taus at cms: goals, status, plans… - texas a&m...

Taus at CMS: Goals, Status, Plans…

Simone Gennai (INFN Pisa)Alexei Safonov (Texas A&M)e e Sa o o ( e as & )On behalf of PFTau Group

GoalsTh t’ th i t tThat’s the easiest part…Provide efficient and well understood tau triggers, reconstruction and identification suitable for wide range f h i lof physics analyses

Higgs (heavy and light)SUSYZ-prime… (unexpected)

Real life puts constraints on what we can doExternal constraints (can’t change trigger hardware or remove material from the tracker)

… and how fast we can get there:Manpower!Sufficient amounts of data

A. Safonov, CMS Tau Vertical Integration Meeting, May 21-22, 2008, CERN 2

What’s Special about TausWe understand the desire to have everything commissioned with 10 ipb including taus…

but it is not going to happen:… but it is not going to happen:Visible tau pT spectrum is soft – hit ~x5 vs muEfficiency is lower (or we will be completely overwhelmed by backgrounds) – hit ~x2 vs muFake rate is higher – hit greater than ~x10Altogether a hit of ~x100 Simple math:Altogether a hit of ~x100. Simple math:

If muons commissioning needs 10 ipb, we need 1 ifb!We think we can do (a lot) better than that, but people should realize we won’t be there in December ’08!


Our StrategyC i i i f h d i t i i h tl diff tCommissioning of hadronic taus is inherently different from other lepton cases:

Very high backgrounds prevent selection of clean samplesample

“Tag and probe” and alike won’t workOne has to factorize effects and make many complementary measurementscomplementary measurements

Low acceptance due to escaping neutrinos limits statistics

Need larger datasets and efficient triggeringg gg gComplexity of the tau object

Therefore early commissioning strategy is to focus on ensuring efficient data collection e su g e c e da a co ec o

Even if accurate efficiency measurements are to come later, those efficiencies have to turn out to be high


Three ComponentsSuccessful execution of physics program with taus relies on several inter-related ingredients:Triggers:Triggers:

High efficiency at tolerable rateAbility to measure efficiency

Offline Reconstruction:High efficiency at acceptable fake rateAbili d d d ffi iAbility to understand and measure efficiency

Standard candle proto-analyses:Measurement of efficiencies requires reasonably cleanMeasurement of efficiencies requires reasonably clean samplesSelection of clean samples can only be by advancing t d d dl l


standard candle analyses

Triggers: StatusMost critical area, therefore large fraction of our manpower was directed there

Main challenge is high rates at L1 also have to watch forMain challenge is high rates at L1, also have to watch for HLT timingHad to simplify and improve the overall setup for easier

bilit d i tmanageability and maintenanceFocus on increasing background rejection as early in the trigger chain as possiblegg p

Lower rate out of L1 and L2 directly helps timing as less events to processM i h i f L3 (Si) t L2 5 ( i l )Moving emphasis from L3 (Si) to L2.5 (pixels)

Can do a lot there before the time consuming L3 kicks in


Level 1 TriggersR t l ( d b TSG)Recent proposal (approved by TSG):

L1 tau rates down by a factor of 2 per jetEfficiency nearly intacty y

C.N. NguyenS. Maruyamay

Concerns about triggers in the short term are largely alleviated

Long term scenarios (higher inst. luminosity) need


g ( g y)manpower

HLT: Level 2L2 optimization is nearly completed (code is ported to HLT, validation and fine tuning are finishing)

Can decrease L2 output rates by additional factor of ~3 compared to the HLT exercise times

Can further increase rejection, e.g. by heavier use of HCAL,Can further increase rejection, e.g. by heavier use of HCAL, but because of noise concerns we prefer to tune these cuts with data

M. Bachtis


HLT: Level 2.5Thi t d h b l iThis study has been legging behind, but as of a few days ago we started rolling:M i f i iMain focus on improving efficiency:

Already implemented a couple of improvementsof improvementsStarting to look in detail into sources of inefficiencyHave ideas on improvements:Have ideas on improvements:

Hit (finding) efficiency:Add inner Si layer to loosen requirement of 3 pixel hits?

Resolution: Pixel tracking plus beam constrain might help


Offline ReconstructionDeliverable: efficient/robust reconstruction codeImplementation of PF-based tau has been largely completed now working out and adding new andcompleted, now working out and adding new and better ID variablesCore reconstruction improvements:

Higher efficiency at lower ETwith new cone definition (critical for light higgs)g gg )Iterative tracking and tuning of track quality cuts: ~10% increase in tau ID efficiencyy

Further improvements in tracking, especially at low pT(0.5-2 GeV) side would be very h l f l E Friis


helpfulConsistent infrastructure for more elaborate selections

E. Friis

IdentificationStrongest discriminator is isolation (is it ID or not ID?)But other ID cuts are necessary and important:

Electron/muon rejectionElectron/muon rejectionTau shower shape and properties:

