Bologna
Istituto Nazionale
di Fisica Nucleare
Top quark couplings and
Polarization
Giuseppe Codispoti
for the CMS Collaboration
22/07/2014
G. Codispoti @ BEACH14, Birmingham - UK
The Top Quark in short
2
β€Ί The heaviest known fundamental particle:
– 𝑀𝑑 ~173.34 ± 0.76 𝐺𝑒𝑉
β€Ί Short lived: decays before hadronization
β€Ί study as a free quark
β€Ί G𝑁𝐿𝑂
= 1.42 𝐺𝑒𝑉
𝑑
1
βˆ’1
β€Ί t𝑑 = Ξ“ = ~10βˆ’24 𝑠 > Lβˆ’1
~10βˆ’23 𝑠
𝑄𝐢𝐷 ~(100𝑀𝑒𝑉)
𝑑
β€Ί Bare properties directly accessible: mass, charge, spin, polarization…
β€Ί
Their precise measurement provides a powerful test of the SM
β€Ί Decays (almost exclusively) through: 𝐭 β†’ 𝑾𝒃 ∝ |𝑽𝒕𝒃 |𝟐
β€Ί Large mass implies large coupling to Higgs:
β€Ί l𝑑
β€Ί
2π‘šπ‘‘
~1
𝑣
special role in EWSB?
β€Ί Special role in new physics models
β€Ί Main background for SM processes, (e.g. especially Higgs ) and beyond SM
22/07/2014
G. Codispoti @ BEACH14, Birmingham - UK
Production and decay
3
single top production
t-channel
87.2 𝑝𝑏 @ 8 𝑇𝑒𝑉
65.9 𝑝𝑏 @ 7 𝑇𝑒𝑉
2.08 𝑝𝑏 @ 1.96 𝑇𝑒𝑉
𝑑𝑑 pair production
249 𝑝𝑏 @ 8 𝑇𝑒𝑉
172 𝑝𝑏 @ 7 𝑇𝑒𝑉
7.08 𝑝𝑏 @ 1.96 𝑇𝑒𝑉
β€Ί Top Decay
– Hadronic: 3 jets (1 b-jet)
– Lepton + jets : b-jet, lepton, πΈπ‘‡π‘šπ‘–π‘ π‘ 
β€Ί => 𝑑𝑑 final states
–
–
–
–
Hadronic (45.7%): 6 jets
Lepton+jets (34.5%) : 1 lepton, 3 jets, πΈπ‘‡π‘šπ‘–π‘ π‘ 
Dilepton (6.5%): 2 leptons, 2 jets, πΈπ‘‡π‘šπ‘–π‘ π‘ 
Also relevant the transverse mass of the reconstructed W
tW-channel
22.2 𝑝𝑏 @ 8 𝑇𝑒𝑉
15.6 𝑝𝑏 @ 7 𝑇𝑒𝑉
0.22 𝑝𝑏 @ 1.96 𝑇𝑒𝑉
s-channel
5.55 𝑝𝑏@ 8 𝑇𝑒𝑉
4.56 𝑝𝑏 @ 7 𝑇𝑒𝑉
1.04 𝑝𝑏@ 1.96 𝑇𝑒𝑉
β€Ί Main Backgrounds:
–
–
–
–
–
QCD multijet
Boson+jets (V+jets)
Di-Bosons (VV)
Single-t for 𝑑𝑑 pairs
𝑑𝑑 pairs for single-t
22/07/2014
G. Codispoti @ BEACH14, Birmingham - UK
In this talk
4
β€Ί CMS recent measurements:
– |𝑉𝑑𝑏 | measurements:
β€Ί 𝑅 = (𝑑 β†’ π‘Šπ‘)/(𝑑 β†’ π‘Šπ‘ž)
