1/15

Sensitivity to withB D(KK)K Decays

CP Working Group Meeting - Thursday, 19CP Working Group Meeting - Thursday, 19thth April April 20072007

• Introduction• B DKDalitz Analysis• Summary of Selection & Bkg Results

• Model• Signal Acceptance Across Phase Space• Background Distributions in Phase Space

• Simulation• Overview• Results

Jim Libby, Andrew Powell, Jonas Rademacker, Guy Wilkinson

2/15

IntroductionFour-Body Dalitz [Phys. Lett. B 647 (2007) 400]

• Extension to conventional three-body technique

• Jonas and Guy’s initial sensitivity study performed with NO background ~or detector effects incorporated

• Assuming signal sample of 1,000 events, rB = 0.1,

Following results of the B D(KK)K DC04 selection and background study (CP WG meeting – 14th December) , we now perform an LHCb specific sensitivity study

Selection Results [LHCb 2007-004 PHYS]

S = 1,700 events

Signal Yield per 2fb-1

ReflectionsReflections 400 ± 136Partially Reco.Partially Reco. 262 ± 185CombinatoricCombinatoric 840 ± 593

1,500 ± 640BTot

Background per 2fb-1

3/15

Selection Efficiency Across Phase SpaceQuestion: Do we need to incorporate

an acceptance function into our study?• Compare the distributions formed in the ~10 kinematic projections (sij, sijk) of:

• Original MC generator level events• Corresponding reconstructed offline events100k MC events (uniform in phase space)

2,012 offline reconstructed events

• Two tests of similarity:• ratio of distributions (bottom plot)• Kolmogorov-Smirnov (K-S) test

Ratio plots, given the limited reco. statistics, suggests a flat acceptance

K-S test confirms this, returning probabilities of between 0.9 – 0.7 that the reco. distribution is a subset of the MC truth distribution

Example plots: s24

Answer: No.

4/15

Background Description in Phase Space ITo do this, we first classify the background into the following 3 categories:

1. Reflection Event:

2. Combinatoric Event:

3. Combinatoric Event:

1. Reflection Event B D• Dangerous! 10xBR(B DK)

• Controlled with RICH PID: B/S = 0.24

• The interference between these paths is ~greatly suppressed due to the additional ~CKM suppression (DCS)

• Effective suppression , thus, ~ignore interference (no CPV) and only ~consider favoured modes

Therefore, PDFs for this background:

5/15

Background Description in Phase Space II

3. Combinatoric D

• Genuine D meson, generally from a D* cascade decay, combined with a ~combinatoric K meson (either true or fake)

• Equal probability of either a K- or K+ being wrongly associated with the ~D0/D0

2. Combinatoric Kaon:

• Naively expect this background to ~occupy phase space un-biasedly

• Need to check explicitly

• Appears to be the case:

• Model, therefore, with a flat PDF in ~phase space

• Incorporate with B/S = 0.32

• Incorporate with B/S = 0.32

6/15

Fit Likelihood Function• Simultaneous likelihood fit to B- and B+ with the following overall PDF:

• Fit fractions: fD, ffakeK, fPS

• Fixed in fit (not free parameters)

• Justified, since these values will ~be known from sideband studies ~and a D control sample

• Use RooFit based framework written by Jonas Rademaker to generate and ~fit toy experiments

• Each toy experiment generates 1,700 signal events with appropriate ~quantities of background

• Input values: = 60°, B = 130°, rB = 0.10

• Several studies performed:• Individual backgrounds incorporated separately at nominal levels• All backgrounds incorporated at nominal, (2 x nominal) and ~(½ x nominal) levels w.r.t signal

7/15

Results

8/15

Considering Backgrounds Separately

Example: Accumulated plots for fits incorporating just Dbackground

• Generate 100 toy experiments for each background configuration

9/15

Considering Backgrounds TogetherNominal Background (S/B =1.1)

B-

B-

B+

B+

10/15

Example: Accumulated plots for fits to

• 300 toy experiments with ALL backgrounds included at ‘nominal’ levels

Considering Backgrounds Together

11/15

Considering Backgrounds Together2 x Nominal Background (S/B =0.57)

B-

B-

B+

B+

12/15

Considering Backgrounds Together• 100 experiments with ALL backgrounds included at ‘2 x nominal’ levels

Example: Accumulated plots for fits to

13/15

Considering Backgrounds Together½ x Nominal Background (S/B =2.27)

B-

B-

B+

B+

14/15

Considering Backgrounds Together• 100 experiments with ALL backgrounds included at ‘½ x nominal’ levels

Example: Accumulated plots for fits to

15/15

Summary• The sensitivity to using B D(KK)K decays with a four-body ~Dalitz amplitude analysis at LHCb has been studied

• Various configurations of the background about its estimated nominal ~contribution have been simulated within 2fb-1 data sets:

• A public note fully documenting this sensitivity study is in preparation