Status of Charmonium Spectroscopy

Status of Charmonium Spectroscopy

Matteo Negrini

INFN Ferrara

Panda collaboration meeting

Dubna, July 3, 2007

M. Negrini - Panda Meeting Dubna - July 3, 2007 2

Outline

• Overview of charmonium production mechanisms• Conventional charmonia states• New states in the charmonium mass region


The charmonium spectrum

3.73DD threshold

3.87DD* threshold


Charmonium production

• e+e- machines (MARK I-II-III, TPC, Crystal Ball, DASP, PLUTO, LEP, CLEO, KEDR, OLYA, CLEO-c, BES, BaBar, Belle)– direct formation (JPC = 1-- states)– production– initial state radiation– B meson decay– double charmonium production

• pp annihilation (R704, E760, E835, PANDA)• hadroproduction (CDF, D0, LHC)• electroproduction (HERA-B, H1, ZEUS)


Direct formation in e+e- annihilation

• Only states with the photon quantum number (JPC=1--)

• Other states may be accessed through radiative decays

i.e. e+e- ' cJ

Photon spectra observed by Crystal Ball

ccee

PRL 45,1150 (1980)

CBAL


Initial state radiation processes

• At B-factories: formation of 1-- states with m<10.58 GeV is possible after radiation of a photon from the e± in the initial state that lower the s of the interaction

• ISR cross section for production of final state f:

ccee ISR

))1((),( xsxsWdx

df

f

211ln2

2),(

2xx

m

s

xxsW

e

x=2E/s

s’=s(1-x)

Probability of ISR photon emission:


production

• Interaction of at e+e- machines

• Production of C=+ states• The state is usually identified

by its hadronic decays• The cross section for this

process scales with BR(cc)

cceeee

C=+


B meson decay

• Color suppressed B decays to charmonium states

• Branching ratios of the order of 10-4 but large samples available at the B factories

• Large discovery potential for the B factories in charmonium physics (c', X(3872))

ccKB (*)


Inclusive charmonia in B decayee-- DD**

ee++

BBrecoreco

BBsignalsignal KK

XX

• Fully reconstruct Breco in hadronic modes• The X mass distribution can be obtained from the momentum distribution of K± • Huge background due to secondary K± tracks• Observation of X states independent from the decay mode• Absolute measurement of BR(BXK)

low mass region

high mass region

PRL 96, 052002 (2006)


Double charmonium production• Associated production of 2

charmonium states in e+e- interaction

• Reconstruct a J/ and compute the recoiling invariant mass

• Observation of C=+ states• Cross section one order of

magnitude larger than NRQCD predictions

ccJee /

pb

tracksBRJee cc

011.0033.0

)4()/(

PRL 89, 142001 (2002)

c

c0

c

C=+


Direct formation in pp annihilation

• Coherent annihilaton of the 3 quarks with the 3 antiquarks into a cc pair

• Direct formation of states with all quantum numbers

• Perform precision spectroscopy measurements through direct scan of the resonances

• Large hadronic background

ccpp


pp annihilation: experimental technique• Antiproton beam on H gas target• The total energy is precisely known

from the beam parameters (the detector resolution is not crucial)– Gaussian beam energy distribution

~400 keV (' width 300 keV)

• Measured cross section obtained counting events in the final state f– Convolution between resonance cross

section and beam energy distribution

)')'()'(( dEEEEILumN BWbeambkgev

222 /)(41

)()()12()(

RRBW ME

fRBRRppBRJ

kE


Direct measurement of the ' width• pp scan of ' observing e+e-X final state• Energy determination:

• The largest systematic uncertainty on the width comes from the determination of the factor

• 2 scans performed with different techniques:– constant B: the measured width has a negative correlation with – constant orbit: the measured width has a positive correlation with

• Combining two scan of similar luminosity the dependence of the result from can be reduced

E835hep-ex/0703012

2232

)1(2

L

L

f

f

E

dE

CM

CM

f

f

p

p

1

f = revolution frequencyL = orbit length = phase-slip factor (machine parameter)


Direct measurement of the ' widthE835

hep-ex/0703012


The c (11S0)

• The ground state of charmonium (JPC=0-+)

• The mass difference M(J/)-M(c) is a key parameter for the potential model

• Observed in:– M1 radiative decays of J/ and '– pp annihilation– fusion– B decay– double charmonium production