Energy profile, tau invariant mass, photon counting, neutral hadrons (should not be present)neutral hadrons (should not be present)If successful, could give ~x2-3 in extra jet rejection

Requirements for selecting ID variables:Robust w.r.t. expected detector miscalibrations and noiseHighly discriminating

Hard to avoid efficiency losses in basic reconstruction are quite substantial, we don’t want to loose even more

Measurable without inflating systematics


Light Lepton RejectionElectrons and sometimes muons faking taus can be nasty backgrounds

Tevatron-like methods still work, but at a huge price in efficiency (20 25%) Traditional at a huge price in efficiency (20-25%)Common sense says it shouldn’t be that bad

A better strategy should be not to hit a

approaches

gytau on the head based on some average characteristics, but to recognize an electron (or muon) from “difficult” categorydifficult category

Essentially the idea behind the whole PF concept

Teamed up with PF experts to improve

New

Teamed up with PF experts to improve lepton rejection

Work is still ongoing, but already a large improvement is seen S. Maruyama


yC.N. NguyenK. Petridis

Tau ID: Shower Shapes and ConversionsC b it h l f l i d i j t b k dCan be quite helpful in decreasing jet backgrounds

With other items clearing up, need to start a concerted effort there

Lack of available qualified manpower is a problemLack of available qualified manpower is a problemDiscrimination will increase with overall CMS improvements, e.g. pion tracking efficiency at lower pT

D. Jang

Lack of conversion reconstruction could be a serious obstacle

Electrons reconstructed as photons smear the shape of taus N. Marinelli

A. Anastassovphotons smear the shape of tausThat’s in addition to worsening energy resolution and a decrease in efficiency of photon isolation

We feel that conversions became a critical path item for us and more progress is needed there

in efficiency of photon isolation


Later talk today will discuss progress in this area

Commissioning GoalsKey elements: Triggers, Offline, IDCommissioning steps similar for each component (time ordered):)

Debug, tune and validate performanceEstablish continuous monitoringProvide efficiency measurementsProvide efficiency measurements

Short term goal: ensure efficient data collectionefficient data collectionLong term goal: deliver one of the standard candle physicscandle physics signatures and well understood efficiencies

L. Lusito (100 pb-1)


Much more on this today in Kostas’ talk!

Trigger EfficienciesMeasure trigger efficiencies with respect to our “standard” tau object

“Standard” tau is ~95% defined, but a moving target as , g gwe still put in improvements

Fortunately, trigger efficiencies will be a weak function of remaining improvements

Thus defined trigger efficiencies are generally high and can be measured with ~x10 pb-1:

Bulk of inefficiency is due to trigger isolations, but we can y ggstudy those using Z electrons (plus a small correction) and high quality tau fakes from jets

Will need to break-up and parameterize sources of inefficiency to not acquire a bias (from “fakeness” of taus)

Will cross-check (and tune, if needed) with real taus


More data will be needed, probably ~x100 pb-1

Offline and ID EfficienciesOur definition made trigger efficiency measurement “quick and easy”, but someone still needs to measure offline & ID efficiencyoffline & ID efficiencyDifficult: plot below is made with very harsh cuts on taus (very stiff leading track pT, jet ET, ID cuts)

Need to understand softer taus (or no SUSY and low acceptance in light higgs)Obviously, one can’t y,measure efficiencies if cuts are already applied

Need to drop all or almostL. Lusito (100 pb-1)

Need to drop all or almost all cuts

Including PF jet pT cut


…but backgrounds will go through the roof

Offline and ID EfficienciesIdeal denominator is a soft calorimeter jet, but not feasible due to high backgrounds

OK denominator is above plus a ~5-6 GeV track Someone does pion tracking efficiencies for us

Backgrounds still too high. So next step: IsolationVery powerful against QCD; in taus it is ~decoupled from

h iother tau properties Luckily, can be measured elsewhere, e.g. in Z→μμNew denominator: 10 GeV jet with a 5 GeV track with (loose or tight) isolations applied(loose or tight) isolations applied

Still hard, but can pick better sample and do whatever except touching taus

Z→ττ→μτ plus clean up e g extra jet veto etcZ→ττ→μτ plus clean up, e.g. extra jet veto etc Beat muon hard to suppress backgrounds

pT, isolations, secondary vertices etcSee how far we can get (work in progress very


See how far we can get (work in progress, very iterative), may have to cut back a bit on the scope

SummaryTaus are complex objects, much more like b-jets than e or μ:

We can never be on par with e/mu progress in early stagesCore reconstruction is in place, any further big improvements will

d ki i d i fi dineed tracking improvements and conversion findingIdentification:

Recent focus on e/mu rejection has yielded very promising results (~15% extra efficiency)( 15% extra efficiency)Next focus should be on energy profile and shower shapes, but conversions need to be there

Commissioning goals and plans (trigger much faster than offline):B i i i i ill b hi d ith 10 100 i b f f l d tBasic commissioning will be achieved with 10-100 ipb of useful dataReasonable estimates of efficiencies can be achieved with less than 100 ipb

Based on non-tau samplespFull physics commissioning requires relatively clean tau samples

We likely talk about ~a couple x100 pb-1 of data on tape The group is severely undermanned

7 l ith l FTE t tl ( d) t d t


~7 people with large FTE on taus, mostly (very good) studentsModerate investment of manpower (~3 FTE) will go a long way

BACKUP SLIDES


Tau Efficiencies: Big PictureWhat is it we need to measure?

