Update from the Photons + MET Group Bruce Schumm UC Santa Cruz / SCIPP 26 August 2010 SUSY/MET Meeting

26 August This presentation is largely informal and unofficial Vacation/conferences: no official strategizing session yet Some opinions/thoughts will be presented, but are only from a subset of the group Intended to prompt discussion, or at least show the issues we’re considering as we re-group

26 August nb -1 Analysis: not approved! Single-  Two-  Statistics dictated that we concentrate on a single-photon analysis, even though we expect to require two photons in the photons+MET analysis to reject SM backgrounds (e.g. setting GMSB limits).

26 August Why not approved? Main (QCD) background scaling not understood –K factors and ad-hoc scaling factors –Mis-id rates –Dijet vs.  +jet contributions –MET spectrum too hard? Could not benchmark against direct photon analysis at low MET Non-standard analysis steps (isolation)? No independent constraints on mis-ID rates (jet  )

26 August Some Developments Since Late July

Photon Purity for GMSB Photon Sample  Benchmark analysis against Direct Photon study Daniel Damiani

26 August Direct Photon Note Purity Method Method for photon purity calculation was taken from ATLAS-CONF A two dimensional side-band background subtraction was used to measure the purity Two sets of cuts were reversed: –Tight Photon Strip Isem cuts DeltaE Fracm Wetalc DEmaxs1 –Isolation Etcone40 – (underlying event correction) 5 GeV used as reversed cut Underlying event correction was on average about 500 MeV

26 August Direct Photon Note Purity Method

26 August Direct Photon Note Purity Method Formula used to calculate the purity in direct photon note: Data set used: 15.8nb -1 Extracted purity 0.72±0.07 for tight photons with p T > 20 GeV

26 August Purity Measurement – GMSB Sample Used 305 nb -1 of 7 TeV data Same shower shape cuts were reversed Direct photon note-like isolation cut –Etcone40 5GeV –N A : N B : 5023 M A : 460 M B : 213 –Purity – 0.64  Compare to 0.72 GMSB note isolation cut –Etcone20/et –N A : N B : 9081 M A : 201 M B : 405 –Purity – 0.46

Breakdown of Background Sources  Data-driven background estimation strategy may be source-dependent Andrea Bangert

26 August selection cuts event must fire EF_g10_loose trigger all jets must pass jet quality cuts event must produce primary vertex with at least four tracks event must produce at least one reconstructed photon pseudorapidity of cluster in 2 nd sampling is |η| < 2.47 cluster is not in the crack region, 1.37 < |η| < 1.52 E T (ΔR < 0.2) < 10 GeV photon passes isEM tight criteria p T > 20 GeV no cut was placed on MET no cut was placed on number of jets matching was performed using ΔR = √[(Δη) 2 + (Δ ϕ ) 2 ]; may want to update?

26 August samples JF17 10 million initial events selected reconstructed photons JF35 5 million initial events selected reconstructed photons gamma + jets pythia sample number ,000 initial events selected reconstructed photons diphoton pythia sample number ,000 initial events selected reconstructed photons ttbar sample number ,000 initial events 6943 selected reconstructed photons negative event weights have not been taken into account (12% effect)

26 August fraction of selected reconstructed photons attributed to various truth objects object matched to reco photon JF17JF35gamma + jet diphotonttbar photon from hard scatter photon radiated by quark or gluon hadrons (56 photons) (6 photons) bremsstrahlung photon photon radiated by W or Z (2 photons) (4 photons) photon radiated by heavy lepton (5 photons) (23 photons) electron from W -> ev or Z -> ee (52 photons) (135 photons) electron from decay of B or D (77 photons) (73 photons) (34 photons) unknown object (124 photons) (1 photon) (muons, taus, ν)

26 August fraction of reconstructed photons matched to various stable hadrons JF17JF35gamma + jetsdiphotonttbar neutral pion (49 photons) (2 photons) eta or eta’ (5 photons) (1 photon) (27 photons) omega (1 photon) (2 photons) neutral kaon (285 photons) (1 photon) (15 photons) charged pion or charged kaon (315 photons) (2 photons) (19 photons) sigma (4 photons) 000 proton (5 photons) (16 photons) (1 photon) neutron (12 photons) (16 photons) (1 photon) 0 heavy ions Denominator is all reconstructed photons that were matched to true hadrons.

26 August Conclusions from Background Component Study QCD processes that do not produce photons in the hard scatter are modeled by JF17 and JF35 (Note that the ~10% of events with photons in the hard scatter were not removed, they were merely counted.) 60% - 70% of the selected reco photons are attributed to hadrons 80% of these are attributed to neutral pions 10% are attributed to eta or eta’ 20% of the selected reco photons match a photon radiated by a quark or a gluon 4% of the selected reco photons match a bremsstrahlung photon

26 August Where from Here? One thought: 10 pb -1 prototype analysis (i.e data set) 10 pb -1 not enough to improve, e.g. on Tevatron GMSB (SPS8) limits Should be enough to –Develop analysis (background estimation) techniques –Prepare for publishable limit –[Generate PhD theses]

26 August pb -1 “proto”-Analysis Scaling up, would have diphoton events Perform analysis optimized for scaled- back limit (MET, HT cuts); fast-MC-based re-optimization underway Would likely circumvent issues encountered in late July (second photon likely to greatly suppress QCD backgrounds)

26 August Summary The strong and weak production mechanisms contribute as we had come to suspect There is a third intermediary type of events, but its cross section is very small Strong production component is already pretty small at Λ=90 for 7 TeV and drops off quite quickly from there No real revelations here but at least it conforms what we had suspected was going on

26 August definitions truth objects were required to enter the fiducial area of the detector |η| < 3.0 truth objects were required to have E > 10 GeV “photons” include both photons and electrons from pair production “electrons” include both electrons and bremsstrahlung photons “hadrons” include hadrons deemed stable by the generator π 0, π ±, η, ϖ, K, Σ, p, n, heavy ions “hadrons” include hadrons, photons from hadron decays electrons from pair production for example, “neutral pions” include π 0, photons from π 0 -> γγ e ± from π 0 -> γγ followed by γ -> e + e -

26 August fraction of reconstructed photons matched to hadron, photon, electron JF17JF35gamma _ jets diphotonttbar π0π (17 photons) 0.5 (1 photon) γ from π 0 -> γγ (17 photons) e from γ ->ee (15 photons) 0.5 (1 photon) JF17JF35gamma _ jets diphotonttbar η0η (1 photon) (8 photons) γ from η 0 -> γγ (1 photon) 1 (1 photon) (15 photons) e from γ ->ee (3 photons) (4 photons) The denominator includes all reco photons matched to neutral pion (or photon or electron). The denominator includes all reconstructed photons matched to an eta, a photon from decay of an eta, or a conversion electron.

26 August fraction of reconstructed photons attributed to radiation from quark or gluon that convert JF17JF35gamma + jetdiphotonttbar q -> q gamma (12 photons) (3 photons) q -> q gamma followed by gamma -> ee (8843 photons) The denominator is the number of reconstructed photons attributed to radiation from a gluon (or a quark). The numerator is the number of those reconstructed photons that were matched to a true electron from a conversion. JF17JF35gamma + jetdiphotonttbar g -> g gamma (4 photons) (7 photons) g -> g gamma followed by gamma -> ee (7410 photons) (8 photons)