J/ Physics at BESIII/BEPCII

Xiaoyan SHEN

Institute of High Energy Physics, CAS

BESIII/CLEO-c Workshop, Jan. 13-15, 2004, Beijing

Outline Introduction

BESIII/BEPCII project

Physics at BESIII/BEPCII -- non-qq states -- meson spectroscopy -- baryon spectroscopy -- probing new physics

-- c physics

Summary

Introduction

• Strong interaction is described by non-Abelian gauge field theory – QCD interaction of quarks and gluons.

• QCD predicts the existence of a new type of hadrons with explicit gluonic degrees of freedom.

• Study of the hadron spectroscopy helps to understand the strong interaction.

• Confirmation of the glueball or hybrid state is a directly test of QCD.

Experiments

Hadronic peripherial production

K-p experiment (LASS,…)

-p experiments (BNL E852, VES, GAMS …) Central production

(WA76, WA91, WA102, …) annihilation

(E760 and E835 at FNAL, Crystal Barrel at CERN)

annihilation (OBLIX at CERN) Electro- and photo-production experiments e+e- storage ring facilities

(Crystal Ball, MarkIII, DM2, BES)

(two photon collisions in CLEO and LEP)

(recently Babar and Belle exps.)

sf pXppp )( 0

pp

pn

BESIII/BEPCII project

BEPCII design goal:

MDC: Momentum resolution:

dE/dX resolution: 6-7%

EMC : CsI(Tl) crystals

Energy resolution: 2.5%@1GeV Position resolution: 6mm@1GeV

luminosity: 11033 @ 1.89 GeV

%37.0%32.0 t

P

Pt

BESIII design goal:

J/ Physics at BESIII/BEPCII

Search for glueballs, hybrids and multi-quark states

Systematic study of light hadron spectroscopy

Study of the excited baryon states Search for more J/ decay channels Probing for new physics in J/ decays c physics

• Some QCD-based theories make predictions to the glueball mass.

• LQCD predicts the lowest glueball state is 0++. The mass is around 1.5 GeV – 1.7 GeV.

• LQCD predicts the next lightest glueball is 2++. The mass is around 2.4 GeV.

• The mix of glueball with ordinary qq meson makes the situation more difficult.

Glueball candidates: f0(1500), f0(1700), (2230), ...

Search for glueballs

Morningstar 1997

Glueball search and study at BESII (58M J/)

PWA of J/KK shows a dominant 0++ in 1.7 GeV mass region.

PWA of J/ and to study 0++ glueball candidates.

PWA of J/ and KK to study 0-+ structures around 1.44 GeV.

(2230) was observed by MARKIII, BESI etc..

Not seen in the mass spectra of KK, and pp

by BESII. Careful PWA is being performed by BESII.

K+K-

K K0s0s

BKG

(1525)f '2

f0(1710)

After acceptanceand isospin corr-ections

BESII 58M J/

BESII and KK /J 0S

0SKK

/J

00/ J

/J

KsKJ /

0/ KKJ

Search for exotic 1 －＋ state at BESII (58M J/)• The JPC of the ordinary qq meson cannot be the exotic numbers 0+-, 0--, 1-+, 2+-, 3-+, …

• The hybrid states with the exotic quantum numbers would be evidence for non-qq degrees of freedom.

• Theoretical model predicts : exotic hybrid state preferentially to pairs of S wave and P wave mesons, such as f1(1285), b1(1235).

• Theoretical model predicts: M 1-+ 1.9 GeV

• BES is analyzing J/ 0 to search for 1-+ state.

Search for other non-qq states at BESII

Near pp threshold enhancement in ppJ /

enhancement

c

Fit reults

Mass: M=1859 MeV/c2

Width: < 30 MeV/c2 (90% CL)

J/pp

M(pp)-2mp (GeV)0 0.1 0.2 0.3

BG curve Eff. curve

2/dof=56/56

Fitted peak

Fitted curve +3 +510 25

This enhancement is important:

excluded from the known particles

cannot be explained by theories, such as FSI.

mass≤2mp ， width is narrow Hard to be explained as a conventional qq meson Important in testing and developing QCD !

BESII 58M J/

in J/

Before K*(892) 0 cut

After K*(892) 0 cut

in J/K+K- and K*K

Meson spectroscopy

The low mass 0++ states have been confusing for many years. There are so many 0++s’, such as f0(1370), f0(15

00), f0(1710) …. PWA of J/ … Two ground-state isoscalar 1++ states at 1240 and 148

0 MeV in the quark model. But there are 3 1++ states in this region -- f1(1285) , f1(1420), f1(1530).

whether 0++ f0(980) and a0(980) are molecular states

or not. PWA of J/ , KK, … extra 2++ states

PWA of J/ and KK, …

Baryon spectroscopy The understanding of the internal quark-gluon structure of baryons is

one of the most important tasks in both particle and nuclear physics.

The systematic study of various baryon spectroscopy will provide us with critical insights into the nature of QCD in the confinement domain.

Jefferson Lab, ELSA, GRAAL, SPRING8 and BES have started to study the baryon and excited baryon states.

The available experimental information is still poor, especially for the excited baryon states with two strange quarks, e.g., *. Some phenomenological QCD-inspired models predict more than 30 such kinds of baryons, however only two are experimentally well settled.

Totally only about 10% excited baryons are observed.

Advantages of studying excited baryons from J/ decays

• excited baryons can be produced through J/ decays.

• for J/ NN and NN decays, the N and N systems are limited to be pure isospin ½ due to isospin conservation.

