γ Detection efficiency for DM Searches with Single-Multi γ

J-J.Blaising, LAPP/IN2P3 1

γ Detection efficiency for DM Searches with Single-Multi γ

CLIC-WS February 2014

OUTLINE• Motivation and Goal• Measurement Method of Systematic error of γ Detection Efficiency. • Full Simulation Results using:

1. e⁺ e⁻→ µ⁺ µ⁻ γ2. e⁺ e⁻→ e⁺ e⁻ γ

• Summary and Prospects


Motivation and Goal


At CLIC at 500 GeV, with ∫L=500 fb⁻¹ could perform a high precision measurement of the e⁺ e⁻→ ν ν γ cross section.Left plot dN/dEγ: for e⁺ e⁻→ ν ν γ events; high energy ISR γs from Z return events and low energy γs Eγ < 200 GeV.Right plot dN/dEγ: e⁺ e⁻→ ⁰₁ χ̃� ⁰₁χ̃� γ, (model III, m ⁰=100 GeV).χ̃�An excess in the low E part of the measured dN/dEγ spectrum w.r.t the SM spectrum would be a hint of BSM physics; e.g Susy, large ED…


Motivation and Goal


For 10 GeV < Eγ < 200 GeV, σ(e⁺ e⁻→ ν ν γ) =2414 fb.with ∫L=500 fb⁻¹, a sensitivity of ~ 20 fb can be reached provided that the systematic errors on: • the detection efficiency εγ (signal) • the veto efficiency εv (backgrounds) are controlled with an accuracy ~ 10⁻³ . To minimize the dependence from the MC the γ detection and identification efficiency should me measured using “data”.In e⁺ e⁻→ µ⁺ µ⁻ , ( e⁺ e⁻) interactions (µ⁺+µ⁻)t , (e±) ~ 0.In e⁺ e⁻→ µ⁺ µ⁻ γ, (e⁺ e⁻ γ) interactions (µ⁺+⁻)t , (e±) = (∑γ)t. The correlation between (∑γ)t and (L⁺+L⁻ )t is used to tag events with γs.

J-J.Blaising, LAPP/IN2P3

Tagging Method

CLIC-WS February 2014 4

In e⁺ e⁻→ µ⁺ µ⁻ γ interactions there are two types of γ’s: • High energy ISR γs (Z return) Plot (∑γ)t vs (µ⁺+⁻)t Requiring (µ⁺+⁻)t > 45 GeV Tags events with 10⁰< θγ < 170⁰

• Low energy ISR and FSR γsPlot (∑γ)t vs (µ⁺+⁻)t Requiring (µ⁺+⁻)t > 10 GeV Tags events with 10⁰< θγ < 170⁰Same for e⁺ e⁻→ e⁺ e⁻ γ interactions


Simulationand Reconstruction


Events generated with whizard1.95Simulation and reconstruction using:• CLIC_ILD_CDR geometry • Mokka and Marlin CDR software versions


e⁺ e⁻→ µ⁺ µ⁻ γ


R and T μ± invariant mass Mμ± good R/T agreement.Right : ∆P=P(T)-P(R) rms=0.9 GeV (µ⁺+⁻)t (R) vs (µ⁺+⁻)t (T) using the selection of slide 4. good R/T correlation; all events have γ, θγ>10⁰


γ Detection Efficiencye⁺ e⁻→ µ⁺ µ⁻ γ


Left: (∑γ)t (R) vs (µ⁺+⁻)t (R) ; events with γ (blue) ; without γ (red)good correlation; 48 events without γ => εγ=0.998 ; 27 have a N PfoRight: R and T dN/dEγ of the most energetic γ.Eγ (T) smeared assuming ∆E/E=0.009+.25/√Eγ; reasonable agreement.


e⁺ e⁻→ µ⁺ µ⁻ γdN/d∆Eγ


Left : dN/d∆Eγ of most energetic γ with R/T θ match ; rms=6.1 GeVUnderflow: 2 or 3 True γ ~ same θγ reconstructed as one γ; ok.Overflow: bad measurements or γs broken into γ +N (45% of evts)Right: dN/d∆Eγ for events without N, ∆Eγ improved; rms=4.5 GeV


e⁺ e⁻→ µ⁺ µ⁻ γSummary


The good μ± momentum resolution allows tagging of events with 10 < θγ < 170 ⁰ using the correlation between (∑γ)t and (µ⁺+⁻)t .

In ~ 45% of events Pandora breaks γ into γ + N; it degrades ∆Eγ but the efficiency measurement is still possible.

