First Observation of Bottom Baryon Sigma_b States at CDF

0.24 MB·English

by  Igor V. Gorelov

FERMILAB-CONF-07-027-E
First Observation of Bottom Baryon
Σ States at CDF
b
7
Igor V. Gorelov 1
0
0 (For the CDF Collaboration)
2
Department of Physics and Astronomy,

n University of New Mexico,
a 800 Yale Blvd. NE, Albuquerque,NM87131, USA
J
E-mail: [email protected]
1
3

1
v
6
5
0
1 Abstract. We present the latest results on the search for bottom baryon states Σb using
0 1fb−1 of CDF data. The study is performed with the world’s largest sample of fully
7 r∼econstructed Λ0 decayscollected byCDFIIdetectorat √s=1.96TeV in thehadronictrigger
b
0 path. We observe4 new states consistent with Σ(∗)± bottom baryons.
/ b
x
e
-
p
e
h 1. Introduction
v: Highenergyparticlecollidersprovideawealthofexperimentaldataonbottommesons. However,
i only one bottom baryon, the Λ0, has been directly observed [1, 2, 3, 4].
X b
Heavy baryons containing one heavy quark and a light diquark became a nice 3-body
r
a laboratory to test QCD models. In the limit of heavy quark mass mQ , heavy baryons’
→ ∞
properties are governed by the dynamics of the light diquark in a gluon field created by the
heavy quark acting as a static source. The heavy baryon like Λ0 can be considered as a “helium
b
atom” of QCD. In this Heavy Quark Symmetry (HQS) approach [5] at the heavy quark limit a
heavy quark spin does not interact with the gluon field, the spin decouples from the degrees of
freedom of the light quark and the quantum numbers of the heavy quark and the light diquark
are separately conserved by the strong interaction. Consequently the light diquark momentum
j = s +L , theheavy quark spins and total momentum J = s +j are considered
qq qq qq Q Qqq Q qq
asgoodquantumnumbers. BasedontheHQSprinciplesaneffectivefieldtheorywasconstructed
where 1 correctionscanbesystematically includedintheperturbativeexpansions. Thetheory
mQ
was named as Heavy Quark Effective Theory (HQET) (see [6] and references therein).
For the bottom Q b baryons with a single heavy quark and two light ones (see Table 1)
the bottom quark spin≡, s = 1+, is combined with the light diquark momentum j comprised
Q 2 qq
1 talk given on behalf of theCDF Collaboration at the Second Meeting of the APS Topical Group on Hadronic
Physics, GHP 2006, October 22 - 24, 2006, Nashville, Tennessee.
of spin s = 0+ 1+ and its angular momentum L . The baryons with a diquark having
qq qq
⊕
s = 0+ and isospin I = 0 are called Λ- type, while the states with s = 1+ and isospin I = 1
qq qq
are called Σ- type. The ground state Λ0 baryon has I = 0, JP = 1+. A doublet of ground Σ-
b 2
like bottom baryons comprises Σ with I = 1, JP = 1+ and Σ∗ with I = 1, JP = 3+.
b 2 b 2
The combination of an orbital momentum L = 1− of a diquark with its spin of s = 0+
qq qq
addstothespectroscopy anumberof excited P-wave bottom Λ-states. Thelowest lyingorbital
excitations are Λ∗0 with JP = 1−, 3− [7, 8, 9].
b 2 2
Table 1. Bottom baryon Λ- and Σ- states and their quantum numbers. The [q q ] denotes a
1 2
pair antisymmetric in flavor and spin. The q q denotes a pair symmetric in flavor and spin.
1 2
{ }
State Quarks JP (I,I )
3
Λ0 b[ud] (1/2)+ (0,0)
b
Σ+ buu (1/2)+ (1,+1)
b
Σ0 b ud (1/2)+ (1,0)
Σb− bd{d } (1/2)+ (1, 1)
Σb∗+ buu (3/2)+ (1,+−1)
b
Σ∗0 b ud (3/2)+ (1,0)
Σb∗− bd{d } (3/2)+ (1, 1)
b −
Λ∗0 b[ud] (1/2)− (0,0)
b
Λ∗0 b[ud] (3/2)− (0,0)
b
Theoretical expectations for ground bottom baryon states are summarized in Table 2. The
calculations have been done with non-relativistic and relativistic potential quark models, 1/N
c
expansion, quark models in the HQET approximation, sum rules, and finally with lattice QCD
models [10].
