Backgrounds using v7 Mask in 9 Si Layers at a Muon Higgs Factory

1. Backgrounds using v7 Maskin 9 Si Layers at a Muon Higgs Factory T. Markiewicz & T. Maruyama / SLAC MAP Collaboration Meeting 5 December 2014

2. Motivation Using tools developed for ILC studies and masking design from the MARS team • Verify level, source and composition of backgrounds • MARS versus FLUKA • Understand effectiveness of the timing cut in reducing backgrounds • Depends on background particle: photon, e+/-, neutron, h+/- • Depends on location/size of each silicon layer • Develop figure of merit and compare it to ILC values to evaluate “is a muon collider detector readout possible” • Hits/(readout area)/(readout time) • Readout area • VXD 20um x 20um pixels • Tracker 50um x 1cm strips • ECAL front face 1cm x 1cm • Two relevant readout times • Per train (read 1000 BX, buffer & readout between fills: ILC approach) • Per BX T. Markiewicz

3. FLUKA Geometry 2013: v2 Mask 2014: v7 Mask Takashi Maruyama • In all plots: • 1 beam only • beam enters from R side • Beam starts at • X=-1.947m • Z=22.5077m • S=22.71m • T0=75.7ns T. Markiewicz

4. For May 2014 Meeting Used “v2 cone mask” This talk: version 7 maskMasks v2 versus v7 Locations where design was tweaked: tip of cone and radius of beampipe the most critical T. Markiewicz

5. Comparison of SLAC FLUKA with Striganov MARS(2 bunches, 1 BX): Message: Reasonably consistent except for v7 e channel Hits FLUKA/ MARS 350cm/ 600cm V7/V2 MARS V7/V2 FLUKA FLUKA/ MARS v2 v7 Seem anomalous T. Markiewicz

6. Study Hit Density per Readout Plane • Geant 3 Detector planes • Each 320um Silicon • Track Fluka generated particles in 4 Tesla field • Record hit position and hit time • Find hit density per readout time w/ and w/o timing cut • Figure of merit for ILC backgrounds and detectors • Some preliminary discussions of readout electronics required T. Markiewicz

7. Pythia TOF used to set a timing gate for each layerTiming resolution not considered Barrel 1 Barrel 2 Barrel 3 1.5-4ns 4-10ns 0-1ns Z (cm) Time (ns) Endcap 3 Endcap 1 Endcap 2 6.5-9ns 0.5-1.5ns 3-4ns R (cm) T. Markiewicz

8. Converted Photons on the Si Planes T. Markiewicz

9. Time and z of converted FLUKA photon background for all Si LayersIdentify from where & when “parent” background comes T(ns) Late x100 to get background associated with one bunch Early Z(cm) Cone Tips Z(cm) Downbeam Upbeam Upbeam Downbeam Downbeam Upbeam T(ns) T. Markiewicz Cone Tips Z(cm)

10. Hit multiplicity (all layers) • 0.59% of FLUKA photons entering the “detector volume” covert in a 320um Si layer • Each “parent” photon can produce an electron that spirals and hits in the Si layer ≥ 1 x • The long tail (cut in GEANT at 200) skews the mean multiplicity • What is the correct multiplicity to use? Si Hits per converted g Plot cut at 20 Si Hits per converted g <>~10 <>~3 Tail T. Markiewicz

11. What is the best way to simulate secondary detector hits?Beyond the scope of this exercise, but effect is realMessage: there may be an additional factor that needs to be applied  • Setup massless scoring plane, score photon crossings and apply fixed conversion efficiency x hit multiplicity(2%). • Under estimate spirals. • Technique for ILC studies • Setup Si layer and massless scoring plane, and score only charged particle crossings. • There are very low energy spirals inside the scoring volume . • There are low energy electrons that don’t come out of Si. • Setup only Si layer and score only energy depositions. T. Markiewicz

12. Innermost VXD Layer-Converted Photons(Example of procedure applied to each of the 3 Barrel & 6 Endcap Silicon Layers) 0-1nsTOF cut .064%<1ns <>=311; Peak/<>~2 34.4% remain after 0-1ns cut Peak/Average hit density an issue T. Markiewicz

