Glueball Searches and PWA at BESIII Shan JIN Institute of High Energy Physics (IHEP) email@example.com PWA Workshop Beijing, January 26, 2006
Outline • Physics goal of hadron spectroscopy at BESIII • What can we learn from BESII results? • Selected topics on glueball searches • PWA at BESIII (with discussions)
Multi-quark State, Glueball and Hybrid • Hadrons consist of 2 or 3 quarks： Naive Quark Model： • New forms of hadrons: • Multi-quark states：Number of quarks >＝ 4 • Hybrids：qqg，qqqg … • Glueballs：gg， ggg … Meson（ qq ） Baryon（q q q） How quarks/gluons form a hadron is far from being well understood.
Multi-quark states, glueballs and hybrids have been searched for experimentally for a very long time, but none is established.
J/ decays are an ideal factory to search for and study light exotic hadrons: • The production cross section of J/ is high. • The production BR of hadrons in J/ decays are one order higher than ’ decays (“12% rule”). • The phase space to 1-3 GeV hadrons in J/ decays are larger than decays. • Exotic hadrons are naively expected to have larger or similar production BR to conventional hadrons in J/ decays. • Clean background environment compared with hadron collision experiments, e.g., “JP, I” filter.
Physics Goal (I) With 1010 J/psi events, we hope to answer: • Whether glueballs exist or not? • Naively, we estimate in each exclusive decay mode: • If the eff. is about 20%, we would have 20000 events for each decay mode we should observe a relative narrow (width: 50~200MeV) glueball if it exists.
Physics Goal (II) • Is there any gluon content in hadrons – hybrid mesons and baryons? • Whether multiquark mesons and baryons exist in the nature? • Understanding conventional mesons and baryons How quark/gluon form a hadron? QCD cannot “escape” from answering these fundamental questions finally.
Difficulties (I) • Theoretically (glueball as an example) • Predictions on glueball masses from LQCD may be unreliable due to quench approximation. • No predictions on the widths so far (even the order). • No prediction on the production rate (J/ G). • Mix with qqbar mesons or even with 4q, qqg mesons? (dirty?)
Difficulties (II) • Experimentally: • Data sample is not big enough (it is not a problem for BESIII) • No good way modeling background at low energy, in many cases we have to study bck via data. • Interferences among mesons make the mass/Dalitz plots very complicated • PWA is a must for hadron spectroscopy at BESIII • But PWA face many uncertainties (see the discussions on PWA)
A number of unexpected new observations at BESII • A possible bound state: mass threshold enhancement in and new observation of X(1835). • mass threshold enhancement in • mass threshold enhancementin • mass threshold enhancement in J/ • New observation of a broad 1- - resonance in J/ K+K- 0
Phys. Rev. Lett. 91, 022001 (2003) Observation of an anomalous enhancement near the threshold of mass spectrum at BES II J/ygpp BES II acceptance weighted BW +3 +5 -10 -25 M=1859 MeV/c2 G < 30 MeV/c2 (90% CL) c2/dof=56/56 0 0.1 0.2 0.3 M(pp)-2mp (GeV) 3-body phase space acceptance
Observation of X(1835) in Statistical Significance 7.7 The +- mass spectrum for decaying into +- and
Mass spectrum fitting The +- mass spectrum for decaying into +- and 7.7 BESII Preliminary
Re-fit to J/p pbar including FSI Include FSI curve from A.Sirbirtsev et al. ( Phys.Rev.D71:054010, 2005) in the fit (I=0) M = 1830.6 6.7 MeV = < 153 MeV @90%C.L. In good agreement with X(1835)
A Possible ppbar Bound State • X(1835) could be the same structure as ppbar mass threshold enhancement. • It could be a ppbar bound state since it dominantly decays to ppbar when its mass is above ppbar mass threshold. • Its spin-parity should be 0-+: this would be an important test PWA is needed
Phys. Rev. Lett. 93, 112002 (2004) Observation of an anomalous enhancement near the threshold of mass spectrum at BES II BES II 3-body phase space For a S-wave BW fit: M = 2075 12 5 MeV Γ = 90 35 9 MeV
Observation of a strong enhancement near the threshold of mass spectrum at BES II NX* BES II PS, eff. corrected (Arbitrary normalization)
A strong enhancement is observed near the mass threshold of MKat BES II. • Preliminary PWA with various combinations of possible N* and Λ* in the fits —— The structure Nx*has: Mass 1500~1650MeV Width70~110MeV JP favors 1/2- The statistics is not high enough to tell what it is. The most important is: It has large BR(J/ψ pNX*) BR(NX* KΛ)2 X 10-4 , suggesting NX* has strong coupling to KΛ. It could be an KΛ bound/resonant state (5-quark system).
An mass threshold enhancement is observed background X(1810) M2(g) M2(gw) M() JPC favors 0++ Phys. Rev. Lett., 96 (2006) 162002 It could be a multiquark/hybrid/glueball state.
