M. Pilar Casado1

Triggering on hadronic taus: plans & performance studies in ATLAS/CMS

CH±arged 2006 (Uppsala University,Sweden, 13-16 September 2006)

M. Pilar Casado (IFAE & UAB) on behalf of ATLAS & CMS

M. Pilar Casado2

Outline

• CMS & ATLAS

• Trigger System

• Tau selection at LVL1

• Tau selection in the HLT

• Timing measurements

• H± → ± channel

• Plans & conclusions

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CMS & ATLAS

• Silicon pixel and silicon strip detectors in

|| < 2.5 (a TRT detector also in ATLAS)

ATLAS: ~20 GeV, (1/pT) ~1.1 TeV-1 up to =1.5

CMS: ~100 GeV, (pT/pT) ~1-2% up to =1.6

• Em calorimeter with resolution:

ATLAS: E/E<10% /√E ±0.5%

CMS: E/E=3% /√E±0.5%

CMS

ATLAS

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Trigger system(1

) A

TL

AS

mul

tile

vel t

rigg

er

(2)

Reg

ion

of in

tere

st

mec

hani

sm

(CM

S &

AT

LA

S)

• In CMS there is one entity (HLT)and various selection steps.

HLT

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Tau selection at LVL1

ATLAS CMS

Tau trigger algorithms at LVL1 in ATLAS & CMS., = 0.1

• Core: 2x1 em towers with the highestenergy deposition + Had Core (2x2)•EmIsol and HadIsol: Surrounding towers between 2x2 & 4x4.

• Core: must follow one of the patterns on the right (em & had)• EmIsol and HadIsol: Area outside the pattern drawn above. Only 2 fired towers are allowed in the isolation region.• The difference between em & had is in the threshold applied.

, = 0.09

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Performance of LVL1

ATLAS ATLAS

• No isolation is required.L = 1033 cm-2s-1

• To obtain a reasonable single trigger rate

at 25 GeV one must to combine it with xET or double trigger.

• A nominal cut of 43 GeV corresponds toa 95% efficiency cut of ~80 GeV.

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Performance of LVL1

• For H→ (mH = 200 GeV) applying a thres. of 93 GeV in the L1 single tau trigger& 60 GeV in the L1 double tau trigger, an efficiency of 78% is achieved.

CMSCMS

• The cutoff on this figure represents a valueof the calibrated energy.•A threshold of 40 GeV (~3kHz) in ATLAS corresponds to ~90 GeV (~2kHz) in CMS (single tau). Different objects.

• For 3 kHz the 95% efficiency cut is ~80 GeV,while the same rate is achieved with a cut of ~55 GeV for 2 taus.

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Tau selection in the HLT (ATLAS)

Refine (,) with thecalorimeter and calculate

shape variables

Tracking

Matching of calorimeter cluster and track collection

Calorimeter based approach

Perform tracking

and obtain (,)

Calorimeter variables

Fill objects with calorimeter/tracking

information

Tracking based approach

Both running!

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Tau selection in the HLT (ATLAS)

- Taus- Jets

Em radius Isolation fraction

Examples of calorimeter variables:

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Tau selection in the HLT (ATLAS)

Effect of a sampling calibration in the energy of the tau cluster:

ATLAS

• For the moment apply calibration to EM and HAD compartments separately.• Take into account dependency in , but no energy parametrisation.

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Tau selection in the HLT (ATLAS)

Number of tracks in a region of || < 0.15 & || < 0.15 RoI size comparing track and calo

coordinates.

- W→- dijets (J2)

tau10i tau35i

252959

**() %

30 Hz80 Hz120 Hz

Rjet

L= 1031 cm-2s-1

460 Hz35L2Track1.1 kHz42L2calo2.7 kHz60L1

Rjet *() %

* use Whad , ** use A

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Tau selection in the HLT (CMS)

• Calo + Pxl approach

• Tau Track approach

Refine position.

In the next slide.

• The efficiency is normalized with respect to eventswhich pass the single or double Level 1 tau trigger.• The rejection factor for jets is between 1-10.• This is a very fast approach which reconstructs the

tau jet with low pT resolution.

Simplified pixel tracking (see next slide).

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Tau selection in the HLT (CMS)

Rs ~0.07, Rm ~ 0.1, Ri ~0.2-0.5

• Calo + Pxl approach

• Tau Track approach

Refine position with calorimeter.