The c mass and widthLarge widthM and measured by several experiments but discrepancies still present

M = 2980.4±1.2 MeV = 25.5±3.4 MeV

PDG 2006


Some recent c width measurements

Babar:(c) = 34.3±2.3±0.9 MeV

E835:(c) = 20.4+7.7

-6.7±2.0 MeV

CLEO:(c) = 24.8±3.4±3.5 MeV

PRL 92,142001 (2004)

PRL 92,142002 (2004) PLB 566,45 (2003)

pp

KKS

KKS

E835


The cJ (13PJ)

• Produced in ' decay– BR('c0) = 9.2±0.4%

– BR('c1) = 8.7±0.4%

– BR('c2) = 8.1±0.4%

• c0 and c1 produced in B decay

• c0 observed in double charmonium production

• c0 and c2 produced in fusion

• All can be directly formed in pp annihilationPDG06 c0 c1 c2

M (MeV) 3414.76±0.35 3510.66±0.07 3556.20±0.09

(MeV) 10.4±0.7 0.89±0.05 2.06±0.12


cJ scan at pp machines

• Precision measurements of cJ masses and widths obtained through direct scan at pp machines

• Count the number of J/e+e- in the final state (background ~0)

NPB 717, 34 (2005)

PLB 533, 237 (2002)

c0 c1 c2

c2c1

E835

/Jpp cJ


Study of neutral hadronic channels at E835

• Study of hadronic decay modes of charmonium in pp annihilations

• Small signals in presence of a large background• Possible observation through study of the interference

between resonant and non-resonant amplitudes


Interference measurement of c000

00pp

22

),( BA iiR BeAeix

Azx

dz

d

2/0

0

MEx CM

*cosz

ResonantInterfering(helicity 0)

Non-Interfering(helicity 1)

PRL 91, 091801 (2003)E835


The c' (21S0)• First c' candidate observed by

Crystal Ball in 1982– Observation of 5582±1270

photons from 'c' decay

– M = 3594±5 MeV– < 8 MeV (95% CL)

• Never confirmed by other experiments

• M('-c')=92 MeV

• PQCD prediction for the M(')-M(c') mass splitting:

PRL 48, 70 (1982)MeVSM

JM

M

eeJ

eeSM 68)1(

)/(

)'(

)/(

)'()2(

2

2

Photon energy distribution

CBAL


The c' (21S0)

• Twenty years later (2002) observation of the c' by Belle– M = 3654±6±8 MeV– < 55 MeV (90% CL)– Observation of 56 events with

21±2 expected background from BKKsK- decay

• Studied also by other experiments (Babar and CLEO) and with different techniques (, double charmonium) PRL 89, 102001 (2002)

KKKB S


Mass and width of the c' (21S0)

Experiment Mass (MeV) Width (MeV) Technique

Belle 3654±6±8 <55 (90% CL) B decay

BaBar 3630.8±3.4±1.0 17.0 ±8.3±2.5 production

CLEO 3642.9±3.1±1.5 6.3±12.4±4.0 production

BaBar 3645.0±5.5+4.9-7.8 22±14 double

charmonium

Belle 3626±5±6 - double charmonium

The mass and width are not precisely knownSeveral measurement, all consistent but with large errors


The hc (11P1)

• Quantum numbers: JPC = 1+- • Expected to have small width: < 1 MeV • Hard to access. Can be produced in:

– pp annihilation (unknown BR)

– radiative E1 decay from c'

• One of the main decay modes should be hc c

• Precision measurements of the hc parameters give unique possibility to test the hyperfine splitting potential. The hc is expected to be within a few MeV from the center of gravity of the cJ states:

MeVMMM

hM cccc 36.3525

9

)(5)(3)()( 210


The hc (11P1)Observation by E760 of pp hc J/0 The decay is isospin violating Not confirmed by E835 with larger statistics (2 running periods)

E760 E835-1997E835-2000

PRL 69, 2337 (1992)

PRD 72, 032001 (2005)

E760:M = 3526.3±0.2±0.2 MeVNarrow ( < 1.1 MeV at 90% CL)

E835


hc c - E835Excess of hc c, c events observed by E835

PRD 72, 032001 (2005)

M = 3525.8±0.2±0.2 MeVNarrow ( < 1 MeV)

