0 mixing D 0 D mixing in D 0 meson system considerably smaller than - - PowerPoint PPT Presentation

▶
0 mixing d 0 d
SMART_READER_LITE
LIVE PREVIEW

0 mixing D 0 D mixing in D 0 meson system considerably smaller than - - PowerPoint PPT Presentation

Sep 24, 2022 738 likes •932 views

BELLE SEARCH FOR CP VIOLATION IN D 0 KK , , K AND D 0 0 0 Tara Nanut on behalf of the Belle Collaboration 7th International Workshop on Charm Physics May 2015 1 { 17 Search for CP violation in D 0 KK , , K and D 0

slide-1
SLIDE 1

BELLE

SEARCH FOR CP VIOLATION IN D0 Ñ KK, ππ, Kπ AND D0 Ñ π0π0

Tara Nanut

  • n behalf of the Belle Collaboration

7th International Workshop on Charm Physics May 2015

Tara Nanut Search for CP violation in D0 Ñ KK, ππ, Kπ and D0 Ñ π0π0 1/17

1{17

slide-2
SLIDE 2

D0 ´ D

0 mixing ‚ mixing in D0 meson system considerably smaller than in K 0, B0

|D0

1,2y “ p|D0y ˘ q|D 0y

‚ mixing parameters x “ ∆m{Γ, y “ ∆Γ{2Γ ‚ if p ‰ q Ñ |D0

1,2y not CP eigenstates Ñ CPV

Tara Nanut Search for CP violation in D0 Ñ KK, ππ, Kπ and D0 Ñ π0π0 2/17

2{17

slide-3
SLIDE 3

From mixing to CPV

From mixing arises a difference in effective lifetime of CP eigenstates (KK, ππ) and flavour eigenstates (Kπ):

yCP “ τpD0 Ñ K ´π`q τpD0 Ñ K `K ´q ´ 1 “ “ y cospφq ´ 1 2AMx sinpφq

no CPV

“ y (1) φ “ argpp{qq

no CPV

“ AM “ |q{p| ´ |p{q|

no CPV

“

Difference in effective lifetimes of CP eigenstates of D0, D

0 gives a

non-zero asymmetry:

AΓ “ τpD

0 Ñ K ´K `q ´ τpD0 Ñ K `K ´q

τpD

0 Ñ K ´K `q ` τpD0 Ñ K `K ´q

“ “ 1 2AMy cospφq ´ x sinpφq

no CPV

“ (2)

SM CPV in charm Op10´3q Ñ anything larger indicates NP.

Tara Nanut Search for CP violation in D0 Ñ KK, ππ, Kπ and D0 Ñ π0π0 3/17

3{17

slide-4
SLIDE 4

D0 Ñ KK, ππ, Kπ

update of PRL 98, 211803 (2007)

TIME-DEPENDENT ANALYSIS

‚ measure only indirect CPV - common to all D0 decay modes ‚ get yCP, AΓ from measurements of proper decay time

Updated analysis:

‚ twice as large data sample: 976 fb´1

(Υ(4S), Υ(1S), Υ(2S), Υ(3S), Υ(5S))

‚ improved analysis method - take into account ˝ two different configurations of SVD ˝ polar angle dependence ‚ final results are shown here

Tara Nanut Search for CP violation in D0 Ñ KK, ππ, Kπ and D0 Ñ π0π0 4/17

4{17

slide-5
SLIDE 5

D0 Ñ KK, ππ, Kπ

Selection Flavour tag D˚` Ñ D0π`

S

vertex fit p value ą 10´3 pCMS(D˚`) ą 2.5 GeV (3.1 GeV for Υ(5S)) window in m(D0q 2.25σMpσM « 6 ´ 8 MeV) window in q 0.66 MeV (SVD1), 0.82 MeV (SVD2) σt ă 440 fs (SVD1), 370 fs (SVD2)

Table: Selection criteria.

Optimisation: minimal statistical error on yCP.

M (GeV/c2) Events per 0.45 MeV/c2

sideband sideband

(a) D0 → K +K -

2000 4000 6000 8000 1.82 1.84 1.86 1.88 1.9

Signal yield: 242ˆ103

M (GeV/c2) Events per 0.45 MeV/c2

sideband sideband

(b) D0 → π+π-

500 1000 1500 2000 2500 1.82 1.84 1.86 1.88 1.9

Signal yield: 114ˆ103

M (GeV/c2) Events per 0.45 MeV/c2

sideband sideband

(c) D0 → K -π+

10000 20000 30000 40000 50000 60000 70000 1.82 1.84 1.86 1.88 1.9

Signal yield: 2.61ˆ106

Tara Nanut Search for CP violation in D0 Ñ KK, ππ, Kπ and D0 Ñ π0π0 5/17

5{17

slide-6
SLIDE 6

D0 Ñ KK, ππ, Kπ

Lifetime fit

‚ Proper decay time t distribution:

Fptq “ N τ ż e´t1{τRpt ´ t1qdt1 ` Bptq

‚ Perform simultaneous binned maximum likelihood fit to all 3

channels (KK, ππ, Kπ), separately for SVD1,2.

