High Energy Physics in BES-III

byHaichuan Cao

Matthew TilleyYangyang Yu

Yunxiao LiZiyan Yang

What is the BES-III?

The Beijing Spectrometer (BESIII) detector of the Beijing positron electron collider (BPECII)

Brief overview

• Up to 4.6GeV center of mass energy

• Originally designed as a charm factory

Some goals of BESIII:– Charmonium Physics

– Exotic hadronic states

– Precision measurements

• Drift chamber• Electro-

magnetic calorimeter

• Time of flight system

• Super-conducting magnet

• Muonchamber

The BES-III detector

J/Ψ and Ψ(2s) • Meson formed from C and C bar pair

• Strange name for the J/Ψ due to a near simultaneous discovery

• J/Ψ is found at a mass 3.10GeV

• Ψ(2s) or Ψ’ is a second resonance at 3.77GeV

SLAC-SPEAR: Burton Richter et al. (1974) BNL: Samuel Ting et al. (1974)

Zc+(4050) is believed to be a very short lived tetra-quark state!

- -

c c u d

Y(4260) and Z_c(3900)

• Y(4260) was found at BaBar in 2006

• Z_c(3900) was found in 2013 at BESIII and KEK

Brief look at results

• Use these simple fits to the Ψ(2s) mass on data and monte-carlo to calculate cross sections

Brief look at results

Brief look at results

Z(4450) in here somewhere!

𝑒+ + 𝑒− → 𝜙 + 𝜋+ + 𝜋−

𝜙 → 𝑘+ + 𝑘−

Kate Yang FPISC camper in High Energy Lab

𝑇ℎ𝑒 𝑘+𝑘−𝜋+𝜋− 𝐹𝑖𝑛𝑎𝑙 𝑆𝑡𝑎𝑡𝑒

What is MC?

• MC is short for Monte-Carlo methods.

• They are a broad class of computational algorithms that rely on repeated random sampling to obtain numerical results.

The original data

MC simulation Real Data

Fit of the scatter diagram

MC data dual-Guass fit Real data dual-Guass fit There is another peak

𝑇ℎ𝑒 𝑘+𝑘−𝜋+𝜋− 𝐹𝑖𝑛𝑎𝑙 𝑆𝑡𝑎𝑡𝑒

𝜒2Distribution with background mass distribution

Yangyang Yu

FPISC camper in High Energy Lab

Invariant-mass distribution

Preliminary study of e−e+ → ϕπ0π0

ϕ→K+K- ; π0 →2𝛄

Yunxiao Li

FPISC camper in High Energy Lab

Motivation

• Confirm the decay ϕ→K+K-

• Measure the cross section of this process

e−e+ → ϕπ0π0

Data sample

• Boss version 6.6.5

• Date sets

Data of BEPCII from April.3rd to April.9th,

1 energy point : 2.175GeV

• Monte Carlo Data

e−e+ → ϕπ0π0

Event selection criteria(I)

• Charged Tracks:

• |Vr|<1.0 && |Vz|<10.0 && |Cosθ|<0.93; Ngood=2 ||1 ;

• Particle Identification:

• Kaon: prob_K> prob_P&& prob_K> prob_𝛑; Ngood=2 : N(K+)=N(𝑲-)=1;

Ngood=1 : N(K+)||N(𝑲-)=1;

• Good Photon:

• Ebarrel>25 MeV; Eendcap>50 MeV ; 𝜽𝒎𝒊𝒏(𝛄,charge)>10∘ ; 0≤ TDC ≤14 ; N𝜸≥𝟒;

Event selection criteria(II)

• 𝜋0 reconstruction

• 𝝌𝟐=(𝑴𝜸𝟏𝜸𝟐−𝑴𝝅𝟎)/𝟐+(𝑴𝜸𝟑𝜸𝟒−𝑴𝝅𝟎)/𝟐

• 1C kinematic fit : (4γ𝑲±)

40ev

Event selection criteria(III)

|Cos(𝛉)=(𝑬𝜸𝟏−𝑬𝜸𝟐 )/𝑷𝜸𝟏𝜸𝟐|<0.95

ϕ𝝅𝟎𝝅𝟎 cross section measurement MC signalReal events

ϕ𝝅𝟎𝝅𝟎 fit ϕ signalFitting function: Signal MC ⨂ Gauss + Argus

ϕ𝝅𝟎𝝅𝟎 cross section calculation

• Calculation Function: 𝝈 =𝑵 / 𝓛𝒊𝒏𝒕(𝟏 + 𝜹)𝝐𝑩𝒓

• 𝝐 : efficiency of mc data 22.16%

• 𝓛𝒊𝒏𝒕; (𝟏 + 𝜹) : constants depending on energy (2.175GeV in this analysis)

• 𝑵 : number of events selected in the end

(197 ± 3)

• 𝑩𝒓 : 0.489*0.988*0.988

• 𝝈 = 179.62 ± 2.74 pb

Introduction

𝑒+𝑒− → ℎ𝑎𝑑𝑟𝑜𝑛𝑠 𝑐𝑟𝑜𝑠𝑠 𝑠𝑒𝑐𝑡𝑖𝑜𝑛sand the 𝑅ℎ𝑎𝑑 Value

Haichuan CaoFPISC camper in High Energy Lab

What is the R value?

