mark thomson timing, tungsten and high energy jets

Mark Thomson

Timing, Tungsten and HighEnergy Jets

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

2CERN, 3rd August 2010 Mark Thomson

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


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 KLs (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


Tungsten vs Steel: 25 GeV KL

Steel

TungstenTungsten

Tungsten much “slower” only 80 % of energy in 25 ns only 90 % in 100 ns how much due to thermal n ?


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

En

erg

y/G

eV

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)


Tungsten vs Steel: 25 GeV KL

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 !


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”


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


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 GeV 24.0 % 3.5 %

100 GeV 27.4 % 2.7 %

250 GeV 43.7 % 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…


1 TeV uds (SLAC stdhep)

1 TeV uds (Cambridge stdhep): Pythia, gluon radiation on, OPAL tune

Example 1 TeV Events


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 GeV 24.0 % 3.5 %

100 GeV 27.4 % 2.7 %

250 GeV 43.7 % 2.8 %

500 GeV 77 % 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


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 …


mark thomson timing, tungsten and high energy jets

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