Measurements of time-integrated CP and other asymmetries ) r k - - PowerPoint PPT Presentation

▶
measurements of time integrated cp and other asymmetries
SMART_READER_LITE
LIVE PREVIEW

Measurements of time-integrated CP and other asymmetries ) r k - - PowerPoint PPT Presentation

Feb 17, 2024 103 likes •411 views

Measurements of time-integrated CP and other asymmetries ) r k e c t e s e b h a c s n n r o e a G M i t a r o f o o c b r y a a t M l i l s o r c e v b i n C U H L e h e T h ( t

slide-1
SLIDE 1

Measurements of time-integrated CP 
 and other asymmetries

M a r c

  • G

e r s a b e c k 
 ( T h e U n i v e r s i t y

  • f

M a n c h e s t e r )

  • n

b e h a l f

  • f

t h e L H C b c

  • l

l a b

  • r

a t i

  • n

C H A R M 2 1 5 , D e t r

  • i

t , 1 9 M a y 2 1 5

slide-2
SLIDE 2

Two-body final states Multi-body final states

Outline

2

Raw asymmetries Production and detection asymmetries CP violation

slide-3
SLIDE 3

Measured asymmetries

  • Measure
  • Get to first order

Araw(D→f) = ACP(D→f) + Aprod(D) + Adet(f) + Adet(tag)

  • Need to constrain

➡Production asymmetry ➡Detection asymmetry (final state and flavour tag)

  • General idea

➡Use similar Cabibbo-allowed processes 
 and assume ACP(D→f) = 0

3

N(D→ f) − N(D̅→ f ̅ )
 N(D→ f) + N(D̅→ f ̅ ) Araw(D→ f) =

particle tagging 
 D and D̅

slide-4
SLIDE 4

Production asymmetries

  • Particular to pp collider

➡ “Replaces” forward-backward asymmetry at e

+e − and

pp̅

  • Valence quarks favour the production of matter baryons

➡ Favours antimatter mesons

  • Production asymmetry can 


depend on kinematics ➡ Accounted through 
 binning / re-weighting

4

PLB 718 (2013) 902 D+

Fit

slide-5
SLIDE 5

Detection asymmetries

  • Material interaction


can be asymmetric ➡ Strange quark can 
 produce hyperons

  • Detector can be 


asymmetric ➡ Causes asymmetry 
 through different 
 bending of positive 
 and negative tracks ➡ Regularly revert dipole polarity

5

in GeV/c

lab

p 1 10

2

10 Cross-section in mb 20 40 60 80 100

d

  • K

d

+

K

Data from K.A. Olive et al. (PDG), CPC 38 (2014) 090001 JHEP 07 (2014) 041 average

slide-6
SLIDE 6

Results

Two-body decays

slide-7
SLIDE 7

First example

  • Measurement
  • Extract CP asymmetries using control modes

7

JHEP 10 (2014) 025

slide-8
SLIDE 8

Results for KSh

  • Charged D two-body modes are 


challenging due to neutral 
 particles involved

  • Measurement based on 3 fb
  • 1
  • Uses weighted control mode kinematics and average
  • f dipole magnet polarities
  • All approximately zero

8

JHEP 10 (2014) 025

low-mass signal cross-feed combinatorial total

slide-9
SLIDE 9

The ΔaCP saga*

  • What is ΔaCP?
  • Interplay of direct and indirect CP violation
  • Individual asymmetries are expected to

have opposite sign due to CKM structure

9

EPJC 73 (2013) 2373

*after A. Lenz @ CHARM 2013, arXiv:1311.6447

slide-10
SLIDE 10

Latest results

  • D*-tagged (1 fb-1, preliminary)
  • muon-tagged (3 fb-1)

10

D0 πs+ μ- D0 B

LHCb-CONF-2013-003 JHEP 07 (2014) 041

slide-11
SLIDE 11

11

measure want

Individual asymmetries

araw(K-K+) aCP(K-K+) aD(μ+) aP(B)

average

slide-12
SLIDE 12

11

measure want

Individual asymmetries

araw(K-K+) aCP(K-K+) aD(μ+) aP(B)

D from B

average

slide-13
SLIDE 13

11

measure want D0→K-π+

Individual asymmetries

araw(K-K+) aCP(K-K+) aD(μ+) aP(B)

D from B

average

slide-14
SLIDE 14

11

measure want D0→K-π+ aD(K-π+)

Individual asymmetries

araw(K-K+) aCP(K-K+) aD(μ+) aP(B)

D from B

average

slide-15
SLIDE 15

11

measure want D0→K-π+ aD(K-π+) D+→K-π+π+

Individual asymmetries

araw(K-K+) aCP(K-K+) aD(μ+) aP(B)

D from B Prompt D

average

slide-16
SLIDE 16

11

measure want D0→K-π+ aD(K-π+) D+→K-π+π+ aP(D+), aD(π+)

Individual asymmetries

araw(K-K+) aCP(K-K+) aD(μ+) aP(B)

