Heavy quark pair production at ILC · Heavy quark pair production at ILC R. Yonamine KEK-PH...
Transcript of Heavy quark pair production at ILC · Heavy quark pair production at ILC R. Yonamine KEK-PH...
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Heavy quark pair production at ILC
R. Yonamine
KEK-PH Lectures and Workshops, 4 Aug. 2020
This presentaion is mainly based on
tt :
cc :
bb :
“Production and measurement of e+e>cc signagures at the 250GeV ILC”
“Determination of the electroweak coulings of the 3rd generation of quarks at the ILC”
https://arxiv.org/abs/2002.05805
https://pos.sissa.it/364/624/pdf
“The International Linear Collider A Global Project”https://arxiv.org/abs/1903.01629
9>>=
>>;
Main focus in this talk
https://indico.fnal.gov/event/43738/contributions/188210/attachments/129309/156813/talk110620.pdf
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Introduction
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3ILC❖ e+e- collider Controllable initial particle energy √s=250 GeV (Higgs factory) L=2000fb-1 (~10 years)
❖ Linear collider Energy extendability Controllable beam polarization
(baseline plan)(Pe� , Pe+) = (±0.8,±0.3)
Total cross section can be measured w/o looking at H itself !
?
e.g. μμ
Higgs-strahlung process
Two polarization for each beam provides 4 distinct datasets ➡ - Measure helicity-dependent electroweak couplings
- Suppress background and enhance signals - Cancel large parts of the experimental systematic uncertainties
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4ILD: One of detector concepts for ILC
Optimized for Particle Flow Approach
To achieve ideal jet energy resolution (3% jet energy resolution above 100 GeV)
TPC as central trackerLow material budget Continuous tracking (# of hits > 200) dEdx resolution ~ 5%
Vertex detectorFirst layer at 16 mm from IP
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5Simulation & Reconstruction
Following results were done in realistic simulation and reconstruction
Realistic simulation - Beam energy spectrum, ISR, beam-beam background
- Full detector simulation with detailed detector descriptions
Realistic reconstruction - Flavour tagging with multivariate analyses - Vertex charge assignment with track charges and Kaon charge identification(~80% of B-mesons yield charged Kaons)(90% purity at 88% efficiency in bb/cc processes, |cosθ|<0.9, p > 3GeV)
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Motivation for (heavy) quark pair production
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7Anomalies in LEP/SLD data
Re-measuring bb production with higher precision is desired
SLD extracted sin2θw from ALR ALR : asymmetry in Z interaction b/w eL and eR
LEP I extracted sin2θw from AFB(b,c)
Discrepancy of 3σ in sin2θw b/w them !
Al(SLD)
AFB0,b
arXiv:1803.01853Global EW fit
bR-Z coupling is not well constrained by earlier experiments compared to bL-Z one
Some BSM models predict a large correction for gR while that of gL remains small.
arxiv:hep-ph/0610173e.g.
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8BSM effects may appear
Permil-level precision would identify models
e.g. GUT Inspired Grand Higgs Unification Model arxive:2006.02157
θH=0.10 mKK=13 TeVU : unpolarized
L : (Pe-, Pe+) = (-0.8,+0.3) R : (Pe-, Pe+) = (+0.8,-0.3)
√s = 250 GeV with 250 fb-1
Deviation of differential cross section from SM
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Quark pair production
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10Fermion pair production with beam polarization
All four helicity amplitudes only available with polarized beams
Z/�
e�
e+
f
fd�(e�Le
+R ! ff)
d cos ✓f⇠ (LeLf )
2(1 + cos ✓f )2 + (LeRf )
2(1� cos ✓f )2
Differential cross section at Born level (bb, cc)
d�(e�Re+L ! ff)
d cos ✓f⇠ (ReRf )
2(1 + cos ✓f )2 + (ReRf )
2(1� cos ✓f )2
Helicity amplitudes containing couplings gL and gR
Polar angle spectra with 2 independent datasets by 2 different beam polarization configurations can disentangle 4 helicity amplitudes
> Polar angle distribution of b and c
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XeXq / QeQq +XeZXqZ
sin2 ✓W cos2 ✓W
s
s�M2Z
+X
Z0
XeZ0XqZ0
sin2 ✓W cos2 ✓W
s
s�M2Z0
X : L,R
q : b, c
We get these values from polar angle distributions These contains couplings
XeXq, XeZ , XqZ
Z couplingsElectric charges Z’ couplings
Helicity amplitudes
A deviation of from SM indicates BSMXeXq, XeZ , XqZ
11Breakdown of helicity amplitude
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12Observables by LEP and SLD
Ratios are optimal to remove systematic uncertainties
: Total cross section normalized to the total hadronic cross section
total cross section for given q-quark flavour
total cross section for all quark flavours
�qqF
�qqB
Cross section that q flies in forward hemisphere
Cross section that q flies in backward hemisphere
Rq
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13Background at 250 GeV
❖ Radiative return to the Z-pole cut on ISR photon energy estimator
❖ WW/ZH/ZZ events with hadronic decays cut on y(Durham distance), the sum of two jet masses
https://agenda.linearcollider.org/event/8533/
(use only two jet angles)
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14ILC-GigaZ program
Z/Z’
e�
e+
f
f
�/Z/Z’
e�
e+
f
f
arxive:1905.0020
Measurements at the Z-pole allow us to conclude whether a deviation comes from Z coupling anomalies or presence of Z’ propagators.
