τ 粒子へ崩壊するHiggs粒子の探索

津野 総司（高エネ研）

Martch.28th.2008

LHC Kenkyukai, S. Tsuno

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What’s ingredient ?
Focusing on new physics searches at LHC
Experimentalist :Limited proofs (σ, m, ratio, angles…)
Model independent searches (SUSY) Extension of SM measurements (Higgs)
Theorist :Many models ( (A…X,Y,Z)MSSM,GDM…)Interpretation of experimental data (New physics)
 Perturbative expansion (Higher order BSM/QCD)@MoriondEW2008

In term of Higgs searches,
How do experimentalists collaborate with theorist ?
SM, MSSM Higgs ( ττ) is a pretty tight theory.
 Many theoretical uncertainties in SM background prediction.
Martch.28th.2008

LHC Kenkyukai, S. Tsuno

discuss later
2

Contents
1) Briefly summarize current baseline analysis.
2) Topics toward “discovery”. (experimentalist)‐‐ SM DY Z ττ measurement. (MSSM, Z’ searches)‐‐ Jet Veto study.
‐‐ Missing pT and Forward jets.
‐‐ ELWK Z measurement.
3) Discussion toward “discovery” (theorist)‐‐ Analysis for “exclusion”.
‐‐ SM background prediction.

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Higgs粒子探索
Tevatronから間接的にlow mass Higgsが好まれる。
LHCでのSM Higgs生成素過程は、Gluon fusion

Vector Boson Fusion (VBF)

Gluon fusion

Gluon fusion ~ 10‐50pb (~10,000 evts at 1fb‐1)
VBF production ~ 2‐8pb (~2000 evts at 1fb‐1)

VBF production

VBFは２番目に大きな断面積
VBF productionは、前後方にジェットを生み出すのが特徴。

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Hττ analysis

質量再構成できる数少ないチャンネル。
H
 H
 H

γγ (σMH~1.7 GeV)ZZ 4l (σMH~2.3 GeV)ττ (σMH~9 GeV)

(H
 (H

bb (σMH~20 GeV) )μμ (σMH < natural width) )

解析はバックグラウンドとの戦い。
High bkg. rejection … VBF Higgs
Large cross section … MSSM H ττHigh Mass resolution … MSSM H μμ

1000
Higgs

Analysis for “Discovery”
Expecting ~100% uncertainty.
Target ~20 “signal” events(cut‐based analysis)
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VBF Hττ

ATLAS 2003

110GeV ~ 130GeVで最も感度が高い。
解析モード：VBF H

ττll‐channel : Br.~12%, Trig.Acc~ 9.1%(e), 9.9%(μ)
lh‐channel : Br.~46%, Trig.Acc~ 9.1%(e), 9.9%(μ)(High pT lepton, e pT>25GeV, μ pT>20GeV)
hh‐channel : Br.~42%, Trig.Acc~3.7%(Hadronic τ(pT>35GeV, MET>40GeV)
Jet veto

Forward jet
広範囲に渡って、
日本groupがcontribute
Tau ID: Likelihood, NN (KEK/東大)Forward jet : Efficiency/Calibration (東大)Missing Et : Resolution (寺師氏、next talk)
Trigger: Combined Trigger
Central Jet veto : 鈴木氏、next talk(b‐jet veto) : 廣瀬氏、next talk

解析に必要な事：τMET
trigger
hadronic
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MSSM Higgs Associated bbhττ/μμ
CMS Physics TDR 2006

Promising channel in large tanβAssociate production with b‐quark
τ,μ

τ,μ

τ,μ

τ,μ

Large coupling or narrow peak (experimental)(Hττ)(H μμ)CMS Physics TDR 2006

SN‐ATLAS‐2007‐063
10fb‐1significance forh μμ search

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Mass reconstruction

Asymmetric :due to mll < mcol

Collinear Approximation
H ττ mass reconstruction
τ decay products
τ1

Mis‐calibrated MET causes“mass shift”.
Z

H(120)

Collinear Mass

Understandingof MET is crucial.

missing pT
τ2Collinear Mass(GeV)

where,
Still asymmetric.
(MET mis‐calibration)

Jacobian(which makes asymmetric behavior.)

