the light meson spectroscopy program
DESCRIPTION
The light meson spectroscopy program . Landscape Experiments BES III (J/ y decays) COMPASS ( p − beam) CLAS ( g beam) Outlook. Elton S. Smith, Jefferson Lab 13 th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon. Light Mesons. q. q. q. q. q. - PowerPoint PPT PresentationTRANSCRIPT
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 1
The light meson spectroscopy program
Elton S. Smith, Jefferson Lab13th International Conference on Meson-Nucleon Physics and the
Structure of the Nucleon
Landscape Experiments BES III (J/y decays) COMPASS (p− beam) CLAS (g beam)
Outlook
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 2
Light Mesons
Quark model mesons (u, d, s quarks) qq
Glueballs (gluons and no quarks)
Multiquarks (quark-antiquark pairs)
q q
Hybrids (quarks and gluons, which contribute to static properties)
Call these the “ABC” statesKlempt Zaitsev Phys Rep 454 (2007) 1
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 3
Normal Mesons – qq color singlet bound statesSpin/angular momentum configurations & radial excitations generate
the known spectrum of light quark mesons.
Starting with u - d - s we expect to find mesons grouped in nonets - eachcharacterized by a given J, P and C.
JPC = 0– – 0+ – 1– + 2+ – …
Not-allowed: exotic
JPC = 0– + 0++ 1– – 1+ – 2++ …Allowed combinations
K+
p−
K−
p+p0 h’h
K0
K0 K*
r
K*
wf
Spin 0 Spin 1
S = S1 + S2J = L + SP = - (-1)L
C = (-1)L+S
S1
S2
L
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 4
Nonets of Scalar (0++) Mesons
Jaffe Phys Rev D15 (1977) 267Crede Meyer Prog Part Nucl Phy 63 (2009) 74
q q
I3
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 5
BESIII: e+e- in the charmonium regionOperating since 2008, √s = 2 − 4.2 GeV
Wei Moriond QCD and High Energy Interactions 2013
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 6
BES III: pp mass threshold enhancement
Possible interpretations Conventional meson ppbar bound state / multi-quark glueball
Chinese Phys C 34 (2010) 421
Confirmation of enhancement first observed by BES II
M ~ 1.83-1.86 GeV
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 7
BES III: pp mass threshold PWA
Breit-Wigner and S-wave FSI describes structure M = 1832 ± 19 MeV G = 13 ± 39 MeV Spin-parity of 0-+
strongly favored by PWA fit
Chinese Phys C 34 (2010) 421 Ablikim PRL 108 (2012) 112003
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 8
Angular distribution of X(1835) consistent with 0-+ assignment
Pure glue lattice expects lowest 0-+ glueball mass ~ 2.5 GeV
X(2370) M = 2376 ± 9 MeV G = 83 ± 17 MeV
X(2120) M = 2122 ± 7 MeV G = 83 ± 16 MeV
X(1835) M = 1837 ± 3 MeV G = 190 ± 9 MeV
BES III: X(1835) structures in J/y->gh’p+p-
Ablikim PRL 106 (2011) 072002
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 9
BES III: X(1870) in J/y->wX, X->hp+p-
Identification of X(1870)? Spin-parity 0-+? Is it the X(1835)? h2(1870)? Need PWA!
w
Ablikim PRL 107 (2011) 182001
X(1870) M = 1877 ± 6 MeV G = 57 ± 12 MeV X-> a0(980)p, a0->hp
f1(1285)h(1405)
X(1870)
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 10
BES III: Summary and prospects Huge data samples collected for charmonium decays at BES
III Data based on 200 M J/y events Confirms of the ppbar mass threshold enhancement at 1832
MeV Confirms of the X(1835)->h’p+p- and finds two new structures:
X(2120) and X(2370) Observes the new structure X(1870) in J/y -> wX(hp+p-) 1.2 billion J/y and 500 million y events already collected
Expect rich physics results in the coming years from BES III
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 11
Spectrum of 1−+ exotic signals
Meyer Van Haarlem Phys Rev C82 (2010) 025208
Expectation from LQCD
Unlikely HybridDynamical origin?
