W-> Observation at ATLAS University of Pennsylvania HEP Seminar - - PowerPoint PPT Presentation

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W-> Observation at ATLAS University of Pennsylvania HEP Seminar - - PowerPoint PPT Presentation

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W-> Observation at ATLAS University of Pennsylvania HEP Seminar Tuesday, April 5, 2011 Sarah Demers Yale University 2 Sarah Demers, Yale Tuesday, April 5, University 2011 Outline SHORT ATLAS

slide-1
SLIDE 1

W-> τν Observation at ATLAS

University of Pennsylvania HEP Seminar Tuesday, April 5, 2011 Sarah Demers Yale University

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SLIDE 2

Outline

  • SHORT ATLAS Introduction
  • Why W-> τν ?

▫ Why taus?

  • Event Selection

▫ Trigger ▫ Offline

  • Observation
  • Future Plans

Tuesday, April 5, 2011

2

Sarah Demers, Yale University

Special Mention of the analyzers for the observation: Guilherme Nunes Hanninger (Bonn) Lidia Dell’Asta (INFN, Milano) Zofia Czyczula (Yale, now Oslo) Current analysis team includes many others! π±
 π±
 π±
 ν

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SLIDE 3

The ATLAS Detector at CERN’s LHC

  • Tracking detectors for momentum and

charge (and in the case of the TRT) particle ID

  • Sampling Calorimeters
  • Trigger and Data Acquisition

Tuesday, April 5, 2011

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Sarah Demers, Yale University

Pixels Silicon Microstrips TRT

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SLIDE 4

The ATLAS Detector at CERN’s LHC

  • Tracking detectors
  • Sampling Calorimeters for energy deposits

with fine granularity for shape discrimination

  • Trigger and Data Acquisition

Tuesday, April 5, 2011

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Sarah Demers, Yale University

LAr EM Tile HAD

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SLIDE 5

The ATLAS Detector at CERN’s LHC

Trigger and Data Acquisition capable of handling 40 MHz interaction rate and writing

  • ut events at a rate of O(100 Hz)

Tuesday, April 5, 2011

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Sarah Demers, Yale University

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SLIDE 6

Tuesday, April 5, 2011 Sarah Demers, Yale University

6 Muons

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SLIDE 7

Visible energy and momentum

π±
 π±
 π±
 3-prong tau decay signal
cone

 isola)on
annulus

 ν Energy carried away by neutrino

Tuesday, April 5, 2011

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Sarah Demers, Yale University

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SLIDE 8

Some tau-specific details

The ”taus” we identify are actually hadronic decay products. IP


Primary Vertex Secondary Vertex

Tuesday, April 5, 2011

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Sarah Demers, Yale University

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SLIDE 9

Outline

  • SHORT ATLAS Introduction
  • Why W-> τν

τν ?

▫ Why taus?

  • Event Selection

▫ Trigger ▫ Offline

  • Observation
  • Future Plans

Tuesday, April 5, 2011

9

Sarah Demers, Yale University

π±
 π±
 π±
 ν

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SLIDE 10

Why W-> τν ? Taus as Probes for “New” Physics

The tau, the heaviest lepton, couples strongly to the Higgs, and is key to a 5σ discovery in the important, but challenging, range of 115 – 125 GeV. This analysis will rely (at least partially) on tau triggers!

Tuesday, April 5, 2011

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Sarah Demers, Yale University

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SLIDE 11

Charged Higgs (SUSY)

Tuesday, April 5, 2011 Sarah Demers, Yale University

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SLIDE 12

Neutral Higgs (SUSY)

Tuesday, April 5, 2011 Sarah Demers, Yale University

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SLIDE 13

Life without the Higgs?

Tuesday, April 5, 2011 Sarah Demers, Yale University

13 0
 102
 104
 106
 108


νe
 νu
 νt
 µ
 τ
 e
 u
 d
 s
 c
 b
 t
 W
 Z
 g
 γ


Par)cle
Masses
(eV)
 Many Higgless theories include new particles with preferential couplings to the third generation, often motivated by trying to explain the very heavy top quark

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SLIDE 14

Understanding New Physics

  • All decay modes should be explored to

understand the new physics

▫ Not just electrons and muons!

