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

2. NA49 signal proton beam, liquid hydrogen target, NA49 (CERN):
C. Alt et al., Phys. Rev. Lett. 92, (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

3. 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)

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

5. 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

6. 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

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

8. - 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

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

10. 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

11. (1530)0 and (1530)0 signals (1530)0: 1090 ± 90 events

12.  mass spectra

13. Results
Assuming:
(COMPASS)
(NA49)
we would thus expect: 400  - - pentaquarks in COMPASS
Upper limit: 70 events (99% CL)
Negative results were also reported by:
...
Presently NA49 seems to be the only one seeing this state

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

15. 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)
•109 interactions were recorded