‚ cospθ˚q dependence Ñ perform fit in bins of cospθ˚q. ‚ Combine results from all bins with least squares fit to constant to

  • btain the final result.

‚ Fit tested on MC, linearity tests show no bias.

Tara Nanut Search for CP violation in D0 Ñ KK, ππ, Kπ and D0 Ñ π0π0 6/17

6{17

slide-7
SLIDE 7

D0 Ñ KK, ππ, Kπ

Lifetime fit

t (fs) pull

  • 4
  • 2

2 4

  • 2000 -1000

1000 2000 3000 4000

Events per 41 fs (a) D0 → K +K - 1 10 10 2 10 3 10 4 t (fs) pull

  • 4
  • 2

2 4

  • 2000 -1000

1000 2000 3000 4000

Events per 41 fs (b) D

0 → K +K -

1 10 10 2 10 3 10 4 t (fs) pull

  • 4
  • 2

2 4

  • 2000 -1000

1000 2000 3000 4000

Events per 41 fs (c) D0 → π+π- 1 10 10 2 10 3 t (fs) pull

  • 4
  • 2

2 4

  • 2000 -1000

1000 2000 3000 4000

Events per 41 fs (d) D

0 → π+π-

1 10 10 2 10 3 t (fs) pull

  • 4
  • 2

2 4

  • 2000 -1000

1000 2000 3000 4000

Events per 41 fs (e) D0 → K -π+ + cc 10 10 2 10 3 10 4 10 5

Tara Nanut Search for CP violation in D0 Ñ KK, ππ, Kπ and D0 Ñ π0π0 7/17

7{17

slide-8
SLIDE 8

D0 Ñ KK, ππ, Kπ

Systematics and result Source ∆yCP (%) ∆Aγ (%) SVD misalignment 0.060 0.041 Mass window position 0.007 0.009 Background 0.059 0.050 Resolution function 0.030 0.002 Binning 0.021 0.066 Total 0.092 0.066

Table: Systematic uncertainties.

FINAL RESULT: AΓ “ r´0.03 ˘ 0.20pstat.q ˘ 0.07psyst.qs% yCP “ r1.11 ˘ 0.22pstat.q ˘ 0.09psyst.qs%

4.7σ significance consistent with no CPV

Tara Nanut Search for CP violation in D0 Ñ KK, ππ, Kπ and D0 Ñ π0π0 8/17

8{17

slide-9
SLIDE 9

D0 Ñ KK, ππ

TIME-INTEGRATED ANALYSIS

‚ measure direct + indirect CPV ‚ asymmetry due to a difference in time-integrated decay rates of

D0 Ñ f , D

0 Ñ f :

ACP “ ΓpD0 Ñ f q ´ ΓpD

0 Ñ f q

ΓpD0 Ñ f q ` ΓpD

0 Ñ f q

Experimentally measured quantity: Araw “ NpD0 Ñ f q ´ NpD

0 Ñ f q

NpD0 Ñ f q ` NpD

0 Ñ f q

“ “ ACP ` AFB ` Aπ`

S

‚ get ACP from extracted signal yields and corrections for

detector-induced asymmetries and asymmetries in production

Tara Nanut Search for CP violation in D0 Ñ KK, ππ, Kπ and D0 Ñ π0π0 9/17

9{17

slide-10
SLIDE 10

D0 Ñ KK, ππ

Detector-induced and production asymmetries

DETECTOR-INDUCED ASYMMETRY

‚ due to different reconstruction efficiencies for π`

S , π´ S

‚ determined from tagged and untagged D0 Ñ Kπ decays ‚ evaluated in bins of pπS, θπS

PRODUCTION ASYMMETRY

‚ forward-backward asymmetry in production of D˚` and and D˚´

(γ ´ Z 0 interference and higher order QED effects in e`e´ Ñ cc)

‚ assumed same for all charm mesons ‚ odd function of θ˚, correct for using:

ACP “ 1 2rAcorr

rec pcos θ˚q ` Acorr rec p´ cos θ˚qs and

AFB “ 1 2rAcorr

rec pcos θ˚q ´ Acorr rec p´ cos θ˚qs

where Acorr

rec is after Aπ`

S correction Tara Nanut Search for CP violation in D0 Ñ KK, ππ, Kπ and D0 Ñ π0π0 10/17

10{17

slide-11
SLIDE 11

D0 Ñ KK, ππ

Selection and ACP extraction all KK Kπ ππ Flavour tag D˚` Ñ D0π`

S

vertex fit p value ą 10´3 pCMS(D˚`) [GeV] ą 2.5 (3.1 for Υ(5S)) window in m(D0q [MeV] 17.8 17.8 17.2 window in q [MeV] 1.00 1.85 0.90

Table: Selection criteria.

Optimisation: minimal error on asymmetry (σA).

‚ Extract signal yield from signal window via background

subtraction.

‚ Determine background from 2 sidebands ˘20 MeV from mpD0

nom).

‚ Limit to |cos θ˚| ă 0.8 to decrease AπS-related systematics. ‚ ACP extracted via fit to constant.

