29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP1 Searches for Pentaquark...

29 June 2004 Steve Armstrong - Searches for Pentaquark Production at LEP 1

Searches for Pentaquark Production at LEP

Steve Armstrong(ALEPH Collaboration)

Brookhaven National Laboratory

29 June 20046th International Conference on Hyperons, Charm & Beauty Hadrons (BEACH04)

Illinois Institute of TechnologyChicago, Illinois, USAJune 27 – July 3 2004


¶ MOTIVATION FOR LEP PENTAQUARK SEARCHES

¶ THE LEP EXPERIMENTAL PROGRAM AT CERN

¶ SEARCHES FOR PENTAQUARK PRODUCTION

¶ SUMMARY

OUTLINE


PENTAQUARK MOTIVATION: THEORY

• QCD does not forbid more complicated color singlet hadron states other than qq mesons and qqq baryons

• Various quark models as well as Skyrme and chiral soliton models predict SU(3) J = 1/2 anti-decuplet {10} of “exotic” baryons

• Diakonov et al. predict an isosinglet lowest mass member with mass near 1.53 GeV/c2 with a narrow width of ~ 15 MeV/c2 and valence quark configuration of uudds (i.e., S = +1) now denoted as + which is in astonishing agreement with compelling experimental evidence

• Miraculously, the anti-decuplet also contains exotic states (-- and 0) consistent with NA49 observations of states near 1.86 GeV/c2

• A natural consequence would be the replacement of anti-strange quark(s) with anti-charm or anti-beauty heavy flavour pentaquarks (i.e., + and +)b c

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PENTAQUARK MOTIVATION: EXPERIMENT (N REACTIONS)

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PENTAQUARK MOTIVATION: EXPERIMENT

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¶ SUMMARY

OUTLINE


LEP PROGRAM AT CERN

Large Electron Positron (LEP) Collider at CERN

LEP1: Starting in 1989 at Ecm = 91 GeV (MZ)

LEP2: Starting in 1995, sucessive upgrades to higher Ecm

Large Electron Positron (LEP) Collider at CERN

LEP1: Starting in 1989 at Ecm = 91 GeV (MZ)

LEP2: Starting in 1995, sucessive upgrades to higher Ecm

Terminated in November 2000

Accelerator Lattice and Experiments dismantled (for LHC)

Terminated in November 2000

Accelerator Lattice and Experiments dismantled (for LHC)

LEP1 (1989 – 1995)200 pb–1 per experiment


THE ALEPH DETECTOR

Muon Chambers

Hadron Calorimeter

SuperconductingMagnet Coil

Electromagnetic Calorimeter

Time ProjectionChamber

Inner TrackingChamberSilicon Vertex

Detector


THE DELPHI DETECTOR


THE L3 DETECTOR


HADRON SYNTHESIS IN ELECTRON-POSITRON INTERACTIONS

Hadronic Z Decays

Two Photon Interactions





• HADRONIC Z DECAYS (ALEPH & DELPHI)

• TWO PHOTON (L3)

¶ SUMMARY

OUTLINE


DATA AND MONET CARLO SAMPLES

•ALEPH: Hadronic Z decays between 1991 – 1995 (LEP1)•DELPHI: Hadronic Z decays recorded during 1994 and 1995 during which Time Projection Chamber and Ring Imaging Cherenkov detectors were functioning optimally

•L3: 1998-2000 (LEP2) data with Two Photon preselection for W > 5 GeV

•Hadronic Z: Based on JETSET with parameters tuned to agree with well-established measurements

•Two Photon: PYTHIA with jet hadronization simulated with JETSET

•Simulated only octet and decuplet Baryons•Full detector simulation

DATADATA

MONTE CARLOMONTE CARLO


ALEPH PARTICLE IDENTIFICATION

To identify particles of type i, cuts are placed on pull of dE/dx from Time Projection Chamber

1.3x106 proton candidates selected:52% purity in high momentum range96% purity in low momentum range


DELPHI PARTICLE IDENTIFICATION

PionsKaons

Protons


ALEPH NON-EXOTIC pK± MASS SPECTRA

Smooth deviation from simulated pK+ mass spectrum observed at few percent

level. Understood to be caused by imperfect simulation of dE/dx for

spatially close track pairs. Corrected from doubly charged combinations.

Smooth deviation from simulated pK+ mass spectrum observed at few percent

level. Understood to be caused by imperfect simulation of dE/dx for

spatially close track pairs. Corrected from doubly charged combinations.

