Meson and Baryon Spectroscopy at HERA

Meson and Baryon Meson and Baryon Spectroscopy at HERASpectroscopy at HERA

1.1. IntroductionIntroduction

2.2. Neutral Meson Neutral Meson SpectroscopySpectroscopy

3.3. KKs s KKs s resonances in DISresonances in DIS

4.4. KKs s p resonances in DISp resonances in DIS

5.5. SummarySummary

Lake Louise Winter Institute 2004Alberta, Canada15 – 21 February

CollaborationsCollaborations

McGill University McGill University DESYDESY

Mauricio Mauricio BarbiBarbi

forfor

M. Barbi, Feb. 2004M. Barbi, Feb. 2004 Lake Louise, Alberta, CA. Lake Louise, Alberta, CA. 22

Constituent quark model

QCD allows multiquark (> 3q), hybrid (quarks + gluons) and gluonic states “exotics” in the constituent quark model.

Hadron spectroscopy QCD in the non-perturbative regime. How does confinement works? Insight on the degrees of freedom which determine the spectrum of hadrons.

Powerful tool for testing the QCD bases.

IntroductionIntroduction

qq qq qq

baryonsbaryons

qq qq

mesonsmesons

Mauricio


Insight on long-lived hadron production. Hadronic collisions particle production at central values of rapidity governed only by the properties of the QCD vacuum. Production at HERA at similar energy as at RHIC, but in light hadron collisions.

H1 data, 38.7 pb-1, luminosity at an average photon-proton CM energyof 210 GeV

central central rapiditiesrapidities

Inclusive Inclusive Photoproduction of Photoproduction of , , 00, f, f00(980) and f(980) and f22(1270) (1270) -- H1-- H1


Invariant Mass Distribution

ρ0

f0f2

H1 preliminary

Comb bg

K*

|y|<10, f0, f2 +-

(Central Jet Chamber)

Fit with 3 relativistic BWs, a bkg function and reflection contribution mainly

from and K*.

(LAr Calorimeter)

3<pT<8 GeV, |y|<1

η

Mγγ[GeV]

H1 preliminary

dN

/dM

[1/

GeV

]

Fit with 1 gaussian + polynomial bkg

Rapidity limited to |y|<1

M [GeV]

))((Re2

)()(

)()(

2432

1

3

122

,022

,02

,0

mfemma

mmmm

mmmAmF

mamaa

i iii

ii


f2

η

f0

ρ0

d/

dy

[nb

]

y pT [GeV]d

/(d

ydp T

2 ) [

nb

/GeV

2 ]

Differential cross sectionsH1 preliminary H1 preliminary Flat in

rapidity.

Power law in pT compatible with thermodynamic- based approach.

Differential cross section as a function of rapidity (y) and PT


ρ0

f2

η

f0

+

m + pT [GeV]

1/(2

j+1)

d/

(dyd

pT

2 ) [

nb

/GeV

2 ]

H1 preliminary

(published)

Cross sections follow similar power law as for pions at same p collision energy.

Dependence mainly on the hadron’s mass and pT

support universality of long-lived hadron production.

Differential cross sections as a function of ( mass + PT )


Scalar JPC=0++ Nonet

f0(1370) ~ uu+ddf0(1500) ~ ??f0(1710) ~ ??

f0(8)

f0(1)

f0(1710) is a glueball candidate

3 candidates for 2 spots

f0(1)

K0(1430)0

K0(1430)0 K0(1430)+

f0(8)

a0(????)0 a0(????)- a0(????)+

K0(1430)-

Scalar meson nonet not well understood; a state yet to be confirmed, and an excess of candidates for the available positions in the nonet;

Lattice QCD predicts lightest glueball with JPC=0++ and mass between 1.4-1.8 GeV;

ep collisions at HERA as a new environment for resonance studies; gluon rich initial state in ep deep inelastic scattering (DIS);

K studied at HERA before; clean sample;

K K couples to meson states with JPC=(even)++.

ss

K K SSK K SS resonances in resonances in Deep Inelastic Deep Inelastic Scattering (DIS) at Scattering (DIS) at HERA HERA -- ZEUS-- ZEUS

0s

0s

0s


Event Selection

Kinematical region limited by event selection requirements and limit for HERA running with 920 GeV protons.

K0s

VTX

SVTX

Take only K in the region of 10 MeV around the fitted K mass;

0s

0s

e 'e

p pP

pq xPP

2Q

Integrated Integrated luminosity of 121 luminosity of 121 pbpb-1 -1 (1996-2000 (1996-2000 data);data);

Q2 = photon virtualityx = Bjorken scaling variable y = fraction of the lepton energy transferred to the proton in the proton rest frame

enesmcs

xysQ

...

