The document summarizes the author's 2014 summer research analyzing decay data from the LHCb detector. The author analyzed several decay channels including Λ c → Ξ− K+ π+, Ω b − → Ω− J/ψ, and D s + → K− K+ π+. For the Λ c decay, the author found evidence of a Ξ0 resonance. For the Ω b decay, the author measured the mass but found the lifetime fit was off. For the D s decay, the author observed decays through φ(1020) and K*(892) resonances. The author was unable to find evidence of the hypothesized Ω cb 0 baryon due

1. Baker 1
Analysis and investigation into B-hadron
decays from pp collisions at the LHC
2014 Summer QuarkNet Research – LHCb Detector
TheodoreJ. Baker– WalnutHills High School
KyleDeBry – Anderson High School
Brenda Shen – Sycamore High School
RebeccaSwertfeger – Turpin High School
DaveWhittington– Fairfield HighSchool
Dr. MikeSokoloff – University of Cincinnati
A b s t r a c t
The purpose of my summer research was to analyzehigh-energy decay data collectedfrom
the LHCb detector in Geneva, Switzerland. Overthe course of my six weeks at UC, I worked
with current particle physics graduate students as wellas three other high schoolers. Using
the ROOT Data Analysis Framework,I was able to analyze and sort through data by making
1, 2, or 3-dimensional histograms. First, I workedwith a well-knownΛ 𝑐decay channel
(Λ 𝑐 → Ξ− 𝐾+ 𝜋+)to gain experience with ROOT.Then, I lookedat the decay channel
Ω 𝑏
−
→ Ω− 𝐽/ψMy resulting mass and decay time for the Ω 𝑏
−
baryonwere consistent with the
paper on this topic published earlier this summer. Next I analyzed the 𝐷 𝑠
+ → 𝐾− 𝐾+ 𝜋+decay
channel and found that the 𝐷 𝑠
+ and 𝐷+ both decay through 𝜑 (1020) and 𝐾∗(892)
resonances. Finally, I tried to confirmthe existence of the Ω 𝑐𝑏
0
baryon, but I could not find
any signal. In order to find this new particle, much more data would be needed. Luckily,this
data willbe available once the Large Hadron Collider (LHC) receives all its upgrades for
2015.
I. Introduction
Particle Physics is the field of physics that
deals with the interactions of fundamental
particles. The Standard Model describes how
these particles interact with each other and
respond to the forces of the universe. These
four forces are, in order of strongest to
weakest, the strong force, the weak
interaction, electromagnetism, and gravity.
Each force has its own gauge boson that
carries its respective force. The gluon
particle carries the strong force, the W±
and
Z0
bosons the weak force, and the photon the
electromagnetic force. The current theory is
that the electromagnetic force and the weak
force are actually the same force and can be
unified into the electroweak force.
The fundamental matter particles of the
Standard Model are called fermions. There
are 12 fermions, six of which are quarks and
six of which are leptons. The leptons consist
of the electron (e-
), the muon (μ-
), and the
tauon (τ-
). Each of these particles has its own
neutrino. There is the electron neutrino (νe),
the muon neutrino (νμ), and the tau neutrino
(ντ). All these particles have their own

2. Baker 2
III. Detector and Methods of Research
1"The LHCb Detector." Large Hadron Collider Beauty Experiment. CERN, 2008. Web. 28 July 2014.
2 J. Beringer et al. (Particle Data Group), Phys. Rev. D86, 010001 (2012) and 2013 partial update for
the 2014 edition.
antiparticle with the same mass and
opposite charge. The six flavors of quarks
are up (u), down (d), charm (c), strange (s),
top, or truth, (t), and bottom, or beauty, (b).
The u, c, and t quarks all have a charge of +⅔
and the d, s, and b quarks a charge of -⅓.
Quarks and their antiquarks can combine
with each other to form composite particles
known as hadrons.
Hadrons can either be a baryon, a composite
particle made of three quarks, or a meson, a
composite particle made of a quark and an
anti quark. Baryons and 1mesons are
classified by their composition of quarks.
For example, the baryon made of a u, u, and d
(notated |𝑢𝑢𝑑⟩) is known as a Δ+
. Through
the weak interaction, hadrons decay into
lighter particles. By emitting a W±
boson, a
quark decays to a lighter state. The W±
can
then either change the flavor of another
quark (exchange decay) or turn into a
quark-antiquark pair (spectator decay). The
strong force also plays a role in hadronic
decays. If two quarks begin to move away
from one another, a vacuum is created and
connects the two quarks. If they move far
enough apart, the energy in the system
becomes so immense that two quarks (a
quark and an antiquark) are generated from
the vacuum. In this paper, I analyze the
decay channels Λ 𝑐 → Ξ− 𝐾+ 𝜋+, Ω 𝑏
−
→ Ω− 𝐽/𝜓,
𝐷 𝑠
+ → 𝐾− 𝐾+ 𝜋+, and Ω 𝑐𝑏
0
→ Ω− 𝐷 𝑠
+.
The “Large Hadron Collider beauty” (LHCb)
detector is a b-factory – a producer of
copious events containing the beauty quark1.
These events are collisions of protons
travelling at very close to the speed of light.
Because of this, special relativity is in play
for these particles. The masses must be
calculated from the measured energy and
momentum of the particles using the
equation:
m2 = E2 – px2 – py2 – pz2
where m is the invariant mass – the rest
mass – of the particle, E is its energy, and px,
py, and pz are the particle’s momenta in the x,
y, and z direction respectively.
All of these variables are measured in MeV.
This collected data is housed in files known
as N-tuples. Using the ROOT Data Analysis
Framework, I wrote macros that were able
to sort through the data and analyze certain
variables of interest. Results were usually
graphed in either 1 or 2-D histograms and
then fitted to a function. These functions
could be exponentials (for lifetime fits) or
normal Gaussian distributions (for mass
fits). 2-D histograms, known as Dalitz plots,
are especially helpful in looking at a 3-body
decay (i.e. 𝐷 𝑠
+ → 𝐾− 𝐾+ 𝜋+) and determining
whether there is a resonance structure that
is not clearly visible by looking at the
beginning and ending states.
Signal for these mass distributions was
found by applying cuts to other variables in
the N-tuple in order to narrow down the
number of events. Cuts could be made on
variables like the probability that a 𝜇− is a
𝜇+ and the known mass of a daughter
particle. After fitting the data to Gaussian
distribution, I then compared the mass to
the accepted value on PDG Live2.

