Q+ Pentaquark at Spring-8? Q+ decay modes: + photo-production - K+ n Qgn K • Q + K + n • need to deal with the neutron • Q + K 0 p • cannot tag the strangeness K+ Q+ need a neutron target (1 st experiment used 12 C tgt) n u+2/3 s+1//3 -1/3 d u+2/3 d-1/3 S=+1

Results gn K- K+n CLAS-D (2005) Q+ K + n ? gn K- K+n Q+ K + n ? ? ? ? Width consistent with (11 Me. V) resolution T. Nakano et al (LEPS) PRC 79, 025210 (2009) B. Mc. Kinnon et al (CLAS) PRL 96 212001 (2006)

- - in NA 49 Expt at CERN? L & signals are very clean p + p+ + _ +p M( p)5 = 1862± 2 Me. V G 5<18 Me. V S = 4. 2 s

No sign of X- - in CDF X*(1530) X-p+ No peaks around M(Xp) = 1860 Me. V/c 2 for X-p+ and X-p-

Positive pentaquark sightings since 2003

Negative pentaquark sightings since 2003

“The story of pentaquark shows how poorly we understand QCD” – F. Wilczek, 2005

Pentaquarks in a gluon-rich environment less complicated than: (1 S) - - + X (1 S) anti-deuteron + X p n p b (1 S) p p d b (1 S) b p b CLEO: Bf( (1 S) anti-deuteron + X)=3 x 10 -5 an appropriate comparison process A limit on Bf( (1 S) - - + X) below 10 -5 would be “compelling evidence” that Pentaquarks do not exist.

H dibaryon? d u d s _ 3 du d u u s antitriplet d s _ 3 u s antitriplet d u s s du _ 3 ds u s antitriplet ! ! kly s y ca de R. L. Jaffee, PRL 38, 195 (1977): S=-2 di-hyperon with M<2 ML a we

The “Nagara”LL 6 He emulsion event MH > 2 ML-7. 7 Me. V 6 LLHe 5 He L H. Takahashi et al, PRL 87, 215502 (1977)

H dibaryon decay modes MH(Me. V) H n or LL strong decay probably wide 12 C(K-, K+LLX) M + M N (2260 Me. V) H LL strong decay 2 ML (2223 Me. V) H L n weak decay 2215 Me. V Ruled out by Nagara mo st int e C. J. Yoon et al (KEK-PS E 522) PRC 75, 022201 (2007) res tin g

Production via gluons S=-2 B=+2 p p Need to: produce 6 quark-antiquark pairs (including two ss quark pairs) very close in phase space d u s s du Is this likely? ? ?

Anti-deuteron production p p Similar process!! d p n

Experimental signatures MH(Me. V) H n or LL M + M N (2260 Me. V) H LL 2 ML (2223 Me. V) H L n weak decay 2215 Me. V H L n is hard, but H L n is possible advantage of gluon production is equal rates for H and H

Pentaquark & H-dibaryon searches via gluonic systems with sensitivites below the d production rate should be conclusive.

The “XYZ” exotic meson candidates

The XYZ Mesons

B-factories e+e–→ (4 S) and nearby continuum: Ecms ~ 10. 6 Ge. V L ~ 1034/cm 2/s 1000+530 fb-1 in total At KEK in Japan At SLAC in California

cc production at B factories

Strategy: Search for a meson that decays to a final state containing a c and c quark, If it is a standard qq meson, it has to occupy one of the unfilled states indicated above. If not, it is exotic. predicted measured

The X(3872)

Study p+p J/ produced in B K p+p J/ decays ? ?