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Δ M (rec.‐truth) (GeV)8

Forward Jet tagging

topology requirement

Leading jet pT>40GeV
Jet pT>20GeV, |η|<4.8
Forward jet reco. εLeading jet ηOpposite hemisphere ( ηj1 x ηj2<0 )Δηjj>4.4, mjj>700GeV
no 3rd jet
Di‐jet separation η

cut

cut

Di‐jet mass
N‐jetscut

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Central Jet Veto (CJV)
no color connection between final state partons.
less hadron activity
in central

high density

less (color‐ string)density

Jet vetoqqqq

Forward jetτ

ISR parton???????

MET

optimization

trigger
hadronic

Big uncertainty in “Theory”.

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Acceptance (VBF H)

Unit fb

Signal MH=120GeV

Detector oriented
selection
control sample
Kinematics oriented
selection

4400

Remarks :Irreducible background : Zττ+jets
Reducible background : ttbar/W+jets etc. (ttbar is complicated object. )(5% ll‐mode, 45% real‐tau mode, 50% l+jets mode)

Kinematics‐oriented selection : factor ~4 for signal , ~400 for backgrounds.
S/B ~ 100
Overall rejection ~107‐8 rejection for reducible backgrounds.
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Summary of background (VBF H)
lh‐channel

Note : QCD Z/W+jets : Alpgen, k‐factor w.r.t. NNLO inclusive Z prod. is applied.
ELWK Z+jets : Sherpa , ttbar /di‐boson : MC@NLO
Signal (H120) : 0.61 fb
Irreducible Z+jets : 0.15 fb
Reducible backgrounds (ttbar/W+jets etc.) : < 0.08
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Background estimation ( I )real dataを使って、バックグラウンドを評価。
Shape and acceptance estimation by DATA.
control dataμmanipulated sample
e,μ ν

μ
jet
jet

replace μ to τνjethadronsjet1) Replace muon to tau.
2) Re‐run TAUOLA.
3) Re‐simulation again.
Missing Et is modeled by DATA.
Important for tail structure.
 Acceptance is also handled correctly.
Martch.28th.2008

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ID Iso active

Background estimation ( II )real dataを使って、バックグラウンドを評価。
Overall QCD fake estimation(at Control region)

Track multiplicity fit:
‐ count the track outside tau core region.
‐ fit the n‐tracks by likelihood.

e
tau
jet

(fit the ratio)‐ shape (pdf) are modeled by real‐data.
(ex. QCD jet shape by JET triggered data)
expected errorof “ratio of tau”
in the events
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Shape signal parameterization
Signal / irreducible Z+jets :Make use of Jacobian to handle “non‐gaussian tail”.
Divide three regions, then fix the fraction in each component.
Fit with three gaussian but fixed ratio and widths given by Jacobian.

mass shiftcorrection

Note : fitting parameters (m, σ) (2‐parameters)
Z+jetsMartch.28th.2008

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Higgs

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Shape QCD parameterization
Because of lack of MC statistics, we put 50% shape uncertainty.
So that all reducible background shape are categorized as “QCD”.
Parameterization :4 fitting parameters

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Likelihood fitting

Overall contrain

Likelihood function

Fit at once in “control region”.

Shape uncertainty is correctly handled.

Fit in signal region w/ Higgs event.
Fit background shape again.

Simultaneous fit unbined
Control Region
Signal Region(bkg. domain,(S:21 evts,
12,000 evts
B:70 evts
at 30 fb‐1 )‐1
at 30 fb )Large stat.

pull width
10k Pseudo‐experiment

Small stat.
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Signal sensitivity
LLR(mass fit)によるsignificance。
Background shape systematics : Z+jets: 10%
 QCD (ttbar/W+jets) : 50%

ATLAS CSC2008
Fixed mass w/ syst.