β€Ί in 𝑑-channel
β€Ί in π‘‘π‘Š associated production
– 𝑑𝑑 and W/Z/g associated production
– Properties
β€Ί spin correlation in 𝑑𝑑
β€Ί polarization in 𝑑𝑑 and single top
β€Ί W helicity in 𝑑𝑑
22/07/2014
G. Codispoti @ BEACH14, Birmingham - UK
𝑅 = (𝑑 β†’ π‘Šπ‘)/(𝑑 β†’ π‘Šπ‘ž) in dilepton channel
5
+0.000021
β€Ί Top dominant decay W+b: |Vtb|= 0.999146βˆ’0.000046
CMS PAS TOP-12-035
PLB 736 (2014) 33
– Tension in the most precise measurement in D0
β€Ί
R = 0.90±0.04 (stat.+syst.) [Phys.Rev.Lett. 107 (2011) 121802]
β€Ί Likelihood fit on jet multiplicity accounting for
– Fraction of 𝑑𝑑 signal and single-top
– Fraction of event with correct jet assignment
– b-tag efficiency and mis-identification
β€Ί
𝑽𝒕𝒃 calculated assuming unitarity of the CKM matrix and
its three-generation structure
β€Ί Main systematics:
– 𝑑-channel cross
section
– B tag efficiency
R=1.023+𝟎.πŸŽπŸ‘πŸ”
βˆ’πŸŽ.πŸŽπŸ‘πŸ’ (𝒔𝒕𝒂𝒕. +π’”π’šπ’”π’•. )
𝑽𝒕𝒃 = 𝟏. 𝟎𝟏𝟏+𝟎.πŸŽπŸπŸ–
βˆ’πŸŽ.πŸŽπŸπŸ• (𝒔𝒕𝒂𝒕. +π’”π’šπ’”π’•. )
𝑅 ≀ 1 β‡’ 𝑹 > 𝟎. πŸ—πŸ’πŸ“ at πŸ—πŸ“% π‘ͺ𝑳
𝑽𝒕𝒃 > 𝟎. πŸ—πŸ•πŸ @ πŸ—πŸ“% π‘ͺ𝑳
|𝑉𝑑𝑏 | measurement in t-channel
22/07/2014
G. Codispoti @ BEACH14, Birmingham - UK
β€Ί lepton+jets final state
6
–
–
–
–
CMS PAS TOP-12-038
1 isolated lepton
JHEP 06 (2014) 090
1 light forward jet
1 central b-jet (second b-jet escapes detection)
πΈπ‘‡π‘šπ‘–π‘ π‘ 
β€Ί Template analysis |πœ‚π‘— β€² |
– fit to the πœ‚ of the recoil jet in the signal region
130 < π‘šπ‘‘ < 220 𝐺𝑒𝑉
– W/Z+jets from sidebands
– 𝑑𝑑 background shapes are estimated from 3-jets data
– QCD from a control sample with inverted isolation cut
πˆπ’•βˆ’π’„π’‰ = πŸ–πŸ‘. πŸ” ± 𝟐. πŸ‘ 𝒔𝒕𝒂𝒕. ± πŸ•. πŸ’ π’”π’šπ’”π’•.
𝑁𝑁𝐿𝑂
[ πœŽπ‘‘π‘Š
= 87.2+2.8
βˆ’1.0 π‘ π‘π‘Žπ‘™π‘’
+2.0
βˆ’2.2 (𝑃𝐷𝐹)𝑝𝑏]
Combination 7+8 TeV for t-channel assuming 𝑉𝑑𝑑 , 𝑉𝑑𝑠 β‰ͺ 𝑉𝑑𝑏 β‰ˆ 1