D from B Prompt D

average

slide-17
SLIDE 17

11

measure want D0→K-π+ aD(K-π+) D+→K-π+π+ aP(D+), aD(π+) D+→KSπ+

Individual asymmetries

araw(K-K+) aCP(K-K+) aD(μ+) aP(B)

D from B Prompt D

average

slide-18
SLIDE 18

11

measure want D0→K-π+ aD(K-π+) D+→K-π+π+ aP(D+), aD(π+) D+→KSπ+ aCP/I(KS)

Individual asymmetries

araw(K-K+) aCP(K-K+) aD(μ+) aP(B)

D from B Prompt D

average

slide-19
SLIDE 19

11

measure want D0→K-π+ aD(K-π+) D+→K-π+π+ aP(D+), aD(π+) D+→KSπ+ aCP/I(KS) assume no CPV in Cabibbo-favoured final states

Individual asymmetries

araw(K-K+) aCP(K-K+) aD(μ+) aP(B)

average

slide-20
SLIDE 20

11

measure want D0→K-π+ aD(K-π+) D+→K-π+π+ aP(D+), aD(π+) D+→KSπ+ aCP/I(KS)

Individual asymmetries

araw(K-K+) aCP(K-K+) aD(μ+) aP(B)

JHEP 07 (2014) 041 average

slide-21
SLIDE 21

(Δ)aCP results

  • Ignoring contribution from indirect CPV

12

JHEP 07 (2014) 041

slide-22
SLIDE 22

Results

Multi-body decays

slide-23
SLIDE 23

On Dalitz plots

  • Many ways to reach multi-body final states through intermediate

resonances

  • Resonances interfere and can carry different strong phases

➡ Superb playground for CP violation

  • Look for local asymmetries

➡ Model-dependent: 
 Fit all contributions to phase-space and 
 look for differences in fit parameters ➡ Model-independent: 
 Look for asymmetries in regions of 
 phase space by “counting”

14 K*(892)- K*(892)+ ρ(770)0 Courtesy of S. Reichert

slide-24
SLIDE 24

D+ → 3π

  • Model-independent 


searches for CP violation ➡ Over 3M D+ & D- decays in 1 fb-1 ➡ Search for asymmetry significances in bins

  • f phase space

➡ Search for local asymmetries through un- binned comparison with nearest neighbours

15

PLB 728 (2014) 585-595

slide-25
SLIDE 25

Binned method

16

PLB 728 (2014) 585-595

p-values for no-CPV hypothesis
 > 50% for different binnings removes sensitivity to global asymmetries

LHCb

slide-26
SLIDE 26

Binned method

16

PLB 728 (2014) 585-595

p-values for no-CPV hypothesis
 > 50% for different binnings removes sensitivity to global asymmetries

LHCb

Similar results also obtained with un-binned kNN method*

*reduced sensitivity due to inclusion of few neighbours

slide-27
SLIDE 27

Why not un-binned?

  • Need to compare each event with every other

➡ Computationally challenging for O(1M) events ➡ Use GPUs to exploit massive parallelisation ➡ Applied to D

0→π +π −π 0 decays

  • Energy test (M. Williams, PRD 84 (2011) 054015)

➡ Test statistic (T) comparing pairwise 
 weighted distances in phase space ➡ Compare 
 D

0↔D 0


D̅

0↔D̅ 0


D

0↔D̅

➡ Expect T~0 (no CPV) or T>0 (CPV)

17 PLB 740 (2015) 158

slide-28
SLIDE 28

All π0s

  • Reconstructing merged and resolved π

0s

  • Merged photon clusters

➡ High energy, small opening angle, small m(π

+π −)

  • Resolved photon clusters (includes conversions)

➡ Small energy, large opening angle, large m(π

+π −)

  • Complementary phase-space coverage

18 PLB 740 (2015) 158

γ γ π0 γ γ π0 resolved π0 merged π0

slide-29
SLIDE 29

Results

  • 8×larger sample than BaBar

➡ 420k resolved π0, 250k merged π0 ➡ Similar or better sensitivity

  • Using permutations with randomly

assigned flavour tags to obtain no- CPV sample ➡ Reference T distribution

  • Result based on 1000 permutations

➡ P-value as fraction above nominal T value ➡ (2.6±0.5)%

19 ]

4

c /

2

) [GeV π

+

π (

2

m

1 2 3

]

4

c /

2

) [GeV π

−

π (

2

m

1 2 3

Significance

  • 3
  • 2
  • 1

1 2 3

LHCb simulation

4

c /

2

= 0.3 GeV σ

PLB 740 (2015) 158 PRD 78 (2008) 051102

slide-30
SLIDE 30

CP violation in decay

  • Range of new measurements with increasing precision in

several decay modes ➡ 2-body (KSh, hh) ➡ Multi-body (model-independent, including π

0)

  • Route forward:

➡ Measurements in related modes (two-body, resonances) to identify potential sources of CP violation ➡ Model-independent measurements are discovery strategies ➡ Need model-dependent measurements for quantitative interpretation

  • Future expectations

➡ See Chris’s talk on Friday

20