Track reconstruction &isolation with full tracking information.

• One looks for tracks above a certain pT in the

matching region (Rm).• The track with highest pT is considered and tracks

in a signal cone (Rs) around the first one are supposedto come from the same tau.• One requires that no other tracks are present in the

isolation cone (Ri).

• This algorithm gives good performance for H±

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Tau selection in the HLT (CMS)

Efficiency of the “Calo+Pxl” trigger appliedto both tau jets for signal events versus QCD multi-jet events. The efficiencies are shown for 2 Higgs masses. The isolation coneRi is varied from 0.2-0.6, Rs =0.07, Rm = 0.1, and pT of the leading tracks is required to exceed 3 GeV/c.

Efficiency of the “Trk-Tau” trigger appliedto both tau jets for signal events versus QCD multi-jet events. The efficiencies are shown for 2 Higgs masses. The isolation coneRi is varied from 0.2-0.45, Rs =0.07, Rm = 0.1, and pT of the leading tracks is required to exceed 6 GeV/c.

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Timing measurements in the HLT

• ATLAS:– Level 2 calorimeter algorithm in x = 0.3x0.3 ~ 3.97ms (Intel Xeon

2.8 GHz, RAM 2055 MB)

– Typical level 2 inner detector algorithm in x = 0.1x0.1 (top events excluding unpacking)~ 4.8 ms/jet (Xeon 2.4 GHz).

– Event Filter (calorimeter + tracking) ~98 ms (Pentium III @ 1.4 GHz)

• CMS:– Calo algorithm in x = 0.5x05: ~10 ms/RoI (PIII @ 1 GHz)

– Pixel algorithm (globally): ~60 ms/RoI (PIII @ 1 GHz)

– Trk-Tau algorithm in x = 0.5x05 (QCD events) : 300 ms/jet (PIII @ 1 GHz)

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H± selection using ’s (CMS)

• “Track Tau” trigger efficiency for the signal andQCD background events passing the Level 1 single-Trigger.• The different points correspond to varying the leading

track pT from 1 to 30 GeV/c.• A rejection factor of 30 can be reached with a 20 GeV/crequirement on pT at low luminosity.

• Efficiency of the “Track Tau” triggerfor a background suppression of ~30.

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H± selection using ’s (ATLAS)

improvement in the signal to bkg ratio

wrt H+tb channel (large combinatorial bkgs)

mH±> mtop

• Signature: High pT jets & ETmiss→

Jets + xET or + xET triggers

30 fb-1

30 fb-1

mH± can be extracted from mT distribution.

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H± selection using ’s (ATLAS)mH±< mtop

• Consider hadronic channel tH+b; H+; hadr.

(Jet +ETmiss) or (+ETmiss) trigger

ATLAS all MSSM Higgses (10 fb-1)

'- W; qqbWt

mH± can be extracted from mT distribution.

Region specially important for this analysis

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Plans

• ATLAS:– New determination of LVL1 efficiencies & rates for different data

samples & luminosities.

– In the HLT, study menus for 1031 cm-2s-1, 900 GeV & 1034 cm-2s-1 in the new framework.

– Continue trigger aware analyses.

• CMS:– Trigger studies for 1031 cm-2s-1 and 900 GeV.

– Finalize migration to new framework and perform trigger studies.

– Continue trigger aware analyses.

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Conclusions

• The baseline of tau trigger strategy is established and well determined. Some work to do on initial center of mass energy and luminosity.

• For high pT a single tau trigger seems to be feasible, while for medium-low pT is desirable to combine it: with ETmiss (ATLAS), double tau trigger (CMS).

• For the H± depending on the pT range all the previous trigger menus will be used.

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References

• “The CMS high level trigger”, by the CMS collaboration, Eur. Phys. J. C 46, 605-667

• “Tau Jet reconstruction and tagging with CMS”, by the CMS collaboration, Eur. Phys. J. C (2006)

• ATLAS High Level Trigger, Data Acquisition and Controls, Technical Design Report, ATLAS TDR-016. ATLAS HLT/DAQ/DCS Group.

• “The hadronic tau decay of a heavy H± in ATLAS”, by K. Assamagan & Y. Coadou, Acta Physica Polonica B, Vol. 33 707-720 (2002)

• “Charged Higgs search in top quark decay with the ATLAS detector”, by C. Biscarat & M. Dosil, ATL-PHYS-2003-038.