• 𝑅ℎ𝑎𝑑 , by proper definition, is

the ratio of the total cross

sections according to following

equation,

• 𝑅ℎ𝑎𝑑≡σ(𝑒+𝑒−→ℎ𝑎𝑑𝑟𝑜𝑛𝑠)

σ(𝑒+𝑒−→μ+μ−)

= 𝑞 σ(𝑒

+𝑒−→𝑞𝑞)

σ(𝑒+𝑒−→μ+μ−)

How to measure the R value in experiment?

• 𝑅ℎ𝑎𝑑≡σ(𝑒+𝑒−→ℎ𝑎𝑑𝑟𝑜𝑛𝑠)

σ(𝑒+𝑒−→μ+μ−)=

1

σ μμ0 (𝑒+𝑒−→μ+μ−)

∗𝑁ℎ𝑎𝑑−𝑁𝑏𝑘𝑔

𝐿∗εℎ𝑎𝑑∗ε𝑡𝑟𝑖𝑔𝑔𝑒𝑟(1+δ)

• σμμ0 ：born-level cross section for 𝑒+𝑒− → μ+μ−

• 𝑁ℎ𝑎𝑑: number of hardonic events

(It’s what I need to measure in this experiment )

• 𝑁𝑏𝑘𝑔: number of background hadronic events (noises)

• L：integrated luminosity

• εℎ𝑎𝑑:detection efficiency for hadrons

• ε𝑡𝑟𝑖𝑔:trigger efficiency (100% in this experiment)

• 1 + δ: radiative correction factor

Why need I measure the R value?

• One of the most fundamental quantities in particle physics that directly reflect the flavor and the color of the quarks.

• A necessary input for other physical quantities. Such as:

α(s)-electromagnetic running coupling constant

𝑎μ- anomalous magnetic moment of the muon

Potential backgrounds (noises)

• QED(Quantum Electrodynamics) process:

• Bhabha(𝑒+𝑒− → 𝑒+𝑒−)，γγ，μ+μ−,τ+τ−

• 𝑒+𝑒− → 𝑒+𝑒−+hadrons

• Cosmic ray

• Beam-associated backgrounds; beam-wall; beam gas

Event Selection I (To exclude the noises)

Veto Bhabha and 𝑒+𝑒− → γγTwo showers with maximum deposited energy

θ1 + θ2 − 180° < 10°&E>0.65∗ 𝐸𝑏𝑒𝑎𝑚

Good hadronic tracks(track level)𝑉𝑟 <1.0 cm, cos θ < 0.93

Momentum<1.1*𝐸𝑏𝑒𝑎𝑚*(1+5σ)

( 𝑑𝐸𝑑𝑥𝑚𝑒𝑎

− 𝑑𝐸𝑑𝑥𝑝𝑟𝑜𝑡𝑜𝑛

)/σ𝑝𝑟𝑜𝑡𝑜𝑛 < 10

Veto large momentum electrons, if E/p>0.8 &p>0.65 𝐸𝑏𝑒𝑎𝑚

Veto gamma conversion, if Momentum(𝑒+𝑒−)<0.1 and angle(𝑒+𝑒−)<15°

Event Selection II

• Hadronic event candidates

• 𝑁𝑔𝑜𝑜𝑑 ≥2;Visible energy >0.4*𝐸𝑏𝑒𝑎𝑚

• If 𝑁𝑔𝑜𝑜𝑑=2:

• Veto: θ1 + θ2 − 180° < 15°& Φ1 − Φ2 − 180 < 10°

• Number of isolated photon≥2

• If 𝑁𝑔𝑜𝑜𝑑 ≥3：

• Vote: Angle of two largest energetic tracks,

• : θ1𝑠𝑡 + θ2𝑛𝑑 − 180° < 15°& Φ1𝑠𝑡 − Φ2𝑛𝑑 − 180 < 10°

So, if the energy of 𝑒+𝑒−is between 2.2-3.6 Gev, the R value will be a constant!