DIS2003 Erika Garutti 1

Electro-production of f0(980) scalar meson at HERMES

Erika Garutti (DESY)

On behalf of the HERMES collaboration

• Physics introduction on scalar mesons - present knowledge on f0(980)

• Observation of f0(980) in the semi-inclusive channel

- mass peak determination - study of kinematics dependences - extrapolation to 4

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Why are scalar mesons interesting?

• Scalar mesons in Constituent Valence Model:- qq state with JPC = 0++ S=1, L=1- expected mass ~ 1.2 – 1.5 GeV

but f0(980), a0(980)

• Theoretical prediction for lightest glueball: - scalar quantum numbers mixing with scalars - mass between 0.9 –1.7 GeV

• Requirements to identify gluonic state: - good knowledge of light scalar meson nonet

(Thoma) - one isoscalar state in excess for the nonet (Ableev et. al)• Alternative non-qq interpretations for scalar mesons:

- qqqq state (Jaffe, Alford)

- vacuum scalar state (Dokshitzer,Gribov,Nyiri)

- KK molecule (Close, Isgur, Khoze, Ryskin)

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Present knowledge on f0(980)

E687: N X OPAL: X

NOMAD: C X

PDG: Mf0 = 0.980 ±0.010 GeV f0 = 0.040 - 0.100 GeV

E = 220 GeVMf0 = 0.968±0.0005 GeV f0 = 0.050±0.0024 GeV

Mf0 = 0.957±0.006 GeV Study alsochannel

E = 30 - 60 GeVComparison to JETSET where f0 is afragmentation product made of uu+dd

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HERMES experiment

P/P < 2.6 %, mraddetector eff. 99% (e+), RICH eff. 98%p)nucl/cm-2 , gas: 1H, 2H, 3He, 4He, 14N, 20Ne, 84Kr

•Tracking: •Particle ID:•Target:

• Ebeam = 27.5 GeV

DIS selection:

• W2 > 4 GeV2

• y < 0.85• Ecalo (e+) > 3.5 GeV

Hadron selection:

• P > 2.5 GeV

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Invariant mass distribution

Channel: f

Target: hydrogen

Event type: ep eX

Mf0 = 0.980±0.007 GeV f0 = 0.039±0.015 GeV

Significance: 4.1

Ks 0

f0

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Kinematics dependences

Studied dependences on: Q2, Pt

2, z and in the HERMES acceptance

Comparison to PYTHIA/JETSET:f0(980) produced in uu + ddfragmentation

good agreement with MC

peaking of data at <z> 0.5

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Acceptance corrected results

DIS processes (1/Q2)2

f0-production at Q2 > 1 GeV2

= 1.8 0.3 consistent with DIS prod.

Exponential fit to Pt2-dependence

slope parameter b= 4.4 1.2 GeV-2

consistent with NOMAD b= 5.3 0.2 GeV-2

Using JETSET for acceptance corr. model dependent results !!!

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Conclusions

• First observation of f0(980) scalar meson electro-production

• Mass and width consistent with PDG and previous measurements

• Kinematics dependences in acceptance reproduced by PYTHIA/JETSET - z dependence more peaked in the data

• Extrapolation to 4 using MC strongly model dependent

- Q2 -dependence of f0 acc. corr. yield consistent with DIS production mechanism

- Pt2-dependence of f0 acc. corr. yield described by

exponential behavior consistent with NOMAD findings

• No MC exist for comparison to alternative non-qq interpretations

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Outlook

• Optimization of MC tune + increased MC statistics

• Extraction of multiplicities from acceptance corrected yields

• Extraction of f0(980) on nuclear targets (2H, N, Ne, Kr)

study A-dependence of yield and peak position

• Investigate decay channel

• Comparison to other MC predictions (when available!)