In a physics reality m is finite and a degeneration of a Σ , Σ∗ doublet is resolved by
Q { b b}
a hyperfine mass splitting between its states. There is also an isospin mass splitting (see
Table 2) between members of Σ and Σ∗ isotriplets [11, 12, 13, 14]. As it was pointed
b b
out [14] the value of the isospin splitting within Σ triplet does differ from Σ∗ triplet, namely
b b
(Σ∗+ Σ∗−) (Σ+ Σ−) = 0.40 0.07MeV/c2. This number contributes to systematic
b − b − b − b ±
uncertainty of our experimental results (see Section 5).
(∗)±
Table 2. Mass and width predictions for Σ .
b
Σ property MeV/c2
b
m(Σ ) m(Λ0) 180 210
b − b −
m(Σ∗) m(Σ ) 10 40
m(Σb−)− m(Σb+) 5 −7
b − b −
m(Λ0), fixed 5619.7
b
from CDF II 1.2 1.2
± ±
Γ(Σ ),Γ(Σ∗) 8, 15
b b ∼ ∼
see below
According to HQS the physics of pion transitions between heavy baryons is governed by the
light diquark. The one or two pions are emitted from the light diquark while the heavy quark
propagates unaffected by the pion emission process. Various pion transitions of bottom baryons
into the lower ground states are summarized at the Figure 1. The mass predictions for the S-
wave (i.e. ground state) Σ- like baryons show that there is enough phase space for the both Σ
b
and Σ∗ to decay into Λ0 via single-pion emission. The two excited (P-wave) Λ∗0 states might
b b b
decay into Λ0 via two-pion transitions provided a sufficient phase space.
b
2
c
I=0 I=1
/
V 3/2- Figure 1. Transitions of ground
Ge L *b 1-˜ 1/2+ 1/2- Pion Transitions sgtraotuensdΣstba,teΣΛb∗0binvtioa aa slionwgle-lpyiionng
emissioninaP-waveasthediquark
p p with jqq = 1+ is converted to one
p s-wave s-wave with jqq = 0+. If Λ∗b0 states
p p havemassessufficientlyhigherthan
p
p-wave p the decay thresholds, the two-pion
p-wave
d-wave transitions into Λ0 or a single-pion
3+ S * b
1+˜ 1/2+ 2 b decays into Σb or Σb∗ states are
1+ S possible (see also a discussion [7,
p p 2 b 8, 9]). Λ∗0 single-pion transitions
b
p-waves to Λ0 are forbidden due to isospin
b
conservation and also by parity (for
L b 0+˜ 1/2+ 1/2+ notation: jPqq˜ sPQ the higher JP = 3− state).
2
b[qq] b{qq}
antisymm symm
(∗)
It is important for our experimental expectations to understand the natural width of Σ
b
baryons. As we expect that Σ(∗) masses lie within (180 210)MeV/c2 above Λ0 and well above
b − b
a threshold for a single-pion mode, we would expect that the single-pion P-wave transition will
dominate the total width [15, 16]. The authors [16] find
Γ = 1 MΛQ f 2 p~ 3,
ΣQ→ΛQπ 6πM | p| | π|
ΣQ
where p~ is the three-momentum of soft π , f g /f , f = 92MeV and g is the axial
π ΣQ p ≡ A π π A
vector coupling of the constituent quark for the nucleon. A fit of this formula to the known
PDG width measurements [17] of charm states Σ and Σ∗ yields g = 0.75 0.05 which is in
c c A
±
excellent agreement with g = 0.75 numerical theoretical value for the nucleon. Using the fit
A
(∗)
results we have estimated Γ(Σ ), see the Table 2. The error of the fitted g contributes as a
b A
systematic uncertainty to our experimental measurements (see Section 5).
2. Principle of the Analysis
(∗)
The topology of the event with Σ state produced in Tevatron collisions is demonstrated in
b
Figure 2. The Σ(∗) candidates are searched in the decay chain2:
b
Strong decay Σ(∗)± Λ0π± with both Λ0 Λ+π− and its daughter Λ+ pK−π+ in
• b → b Σb b → c c →
weak decay modes.