– |𝑽𝒕𝒃 |=
πˆπ’•βˆ’π’„π’‰
πˆπ’•π’‰
π’•βˆ’π’„π’‰
= 𝟎. πŸ—πŸ—πŸ– ± 𝟎. πŸŽπŸ‘πŸ– 𝒆𝒙𝒑. ± 𝟎. πŸŽπŸπŸ”(𝒕𝒉. )
– 𝑽𝒕𝒃 > 𝟎. πŸ—πŸ @ πŸ—πŸ“% π‘ͺ𝑳 after 𝑉𝑑𝑏 ≀ 1 π‘Žπ‘›π‘‘ |𝑓𝐿𝑣 |=1
Single top and W associated production (π‘‘π‘Š)
G. Codispoti @ BEACH14, Birmingham - UK
β€Ί 2 leptons 1 b-jet signal (β€˜1j1tag’)
CMS PAS TOP-12-040
Phys. Rev. Lett. 112 (2014) 231802
– Excluded resonant single-top/𝑑𝑑 NLO diagrams
β€Ί β€˜2jet1tag’ and β€˜2jets2tags’ events used as 𝑑𝑑 control region
– simultaneously constrains the 𝑑𝑑 normalization and the b-tagging efficiency
in situ
β€Ί DY+ jets corrected using Z/g* +jets enriched
– πΈπ‘‡π‘šπ‘–π‘ π‘  from Z/g* +jets enriched region |π‘šπ‘™π‘™ βˆ’ π‘šπ‘§ | < 20𝐺𝑒𝑉
β€Ί Fit of a discriminant built from kinematic quantities combined
with a multivariate technique
– cross-checks using event-counting and a kinematic variable fit
πˆπ’•π‘Ύ = πŸπŸ‘. πŸ’+πŸ“.πŸ“
βˆ’πŸ“.πŸ’ 𝒑𝒃, 𝐬𝐒𝐠. = πŸ”. 𝟏𝝈
22/07/2014
[
7
𝑁𝑁𝐿𝑂
πœŽπ‘‘π‘Š
Signal
= 22.2 ± 1.5𝑝𝑏]
π‘‘β„Ž
Assuming 𝑉𝑑𝑏 = 1 for πœŽπ‘‘π‘Š
calculation:
– 𝑽𝒕𝒃 =
πˆπ’•π‘Ύ
πˆπ’•π’‰
𝒕𝑾
= 𝟏. πŸŽπŸŽπŸ‘ ± 𝟎. 𝟏𝟐 𝒆𝒙𝒑. ± 𝟎. πŸŽπŸ’(𝒕𝒉. )
– 𝑽𝒕𝒃 > 𝟎. πŸ•πŸ– @ πŸ—πŸ“% π‘ͺ𝑳
22/07/2014
G. Codispoti @ BEACH14, Birmingham - UK
Summary of |𝑉𝑑𝑏 | measurements
8
π‘‘π‘Š
production
𝑑 βˆ’ π‘β„Žπ‘Žπ‘›π‘›π‘’π‘™
cross section
𝑅=
(𝑑 β†’ π‘Šπ‘)
(𝑑 β†’ π‘Šπ‘ž)
22/07/2014
G. Codispoti @ BEACH14, Birmingham - UK
𝑑𝑑 and W/Z boson associated production
9
β€Ί π‘‘π‘‘π‘Š : same-sign dileptons
(lepton+jets only top decay)
β€Ί 𝑑𝑑𝑍: 3-leptons and 4-leptons
+21
β€Ί πœŽπ‘‘π‘πΏπ‘‚
π‘‘π‘Š = 202βˆ’23 𝑓𝑏
+22
β€Ί πœŽπ‘‘π‘πΏπ‘‚
𝑑𝑍 = 197βˆ’25 𝑓𝑏
CMS PAS TOP-12-036
22/07/2014
G. Codispoti @ BEACH14, Birmingham - UK
𝑑𝑑 and photon associated production in m+jets
10
CMS PAS TOP-13-011
β€Ί m+jets channel
β€Ί High 𝑝𝑇 photon (> 20𝐺𝑒𝑉)
