Christof Roland 1 Ions at FCC, Jan 29 2014

Prospects for jet measurements at HL-LHC with CMS

Ions at the Future Hadron Collider Meeting 29 January 2014

Christof Roland/MIT

Christof Roland 2 Ions at FCC, Jan 29 2014

Heavy Ion Projections for HL-LHC

• Disclaimer:– Due to the QM preparation we can not allocate

manpower or computing resources to FCC studies now– All material shown today is from the document prepared

for the ECFA meeting in Aix-les-bains last year

• Documentation– PAS (FTR-13-025) on CDS

• http://cds.cern.ch/record/1610789?ln=en

– Twiki with figures:• https://twiki.cern.ch/twiki/bin/view/CMS/FTR-13-025

Christof Roland 3 Ions at FCC, Jan 29 2014

Overview of FTR-13

• Studies in: – hadron spectra– high-pT probes and jets– (quarkonia)– electroweak bosons

• Frontiers explored:– pT reach : spectra, jets, b-jets, electroweak– (most peripheral : quarkonia, dijets, spectra)– event-shape engineering : dijets, quarkonia– new rare probes : ttbar

• Extrapolations based on yields observed in the currently available dataset + xT scaling

Christof Roland 4 Ions at FCC, Jan 29 2014

HI program timeline

Rate: ~30kHz ~50kHz >50kHz

New Tracker-Extended Coverage ||<4New Forward calorimetry1 MHz DAQ

HL-LHCNew Machine!

HL-LHC for HI

CMS:

Christof Roland 5 Ions at FCC, Jan 29 2014

HI program timeline -Updated Schedule

Rate: ~30kHz ~50kHz >50kHz

New Tracker-Extended Coverage ||<4New Forward calorimetry1 MHz DAQ

HL-LHCNew Machine!

HL-LHC for HI

CMS:Pixel detector upgrade3 Layers -> 4 Layers

LS2 LS3

Christof Roland 6 Ions at FCC, Jan 29 2014

High pT Hadrons

• Charged particle spectra– Use Pythia ProQ20

• Cross section for pThat=380 at 5.5 TeV: σ=0.14 nb

– 61k events in 10nb-1 5.5 TeV PbPb collisions

• generate this number of events to illustrate pT reach

• Add other pThat samples for a realistic pT spectrum

– Leading-order only

– Experimentally easily accessible with jet or track triggers

Christof Roland 7 Ions at FCC, Jan 29 2014

Plenty of dijet events in 10/nb:After pT selection, select dijets based on:centrality (0-10%) : 30% of dijetsv2 : 10%event-plane angle : 25%result : 0.0075 of dijets

in a single bin

Dijets: Event-shape engineering

• 10/nb expectation obtained by randomly using events in the current dijet sample corresponding to the relevant statistics

• The leading jet cut is 180 GeV so that the surface bias due to missing away side jet is reduced.

Christof Roland 8 Ions at FCC, Jan 29 2014

b-tagged Dijets

• Estimated yield of doubly tagged b-dijets

• Select dijet sample from current PbPb data to represent 10/nb.

Christof Roland 9 Ions at FCC, Jan 29 2014

Colorless Probes

• Estimated from pure Pythia (unquenched) simulations at 5.5 TeV for the estimated statistics.

Z+Jet+Jet

Christof Roland 10 Ions at FCC, Jan 29 2014

Summary – High-pT Probes

Christof Roland 11 Ions at FCC, Jan 29 2014

Summary of Electroweak Bosons

04/19/23 FTR-13-025 11

Christof Roland 12 Ions at FCC, Jan 29 2014

Jet Reconstruction in CMS

• Reconstruct physics objects from detector signals– Tracks+Calo Clusters -> Hadrons, Photons, Muons etc

• Particle momentum from high precision tracking

– Jet Finding • Apply underlying event subtraction• Cluster physics objects

Christof Roland 13 Ions at FCC, Jan 29 2014

Some considerations on Jet Reco

• Expected HI HL-LHC jet reco performance– Assumption: Future HI =~ Current pp

• Improved tracking performance to help particle flow reco• Significant improvement from 4 layer pixel system• Finite tracking efficiency in HI is currently the limiting factor

in the jet reconstruction performance (in CMS)• Modulo irreducible underlying event fluctuations

• Expect only a moderate increase in event multiplicity from 2.76 to 5.1 TeV

• Underlying event subtraction significant room for improvement over current Iterative Pileup algorithm

• e.g. the Voronoi subtraction method• Uses the full PF candidate granularity and explicitly

accounts for the azimuthal anisotropy of the events

Christof Roland 14 Ions at FCC, Jan 29 2014

Pb Pb

top quark• ttbar events

– Decay before thermalization – probe very early stages of medium– Alternative channel for b-quark energy loss

