提升对CKM相位γ敏感性的B-→DK-衰变分析

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"通过改进D→K +π-π-π+衰变中的相空间分仓策略，提高了对CKM相位γ的敏感性" 在粒子物理学领域，Cabibbo-Kobayashi-Maskawa（CKM）矩阵是描述夸克间弱相互作用的重要工具，其中的γ角是理解CP违反（即粒子与反粒子行为差异）的关键参数之一。这篇由T.Evans等人发表在Physics Letters B的文章提出了一种新的方法，旨在提升对γ角的测量精度。他们针对B-→DK-衰变过程中的D meson进一步细分了D→K+π-π-π+的相空间，这是一种称为"分仓"的技术。文章描述了一种四仓分仓方案，该方案基于LHCb合作近期提出的振幅模型。这个方案的创新之处在于能够更有效地提取出与γ角相关的物理信息。作者假设，即使在实际数据应用中，这个经过模型优化的四仓策略也能保持相似的敏感性。据估计，如果应用此方法，LHCb实验迄今为止收集的B介子样本可以将γ角的统计不确定性降低到大约5度，这将是单个B-→DK-衰变模式中对γ角测量的最高精度之一。为了实现这一目标，研究人员分析了CLEO-c实验积累的量子关联DD数据，以获取四个仓中的相干因子和平均强相差的第一手约束。这些约束条件对于执行测量至关重要。论文详细比较了这些约束与模型的预测，深入讨论了如何将这些信息用于改进γ的测量结果。关键词包括： Charm衰变、CP违反。文章的接收日期为2019年9月24日，修订后再次提交日期为2019年12月20日，最终接受日期为2019年12月24日，并于2020年1月6日在线发布。编辑为L.Rolandi。这项工作通过精细的相空间分仓技术，提升了对标准模型中关键CP违反参数γ角的测量能力，这对于理解和探索宇宙中的物质-反物质不对称性具有深远意义。

Physics Letters B 802 (2020) 135188

Contents lists available at ScienceDirect

Physics Letters B

www.elsevier.com/locate/physletb

Improved sensitivity to the CKM phase γ through binning phase space

in B

−

→ DK

−

, D → K

−

decays

T. Evans

a,∗

, J. Libby

, S. Malde

, G. Wilkinson

European Organisation for Nuclear Research (CERN), 1211 Geneva 23, Switzerland

Indian Institute of Technology Madras, Chennai 600036, India

University of Oxford, Denys Wilkinson Building, Keble Road, OX1 3RH, United Kingdom

a r t i c l e i n f o a b s t r a c t

Article history:

Received

24 September 2019

Received

in revised form 20 December 2019

Accepted

24 December 2019

Available

online 6 January 2020

Editor:

L. Rolandi

Keywords:

Charm

decay

CP violation

A binning scheme is proposed for D → K

−

phase space that will improve the sensitivity of a

−

→ DK

−

analysis to the angle γ of the Cabibbo-Kobayashi-Maskawa Unitarity Triangle. The scheme

makes use of amplitude models recently reported by the LHCb collaboration. Assuming that a four-bin

scheme optimised on the models retains a similar sensitivity when applied in data, it is estimated that

the statistical uncertainty on γ from the B-meson sample so far collected by the LHCb experiment will

be as low as 5 degrees. This will be one of the most precise results available for any single decay mode

in a B

−

→ DK

−

measurement. Quantum-correlated D

D data accumulated by the CLEO-c experiment are

analysed to provide ﬁrst constraints on the coherence factors and average strong-phase differences in

the four bins, which are necessary inputs for the measurement. These constraints are compared with the

predictions of the model, and consequences for the measurement of γ are discussed.

(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP

1. Introduction

An important goal of ﬂavour physics is to determine the an-

gle

γ = arg(−V

∗

) of the Cabibbo-Maskawa-Kobayashi

(CKM) Unitarity Triangle with the best possible precision. Sensi-

tivity

to this weak phase (also denoted φ

) can be obtained by

measuring CP -violating and associated observables in the decay

−

→ DK

−

, where D indicates a neutral charm meson recon-

structed

in a ﬁnal state common to both D

and

. (The inclusion

of charge-conjugate processes is implied throughout, unless oth-

erwise

stated.) First measurements of γ using this strategy were

performed at the B-factory experiments [1,2], but the most pre-

cise

ensemble of results now comes from the LHCb collaboration,

which has exploited a wide selection of D-decay modes

to estab-

lish

γ = (74.0

+5.0

−5.8

)

◦

[3]. This value is consistent with, but signiﬁ-

cantly

less precise than the prediction of (65.6

+1.0

−3.4

)

◦

, which comes

from the knowledge of the sides and other angles of the Unitarity

Triangle [4], with a similar prediction in Ref. [5]. Hence more data

and new approaches are required to improve the precision of the

Corresponding author.

E-mail

address: timothy.david.evans@cern.ch (T. Evans).

Additional inputs to this result come from analogous strategies involving B

decays and from time-dependent B

and B

measurements.

direct measurement and to allow for more stringent tests of the

CKM paradigm.

One

input to the LHCb determination of γ is the measure-

ment

of observables involving D → K

−

decays, where

this mode is reconstructed inclusively as part of the B

−

→ DK

−

decay chain. Here there are contributions from both Cabibbo-

favoured

(CF) and doubly Cabibbo-suppressed (DCS) amplitudes in

the charm-meson decay, as well as favoured b → c and suppressed

b →u amplitudes in the B-meson decay, the net effect of which is

to introduce interference effects sensitive to γ [6]. There are four

possible decay conﬁgurations, with rates given by

(B

∓

→ (K

∓

)

∓

)

∝ (

)

+(r

K 3π

)

+2r

K 3π

cos (δ

+δ

K 3π

∓γ ) (1)

(B

∓

→ (K

∓

)

∓

)

∝

1 + (r

K 3π

)

+2r

K 3π

cos (δ

−δ

K 3π

∓γ ), (2)

where r

∼ 0.1is the absolute ratio of B

−

→

−

to B

−

→

−

amplitudes. The phase difference between these two am-

plitudes

is (δ

− γ ), where δ

is a CP -conserving strong phase.

(These expressions neglect small corrections from D

mixing,

which can be included in a straightforward manner [7].)

The

other parameters in Eqs. (1) and (2)relate to the phase-

space

averaged contribution of intermediate hadronic resonances

https://doi.org/10.1016/j.physletb.2019.135188

0370-2693/

SCOAP

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