To remove a contribution due to a mass resolution of each Λ0 candidate and to avoid absolute
b
(∗)±
massscalesystematicuncertainties,theΣ candidatesarereconstructedinthemassdifference
b
Q-value spectra defined as
Q = M(Λ0π± ) M(Λ0) M (π±).
b Σb − b − PDG
ThenarrowsignaturesaresearchedforintheQ-spectrumconstructedseparatelyforeverycharge
state of Σ(∗)± candidates. The subsample of Σ(∗)− contains Λ0π− and Λ0π+ combinations from
b b b b
(∗)− (∗)+
the decays of the particles Σ and the antiparticles Σ , respectively. The subsample of
b b
Σ(∗)+ contains Λ0π+ and Λ0π− combinations from the decays of the particles Σ(∗)+ and the
b b b b
(∗)−
antiparticles Σ , respectively.
b
Figure 2. Sketch of the event topology
of a Σ produced in the CDF detector [18].
b
The bottom baryon Σ is produced at the
b
collision origin, i.e. primary vertex of the
event. The Σ decays strongly into Λ0 with
b b
p soft π± emitted. Due to a fast nature of the
Σb
strong decay the soft pion originates from the
primary vertex. The Λ0 and its daughter Λ+
b c
L decay weakly with a secondary decay vertex
p
S c K
measured in SVX II[19]. The tracks with
b (cid:0)(cid:0)(cid:0)(cid:0)(cid:1)(cid:1)(cid:1)(cid:1)(cid:0)(cid:0)(cid:0)(cid:0)(cid:1)(cid:1)(cid:1)(cid:1)(cid:0)(cid:0)(cid:0)(cid:0)(cid:1)(cid:1)(cid:1)(cid:1)(cid:0)(cid:0)(cid:0)(cid:0)(cid:1)(cid:1)(cid:1)(cid:1)(cid:0)(cid:0)(cid:0)(cid:0)(cid:1)(cid:1)(cid:1)(cid:1)(cid:0)(cid:0)(cid:0)(cid:0)(cid:1)(cid:1)(cid:1)(cid:1)(cid:0)(cid:0)(cid:0)(cid:0)(cid:1)(cid:1)(cid:1)(cid:1)(cid:0)(cid:0)(cid:0)(cid:0)(cid:1)(cid:1)(cid:1)(cid:1)(cid:0)(cid:0)(cid:0)(cid:0)(cid:1)(cid:1)(cid:1)(cid:1) p + arelacotimvemtoonasepcroimndaarryyvevretretxexanadrethdeispprlaoctoedn
P.V. (cid:0)(cid:1)L (cid:0)(cid:1)(cid:0)(cid:1)(cid:0)(cid:1)
bb from Λ+c decay and π− from Λ0b decay most
p - likely contribute to the CDF hadron Two
Track Trigger (see Section 3 and [20]).
The Σ(∗)± signal region at Q- value spectrum is defined as 30MeV/c2 <Q <100MeV/c2,
b
based on the theoretical expectation (see Table 2). We pursued a blind anal∼ysis ∼and developed
(∗)±
the Σ selection criteria using only the pure background sample in the upper and lower
b
sideband regions of 0MeV/c2 <Q <30MeV/c2 and 100MeV/c2 <Q <500MeV/c2. The signal
was modeled by a PYTHIA [∼21] M∼onte Carlo. ∼ ∼
3. Triggers and Datasets
Our results are based on data collected with the CDF II detector [18] and corresponding to an
integrated luminosity of 1.1fb−1. As pp collisions at 1.96TeV have an enormous inelastic
∼
total cross-section of 60 mb, while b- hadron events comprise only 20 µb (η < 1.0),
∼ ≈ | |
triggers selecting b- hadron events are of vital importance. Our analysis is based on a data
2 Unlessotherwisestatedallreferencestothespecificchargecombinationimplythechargeconjugatecombination
as well.
sample collected by a three-level Two displaced Track Trigger. It reconstructs a pair of high
p > 2.0GeV/c tracks at Level 1 with the CDF central tracker and enables secondary vertex
T
selection at Level 2. This requires each of the tracks to have an impact parameter measured
by the CDF silicon detector SVX II [19, 20] to be larger than 120µm. The excellent impact
parameter resolution of SVX II makes this challenging task possible. The trigger proceeds with
a full event reconstruction at Level 3. The Two displaced Track Trigger is efficient for heavy
quark hadron decay modes (see Figure 2 and its caption).
