Report on the UCSCSCIPP Beam Cal Simulation Effort

Report on the UCSC/SCIPP Beam. Cal Simulation Effort ECFA Linear Collider Workshop Palacio de la Magdalena Santander, Cantabria, Spain May 30 – June 5, 2016 Bruce Schumm UC Santa Cruz Institute for Particle Physics

The SCIPP Beam. Cal Simulation Group The group consists of UCSC undergraduate physics majors (and one engineering major) • Christopher Milke (Lead)* Heading to SMU’s doctoral program in fall • Jane Shtalenkova, Luc D’Hauthuille, Spenser Estrada, Benjamin Smithers, Summer Zuber, Cesar Ramirez • Alix Feinsod Led by myself, with technical help and collaboration from Jan Strube, Anne Schuetz, Tim Barklow • • • Power consumption for irradiated Si sensors VXD Occupancy / Anti-Di. D Field Determining ILC IP parameters with the Beam. Cal Bhabha events and the two-photon physics veto SUSY in the degenerate limit 2

Power Draw of the Beam Calorimeter as a function of Temperature & Radiation Dosage Luc d'Hauthuille Bruce Schumm University of California, Santa Cruz

Motivation ● ● Folk wisdom suggests that Si diode sensors are not ideal for high-radiation environments due to their development of significant leakage current This may be correct, but is it truly a problem? We have taken extensive IV data as a function of ambient and annealing temperature, for a P-type sensor exposed to 270 Mrad (~ 3 years) of electromagnetically-induced radiation. Here, we estimate the resulting distribution & sum of the dark-current power draw in the Beam. Cal

Assumptions ● Power modeled as a function of radiation and temperature ● Power drawn scales linearly with radiation dosage ● Temperature dependent IV data was taken at SCIPP for a Si sensor exposed to 270 MRads of radiation after a 60˚C annealing process, by Cesar Gonzalez & Wyatt Crockett. ● A 3 rd degree polynomial was fit to this I vs. T data, for a Bias Voltage = 600 V

Overview ● The LCSIM framework was used to compute the energy deposited from 10 simulated background events (bunch crossings at 500 Ge. V collision energy) ● Energy deposited was then extrapolated for 3 years of runtime, and converted to radiation dosage ● Temperature was input and combined with radiation dosage to compute the power draw for each mm^2 pixel, at each layer, for 600 V bias (charge-collection about 90% after 270 Mrad) ● Power draw of these pixels was plotted on a heatmap for a range of temperatures (-7, 0, 7, 15 ˚C)

IV Curves at various Temperatures

Polynomial Fit for Temperature Dependent Current (600 V)

Model for Power Draw Using these assumptions, power drawn by a pixel is: P(R, T) = (R/270 MRads)*(600 V)*I(T) where R is radiation dosage, T is temperature, 600 V is the Bias Voltage and I(T) is the current given by the fit.

Layers 2 & 10 of Beam. Cal at T = 0˚C P_max = 4. 59 m. W (for a single mm 2 pixel)

Layers 2 & 10 of Beam. Cal at T = 15˚C P_max = 23. 16 m. W (for a single mm 2 pixel)

Power Drawn(Watts) of Beam. Cal collapsed T = -7 ˚C T = 0 ˚C P_total = 4. 467 W P_max = 1. 86 m. W (for a single pixel) P_total = 11. 01 W P_max = 4. 59 m. W (for a single pixel)

Total Power Draw Operating Temperature (0 C) Total Power Draw (W) Maximum for 1 mm 2 Pixel (m. W) 15 7 0 -7 56 25 11 4. 5 23 10 4. 6 1. 9

Further investigations ● ● Power draw maps can provide an input to design a system that avoids thermal runaway Three other types of Si sensors (NF, PC, NC) have been irradiated to 300 MRads and the PF sensor to 500 MRads, which await damage measurements

Bhabha Events Issue: • Degenerate SUSY has background from two-photon events • Hope to reduce by detecting scattered primary e+/- in Beam. Cal and vetoing the event • If a SUSY event is overlain with a Bhabha event with an e+/- in the Beam. Cal, we will reject SUSY What is the rate of Bhabha events with e+/- in the Beamcal? Bhabhas with virtuality -Q 2 > 1 Ge. V (~ 4 mrad scatter) available at ftp: //ftp-lcd. slac. stanford. edu/ilc 4/DBD/ILC 500/bhabha_inclusive/stdhep/bhabha_inclusive*. stdhep with cross section = 278 nb Raw rate of 0. 76 Bhabha events per beam crossing 15

Bhabha Event Classes Bhabha events fall into three classes Miss-Miss: Both e-/e+ miss the Beam. Cal; not problematic Hit-Hit: Both e-/e+ hit the Beam. Cal; should be identifiable with kinematics (need to demonstrate) Hit-Miss: One and only one of e-/e+ hit the Beam. Cal; background to twophoton rejection. Event Type Fraction of Q 2 > 1 Bhabhas Fraction of Beam Crossings Miss-Miss 23% 18% Hit-Miss 14% 11% Hit-Hit 63% 48% Naively, 11% of SUSY events would be rejected due to Hit-Miss events, plus whatever fraction of the 48% of Hit-Hit crossings aren’t clearly identified 16 based on e+/- kinematics.

