# Presentation: 181180

## LHC2003 Symposium
FNAL May 2003

Bryan Caron
University of Alberta
caron@phys.ualberta.ca
(on behalf of the ATLAS Collaboration)

- FNAL May 2003
- Bryan Caron
- University of Alberta
- _[caron@phys.ualberta.ca](mailto:caron@phys.ualberta.ca)_
- (on behalf of the ATLAS Collaboration)

- Hadronic Calorimetry and Jet//ETmiss Performance in ATLAS

## Outline

- ATLAS Calorimetry
- Jets
- Algorithms, energy scale and calibration
- Forward jet tagging
- -jets
- Reconstruction efficiency
- jet rejection
- ETmiss
- Resolution and tails
- Summary

-     Signatures for new physics at
- the LHC (SUSY, compositeness, ...)

- B. Caron

- LHC2003 Symposium

## ATLAS Experiment

- B. Caron

- LHC2003 Symposium

## ATLAS Calorimetry

- Tile Calorimeters

- Electromagnetic Liquid Argon
-  Calorimeters

- Hadronic Liquid Argon EndCap Calorimeters

- Forward Liquid Argon Calorimeters

- η=1.475

- η=1.8

- η=3.2

- B. Caron

- LHC2003 Symposium

## Hadronic Tile Calorimeter

- Fe absorber with scintillator tile readout with                    Δη x Δφ = 0.1 x 0.1, 3 longitudinal samplings, || < 1.7

- B. Caron

- LHC2003 Symposium

## Hadronic LAr Endcap Calorimeter

- Cu absorbers in a parallel plate geometry, Δη x Δφ = 0.1 x 0.1 (1.5<|η|<2.5), Δη x Δφ = 0.2 x 0.2 (2.5<|η|<3.2),     4 samplings

- B. Caron

- LHC2003 Symposium

## Hadronic LAr Forward Calorimeter

- electromagnetic module FCal1 (Cu absorber), two hadronic modules FCal2 and FCal3 (W absorber)
- the modules are 28/91/89 radiation lengths and 2.7/3.7/3.6 hadronic interaction lengths deep (FCal1/2/3)
- Principle coverage is 3.1<|η|<4.9, with cells of       Δη x Δφ ≈ 0.2 x 0.2                  – but non-projective
- FCal fully integrated into rest of the calorimetry, minimizing cracks – Premium for physics

- FCal1

- FCal2

- FCal3

- Cryostat walls
- (warm/cold)

- to interaction
- vertex

- Hadronic EndCap
- (2 wheels)

- Electromagnetic
- EndCap

- p from LHC

- Cu Shielding

- B. Caron

- LHC2003 Symposium

## Jet Reconstruction

**Physics effects**
- Fragmentation
- Initial and final state radiation
- Underlying event
- Minimum bias events
**Detector performance effects**
- Non-linear response
- Magnetic field
- Dead material and cracks between calorimeters
- Longitudinal leakage
- Lateral shower size and granularity
- Finite cone size (out-of-cone loss)
- Electronic noise

**Design Goals**
- Energy resolution                             (in |< 3)
- Non-linearity < 3%
- Jet tagging efficiency  > 90%
- Absolute E scale 1% (Jets)
-                                 for         ET > 100 GeV (in 3 < || < 5)
- Granularity:  x  = 0.1 x 0.1 (in || < 3) adapted to hadron shower size

- B. Caron

- LHC2003 Symposium

## Jet Algorithms

**Cone Algorithm**
- Highest ET tower for jet seed + cone
- Iteration of cone direction, jet overlap, energy sharing, merging
**K****T**** Clustering Algorithm**
- Pairs closest calorimeter towers, merging all particles into jets
- Cone size influence on reconstructed jet energy and resolution

- ******R=0.4**
******R=0.7**
******R=1.5**

|  | a (%GeV1/2) | b (%) |
| --- | --- | --- |
| Full Calo | 48.2 ± 0.9 | 1.8 ± 0.1 |
| R=0.7 | 52.3 ± 1.1 | 1.7 ± 1.1 |
| R=0.4 | 62.4 ± 1.4 | 1.7 ± 0.2 |

- B. Caron

- LHC2003 Symposium

## Dead Material and Crack Regions

- Transition Regions
- Barrel to endcap
- Vertical crack at ||=1
- End of coil and corners of cryostat walls at || ~1.45
- Hadronic Endcap and Forward calorimeter
- || ~ 3.2
- ITC + scintillator in the crack region to recover the E loss
- Calibration procedure includes weights for each calorimeter compartment with correction terms for energy loss in dead material

- B. Caron

- LHC2003 Symposium

## Electronic Noise and Pile-up

- R=0.4
- ⋆ e-noise +
-     pileup
- □ e-noise

- ● (○)  no e-noise
- ■(□) e-noise
- ▲ (△) 2.5 cut
- R=0.7 (0.4)