13. Converted photon hits on r=50cm and r=131cm barrel layers 92.3% in 4-10ns 50.8% in 1.5-4ns <>=301; Peak/<>~2 <>=131; Peak/<>~2 T. Markiewicz

14. e± backgrounds Good comparison v2 versus v7Show a few examples of e ± given discrepancy of MARS and FLUKA in this channel T. Markiewicz

15. e+e- backgrounds: All scoring planes v7 v2 Time of parent Time of parent v7 v2 Z(cm) of parent Z(cm) of parent T. Markiewicz

16. e+e- backgrounds: All scoring planes v7 v2 #Si hits per incident e± #Si hits per incident e± v7 v2 Time of Si hit Time of Si hit T. Markiewicz

17. Time Distribution of e+e- hits on Innermost Barrel 5.3% time=time_parent+time_child 0-1ns gate v7 v2 <>=162 Peak/<> ~ 5.5 T. Markiewicz

18. Relatively few e+/e- Backgrounds make it to the r=50cm barrel but those hits are “in time” with physics events v7 v2 v7 v2 T. Markiewicz

19. Neutrons • In this simulation, neutrons do not interact with Si in layers but can hit the layer more than 1 time or can hit more than 1 layer. <N_hits/incident n> ~ 2 • Would have needed to create a FLUKA detector model to do it right • Separate FLUKA studies (included with supplemental material) indicate that the probability for a neutron to produce a signal in silicon is ~ 0.1% • While neutron hit densities shown here are an overestimate, they are all very effectively eliminated by the timing cut T. Markiewicz

20. Parent Neutrons Leaving Mask Transition to B-CH2 T. Markiewicz

21. Z and Time Distribution of all Parent Neutrons(note the large time & distance scales) Transition to B-CH2 Time parent neutron enters detector T. Markiewicz

22. ALL Layers-Children of Parent Neutrons Time parent neutron takes to hit silicon Total time of Si hit relative to bunch crossing time T. Markiewicz

23. Neutrons hitting Innermost Tracker Layer at r=50cmShown to highlight effectiveness of time cut for neutrons 6.7E-4 in 1-4ns <>=1287; Peak/<>~2 T. Markiewicz

24. Charged HadronsWill not go through individual plots as they are not a dominant factor in the overall hit densitySee plots included as supplementary material if interested T. Markiewicz

25. ILC Readout Design has 4-deep buffer for train Background Summary Time cut Effectiveness Detector granularity T. Markiewicz

26. Contributions to Average Hit Density Before Timing Cuts T. Markiewicz

27. Contributions to Average Hit Density After Timing Cuts T. Markiewicz

28. Sum of all Background Sources after Timing CutsPeak Background per Silicon LayerIgnore density variation in Phi T. Markiewicz

29. Conclusions • Change to the version 7 conic mask design with larger beampipe radius reduces backgrounds x2-3 • We do not see the x30 reduction in the e- channel shown by MARS • Irreducible backgrounds in the photon and electron channels emanate from the IP area, predominately from the downbeam cone tip, and are thus largely in time with the collision • Nonetheless, timing in tight gates can reduce these backgrounds ~x2 • Neutrons and charged hadrons emanate from the body of the conic mask • Timing can reduce the charged hadron background by x3-10 • The neutrons, which dominate the hit density outside the barrel VXD, are very slow and are very effectively eliminated by timing: only .05-.15% remain after cuts • An accurate determination of hit density requires a detailed detector model, ideally with clustering. The simplified model used in this analysis has shown • Photon backgrounds convert with 0.6% probability in 320um layers of Silicon • While the “most probably” number of hits per converted photon is 2-3, there is a long tail (artificially cut at 200) that drives the mean number of hits to >10. • The average separation of these hits is ~1mm, so it seems like they would “count” in the tracking & vertex detectors • ILC analyses assumed 2% for the product of conversion probability and hit multiplicity; the analysis here results in ~ 6% • As all the neutrons are cut by the timing gate, we have only SCORED them in this analysis • Separate studies indicate that these low energy neutrons will produce visible hits in thin Si 0.1% of the time • Signal in calorimetry has not been studied • Timing cuts not particularly effective given (in this IR geometry) proximity of cone tips to the IP (±0.7ns away) • Silicon strip tracker (50um x 1cm) show 100%-500% occupancy per BX to be compared to ILC performance of 1-2%. Can argue what is max. allowed (10% ?), but 100% does not work. • Hits per readout unit per train (1000 BX) >> 4 buffers designed for the ILC Readout architecture (“KPIX”) • Reading each readout element each bunch crossing probably required • Barrel backgrounds more important than endcap backgrounds • Endcap hits caused by spiraling e+e- are out of time when they hit endcap trackers • Tracker backgrounds with 50um x 1cm strips >> VXD backgrounds with 20 um x 20um pixels • Barrel and Endcap ECAL need to passively absorb 50-200 ~1 MeV photons/pad/BX without showing a hit T. Markiewicz

