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Recent argus results on charmed mesons and baryons
745c
Nuclear Physics AS27 (1991) 74%748~ North-Holland, Amsterdam
RECENT ARGUS RESULTS ON CHARMED MESONS AND BARYONS J. STIEWE Universitit Heidelberg 1.
THE DECAY D$ -+ $a+
We have performed a new measurement reconstructing the D$ in (7’~~) - combinations with 17’-t ~‘7, p” + ~+a-, and 17’+ T]~+T-, 17+ ~7.‘) Fig. 1 shows the D$ - signal with 7’ + p’y. Using the ARGUS value a(D:+D,).BR(D$ + @r+) = (7.8ztO.8f1.3)pb at fi =10.15 GeV, and taking the weighted average of both 7’ channels, we get BR(D: --+ + &r+) = 2.5 f 0.5 f 0.3. $r+)/BR(Df
OC 1.7
2.1
1.9
2.3
+b+
Fig. 1: 2.
M($r+)
[GeV/c2]
with 9 + p’y.
THE DECAYS e+v AND D$ + qSe+v The only source for leptons in the continuum are charm decays. We have looked for
??*’ and 4 in the presence of an electron; since only ??*‘e+, but no R*‘e- combinations can come from charm decays, one can use the latter to estimate the background contributions. Table 1:
Results for the decays D+ + ??“e+v K*Oe+
Combinations observed
1441 f
and D$ + qie+v
K*“e96
573 f 80
&+ 200 * 21
Fakes
256 f
51
259 f 52
455
Fragmentation
185 f
46
260 f 46
35% 11
T(45) Remaining
22Ok
52
67 f 29
880 f 129
(-13 f 119)
16f
9 7
104 f 26
0375~9474/91/$03.500 1991 - Elsevier Science PublishersB.V. (North-Holland)
746~
.I. Stiewe / Charmed mesons and batyons
The resulting D$
decay
+
4e+v)/BR(D$ The numbers 3.
branching
$e+v,
ratio is BR(D+
4
= (5.0 f 0.7 f
r*‘e+~)
we apply
the
PARITY
NON-CONSERVATION
analogous
1.2)s.
For the
procedure.
Here we obtain BR(Dz -+ ++) = 0.57 & 0.15 k 0.15 and BR(D$ + &T+) = (3.0 f 1.2) of signal and background combinations are given in Table 1.
EVIDENCE
FOR
IN THE
DECAY
A;
--+ %.
--$ AT+
In the decay of an unpolarized AZ h AT+, A b pr-, parity nonconservation gives rise to an asymmetry in the helicity angular distribution of the proton. Fitting the (A&) mass in bins of the cosine of the helicity angle using the parmetrization W(0) 0; l+or~;a~cos(d), where oat and O(A are the decay asymmetries of At and A(o* = 0.642 = 0.642~tO.013 from PDG), we fit the slope to be (-0.62 f 0.26) and get o,,t_ = (-0.97 * 0.41) consistent with maximum parity violation (Fig. pK-s+) = (18 ztz3 f 4) %.
2).
we get BR(Az
As a byproduct,
-+ Ax+)/BR(A$
+
dN N dcosJ.
0
,,..!
-0.5
4.
MEASUREMENT
2:
Decay proton
OF THE
0.5
0.0 cos
Fig.
1
I,.,
L,..
-1.o
29
helicity
CHARMED
1 .o
angle
distribution
STRANGE
BARYONS
2:
and E:
We observe the charmed strange baryons Ez and Sf in the decay channels Z: + z-r+r+, zoc + Z-n+ and E:-n+r+rr-. The latter channel has been observed here for the first time (Fig.3). The measured mass values are given in Table 2. Table 2: Decay ?0 -C d
Mode
z-x+
‘=o ---) t-r+n+rIC Ez,
weighted
22
-_$ x-x+K+
M(q)
mean
- M(EE)
Measured
Massea
and 0. BR
Mass (MeV/c)*
fOT
S!
0. BR,
and 52 z,, > 0.5 pb)
u
. BR,
all zp (pb)
2475.7 & 6.2 f 3.2
0.48 zt 0.15 f 0.08
0.77 l 0.24 f 0.16
2471.2 f 3.0 + 1.6
1.59 f 0.40 & 0.17
2.55 f 0.64 & 0.39
0.95 f 0.25 f. 0.10
1.50 f 0.39 f 0.23
2472.1 & 2.7 f 1.6 2465.1 f 3.6 f -7.0
1.9
f 4.5 f 2.2
74-k
0 1.9
2.2
2.5
3.1
2.8 [CeV/F]
Adding the charmels Z$ -+ Z-&r+ and $! -+ Z-~+@rr-, we extract the sp spectrum and fit the Peterson function with q+terson = 0.24 i 0.08 . The vaiues for cross section times branching ra.tio (for zp, > 0.5 and, using the above value for cc, for the entire X~ range), are listed in Table 2. Our value for the isospin splitting A@$> - M(Ez) = (-7.0 * 4.5 f 2.2)MeV is in excellent agreement with those obtained by CLE02) and ACCMOR..3) REFERENCES 1. H. Albrecht et ad., “Observation of the Decay D$ 4 q’&,” (1990). 2. M. S. A&n
et al., Phys. Lett. 226B (1989) 401.