4. Event Selection
The candidates of the basic state in our analysis, Λ0, have been reconstructed in the mode
b
Λ0 Λ+π− with Λ+ pK−π+. The Two displaced Track Trigger requirements (see
b → c c →
Section 3) are confirmed offline for each Λ0 candidate. The Charm Λ+ and bottom Λ0
b c b
candidateshave bothbeensubjectedto3-dimensionalvertex fits. Thecollection ofthefittedΛ+
c
candidates has been confined to a mass range of mPDG 16MeV/c2 [17]. To suppress a prompt
Λ+c ±
background we apply a cut on the proper decay time cτ(Λ0) > 250µm with its significance
b
cτ(Λ0b)/σcτ > 10. The proper decay time of Λ+c with respect to the Λ0b vertex is required to be
70µm < cτ(Λ+ Λ0) < 200µm. We define the topological quantities as cτ L m /p
− c ← b ≡ xy · ΛQ T
and L = D~ p~ /p where D~ , p~ are the vectors of corresponding distance or momentum
xy xy T T xy T
·
in a transverse plane. To reduce combinatorial background and contribution from partially
reconstructed modes the impact parameter d (Λ0) is also restricted to be below of 80µm, where
0 b
d = D~ p~ /p . The kinematic cuts for Λ0 and Λ+ candidates, p (Λ0) > 6.0GeV/c and
0 | xy × T T| b c T b
p (Λ+)> 4.5GeV/c are applied as well.
T c
The powerful Λ0 Λ+π− signal is shown in Figure 3 with a binned maximum likelihood fit
b → c
superimposed. The background from physical states contributing to the left side of the signal is
analyzed with Monte Carlo simulations. The fit to the invariant Λ+π− mass distribution yields
c
3125 62(stat) of Λ0 Λ+π− candidates. We posses the world’s largest Λ0 sample.
± b → c b
CDF II Preliminary, L=1.1fb−1 Figure 3. Fit to the invariant
mass of Λ0 Λ+π− candidates.
b → c
Fully reconstructed Λ0 decays such
22cc11660000 Total Fit as Λ0 Λ+π− and Λb 0 Λ+K−
MeV/MeV/11440000 Partially-reconstructed L b arenbot→indiccatedonthebfi→gure.cThe
0 0 Fully-reconstructed B Λ0 signal region, 5.565GeV/c2 <
2211220000 b
r r Partially-reconstructed B m(Λ+π−) < 5.670GeV/c2, consists
ee c
s ps p11000000 Fake L b primarily of Λ0b baryons, with some
tete Data contamination from B mesons and
aa 880000
dd
didi combinatorial events. The left
anan 660000 side band is enriched by partially
CC
reconstructed Λ0 decays like Λ0
440000 b b →
Λ∗+π− and by fully reconstructed
c
220000 4-prongB-mesondecays likeB0
→
D+π−, D+ K−π+π+. The
00
55..22 55..33 55..44 55..55 55..66 55..77 55..88 55..99 66 66..11 66..22 →
mm((LL ++ pp --)) GGeeVV//cc22 right side band consists from a
cc
combinatorial background.
5. Σ Candidates and Signals
b
Following a method outlined in a Section 2 the Λ0 candidates (see a Section 4) from a signal
b
region of [5.565,5.670]GeV/c2 have been coupled with the pion tracks π± to create Σ(∗)±
Σb b
candidates and the pairs Λ0π± have been subjected to a common vertex fit.
b Σb
(∗)
The Σ analysis cuts are optimized according to a blind analysis technique using the upper
b
and lower sideband regions (see a Section 4) of experimental Q- value spectrum while the signal
is modeled by a PYTHIA [21]. The following kinematic and topological variables are used :
p (Σ ), the soft pion track impact parameter significance d /σ (π ), and the polar angle of
T b | 0 d0| Σb
thesoftpioninaΣ -restframe,cosθ∗(π ) =p~ ~p∗/(p~ p~∗ ). Afigureofmeritisdefined
b Σb Σb · π | Σb|·| π|
as ǫ(S )/√B, where ǫ(S ) is the signal efficiency measured in the Monte Carlo sample and
MC MC
B is the background in the signal region estimated from the upper and lower sidebands. The
maximum of the figure of merit is reached for p (Σ ) > 9.5GeV/c, d /σ (π ) < 3.0, and
T b | 0 d0| Σb
cosθ∗ > 0.35.