at Z-pole above Z-pole
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Experimental challenges
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16Principle of flavour taggingParton level
Reco. level
cb
W
s
W
B decay C decay
O decay
O decayIP B-hadron C-hadron
Other semistablesOther semistables
Jet cone
Basic idea to identify signatures of heavy flavour hadrons :- vertex info. (position, mass, # of tracks) - Isolated leptons
https://arxiv.org/pdf/1506.08371.pdfLCFIPlus
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17Flavour tag performance
b and c separation is more challengingBtag rate
0 0.2 0.4 0.6 0.8 1
Back
grou
nd ra
te
4−10
3−10
2−10
1−10
1preliminary ILD =500GeVs6q,
c bkg. IDR-L
c bkg. IDR-L
uds bkg. IDR-L
uds bkg. IDR-S
Ctag rate0 0.2 0.4 0.6 0.8 1
Back
grou
nd ra
te
4−10
3−10
2−10
1−10
1preliminary ILD =500GeVs6q,
b bkg. IDR-L
b bkg. IDR-S
uds bkg. IDR-L
uds bkg. IDR-S
IDR-L : Nominal (IDR-S : Smaller radius & stronger B field version)
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Trend : Deep Neural Network for Vertex finding and Flavour tagging
N. Kishida et.al @ LCWS2019
https://agenda.linearcollider.org/event/8217/contributions/44677/
K. Goto @ 66th General Meeting of ILC Physics Subgroup
https://agenda.linearcollider.org/event/8568/contributions/45872/attachments/35606/55264/200701_general_physics_meeting.pdf
DNN seems to have gained ground on multivariate analyses. DNN literacy is being essential?Looks very promising
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19Quark charge measurement
❖ Vtx-method Use the charge sum of the tracks associated to secondary vertices
❖ K-method Use the charges of Kaons that are identified with TPC
Two methods :
Since we have two quarks in each pair production event, we have some combinations how to assign quark charges e.g.
These combinations are classified as “categories”.
w/ Vtx-method
w/ K-method
bb
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20Quark charge measurementPurity depending on categories Selection efficiency (Opposite sign cases only)
Current vertexing is aiming for high purity. This is not always best especially for this charge measurements.
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21Correction technique of quark charge assignment
This correction method without generator information
Basic idea :
Accepted events can be originated from (recall that we accept only opposite sign cases) 1) two quark charges correctly assigned cases 2) two quark charges incorrectly assigned cases
Given a probability (p) to assign correct charges, The probability of 1) and 2) can be written with p.
(No generator information used!)
Naccept = p2Ntotal + (1� p)2Ntotal
1) 2)
arxiv:1709.04289
Since and can be measured, we can compute p. Naccept Ntotal
N�accept = p2N�
true + (1� p)2N+true
N+accept = p2N+
true + (1� p)2N�true +: forward events
- : backward events and can be measuredN+accept N�
accept
and can be obtainedN+true N�
true
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Some results
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23Top pair production at threshold
Precise top mass measurement is possible
> Very accurate predictions are available to compare experimental measurements.
arxiv:1309.6323, arxive:1411.7318,
https://agenda.linearcollider.org/event/7371/contributions/37970/
https://agenda.linearcollider.org/event/8217/contributions/44657/
Kacper Nowak @ LCWS2019See also
https://agenda.linearcollider.org/event/8217/contributions/44591/Marcel Vos et. al @ LCWS2019
Phys.Rev.Lett. 115 (2015) 192001
The theory of the top quark threshold has been worked out to high precision.
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24Top pair production above threshold
Polarized beams enable us to measure the individual couplings of each polarization state of the top quark to Z and W.
500 GeV with 500fb-1
semi-leptonic mode (hadronic mode is on-going)
arxive:1307.8102
-0.8,+0.3 and +0.8, -0.3 equally shared beam polarization
arxive:1506.05992
Extrapolation to the full ILC data set (4ab-1) a relative precision of 0.6% on tL coupling 1.0% on tR coupling
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25Bottom pair production at 250 GeVfit : |cosθ|< 0.8Reconstructed polar angle distributions
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26Charm pair production at 250 GeVReconstructed polar angular distributions
Total experimental uncertainties of Rc and AFB are expected to be ~0.2% for the full 2000 fb-1Theoretical high order corrections, particularly the EW corrections, are required.
fit : |cosθ|< 0.75
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27Prospects for BSM discoveries
Remidner : beam polarization disentangles 4 helicity amplitudes
Expected number of standard deviations for different BSM scenarios when determining the different EW couplings to c- and b-quark
GigaZ program running assumed to improve by a factor ~5 the current precision on the SM Z couplings to the different quarks measured at the Z-pole.
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28
Summary
• Not only top but also b- and c-quark productions play important role to
probe BSM models
• Beam polarization is a powerful tool
• Flavour tagging and charge identification are the key for these analyses