Charmonium Physics at BESIII

Charmonium Physics at BESIII

Changzheng YUAN Changzheng YUAN

IHEP, BeijingIHEP, Beijing

Jan. 14, 2004Jan. 14, 2004

•There were many discussions on charmonium physics•There were talks on BESIII•Here is a talk connect these two topics

Ecm of BEPCII 2.0 GeV-4.2 GeV

Charmonia production at BESIII•J/ (2S)(3770)(4040)(4160)

charmonium + states from their decays

Charmonia production at BESIII

ISR also need to be considered:

Observed cross section:

At BESIII:

Charmonia production at BESIII

•The big (2S) sample is extremely useful for the charmonium physics study, since it can produce all n=1 charmonium states and n=2 S-wave spin-singlet state c(2S).

•The huge J/ sample for light hadron spectroscopy study, the big samples (many years’ data taking) of (3770), (4040) and (4160) for charmed meson studies also supply information for charmonium physics study.

Res.

Number

of Evts

in 1 yr

Peak luminosity

(1033 cm-2s-1)

J/ 10×109 0.6

(2S) 3×109 1.0

(3770) 40×106 1.0

(4040) 30×106 0.6

(4160) 20×106 0.6

Average lum.=0.5×peak lum.1yr=107s data taking time

Here we will focus on ---

1. Search for hc(1P1) state2. Hadronic decay dynamics and “” puzzle3. The continuum amplitude and the data taking

strategy4. J/ψ study via ψ(2S) sample5. e+e-charmonium+X for a study of charmoni

um production mechanism

n 2S+1 L J

Search for hc(1P1) state

Charm thresholdψ(3770)

hc(1P1): the only missing charmonium state below charm threshold.

– Inconclusive evidence from R704 at ISR (1984), 5 events,

m=3525.4±0.8 MeV– Better evidence claimed by E760 (198

9-91) in pp→ hc →JJ→ee. m=3526.20±0.25 MeV Mass close to the center-of-gravity of the trip

let P-states (as expected if there are no long range spin-spin interactions)

– More statistics taken by E835 Not confirmed.– Not observed in B decays in the light

hadron channel for ηc’ observation.

E760

Where it can be found:1. B decays at B factories2. ψ(2S) decays at CLEOc

(if take data!)3. Hera-B or a similar hadron machine [ PRD63, 014007(2001) ]4. BESIII

Search for hc(1P1) state (in history)


Mass: c.o.g. of cJ states ≈ 3526 MeVtot ～ 510 keV (pQCD) ～ 1100 keV (NRQCD)

(ψ’hcπ0)=0.12(αM/αE) keVB(ψ’hcπ0)=(4.3±0.5) (αM/αE) ×10-4

(αM/αE =1-3)

With S-D mixing (θ=-12°)(ψ’hcπ0)=0.06(αM/αE) keVB(ψ’hcπ0)=(2.2±0.2) (αM/αE) ×10-4

(ψ’hcπ0)=0.84 keVB(ψ’hcπ0)=30 ×10-4

Kuang, Tuan, YanPRD37, 1210 (1988)

Kuang, PRD65, 094024 (2002)

B(ψ’hcπ0)=(2-30) ×10-4(0.6-9.0) ×106 ψ’hcπ0

in 3 ×109 produced ψ’s.

P. Ko, PRD52, 1710 (1995)


PQCD:B(hcγηc)=88%B(hcLH)=8.8%

NRQCD:B(hcγηc)=41%B(hcLH)=48%

PQCD:B(hcγηc)=80% B(hcLH)=13%

Kuang, Tuan, YanPRD37, 1210 (1988)

Kuang, PRD65, 094024 (2002)

•In all cases, hcγηc is the dominant decay mode, so one cansearch for hc with the hadronic decay channels of ηc.•In some cases, direct search for hc in hadronic decays also possible.


S) hc(1P1) c

ackgrounds: S) c1, c2,, Very small!

There are many more exclusive c decay modes!

r = (0.5 – 7.5)×10-6

60-900 events/year


In case observed by others, what BESIII can do:

1. Precision measurements of mass, decay modes

2. Absolute decay branching fractions

3. Production rates in ψ’ decays, χc2 decays …

Search for hc(1P1) state in inclusive π0 spectrum

Raw γγ massχ2 of 1C fit

Cut here

ψ’π0 hc(1P1)

Momentum resolution (4.0 MeV/c)

Efficiency is about 30%!

