ATLAS探测器发现希格斯玻色子新衰变模式：H→aa→4b在13 TeV pp碰撞中的实验研究

Open

Access

112 浏览量更新于2024-07-16 收藏 1.11MB PDF 举报

身份认证购VIP最低享 7 折!

30元优惠券

资源详情

资源推荐

JHEP10(2018)031

The number of fake or non-prompt leptons satisfying the tight criteria can then be

calculated by inverting the matrix deﬁned by the two equations:

= N

+ N

, N

= ε

+ ε

where N

) is the number of events in data satisfying the loose (tight) lepton selection,

) is the number of events with a real prompt (fake or non-prompt) lepton in the

loose lepton sample, and ε

(ε

) is the eﬃciency for these events to fulﬁl the tight lepton

selection. By generalizing the resulting formula to extract ε

, a weight is assigned to

each event selected in the loose lepton data sample, providing a prediction for both the

yields and the kinematic distributions of the fake and non-prompt lepton background.

When applying the matrix method in the case of high jet and b-tagged jet multiplicities,

the number of events in data satisfying the loose and tight lepton selections is signiﬁcantly

reduced, leading to large ﬂuctuations in the background predictions. In order to mitigate

this problem, instead of tagging the jets by applying the b-tagging algorithm, their proba-

bilities to be b-tagged are parameterized as a function of the jet p

. This allows all events

in the sample before b-tagging is applied to be used in predicting the normalization and

shape of the background from fake or non-prompt leptons after b-tagging. The tagging

probabilities are derived using an inclusive sample of fake or non-prompt leptons and the

resulting predictions of this background estimate are in agreement with those obtained by

applying the b-tagging algorithm and have greatly reduced statistical uncertainties.

In the dilepton channel, the background contribution from fake or non-prompt leptons

is very small and is estimated from simulation and normalized to data in a control region

with two same-charge leptons.

5 Event categorization

Events satisfying the object selection are categorized into analysis regions according to the

number of leptons, jets and b-tagged jets. The regions enhanced in signal H → aa → 4b

events relative to the backgrounds are referred to as signal regions (SRs). The other regions,

referred to as control regions (CRs), are used to constrain the background predictions and

related systematic uncertainties (see section 7) through a proﬁle likelihood ﬁt to the data

(see section 8). The signal and backgrounds are derived consistently in the signal and

control regions in a combined ﬁt. The discrimination of signal from background is further

enhanced in the signal regions by using multivariate techniques, as described in section 6.

The H → aa → 4b decay chain is expected to have multiple b-tagged jets, often three

or four, satisfying the object selection. The dominant background arises from t

t events in

the single-lepton channel and Z + jets events in the dilepton channel, which can also have

diﬀerent jet and b-tagged jet multiplicities or leptons of diﬀerent ﬂavour in the case of the

dilepton channel. The regions are referred to as (n

`, n

j, n

b) indicating n

leptons, n

selected jets and n

b-tagged jets. The SRs contain at least three b-tagged jets and are (1`,

3j, 3b), (1`,4j, 3b) and (1`, 4j, 4b) for single-lepton events, and (2`, 3j, 3b), (2`, ≥4j, 3b)

and (2`, ≥4j, ≥4b) for same-ﬂavour dilepton events. The CRs are (1`, 3j, 2b), (1`, 4j, 2b),

(1`, ≥5j, 3b) and (1`, ≥5j, ≥4b) for single-lepton events, (2`, ≥3j, 2b) for same-ﬂavour

– 8 –

JHEP10(2018)031

SR SR SR

W + jets

t + light

t + b

Z + jets

t + c ¯c/b

t + b

(≥5j, ≥4b)(4j, 4b)(≥5j, 3b)(4j, 3b)(3j, 3b)(≥5j, 2b)(4j, 2b)(3j, 2b)

Single-lepton

Dilepton

same-ﬂavor

Dilepton

diﬀerent-ﬂavor

Figure 2. Deﬁnition of the signal and control regions (SR and CR, respectively) in the single-

lepton and dilepton channels. The main background component probed with the CR is indicated.

The vertical axis shows the lepton selection, while the horizontal axis shows the jet and b-tagged

jet multiplicities.

dilepton events, and (2`, ≥3j, 3b) and (2`, ≥4j, ≥4b) for diﬀerent-ﬂavour dilepton events.

The signal and control regions are summarized in ﬁgure 2, indicating the main background

sources probed in the CRs. Figure 3 summarizes the background composition in the signal

and control regions.

