1. SULI Symposium – Todd Denning
Search for Four-Quark Particles
in the Data from the Early Belle II
Experiment
TODD DENNING
Pacific Northwest National Laboratory
SULI Symposium
July 28, 2016 1

2. SULI Symposium – Todd Denning
Abstract
October 31, 2016 2
The Belle II detector at the SuperKEK B-factory in Tsukuba, Japan, will
examine 𝑒+ 𝑒− collisions at forty times greater instantaneous luminosity than
the previous Belle detector. This increase opens the door for analysis of
unexplored physics, such as the higher energy bound states of 𝑏 𝑏 quarks,
known as “bottomonium.” One of these bottomonium states is the Υ(6𝑆)
meson, currently the most energetic form of bottomonium to have been
discovered. Additionally, results from Belle indicate the Υ(6𝑆) may decay to
a unique-charged four-quark state, called 𝑍 𝑏
±
. The feasibility of analyzing the
decay Υ 6𝑆 → 𝜋− 𝑍 𝑏
±
, 𝑍 𝑏
±
→ 𝜋+Υ 𝑝𝑆 , Υ 𝑝𝑆 → 𝜇+ 𝜇−(where 𝑝=1,2,3)
during early Belle II operations is presented.

3. SULI Symposium – Todd Denning
Introduction
July 28, 2016 3
Physics Background
The Standard Model and Quarkonium
𝑍 𝑏 and past results
The Belle II Detector and Experiment
My Research Project
Scope of My Project
Simulation and reconstruction
Analysis of the decay Υ 6𝑆 → 𝜋−
𝑍 𝑏
±
, 𝑍 𝑏
±
→ Υ 𝑝𝑆 𝜋+
, Υ 𝑝𝑆 → 𝜇+
𝜇−
Results
Conclusions

4. SULI Symposium – Todd Denning
The Standard Model and Quarkonium
October 31, 2016 4
The Standard Model: fundamental theory
of particle physics describing the basic
particles that make up matter and the
forces that interact between them
Matter consists of quarks (𝑞) and leptons
Leptons: fundamental (𝑒, 𝜇, 𝜏, 𝜈)
Mesons: 𝑞𝑞 pairs (𝜋, Κ, Ψ, Υ)
Baryons (𝑝, 𝑛)
Quarkonium: meson whose constituents
are a quark and its antiquarks (𝑞 𝑞)
Bottomonium: 𝑏 𝑏
Charmonium: 𝑐 𝑐
Particular interest: Υ 6𝑆
(highest discovered energy state of
bottomonium)

5. SULI Symposium – Todd Denning
Discovery of 𝒁 𝒃 and Past Results
July 28, 2016 5
Belle recently discovered an “exotic” particle, named 𝑍 𝑏
Two kinds: 𝑍 𝑏
±
10610 and 𝑍 𝑏
±
(10650)
Decay from the Υ 5𝑆 and Υ 6𝑆 mesons
Focus of study due to unique properties
Composed of weakly bound “pairs” of four quarks
(referred to as a “molecule” or “tetraquark”)
Zb

6. SULI Symposium – Todd Denning
The Belle II Experiment and SuperKEKB
July 28, 2016 6
Located in Tsukuba, Japan
𝑒+ 𝑒− collisions at 𝐸𝑐𝑚 ~10.58 GeV
50 times the data of the original Belle experiment
Opens door for new physics complementary to LHC searches
Requires major detector and accelerator upgrades

7. SULI Symposium – Todd Denning
Timeline of the Experiment
July 28, 2016 7
“BEAST” Phase 1
Background/beam
characterization
“BEAST” Phase 2
Partial detector (no VXD)
Opportunity to run at
Υ 6𝑆 energy
Phase 3/Run 1
1-2 ab-1
Ultimate goal: 50 ab-1

8. SULI Symposium – Todd Denning
Scope of the Project and Data Analysis
July 28, 2016 8
Project goal: Demonstrate the feasibility of studying the decay
Υ 6𝑆 → 𝜋− 𝑍 𝑏
±
, 𝑍 𝑏
±
→ Υ 𝑝𝑆 𝜋+, Υ 𝑝𝑆 → 𝜇+ 𝜇−
Approach:
1. Simulate particle physics decays (EvtGen)
2. Model interactions with Belle II detector (GEANT)
3. Reconstruct the individual particles (basf2)
4. Optimize data selection to enhance signal vs. background (ROOT)
5. Determine expected feasibility/efficiency
Υ(6𝑆)