2

Use the ZEUS Central Tracker Detector


0

0

*,*,

2

3

122222

,*,

2

)()(

sK

s

ii

mMCB

K

i i

idi

emMA

mMm

m

dM

dNMF

Results / Discussions

Fit with 3 modified relativistic Breit-Wigners and a background function.

First observation of JPC=(even)++ in DIS:

- a state consistent with f2’(1525),

with peak at MeV, width

of MeV and candidates

- X(1726) ( is this the f0(1710) ?)

with peak at MeV, width

of MeV and candidates

A third state is observed in the 1300 MeV mass region, consistent with the

interference.

(1320)(1270)/af 022

981537

342250

413184

71726 201438

292374



93% of the K K production is in a region where sizeable initial state gluon radiation may be expected.

0

s

0

s

93% of the KsKs pairs are in the target region

Current

Target



1700 MeV mass region

L3: mass 1767±14 MeV; width 187±60 MeVBELLE: mass 1768±9.6 MeV; width 323±29 MeVBES: mass 1722±17 MeV; width 167 MeVZEUS: mass 1726±7 MeV; width 38 MeV

BELLEhep-ex/0104024

ZEUSAccepted by Phys. Lett. B

Hep-ex/0308006

BEShep-ex/0307058

3729

2014

Confronting L3, BELLE, BES and ZEUS L3

Phys. Lett. B501 (2001) 173-182

PDG 2002 values (MeV) 107651525

mass width1012561713

mass width

f2’(1525) : f0(1710) :


Evidence for exotic Evidence for exotic baryons in K baryons in K S S p final p final state in DIS at HERA -- state in DIS at HERA -- ZEUSZEUS Recent calculations based on chiral soliton model (Diakonov et al) predict the existence of a narrow S=+1 state with mass around 1530 MeV

Some experiments have reported the observation of a narrow resonance around 1530 MeV

suudd

Anti-decuplet

1530 MeV

1710 MeV

1890 MeV

2070 MeV


Selection

Preliminary

can decay to K0p or K+n

Search for resonances in inclusive DIS, using 121 pb-1 of ZEUS data.

DIS event selection and K0 reconstruction similar to those in KsKs

analysis.

Use Central Tracker Detector dE/dX to select (anti)proton.

)(0 ppK s

±

K±

p


Combined fit

Preliminary Ks in the mass region 480-510 MeV.

(Anti)protons in the dE/dX proton band and with p < 1.3 GeV

Remove K*(892) reflection

Resolution of 5 MeV in the 1530 MeV region

Fit: Gaussian + P3 (free parameters)

372±75 candidatesPeak at 1527±2(stat) MeVWidth of 10±2(stat) MeVSignificance of ~5


Fitting (K s p) and (K s anti-

proton) separately Preliminary

Preliminary

393±86 candidatesPeak at 1523±3(stat) MeVWidth of 16±3(stat) MeV

126±50 candidatesPeak at 1529±3(stat) MeVWidth of 7±3(stat) MeV

(1480)???

(1480)???


Confronting with other

measurements

M (MeV) (MeV)

SPring8 1540 10 5 < 25 (4.6 DIANA 1539 2 “few” < 9 (4.4 CLAS (d) 1542 2 5 21 (5.3 SAPHIR 1540 4 2 < 25 (4.8 ITEP (v’s) 1533 5 < 20 (6.7 CLAS (p) 1555 1 10 26 7 (4.3 HERMES 1528 2.6 2.1 19 5 2 (5.6

ZEUS (Prel.) 1527±2 10±2 (5.0

Significance

Experiment


Neutral meson spectroscopy• First measurement of cross section for inclusive photoproduction of , 0, f0(980) and f2(1270) at p average energy of 210 GeV;• Differential spectra similar to those of light, long-lived hadrons.

KsKs resonances in DIS• First observation of resonances in KsKs final state in DIS was reported;• A state is observed at MeV, consistent with the f2’(1525);• Another state X(1726) is observed at MeV, probably the f0(1710) (glueball candidate). More stat. is needed to establish its width;• States are in a region where sizeable initial state gluon rad. is expected.

Ksp resonances in DIS

• was studied in inclusive DIS sample at HERA;• A signal is observed at 1527±3 MeV with width of 10±2(stat) MeV, consistent with the predicted pentaquark;• First evidence for pentaquark in HEP colliding experiment;• Evidence for anti-pentaquark ( ).

