SULI Symposium – Todd Denning 1

Search for Four-Quark Particles in the Data from the Early Belle II ExperimentTODD DENNINGPacific Northwest National LaboratorySULI Symposium

July 28, 2016

SULI Symposium – Todd Denning May 1, 2023 2

Abstract

The Belle II detector at the SuperKEK B-factory in Tsukuba, Japan, will examine 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 quarks, known as “bottomonium.” One of these bottomonium states is the meson, currently the most energetic form of bottomonium to have been discovered. Additionally, results from Belle indicate the may decay to a unique-charged four-quark state, called . The feasibility of analyzing the decay , (where =1,2,3) during early Belle II operations is presented.

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Introduction

July 28, 2016

Physics BackgroundThe Standard Model and Quarkoniumand past results

The Belle II Detector and ExperimentMy Research ProjectScope of My Project

Simulation and reconstructionAnalysis of the decay

ResultsConclusions

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The Standard Model and Quarkonium

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 () and leptonsLeptons: fundamental (Mesons: pairs ()Baryons ()

Quarkonium: meson whose constituents are a quark and its antiquarks ()

Bottomonium: Charmonium: Particular interest:

(highest discovered energy state of bottomonium)

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Discovery of and Past Results

July 28, 2016

Belle recently discovered an “exotic” particle, named Two kinds: and Decay from the and mesons

Focus of study due to unique propertiesComposed of weakly bound “pairs” of four quarks (referred to as a “molecule” or “tetraquark”)

Zb

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The Belle II Experiment and SuperKEKB

July 28, 2016

Located in Tsukuba, Japan collisions at ~10.58 GeV 50 times the data of the original Belle experimentOpens door for new physics complementary to LHC searchesRequires major detector and accelerator upgrades

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Timeline of the Experiment

July 28, 2016

“BEAST” Phase 1Background/beam characterization

“BEAST” Phase 2Partial detector (no VXD)Opportunity to run at energy

Phase 3/Run 11-2 ab-1

Ultimate goal: 50 ab-1

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Scope of the Project and Data Analysis

July 28, 2016

Project goal: Demonstrate the feasibility of studying the decay

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)

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Exclusive vs. Inclusive Analysis

July 28, 2016

Exclusive: reconstruction of a specific decay chain, e.g.

Only occurs ~2% of the timeLow background, low signal

Signal particles of interest include and Background sources include unwanted

eventsSimulated events for Phase 2 and 3

Inclusive: reconstruction of all decay modes, e.g.(6S) Includes all decaysHigh background, high signal

Υ (1𝑆 ) , Υ (2𝑆 ) ,Υ (3𝑆)

Mass (GeV)

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Exclusive Optimization

July 28, 2016

Final state Upsilon mass: combination of two muonsnTracks: number of charged tracks reconstructed in the event

Υ (1𝑆)

Number of tracks

Υ (1𝑆)

SignalBackground

nTracks

SignalBackground

-160MeV +140MeVnTracks=4

Mass(GeV)

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Inclusive Optimization

July 28, 2016

nTracks: more tracks in inclusive decay“R2” and “CosTBTO” related to the “shape” of the physics events

(6S) nTracks R2 CosTBTO

SignalBackground

SignalBackground

SignalBackground

nTracks R2<0.2 CosTBTO<0.8

Mass

-20MeV +20MeVSignalBackground

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Before and After Cuts

July 28, 2016

No cuts, with cutsResult of optimizationPreferentially select signal and reject background

Inclusive Mass SignalInclusive Mass SignalExclusive

Mass (GeV) Mass (GeV) Mass (GeV)Inclusive Mass Background Inclusive Mass Background

Mass (GeV) Mass (GeV)

Exclusive Exclusive

Mass (GeV) Mass (GeV)

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Exclusive Efficiency

July 28, 2016

Blue Gaussian represents the fit to the signal eventsGaussian fit is used to approximate number of events to determine efficiencySecond peak is due to “wrong”

𝑍 𝑏Mass (Υ (1S ))

𝜎 49MeV 𝜎 50.8MeV 𝜎 67.1MeV

Mass(GeV) Mass(GeV) Mass(GeV)

Υ (6𝑆 )→𝜋−𝑍𝑏±→Υ (𝑝𝑆 )𝜋+¿ ¿

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Inclusive Efficiency

July 28, 2016

Gaussian used to fit the functionArea under peak yields the number of candidatesRatio of area of peak to total number of events gives the efficiency

𝑍 𝑏Mass (Υ (1S )) 𝑍 𝑏Mass (Υ (3S ))

𝜎 12.5MeV 𝜎 14.1MeV 𝜎 15.9MeV

Mass(GeV) Mass(GeV) Mass(GeV)

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SummaryPreliminary analysis of an important physics process in early Belle IIStudy of simulated data to optimize signal and background selectionInvestigation of issues to occur in the real experiment (resolution, efficiency)

Next stepsImprove mass resolution in exclusive decay modeImprove optimization for individual decay modesPredict signal/background yield under different Belle II operating conditions

Conclusions and Next Steps

July 28, 2016