ATLAS CSC2008

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Systematic uncertainty
Dominant source of systematics:‐ Jet Energy Scale(20%)‐ Central Jet Veto (Theory) (30%)

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Summary
新しい事：

発見のためのBaseline Analysis の確立。
‐‐ 基本的にすべてFull simulation‐‐ Background estimationは、Data‐driven analysis‐‐ Mass Fitter の開発。
‐‐ 一つの解析チャンネルをグループとして解析。
（Author list 47人、12 グループ）



発見のためのロードマップの確立。
‐‐ 実験が始まるまでに必要な研究課題の把握。
‐‐ 実験開始から発見までに必要な研究課題の把握。
詳しくは、「LHCが切り開く物理」研究会で。

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Early physics to discovery

Martch.28th.2008

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Study planlh‐channel

Signal MH=120GeV

The first part of event selection
is exactly same as
Detector oriented
selection

SM DY Z ττ measurement
 MSSM H and Z’ searches

control sample

VBF specific study （並行して）
ELWK Z measurement
 Central Jet Veto Fitter, MET, jets etc…


Kinematics oriented
selection

基本的に全く同じ解析
SM Z

ττ

+ Jet kinematical cut
ELWK Z
Z’ / SUSYMSSM HSM VBF H
high mass bumpTime
100pb‐1
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1fb‐1

10fb‐1LHC Kenkyukai, S. Tsuno

30fb‐1
jet veto/MET etc.
22Z ττ(lh) measurement in early data
Soshi Tsuno and Junichi Tanaka
Univ. of Tokyo

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Brief analysis procedure:
1) Make n track distribution just before requiring
the 1‐ or 3‐ prong events.
2) QCD jets (fake) likely distributes higher track
multiplicity region.
3) Fit the signal and (modeled) background shapeby likelihood. (need more points and factorized bkg.)4) Then, obtain the overall number of signal andbackground.
Problem :

TauRec likelihood is optimized up to 3 tracks.
(The track multiplicity is part of likelihood variables.)

1P3P is the algorithm for few track objects.
(1‐prong and 3‐prong + a few addition)

After all, the track multiplicity is suppressed in the algorithm level.

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ID Iso active

Track re-counting method
Two Track Correlation Method :Count the tracks in wider region (0.2<ΔR<0.7).



To obtain the good separation to fake‐tau (jet),make use of the two track momentum fraction
weighted by the separation angle.
(If pTi / (pTτ trk ΔR) > const. , count it.)tau

underlying
activity
low pT

fake taujetsame order pT
QCD jets

Re‐calculate number of tracks
in tau.

# of tracks(w/ searching cone)

It also work further QCD rejection.
Martch.28th.2008# of tracks(in core region)

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Summary of tau identification
Reco+id efficiency:

Fake rate (TopoC4):

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Event selection

Electron reco+id efficiency:
Medium~75%

RefMET

Missing Et(GeV)
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Cut flow

Note that These numbers are used as the input of the fitting. (not a final number) The contribution form QCD jet is unknown.
Should be estimated by fit.
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Track multiplicity fit
Extended likelihood function:

Fitting parameters:
nexp : number of events expected by fit,rtau : event fraction of tau contribution wrt nexp ,rlep : event fraction of lepton contribution wrt nexp .
Observables:
Nobs : number of observed events.
(Nlep : number of estimated events from the another measurements.)
Probability function:
ftau : probability function of the track multiplicity for tau candidates,
flep : probability function of the track multiplicity for lepton candidates,
fjet : probability function of the track multiplicity for QCD jet candidates.
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Probability function
Cut‐based TauRec:

Cut‐based Tau1P3P:

Likelihood‐based TauRec:

Modeling : tau signal from MC lepton(electron) from DATA QCD jet from DATA

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Systematics(associated with the track multiplicity.)

Model uncertainty:
low pT jet v.s. high pT jet shape cut‐bias (before/after MET cut)(high pT jet becomes narrow.)

Note that we should consider more systematics.

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Pseudo-experiment
Purpose:Check our fitting procedure is correct or not.
 Estimate correct statistical error.


Make “pseudo‐DATA”.
Suppose : QCD jets contribute twice larger
from the estimation by the cut‐flow table.
Pseudo‐DATA is produced by the template histogramsof the track multiplicity distribution.
After 2000 pseudo‐experiments,
Outcome from fitter should be correct
statistical error.
Should be normal gaussian.
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Results
Measurement accuracy
as a function of luminosity.
Scenario (A) :No constrain in the fit.
Scenario (B) :Constrain in the lepton
normalization.
The absolute cross section
can be determined with~35% accuracy w/o constrain~10% accuracy w/ constrain
at 200 pb‐1 .
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Update of Track‐based Jet Veto Study for VBF
Higgs analysis

S. Tsuno, Univ. of Tokyo
Previous talk was given in July.19.2006 at Higgs Meeting.

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IntroductionNaïve jet veto with “Calorimeter‐based Jet Veto” (currently used)will have large systematics by the multiple interaction and pile‐up events.
 On the other hand, the signal sensitivity gets worse with higher thresholdof the jet energy for the veto.
 Basically, jet is weak to correlate between characteristics for the jet vetoin VBF process and multiple‐interactions.
The “calorimeter‐based jet” is not good quantity to avoid
the multiple/pile‐up events.
Rome sample

Different pile‐up sample, 0, 2.3, 4.6.
Jet Multiplicity
ET > 20 GeV

SumEt

Now, we cut
3rd jet contribution.

