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Lake Louise Winter Institute 2004 Alberta, Canada 15 – 21 February. Meson and Baryon Spectroscopy at HERA. McGill University DESY. Mauricio Barbi. Introduction Neutral Meson Spectroscopy K s K s resonances in DIS K s p resonances in DIS Summary. for. Collaborations.

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Meson and Baryon Spectroscopy at HERA

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Lake Louise Winter Institute 2004

Alberta, Canada

15 – 21 February

Meson and Baryon Spectroscopy at HERA

McGill University DESY

Mauricio Barbi

  • Introduction

  • Neutral Meson Spectroscopy

  • Ks Ks resonances in DIS

  • Ks p resonances in DIS

  • Summary

for

Collaborations


mesons

baryons

q

q

q

q

q

Introduction

  • 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.

Lake Louise, Alberta, CA.


central rapidities

Inclusive Photoproduction of , 0, f0(980) and f2(1270) -- H1

  • 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 energy

    of 210 GeV

Lake Louise, Alberta, CA.


 

(LAr Calorimeter)

H1 preliminary

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

dN/dM [1/GeV]

η

Fit with 1 gaussian + polynomial bkg

M [GeV]

æ

ö

G

m

m

(

m

)

3

å

ç

÷

0

,

i

i

=

+

F

(

m

)

A

ç

÷

2

-

+

G

2

2

2

2

(

m

m

)

m

(

m

)

è

ø

Mγγ[GeV]

=

1

i

0

,

0

,

i

i

i

(

)

å

2

-

-

a

-

+

a

m

a

m

a

m

2

m

e

(Re

f

(

m

))

2

3

4

p

1

Invariant Mass Distribution

Rapidity limited to |y|<1

H1 preliminary

0, f0, f2+-

(Central Jet Chamber)

ρ0

|y|<1

Comb bg

Fit with 3 relativistic BWs, a bkg function and reflection contribution mainly from  and K*.

K*

f0

f2

Lake Louise, Alberta, CA.


ρ0

f0

f2

η

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

Differential cross sections

  • Flat in rapidity.

  • Power law in pT

    compatible with

    thermodynamic-

    based approach.

H1 preliminary

H1 preliminary

d/dy [nb]

d /(dydpT2) [nb/GeV2]

y

pT [GeV]

Lake Louise, Alberta, CA.


H1 preliminary

1/(2j+1)d/(dydpT2) [nb/GeV2]

ρ0

f0

f2

η

+

(published)

m + pT [GeV]

Differential cross sections as a function of

( mass + PT )

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

  • Dependence mainly on the hadron’s mass and pT

    support universality of long-lived hadron production.

Lake Louise, Alberta, CA.


f0(1)

0

s

Scalar JPC=0++Nonet

K0(1430)

K0(1430)

0

+

f0(8)

0

f0(1370) ~ uu+dd

f0(1500) ~ ??

f0(1710) ~ ??

f0(8)

0

s

s

f0(1)

a0(????)

-

a0(????)

a0(????)

+

0

3 candidates for 2 spots

f0(1710)is a glueball candidate

K0(1430)

K0(1430)

-

0

K SK S resonances in Deep Inelastic Scattering (DIS) at HERA -- ZEUS

  • 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 lightestglueball 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)++.

Lake Louise, Alberta, CA.


0

0

s

s

SVTX

0

K

s

VTX

p

Event Selection

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

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

Use the ZEUS Central Tracker Detector

Q2= photon virtuality

x = Bjorken scaling variable

y = fraction of the lepton energy

transferred to the proton in

the proton rest frame

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

Lake Louise, Alberta, CA.


Results / Discussions

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

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

    • - a state consistent withf2’(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.

Lake Louise, Alberta, CA.


0

s

Current

93% of the

KsKs pairs

are in the target region

Target

0

s

Results / Discussions

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

Lake Louise, Alberta, CA.


mass

width

mass

width

PDG 2002 values (MeV)

f0(1710) :

f2’(1525) :

L3

Phys. Lett. B501 (2001) 173-182

BELLE

hep-ex/0104024

BES

hep-ex/0307058

Results / Discussions

Confronting L3, BELLE, BES and ZEUS

ZEUS

Accepted by Phys. Lett. B

Hep-ex/0308006

1700 MeV mass region

L3: mass 1767±14 MeV; width 187±60 MeV

BELLE: mass 1768±9.6 MeV; width 323±29 MeV

BES: mass 1722±17 MeV; width 167 MeV

ZEUS: mass 1726±7 MeV; width 38 MeV

Lake Louise, Alberta, CA.