MC samples: a) 2M inclusive ψ’ decays by lund_charmb) 1M ψ’π0 hc(1P1) c by phase space

Input hc(1P1) parameters: mass: 3525 MeV width: 1 MeV

BESIII 2004Simulation(very preliminary)

1M ψ’π0 hc(1P1)

2M ψ’anything

3G ψ’anything

Parametri-zation, Scaling, sampling

Data=inclusive+signal×BRFit with polynomial+ Gaussian smeared BW



B(ψ’hcπ0)=2×10-4 B(ψ’hcπ0)=4×10-4

B(ψ’hcπ0)=10×10-4

B(ψ’hcπ0)=20×10-4B(ψ’hcπ0)=30×10-4

Even the signal cannot beSeen by eyes, significanceStill can be large!



•Very rough simulation indicates observation of hc(1P1) is possible if the BR is not very small, so that absolute hc

(1P1) decay branching fractions can be measured.

•A better simulation code is desired, and a set of optimized π0 selection criteria is needed (background will be lower, efficiency will be higher).

•The parameterization of the background shape is crucial for the fitting procedure.

•The non-Gaussian tails of the resolution function need careful measurement from real data.


Absolute BR of ηc(2S) at BESIII

Detector Calorimeter

crystalsE at 100M

eV

Crystal Ball NaI(Tl) 4.8 MeV

CLEOc CsI(Tl) 4.5 MeV

BES-III CsI(Tl) 5.0 MeV

One expects small bumpin the photon spectrum for the ηc(2S) at E = 48 MeV!

ηc(2S) mass: 3638 MeV width: 18 MeV


Energy resolution6 MeV.

100k ψ(2S)γηc (2S)

Absolute BR of ηc(2S) at BESIII

More studies needed to further improve the S/N at low energy!


2M ψ(2S)anything (lund_charm)

100k ψ(2S)γηc (2S) (phase space)

It could be hard to observe in the inclusive photon spectrum, considering the expected extremely low production rate in ψ(2S) decays.

pQCD rule and “ρπ puzzle”

Qh = )ee/J(B)ee)S2((B

)/J())S2((

)ggg/J(B)ggg)S2((B

3s

3s

≈ 12%

“15% rule”, “14% rule”, “12% rule” in literatures ----- “pQCD rule”

Mark-II at SPEAR found while many channels give ratios around 12%, ψ(2S) and J/ψρπ violate “pQCD rule”, so does K*K. ψ(2S) decays suppressed ----- “ρπ puzzle”

The assumptions: 1. pQCD is valid at c-quark mass 2. “pQCD rule” derived for inclusive decays holds for exclusive channels.

pQCD predicts

ρπ

K*K

Review

pQCD rule and “ρπ puzzle”

Many experimental results (esp. from BES)Many theoretical modelsExplanation still not satisfactory

Questions need to be fixed:1. Is the abnormal in J/ψ or in ψ(2S) decays

or in both?2. Are there assumptions behind the

experiments and/or theories?3. What is the key issue to solve the problem?

*&^%$#@ضء*()&%*)(#%дмфёЊ

ؤضء٣حشع ž¤&ùÐ…

The puzzle remains a puzzle …Both experimentalists and theorists are working hard …

Review

pQCD rule and “ρπ puzzle” Recent progress

•Continuum amplitude is very important in ψ decay study [Ping Wang, Changzheng Yuan and Xiaohu Mo] --the experimental data need to be revised --theoretical inferences need to be reexamined

•The missing ψ’ρπ may due to mixing of ψ(2S) and ψ(1D) [J. L. Rosner] --pQCD hold for J/ψ and ψ(2S) --abnormal is in ψ(1D) decays

The continuum amplitude

In e+e- annihilation experimentfor charmonium production,continuum amplitude contributesto all decay channels …

e+e-ψ(2S) @ BESII

Except for scan experiment,the continuum amplitude has been overlooked in bothexperiment and theory!


σtheo

σ’exp


At ψ(2S)

Born ISR =1.3MeV

RES (nb) 7887 4046 640

CON (nb) ~14 ~14 ~14Continuum contribution becomes larger after considering ISR and beam spread!

1. |aggg|=02. |aggg|=|a|3. |aggg|=3.4|a|4. |aggg|=5|a|5. |aggg|=10|aγ|

The continuum amplitude2

3

2

3

2

3 |||||||| 3

i

g

ii

ggB eaaeaeaaa aga 2

3

2

3

2

3 |||||||||||| 3

i

c

i

g

i

c

ii

gcgB eaeaaeaeaeaaaa caaga

exp

expexp

k

ψ(2S)

J/ψ

There is interference…


The consequences: 1. Results from different experiments not comparable a) beam spread (reduce/shift peak) b) data taking energy (hadron peak) c) selection criteria (s-dependent)

2. Wrong theoretical inferences a) the form factors b) the relative phase between strong and electromagnetic decays

0.5 MeV shift

90-95 % RES

BEPC2

CESRc

PLB574, 41 (2003)

(e+e-ρπ) atEcm=mψ(3770).