3. Baker 3
IV. 𝚲 𝒄 → 𝚵−
𝑲+
𝝅+
Decay Channel
The decay of theΛ 𝑐 is one that has already
been determined and studied. I used the data
from this decay to become accustomed to
ROOT and the particle physics field in
general. In the decay, Λ 𝑐 |𝑢𝑑𝑐⟩ goes to the
baryon Ξ− |𝑑𝑠𝑠⟩ and mesons 𝐾+ |𝑢𝑠̅⟩ and
𝜋+|𝑢𝑑̅⟩. Since this is a 3-body decay, I made
Dalitz plots to check for resonances. The axes
of a Dalitz plot are two of the particles’
invariant masses squared. So on “Dalitz Plot
1,” (see Figure 1) the square of the sum
invariant mass of Ξ− and 𝐾+ is on the x-axis
and the square of the sum of the invariant
mass of the 𝐾+ and 𝜋+ is on the y-axis.
Looking at “Dalitz Plot 2” and “Dalitz Plot 3,”
(Figure 3) there is a signal band on each. In
the first one, there is a diagonal signal. This is
due to the fact that each Dalitz plot is the
same graph but oriented in a different way.
There is an imaginary axis along the line
𝑦 = 𝑥 made of the particle combination not
on the y or x-axis. The signal is at around at
2,300,000 MeV2 on the 𝜋+ + Ξ− axis.
Taking the square root, the mass in MeV
comes out to around 1531, which is the
mass of the Ξ0 baryon. Checking PDG Live,
the Ξ0 does in fact decay into the π+ and Ξ−.
From this, it can be deduced that the Λ 𝑐
decays to the meson 𝐾+ and the resonance
structure Ξ0. The Ξ0 then decays to a Ξ−
and a π+.
V. 𝛀 𝒃
−
→ 𝛀−
𝑱/𝝍
In the Ω 𝑏
−
→ Ω− 𝐽/𝜓 decay, the mother
particle contains a beauty quark. The b
wants to decay into a top quark, but since
the t is so much more massive than the b, it
actually decays into a charm quark.
Through the weak interaction, the emitted
𝑊± decays into an s and a 𝑐̅. These then
combine with the other quarks from the
Figure 1: Plot of 𝑚2
(𝐾+
𝜋+
) vs 𝑚2
(𝛯−
𝐾+
)
Figure 2: Plot of 𝑚2
(𝜋+
𝛯−
) vs 𝑚2
(𝐾+
𝜋+
)
Figure 3: 𝑚2
(𝛯+
𝐾+
) vs 𝑚2
(𝜋+
𝛯−
)
Figure 4: Feynman diagram of the 𝛺 𝑏
−
decay