Evidence for exotic baryons in K S p final state in DIS at HERA -- ZEUS

  • Recent calculations based on chiral soliton model (Diakonov et al) predict the existence of a narrow S=+1 state Q+ with mass around 1530 MeV

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

Anti-decuplet

1530 MeV

1710 MeV

1890 MeV

2070 MeV

Lake Louise, Alberta, CA.


Selection

  • Q+ 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.

Preliminary

p

Lake Louise, Alberta, CA.


Combined fit

  • 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

Preliminary

372±75 candidates

Peak at 1527±2(stat) MeV

Width of 10±2(stat) MeV

Significance of ~5s

Fit: Gaussian + P3 (free parameters)

Lake Louise, Alberta, CA.


S(1480)???

S(1480)???

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

126±50 candidates

Peak at 1529±3(stat) MeV

Width of 7±3(stat) MeV

Preliminary

Preliminary

393±86 candidates

Peak at 1523±3(stat) MeV

Width of 16±3(stat) MeV

Lake Louise, Alberta, CA.


Confronting with other measurements

Experiment

M (MeV)

Significance

G (MeV)

SPring8 1540  10  5 < 25 (4.6s)

DIANA 1539  2  “few” < 9 (4.4s)

CLAS (d) 1542  2  5 21 (5.3s)SAPHIR 1540  4  2 < 25 (4.8s)

ITEP (v’s) 1533  5 < 20 (6.7s)

CLAS (p) 1555  1  10 26  7 (4.3s)

HERMES 1528  2.6  2.1 19  5  2 (5.6s)

ZEUS (Prel.) 1527±2 10±2 (5.0s)

Lake Louise, Alberta, CA.


Summary

Three results were reported in hadron spectroscopy:

  • Neutral meson spectroscopy

    • First measurement of cross section for inclusive photoproduction of

    • , 0, f0(980) and f2(1270) at gpaverage energy of 210 GeV;

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

  • KsKs resonances in DIS

    • First observation of resonances in KsKsfinal 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 Q+ pentaquark;

    • First evidence for pentaquark in HEP colliding experiment;

    • Evidence for anti-pentaquark ( ).

Lake Louise, Alberta, CA.


Extras….. KsKs final state

Lake Louise, Alberta, CA.


Summary

  • First measurement of cross section for inclusive photoproduction of , 0, f0(980) and f2(1270) at gpaverage energy of 210 GeV.

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

Lake Louise, Alberta, CA.


0

s

0

s

Summary

  • First observation of resonances in KKfinal 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.

Lake Louise, Alberta, CA.


Summary

  • 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 Q+ 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!

Lake Louise, Alberta, CA.


0

s

0

0

s

s

K SK S resonances in Deep Inelastic Scattering (DIS) at HERA -- ZEUS

  • 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)++.

Some production processes at HERA

Quark jets

Odderon exchange

Radiative VM decay

Gluon ladder

Lake Louise, Alberta, CA.


Event Selection

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

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

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

ZEUS Detector

RCAL

CTD

Lake Louise, Alberta, CA.


Q2= photon virtuality

x = Bjorken scaling variable

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

p

Event Selection

DIS variables

Lake Louise, Alberta, CA.


0

0

s

s

SVTX

0

K

s

VTX

Event Selection

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

Lake Louise, Alberta, CA.


0

0

s

s

K

K

0

0

0

0

0

0

0

0

s

s

s

s

s

s

s

s

K K system does not open at threshold

meson fJ

Event Selection

Remove enhancement at K K invariant mass threshold due to the presence of the f0(980)/a0(980) state.

2553 K K candidates found in the range

0.995 < M(K K ) < 2.795 GeV

Lake Louise, Alberta, CA.


Current region in DIS is

equivalent to an e+e- hemisphere

Breit Frame

Current

93% of the

KsKs pairs

are in the target region

Target

0

0

s

Pz(KsKs)<0

s

93% of the K K production is in a

region where sizeable initial state gluon

radiation may be expected.