In the single-lepton signal regions, background t

t events can only satisfy the selection

criteria if accompanied by additional b-tagged jets. The t

t + light background is dominant

in the sample of events with exactly two or three b-tagged jets. The background processes

t+c¯c and t

t+b

b become more important as the jet and b-tagged-jet multiplicities increase.

In particular, the t

t + b

b background dominates for events with ≥5 jets and ≥4 b-tagged

jets. In the case of (1`, 3j, 3b) or (1`, 4j, 3b), the main sources of t

t background are events

with jets mistagged as b-tagged jets, particularly from W → cs decays, where the c-jet is

misidentiﬁed, and from W → τν, where the τ-lepton decays hadronically and is likewise

mistagged. In the case of (1`, 4j, 4b), the t

t background includes more events with genuine

b-quarks from gluon splitting to b

b pairs.

In the dilepton channel, the background is mainly composed of t

t and Z + jets events.

In the case of the t

t background, most events contain two prompt leptons from the leptonic

decays of the two W bosons, and two b-jets from the top-quark decays. Additional jets arise

from gluon splitting into b

b and c¯c and from jets from initial-state radiation and pile-up.

In each of these cases, the third and fourth b-tags in the event are from additional b-tagged

jets, or from the mistag of additional c- or light-jets. In the samples with exactly three

or four jets and exactly three b-tagged jets, the contributions of each of these sources is

similar. In the case of the sample with exactly four jets and exactly four b-tagged jets, the

contribution from events with real additional b-tagged jets, such as from gluon splitting

into b

b, dominates.

In the case of the Z + jets background, the dominant contribution is from Z bosons

produced in association with multiple heavy-ﬂavour jets, for example from gluon splitting

– 9 –

剩余47页未读，继续阅读

weixin_38532849

粉丝: 7
资源: 952

ATLAS探测器发现希格斯玻色子新衰变模式：H→aa→4b在13 TeV pp碰撞中的实验研究

使用ATLAS探测器在s = 8 $$ \ sqrt {s} = 8 $$ TeV的pp碰撞中搜索衰减到W玻色子对的高质量希格斯玻色子

在s = 13 $$ \ sqrt {s} = 13 $$ TeV的最终状态下，电子，介子和强子衰变τ轻子在最终状态下与希格斯玻色子相关联产生的证据。

在s = 13 $$ \ sqrt {s} = 13 $$ TeV的质子-质子碰撞中，使用大面积射流搜索四夸克最终态中希格斯玻色子对的产生

搜索在s = 8 $$ \ sqrt {s} = 8 $$ TeV下与pp碰撞中的底夸克相关联的轻拟标量希格斯玻色子

使用ATLAS探测器在s = 13 $$ \ sqrt {s} = 13 $$ TeV下搜索希格斯玻色子的Zγ衰减模式和pp碰撞中的新的高质量共振

使用ATLAS探测器在s = 13 $$ \ sqrt {s} = 13 $$ TeV下在H→ZZ ∗→4ℓ衰减通道中测量希格斯玻色子耦合特性

在s = 13 $$ \ sqrt {s} = 13 $$ TeV的质子-质子碰撞中的H±→τ±ντ衰变通道中搜索带电的希格斯玻色子

使用ATLAS探测器在s = 8 $$ \ sqrt {s} = 8 $$ TeV的pp碰撞中使用矢量-玻色子融合搜索希格斯玻色子的无形衰减

在s = 8 $$ \ sqrt {s} = 8 $$ TeV的pp碰撞中搜索带电的希格斯玻色子

在具有希格斯或Z玻色子的事件中搜索直接的顶级副产生，并在与ATLAS探测器发生s = 13 $$ \ sqrt {s} = 13 $$ TeV pp碰撞的情况下丢失横向动量

在s = 7 $$ \ sqrt {s} = 7 $$和8 TeV的pp碰撞中在四轻子衰变通道中希格斯玻色子产生的希格斯玻色子的差分和积分基准横截面的测量

使用H→WW衰减测量在s = 8 $$ \ sqrt {s} = 8 $$ TeV pp碰撞中产生的希格斯玻色子的横向动量谱

用ATLAS探测器在s = 8 $$ \ sqrt {s} = 8 $$ TeV下测量希格斯玻色子衰变到WW ∗→eνμν的希格斯玻色子的胶子融合产生的基准微分截面。

在s = 8 $$ \ sqrt {s} = 8 $$ TeV的质子-质子碰撞中搜索具有单个上夸克的希格斯玻色子的相关生产

最新资源