β€Ί Template fit on the hadronic isolation
– main source of mis-identified photons is hadronic
β€Ί Signal from MC
– Normalization is the
dominant systematic
β€Ί Background from
sidebands
– Modeling is second
source of systematic
Measured ∢ 𝑅 =
πœŽπ‘‘π‘‘π›Ύ
πœŽπ‘‘π‘‘
Assuming πœŽπ‘‘πΆπ‘€π‘†
= 227 ± 15 𝑝𝑏
𝑑
πˆπ’•π’•πœΈ = 𝟐. πŸ’ ± 𝟎. 𝟐 𝒔𝒕𝒂𝒕. ± 𝟎. πŸ” π’”π’šπ’”π’•. 𝒑𝒃
πœŽπ‘‘πΏπ‘‚
𝑑𝛾 = 1.8 ± 0.5𝑝𝑏
22/07/2014
G. Codispoti @ BEACH14, Birmingham - UK
Polarization and spin correlation in dilepton
11
β€Ί SM predicts small polarization and ~100% spin correlation between top and anti-top
β€Ί
1 π‘‘πœŽ
𝜎 𝑑 cos πœƒπ‘–
1
2
= (1 + 𝛼𝑖 cos πœƒπ‘– ),
CMS PAS TOP-13-003
Phys. Rev. Lett. 112 (2014) 182001
β€Ί 𝛼𝑖 is the spin analyzing power
β€Ί
1
𝑑2 𝜎
𝜎 𝑑 cos πœƒ+ 𝑑 cos πœƒβˆ’
1
4
= (1 + 𝛼+ 𝑃+ cos πœƒ+ + π›Όβˆ’ π‘ƒβˆ’ cos πœƒβˆ’ + 𝐴𝛼+ π›Όβˆ’ cos πœƒ+ cos πœƒβˆ’ )
β€Ί Studied through angular asymmetry variables
– Angular asymmetry variables unfolded to the parton level
– Backgrounds from MC, validated using data
– Top 𝑝𝑇 modeling is the major source of uncertainties
β€Ί Polarization as a function of the helicity angles:
– Requires full event reconstruction
– 𝑷 = πŸπ‘¨π‘· ≑ 2 βˆ™
𝑁 cos πœƒπ‘™βˆ— >0 βˆ’π‘ cos πœƒπ‘™βˆ— <0
πœƒπ‘™βˆ—
𝑁 cos πœƒπ‘™βˆ— >0 +𝑁 cos πœƒπ‘™βˆ— <0
β€Ί 𝑨𝑷 = 𝟎. πŸŽπŸŽπŸ“ ± 𝟎. πŸŽπŸπŸ‘(𝒔𝒕𝒂𝒕. ) ± 𝟎. πŸŽπŸπŸ’(π’”π’šπ’”π’•. ) ± 𝟎. πŸŽπŸŽπŸ–(𝒑𝑻 π’“π’˜)
Spin correlation in dilepton
22/07/2014
G. Codispoti @ BEACH14, Birmingham - UK
β€Ί As a function of pure leptons angular variables:
12
– π΄βˆ†πœ™ =
𝑁 βˆ†πœ™π‘™βˆ—+ π‘™βˆ’ >πœ‹ 2 βˆ’π‘ βˆ†πœ™π‘™βˆ—+ π‘™βˆ’ <πœ‹ 2
𝑁 βˆ†πœ™π‘™βˆ—+ π‘™βˆ’ >πœ‹ 2 +𝑁 βˆ†πœ™π‘™βˆ—+ π‘™βˆ’ <πœ‹ 2
π‘¨βˆ†π“ = 𝟎. πŸπŸπŸ‘ ± 𝟎. 𝟎𝟏𝟎(𝒔𝒕𝒂𝒕. ) ± 𝟎. πŸŽπŸŽπŸ”(π’”π’šπ’”π’•. ) ± 𝟎. 𝟎𝟏𝟐(𝒑𝑻 π’“π’˜)
+𝟎.πŸŽπŸπŸ’
𝑨𝒄𝒐𝒓𝒓.
βˆ†π“ = 𝟎. πŸπŸπŸ“βˆ’πŸŽ.πŸŽπŸπŸ”
NLO
+0.013
𝐴𝑒𝑛𝑐.
