JHEP09(2017)083
Note that soft drop multiplicity is a special case (κ = 0) of this more general observable,
with the same criteria for IRC safety. We study the weighted multiplicity in detail in
appendix A, but find its quark/gluon discrimination power to be inferior to the discrete
κ = 0 case. In fact, LL reasoning leads one to expect the soft drop multiplicity n
SD
to have
the best discrimination power of any observable defined on the (z
n
, θ
n
) values; see the end
of section 3.3 for a short discussion.
Nevertheless, several other promising variants of soft drop multiplicity might prove
useful:
• The weighted soft drop multiplicity in eq. (2.8) only refers to the momentum fractions
z
n
in the sum over emissions. One could also consider an angle-weighted variant
X
n
z
κ
n
θ
α
n
, (2.9)
or indeed any function of z
n
and θ
n
. The potential advantage of including θ
n
infor-
mation is that even for θ
cut
= 0, such observables would be collinear safe for α > 0.
• Instead of counting emissions only from the trunk of the C/A tree, we could extend the
sum to include all branchings down to the angular resolution θ
cut
. This multiplicity
variant would require a modification of the ISD algorithm: in step 4
0
, the recursion
would be applied to both subjets i and j, not just the harder one. This is a step in
similarity towards full hadron multiplicity, reducing to it exactly when z
cut
= θ
cut
= 0.
This variant of soft drop multiplicity is more difficult to study analytically, however,
due to the nonlinear structure of the recursion. Moreover, it is not clear that this
variant would provide a performance advantage over n
SD
. While gluons emitted
from the hard core of a quark (gluon) jet give rise to factors of C
F
(C
A
), subsequent
emissions from those gluons give rise to factors of C
A
regardless of the jet flavor; this
might wash out quark/gluon discrimination power.
• The original soft drop algorithm uses a C/A tree to mimic the angular-ordered struc-
ture of the parton shower. One could also study variants based on reclustering with
the generalized-k
t
algorithm with exponent p [49, 50]. The C/A algorithm used above
corresponds to p = 0, while the k
t
algorithm uses p = 1. For this variant, it would
make sense to replace the angular cut θ
cut
with a cut d
cut
on the generalized distance
measure d
ij
.
This last k
t
variant is of particular interest, given the discussion below in section 3.3.
Nonperturbative physics typically dominates when k
t
' Λ
QCD
, so it makes sense to use a
clustering algorithm where the clustering scale is “parallel” to the nonperturbative scale.
This variant of n
SD
would then allow the nonperturbative phase space to be clearly sepa-
rated from the perturbative region and avoided. This would open up as much perturbative
phase space for measured emissions as possible. We note that it is possible to mimic some
of the LL structure of the k
t
variant by using ISD with β = −1, though there would be
differences going to NLL order.
– 8 –
剩余46页未读，继续阅读
weixin_38630853
- 粉丝: 4
- 资源: 952
我的内容管理
展开
最新资源
- 多模态联合稀疏表示在视频目标跟踪中的应用
- Kubernetes资源管控与Gardener开源软件实践解析
- MPI集群监控与负载平衡策略
- 自动化PHP安全漏洞检测：静态代码分析与数据流方法
- 青苔数据CEO程永：技术生态与阿里云开放创新
- 制造业转型： HyperX引领企业上云策略
- 赵维五分享：航空工业电子采购上云实战与运维策略
- 单片机控制的LED点阵显示屏设计及其实现
- 驻云科技李俊涛：AI驱动的云上服务新趋势与挑战
- 6LoWPAN物联网边界路由器：设计与实现
- 猩便利工程师仲小玉：Terraform云资源管理最佳实践与团队协作
- 类差分度改进的互信息特征选择提升文本分类性能
- VERITAS与阿里云合作的混合云转型与数据保护方案
- 云制造中的生产线仿真模型设计与虚拟化研究
- 汪洋在PostgresChina2018分享：高可用 PostgreSQL 工具与架构设计
- 2018 PostgresChina大会：阿里云时空引擎Ganos在PostgreSQL中的创新应用与多模型存储
资源上传下载、课程学习等过程中有任何疑问或建议，欢迎提出宝贵意见哦~我们会及时处理！
点击此处反馈