(pp)BR(c) ~ 12.0±4.5 eVcompatible with expectations

E835


hc c - CLEO))((' 0

cchee The ' decay mode is isospin violating

PRL 95, 102003 (2005)

Exclusive analysis (c hadrons)The c is reconstructed in 7 decay modes (sum of BR ~ 10%)

Inclusive analysis Invariant mass recoiling against a 0 (after background rejection for events consistent with a radiative decay to c)

CLEO results:

MC data


Charmonium states above the DD threshold

• Region above DD mass threshold (3.72 GeV) is poorly known

• Interesting region, rich of new states

• Excited vector states investigated at e+e- machines (latest results by BES)

• Only (3770) clearly observed– considered to be the 3D1

charmonium state

Compilation of R measurements in the region 2-5 GeV and latest BES measurement in the region 3.7-4.6 GeV

PRL 88, 101802 (2002)

(3770)

(4040) (4160) (4415)

BES


The new states• New states in the charmonium mass region have been

recently observed at the B factories• Their nature is still unknown• Several hypothesis:

– Charmonium (1),(2),(3) – D-D(*) molecules (4),(5) – Diquark-antidiquark (cu-cu) state (6) – Threshold effects– ... and others!

(1) Barnes and Godfrey, PRD 69, 054008 (2004) (4) Swanson, PLB 588, 189 (2004)

(2) Eichten, Lane and Quigg, PRD 69, 094019 (2004)

(6) Maiani, et. al., PRD 71, 014028 (2005)

(5) Tornqvist, PLB 590, 209 (2004)

(3) Suzuki, PRD 72, 114013 (2005)

Need experimental result to test models:• Quantum numbers• Decay modes• Branching ratios• Angular distributions• Charged partners?

A few references:


X(3872)

BABARPRD 71, 071103 (2005)

D0PRL 93, 162002 (2004)

CDFPRL 93, 072201 (2004)

BELLEPRL 92, 262001 (2003)

Discovered by Belle

B+ K+ X(3872) X(3872)J/ +- (compatible with J/ 0)

Confirmed by:• CDF• D0• BaBar

MX=3871.9±0.5 MeV/c2 X<2.3 MeV/c2 at 90%CLat D0D0* thresholdJPC=1++ favored


X(3872) - +- mass distribution

The invariant mass distributionis consistent with J/0 decay(isospin I=1)

hep-ex/0505038

PRL 96, 102002 (2006)


X(3872) - angular distribution

0++ and 0-+ ruled out by Belle

2/dof = 34/9

2/dof = 34/9

1++ and 2-+ favored by CDF

hep-ex/0505038 PRL 96, 102002 (2006)

JPC = 0++, 1++, 2-+, 1--


Inclusive charmonia in B decayee-- DD**

ee++

BBrecoreco

BBsignalsignal KK

XX

high mass region

PRL 96, 052002 (2006)

No X(3872) signal observedBR(B±X(3872)K±)<3.2·10-4 at 90% CLFrom BaBar-Belle average:BR(B±X(3872)K±, X(3872)J/+-)=

=(13.3±2.5)·10-6

BR(X(3872)J/+-)>4.2% at 90% CL


X(3872) J/ Belle and BaBar see J/ decay of X(3872) in B decays (B J/ K)

Implications:• C=+ for the X(3872)• I=1 for the () in J/+- • forbidden J/00, J/0, and J/ decays

If X(3872) has I=0 the J/+- decay must occur with isospin violation

1.03.0)πψπB(X(3872)

ψγ)B(X(3872)

610)3.00.13.3(ψγ)X,X(3872)KB(B

hep-ex/0505037

N=13.6±4.4

610)1.06.08.1(ψγ)X,X(3872)KB(B

PRD 74, 071101 (2006)


X(3872) J/ Observation of J/ decay by Belle in B decays (B J/ K, +-0)

hep-ex/0505037

1~)/)3872((

)3/)3872((

JXBR

JXBR

Branching ratio comparable to J/:

Hint for strong isospin violation effectin X(3872) decays: suggestions of X(3872) as I=0 and I=1 mixture


X (3872) D0D00

PRL 97, 162002 (2006)

Observation of D0D00 decay of X(3872) in B decays (B K D0D00)

