γ detection efficiency for dm searches with single-multi γ
DESCRIPTION
γ Detection efficiency for DM Searches with Single-Multi γ. OUTLINE Motivation and Goal Measurement Method of Systematic error of γ Detection Efficiency. Full Simulation Results using: e ⁺ e⁻→ µ ⁺ µ⁻ γ e⁺ e⁻→ e ⁺ e ⁻ γ Summary and Prospects. Motivation and Goal. - PowerPoint PPT PresentationTRANSCRIPT
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
J-J.Blaising, LAPP/IN2P3 2
Motivation and Goal
CLIC-WS February 2014
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…
J-J.Blaising, LAPP/IN2P3 3
Motivation and Goal
CLIC-WS February 2014
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
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Simulationand Reconstruction
CLIC-WS February 2014
Events generated with whizard1.95Simulation and reconstruction using:• CLIC_ILD_CDR geometry • Mokka and Marlin CDR software versions
J-J.Blaising, LAPP/IN2P3 6
e⁺ e⁻→ µ⁺ µ⁻ γ
CLIC-WS February 2014
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
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γ Detection Efficiencye⁺ e⁻→ µ⁺ µ⁻ γ
CLIC-WS February 2014
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.
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e⁺ e⁻→ µ⁺ µ⁻ γdN/d∆Eγ
CLIC-WS February 2014
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
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e⁺ e⁻→ µ⁺ µ⁻ γSummary
CLIC-WS February 2014
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%
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e⁺ e⁻→ e⁺ e⁻ (γ)
CLIC-WS February 2014
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
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e⁺ e⁻→ e⁺ e⁻ (γ)
CLIC-WS February 2014
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
J-J.Blaising, LAPP/IN2P3 12
e± Momentum Resolutione⁺ e⁻→ e⁺ e⁻ (γ)
CLIC-WS February 2014
∆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
J-J.Blaising, LAPP/IN2P3 13
γ Detection Efficiencye⁺ e⁻→ e⁺ e⁻ (γ)
CLIC-WS February 2014
(∑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
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e⁺ e⁻→ e⁺ e⁻ (γ)dN/dθγ and dN/dEγ
CLIC-WS February 2014
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
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e⁺ e⁻→ e⁺ e⁻ (γ)dN/d∆Eγ
CLIC-WS February 2014
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.
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e⁺ e⁻→ e⁺ e⁻ γSummary
CLIC-WS February 2014
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.
J-J.Blaising, LAPP/IN2P3 17
e⁺ e⁻→ e⁺ e⁻ γSummary
CLIC-WS February 2014
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 =>
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e⁺ e⁻→ e⁺ e⁻ γEvents with N
CLIC-WS February 2014
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 ?
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e⁺ e⁻→ e⁺ e⁻ γEvents with N
CLIC-WS February 2014
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 ?
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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.
CLIC-WS February 2014
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e⁺ e⁻→ µ⁺ µ⁻ γEvent Tagging
CLIC-WS February 2014
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
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e⁺ e⁻→ e⁺ e⁻ (γ) ILC
CLIC-WS February 2014
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