New observation of a broad 1- - X(1580) in J/ K+K- 0 Background Phys. Rev. Lett. 97 (2006) 142002
How to understand broad X(1580)? • Search of a similar structure in J/ KSK will help to determine its isospin. • X(1580) could have different nature from conventional mesons: • There are already many 1- - mesons nearby. • Width is much broader than other mesons. • Broad width is expected for a multiquark state.
What do we learn from BESII results • J/ψ decay is an ideal place to study exotic structures. • The statistics at BESII is not high enough yet. • We would expect: more unexpected discoveries on hadron spectroscopy at BESIII —— the more, the better !
Selected topics on glueball searches • J/ , • 2++ glueball candidates • Where to search for the 0-+ glueball?
J/ , • These two processes are believed to be an ideal place to tag the flavor of mesons. • BESII studied these two channels (PLB549, 47(2004)): (1440) from J/0KK bck
J/ , • At BESII, we only observe ’, (1440) , f1(1285) in J/ , no clear peak in J/ • At BESIII: • The background could be very high when searching for other glueball candidates. Hope BESIII much better detector can strongly suppress the background we will perform MC studies on this. • PWA is needed.
2++ glueball candidates • Lattice QCD predicts the 2++ glueball mass in the range of 2.2~2.4 GeV • (2230) was a candidate of 2++ glueball: • It was first observed at MARKIII in J/KK • It was observed at BES I in J/KK, , ppbar • It was not observed at DM2.
BES-I (2230) Result (2230)
The situation at BESII • The mass plots shows no evident (2230) peaks in J/KK, , ppbar, which is different from BESI. • Difficult to draw firm conclusion at present. PWA is needed to draw firm conclusion on it.
(2230) could be similar to f0(980) at BESII • We saw a clear f0(980) mass peak in J/ at BESI, but we do not see a clear f0(980) peak in the mass plot at BESII. • However, we need a significant contribution of f0(980) in PWA of J/ at BESII J/ BESII M(+-)
Other 2++ glueball candidates • No other obvious good candidates have been observed in J/psi radiative decays in the mass range predicted by LQCD. • What does it mean: • LQCD prediction is not very reliable, or • BR(J/ G)xBR(Ghh) is small ( <10-4 ) so that we don’t have the sensitivity to observe it ( quite possible ), or, • The width of a glueball is very large ( ~1GeV, E.Klepmt ).
Where to search for the 0-+ glueball? • Lattice QCD predicts the 0-+glueball mass in the range of 2.3~2.6 GeV. • (1440) and X(1835) were suggested being possible candidates, but their masses are much lower than LQCD predictions.
No 0-+ glueball candidate observed in the mass range 2.3~2.6 GeV • No evidence for a relatively narrow state ( 100 ~ 200 MeV width ) above 2GeV in • Again: • LQCD reliable? • Production rate could be very low. • Glueball width could be very large.
PWA is crucial to most analyses at BESIII • Not only to the spin-parity determination of new hadrons • But also to the measurement of decay BR: e.g.: BR(J/K*K) BR(J/K*(1410) K) Also for D decays… From interference
With huge data samples at BESIII, PWA is possible. • However , there are many difficult problems to be solved. How to obtain robust PWA results with high speed?
Q1: How to speed up the PWA fit? • We will have 200 times larger data sample at BESIII: • Typical size of a data sample at BESII: 10000 events. Usually it takes 1- 3 years to publish one PWA result (with more than 20 CPU fully used). From previous talks at BESII, we have leant how we obtained the PWA results, including how we dealt with systematic uncertainties • Naively, we would have 2M events for one data sample at BESIII The speed will be about 100 times slower How many years do we need?
Q1: How to speed up the PWA fit? • PWA procedure at BESII: Global fit • The PWA input contains 4-momentum of all events (the whole mass range). • Various fits are tried with different combinations of the possible components/resonances/amplitudes, finding minimum –lnL of all these combinations. • One possible solution at BESIII: bin-by-bin fit • Divide the mass spectrum into many (~100) bins. • In each bin, we only fit various JPC components without BW structure. • We can perform PWA fits for all bins on 100 CPU.
Bin-by-Bin Fit • Advantages • Model independent for each JPC component in each mass bin. • Phase shift measured automatically • Fast • Disadvantages • Detail mass information lost • The constraint on the phase in nearby mass bin lost.
MC Input/Output Checks of Bin-by-Bin Fit • We have a working group to check whether the bin-by-bin fit can reproduce the input values based on extensive MC studies. Here I would only show some examples
Example 1: One 0++ resonance & one 2++ resonance Generated KK mass plot in J/KK (160K evts) int All 0++ 2++
Error bar: bin-by-bin fit result Histogram: generated mass plot 0++ 2++ MKK
Example 2: Two 2++ resonances Generated KK mass plot in J/KK (140K evts) 2++ A All 2++ B
0++ is not significant 0++ 2++
Example 3: Phase Shift Measurement 2++ 0++ Input : 0++: m=2.5GeV, =0.2GeV, =60 2++: Phase Space =0 • Output (fitting the phase shift curve): • =61.49±6.90 • M(0++)=2.5012±0.005GeV • (0++)=0.206±0.012GeV • M(2++)=1.227±0.403GeV • (2++)=32.273±17.906GeV
Bin-by-bin approach looks promising… • However