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

1. Triggering on hadronic taus: plans & performance studies in ATLAS/CMS M. Pilar Casado (IFAE & UAB) on behalf of ATLAS & CMS CH±arged 2006 (Uppsala University,Sweden, 13-16 September 2006)

2. Outline • CMS & ATLAS • Trigger System • Tau selection at LVL1 • Tau selection in the HLT • Timing measurements • H±→ t±nt channel • Plans & conclusions

3. CMS & ATLAS ATLAS • Silicon pixel and silicon strip detectors in • |h| < 2.5 (a TRT detector also in ATLAS) • ATLAS:~20 GeV, s(1/pT) ~1.1 TeV-1 up to h=1.5 • CMS: ~100 GeV, s(DpT/pT) ~1-2% up to h=1.6 • Em calorimeter with resolution: • ATLAS: DE/E<10% /√E ±0.5% • CMS: DE/E=3% /√E±0.5% CMS

4. Trigger system (2) Region of interest mechanism (CMS & ATLAS) (1) ATLAS multilevel trigger HLT • In CMS there is one entity (HLT) • and various selection steps.

5. Tau selection at LVL1 Tau trigger algorithms at LVL1 in ATLAS & CMS. Dh, Df = 0.1 ATLAS CMS Dh, Df = 0.09 • 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. • Core: 2x1 em towers with the highest • energy deposition + Had Core (2x2) • EmIsol and HadIsol: Surrounding towers • between 2x2 & 4x4.

6. Performance of LVL1 ATLAS ATLAS L = 1033 cm-2s-1 • No isolation is required. • To obtain a reasonable single t trigger rate • at 25 GeV one must to combine it with xET • or double t trigger. • A nominal cut of 43 GeV corresponds to • a 95% efficiency cut of ~80 GeV.

7. Performance of LVL1 CMS CMS • 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. • The cutoff on this figure represents a value • of the calibrated energy. • A threshold of 40 GeV (~3kHz) in ATLAS • corresponds to ~90 GeV (~2kHz) in CMS • (single tau). Different objects. • For H→tt (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.

8. Tau selection in the HLT (ATLAS) Calorimeter based approach Tracking based approach Refine (h,f) with the calorimeter and calculate shape variables Perform tracking and obtain (h,f) Tracking Calorimeter variables Fill objects with calorimeter/tracking information Matching of calorimeter cluster and track collection Both running!

9. Tau selection in the HLT (ATLAS) Examples of calorimeter variables: - Taus - Jets Isolation fraction Em radius

10. 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 h, but no energy parametrisation.

11. L= 1031 cm-2s-1 tau10i tau35i *()% Rjet **() % Rjet L1 60 2.7 kHz 59 120 Hz L2calo 42 1.1 kHz 29 80 Hz L2Track 35 460 Hz 25 30 Hz Tau selection in the HLT (ATLAS) - W→tn - dijets (J2) Number of tracks in a region of |Df| < 0.15 & |Dh| < 0.15 RoI size comparing track and calo coordinates. * use Whad , ** use A

12. Tau selection in the HLT (CMS) Refine position. • Calo + Pxl approach • Tau Track approach Simplified pixel tracking (see next slide). In the next slide. • The efficiency is normalized with respect to events • which 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.

13. Tau selection in the HLT (CMS) Refine position with calorimeter. • Calo + Pxl approach • Tau Track approach 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 supposed • to 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± Rs ~0.07, Rm ~ 0.1, Ri ~0.2-0.5

14. Tau selection in the HLT (CMS) Efficiency of the “Trk-Tau” trigger applied to both tau jets for signal events versus QCD multi-jet events. The efficiencies are shown for 2 Higgs masses. The isolation cone Ri 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. Efficiency of the “Calo+Pxl” trigger applied to both tau jets for signal events versus QCD multi-jet events. The efficiencies are shown for 2 Higgs masses. The isolation cone Ri 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.

15. Timing measurements in the HLT • ATLAS: • Level 2 calorimeter algorithm in DhxDf = 0.3x0.3 ~ 3.97ms (Intel Xeon 2.8 GHz, RAM 2055 MB) • Typical level 2 inner detector algorithm in DhxDf = 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 DhxDf = 0.5x05: ~10 ms/RoI (PIII @ 1 GHz) • Pixel algorithm (globally): ~60 ms/RoI (PIII @ 1 GHz) • Trk-Tau algorithm in DhxDf = 0.5x05 (QCD events) : 300 ms/jet (PIII @ 1 GHz)

16. H± selection using t’s (CMS) • “Track Tau” trigger efficiency for the signal and • QCD background events passing the Level 1 single-t • 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/c • requirement on pT at low luminosity. • Efficiency of the “Track Tau” trigger • for a background suppression of ~30.

17. improvement in the signal to bkg ratio wrt H+tb channel (large combinatorial bkgs) H± selection using t’s (ATLAS) mH±> mtop 30 fb-1 • Signature: High pT jets & ETmiss→ • Jets + xET or t + xET triggers 30 fb-1 mH± can be extracted from mT distribution.

18. ATLAS all MSSM Higgses(10 fb-1) H± selection using t’s (ATLAS) mH±< mtop • Consider hadronic channel • tH+b; H+; hadr.  • (Jet +ETmiss) or (t+ETmiss) trigger Region specially important for this analysis mH± can be extracted from mT distribution.

19. 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.

20. 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.

21. 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.