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

Introduction

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

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

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)

Motivation for (heavy) quark pair production

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.

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

Quark pair production

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

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

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

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)

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

Experimental challenges

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

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)

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

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

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.

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

Some results

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.

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

25Bottom pair production at 250 GeVfit : |cosθ|< 0.8Reconstructed polar angle distributions

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

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.

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