Assuming ∫L=500 fb⁻¹ e⁺ e⁻→ µ⁺ µ⁻ γ events allow the γ detection and identification efficiency measurement with statistical accuracy of 4.2 10⁻³

The γ angular distribution is flat => in the forward region10 < θγ < 30 the statistical accuracy is ~ 1%


e⁺ e⁻→ e⁺ e⁻ (γ)


Left: (⁺+⁻)t (R) vs (⁺+⁻)t (T) using selection of slide 4.No correlation at low (⁺+⁻)t ; evts θγ<10 Right : ∆P=P(T)-P(R) ; long low side tail, bad rmsdN/dMe± ; bad R/T agreement at high M.Origin is Bremsstrahlung in material


e⁺ e⁻→ e⁺ e⁻ (γ)


Left: (⁺+⁻)t (R) vs (⁺+⁻)t (T) usingselection of slide 4 and rejecting the events with bremsstrahlung (simulation info)Good correlation, all events have γ with θγ>10⁰Right : ∆P=P(T)-P(R) =2.8 GeVdN/dMe±, good R/T agreement


e± Momentum Resolutione⁺ e⁻→ e⁺ e⁻ (γ)


∆P = 2.8 GeV for e± events and 0.9 GeV for μ± events; why? Left: dN/dθe for events with ∆P<5 GeV and ∆P > 5 GeV; ∆P > 5 GeV correlated with low θe values. More F tracks in e± events It affects the momentum resolution of high momentum e±Right plot: dN/dEe


γ Detection Efficiencye⁺ e⁻→ e⁺ e⁻ (γ)


(∑γ)t (R) vs (⁺+⁻)t (R); events: with γ (blue) ; without γ (red)Left : selection (⁺+⁻)t > 10 GeV; no Bremsstrahlung; εγ=0.985Right: selection (⁺+⁻)t > 15 GeV; no Bremsstrahlung; εγ=0.993Better correlation for low (⁺+⁻)t values.16 events without γ, but 10 have a N; 66 % of events have a N PFO


e⁺ e⁻→ e⁺ e⁻ (γ)dN/dθγ and dN/dEγ


Left: R and T dN/dθγ ; strongly peaked forward Right: R and T dN/dEγ; energy range covered down to 10 GeVadequate for ISR γ efficiency measurement


e⁺ e⁻→ e⁺ e⁻ (γ)dN/d∆Eγ


Left: dN/d∆Eγ; Underflow: 2 or 3 True γ ~ same θ reconstructed as one γ (ok). Overflow: γ broken into γ+N or bad measurement.Right: dN/d∆Eγ; events without N; still low side tail. Debug [-40,-30]: Pe± well measured; e/γ confusion due to θγ ~ θe ? Not crucial for the γ efficiency measurement but understanding the origin would improve the γ energy resolution.


e⁺ e⁻→ e⁺ e⁻ γSummary


The e± momentum measurement is strongly affected by bremsstrahlung in material.

To reach a momentum resolution allowing the tagging of radiative events requires:• Measurement of e± after γ radiation• Or rejection of events with bremsstrahlung electrons

In this study bremsstrahlung events identified using simulation info. Not applicable with real data => need a dedicated Marlin processor allowing their identification.


e⁺ e⁻→ e⁺ e⁻ γSummary


In ~ 66% of events Pandora breaks γ into γ + N; it degrades ∆Eγ;

Despite this bias, assuming ∫L=500 fb⁻¹, e⁺ e⁻→ e⁺ e⁻ γ events allow the γ detection and identification efficiency measurement with a statistical accuracy < 10⁻³ (provided that bremsstrahlung events are rejected or the momentum resolution of bremsstrahlung tracks is improved).

To provide some input about γ into γ + N breaking I viewed some events =>


e⁺ e⁻→ e⁺ e⁻ γEvents with N


e ± well measured; Eγ (T)=69.9 GeV, Eγ (R) =44.9 GeV ; En(R)=4.9 GeV ; Why is there a N? ; why ∆Eγ = 20 GeV ? ; Leakage in Hcal ?


e⁺ e⁻→ e⁺ e⁻ γEvents with N


e ± well measured, Eγ (T)=24.1 GeV, Eγ (R) =2.5 GeV ; En(R)=2.7 GeV Why is there a N? because the γ and e are close to a detector crack ?


Prospects• Can one improve the momentum resolution of e± with

bremsstrahlung in material or identify such events? I asked F.Gaede to help to address this issue.• Can one optimize Pandora to minimize γ into γ + N

breaking for isolated μ, e ? According to J.Marshall the Pandora version used for the ECAL optimization studies could reduce the γ misidentification => redo analysis.• If these issues are addressed successfully, next step:

estimate forward tagging systematic error reachable using radiative Bhabha events.



Backup



Event Tagging



e⁺ e⁻→ µ⁺ µ⁻ γEvent Tagging


At 500 GeV: √s/2 =250, Requiring:• Pµ⁻⁺ > 242 GeV => Eγ1 < 8 GeV and Pµ⁺⁻ > 200 GeV => Eγ2 < 50 GeVand (Pµ⁺ + Pµ⁻)t > 9 GeV => Eγ > 9 Gev =>γ radiated by µ⁺⁻ with 9 < Eγ < 50 Gev Sin(θγmin) = PtCut/Eγ (PtCut=9 GeV)For Eγ=50 GeV => θγ=10⁰ For Eγ=20 GeV => θγ=27⁰

For all other events requiring(Pµ⁺ + Pµ⁻)t > 45 GeV => Eγ>45 GeV=> Select high E γsFor Eγ=250 GeV => θγ=10⁰ Cut

Cut


e⁺ e⁻→ e⁺ e⁻ (γ) ILC


Andre suggested that more recent ILC tracking software could improve ∆Pe±. => Same analysis using ILC_LCD geometry, Mokka 080003 and Marlin 0116.Left plot: dN/dΔPe± ; no improvement w.r.t slide 15.Right plot: (θγT-θγR) vs θγT ; θγR problem fixed

γ Detection efficiency for DM Searches with Single-Multi γ

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