M = 3875.2±0.7+0.3-1.6±0.8 MeV

Significance: 6.4

BR(DD)>40% (from BR(J/)>4.2%)JPC=1++ favored (the DD decay is expected to be be suppressed for J=2 states)But the measured mass is ~2 above the X(3872) measured mass

10~)/)3872((

))3872(( 000

JXBR

DDXBR


Search for X(3872) in B0 decays

B±X(3872)K± B0X(3872)Ks

N=61.2±15.3M=3871.3±0.6±0.1 MeV/c2

N=8.3±4.5M=3868.6±1.2±0.2 MeV/c2

2.56.1

BR(B0X(3872)Ks)/BR(B±X(3872)K±)=0.50±0.30±0.05M=2.7±1.3±0.2 MeV/c2

Not conclusive: more data needed

211 fb-1

PRD 73,011101 (2006)

Diquark-antidiquarkmodel predicts the existence of two X(3872) states (Xu and Xd) with slightly different masses:M~8±3 MeV

Different amounts of Xu and Xd produced in B± andB0 decays

DD* moleculemodel predict B0X(3872)K0 to be suppressed by one order of magnitude


Search for X(3872) charged partners

3872

B0X(3872)+K-

Inclusive K± momentum on B0 recoilNo signal is observed for charged partners

BR(B0X (3872)+K-)<5·10-4 at 90% CL

B0J/-0K+ B-J/-0Ks PRD 71, 031501 (2005)

No charged partner observed

BR(B0X(3872)-K+, X(3872)-J/-0)<5.4·10-6 at 90% CL

BR(B-X(3872)-K0, X(3872)-J/-0)<22·10-6 at 90% CL

PRL 96, 052002 (2006)

38723872

1. Exclusive reconstruction technique

2. Inclusive search using recoil technique

Isospin multiplet: search for charged partners produced in B decays


X(3872)

• The charmonium interpretation starts being in trouble– The decay to c1,2 has been searched by Belle but not

observed– The decay to J/ was searched by Babar but not observed– No clear assignment on the basis of predicted mass spectra

• All other interpretations assume that the X(3872) has a dominant 4 quarks Fock space component (cc qq) – The main difference between the models is the spatial, color and

spin configuration of the state, driven by different assumed dynamics

– Different quark dynamics yield different qualitative predictions that need to be tested experimentally


X(3872): testing the interaction dynamicsDifferent assumptions yield different predictions that can be tested

1. (c q)3S=1 (cq)3

S=0 + (c q)3S=0 (cq)3

S=1 : diquark-antidiquark

– model assumes clustering of heavy-light color triplet diquarks

– two states Xu and Xd with different masses and two charged partners may exist

– mass spectrum of states predicted

2. (cq)1S=0 (qc)1

S=1 + (cq)1S=1 (qc)1

S=0 : D0D0* molecule

– assumes that D0D0* is the dominant Fock space component

– short range (cc)1S=1 (qq)1

S=1~J/, component included

– a prediction (J/+-)~(J/+-0) is consistent with Belle data– a prediction (J/+-)~20 (D0D00) is off by 2 orders of magnitude

3. (cc)8S=1 (qq)8

S=1 : molecular model

– assumes that the dominant Fock space component are a cc and qq in color octet (similar to case 2)

– decays into charmonium with light pseudoscalar mesons are suppressed wrt charmonium with light vector mesons

– two neutral states and two charged partners are predicetd

No definitive conclusion can be drawn based on present data

Failures in predictions can be due to suboptimal tuning of a phenomenological hamiltonian rather than real failure of models

an executive summary: hep-ph/0611310


X(3940)hep-ex/0507019

XJee / M = 3936±14 MeV < 50 MeVN = 266±63 events (Signif.: 5 Candidate for c''(31S0)

Mrecoil for events tagged as J/DD or J/DD*X(3940) DD not seenX(3940) D*D seen

X(3940) DD

X(3940) D*D

Compute invariant mass recoiling against a J/ in e+e- interactions at s=10.58 GeVAccess C=+ states


Y(3940)PRL 94, 182002 (2005)

/JKB

M = 3943±11±13 MeV = 87±22±26 MeVN = 58±11 eventsSignificance: 8.1 Candidate for c1' ?

phase spacethreshold

phase spacethreshold +Breit-Wigner

Reconstruct B in J/K decays andcount the number of B in M(J/) bins


Z(3930)

sin4 (J=2)

