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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

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


Meson and baryon spectroscopy at hera

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.


Meson and baryon spectroscopy at hera

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.


Meson and baryon spectroscopy at hera

 

(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.


Meson and baryon spectroscopy at hera

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.


Meson and baryon spectroscopy at hera

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.


Meson and baryon spectroscopy at hera

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.


Event selection

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

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.


Results discussions1

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.


Results discussions2

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

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

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

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.


Fitting k s p and k s anti proton separately

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

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

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.


Meson and baryon spectroscopy at hera

Extras….. KsKs final state

Lake Louise, Alberta, CA.


Meson and baryon spectroscopy at hera

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.


Summary1

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.


Summary2

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.


Meson and baryon spectroscopy at hera

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 selection1

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.


Event selection2

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.


Event selection3

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.


Event selection4

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.


Results discussions3

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.


Results discussions4

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.


Meson and baryon spectroscopy at hera

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


Meson and baryon spectroscopy at hera

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.


Scalar and tensor mesons

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.


Meson and baryon spectroscopy at hera

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.


Meson and baryon spectroscopy at hera

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

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.


Event selection5

Armenteros-Podolanski variables

Photon conversion

Event Selection

  • Armenteros-Podolanski variable

  • to remove photon conversions

  • and ;

Lake Louise, Alberta, CA.


Results discussions5

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.


Results discussions6

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.


Meson and baryon spectroscopy at hera

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.


Meson and baryon spectroscopy at hera

Observation of J=even meson resonances in ep

cosKK < 0.92 cut

Lake Louise, Alberta, CA.


Meson and baryon spectroscopy at hera

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

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 g gg g k s k s

e+e-ggggKsKs

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

Lake Louise, Alberta, CA.


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