Leading track finding efficiencyIsolation efficiencies (tracks/photons)Efficiencies of other ID cuts

e/μ rejection, tau shape, neutral hadrons fraction etc

Energy calibration (affected by track and photonEnergy calibration (affected by track and photon reco efficiencies, e.g. a lost photon will lead to an under-measurement of energy – PF part of PFTau))

Above roughly replicates basic tau reco stepsMostly similar measurements for trigger and offline

Trigger relies on seeding/isolations, not much on “other ID”Trigger efficiencies are “easier” as they will be measure w r t offline selections which means


measure w.r.t. offline selections, which means cleaner samples

Efficiency MeasurementsOur ability to measure offline efficiencies is driven by these samples:

M t Eff t P i it / M th d H d?Measurement Effect (Inefficiency)

Pre-requisite / Method Hard?

Leading track Large π sample we hope it comes from YesLeading track finding

Large π sample, we hope it comes from somewhere else (Track DPG?). Can do cross-checks with Z→ττ.

Yes

Isolations with Large Clean sample of 100’s of Z→ee/μμ NoIsolations with tracks/photons

Large Clean sample of 100 s of Z→ee/μμevents, photon iso requires better understanding of conversions

No /Yes

other ID cuts Smaller Clean sample of 100’s of taus (Z→ττ) Yes( )

Energy lib ti

Small? Clean sample of 100’s of Z→ττ (to fil d ’ d Z )

Yes


calibration measure profiles and reco’ed Z mass) – shared work with PF

Commissioning Plan: TriggersEstablishing basic trigger functionality:

Tuning initial L1 tau definition and veto bitsWant to run triggers during CRAFT - HCAL noise could be an issue

0-0.1 ipb

Two tower trigger (“loose initial electron”) – use as calibration trigger and validate L1 logic vs expectation

Either with L1 emulator or with a simple emulation tool

1 10 i bTau trigger efficiency measurement using offline electrons and jets:

1-10 ipb

Use inclusive electron/jet triggersCh k ll f ti lit d i l ti C.N. NguyenChecks overall functionality and isolationsTools: trigger emulation and bit counting for electrons, more specialized tools for jets

Calibration triggers: inclusive electron and jets/MB

Monitoring: simple plots based on above studies:


Dedicated pre-scaled triggers

Commissioning Plan: TriggersT i ffi i t ith t l tTrigger efficiency measurements without real taus:

Measurement using offline electrons:Use inclusive electron triggerChecks overall functionality and isolations 10-100 ipb?Checks overall functionality and isolationsTools: customized trigger emulation for L1 (basically working, but needs further tuning)

Measurement with tight offline “taus” (fakes):U i l i t i ( t i t )

p

Use inclusive muon triggers (mu+tau signature)Tools: customized trigger emulation to understand reasons for trigger failures and develop efficiency parameterization“Pretty good” understanding of the trigger selections w.r.t. offline

Final validation will need clean tau samplesRe-measure efficiencies using clean Z→μτ(eτ) Use inclusive μ(e) triggers

A l ill i t i ffi i i f d l t100-500 ipb?

Analyses will require trigger efficiencies for muons and electrons at “medium” pT’s (10-25 GeV)

Can be done with conversions and e.g. UpsilonsCan we expect these to be performed by EGamma and Muon


Can we expect these to be performed by EGamma and Muon DPGs?

Commissioning Plan: Offline

Use Z→ee/μμ data coming off e/μtriggers

10-100 ipb?Establishing basic functionality:Offline efficiency measurement using high quality electrons:

triggersBasic check of overall functionality

Offline isolation selections and tuning (including track/photon quality)

R. Vasquez

Use Z→ee/μμ data coming off e/μtriggersYields reliable isolation efficiency measurementmeasurement

Basic understanding of conversion finding:Count tagged tridents from Z→ee and W→eν data?

100-500 ipb?

Count tagged tridents from Z→ee and W→eν data?

Further progress requires clean tau samples:Measure “other” ID efficiencies, energy calibration etc


, gyUse Z→μτ(eτ) using inclusive μ(e) trigger

Pre-RequisitesStandard requirements (common to all POGs):

Ecal, Hcal and Tracker alligned A. Nikitenko

and calibratedL1 CAL and MUON triggers reasonably functioningReasonably functioning electron, muon and tracking reconstruction/selection

“Special” requirements:Measured track reconstruction efficiency for pions

Different from e/μDifferent from e/μLimiting factor for full measurement is our ability to select clean samples of taus

Q i k d l i l i t t!


Quick progress on developing analyses important!

taus at cms: goals, status, plans… - texas a&m...

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