The form factors 0 and +-

2222

Re12

)(MMs

st

fes

Born

)(4

)(2

2/3

3

ss

s ffConBorn PF

)()()(214

)(22

2/3

3

ssBsBs

s ffBorn PF

)90,0(,/3

)(2

i

t

e eMiMs

ssB

Proportion RES CON INT

BES

(1.3MeV)

0

40.9 % 60.4% – 1.3%

+–

41.4 % 60.0% – 1.4%

[scan] +– 43.8% 55.1% +1.1%

DORIS

(2.0Mev)

+– 32.7 % 68.5% – 1.2%

P. Wang et al., PLB557, 192(2003)

The universal -90°phase

J/ψ Decays: 1. AP: 90 ° M. Suzuki, PRD63, 054021 (2001) 2. VP: (106 ±10) ° J. Jousset et al., PRD41, 1389 (1990) D. Coffman et al., PRD38, 2695 (1988) N. N. Achasov, talk at Hadron2001 3. PP: (90 ±10) ° M. Suzuki, PRD60, 051501 (1999) (103 ±7) ° BES, PRD69, (2004) 4. VV: (138 ±37) ° L. Köpke and N. Wermes, Phys. Rep. 74, 67 (1989) 5. NN: (89 ±15) ° R. Baldini et al., PLB444, 111 (1998)

ψ(2S)VP 1. φ=180 ° (± 90 ° ruled out!) M. Suzuki, PRD63, 054021 (2001)

|φ|The phase between strong and EM decays of resonance

The universal -90°phase VP

a

a g3C F MiMs

ssB

t

e

2

/3)(

Four equations for four unknowns:

g

g

a

a

3

3 R

Haber and Perrier, PRD32, 2961(1985)

The universal -90°phase J/ψVP

Two solutionsWith oppositeSign!

hep-ph/0303144with continuum!

The universal -90°phase ψ(2S)VP

Assuming Rψ(2S)=RJ/ψ

hep-ph/0303144with continuum!

PRD63, 054021 (2001)Without continuum!

1. Can’t rule out (nearly) orthogonal phase

2. The phase is negative

–82±29° 121 ±27 °

Yuan, Wang, Mo

PLB567 (2003)73

K+K– & + inputs ;Input 1:DASP;Input 2:BESI ;Input 3: K+K–

from BESI & + by form factor.

The universal -90°phase ψ(2S)PP

BESIIhep-ex/0310024

B ((2S)

KS K

L

) =5.24

10 – 5

First

measurement of

the phase in

(2S) decays

φ

ψ(2S) π+π-

ψ(2S) K+K-

ψ(2S) KS KL

The universal -90°phase ψ(3770)ρπ

Using mixing angle θ=12°, assuming ψ(2S)ρπ completely missing, ψ(3770)ρπ is enhanced!

or

Using ωπ form factor to estimate ρπ form factor: Comparable!

Interference?

The universal -90°phase ψ(3770)ρπ

To measure B(ψ(3770)ρπ), the best way is to do the energy scan!

The band is for non-zero B(ψ(2S)ρπ)!

Wang, Yuan and MoPLB574, 41(2003).

MK3 UL (<6.3pb)Favors φ=-90°!

σ(K*0K0+c.c.)For φ=-90°!

Missing ρπ signal and/orenhanced K*0K0 signal indicate BRs at 10-4 level.

Destructive/constructive interference

The hidden assumptions

VP:

PP:

Assumptions:1. EM amplitude (EM form

factor) only depends on the quark charge

2. a3g and ε have same phase3. Higher order term negligible4. ISR affects all channels the

same (all measurements assumed ISR negligible)

Need high precision ψ’ and J/ψ data to check!

Rosner’s model for “ρπ puzzle”

Using mixing angle θ=12°

This means a big ψ(3770) ρπ decay partial width (9 keV!), or, big 1D ρπ transition matrix element. Why?

Assumptions:• pQCD works for ψ(1S) and ψ(2S) ρπ • Missing ψ’ ρπ due to 2S and 1D mixing

Rosner’s model for KSKL mode

Using mixing angle θ=12°

Current data can reach upper bound, CLEOc/BESIII can reach lower bound!

Assumptions:• pQCD works for ψ(1S) an

d ψ(2S) KSKL

• Enhanced ψ’ KSKL due to 2S and 1D mixing

BES2003:B(ψ’ KSKL) =(5.24±0.47 ±0.48) ×10-5

B(J/ψ KSKL)=(1.82±0.04 ±0.13) ×10-4

Qh=(28.2 ±3.7)%

B(ψ(3770) KSKL)=(0.12-4.0) ×10-5

Range due to phase between two amplitudes

Wang, Mo, Yuan

Test of the Rosner’s model

Measurement of the light hadron decays of ψ(3770) is crucial for testing this model for solving the “ρπ” puzzle.