Pz(KsKs)>0

Results / Discussions

Lake Louise, Alberta, CA.


PDG 2002 values (MeV)

mass

width

mass

width

Results / Discussions

ZEUS fit values (MeV)

2/N

width

events

mass

width

events

mass

  • Correlations between the parameters are accounted;

  • Sensitivity of the data to the widths of the resonances is checked.

Lake Louise, Alberta, CA.


central values of rapidity

H1

  • How do quarks and gluons convert to colourless hadrons?

  • pQCD does not apply

  • phenomenological models of hadronisation

H1prel. Data vs MC (selected events)

Inclusive photoproduction of

neutral hadronic resonances:

, 0, f0(980) and f2(1270)

Ntrack

θtrack

Ecluster [GeV]

Rtransv [cm]

Dtrack-cluster [cm]

|cos α|

Test universality of hadroproduction

Lake Louise, Alberta, CA.

good agreement


ρ0

ρ0

f0

f0

f2

η

f2

+

η

H1

Differential photoproduction cross sections

H1 preliminary

1/(2j+1)d/(dydpT2) [nb/GeV2]

d/dy [nb]

d /(dydpT2) [nb/GeV2]

(published)

y

pT [GeV]

meson mass + pT [GeV]

2000 data: 39 pb-1

|ylab| < 1

<Wp> = 210 GeV

Same behaviour as for light, long-lived hadrons

Lake Louise, Alberta, CA.


Quark Model

(u,d,s)

Scalars

JPC = 0++

S=1

I=0

S

q

q

L=1

JPC = 2++

I

Tensors

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

C = (-1)L+S

J = 0 or 2

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

Scalar and Tensor Mesons

Lake Louise, Alberta, CA.


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

Is this a qq state?

mix

g

f0(1370)

f0(1500)

f0(1710)

Observed States

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

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

KsKs final state couples only to JPC=(even)++ and it is CLEAN.

This is the golden channel (given statistics) to look for scalar

and tensor meson resonances

Lake Louise, Alberta, CA.


TensorJPC=2++ Nonet

f2(1270) ~ uu+dd

f2(1525) ~ ss

f2(8)

K2(1430)

K2(1430)

0

+

f2(1)

f2(8)

f2(1)

a2(1320)

-

a2(1320)

a2(1320)

+

0

K2(1430)

K2(1430)

-

0

Lake Louise, Alberta, CA.


Production mechanisms in DIS

Odderon

Exchange

Gluon poor processes

VM Radiative

decays

Gluon rich processes

In quark Jets

In gluon jets

Lake Louise, Alberta, CA.


Armenteros-Podolanski variables

Photon conversion

Event Selection

  • Armenteros-Podolanski variable

  • to remove photon conversions

  • and ;

Lake Louise, Alberta, CA.


Results / Discussions

2/N

width

width

events

mass

width

events

mass

widh

events

mass

events

mass

PDG 2002 values (MeV)

  • Correlations between the parameters are accounted;

  • Sensitivity of the data to the widths of the resonances is checked.

Lake Louise, Alberta, CA.


Current region in DIS is

equivalent to an e+e- hemisphere

Results / Discussions

Breit Frame

78% of the

KsKs pairs

have xp>1

Increasing

xp

More gluons

Pz(KsKs)<0 (7%)

Pz(KsKs)>0 (93%)

High xpcorresponds to production in a

region where sizeable initial state gluon

radiation may be expected.

Lake Louise, Alberta, CA.


KS0KS0 final state in DIS

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

  • a state consistent with f2’(1525)

  • X(1726) (is this the f0(1710) ?)

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.

Threshold Enhancement

due to f0(980)/a0(980)

Fit 3 Breit-Wigner and a backg. function:

Problematic

region

Lake Louise, Alberta, CA.


Observation of J=even meson resonances in ep

cosKK < 0.92 cut

Lake Louise, Alberta, CA.


KS0KS0 final state in DIS

Fit with 4 Breit-Wigner

Þ Attempt to include the 1980 MeV mass region

Lake Louise, Alberta, CA.


How well a smooth background describes the data:

It is less than 1% likely that a smooth

distribution describes the data.

Lake Louise, Alberta, CA.


e+e-ggggKsKs

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

Lake Louise, Alberta, CA.


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