new method for measurement of the Higgs boson mass at...

new method for measurement of the Higgs boson mass at e+e-

Junping Tian (U’ of Tokyo) International Workshop on High Energy

Circular Electron Positron Collider @ IHEP, Nov. 6-8, 2017

2

introduction: methods to measure Higgs mass

at LHC: direct reconstruction from decay, e.g. H—>γγ or H—>ZZ—>4l

at e+e-: recoil mass against Z—>ll1604.07524�mH20

H = 14MeV

1503.07589

ILC250

mRun1H = 125.09 ± 0.21(stat) ± 0.11(sys)GeV

Z

H

μ+

μ−

e+

e−

Z X

3

introduction: why δmH is important

partial widths of H->ZZ*/WW* is very sensitive to the Higgs boson mass (due to phase space)

δmH becomes one main source of systematic errors for theory prediction of Γ(H->ZZ) and Γ(H->WW)

1404.0319

e.g. if ∆mH = 200 MeV —> δZ ~ 1.2% (>> other sources)

ILC 250: ∆mH = 14 MeV —> δZ ~ 0.1%

note: δZ is relative error for HZZ coupling, which is defined as 1/2 of relative error of partial width of H->ZZ*

�W = 6.9 · �mH �Z = 7.7 · �mH

4

introduction: the motivation for a new method

ILC H20: why, for significant fraction of time, the 500 GeV machine is running at 250 GeV? (was really a pity to me)

5

introduction: the motivation for a new method

at Ecm=250 GeV: ∆mH = 14 MeV

can we improve ∆mH at e.g. √s >= 500 GeV?

at Ecm=500 GeV: ∆mH = 218 MeV

1604.07524

6

idea of a new method for measurement of mH

require momentum balance only in transverse direction

use measured jet direction, but not energy

two constraints -> two unknown (p1, p2)

insensitive to beam energy

insensitive to beamstrahlung/ISR

insensitive to (b)-jet energy resolution

strategy

advantage

e-

p2

p1

pZ

e+H

Z

(talk at LCWS16)

7

analytic results

� = �1 � �2 pt =�

p2x + p2

y

�p1

p2

�=

pt

sin �

�sin(��2)

sin �1sin(�1��)

sin �2

�

p1 sin �1 cos�1 + p2 sin �2 cos �2 = px

p1 sin �1 sin �1 + p2 sin �2 sin �2 = py

e-

p2

p1

pZ

e+H

Z

(px, py: measured from pZ)

8

results for full simulation — resolutions

(rec.-truth)/truth-1 -0.5 0 0.5 1

Nor

mal

ised

to 1

0

0.05

0.1

0.15

0.2

jθcos

jφ

jE

e+e� � µµH,H � bb̄�

s = 500 GeV w/o overlay

comparison between momentum of jets and b-quarks

9

performance of new method (compared with others)

Higgs Mass [GeV]100 200 300 400

Entri

es /

1 G

eV

0

1000

2000

3000New MethodRecoil MassDirect M(JJ)

@ 500 GeVbb→H, Hµµ→-+e+e

ILD full simulation

10

results for full simulation — including full SM background

Higgs Mass [GeV]50 100 150 200 250

Entri

es /

1 G

eV

0

20

40

60

80 Hµµsignal

2f Background

4f Background

6f Background

Recoil Mass [GeV]50 100 150 200 250

Entri

es /

1 G

eV

0

10

20

30Hµµsignal

2f Background

4f Background

6f Background

∆mH ~ 70 MeV ∆mH ~ 218 MeV


s = 500 GeV

�Ldt = 500 fb�1

P (e�, e+) = (�0.8, +0.3)

new method recoil method

(leptonic channels & only 500 GeV data in H20)

11

back to LCWS16

new method:very promising mH measurement at 500 GeV

was about to include Z->qq channel

maybe we can forgot about 250 GeV running

e.g. some variation of

G-20

12

another news from LCWS16

in that case, isn’t recoil method good enough?

we would have to run ILC at √s = 250 GeV first anyway…

J.List @ LCWS17

in fact, I did forget about my study of new method

higher luminosity at 250 GeV

• luminosity can be increased by higher δBS (beamstrahlung energy loss, which is 1% at TDR)

• higher δBS can be achieved by smaller εx,n or βx*

• set of new beam parameters with smaller εx,n is being tried —> x1.6 higher luminosity is promising

• if works —> can further try smaller βx*13

K.Yokoya @ AWLC 2017

impact of higher beamstrahlung

14

• set4 : ΔmH larger by ~25% • set15/16: ΔmH larger by ~50%

—> ILC250: ∆mH ~ 20 MeV for new beam parameters

D.Jeans @ AWLC 2017

15

new motivation of the new method

insensitive to the beam energy —> complementary in terms of systematic errors

insensitive to beamstrahlung/ISR —> improve statistical error by applying the new method to those events with large beamstrahlung/ISR, e.g. a combined approach

might be useful, in supporting new beam parameters with even higher luminosity at 250 GeV

improve separation between signal background

CEPC

CEPC

CEPC

Higgs Mass [GeV]50 100 150 200

Entri

es /

1 G

eV

0

500

1000

1500

2000

2500 New MethodRecoil MassDirect M(JJ)

@ 250 GeVbb→H, Hµµ→-+e+e

16

performance of new method: single approach at 250 GeV

17

a possible combined approach

h1Entries 2618Mean 131.9RMS 15.4

100 110 120 130 140 150 160 170 180 190 2000

20

40

60

80

100

120h1

Entries 2618Mean 131.9RMS 15.4


100 110 120 130 140 150 160 170 180 190 200

1

10

210

310


M(recoil) M(new)

M(recoil)>130 GeV

~30% of signal


s = 250 GeV

18

a possible combined approach


s = 250 GeV

Higgs Mass [GeV]110 120 130 140 150 160

Entri

es /

0.5

GeV

0

500

1000

1500 Recoil Mass

Combined Method

~10% increase of events in peak area, for free

preliminary

19

test for higher beam-strahlung


s = 250 GeV

recoil mass method

Higgs Mass [GeV]110 120 130 140 150 160

Nor

mal

ized

to 1

0

0.05

0.1

0.15 TDR Beam-strahlung

Larger BS (test)

preliminary

Higgs Mass [GeV]110 120 130 140 150 160

Nor

mal

ized

to 1

0

0.01

0.02

0.03

0.04 TDR Beam-strahlung

Larger BS (test)

20

test for higher beam-strahlung


s = 250 GeV

new method

preliminary

21

summary & next step

mH measurement is important: ∆mH=14 MeV -> 0.1% systematic error for HZZ, HWW couplings

a new method for mH measurement is proposed

insensitive to beam energy, beamstrahlung/ISR

a factor of 3 better at √s >= 500 GeV than recoil method

a combined approach is promising at √s = 250 GeV

next step: include Z—>qq; systematic errors, e.g. jet direction and jet mass; apply to new beam parameters

backup

24

(rec.-truth)/truth-1 -0.5 0 0.5 1

Nor

mal

ised

to 1

-510

-410

-310

-210

-110 jθcos

jφ

jEµE


s = 500 GeV

(rec.-truth)/truth1− 0.5− 0 0.5 1

Nor

mal

ised

to 1

4−10

3−10

2−10

1−10 jθcosj

φ

jEµE

25


s = 250 GeV

new method for measurement of the Higgs boson mass at...

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