high energy physics in bes-iii - ustchome.ustc.edu.cn/~chc0311/high energy physics in besiii.pdf ·...
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High Energy Physics in BES-III
byHaichuan Cao
Matthew TilleyYangyang Yu
Yunxiao LiZiyan Yang
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What is the BES-III?
The Beijing Spectrometer (BESIII) detector of the Beijing positron electron collider (BPECII)
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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
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• Drift chamber• Electro-
magnetic calorimeter
• Time of flight system
• Super-conducting magnet
• Muonchamber
The BES-III detector
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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)
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Zc+(4050) is believed to be a very short lived tetra-quark state!
- -
c c u d
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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
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Brief look at results
• Use these simple fits to the Ψ(2s) mass on data and monte-carlo to calculate cross sections
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Brief look at results
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Brief look at results
Z(4450) in here somewhere!
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𝑒+ + 𝑒− → 𝜙 + 𝜋+ + 𝜋−
𝜙 → 𝑘+ + 𝑘−
Kate Yang FPISC camper in High Energy Lab
𝑇ℎ𝑒 𝑘+𝑘−𝜋+𝜋− 𝐹𝑖𝑛𝑎𝑙 𝑆𝑡𝑎𝑡𝑒
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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.
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The original data
MC simulation Real Data
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Fit of the scatter diagram
MC data dual-Guass fit Real data dual-Guass fit There is another peak
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𝑇ℎ𝑒 𝑘+𝑘−𝜋+𝜋− 𝐹𝑖𝑛𝑎𝑙 𝑆𝑡𝑎𝑡𝑒
𝜒2Distribution with background mass distribution
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Yangyang Yu
FPISC camper in High Energy Lab
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Invariant-mass distribution
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Preliminary study of e−e+ → ϕπ0π0
ϕ→K+K- ; π0 →2𝛄
Yunxiao Li
FPISC camper in High Energy Lab
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Motivation
• Confirm the decay ϕ→K+K-
• Measure the cross section of this process
e−e+ → ϕπ0π0
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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
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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;
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Event selection criteria(II)
• 𝜋0 reconstruction
• 𝝌𝟐=(𝑴𝜸𝟏𝜸𝟐−𝑴𝝅𝟎)/𝟐+(𝑴𝜸𝟑𝜸𝟒−𝑴𝝅𝟎)/𝟐
• 1C kinematic fit : (4γ𝑲±)
40ev
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Event selection criteria(III)
|Cos(𝛉)=(𝑬𝜸𝟏−𝑬𝜸𝟐 )/𝑷𝜸𝟏𝜸𝟐|<0.95
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ϕ𝝅𝟎𝝅𝟎 cross section measurement MC signalReal events
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ϕ𝝅𝟎𝝅𝟎 fit ϕ signalFitting function: Signal MC ⨂ Gauss + Argus
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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
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Introduction
𝑒+𝑒− → ℎ𝑎𝑑𝑟𝑜𝑛𝑠 𝑐𝑟𝑜𝑠𝑠 𝑠𝑒𝑐𝑡𝑖𝑜𝑛sand the 𝑅ℎ𝑎𝑑 Value
Haichuan CaoFPISC camper in High Energy Lab
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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−)
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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
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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
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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
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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°
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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°
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So, if the energy of 𝑒+𝑒−is between 2.2-3.6 Gev, the R value will be a constant!
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