Need high precision data [ψ(3770)] to check!

High precision data [ψ(4040), ψ(4160)] may also supply information!

Is the “puzzle” in ψ(3770) decays?

hep-ph/0303144

The small BR channels at BESIII: an example

B(ψ’K*+K-+c.c.)=2×10-5

ψ’KSK+π-+c.c. ψ’KSK+π-+c.c.

B(ψ’K*+K-+c.c.)=0.4×10-5

KSπ mass (GeV) KSπ mass (GeV)

Still room to suppress the background!

BR at 10-5 level can be measured in high precision.


Energy scan: the way for high precision BR measurement

e+e-X @ ψ(2S) e+e-ρπ @ ψ(3770)

All the channels should be measured by a energy scan!

Data sample should be taken at a few energy points, instead of at resonance peak only.

Data taking strategy

1. How many points?2. At what energies?3. How to distribute luminosity?

Use toy Monte Carlo to optimize!

To separate continuum from resonance, at least data at three energy points should be taken (if resonance parameters need to be measured, more points needed).

Different channel has different phase and amplitude ratio, three points may not result in optimized precisions for all the channels.

Data taking strategy: the MC model

Data taking strategy: how many points?

Data taking strategy: the energies?

Data taking strategy: the luminosities?

Data taking strategy: summary

We are working hard …

No problem to finish before BESIII running …

J/ψ study using ψ(2S) sample

Advantages:1. High precision total number of events2. No QED background3. No beam associated background4. Trigger efficiency free

Disadvantages:1. Sample is small2. Two more tracks3. J/ψ is moving

It is suitable for 1. High precision measurement

for channels with large BR;2. Searching for some of the

rare decay modes

Need more investigation on the light hadron spectroscopy study using partial wave analysis method with ψ(2S)π+π-J/ψ.

Best precisions on B(J/ψμ+μ-)and B(J/ψπ+π-π0)are achieved with ψ(2S) samples.

J/ψ study using ψ(2S) sample

Measurement of B(J/ψπ+π-π0) /B(J/ψμ+μ-)

3×109 ψ (2S)= 1×109 J/ψ

B(J/ψπ+π-π0)

B(J/ψμ+μ-)

Kinematic fit + (ECAL+dE/dx)for J/ψμ+μ- selection.

J/ψμ+μ-

J/ψe+e- J/ψπ+π-π0

Kinematic fit + (ECAL+dE/dx+MU)for J/ψ π+π-π0 selection.


Measurement of B(J/ψπ+π-π0) /B(J/ψμ+μ-): errors

Lots of systematic errors cancel out! Only the residual differences affect relative BR measurement.

backgroundsSystematic uncertainties on tracking kinematic fit photon/π0 efficiency backgrounds …can be studied with large data sample.

Particle ID is not used!

Measurement of B(J/ψπ+π-π0) /B(J/ψμ+μ-): errors

～ 1% precision on BR is a big challenge!

Current WA dominated by BES result from

about 4 M ψ(2S)

Depends on the precisions of the

background channels and simulation

PDG2002: B(J/ψπ+π-π0)=(1.5 ±0.2 )%!BESII(prel.): B(J/ψπ+π-π0)=(2.10 ±0.12 )%!PDG2010: B(J/ψπ+π-π0)=(2.xxx±0.017)%!

BESII preliminary

J/ψ study using ψ(2S) sample: search

C-parity violating process J/ψγγSensitivity of 10-7 can be reached!

3×109 ψ (2S)= 1×109 J/ψLund_crmScaled!

B=3× 10-7

B=3× 10-8


e+e-charmonium+XC. H. Chang et al., PRD56, R1363(1997)F. Yuan et al., PRD56, 1663(1997)

A test of the COM and a measurement of the COM matrix elements.

Taking data below ψ(2S) peak to avoid background?The data may also be used for τ physics?

Ecm=4.03 GeV

Summary

•Charmonium physics is a most important field at BESIII

•The large ψ’ sample will allow a search of the still missing hc

(1p1) state, and a possible systematic study of hc(1p1) and ηc’, both in inclusive and in exclusive modes.

•The large data samples at J/ψ, ψ’, ψ(3770), ψ(4040) and ψ(4160) will benefit the study of the “ρπ” puzzle and the deep understanding of the charmonium decay dynamics.

•To get the correct high precision branching fractions of the vector charmonium states, the data taking procedure should be optimized, a fine scan with large statistics at each energy point is desired.

•ψ’ π π J/ψ sample can be used for J/ψ physics study.

•Wish charmonium physics a bright future!

Thanks a lot!Thanks a lot!

谢谢！谢谢！

Documents

Charmonium Physics at BESIII