SummarySummary

981537

71726

)(0 ppK s

Three results were reported in hadron spectroscopy:

pK s0


Extras….. KsKs final state


SummarySummary

First measurement of cross section for inclusive photoproduction of , 0, f0(980) and f2(1270) at p average energy of 210 GeV.

Differential spectra similar to those of light, long-lived hadrons.


SummarySummary

First observation of resonances in K K final state in DIS was reported;

An enhancement is observed in the 1300 MeV mass region, but its measurement is affected by the cut to eliminate the presence of the f0(980)/a0(980) at threshold;

A state is observed in the 1500 MeV mass region consistent with the f2’(1525);

Another state X(1726) is observed, probably the f0(1710) (a glueball candidate), but more statistics is needed to establish its width;

The states are produced in a region where sizeable initial state gluon radiation is expected.

0s

0s


SummarySummary

was studied in inclusive DIS sample at HERA.

A signal is observed at 1527±3 MeV with width of 10±2(stat) MeV, consistent with the predicted pentaquark

Separate and spectra also show enhancement at this mass. The shapes are slightly different due to the different CTD response to positive and negative tracks.

First evidence for pentaquark in HEP colliding experiment

First evidence for anti-pentaquark ( )

Improvements ongoing!

)(0 ppK s

pK s0 pK s

0

pK s0


Odderon exchangeOdderon exchangeGluon ladderGluon ladder Radiative VM decayRadiative VM decay Quark jetsQuark jets richGluon

poorGluon

Some production processes at HERA

ep collisions at HERA as a new environment for resonance studies; gluon rich initial state in ep deep inelastic scattering (DIS);

K studied at HERA before; clean sample;

K K couples to meson states with JPC=(even)++.

0s

0s

0s

K K SSK K SS resonances in resonances in Deep Inelastic Deep Inelastic Scattering (DIS) at Scattering (DIS) at HERA HERA -- ZEUS-- ZEUS


Event SelectionEvent Selection

ZEUS DetectorZEUS Detector

RCAL

CTD

Integrated Integrated luminosity of 120 luminosity of 120 pbpb-1 -1 (1996-2000 (1996-2000 data);data);

Events with Events with scattered escattered e-- (e (e++) in ) in Rear Calorimeter Rear Calorimeter (RCAL);(RCAL);

Use only good Use only good tracks measured tracks measured with the Central with the Central Tracking Detectors Tracking Detectors (CTD).(CTD).



DIS variables

e 'e

ppP

pq xPP

2Q

Q2 = photon virtuality

x = Bjorken scaling variable

y = fraction of the lepton energy transferred to the proton in the proton rest frame

energysmcs

xysQ

...

2



• Take only K in the region of 10 MeV around the fitted K mass;

0s

0s

K0s

VTX

SVTX


Remove enhancement at K K

invariant mass threshold due to

the presence of the f0(980)/a0(980)

state.


0s

0s

K K system does not open at threshold0s

0s

92.0cos KK

meson fJ

0

sK

0

sK

KK

2553 K K candidates found in the range 0.995 < M(K K ) < 2.795 GeV

0s

0s

0s

0s


Results / DiscussionsResults / Discussions

Current region in DIS is equivalent to an e+e- hemisphere

Breit Breit FrameFrame

PPzz(K(KssKKss)>0 )>0 PPzz(K(KssKKss)<0 )<0

93% of the KsKs pairs are in the target region

93% of the K K production is in a region where sizeable initial state gluonradiation may be expected.

0s

0s

Current

Target



• Correlations between the parameters are accounted;• Sensitivity of the data to the widths of the resonances is checked.

PDG 2002 values (MeV)

107651525 1012561713 mass width mass width

2/N )1525('2f )1710(0f

02.1

02.1

96.0

97.0

101538

81536

101539

1537 98

76

49

76

50

3021

3422

3129

3827

4131

108

85

30107

84

131728

131726

71727

71726

125

125

2039

38 2014

4138

2824

2923

120

40122

76

74

mass width events mass width events

ZEUS fit values (MeV)


H1H1How do quarks and gluons convert to colourless hadrons?• pQCD does not apply• phenomenological models of hadronisation

Inclusive photoproduction of

neutral hadronic resonances:

, 0, f0(980) and f2(1270)

central values of rapidity

H1 prel. Data vs MC (selected events)

Ntrack θtrack

Rtransv [cm]Ecluster [GeV]

Dtrack-cluster [cm] |cos α|

good agreement

Test universality of hadroproduction


H1Differential photoproduction cross sections

f2

η

f0

ρ0ρ0

f2

η

f0

+

meson mass + pT [GeV]

d/

dy [

nb]

y pT [GeV]

d

/(dydp

T2)

