Transcript Prezentacja programu PowerPoint

Search for X - - Pentaquark in COMPASS
Presented by G.Brona
([email protected])
On behalf of the COMPASS collaboration
Outline:
1. NA49 signal
2. COMPASS experiment
3. Reconstruction of 0 and X4. Observation of X(1530)0
5. X-- pentaquark search results
6. Summary
NA49 signal
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
X - -  0 - -  p - - X -   0 -   p - - 



-
0
X        p   
0
X      -  p   1862 ± 2 MeV
FWHM = 17 MeV
S = 67.5
 = 5.6
COMPASS Collaboration
COmmon Muon and Proton
Apparatus for Structure and
Spectroscopy
~250 physicists
from 28 institutes,
11 countries
Muon and hadron programmes:
• Gluon polarization
• Inclusive DIS asymmetry
• Flavour separation
• Transversity
• Diffractive vector mesons production
•  polarization
• Primakoff effect
• Hadron spectroscopy
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
m
LAS
(>30 mrad, >0.4GeV/c)
SAS
(<30 mrad, >4GeV/c)
X- - search
polarisation>50%
m+
m+’
-

X
-
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: 638 000 ± 2200 events
0 (0 ) in 7 MeV window around the peak are used in the analysis
X- and X+ 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
X- and X+ signals
X -: 17 930 ± 210 events
(1640 for NA49)
X +: 10 620 ± 180 events
(551 for NA49)
X- (X+) in 10 MeV window around the peak are used in the analysis
Reconstruction of X mass spectra
Topology:
 All particles not used in X - 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
X(1530)0 and X(1530)0 signals
X(1530)0: 1090 ± 90 events
X(1530)0: 630 ± 70 events
X mass spectra
Results
Assuming:
 X -- 
 X - 

(COMPASS)
we would thus expect: 400 X
 X -- 
 X - 

(NA49)
- - pentaquarks
1
40
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
 [email protected]/c
 ...
Presently NA49 seems to be the only one seeing this state
Summary
1. The analysis was triggered by NA49 observation
(C. Alt et al., Phys. Rev. Lett. 92, 042003 (2004))
2. Analysis was performed on the 2002-2003 COMPASS data –
statistics (X -) 10 times larger than in NA49 experiment –
400 X -- events expected
3. Signal larger than 70 events excluded (99% CL)
4. COMPASS 2002-2003 data do not confirm the existence of
X -- pentaquark
COMPASS Detector
m filter
Trackers:
Si,SciFi,Micromegas,
GEM,DC,Straw,MWPC
Magnets
Polarised
target
Trigger
hodoscopes
H&E Calorimeters
RICH
LAS
(>30 mrad, >0.4GeV/c)
SAS
(<30 mrad, >4GeV/c)
2002+2003 - 3•109 interactions were recorded