−
CDF II Preliminary, L = 1.1 fb-1 CDF II Preliminary, L = 1.1 fb-1
22eV/ceV/c 34345050 S - LTB0bo HtHaaal +B+ kUUgEE BBkkgg 22eV/ceV/c 5500 S - LT0bo tHaal B+ kUgE Bkg
5 M5 M 3300 b Combinatorial Bkg 5 M5 M 4400 b B Ha + UE Bkg
er er 2255 er er Combinatorial Bkg
pp pp
s s 2200 s s 3300
ee ee
atat 1155 atat 2200
dd dd
didi 1100 didi
nn nn 1100
aa 55 aa
CC CC
4400
3355 S + LT0bo tHaal B+k UgE Bkg 5500 S + LT0o tHaal B+k UgE Bkg
B Ha + UE Bkg b
3300 b Combinatorial Bkg 4400 b B Ha + UE Bkg
2255 Combinatorial Bkg
3300
2200
1155 2200
1100
1100
55
00 00
00..00 00..11 00..22 00..33 00..44 00..55 00..00 00..11 00..22 00..33 00..44 00..55
QQ == mm((LL 00pp )) -- mm((LL 00)) -- mm ((GGeeVV//cc22)) QQ == mm((LL 00pp )) -- mm((LL 00)) -- mm ((GGeeVV//cc22))
bb bb pp bb bb pp
a) b)
Figure 4. a) The three background sources described in the text and their sum are shown
superimposed on the Q distributions, with the signal region blinded. The top plot shows the
Λ0π− distribution, which contains all Σ−. The bottom plot shows the Λ0π+ distribution, with
b Σb b b Σb
all Σ+. The sideband regions are parameterized with a power law multiplied by an exponential.
b
The percentage of each background component in the Λ0 signal region is computed from the Λ0
b b
mass fit (see Figure 3), and is: N(Λ0) 90.1%, N(B) 6.3% and N(combinatorial) 3.6%;
b)TheexcessintheΛ0π− (topplot)bsu≈bsampleis148ca≈ndidatesover268expectedback≈ground
b Σb
candidates, whereas in the Λ0π+ (bottom plot) subsample the excess is 108 over 298 expected
b Σb
background candidates.
The Q- value spectra with blinded signal region are shown in Figure 4a with its detailed
caption. In the Σ(∗) search, the dominant background is from the combination of prompt Λ0
b b
baryons with extra tracks produced in the hadronization process. The remaining backgrounds
are from the combination of hadronization tracks with B mesons reconstructed as Λ0 baryons,
b
and from combinatorial background events.
Upon unblinding the Q signal region in both spectra we observe an excess of events over the
background as shown in Figure 4b with the details explained in the caption.
Next we perform a simultaneous unbinned maximum likelihood fit to the Λ0π− and Λ0π+
b Σb b Σb
(∗)±
subsamples for a signal from each expected Σ state plus the background, referred to
b
as the “four signal hypothesis.” Each signal consists of a Breit-Wigner distribution convo-
luted with two Gaussian distributions describing the detector resolution, with a dominant
narrow core and a small broad component for the tails. The natural width of each Breit-
Wigner distribution is computed from the central Q- value (see a Section 1 and [16]). The
fit shown in Figure 5 results in the yields NΣb+ = 33+−1132, NΣb− = 62+−1154, NΣb∗+ = 82 ± 17,
and NΣb∗− = 79 ± 18 candidates, with the signals located at QΣb+ = 48.2+−12..92MeV/c2,
QΣb− = 55.9+−10..09MeV/c2, and ∆Σb∗ = 21.5+−21..08MeV/c2, where ∆Σb∗ ≡ (QΣb∗ − QΣb).
CDF II Preliminary, L = 1.1 fb-1 Fit Prob. = 78%
22
cc Total Fit
V/V/
ee 5500 S - Background Table 3. Likelihood ratios calculated for the
MM b S - fi L 0p -
r 5 r 5 4400 S b*b- fi L b0bp - alternative signal(h∗)y±pothesis with respect to
ee the one of four Σ states. The strength of
pp b
s s 3300 the signal hypothesis is further given by the
ee
tt likelihood ratio, LR L/L , where L is the
aa 2200 alt
dd ≡
didi likelihood of the four signal hypothesis and
nn 1100 L is the likelihood of an alternate
aa alt
CC hypothesis.