[nb/G

eV

2]

1/(

2j+

1)d/

(dydp

T2)

[nb/G

eV

2] H1 preliminary

2000 data: 39 pb-1

|ylab| < 1<Wp> = 210 GeV

Same behaviour as for light, long-lived hadrons

(published)


Scalar and Tensor Scalar and Tensor MesonsMesonsScalar and Tensor Scalar and Tensor MesonsMesons

q q

S=1

L=1

JPC = 0++

JPC = 2++

Masses 1-2 GeV, scalar and tensor mesons much heavier than the pseudoscalars

Quark Model(u,d,s)

I=0

P = (-1)x(+1)x(-1)L = (-1)L+1

C = (-1)L+S

J = 0 or 2

S

I

Scalars

Tensors


QCD: richer than Quark Model, predicts gluon states with JPC = 0++,2++, I=0

gf0(1370) f0(1500)f0(1710)

Observed States

mix

KsKs final state couples only to JPC=(even)++ and it is CLEAN.This is the golden channel (given statistics) to look for scalarand tensor meson resonances

Ks: has S=L=0, P=-1, C=+1

KsKs: has P=+1, C=+1 J=even

Is this a qq state?


f2(8)f2(1)

f2(1270) ~ uu+dd f2(1525) ~ ss

dduua ~)1320(02

f2(1)

K2(1430)0

K2(1430)0 K2(1430)+

f2(8)

a2(1320)0 a2(1320)- a2(1320)+

K2(1430)-

Tensor JPC=2++ Nonet


Production mechanisms in Production mechanisms in DISDISProduction mechanisms in Production mechanisms in DISDIS

Odderon Exchange

VM Radiativedecays

In quark Jets

In gluon jets

Gluon rich

processes

Glu

on p

oor

proc

esse

s



Armenteros-Podolanski variables

0sK

__

Photon conversion

• Armenteros-Podolanski variable to remove photon conversions and ;

__

,



2/N )1320(/)1270( 022 af )1525('2f )1710(0f )1980(Jf

00.1

02.1

02.1

96.0

97.0

151283

151274

161276

161272

1274 1716

7055

7255

8059

7655

8558

260

251

258

240

244

218122

176131

190141

167122

184125

506

476

480

420

414

1210

98

1540

101538

81536

101539

1537

4330

3021

3422

70

76

49

76

50

5942

3129

3827

4131

116

108

85

30107

84

71727

131728

131726

71727

71726

2315

2014

47

125

125

2039

38

3426

4138

2824

2923

91

120

40122

76

74

33451970

17389138

4074

mass width events mass widthevents mass width events mass widh events

PDG 2002 values (MeV)

9.17.104,6.01318

185,2.11275 4.36.2

1076,51525 10125,61713

• Correlations between the parameters are accounted;• Sensitivity of the data to the widths of the resonances is checked.



PPzz(K(KssKKss)<0 (7%))<0 (7%)

xx

P

Px

QP

q

MAXKKMAX

pqss

1 ,

2

02 qpx

Increasingxp

More gluons

78% of the KsKs pairs have xp>1

Current region in DIS is equivalent to an e+e- hemisphere

Breit FrameBreit Frame

PPzz(K(KssKKss)>0 (93%))>0 (93%)

High xp corresponds to production in a region where sizeable initial state gluonradiation may be expected.


First observation of JCP=(even)++ in DIS. Two states are observed:

a state consistent with f2’(1525) X(1726) (is this the f0(1710) ?)

sK

s

mMCB

K

i ii

ii

emMA

MM

N

dM

dNMF

2

3

122

,0

2

4/)(2)(

Several states have been observed in the 2GeV region (see PDG02)

f0(980)/a0(980) gives Ks pair with very small opening angle in the lab.We would like to remove collinear Ks pairs and then fit the spectrum.

Fit 3 Breit-Wigner and a backg. function:

KKSS00KKSS

00 final state in DIS final state in DIS

Threshold Enhancementdue to f0(980)/a0(980)

Problematicregion


cosKK < 0.92 cut

Observation of J=even meson resonances in ep


Fit with 4 Breit-Wigner

Attempt to include the 1980 MeV mass region

KKSS00KKSS

00 final state in DIS final state in DIS


How well a smooth background How well a smooth background describes the data:describes the data:

122

2/

2

2

2

1

n

x dxeSL

It is less than 1% likely that a smoothdistribution describes the data.


ee++ee--KKssKKss

If f(1710) is a glueball it should have small coupling to

Documents

Meson and Baryon Spectroscopy at HERA