  • Tau decays can carry information about the

polarization of the object that decays into them

▫ Left-handed tau -> neutrino prefers to go in direction of tau

Tuesday, April 5, 2011 Sarah Demers, Yale University

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SLIDE 15

Why W-> τν ? My Version of the ATLAS Tau program

  • Commission tau reco/ID and tau trigger

▫ comparisons between data and monte carlo

  • Measure efficiencies from the data with SM standard candles

▫ Z->ττ ▫ eventually ttbar?

  • Probe for New Physics signatures with taus

Tuesday, April 5, 2011

15

Sarah Demers, Yale University

In Fall, 2009: What if the luminosity profile increases slowly? Ws could provide the first evidence of taus! Can we make an observation (cross section measurement?) with a “simplified” trigger? Why NOT W->τν? Trigger and QCD background challenges Is the physics interesting?

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SLIDE 16

Outline

  • SHORT ATLAS Introduction
  • Why W-> τν ?

▫ Why taus?

  • Event Selection

▫ Trigger ▫ Offline

  • Observation
  • Future Plans

Tuesday, April 5, 2011

16

Sarah Demers, Yale University

π±
 π±
 π±
 ν

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SLIDE 17

Selecting the W-> τν events

  • Trigger
  • Separate the events from background offline
  • W->τν production cross section at 7 TeV at NNLO is

10.46 nb

▫ About ten times higher than the Z->ττ production ▫ Orders of magnitude lower than QCD di-jet production

Tuesday, April 5, 2011 Sarah Demers, Yale University

17 Relevant Analysis Cuts: Missing ET > 30 GeV tau pT between 20 and 60 GeV

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SLIDE 18

The trigger

  • There are only two objects in these events that

we can use to control the trigger rate:

▫ Missing transverse energy ▫ Tau transverse energy

  • Neither provide dramatic enough rate reduction,

so the two need to be used in combination

  • Keeping the rate low and measuring the trigger

efficiency at the end of the day is challenging!

▫ Particularly tricky: correlations between objects

Tuesday, April 5, 2011 Sarah Demers, Yale University

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SLIDE 19

Tuesday, April 5, 2011 Sarah Demers, Yale University

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Level 1 Calo Trigger

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SLIDE 20

Tuesday, April 5, 2011 Sarah Demers, Yale University

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Level 1 Hardware Trigger: 5 GeV Tau + 5 GeV Missing ET

EM Trigger Towers HAD Trigger Towers

+

Threshold Calculation = 2 Adjacent EM Trigger Towers 2x2 HAD Towers behind them 5 GeV L1 Tau Trigger

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SLIDE 21

Tuesday, April 5, 2011 Sarah Demers, Yale University

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Level 1 Hardware Trigger: 5 GeV Tau + 5 GeV Missing ET

20 GeV Threshold Efficiency from W->eν events 20 GeV Threshold Efficiency from W->µν events

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SLIDE 22

Level2 Trigger

  • Only access to small fraction of

data is available (a few percent) via L1 tau region of interest

  • Refined Missing ET

▫ Missing ET > 5 GeV

  • On the tau side, require only a

track

▫ Track in tau RoI > 6 GeV

Tuesday, April 5, 2011 Sarah Demers, Yale University

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SLIDE 23

Trigger Summary

Tuesday, April 5, 2011 Sarah Demers, Yale University

23 Object Cut L1 Missing ET 5 GeV L1 Tau 5 GeV L2 Missing ET 5 GeV L2 Tau (track) 6 GeV EF Missing ET 15 GeV EF Tau

  • Event Filter Missing ET

turn-on curves – very sharp! Trigger is >99% efficient with respect to offline cuts, as measured in MC

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SLIDE 24

Offline Selection

  • Good data quality and cleaning cuts including

▫ Primary vertex w/ 4 tracks pT > 100 MeV ▫ Jets cannot point toward Missing ET ▫ Objects cannot point toward overlap calo region (crack)