q q
I3
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 12
COMPASS: spectroscopy with pion beams Hadron Setup 2008/09
Courtesy of F. Nerling
2004 Pilot Run (4 days 190 GeV, Pb tgt, p-)2008/09 (high statistics, 190 GeV, LH2 tgt, p±, K±, p±)
190 GeV
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 13
COMPASS: Exotic 1-+ p1(1600)->p+p-p-
~0.4 M events Intensity =1.7% of total
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 14
Amplitude analysis 3p system in isobar model
Partial waves (in the reflectivity basis): JPCMe [isobar] L
g (beam)
n (recoil)p (target)
HybridJPCMe
e = + naturale = − unnaturalparity exchange
pa
p (bachelor)
pbRpp
spin S
L1
2
The decay of the 3p system at point 1 to the di-pion resonance Rpp and a bachelor pion is described in the Gottfried-Jackson frame.
The decay of Rpp→ papb at point 2 is described in the helicity frame.
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 15
Toy example: resonant phases
Phase motionBlack – Blue
2 waves
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 16
COMPASS: Diffractive dissociation into 3p
PWA ~ 1M events PWA ~ 24M events
38% of 2008 data
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 17
COMPASS: reproducing known resonances
Phase motion
Intensity
Acceptance corrected53 waves included
a1(1260)->(pp)s p
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 18
COMPASS: reference and exotic signals
Phase motion
Intensity
1-+ Exotic
Mass (GeV)
Acceptance corrected53 waves included
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 19
COMPASS: Primakoff production of p+p-p-
No intensity exotic 1-+ wave near 1.6 GeV Pilot run for Primakoff reaction, t’ < 0.001 GeV2
Photoproduction in the Coulomb field of heavy nucleus
1-+ Exotic
Grube CLAS12 Workshop, Glasgow
t’ < 0.001 GeV2
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 20
COMPASS: Summary and prospects Diffractive production of 3p states
Analysis of 50x statistics of initial pilot run Results for p1(1600)-> p-p-p+ and p1(1600)->p-p0p0
Confirmation of exotic state Ongoing analysis
Pilot Primakoff data sees no exotic in quasi-photoproduction Exotic signals also seen in hp and h’p channels Search for p1(2000) in the KKpp final state
COMPASS has acquired large statistics on many reactions Diffractive dissociation of p, p-, K- on various targets Central production of (pp) in pp reactions, which can be used for
glueball searches. p-g and K-g Primakoff reactions on heavy targets
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 21
CLAS: Photoproduction at 6 GeV
Ie = 60-65 nA Eg = 3.584 – 5.453 GeV 26.2 billion triggers Integrated luminosity
of 68 pb-1
G12 Data Run Conditions
Nozar PRL 102 (2009) 102002
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 22
CLAS: PWA extraction of known resonances
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 23
CLAS: Small non-resonant 1-+ exotic wave
M=1+ and 1-Degenerate wavesfor unpolarized g
M=0Expect Zero For pion exchange
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 24
CLAS: PWA 1−+ − 2−+ Phase Motion
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 25
CLAS: Summary and prospects No evidence for 1−+ exotic resonance in photoproduction
Confirmation of earlier limits with higher sensitivity Intensity of exotic wave < 2% of total Phase of exotic wave consistent with non-resonant signal
Other analyses Study of exotic signal in gp->hp−D++ Searches for strangeonium in gp->pfh[Spec1: D. Schott]
Forward Tagger for CLAS12
[L. Elouadrhiri] GlueX in Hall D at 12 GeV
Commissioning Fall 2014
[P. Eugenio]
[Future Facilities: R. Mckeown]
Elton S. Smith MENU2013 Sep 30-Oct 4, 2013 26
Summary
The spectrum of “ABC” mesons is being investigated in both collider and fixed target experiments
BES III has identified structures with masses ~ 1.8−2.4 GeV Their internal structure is under study and may shed light on
the nature of gluonic interactions. The 1−+ exotic p1(1600)->3p is confirmed by COMPASS in p−
interactions Upper limits are set on the 1−+ exotic wave in CLAS
photoproduction, which are consistent with non-resonant background