9. SULI Symposium – Todd Denning
Exclusive vs. Inclusive Analysis
July 28, 2016 9
Exclusive: reconstruction of a specific
decay chain, e.g.
Υ 6𝑆 → 𝜋− 𝑍 𝑏
±
, 𝑍 𝑏
±
→ Υ 𝑝𝑆 𝜋+
, Υ 𝑝𝑆 → 𝜇+
𝜇−
Only occurs ~2% of the time
Low background, low signal
Signal particles of interest include
Υ 1𝑆 , Υ 2𝑆 , Υ 3𝑆 and 𝑍 𝑏 10610 ,
𝑍 𝑏 10650
Background sources include unwanted
𝑞 𝑞 events
Simulated events for Phase 2 and 3
Inclusive: reconstruction of all decay
modes, e.g.
Υ(6S) → 𝜋±
𝑋, Υ(6S) → 𝜋+
𝜋−
𝑋
Includes all Υ(𝑝𝑆) decays
High background, high signal
Υ 1𝑆 , Υ 2𝑆 , Υ(3𝑆)
Mass (GeV)

10. SULI Symposium – Todd Denning
Exclusive Optimization
July 28, 2016 10
Final state Upsilon mass: combination of two muons
nTracks: number of charged tracks reconstructed in the event
Υ 6𝑆 → 𝜋− 𝑍 𝑏
±
, 𝑍 𝑏
±
→ Υ 𝑝𝑆 𝜋+, Υ 𝑝𝑆 → 𝜇+ 𝜇−
Υ(1𝑆)
Number of tracks
Υ(1𝑆)
Signal
Background
nTracks
Signal
Background
-160MeV +140MeV
nTracks=4
Mass(GeV)

11. SULI Symposium – Todd Denning
Inclusive Optimization
July 28, 2016 11
nTracks: more tracks in inclusive Υ decay
“R2” and “CosTBTO” related to the “shape”
of the physics events
Υ(6S) → 𝜋±
𝑋, Υ(6S) → 𝜋+
𝜋−
𝑋
nTracks R2 CosTBTO
Signal
Background
Signal
Background
Signal
Background
nTracks> 11 R2 < 0.2 CosTBTO<0.8
Υ 𝑝𝑆 Mass
-20MeV +20MeV
Signal
Background

12. SULI Symposium – Todd Denning
Before and After Cuts
July 28, 2016 12
No cuts, with cuts
Result of
optimization
Preferentially
select signal
and reject
background
Inclusive 𝑍 𝑏 Mass SignalInclusive 𝑍 𝑏 Mass SignalExclusive 𝑍 𝑏 Mass Signal
Mass (GeV) Mass (GeV) Mass (GeV)
Inclusive 𝑍 𝑏 Mass Background Inclusive 𝑍 𝑏 Mass Background
Mass (GeV) Mass (GeV)
Exclusive 𝑍 𝑏 Mass Background Exclusive 𝑍 𝑏 Mass Backgroud
Mass (GeV) Mass (GeV)

13. SULI Symposium – Todd Denning
Exclusive Efficiency
July 28, 2016 13
𝑍 𝑏 Mass (Υ 2S ) 𝑍 𝑏 Mass (Υ 3S )
Blue Gaussian represents the fit to the signal events
Gaussian fit is used to approximate number of events to determine efficiency
Second peak is due to “wrong” 𝜋
𝑍 𝑏 Mass (Υ 1S )
𝜎 ~ 49 MeV 𝜎 ~ 50.8 MeV 𝜎 ~ 67.1 MeV
Mass(GeV) Mass(GeV) Mass(GeV)
Υ 6𝑆 → 𝜋−
𝑍 𝑏
±
→ Υ 𝑝𝑆 𝜋+

14. SULI Symposium – Todd Denning
Inclusive Efficiency
July 28, 2016 14
Gaussian used to fit the function
Area under peak yields the number of 𝑍 𝑏 candidates
Ratio of area of peak to total number of events gives the efficiency
𝑍 𝑏 Mass (Υ 1S ) 𝑍 𝑏 Mass (Υ 2S ) 𝑍 𝑏 Mass (Υ 3S )
𝜎 ~ 12.5 MeV 𝜎 ~ 14.1 MeV 𝜎 ~ 15.9 MeV
Mass(GeV) Mass(GeV) Mass(GeV)

15. SULI Symposium – Todd Denning
Summary
Preliminary analysis of an important physics process in early Belle II
Study of simulated data to optimize signal and background selection
Investigation of issues to occur in the real experiment (resolution, efficiency)
Next steps
Improve 𝑍 𝑏 mass resolution in exclusive decay mode
Improve optimization for individual decay modes
Predict signal/background yield under different Belle II operating conditions
Conclusions and Next Steps
July 28, 2016 15