Tara Nanut Search for CP violation in D0 Ñ KK, ππ, Kπ and D0 Ñ π0π0 11/17

11{17

slide-12
SLIDE 12

D0 Ñ KK, ππ

ACP fit D0→K+K- D0→π+π-

4.058 / 3 P1

  • 0.3249E-02

0.2088E-02

|cos θ*| ACP a)

6.537 / 3 P1 0.5470E-02 0.3575E-02

|cos θ*| ACP b) |cos θ*| AFB c) |cos θ*| AFB d)

  • 0.04
  • 0.03
  • 0.02
  • 0.01

0.01 0.02 0.03 0.04 0.2 0.4 0.6 0.8

  • 0.04
  • 0.03
  • 0.02
  • 0.01

0.01 0.02 0.03 0.04 0.2 0.4 0.6 0.8

  • 0.05
  • 0.04
  • 0.03
  • 0.02
  • 0.01

0.01 0.02 0.2 0.4 0.6 0.8

  • 0.05
  • 0.04
  • 0.03
  • 0.02
  • 0.01

0.01 0.02 0.2 0.4 0.6 0.8 Tara Nanut Search for CP violation in D0 Ñ KK, ππ, Kπ and D0 Ñ π0π0 12/17

12{17

slide-13
SLIDE 13

D0 Ñ KK, ππ

Systematics and result AKK

CP p%q

Aππ

CP p%q

∆ACP (%) Signal counting method 0.055 0.023 0.037 πS correction 0.065 0.067 0.014 ACP extraction method 0.06 0.050 0.051 Total 0.085 0.087 0.064

Table: Systematic uncertainties.

FINAL RESULT: AKK

CP “ r´0.32 ˘ 0.21pstat.q ˘ 0.09psyst.qs%

Aππ

CP “ r0.55 ˘ 0.36pstat.q ˘ 0.09psyst.qs%

∆ACP “ r´0.87 ˘ 0.41pstat.q ˘ 0.06psyst.qs% Results consistent with no CPV.

Tara Nanut Search for CP violation in D0 Ñ KK, ππ, Kπ and D0 Ñ π0π0 13/17

13{17

slide-14
SLIDE 14

D0 Ñ π0π0

PRL 112, 211601 (2014)

TIME-INTEGRATED ANALYSIS

Flavour tag D˚` Ñ D0π`

S

pCMS(D˚`) ą 2.5 GeV (3.1 GeV for Υ(5S)) mass window m(D0q (1.758, 1.930) GeV mass window ∆m (0.14, 0.16) GeV

Table: Selection criteria.

Optimisation: minimal error on Arec.

‚ Fit ∆m “ mpD˚`q ´ mpD0q simultaneously for D0, D

0.

‚ Perform fit in bins of (cospθ˚q, pπS

T , cospθπSqq.

‚ Obtain average via a χ2 fit on values in bins of cospθ˚q. ‚ Procedure tested and confirmed on MC.

Tara Nanut Search for CP violation in D0 Ñ KK, ππ, Kπ and D0 Ñ π0π0 14/17

14{17

slide-15
SLIDE 15

D0 Ñ π0π0

∆m fit and asymmetries fit D0

∆ )

2

M (GeV/c ∆ 0.145 0.15 0.155 0.16 )

2

Events/(0.2 MeV/c 0.5 1 1.5 2 2.5

3

10 ×

D

)

2

M (GeV/c ∆ 0.145 0.15 0.155 0.16 )

2

Events/(0.2 MeV/c 0.5 1 1.5 2 2.5

3

10 × ∆

Signal yield: 34460 ˘ 273

|

*

θ |cos

0.2 0.4 0.6 0.8 1

CP

A

  • 0.06
  • 0.04
  • 0.02

0.02 0.04 0.06

θ

0.04

| θ | |

*

θ |cos

0.2 0.4 0.6 0.8 1

FB

A

  • 0.06
  • 0.04
  • 0.02

0.02 0.04 Tara Nanut Search for CP violation in D0 Ñ KK, ππ, Kπ and D0 Ñ π0π0 15/17

15{17

slide-16
SLIDE 16

D0 Ñ π0π0

Systematics and result signal shape 0.03 πS correction 0.07 ACP extraction method 0.07 Total 0.10

Table: Systematic uncertainties.

FINAL RESULT: ACP “ r´0.03 ˘ 0.64pstat.q ˘ 0.10psyst.qs% Result consistent with no CPV.

Tara Nanut Search for CP violation in D0 Ñ KK, ππ, Kπ and D0 Ñ π0π0 16/17

16{17

slide-17
SLIDE 17

Summary and conclusion

‚ We have searched for CP violation in decays of D0 Ñ KK, ππ, Kπ

and D0 Ñ π0π0.

‚ Results are consistent with no CPV (direct or indirect). ‚ Here Belle story finishes... for Belle II prospects, see talk by Marko

Starič (Friday).

Tara Nanut Search for CP violation in D0 Ñ KK, ππ, Kπ and D0 Ñ π0π0 17/17

17{17