• search for “missing” baryon states and hybrid baryon with BESIII/BEPCII.

excited baryon states at BESII

npJ /

N*(1440)

N*(1520)

N*(1535)N*(1650)

N*(1675)

N*(1680)

?

pKJ /N*(1650

)

Probing for new physics in J/ decays

1. Lepton flavor violation (LVF)

--- In SM, lepton flavor symmetries are conserved.

--- neutrinos having mass and flavor oscillation indicate the existence of LVF

--- J/ e, and e are LVF processes

--- some theoretical models predict: Br(J/) 10-5 – 10-8

Br(J/e) 10-5 – 10-7

--- search for J/ and J/e with 1010 or more J/ data.

2. CP test in J/ decays

--- CP violation was first discovered in K system--- CP violation was also found in B system--- no experimental indication of CP violation in other processes--- search for CP violation in other places where SM predicts no or tiny CP violation

With BESIII J/ data, CP test can be done in:

--- J/ particle + antiparticle (), where the polarization can be measured through subsequential decays of .--- J/ , clean sample, but low efficiency because of K decay large sample is needed.

3. Flavor changing processes

--- J/ can decay to single D meson + X--- In SM, these Cabbibo suppressed and/or favored weak decays can proceed through tree and penguim processes and have the branching ratios <10-8.

Since the penguin c u transition is small in SM, the theoretical estimation gives:

Br(J/ D0Xu) 10-10

Br(J/ D+Xu) 10-9

Considering new physics effects,

Br(J/ D/D Xu) 10-5

Br(J/ Ds+K-) 10-5

c physics

c produced from J/ c ( 1.3%)

E 116 MeV good photon detection capability

c multi – charged tracks good PID and good momentum resolution c decays to hadrons through annihilating to two gluons.

The sum of c decay branching ratios < 30%

c decays

c Vector + Vector

PQCD forbidden. Observed c and c,

search for c with BESIII data. c baryon pairs (only have c pp) c two photons More c decay channels CP violation test in c decays.

Simulation of possible 2++ glueball in J/’

(2230) is a 2++ glueball candidate

--- LQCD calculation --- some glueball favored exps. observed it (narrow, flavor blind, …); some didn’t find it --- small coupling to 2-photon process

Theoretical calculations predict: (2230) can be largely coupled to ’ and ’’, if it exists and is a gleuball.

J/’, , ’0, 0+-

might be one of the main decay channels of (2230)

(Take (2230) as an example)

• assuming Br(J/(2230))Br(’) 3 10-6.

• assuming 6109 J/ events • f0(1500), X(1910) and X(2150) are included according to the results from other experiments.

• the backgrounds are included in the simulation.

final state: 42

-- a detector with good photon detection

-- a high statistics.

J/’, , ’0, 0+-

(2230)

Input Output (B=1.0T)

X(1910)M(MeV)(MeV)

Br(10-6)

1910.00150.00

7.20

1909.402.40153.898.67

7.470.30

X(2150)M(MeV)(MeV)

Br(10-6)

2150.00157.00

3.60

2152.209.90167.1321.00

3.660.33

(2230)

M(MeV)(MeV)

Br(10-6)

2230.0025.00

3.0

2231.201.0530.184.543.180.33

Breit-Wigner fit results

Separation of 0++, 2++ and 4++ in J/K+K-

• The structures in the K+K- mass region over 2.0 GeV are quite complicated.

• Distinguishing 0++, 2++ and 4++ in this mass region is important.

• possible resonances included in the simulation for MKK > 2.0 GeV are: (2230) and f4(2050) (f0(2100)).

• main backgound: J/ K* K

• assuming 1109 J/ events

• for (2230), assuming 2++, x=0.5, y=0.5 for f4(2050), assuming 4++, x=0.5, y=0.5

• the JPCs’ of (2230) and f4(2050) being 2++ and 4++ gives the best Log Likelihood value.

• excluding either (2230) or f4(2050) makes the log likelihood value be worse apparently.

• 0++, 2++ and 4++ can be separated clearly in the mass region over 2.0 GeV with BESIII detector.

PWA Results

Crosses are generated Monte-Carlo data,histogram is the PWA fit projection.

• assuming 6 109 J/ events

• J/a0(980), a2(1320), (1390), (2300) are included.

• background included

• PWA can well separate these states

Simulation of J/00

Precise measurement of K* mass splitting

There is mass splitting between the different isospin states (K*(892) and K(892)*0).

Different theoretical models give different m. Precise measurement of m requires a large statistics and a detect

or with good PID and momentum resolution.

),)892(*.(.)892(*/ 0000 ss KKKccKKJ

Signal (6 108 J/):),)892(*.(.)892(*/ 00

ss KKKccKKJ

Background:

The signals are fitted using:

Background is fitted with the 3rd. order polynomial.

When the input m = 6.0 MeV, we obtain the mass splitting as: m = 5.79 0.160.13 Me

V

Simulation of J/Ds+K-

assuming 1010 J/ events main background is J/KK signal channel J/DsK , Ds, KK

Br(J/DsK) = 1.010-6

Br(J/DsK) = 1.010-7

Br(J/DsK+) < 2.48 10-7

at 90% C.L.

Summary

With BESIII/BEPCII:

-- search for non-qq states -- systematic study of meson spectroscopy -- systematic study of baryon spectroscopy -- probing new physics

-- c physics

Is Mpeak really less than 2mp?

No turnover at thresholdpeak mass must be <2mp

weight events by q0/q:(i.e. remove threshold factor)

M(pp)-2mp (GeV)