Hit/Hit events: e+-e- angular correlation “Type a quote here. ” –Johnny Appleseed

After cut of < 1. 0 Mrad, 33% of Hit/Hit Bhabhas remain (16% of crossings). Can possibly eliminate with energy cut (need to balance against two-photon and SUSY events) 18

For Hit/Miss events, there may well be useful kinematic handles… but again, need to compare to two-photon and SUSY signal distributions 19

Degenerate SUSY and Electron Tagging SUSY has a cosmologically-motivated corner where a weakly-coupled particle (stau) is nearly generate with the LSP ( 0) We have generated events at Ecm= 500 Ge. V with • M ~= (100, 150, 250) Ge. V • ~- 0 splittings of (20. 0, 12. 7, 8. 0, 5. 0, 3. 2, 2. 0) Ge. V Concern: Two-photon events provide greater and greater background as splitting decreases. Hope: We can tag the scattered electron or Positron in the Beamcal and veto. But: If photons are from Beamstrahlung, electron/positron 20 do not get a p kick (is this right Tim? )

Two-Photon Event Rate Thanks to Tim Barklow, SLAC, we have ~107 generatorlevel two photons events, with electron/positron photon fluxes given by the Weizsacker-Williams approximation (W) and/or the Beamstrahlung distribution (B). Events have been generated down to M = 300 Me. V. For this phase space, the ILC event rate is approximately 1. 2 events/pulse. 1 year of events corresponds to (1. 2)x(2650)x(5)x(107) events, or about 1. 6 x 1011 events per year. How do we contend with such a large number of events in our simulation studies? 21

Two-Photon Approach Convenient data storage in 2016: ~5 TB Tim Barklow: • 5 TB is about 109 generated (not simulated!) events • 1011 events requires 4000 2 -day jobs Jan Strube: Don’t worry about CPU (really? ) Proposed approach: • Do study at generator-level only. • Except: Full Beam. Cal simulation to determine electron-ID efficiency as a function of (E, r, ) of electron. Parameterize with 3 -D function and use in generator-level analysis • Devise “online cuts” applied at generation that reduce data sample by x 100 (can this be done? ) 22 • Store resulting 109 events and complete analysis “offline”

In Search Of: “Online Selection” For now, looking at three observables: • M: mass of system • S: Sum of magnitudes of p. T for all particles in system • V: Magnitude of vector sum of p. T for particles in system Each of these is done both for Mc. Truth as well as “reconstructed” detector proxy Detector Proxy: Particles (charged ot neutral) detected if • No neutrinos • |cos( )| < 0. 9 23

ISO “Online Selection”: Mass (M) 0 Mass 2 Ge. V Splitting Two-photon background SUSY Signal; ~ Mass = 150 Ge. V Seems like a clean cut, but what is seen in the “detector”? 24

“Detected” Mass (M) 0 Mass Two-photon background SUSY Signal; ~ Mass = 150 Ge. V For 2 Ge. V splitting, even a cut of 0. 5 Me. V removes some signal 25

S Observable: “Detected” 0 Mass SUSY Signal; ~ Mass = 150 Ge. V Two-photon background Fairly promising as well; but is it independent of M? 26

V Observable: “Detected” 0 Mass Two-photon background SUSY Signal; ~ Mass = 150 Ge. V Not as promising; looks better for “true”, but even for Vtrue = 0, reconstructed V has significant overlap 27 with SUSY signal (save for “offline” part of study? )

Cut flow for S, M Distributions News is not the best: • S and M observables very correlated • 3% loss of signal (at 2 Ge. V!) reduces background by only ~2/3 Other discriminating variables? 28

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Forward EMCal Readout Buffer Depth Study Issue: • EMCal read out by KPi. X chip • KPi. X chip has limited number of buffers (currently 4). This limits the number of hits that can be recorded per pulse train • Study backgrounds to determine if buffer depth needs to be extended, and if so, by how much. 32

Event Types Included Pair Backgrounds Gamma-gamma to Hadron Bha Low Cross-section (down 33 to 0. 1 events/train)

Hit Number Distribution (Integrated over a full train) 34

Fraction of Hits Lost During the Train as a Function of KPi. X Buffer Depth 35

But: Are there “Hot Spots”? Fractions of Hits Lost, By EMCal Layer 36

Fractions of Hits Lost, By Radius (Distance from Beam Line) 37

Event Types Included 38

Event Types Included 39

Tiling strategy and granularity study Constant 7. 6 x 7. 6 5. 5 x 5. 5 3. 5 x 3. 5 Variable Nominal/ 2 Nominal/2 40

Parting Thoughts • The SCIPP simulation group is active on a number of fronts. • In addition to expanding our Beam. Cal efforts, we are also looking into the forward EMCal occupancy. • We have a number of studies in mind, largely related to answering design questions about the Beam. Cal. We continue to be open to suggestion or refinements. • Support from Norman and others will remain essential. 41