The X(3872) B K p+p J/ ’ p+p J/ X(3872) p+p J/ S. K. Choi et al PRL 91, 262001 M(pp. J/ ) – M(J/ )

Its existence is well established seen in 4 experiments CDF 9. 4 s 11. 6 s X(3872) D 0 Ba. Bar X(3872)

X 3872 JPC values JPC = 1++ or 2 -+ Angular correlation analysis by CDF: §Fit to M(pp) favors r p+p hep-ex/0505038 JPC = 1++ CDF: PRL 98 132002 PRL 96, 102002(2006)

Ba. Bar: X 3872 g. J/ & g ’ B+ K+g. J/ 3. 6 s G(X g. J/ ) 1/10 G(X p+p-J/ ) 1++ g J/ or g ’ Allowed E 1 2 -+ g. J/ or g ’ Suppressed E 2 B+ K+g ’ M(g. J/ ) JPC = 1++ favored over 2 -+ 3. 5 s PRL 102, 132001 M(g ’)

can it be the ++ 1 cc state? 1++ cc 1’ (the only charmonium possibility) M=3872 Me. V is low, X p+p J/ decay 3872 g p +p (Isospin violating) is a forbidden decay X g J/ is an allowed E 1 transition; should be stronger than p+p-J/ , not 10 x weaker. If it is not the c’c 1, what is it?

X(3872) looks like a molecule 0 0 D* D Predicted by N. A. Tornqvist PLB 590 209 (2004)

M X(3872) ≈ MD 0 +MD*0 <MX>= 3871. 46 ± 0. 19 Me. V new Belle meas. new CDF meas. MD 0 + MD*0 3871. 8± 0. 4 Me. V dm = -0. 35 ± 0. 41 Me. V

X 3872 couples to D*0 D 0 Belle X 3872 D 0 D*0 & ar. Xiv: 08100358 D*→Dγ 414 fb-1 D 0 D 0 p 0 D*→D 0π0 605 fb-1 Ba. Bar X 3872 D 0 D*0

Molecular Picture Since the X couples to D 0 D*0 in an S-wave: ome s t s at lea ≥ 6 fer mis !! E. Braaten et al ar. Xiv: 0907. 3167 of it n o i t frac

X(3872)-J/ relative sizes drms(X 3872) ≈ 6 fm drms(J/ ) ≈ 0. 4 fm Volume(J/ ) ≈ 10 -3 Volume(X 3872) _ • Overlap of the cc necessary to form the J/ in X p+p-J/ decays is rare _ • Probability forming such a fragile object in H. E. pp collisions is small -- ar. Xiv 0906. 0882: s. CDF(meas)>3. 1± 0. 7 nb vs stheory(molecule)<0. 11 nb

_ Produced like the ’ in pp collisions • Fraction from B decays – Long-lived fraction y(2 S) : (drms ≈ 0. 4 fm) 28. 3 1. 0(stat. ) 0. 7(syst. ) % X(3872) : (drms ≈ 6 fm? ? ) 16. 1 4. 9(stat. ) 1. 0(syst. ) % X(3872) behaves similarly to y(2 S). X(3872) mostly prompt.

X(3872)=diquark-diantiquark ? Expect SU(3) multiplets Isospin partners X-= d S=-1 partners Xs-= s doublet of “X(3872)” states DM=8± 3 Me. V Maiani et al PRD 71, 014028

No multiplet partners seen Ba. Bar search for “X-(3872)” p p 0 J/ PRD 71, 031501 B 0 B- X(3872)– M(J/ π–π0) Bf(B 0 K+X-)Bf(X- p-p 0 J/y) Bf(B- K+X 0)Bf(X- p-p-J/y) X(3872)– M(J/ π–π0) < 0. 4 (expect 2)

Lots of interest in the X(3872) line shape C. Hanhart et al ar. Xiv: 1002. 4097 also E. Braaten et al PRD 81 014019 Line shape and very precise mass measurement only possible at FAIR

The 1 - - Y states

produced by ISR must have JPC = 1 - - Y(4350) & Y(4660) e+e- g. ISRp+p- ’ Ba. Bar Y(4260) Ba. Bar e+e- g. ISRp+p-J/ Belle Y(4008)? Belle M(p+p- ’) Ge. V e+e- g. ISRLc. Lc Y(4630) Belle M(p+p-J/ ) Ge. V at least 3, maybe 5 M(Lc. Lc)