βˆ†πœ™ = 0.210βˆ’0.008
πœƒπ‘™βˆ—+
β€Ί As a function of the helicity angles:
β€Ί requires full event recontruction
𝑁 𝑐1 𝑐2 >0 βˆ’π‘ 𝑐1 𝑐2 <0
𝑁 𝑐1 𝑐2 >0 +𝑁 𝑐1 𝑐2 <0
cos πœƒπ‘™βˆ—+ π‘Žπ‘›π‘‘ 𝑐2 = cos
β€Ί 𝐴𝑐1 𝑐2 =
β€Ί 𝑐1 =
βˆ†πœ™
πœƒπ‘™βˆ—βˆ’
π‘¨π’„πŸπ’„πŸ = βˆ’πŸŽ. 𝟎𝟐𝟏 ± 𝟎. πŸŽπŸπŸ‘(𝒔𝒕𝒂𝒕. ) ± 𝟎. πŸŽπŸπŸ“(π’”π’šπ’”π’•. ) ± 𝟎. 𝟎𝟏𝟎(𝒑𝑻 π’“π’˜)
π΄π‘π‘œπ‘Ÿπ‘Ÿ.
𝑐1 𝑐2 = βˆ’0.078 ± 0.006
NLO
𝐴𝑒𝑛𝑐.
𝑐1 𝑐2 = 0
Top Polarization in single top
22/07/2014
G. Codispoti @ BEACH14, Birmingham - UK
β€Ί
13
1 𝑑σ
𝜎 𝑑 cos πœƒπ‘™
=
1
2
CMS PAS TOP-13-001
1
2
1 + 𝑃𝑑 𝛼𝑙 cos πœƒπ‘™ ≑ + 𝐴𝑙 cos πœƒπ‘™
– πœΆπ’ : analyzing power of the angular variable
– πœ½π’ : angle between charged lepton and untagged jet
– Calculated in the top R.F. β‡’ πœ½βˆ—π’
1
2
β€Ί 𝐴𝑙 ≑ βˆ™ 𝑃𝑑 βˆ™ 𝛼𝑙 =
𝑁 ↑ βˆ’π‘ ↓
𝑁 ↑ +𝑁 ↓
the light-quark recoiling against the
top-quark tend to have a direction
parallel to the spin direction of the top
β€Ί QCD orthogonal sample
– Lepton isolation cut reverted
β€Ί Other backgrounds from MC
– W+jets reweighted w.r.t flavor content
– 𝑑𝑑 validated in sample with 3 jets and 1 or 2 b-tags
β€Ί Signal, other-top and VV/V+jets relative contributions are
extracted through a likelihood fit on BDT discriminant
β€Ί 𝑒 + πœ‡ combined results:
β€Ί 𝑨𝒍 = 𝟎. πŸ’πŸ ± 𝟎. πŸŽπŸ” 𝒔𝒕𝒂𝒕. ± 𝟎. πŸπŸ” π’”π’šπ’”π’•. = 𝟎. πŸ’πŸ ± 𝟎. πŸπŸ•
β€Ί 𝛼𝑙 = 1 β‡’ 𝑷𝒕 = 𝟎. πŸ–πŸ ± 𝟎. 𝟏𝟐 𝒔𝒕𝒂𝒕. ± 𝟎. πŸ‘πŸ π’”π’šπ’”π’•. = 𝟎. πŸ–πŸ ± 𝟎. πŸ‘πŸ’
W helicity fractions in top decays
22/07/2014
G. Codispoti @ BEACH14, Birmingham - UK
β€Ί Directly related to V-A electroweak structure
14
β€Ί High sensitivity to BSM physics
Gπ‘₯
β€Ί 𝐹π‘₯ =
β‡’ 𝐹𝐿 +𝐹𝑅 + 𝐹0 = 1
G
direction of the charged lepton
in the W rest frame w.r.t
the W direction in the top rest frame
β€Ί
𝟏
π’…πˆ
𝝈 𝒅 𝒄𝒐𝒔 ΞΈβˆ—
πŸ‘
πŸ’
πŸ‘
πŸ–
πŸ‘
πŸ–
= (𝟏 βˆ’ π’„π’π’”πŸ ΞΈβˆ— )π‘­πŸŽ + (𝟏 βˆ’ 𝒄𝒐𝒔 ΞΈβˆ— ) 𝟐 𝑭𝑳 + (𝟏 + 𝒄𝒐𝒔 ΞΈβˆ— ) 𝟐 𝑭𝑹
W-helicity lepton+jets results
JHEP 10 (2013) 167
CMS PAS TOP-13-008
G. Codispoti @ BEACH14, Birmingham - UK
β€Ί Poisson binned likelihood maximization
– Reweight based on observed and expected events in bins of
π‘π‘œπ‘  ΞΈβˆ—
– accounts for simulated detector acceptance and efficiencies
β€Ί Major background from di-leptons
β€Ί Other backgrounds reduced through b-tag and π‘š 𝑇
–
Data driven validations provided
22/07/2014
