Transcript Dynamical Analysis of V

J.-L Tang
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Dynamical Analysis of V-particles
Decays
Podolanski-Armenteros Plot and its application for V0 particle search
Jaw-Luen Tang
Department of Physics
National Chung Cheng University
Chiayi, Taiwan
2004/8/20
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Introduction
• In 1953, Podolanski and Armenteros devised a method of
analyzing the dynamics of two-body V decays to search for
new unstable neutral particles in terms of measured p1
quantities: p1, p2. (pp1+p2)
p2
• The method based on constructing new variables: 1/P ,
Podolanski-Arementeros parameter a , pT the transverse
momentum or e=2pT/P, that related to the momentum
components of each particles by conservation of
momentum and energy which depend on the decay
schemes.
• It is used to classify the V0-particles and is a convenient
way of displaying ( identifying ) the decay schemes.
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Armenteros analysis of V decay
• Consider the decays of a neutral V0-particle of mass m and velocity
b into two charged particles with mass m1 and m2 , m m1 + m2 + Q.
P  p1  p2
pL  p1L  p2 L  p1 cos 1  p2 cos 2
pT  p1 sin 1  p2 sin 2  p1 p2 sin  / P
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Center of Mass system
Laboratory system
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Armenteros Analysis
• In the laboratory system, only p1,p2,and p can be measured, while the
velocity of decaying particle b is unknown.
2p
2sin 1 sin 2
e T 
• Useful quantities : pT, independent of b.
P
sin 
p1L - p2 L 

a
 p1L  p2 L 
• In the a-pT or a-e planes, the points corresponding to a given decay
scheme lie on an family of ellipses determined by the particle mass
and the velocity b the secondaries.
a  a0  f ( p* ,cos * )
m12 - m22
a0 
m2
(a - a) *2
*
pL 
p  pL*2  pT*2
(2 / bm)
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a - a
2 p
*
2
/ bm 
2
pT2
 * 1
p
 a - a   e2  1
e 2  ( me / P ) 2 ( m e / P ) 2 4
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An Example: E896 H search

K  
0
s
  p
-
  p

-
H  - p
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Another Example: HERA-B
• HERA-B try to verify claims for
different exotic states, mainly they
focus on: + (uudds) -> p K0
Armenteros plot
Ks
+(1540) -> p Ks
Decay chain
+
Ks
p
+
-
Λ
Λ
KSππ
Λpπ
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Taken
from A. Sbrizzi‘s talk
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Another example:
Study of the K*(892)0 signal in pp ALICE events
qt(+)
Armenteros Plot
q(+)
ql(+)
0,4
0,35
rho(770)
0,3
omega(782)
phi(1020)
qt
0,25
0,2
Delta
Lambda
0,1
Lambdabar
K*(892)
0,05
a=
0
-0,5
q(-)
Deltabar
0,15
-1
ql(-)
k0s
0
0,5
1
qt(-)
ql(+) - ql(-)
ql(+) + ql(-)
alpha
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Taken from
Giuseppe’s talk.
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More example:
Exotic Particle Searches with STAR at RHIC
Taken from Sonia Kabana’s talk
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LEPS: 10k  + 10k  events
• Analyzed 10k  + 10k  MC events through current
TPCana0.43 tracking and vertex finder codes.
10k 
10k 
gp->p
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10k  + 10k 
gpK+
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Cuts at invariant mass
Cut1 
nvtx >1, ntrk>4, cdis<2mm, chi2prob<0.02
Cut 2
Ks
Cut 3

Cut5
Cut4 
Cut 6
Cuts 1, in target, Cuts 1, in target, Cuts 1, out target
Vtxy<2mm
Vtxy<2mm
Vtxy>2mm
-1650Vz<-1550 -1650Vz<-1550 -1650Vz<-1550
Cut7
pT<0.2, |a|<0.5
 arm cut
Cut8
pT>0.1, |a|<1
Ks arm cut
Cut9
pT<0.2,a>0.5
 arm cut
Cut10
Cuts 1& 4& 7

Cut11
Cuts 2 & 5 & 8
Ks
Cut12
Cuts 3&6&9

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Data Cuts at Armenteros diagram
Cut1
nvtx >1
Cut 2
Cut 1 + ntrk>4
Cut4
Cuts 1+2+3
[a, pt]<1
Cut 5
Cuts 4 && in target
Vtxy<2mm, Vz cut
Cut 3
Cuts 1+2 q1q2<0,
cdis<2mm, chi2prob<0.02
Cut 6
Cuts 4 && out target
Vtxy>2mm, Vz cut
Cut7
Cut 4 and
 arm cut
Cut8
Cuts 4 and
Ks arm cut
Cut9
Cut 4 and
 arm cut
Cut10
Cuts 5 and
 arm cut
Cut11
Cuts 5 and
Ks arm cut
Cut12
Cuts 9 and
 arm cut
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Runs
28641
To
28847
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