1. Mark Thomson Timing, Tungsten and High Energy Jets

2. Timing: Recap  Distribution dominated by time of flight to HCAL  Long tail from low energy neutrons out to ~1  s  Recently looked at timing for 250 GeV jets in ILD (Steel-Scintillator)  Correct for time of flight using hit position assuming propagates at speed of light  90 % of energy deposited in first few ns 2 CERN, 3 rd August 2010Mark Thomson

3. Steel HCAL HCAL  95 % of energy in 10 ns  99 % in 50 ns Corrected for ToF  Suggests optimal timing window in range 5-10 ns 3 CERN, 3 rd August 2010Mark Thomson

4. Tungsten  What about Tungsten?  Iron (and lead) doubly magic nuclei, i.e. particularly stable  Tungsten: both n and p far from closed shells  naively would expect more nuclear interactions with Tungsten  a priori not a problem (e.g. Uranium for compensation)  but expect longer time profile (decays, secondary interactions)  + not clear how well modeled in Geant 4  Study with CLIC_ILD model  generated single K L s (QGSP_BERT)  copied uds 91, 200, 500 from Grid (thanks Stephane)  repeated previous studies…  NOTE: all at reconstructed PFO level uses 0.3 MiP cut rejection of very isolated hits 4 CERN, 3 rd August 2010Mark Thomson

5. Tungsten vs Steel: 25 GeV K L Steel Tungsten  Tungsten much “slower”  only 80 % of energy in 25 ns  only 90 % in 100 ns  how much due to thermal n ? 5 CERN, 3 rd August 2010Mark Thomson

6. Tungsten: Time vs Energy  Tungsten much “slower”, but not the only difference  distribution of single energy depositions much harder significant number of single hits have energy depositions > few GeV nuclear fragments? Time/ns Hit Energy/GeV  Previously, PandoraPFA reconstruction had (evil) maximum single hit energy of 1 GeV  responsible for poor performance reported by J-J. B. last meeting  now removed (.xml steering) 6 CERN, 3 rd August 2010Mark Thomson

7. Tungsten vs Steel: 25 GeV K L  Study HCAL resolution vs time window for Tungsten vs Steel  removed max hit energy cut and recalibrated for each cut  Dependence much stronger for W HCAL  reflects larger time spread  For decent HCAL performance, i.e.  need to integrate over 20 ns ! 7 CERN, 3 rd August 2010Mark Thomson

8. PFA Performance vs time cut: uds  Look at PFA performance for CLIC_ILD  For no time cut (1000 ns) peformance of CLIC_ILD v. good  somewhat better than ILD (thicker HCAL, larger B)  For high(ish) energy jets – strong dependence on time cut  suggests time window of > 10 ns  need something like 50 ns to get into “flat region” 8 CERN, 3 rd August 2010Mark Thomson

9. Tungsten: Summary  Tungsten leads to a longer time distribution of hits  activity on the timescale of a full CLIC bunch-train  for “reasonable” performance need to integrate over 10s of ns  Is Tungsten is reasonable choice for a CLIC HCAL absorber?  Not clear at this stage – a number of questions  how good is simulation?  what about digital calorimetry with gaseous active material? although digital may bring problems of its own…  how much can be recovered offline  i.e. integrate over some part of bunch train in reconstruction and then tag BX for clusters My Conclusions:  Tungsten NOT an obvious choice for the endcap HCAL where background is significant  In barrel region HCAL occupancy sufficiently low: Tungsten probably OK.  needs serious study 9 CERN, 3 rd August 2010Mark Thomson

10. CLIC_ILD and High Energy Jets  Started to look at performance of CLIC_ILD for high energy jets  Looked at uds events  91, 200, 500 GeV events generated at CERN using Cambridge stdhep files  1 TeV, 2 TeV, 3 TeV events generated at CERN using SLAC stdhep Jet Energy  /sqrt{E}  E /E 45 GeV24.0 %3.5 % 100 GeV27.4 %2.7 % 250 GeV43.7 %2.8 % CLIC_ILD (no timing cut)  E /E 3.7 % 2.9 % 3.3 % ILD  “Low energy” performance looks very good, better than ILD model:  HCAL resolution better (no timing cuts)  Thicker HCAL  Higher B  “High Energy” performance – much worse than expected !  ~110%/√E c.f. ~80%/√E for 500 GeV jets  Events looked suspicious – track multiplicities too low, no thee jet events, jets very narrow… 10 CERN, 3 rd August 2010Mark Thomson

11. 1 TeV uds (SLAC stdhep) 1 TeV uds (Cambridge stdhep): Pythia, gluon radiation on, OPAL tune Example 1 TeV Events 11 CERN, 3 rd August 2010Mark Thomson

12.  Strongly suspect that the stdhep files used for 1, 2, and 3 TeV production have gluon radiation off…  Currently Generating 1 TeV events in Cambridge  Preliminary (only 1500 event) performance looks good…  David Ward produced new 2 TeV and 3 TeV stdhep files Jet Energy  /sqrt{E}  E /E 45 GeV24.0 %3.5 % 100 GeV27.4 %2.7 % 250 GeV43.7 %2.8 % 500 GeV77 %3.4 %  About as expected (from previous ILD studies)  However, some obvious PFA issues…  tail at very high energies due to split tracks CLIC version of LDCTracking helps somewhat, but doesn’t solve problem – needs further study  tail at low energies (e.g. >100 GeV missing)  bad track-cluster matches, e.g. 100 GeV track – 250 GeV cluster  should be handled in reco – needs further study 12 CERN, 3 rd August 2010Mark Thomson

13. Conclusions  Time structure is an issue  Tungsten may not be viable for endcap region not where it is needed – so not a problem  background in barrel region is less of an issue but needs full bunch train studies with background Tungsten: High-Energy Jets:  No obvious problems with CLIC-ILD model  work needed: Tracking optimisation PFA optimisation Study 1 TeV and 1.5 TeV jets General:  Full simulation/full reconstruction studies essential to demonstrate:  PFA with CLIC bunch time structure  Viability of Tungsten calorimetry  Viability of DHCAL at CLIC  … 13 CERN, 3 rd August 2010Mark Thomson