• Decay channels– ll+bb+MET 10%: “observation channel”– l+bb+2jet+MET 44%– bb+4jet 46%

• Estimated production rate– 81pb at 5.5 TeV pp (http://www.lpthe.jussieu.fr/~cacciari/ttbar/)

– 10 nb-1 5.5 TeV PbPb collisions -> 35k ttbar events– Branching ratio into e+e-, u+u- and e+-u+- ~6.5% -> ~2300 ttbar– Current CMS (pp) acc∙eff ~ 23% -> ~500 pairs– In PbPb

• Lepton reco efficiency ~100% (now)• Somewhat lower b-tagging efficiency (close to pp with upgrade)• Larger background -> Lower MET resolution (depends on mult)

Christof Roland 15 Ions at FCC, Jan 29 2014

Jet Reco considerations at FCC• Consider CMS tracker + ATLAS Calorimetry

– CMS style particle flow reconstruction combined with ATLAS style calorimetry (longitudinal segmentation)

• Should give significant improvement over current setups for HI• Should be a conservative assumption for the performance of future

experiments

– Multiplicity evolution• PbPb dn/d evolution steeper than log(sqrt(s))• Extrapolation to FCC energies non trivial

– Compensate with lighter ions?• Potentially higher inst parton luminosity• More managable backgrounds

• Joint pp+HI experiment?– Construction cost favorable– Key ingredient to e.g. top reco performance is the data driven

calibration• Need full pp lumi for calibration for HI

Christof Roland 16 Ions at FCC, Jan 29 2014

Conclusion• The capacity to reconstruct HEP like high pT

physics objects in HI has been well demonstrated by the current LHC experiments– Reliably reconstruct Jets, Z, W, MET, b-Jets etc– Expect increased reconstruction performance with the

Stage 2 CMS and ATLAS detectors– Rich jet physics program at HL-LHC

• FCC physics program– Based on the assumption of a joint pp+HI detector

setup we can expect excellent capability to fully exploit HEP style physics signatures (top, higgs?) in HI

Christof Roland 17 Ions at FCC, Jan 29 201404/19/23 17

Backup slides

FTR-13-025

Christof Roland 18 Ions at FCC, Jan 29 2014

The Voronoi Algorithm

https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsDPSUESubtractionPF

Christof Roland 19 Ions at FCC, Jan 29 2014

• A factor 2 increase in √sNN :

– Estimation of the √SNN impact on the cross-sections:

For ϒ (1S):

– From BPH-10-003

• σpp(ϒ(1S)) at 7TeV = 8.3 nb

– From HIN-10-006

• RAA = 0.63

• dn/dy / TAA (PbPb) = 0.485

• then dσ/dy (pp) = 0.485 / 0.63 = 0.77

• σpp(ϒ(1S)) at 2.76TeV = dσ/dy (pp) x 4 (rap. unit) = 3.1 nb

The scaling factor from 2.76 to 7 TeV for ϒ(1S) is : 8.3nb / 3.1nb = 2.7

For J/ψ:

The scaling factor from 2.76 to 7 TeV for the J/ψ is : 71nb /29nb = 2.45

For 5.5 TeV, we roughly took 2

• Ignore the centrality dependent suppression (conservative estimate)

04/19/23 FTR-13-025 19

Assumptions for dilepton projections

Christof Roland 20 Ions at FCC, Jan 29 2014

Dilepton projections for 10 nb-1 and 5.5 TeV

Yields 10nb-1 [0-100%] = Yields 150 μb-1 [0-100%] x FactorLumi (66,66)x Factor√SNN (2)

Yields 10nb-1 [x-100%] = Yields 10nb-1 [0-100%] * ( 〈 Ncoll(x–100%) 〉 ∕ 〈 Ncoll(0–100%) 〉 ) x binwidth

Example - for Y(1S) :

Yields 10nb-1 [0-100%] (Y(1S))= 2000*66,66*2 *30 = 26667

Yields 10nb-1 [50-100%] = (26667*30 / 363)*0.504/19/23 FTR-13-025 20

Christof Roland 21 Ions at FCC, Jan 29 2014

Summary of Quarkonia

04/19/23 FTR-13-025 21

Christof Roland 22 Ions at FCC, Jan 29 201404/19/23 FTR-13-025 22

Christof Roland 23 Ions at FCC, Jan 29 201404/19/23 23

ProQ20

● Pythia ProQ20 was found to give a good description of the charged particle spectrum at high-pT

HIN-10-005QCD-10-008

FTR-13-025