8 TeV πœ‡ βˆ’ only, leptonic branch
15
β€Ί F0= 0.659±0.015(𝒔𝒕𝒂𝒕) ± 0.0023(π’”π’šπ’”π’•)
β€Ί 7 TeV, 𝑒 + πœ‡
β€Ί FL= 0.350±0.010(𝒔𝒕𝒂𝒕) ± 𝟎. πŸŽπŸπŸ’(π’”π’šπ’”π’•)
β€Ί Hadronic+leptonic
β€Ί FR= -0.0πŸŽπŸ— ± 0.0πŸŽπŸ”(𝒔𝒕𝒂𝒕) ± 𝟎. 𝟎𝟐𝟎(π’”π’šπ’”π’•)
22/07/2014
G. Codispoti @ BEACH14, Birmingham - UK
Conclusions
16
β€Ί CMS has a wide range of measurements of the top quark properties
– In the 𝒕𝒕 strong production
β€Ί Presented : 𝑅 and |𝑉𝑑𝑏 |, 𝑑𝑑 + W Z /Ξ³ production, polarization and spin correlation, π‘Š-helicity
– In the single top electroweak production
β€Ί Presented : |𝑉𝑑𝑏 | in 𝑑-channel and π‘‘π‘Š production, polarization
β€Ί They provide thorough tests to the Standard Model
– high sensitivity to new physics through variations from SM predictions
β€Ί All the measurements show good agreement with the Standard Model,
both with πŸ• 𝑻𝒆𝑽 and πŸ– 𝑻𝒆𝑽 collisions data
β€Ί CMS is preparing for LHC-Run2: new results will come!
Bologna
Istituto Nazionale
di Fisica Nucleare
G. Codispoti for the CMS Collaboration
BEACH14, Birmingham – UK
22/07/2014
BACKUP SLIDES
Bologna
Istituto Nazionale
di Fisica Nucleare
18
G. Codispoti for the CMS Collaboration
BEACH14, Birmingham – UK
22/07/2014
22/07/2014
G. Codispoti @ BEACH14, Birmingham - UK
B-jet multiplicity in tW analysis
19
π‘‘π‘Š production additional information
22/07/2014
G. Codispoti @ BEACH14, Birmingham - UK
β€Ί Signature:
20
– 2 opposite charge isolated
leptons
– b-jet from top + light jet
NLO
β€Ί NLO diagrams mixes single
top and 𝑑𝑑
– Diagram removal approach:
resonant NLO diagrams are
not considered signal
LO
G. Codispoti @ BEACH14, Birmingham - UK
22/07/2014
G. Codispoti @ BEACH14, Birmingham - UK
W-helicity in single top, m+jets
21
CMS PAS TOP-12-020
β€Ί Electroweak process involving Wtb vertex
– alternative to 𝑑𝑑 strong production (qq, gg)
– sensitive to non-SM couplings
β€Ί Fractions obtained from likelihoods with reweighted signal
– Normalization of W+jets also free parameter of the fit, shape
validated using data from control region with no b-tag request
β€Ί F0= 0.7πŸπŸ‘ ± 0.114(𝒔𝒕𝒂𝒕) ± 0.023(π’”π’šπ’”π’•)
β€Ί FL= 0.293±0.0πŸ”πŸ—(𝒔𝒕𝒂𝒕) ± 𝟎. πŸŽπŸ‘πŸŽ(π’”π’šπ’”π’•)
β€Ί FR= -0.0πŸŽπŸ” ± 0.0πŸ“πŸ•(𝒔𝒕𝒂𝒕) ± 𝟎. πŸŽπŸπŸ•(π’”π’šπ’”π’•)
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