3. S. Barlag et ad., Phys. Letd. 236B (1990) 495.
DESY preprint 90-032
Nuclear Physics AS27 (1991) 74%748~ North-Holland, Amsterdam
RECENT ARGUS RESULTS ON CHARMED MESONS AND BARYONS J. STIEWE Universitit Heidelberg 1.
THE DECAY D$ -+ $a+
We have performed a new measurement reconstructing the D$ in (7’~~) - combinations with 17’-t ~‘7, p” + ~+a-, and 17’+ T]~+T-, 17+ ~7.‘) Fig. 1 shows the D$ - signal with 7’ + p’y. Using the ARGUS value a(D:+D,).BR(D$ + @r+) = (7.8ztO.8f1.3)pb at fi =10.15 GeV, and taking the weighted average of both 7’ channels, we get BR(D: --+ + &r+) = 2.5 f 0.5 f 0.3. $r+)/BR(Df
OC 1.7
2.1
1.9
2.3
+b+
Fig. 1: 2.
M($r+)
[GeV/c2]
with 9 + p’y.
THE DECAYS e+v AND D$ + qSe+v The only source for leptons in the continuum are charm decays. We have looked for
??*’ and 4 in the presence of an electron; since only ??*‘e+, but no R*‘e- combinations can come from charm decays, one can use the latter to estimate the background contributions. Table 1:
Results for the decays D+ + ??“e+v K*Oe+
Combinations observed
1441 f
and D$ + qie+v
K*“e96
573 f 80
&+ 200 * 21
Fakes
256 f
51
259 f 52
455
Fragmentation
185 f
46
260 f 46
35% 11
T(45) Remaining
22Ok
52
67 f 29
880 f 129
(-13 f 119)
16f
9 7
104 f 26
0375~9474/91/$03.500 1991 - Elsevier Science PublishersB.V. (North-Holland)
746~
.I. Stiewe / Charmed mesons and batyons
The resulting D$
decay
+
4e+v)/BR(D$ The numbers 3.
branching
$e+v,
ratio is BR(D+
4
= (5.0 f 0.7 f
r*‘e+~)
we apply
the
PARITY
NON-CONSERVATION
analogous
1.2)s.
For the
procedure.
Here we obtain BR(Dz -+ ++) = 0.57 & 0.15 k 0.15 and BR(D$ + &T+) = (3.0 f 1.2) of signal and background combinations are given in Table 1.
EVIDENCE
FOR
IN THE
DECAY
A;
--+ %.
--$ AT+
In the decay of an unpolarized AZ h AT+, A b pr-, parity nonconservation gives rise to an asymmetry in the helicity angular distribution of the proton. Fitting the (A&) mass in bins of the cosine of the helicity angle using the parmetrization W(0) 0; l+or~;a~cos(d), where oat and O(A are the decay asymmetries of At and A(o* = 0.642 = 0.642~tO.013 from PDG), we fit the slope to be (-0.62 f 0.26) and get o,,t_ = (-0.97 * 0.41) consistent with maximum parity violation (Fig. pK-s+) = (18 ztz3 f 4) %.
2).
we get BR(Az
As a byproduct,
-+ Ax+)/BR(A$
+
dN N dcosJ.
0
,,..!
-0.5
4.
MEASUREMENT
2:
Decay proton
OF THE
0.5
0.0 cos
Fig.
1
I,.,
L,..
-1.o
29
helicity
CHARMED
1 .o
angle
distribution
STRANGE
BARYONS
2:
and E:
We observe the charmed strange baryons Ez and Sf in the decay channels Z: + z-r+r+, zoc + Z-n+ and E:-n+r+rr-. The latter channel has been observed here for the first time (Fig.3). The measured mass values are given in Table 2. Table 2: Decay ?0 -C d
Mode
z-x+
‘=o ---) t-r+n+rIC Ez,
weighted
22
-_$ x-x+K+
M(q)
mean
- M(EE)
Measured
Massea
and 0. BR
Mass (MeV/c)*
fOT
S!
0. BR,
and 52 z,, > 0.5 pb)
u
. BR,
all zp (pb)
2475.7 & 6.2 f 3.2
0.48 zt 0.15 f 0.08
0.77 l 0.24 f 0.16
2471.2 f 3.0 + 1.6
1.59 f 0.40 & 0.17
2.55 f 0.64 & 0.39
0.95 f 0.25 f. 0.10
1.50 f 0.39 f 0.23
2472.1 & 2.7 f 1.6 2465.1 f 3.6 f -7.0
1.9
f 4.5 f 2.2
74-k
0 1.9
2.2
2.5
3.1
2.8 [CeV/F]
Adding the charmels Z$ -+ Z-&r+ and $! -+ Z-~+@rr-, we extract the sp spectrum and fit the Peterson function with q+terson = 0.24 i 0.08 . The vaiues for cross section times branching ra.tio (for zp, > 0.5 and, using the above value for cc, for the entire X~ range), are listed in Table 2. Our value for the isospin splitting A@$> - M(Ez) = (-7.0 * 4.5 f 2.2)MeV is in excellent agreement with those obtained by CLE02) and ACCMOR..3) REFERENCES 1. H. Albrecht et ad., “Observation of the Decay D$ 4 q’&,” (1990). 2. M. S. A&n
et al., Phys. Lett. 226B (1989) 401.
3. S. Barlag et ad., Phys. Letd. 236B (1990) 495.
DESY preprint 90-032