- ||=0.3

- ||=0.3

| Cell Cut | a (%GeV1/2) | b (%) | c (GeV) |
| --- | --- | --- | --- |
| No cut
R=0.7 | 52.3 | 1.7 | 3.0 ± 0.1 |
| 2.5
R=0.7 | 52.3 | 1.7 | 2.0 ± 0.1 |
| No cut
R=0.4 | 62.4 | 1.7 | 2.0 ± 0.1 |
| 2.5
R=0.4 | 62.4 | 1.7 | 1.7 ± 0.2 |

| a (%GeV1/2) | b (%) | c (GeV) |
| --- | --- | --- |
| 62.4 fixed | 1.7 fixed | 4.7 ± 0.2 |
| 81.3 ± 2.9 | 1.7 fixed | 3.9 ± 0.3 |

**Pile-up + Electronic Noise**

**Electronic Noise**

**Jet Energy **
**Resolution**

- B. Caron

- LHC2003 Symposium

**Notes:**
Electronic Noise and Pile-up

Electronic Noise
Reference: Section 9.1.1 Figure 9-9

Pile-up (minimum bias)
Reference: Section 9.1.1 Figure 9-10
Q: what is the level of pile-up assumed? Low L? High L? [find details]

## Offline Jet Energy Calibration

- Sampling Method
- Weights applied to different calorimeter compartments
- Enlarged cone size yields increased electronic noise
- H1 Method
- Weights applied directly                   to cell energies
- Better resolution and               residual nonlinearities

- Back-to-back dijet events

- ||=0.3

| Parameter | Sampling Method |  | H1 Method |  |
| --- | --- | --- | --- | --- |
|  | R=0.4 | R=0.7 | R=0.4 | R=0.7 |
| a (%GeV1/2) | 66.0 ± 1.5 | 61.2 ± 1.3 | 53.9 ± 1.3 | 51.5 ± 1.1 |
| b (%) | 1.2 ± 0.3 | 1.4 ± 0.2 | 1.3 ± 0.2 | 2.5 ± 0.2 |
| 2 prob. (%) | 1.6 | 0.8 | 27.3 | 66.7 |

- B. Caron

- LHC2003 Symposium

## ATLAS Test Beam Results

- Combined Test: EM LAr  and Hadronic Tile Calorimeter
-  Energy Resolution
- e/ ratio
- Degree of non-compensation *e/h*

|  | a (%GeV1/2) | b (%) | c (GeV) |
| --- | --- | --- | --- |
| Data | 69.8 ± 0.2 | 3.3 ± 0.2 | 1.8± 0.1 |
| G-CALOR | 61.7 ± 0.1 | 2.9 ± 0.3 | 1.5 fixed |

**e/h=1.35****±****0.04 (94)**

**e/h=1.37±0.01 (96)**

**e/h=1.31±0.01 (G-CALOR)**

- B. Caron

- LHC2003 Symposium

## ATLAS Test Beam Results

- Hadronic Endcap Calorimeter

****** ****Energy Resolution**

**e/********Ratio**

**uncorrected**

** ****corrected**
**for E leakage**

- B. Caron

- LHC2003 Symposium

## ATLAS Test Beam Results

**Hadronic Tile Calorimeter:**** Response to ******** (100 GeV) at ******** = 1.3**
- Clean signal above electronic noise (~40 MeV) in outermost compartment
- Important at high Luminosity where physics ’s may overlap other particles; minimum bias events deposit non-neglible amounts of E in innermost calorimeter layers

**Total Deposited E**

**E in 3****rd**** Compartment**

- Electronic
-   Noise

**E********=100 GeV**

**E********=100 GeV**

- B. Caron

- LHC2003 Symposium

## Jet Energy Scale and Calibration

- Goal of ~1% precision on the absolute jet energy scale
- Difficult to improve due to measurement uncertainties resulting from parton fragmentation, hadronization
- Systematics
- ISR, FSR, out-of-cone energy loss, ...
- Initial (relative) energy scale calibration methods
- E/p measurements for isolated high pT charged hadrons from  decays
- Transfer energy scale calibration from test-beam
- Inter-calibrate various calorimeters
- Constrain absolute energy measurement scale for isolated ±
- Track p measured in ID not obviously matched to the calorimeter E since it is not possible to completely reject ± overlapping with 0

- B. Caron

- LHC2003 Symposium

## in situ Jet Energy Calibration

- W→jj decays from inclusive production
- ±1% jet energy scale systematic uncertainty for pTjet > 70 GeV
- Residual effects
- FSR effects large for pT ~ 50 GeV due to out of cone energy losses (~10%)
- Jet overlap effects for pT > 200 GeV requires 2 jets with R>0.8
- Z+jet events
- pT balance between highest pT jet and leptonic Z decay
- Tight jet veto and >3.06 to reach ±1% sensitivity level

- B. Caron

- LHC2003 Symposium

## Low pT Jet Reconstruction

- Low pT jet veto
- Z+jet(s) events for *in situ* calibration with pT balance between Z and jet(s)
-      background rejection via central jet veto
- Good efficiency and background rejection for 15 (25) GeV jet veto threshold at low (high) L
- Important in the search for Higgs from Vector Boson Fusion

