Search for X - - Pentaquark in COMPASS Presented by G.Brona (gbrona@cern.ch) On behalf of the COMPASS collaboration Outline: NA49 signal COMPASS experiment Reconstruction of 0 and - Observation of (1530)0 -- pentaquark search results Summary

NA49 signal proton beam, liquid hydrogen target, NA49 (CERN): C. Alt et al., Phys. Rev. Lett. 92, 042003 (2004) NA49 (CERN): proton beam, liquid hydrogen target, peak: ~1860MeV, FWHM<20MeV, S=36, =4.0 1862 ± 2 MeV FWHM = 17 MeV S = 67.5  = 5.6

COMPASS Collaboration COmmon Muon and Proton Apparatus for Structure and Spectroscopy Muon and hadron programmes: Gluon polarization Inclusive DIS asymmetry Flavour separation Transversity Diffractive vector mesons production  polarization Primakoff effect Hadron spectroscopy ~250 physicists from 28 institutes, 11 countries SPS (Super Proton Synchrotron) Beryllium target /K beam 160 GeV/c polarized muon beam The beam intensity is 2·108 m+ per spill (4.8 s)

COMPASS Detector LAS SAS m+ (>30 mrad, >0.4GeV/c)

X- - search + +’  -  p  - 0  -  - Good event: polarisation>50% + +’  -  p  - 0  -  - Good event: incoming and outgoing muons identified a primary vertex inside geometrical limits of a 6LiD target

0 and 0 selection Topology: Secondary vertex with 2 outgoing oppositely charged particles downstream from the primary one and located outside the target 2 of a vertex < 4 Kinematical cuts: Momentum of 0 candidate < 140 GeV/c |cos|<0.9, where  is the angle between the 0 momentum vector in the LAB system and the momentum of the  in the 0 CMS

0 and 0 signals 0: 1 245 800 ± 2400 events 0 (0 ) in 7 MeV window around the peak are used in the analysis

- and + selection Topology: All particles not used in 0 reconstruction... ... and which are not muons... ... and do not point into primary vertex are assumed to be pions The closest distance of approach between  and 0 < 0.8 cm ... and is between primary vertex and 0 vertex Kinematical cuts: Momentum of a pion candidate < 140 GeV/c

- and + signals  -: 17 930 ± 210 events (1640 for NA49)  +: 10 620 ± 180 events (551 for NA49) - (+) in 10 MeV window around the peak are used in the analysis

Reconstruction of  mass spectra Topology: All particles not used in  - reconstruction... ... and which are not muons... ... and point into primary vertex are assumed to be pions Kinematical cuts: Momentum of a pion candidate < 140 GeV/c

(1530)0 and (1530)0 signals (1530)0: 1090 ± 90 events

 mass spectra

Results Assuming: » » (COMPASS) (NA49) we would thus expect: 400  - - pentaquarks in COMPASS Upper limit: 70 events (99% CL) Negative results were also reported by: WA89@340GeV/c HERA-B@920GeV/c ZEUS@27-920GeV/c BaBar@9-3.1GeV/c ... Presently NA49 seems to be the only one seeing this state

Summary The analysis was triggered by NA49 observation (C. Alt et al., Phys. Rev. Lett. 92, 042003 (2004)) Analysis was performed on the 2002-2003 COMPASS data – statistics ( -) 10 times larger than in NA49 experiment – 400  -- events expected Signal larger than 70 events excluded (99% CL) COMPASS 2002-2003 data do not confirm the existence of  -- pentaquark

COMPASS Detector LAS SAS 2002+2003 - 3•109 interactions were recorded m filter Trackers: Si,SciFi,Micromegas, GEM,DC,Straw,MWPC Magnets Polarised target Trigger hodoscopes H&E Calorimeters beam m+ RICH LAS (>30 mrad, >0.4GeV/c) SAS (<30 mrad, >4GeV/c) 2002+2003 - 3•109 interactions were recorded