Excess pK– fit to (1520) and eightestablished * resonances

Excess pK– fit to (1520) and eightestablished * resonances


ALEPH NON-EXOTIC pK– RESULTS

•Simultaneous fit to the strengths of eight more or less established resonances over background results in an (1520) excess of 2814 ± 293 combinations.

• If (1520) excess is counted in 30 MeV/c2 window around 1.520 GeV/c2, result is 400 combinations lower conservatively taken as systematic error

•Average acceptance of 0.10 obtained from simulation as well as BR((1520)pK–) = 22.5%


ALEPH EXOTIC pK0 SPECTRAs

K0 are selected from kinematic fit to two opposite charged pions emerging from secondary vertex 1.2 x 106 K0 candidates with 93% purity

s

s

• Seach for maximum number of excess combinations in sliding window of width 20 MeV/c2 over smooth 3rd degree polynomial fit to data

• Mass resolution is ~5 MeV/c2

• Maximum excess in interval of 1.525 to 1.545 GeV/c2 is 57 combinations over background of 2840

• Corresponding 95% confidence level upper limit on excess is 195 combinations


ALEPH EXOTIC pK0 RESULTS

•Use average acceptance of 0.063 and BR(+ p K0) = ¼

•95% Confidence Level upper limit on the multiplicity of + (plus its antiparticle) in hadronic Z decays

•Ratio of + to (1520) production is Z decays

•This limit is roughly a factor of 20 lower than the ratio in d reactions measured by HERMES

N+ < 0.0030

N+/N(1520) < 0.13

s


DELPHI pK MASS SPECTRA AND RESULTS

306 ± 55 eventsN(1520) = 0.0224 ± 0.0027

No excess:N++ < 0.006 (95% C.L.)

pK– pK+ pK0s

No excess:N+ < 0.015 (95% C.L.)


L3 p and pK0 MASS SPECTRA(TWO PHOTON INTERACTIONS)

s

N = (1.57 ± 0.11) x 10-2

per e+e- e+e- hadrons(e+e- e+e-X) = 197.8 ± 13.8 pb

p pK0s

No excess observed95% C.L. limit set:

(e+e- e+e-X) < 20 pb


Sample of 3350 - candidates with a purity of 76% within a mass window of ± 7 MeV/c2

Sample of 3350 - candidates with a purity of 76% within a mass window of ± 7 MeV/c2

ALEPH SEARCH FOR RESONANCES: MASS SPECTRA

No excess observed95% C.L. limit set


ALEPH SEARCH FOR RESONANCES: RESULTS

•Mass spectrum of doubly-charged combinations (--) is well fitted by linear background from 1.62 to 2.1 GeV/c2

• In NA49 signal region (1.835 to 1.885 GeV/c2) observed excess is –2 combinations over background of 436

•Using acceptance of 0.021 and systematic uncertainty of 8%, a 95% Confidence Level upper limit is obtained

N • BR((1862)– – ––) < 4 x 10–4

•For neutral combinations, (1530)0 multiplicity is found to be

in good agreement with previous ALEPH and OPAL results

N+ N(1530)0 = (70 ± 8 ± 6) x 10–4

•95% Confidence Level upper limit on Exotic/Non-Exotic

N • BR((1862)– – ––)/N(1530)0 < 0.06


ALEPH SEARCH FOR CHARM RESONANCES: D0p and D+p MASS SPECTRA

No compelling excess observed95% C.L. limit set


ALEPH SEARCH FOR CHARM RESONANCES: D*+p MASS SPECTRA

No excess observed95% C.L. limit set


ALEPH SEARCH FOR CHARM RESONANCES: RESULTS

•No excess in D*–p channel: 2 combinations between 3.09 and 3.11 GeV/c2 (3.5 combinations expects from Monte Carlo)

•D–p channel (not covered by H1), an slight excess is observed of 5.2 ± 3.7 combinations

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¶ SUMMARY

OUTLINE


SUMMARY

•No evidence of light pentaquark production + observed in Hadronic Z Decays and Two Photon Interactions in ALEPH, DELPHI, L3 data

•No evidence of light pentaquark production observed in Hadronic Z Decays in ALEPH data

•No evidence of heavy flavour pentaquark production c0 observed in Hadronic Z Decays in ALEPH data

N • BR((1862)– – ––) < 4 x 10–4

N+ < 0.0030

N+/N(1520) < 0.13(e+e- e+e-X) < 20 pb

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29 June 2004Steve Armstrong - Searches for Pentaquark Production at LEP1 Searches for Pentaquark...

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