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Track-based Jet Veto
Using track information, we can specify where this track comes from.
Procedure:Count the number of tracks associated with “event vertex”.
 Apply the cut for this track numbers.


Signal(VBF) : less track multiplicity, Background : larger multiplicity.
τ,γ, any

Pile‐up events

jet
H
z
beam

beam
jet
τ,γ, any
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Jet vetoCentral Jet Veto : Less activity in the central regionτ

It is not necessary it can be a “jet”.

METHigh precision
Only charged particles
Calorimeter cluster
Many clusters
Quality cuts
Use timing info.

trigger
hadronic

Track
Many tracks
Quality cuts
Use vertex info.
grouping

grouping
Calorimeter jet
Traditional approach

Track jet
A bunch of tracks
pointing primary vertex

Worse energy
resolution
Martch.28th.2008

Forward jet

Pile‐up and theoreticaluncertainties are serious.

Maybe, energy flow‐like approach may be better(??)

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Event Vertex
Definition depends on the search channels.
For simplicity, this study (VBF H to ττ(lh))
uses “z position of triggered high pT
lepton”.
count

0.92cmlZmean: 0.0019
sigma: 0.236
0.46cmMartch.28th.2008

Not countτ
Then,
Counts the tracks associatedwith the event vertex withinΔz < 0.46 cm.

LHC Kenkyukai, S. Tsuno

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Relative η*

Track multiplicity

jetTracks associated with the event vertex.
Achieve similar performance with“calor‐based” Jet Veto w/o pile‐up effect.
Relative η*= ηtrks −η j1 +η j2
2Absolute ηdet

Absolute detector ηcut

cutΔη* < 1.0

Martch.28th.2008jetΔηdet < 2.4

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Luminosity dependenceInst.Luminosity∝ Number of vertices
Calorimeter Energy

TrackLess stat.

Can be controlled ±1~2 track level.

Martch.28th.2008

Scaling linearly.

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Trigger Study for di‐tau events

Soshi Tsuno (KEK)

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Trigger study for ll- and lh-channel

Trigger Hypothesis on AOD w/ several configuration.
Increase the pT threshold at Level.2.
(TrigL2CaloHypo for electron, Mufast/Mucomb for muon)Single lepton trigger efficiency :Signal : MH=120GeV w/ and w/o pileup are used.

Will make comparable
contribution in muon.

QCD di‐jets rate (Hz) is considered.
Real signal from Min.Bias events is excluded in the rate calculation,
J0‐J4 samples are used for di‐jets fake rate calculation.
Efficiency definition :ε TRIG =ε ID =

identified lepton w/ Trigger decision
identified lepton

identified lepton matched w/ truth (ΔR < 0.2)
truth lepton(event‐by‐event basis)Detector paper (rel.13)

Single electron efficiency :Electron ID : pT > 15GeV, Class:Medium (IsEM&0x3FF)
Cal.Isolation EtCone02/pT < 0.1
ID efficiency : ~70%
TRIG efficiency : ~90%
Overall efficiency for single electron event : ~65%
No sample dependence is observed at Trigger level.
ID efficiency

Overall efficiency

TRIG efficiency(e25i)

ID + e25i

Single muon efficiency :Muon ID : pT>10GeV, Staco : isCombined=1
Cal.Isolation EtCone02/pT < 0.1
ID efficiency : ~90%
TRIG efficiency : ~80%
Overall efficiency for single electron event : ~75%
No sample dependence is observed at Trigger level.
Overall efficiency

ID efficiency
TRIG efficiency(mu20i)ID + mu20i

Trigger acceptance and rate :Many “tau trigger” events are overlap with “electron trigger”.
Di‐lepton channel is “inclusive” for both e‐ and mu‐ triggers.
ideal
default

default
best
best

no isolation

L=1033cm‐2s‐1

Many things to do…
Missing pT, pileup study, forward jets, new fitter,mass reconstruction, fast‐simulation etc…

誰か手伝ってもらえませんか？

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Exclusion and Yukawa couplingHττは、Yukawa couplingを直接検証できる。
もし、このモードで、Higgsが見つからなければ、もしDATAがSM consistentであるとすると、

tanβ < 1
See‐saw ??