Total Fit
5500 Hypothesis LR
S + Background
4400 b SS +b*+ fifi LL 0b0pp++ NTwulol Σ States 12..66×1100169
b b b
3300 No Σ− Signal 3.3×104
b ×
2200 No Σ+ Signal 3
b
No Σ∗− Signal 2.4 104
1100 No Σb∗+ Signal 1.8×104
b ×
00
00..0000 00..0055 00..1100 00..1155 00..2200
QQ == mm((LL 00pp )) -- mm((LL 00)) -- mm ((GGeeVV//cc22)) The alternative hypothesis is estimated using
bb bb pp all systematic variations of the background
Figure 5. Simultaneous fit to the Λ0π− and signal functions. The variation with the
b Σb
(top) and Λ0π+ (bottom) spectra for Σ (∗)∓ largest value of L corresponding to the least
b Σb b alt
candidates shown on a range of favorable hypothesis is taken.
Q [0, 200] MeV/c2.
∈
Systematic uncertainties on the mass difference and yield measurements fall into three
(∗)± (∗)±
categories: mass scale, Σ background model, and Σ signal parameterization. The mass
b b
scale is determined from the difference in the mean of the narrow resonances m(D∗+) m(D0),
−
m(Σ0,++) m(Λ+), m(Λ (2625)+) m(Λ+) between data and PDG[17]. The uncertainties on
c c c c
− −
the background come from the assumption on the sample composition of the Λ0 signal region,
b
the normalization and functional form of the Λ0 hadronization background. The systematic
b
(∗)±
effects related to assumptions made on the Σ signal parameterization are: underestimation
b
of the detector resolution in Monte Carlo, the accuracy of the natural width prediction
from [16], and the fit constraint that (QΣb∗+ − QΣb+) = (QΣb∗− − QΣb−) [14]. All systematic
uncertainties on the Q mass difference measurements are small compared to the statistical
Σ(∗)±
b
uncertainties. The final results [22] for the signal yields, including systematic errors, are
NΣ+ = 33+−1132 (stat.)+−53 (syst.), NΣ− = 62+−1154 (stat.)+−94 (syst.), NΣ∗+ = 82+−1177 (stat.)+−160 (syst.),
b b b
and NΣ∗− = 79+−1188 (stat.)+−156 (syst.). The final results [22] for the masses are QΣ+ =
b b
48.2+−12..92 (stat.)+−00..12 (syst.) MeV/c2, QΣb− = 55.9+−10..09 (stat.)+−00..11 (syst.) MeV/c2, and ∆Σb∗ =
21.5+2.0 (stat.)+0.4 (syst.) MeV/c2. Using the CDF II measurement of m = 5619.7
−1.9 −0.3 Λ0b ±
1.2 (stat.) 1.2 (syst.)MeV/c2 [23], the masses of the four states are [22]:
±
mΣb+ = 5807.5+−12..92 (stat.)±1.7 (syst.) MeV/c2, mΣb− = 5815.2+−10..09 (stat.)±1.7 (syst.) MeV/c2,
mΣb∗+ = 5829.0+−11..67 (stat.)±1.7 (syst.) MeV/c2, mΣb∗− = 5836.7+−21..08 (stat.)±1.7 (syst.) MeV/c2,
where the systematic uncertainties are now dominated by the total Λ0 mass uncertainty.
b
The significance of the signal is evaluated with two methods: using statistical Monte-Carlo
pseudo-experiments and comparing the likelihoods of the default four signal hypothesis with
pessimistic alternate ones. The randomly generated background samples are fit with the four
signalhypothesis. Theprobabilityforbackgroundtoproducetheobservedexperimentalnumber
of signal events or more is found to be less than 8.5 10−8, corresponding to a significance of
×
greater than 5.2 σ. The results on study of likelihood ratios are summarized in a Table 3 and
its detailed caption.
6. Conclusions
In summary, using a sample of 3100 Λ0 Λ+π− candidates reconstructed in 1.1fb−1 of
∼ b → c
CDF II data, we search for resonant Λ0π± states. We observe a significant signal of four states
b
(∗)
whose masses and widths are consistent with those expected for the lowest-lying charged Σ
b
baryons: Σ+,Σ−,Σ∗+ andΣ∗−. ThisresultrepresentsthefirstobservationoftheΣ(∗) baryons.
b b b b b
Acknowledgments
The author is grateful to his colleagues from the CDF B-Physics Working Group for useful
suggestions and comments made during preparation of this talk. The author thanks J. Rosner
forusefuldiscussions. Theauthor thanksS.C.Seidelforsupportofthis workandJ.E.Metcalfe
for reading the manuscript.
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