- B. Caron

- LHC2003 Symposium

## Forward Jet Tagging

**Higgs from Vector Boson Fusion**
- Jets within 2 < || < 5 (end-cap     and forward calorimeters)
- Efficient discrimination between   pile-up and signal jets in FCAL
- Significance (signal/rms) in     R=0.2 cone around seed cell
- Constant fake rate of ~ 1(10)% for double (single) tag in 2 < || < 5

- B. Caron

- LHC2003 Symposium

## -jet Reconstruction

- Benchmark Processes
- Charged Higgs
- Light SM Higgs from VBF
- SUSY at large tanβ
- Backgrounds
- Z →     ,     ,       , and W+jet(s)

**MSSM**

- B. Caron

- LHC2003 Symposium

## -jet Reconstruction

**Identification**
- Well-collimated calorimeter cluster with (1,3) associated charged track(s)
**Distinguishing variables**
**R****em** = jet radius computed using only EM cells in the jet within R=0.7
**Δ****E****T****12** = fraction of ET in EM/hadronic calorimeters within 0.1 < R < 0.2
**N****tr**** **= number of charged tracks pointing to cluster within R = 0.3

****** ****jets**

**QCD jets**

- 15 < pT <   30 (          )
- 30 < pT <   70 (          )
- 70 < pT < 140 (          )

- 15 < pT <   30 (         )
- 30 < pT <   70 (         )
- 70 < pT < 140 (         )

- B. Caron

- LHC2003 Symposium

## -jet Reconstruction

****** ****/ jet separation**
-  _****__** **__**id:**_ Jet with ET>30 GeV, ||<2.5, Rem<0.07, ET12<0.1, Ntr(pT>2) =1(3)
- Good ****/ jet separation over a broad pT range
****** ****efficiency versus jet rejection**
- For  id efficiency of ~20% a rejection factor of 170-1200 against jets from W+jets and      ; factor of 1700 against b-jets
- good sensitivity for identifying ’s in many physics channels, from light Higgs to heavy SUSY

**□ ****70 < p****T**** < 130**
**● ****50 < p****T**** < 70**
**○ ****30 < p****T**** < 50**
**■ ****15 < p****T**** < 30**

- B. Caron

- LHC2003 Symposium

## ETmiss Measurement

- Why is good ETmiss measurement needed at the LHC?
- ETmiss is an important signal for new physics (SUSY)
- Aim
- Minimize fake high-ETmiss tails produced by instrumental effects (poorly measured jets in a calorimeter crack, for example)
- Accurately reconstruct narrow invariant mass distributions for new particles with neutrinos among their decay products
-      qqH → qq →ll
- Critical calorimeter performance characteristics
- Good energy resolution
- Good response linearity
- Hermetic coverage

- B. Caron

- LHC2003 Symposium

## ETmiss Resolution

**Calorimeter calibration**
- Energy loss in dead material (cryostats) and calorimeter transitions (cracks)
- Non-linearity of calorimeter response to low-energy particles outside of clusters (~5% effect)
**Calorimeter coverage**
- For mA=150 GeV,  A→                        ETmiss resolution of 7 GeV
**Contributions:**   barrel (5 GeV),
-                             end-cap (4 GeV),
-                              forward (3 GeV)
**Electronic noise**
- 1.5  cell energy cutoff deteriorates resolution by < 10% (3 GeV)
**Influence of minimum bias events**

- ▲ e-noise + pileup
- □ FCAL alone

**m****A****=150 GeV**
**     ****Low L**

**E****T****(tower) > 1 GeV**

- ▼  **A ****→******

- B. Caron

- LHC2003 Symposium

## ETmiss Tails

**E****T****miss**** signature for SUSY searches**
- Z+jet(s), Z → +
- Well suited to study ETmiss tails for all possible final states
- Simple and well controlled channel
**Real sources of E****T****miss****:** two highest ETmiss events contain ’s
- Highest pT jet for events with         ETmiss > 50 GeV found in crack region between barrel and extended barrel calorimeters

- crack

- Leading jet
- lost

- Fullsim

**E****T****miss**** > 50 GeV**

- B. Caron

- LHC2003 Symposium

## Combined Performance

**W → jj **(low and high L)

**t → b jj **(inclusive tt)

**H → bb **(low L)

**A → ******(high L)

- <mjj>=80.5 GeV

- <mjj>=80.5 GeV

**m****H**** = 100 GeV**

**m****top**** = 175 GeV**

**m****A**** = 150 GeV**

- All results from
- Full Simulation

- B. Caron

- LHC2003 Symposium

## Summary

**ATLAS Calorimetry**
- _Strongest Features:_ Good energy resolution, hermeticity, and granularity
**Jet Reconstruction**
- Good jet energy calibration from H1 method
- In situ calibration for W→jj and Z+jet(s) to 1% level
- Forward jet tagging for Higgs from VBF
**Hadronic ******** decays**
- efficiently reconstructed and identified from calorimeter and inner detector tracking information
**E****T****miss**** performance**
- Calorimeter calibration and coverage dependent
- Cell energy cutoff for electronic noise + pile-up
- No large tails produced from high pT jets in less uniform calorimeter regions

- ATLAS is well suited to deliver upon a large physics potential

- B. Caron

- LHC2003 Symposium