PRL 96, 082003 (2006)

DD

C=+ defined by production mechanismM = 3929±5±2 MeV = 29±5±2 MeVN = 64±18 eventsSignificance: 5.3 Consistent with c2'


Y(4260)

• Broad structure Y(4260): • N=125±23

• MY=4259±8+2-6 MeV/c2

• Y=88±23+6-4 MeV

• JPC=1--

PRL 95, 142001 (2005)

e+e- ISR J/+- J/ e+e-, +-

233 fb-1

’J/ sidebands

dataS wave phase space MC

Study of J/+- production in ISR• ISR not necessarily detected• Small mass recoiling against final state• Low missing transverse momentum• Well known benchmark channel (’)

s’

e-

e+

ISR

JPC=1-- ECM<10.58 GeV


No Y(4260) observed in R scan

4.26R

GeV

)(

)(

ee

hadronseeR


Y(4260) from CLEO-III and Belle

Mass higher than BabarM = 4295±10+10

-3 MeV = 133±26+13

-6 MeVN = 165±24 events

hep-ex/0612006hep-ex/0606016

Y(4260) also observed in e+e- radiative return at CLEO-III and Belle

Consistent with BabarM = 4283+17

-16±5 MeV = 70+40

-25±4 MeV


Y(4260) - CLEO-cPRL 96, 162003 (2006)

Y(4260) observation in e+e- direct scan performed by CLEO-c

e+e- cross section at s=4.26 GeV:

pbJ 458)/( 1210

pbJ 123)/( 12

800

pbKKJ 19)/( 9

5


Search for other Y(4260) decaysPRD 73, 012005 (2006)

Y(4260)

sidebandsD sidebands

+- DD ppISR not detectedISR detected ISR detected

289 fb-1 232 fb-1 232 fb-1

Y(4260)

hep-ex/0607083Preliminary

CL 90% 13.0 ψ)ππB(Y(4260)

)ppB(Y(4260)

CL 90% eV 4.0 )φππB(Y(4260) Yee

CL 95% 6.7 )ψππY(4260)(B

)DD)4260(Y(B

No signal

No signal

No signal

J/

’

(3770)J/: N=438±22

’: N=22±6

Other vector charmonia can be seen in these decay modes


Near threshold e+e- D(*)+D*- cross section

• Measurement of near-threshold e+e- D(*)+D*- cross section by Belle using ISR events

• No signal of Y(4260) in D(*)+D*- final state

• Sharp drop in the D*D* cross section at 4.2 GeV and local minima close to the Y(4260) region

** DDee

*DDee

hep-ex/0608018

4260

4040

4160


Hints for Y(4260) production in B decay

211 fb-1

B±Y(4260)K±

Y(4260)J/ +-

PRD 73,011101 (2006)

5102.07.00.2

)πψπ/)4260(Y(B)Y(4260)KB(B

J

3 excess

N=128±42

Invariant mass of the J/system observed in B decaywith a charged kaon(typical "charmonium" production mechanism atthe B-factories)


A new structure at 4320 MeV/c2

• Recently a new structure has been observed by Babar in '+- decays in ISR events

• Mass significantly larger with respect to the Y(4260)

Clean 'J/+- signal

Does not fit with a Y(4260) peakM = 4324±24 MeV = 172±33 MeV

PRL 98,212001 (2007)


New states summary

• X(3872): ? - simple charmonium hypothesis disfavored

• X(3940): c'' candidate– mass is about 50 MeV below expectations

– mass in agreement with c1' hypothesis (dominant DD* decay), but c1 not seen with the same production mechanism

• Y(3940): cJ' candidate

– but J/ BR seems too large for a c' state above threshold

• Z(3930): consistent with c2'– mass is about 40 MeV below expectations

• Y(4260): ? - candidate for vector hybrid– if so, other states are expected in the region 4.0-4.5 GeV

• Y(4350): ?


Summary

• After more than 30 years from its discovery, charmonium spectroscopy is still an interesting and active research field, with challenging experimental issues

• Precision measurements of the charmonium states are obtained by experiments at e+e- and pp machines

• New states in the charmonium mass region have been recently observed at the B factories. More experimental results are needed to shed light on their nature

Documents

Status of Charmonium Spectroscopy