Only one empty 1 - - charmonium slot is available: predicted measured

Not evident in stot + – (e e →charm) The established 1 - charmonum states Y(4660) ψ (4415) y(4415) Y(4260) 325) Y(4360) ψ(4040) y(4040) ψ(4160) y(4160) Y(4008) ψ(3770) y(3770) R(s) = σ(e+e–→charmed hadrons)/σQED(e+e–→μ+μ-) if Ruds=2. 285 ± 0. 03 Durham Data Base

Y(4660) Y(4260) Y(4350) Y(4008) Not evident in any exclusive charmed hadron channel DD DDπ DD*π D *D * Λ+ c Λ c Charm Exotic 2009

S(exclusive channel measurements) Y(4660) Y(4260) Y(4350) Y(4008) nearly saturate stot Only small room for unaccounted contributions Limited inclusive data above 4. 5 Ge. V

G(p+p-J/y) [G(p+p-y’)] are much larger than seen in ordinary charmonium e. g. G(Y 4260 p+p-J/ ) > 508 ke. V compared to: G( ’ p+p-J/ ) ≈ 89 ke. V & G( 3770 p+p-J/ ) ≈ 45 ke. V (X-L Wang et al. , PLB 640, 182(2007)) (PDG tables)

Z(4430) p+ ’ Smoking gun for charmed exotic? u c d c

B K p ’ (in Belle) M 2(p+ ’) ? ? K*(1430) K+p-? K*(890) K+p- M 2(K+p-)

The Z(4430)± p± ’ peak B K p+ ’ M 2(p± ’) Ge. V 2 Z(4430) M(p± ’) Ge. V M (Kp’) Ge. V M 2(Kp’) Ge. V 2 “K* Veto”

Could the Z(4430) be due to a reflection from the Kp channel?

Cos qp vs M 2(p ’) qp p ’ K +1. 0 22 Ge. V 2 (4. 43)2 Ge. V 2 0. 25 cosqp M 2(p ’) 16 Ge. V 2 M (p ’) & cosqp are tightly correlated; a peak in cosqp peak in M(p ’) -1. 0

S- P- & D-waves in Kp can’t make a peak (+ nothing else) at cosqp≈0. 25 not without introducing other, even more dramatic features at other cosqp (i. e. , other Mp ’) values.

But…

Ba. Bar doesn’t see a significant Z(4430)+ “For the fit … equivalent to the Belle analysis…we obtain mass & width values that are consistent with theirs, … but only ~1. 9 s from zero; fixing mass and width increases this to only ~3. 1 s. ” Belle PRL: (4. 1± 1. 0± 1. 4)x 10 -5

Reanalysis of Belle’s B Kp ’ data using Dalitz Plot techniques

2 -body isobar model for Kp ’ Our default model B K* ’ k ’ K 2* ’ K*(890) ’ KZ+ Kpy’ K*(1410) ’ K 0*(1430) ’ K 2*(1430) ’ K*(1680) ’ KZ+

Results with no + KZ term 2 1 12 3 4 5 C B 3 A 4 A B 5 fit CL=0. 1% C 51

Results with a KZ+ term 1 3 2 4 1 2 3 4 5 A C B C A 5 fit CL=36% B

Compare with previous results K* veto applied With Z(4430) Signif: 6. 4 s Published results Without Z(4430) Mass & significance similar, width & errors are larger Ba. Bar: Belle: No big contradiction -5 = (3. 2+1. 8+9. 6 0. 9 -1. 6 )x 10

Variations on a theme Z(4430)+ significance Others: Blatt f-f term 0 r=1. 6 fm 4 fm; Z+ spin J=0 J=1; incl K* in the bkg fcn

XYZ Summary States with distinct signatures in PANDA

What are hadrons made of? • 40 years after Gell-Mann’s prize, we still don’t know – expected non-qq mesons &/or non-qqq baryons not seen – non-qq meson candidates that are seen defy any comprehensive theoretical understanding. – new ideas needed. • Most progress has been experimentally driven • Lots for PANDA to do.

Thank you