  • Missing ET > 30 GeV
  • 20 GeV > tau candidate > 60 GeV
  • Electron veto (loose electrons)
  • Muon veto (combined muons)
  • Missing ET significance > 6

Tuesday, April 5, 2011 Sarah Demers, Yale University

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SLIDE 25

Tau Identification

Tuesday, April 5, 2011 Sarah Demers, Yale University

25 Jets π±
 π±
 π±
 ν Taus

Sample
 cross
sec)on
X
 branching
ra)o
 #events/8
hours
 (1031)
 dijets


(pT
8
–
17
GeV)
 1.7
X
1010
pb
 5
X
109
 dijets


(pT
17
–
35
GeV)
 1.4
X
109
pb
 4
X
108
 dijets


(pT
35
–
70
GeV)
 9.3
X
107
pb
 3
X
107
 W
→τυ, τ→ had
 1.1
X
104
pb
 3200
 Z
→ττ, 1τ→ had
 1.55
X
103
pb
 450


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SLIDE 26

Tau ID: Early Days

  • “Double Seeded”: 10 GeV energy deposit in the

calorimeter matching 6 GeV track

  • “Tight” Cuts tuned for 30% efficiency for selecting

taus and 2% efficiency for selecting jets using:

▫ Track Radius: pT weighted ΔR of tracks associated with tau candidate ▫ Electromagnetic Radius: ET weighted ΔR of all cells in EM calorimeter associated with tau candidate ▫ Leading track momentum fraction: ratio between pT of lead track and total tau transverse momentum

Tuesday, April 5, 2011 Sarah Demers, Yale University

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X GeV Tau X GeV Jet

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SLIDE 27

Missing ET Significance

Tuesday, April 5, 2011 Sarah Demers, Yale University

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SLIDE 28

First W-> τν candidate at ATLAS May 24, 2010

Tuesday, April 5, 2011 Sarah Demers, Yale University

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SLIDE 29

Outline

  • SHORT ATLAS Introduction
  • Why W-> τν ?

▫ Why taus?

  • Event Selection

▫ Trigger ▫ Offline

  • Observation
  • Future Plans

Tuesday, April 5, 2011

29

Sarah Demers, Yale University

π±
 π±
 π±
 ν

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SLIDE 30

Timeline

  • W-τν Observation

approved by ATLAS Collaboration: Nov 2010

  • 546 nb-1
  • 78 events with excellent

signal/background ratio

Tuesday, April 5, 2011 Sarah Demers, Yale University

30 First W->τν candidate event May 24, 2010 Data Collection Period

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SLIDE 31

Summary

Tuesday, April 5, 2011 Sarah Demers, Yale University

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SLIDE 32

Estimating QCD Background from Data

Tuesday, April 5, 2011 Sarah Demers, Yale University

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SLIDE 33

(Correct for Non-QCD in Control Regions)

Tuesday, April 5, 2011 Sarah Demers, Yale University

33 Estimated 11 QCD events in signal region (A)

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SLIDE 34

Sanity Checks

Tuesday, April 5, 2011 Sarah Demers, Yale University

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SLIDE 35

Track Multiplicity and Tau Charge

Tuesday, April 5, 2011 Sarah Demers, Yale University

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SLIDE 36

Tau-Missing ET angle and Missing ET

Tuesday, April 5, 2011 Sarah Demers, Yale University

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SLIDE 37

Future Plans

  • W->τν Cross Section Measurement

▫ Yale Group Postdoc (Cristobal Cuenca Almenar) supporting trigger efficiency measurement

  • Exploit excellent signal to background in order to

understand our ability to use tau decays to access polarization information

Tuesday, April 5, 2011 Sarah Demers, Yale University

37 Toy Monte Carlo Study by Zofia

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SLIDE 38

Conclusions

  • The W->τν analysis provides a fantastic

benchmark channel for the trigger and a good test-bed for challenging physics studies

  • The success in this channel bodes well for the

future tau physics program at the LHC!

  • Thanks very much to HEP at Penn for the

invitation and to Jean O’Boyle for putting up with making my arrangements!

Tuesday, April 5, 2011 Sarah Demers, Yale University

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