Lepton‐flavor violation:

exclusionで議論できるphysicsはありませんか？
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Central Jet Veto uncertainty

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At parton shower
まだまだ、怪しい。

何とかならないでしょうか？ 理論の方。

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BackupMartch.28th.2008

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Physics strategy
最初の２，３年で、Higgs粒子、SUSY粒子発見。
2008(summer)/09: first 10/14 TeV physics run, initial L ~1031cm‐2s‐1, Lint ~ 1fb‐1
Detector commissioning : alignment, in‐situ calibration / trigger menu
First SM measurements : W/Z/top & min.bias/jets & PDF ~100pb‐1
2009/10 : low luminosity run, instantaneous L ~2x1033cm‐2s‐1, Lint ~ 10fb‐1
First B rare decay searches,First searches : high mass DY(Z’), ADD, BH, SUSY ~1fb‐1
First Higgs discovery : H 4leptons, WW, γγ & MSSM Higgs
2010/11 : low luminosity run, inst.L ~2x1033cm‐2s‐1, Lint ~ 10fb‐1/yr
Light Higgs searches, SUSY measurements (model specific), …
2012~ : high luminosity run, inst.L ~2x1034cm‐2s‐1, L ~ 100fb‐1/yr
many, many …
toward SLHC…

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ATLAS detector

Tevatronにはない広い η の範囲をカバー。
Muon standalone tracking
 Inner tracker coverage |η|~2.7
 Calorimeter coverage |η|~5.0


23m

46m
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Analysis modelRun operation
Full Dress Rehearsal(FDR)

Control roommonitoring
Data quality

Trigger DATA

DAQ

Tier‐0 (CERN)
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trigger
FDR

Useranalysis

Grid throughout
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Demonstration : simplest Likelihood functionNaïve construction :e − ( ns + nb1 + nb 2 L) (ns + nb1 + nb 2 L) N obs N obs ns f s (mH | ν ) + nb1 f b1 (mH | v) + L
Lshape =∏i
N obs !
ns + nb1 + nb 2 + L
We would like to include “constraint term from the (independent)
external measurements”.
Following CDF top mass measurement,
exp
exp
exp
Lbkg = Gauss (nb1 , N bexp
,
σ
)
×
Gauss
(
n
,
N
,
σ
1
b1
b2
b2
b2 )L

The likelihood function is formed as

L = Lshape × Lbkg
The combined likelihood function is formed as

Lcombined = Llh −channel × Lll −channel × Lhh −channel
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Impact on the generator difference
Matthias Roder, Nov.21.2007

Predicts 41% systematics as the
maximum fluctuation.

CSC Full simulation

While predicts 29% difference as thesystematics.

Different event selection,
No collinear mass reconstruction,
AtlfastMartch.28th.2008

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Those difference have to beinvestigated again.
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Good Track definition
Follows tracking/tau group
recommendation.
Hits : Pxl SCT TRT
0.0<|η|<0.6 1
0.6<|η|<1.4 1
1.4<|η|<2.0 1
2.0<|η|1# of tracks

Pixel

SCT

TRT

5 20
5 10
5 20
5 ‐‐‐

Track pT > 1 GeV
No z0 , d0 , χ2 cut appliedat the moment.

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From Mario’s study,
Phys.Rev.D71(2005)112002

Jet Shape
Jet shape is one of the mostwell‐tuned variable in showeringMC.

The track multiplicity distribution
is a good variable for signal andbackground modeling.
(QCD Jets are modeled by DATA.)
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Data set

Includes filter efficiency.

signal1mm G4

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Tau identification
Three tau identifications:cut‐based TauRec ID (Tokyo2007), cut‐based Tau1P3P ID (discriCut==1),
 likelihood‐based TauRec ID … used as referenceCut‐based TauRec (Tokyo2007):

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