30. Supplemental MaterialFollows T. Markiewicz

31. Time Distribution of photon hits on 2 VXD disks at z=30cm, 6.7<r<18.4 After nh<21 cut 78.6% in Gate 0.5<t<1.5ns <>=14; Peak/<>~10 97% hits left after nh cut Peak due to inner barrel VXD layer T. Markiewicz

32. Time Distribution of photon hits on 2 disks at z=92cm, 25.3<r<53.3cm 67.3% in Gate 3<t<4ns <>=4.4; Peak/<>~5 Peak due to inner barrel tracker layer T. Markiewicz

33. Time Distribution of photon hits on 2 disks at z=200cm, 38<r<130.9cm 59% in Gate 6.5<t<9ns <>=4.2; Peak/<>~6 T. Markiewicz

34. Relatively few e+/e- Backgrounds make it to the r=131cm surface of the barrel Ecal, but those hits are “in time” with physics events v7 v2 v7 v2 T. Markiewicz

35. Time Distribution of e+e- hits on z=25cm DisksMany, many spirals before hitting disk delays arrival v2 v7 time=time_parent+time_child 0.5-1.5ns gate 1% in 0.5-1.5ns gate v7 <>=113 Peak/<> ~ 4.4 v2 T. Markiewicz

36. Relatively few e+/e- Backgrounds make it to the z=92cm fwd trackerthe tighter time cuts help further as e+/e- source is far up the cone, away from the IP at large z v7 v2 <>=2.5 Peak/<> ~ 4 v2 v7 2% in 3-4ns gate T. Markiewicz

37. Relatively few e+/e- Backgrounds make it to the z=200cm surface of the Endcap Ecalthe tighter time cuts help further as e+/e- source is far up the cone, away from the IP at large z v7 v2 v2 v7 4% in 6.5-9ns gate T. Markiewicz

38. Charged HadronsWill not go through individual plots as they are not a dominant factor in the overall hit densitySee plots included after talk proper if interested T. Markiewicz

39. Charged Hadrons T. Markiewicz

40. Parent Hadrons Leaving Mask T. Markiewicz

41. Z and Time Distribution of all Parent Charged Hadrons T. Markiewicz

42. ALL Layers-Children of Parent Charged Hadrons T. Markiewicz

43. All Layers--Children of Parent Hadrons T. Markiewicz

44. Innermost VXD Layer-Hadrons 12%<1ns <>=22; Peak/<>~1.5 T. Markiewicz

45. Innermost Tracker Layer at r=50cmCharged Hadrons <>=27; Peak/<>~1.5 20% in 1-4ns T. Markiewicz

46. OuterMostEcal Layer at r=131cmCharged Hadrons 36% in 4-10ns <>=6; Peak/<>~1.8 T. Markiewicz

47. InnerMost VXD Disk at z=30cmCharged Hadrons 16% in 0.5-1.5ns <>=12; Peak/<>~1.3 T. Markiewicz

48. First Tracker Disk at z=92cmCharged Hadrons 20% in 3-4ns <>=8.3; Peak/<>~1.5 T. Markiewicz

49. ECAL Disk at z=200cmCharged Hadrons 35% in 6.5-9ns <>=12.9; Peak/<>~2.3 T. Markiewicz

50. Neutrons T. Markiewicz