4. Baker 4
Figure 5: Histogram of the lifetime (𝜏) of the signal events
mother and form a 𝐽/𝜓 |𝑐𝑐̅⟩ and an Ω− |𝑠𝑠𝑠⟩.
Using the measured values for the energy and
momenta of the 𝐽 𝜓⁄ and the Ω−, I was able to
calculate the invariant mass of the 𝐽 𝜓⁄ and
the Ω−. Then, by making an array of
histograms and cutting on intervals of
0.0002 ns, I found that the most effective cut
was when t > 0.0001 ns. After fitting my
invariant mass histogram with a Gaussian
distribution, I found that even though I had
very few events, my mass correctly matched.
However, the lifetime I fit was off by about
a factor of 10. This could be due to the fact
that I only had 10 entries to fit to find the
mean lifetime. Having more events to fit
would have greatly improved my lifetime
fit and could have made my mass fit
statistically more accurate. both PDG Live
and the recently published Elsevier33 paper
dealing with the masses and lifetimes of
both the Ξ− and Ω 𝑏
−
.
VI. 𝑫 𝒔
+
→ 𝑲−
𝑲+
𝝅+
When a 𝐷 𝑠
+ |𝑐𝑠̅⟩ decays, it does so through a
spectator decay. When the c emits a 𝑊±, it
turns into a 𝜋+. The c turns into an s and
then, along with the 𝑠̅ becomes a 𝜑 (1020)
resonance. The s and 𝑠̅ then begin to
separate and pop a u and a 𝑢̅ out of the
created vacuum, creating a 𝐾+ |𝑢𝑠̅⟩ and
𝐾− |𝑠𝑢̅⟩. But when making a Dalitz plot
(Figure 9) to confirm the 𝜑 (1020), I
noticed there was also I a small signal band
around the 800,000 MeV2. This turned out
to be a 𝐾∗ (892) resonance, which has a
very small branching fraction as compared
to the b.f. for the 𝜑 (1020) (see Table 1).
However, when fitting the invariant mass of
the 𝐷 𝑠
+, I noticed that there was also a peak
Decay Channel Branching Fraction[% ]
Ds
+→π+φ(1020) 4.5 ± 0.4%
φ(1020)→K-K+ 48.9 ± .5%
Ds
+→K*K+ 6.0 ± 3.5 x 10-5%
K*→K-π+ 99.901 ± 0.009%
Table 1: This shows the different decay channels of the
𝐷 𝑠
+
. It can either decay through a 𝜑 (1020) which
happens about 50% of the time, or a 𝐾∗
which happens a
miniscule 6 × 10−5
% of the time.
at about 1870 MeV. After finding that this
particle decays the same way as the 𝐷 𝑠
+, I
concluded that this particle was the 𝐷+
meson. Both the fitted masses for the 𝐷 𝑠
+ and
the 𝐷+ matched their respective, accepted
masses on PDG Live.
33 The Authors. Measurement of the Ξ 𝑏
−
and Ω 𝑏
−
baryon lifetimes. Physics Letters B. Elsevier B.V., 26
June 2014. Web. 22 July 2014.
Figure 6: Invariant Mass Histogram of the 𝛺 𝑏
−
.

5. Baker 5
VII. The Search for the 𝛀 𝒄𝒃
𝟎
Baryon
The Ω 𝑐𝑏
0
Baryon is made with one
strange, one charm, and one beauty
quark. It has been theorized to exist and
decay into an Ω−
|𝑠𝑠𝑠⟩ and a 𝐷 𝑠
+ |𝑐𝑠̅⟩.
Using the information from my previous
𝐷 𝑠
+ study, I cut the N-tuple on the mass of
the 𝐷 𝑠
+ and was unfortunately left with
no signal at all. The expected mass is at
least 6800 MeV. In order to confirm the
existence of the Ω 𝑐𝑏
0
, much more data
would be needed. This data could
become available in 2015 when the LHC
undergoes its much-awaited upgrades.
VIII. Conclusions
During my six weeks as a QuarkNet
intern, I learned a great deal about
particle physics. I analyzed four decays,
3 of which were all new. Working with
the Ωb- and getting the same results as a
paper published only weeks earlier was
a reassuring start to the overall project.
Unfortunately I was not able to find the
elusive Ω 𝑐𝑏
0
. However, more data will
help other students and researchers
discover it in the near future. I look
forward to returning to particle physics
research in the future.
Figure 7: Gaussian fit for the 𝐷+
. PDG gives the
rest mass to be 1,869.62 ± 0.20 𝑀𝑒𝑉 𝑐2⁄ .
Figure 8: Gaussian fit for the 𝐷+
. PDG gives the
rest mass to be 1968.47±0.33 𝑀𝑒𝑉 𝑐2⁄ .
Figure 9: Dalitz plot showing a 𝐾−
𝐾+
resonance at
around 1,000,000 𝑀𝑒𝑉2
: 𝜑 (1020).
Figure 10: Here, the red histogram shows all the data,
and the blue shows the “signal” with appropriate cuts
on the lifetime and mass.Clearly, more data is needed.

6. Baker 6
IX. Acknowledgements
First off, I would like to thank the whole
University of Cincinnati Physics staff. Their
hospitality and acceptance into the
GeoPhysics building and the whole UC
community has been stellar. Next I would
like to thank my AP Physics teacher, Mr.
Chughtai, for teaching me physics and the
opportunity to apply for this internship.
Additionally, Zach Huard for introducing
me to unix, linux, C++ programming, and
the ROOT program. Also, thanks to Dr.
Brian Meadows for his lecture on the
Standard Model and making it so much
easier than I thought it would be to
understand the realm of subatomic
particles.I’d also like to thank Adam for
teaching me about the LHCb detector and
graduate student Jacob Todd and
undergraduate Jenna Stanton for their
help in the computer lab. And of course, I’d
like to thank Mr. Dave Whittington for
helping me everyday and Dr. Mike Sokoloff
for mentoring our research and explaining
the physics behind what I was researching.
And finally I’d like to thank my fellow
interns Kyle Debry, Brenda Shen, and
Rebecca Swertfeger. I will never forget the
six weeks we spent together.