LUMI Simulation : Status and Prospects

1. LUMI Simulation :Status and Prospects N. Arnaud, A. Stocchi, B. Viaud LAL B. VIAUD

2. Overview • Reminder: what’s in place yet • Our present picture of what the next steps should be • What to do with the gamma monitors ? • Discussion: what would you have us do ? B. VIAUD

3. From Reality… GEM Positron / Electron Calorimeters e+ e- Photon Calorimeter B. VIAUD 12/19/2019 3

4. To the GEANT3 Simulation GEM Positron / Electron Calorimeters e+ e- Photon Calorimeter B. VIAUD 12/19/2019 4

5. Simulated Apparatus • Almost all we could think of is included: Materials & Fields, Detector response 12/19/2019 5 B. VIAUD

6. La simulation GEANT3 Detectors’ Materials & Geometry Transfert 2 Transfert 1 Collection Drift GEMs Calorimeters Foil kapton -Cu -kapton z Boite 12/19/2019 6 B. VIAUD 7 mm

7. La simulation GEANT3 Detectors’ Materials & Geometry Photon monitors LEAD Shields Signal acceptance window 7 12/19/2019 B. VIAUD

8. Plan Materials: Vacuum Chamber ‘’Y-tubes’’ 12/19/2019 8 B. VIAUD

9. La simulation GEANT3 Materials : Shielding ‘’SOYUZ ’’ No Soyuz 12/19/2019 9 B. VIAUD

10. La simulation GEANT3 Materials : Shielding ‘’SOYUZ ’’ Soyuz 12/19/2019 10 B. VIAUD

11. Plan Materials : Shielding LEAD walls 12/19/2019 11 B. VIAUD

12. Plan Fields QD0 Quadrupoles • Permanent Magnet • Bx = g.x, By=g.y , g = -2.93 kG/cm 12/19/2019 12 B. VIAUD

13. Plan Fields QF1 Quadrupoles • Permanent Magnet • Bx = g.x, By=g.y , g = 1.25 kG/cm 12/19/2019 13 B. VIAUD

14. Calorimeter’s response • GEANT simulates the shower and calculates the ΔE energy deposit at each tracking step. • We compute the photon yield nγ = Gaussian centred on Cte[#/MeV] х ΔE • We compute the optical attenuation along the tile and the WLS fibers n’γ -> nγ exp(-L1/a1)exp(-L2/a2) L1=Hit(trk) –> Hit(γonWLS) , L2=Hit(γonWLS) -> PM • We finally compute the photoelectrons yields in PM n(γel) = Quant. EffхGainх (1-δGain) хn’γ Green variables: ad hoc values originally plugged in simulation. Reproduce quite well the E resolution we expected, and confirmed with beamtests. Might still deserve data/MC based corrections at a later stage (?) Blue variables: not precisely known initially. Can have a big impact on the simulated E resolution. Determined with beamtests. 12/19/2019 B. VIAUD 14

15. Calorimeter’s response • E reconstruction • Angular dependence Mean~110 RMS~25 σE ~25% 110 γ<=>510 MeV # de γ’s # de γ’s 0 110 230 # γ 20 23 26 θgénéré [deg.] 0 90 180 Φgénéré [deg.] L1 = f(Φ,θ) Beamtest 15

16. Present Performance • The simulation is presently advanced enough to predict the Lumi vs. Rate scaling factor with some precision. Ree->ee(γ) = 450 ± 5 Hz @ L = 1032 /cm2/s OR Corresponds to the trigger selection : coincidence between2 modules above threshold. F. Bossi estimated that threshold  200 +/- 30 MeV. #γ= 43 16

17. Present Performance • The simulation is presently advanced enough to predict the Lumi vs. Rate scaling factor with some precision. Ree->ee(γ) = 450 ± 5 Hz @ L = 1032 /cm2/s OR Corresponds to the trigger selection : coincidence between2 modules above threshold. F. Bossi estimated that threshold  200 +/- 30 MeV. Together with the background subtraction many of you worked on, it leads to the online measurement. 17

18. What Next ?? Ideally: a more precise and background-free measurement. This takes: • A more elaborate selection algorithm => Coincidence in Calo sectors and GEM pads #γ => Improved Energy reconstruction (barycentre method to correct for the angular dependance) • An accurate Simulation, via thorough data/MC studies => Rate variation as a function of the calo sector, GEM ring, Energy cut, … => Check the angular dependence is the same in data/MC • A precise background description, via MC and data 18

19. First Steps toward This… • Set the GEMs position as precisely as possible in the simulation ; • Realistic reconstruction in the GEM ; • Evaluate the background level according to the Touschek simulation ; Determine which other sources can be simulated ; • Set the right length for the WLS in each sector ; • Check if something located around the IP and not yet simulated should be included (more accurate Siddharta, additional shielding, support, etc…) • Realistic Luminous region in the simulation. 19

20. Gamma Monitors • Also included in the simulation ; • Performance depends on S/B : we plugged Manuela’s Touschek simulation in our own simulation ; • Yet a few open questions : • Signal rate at very low angle, • Reconstruction : up to now, similar to what is done in the CALO ; • Enough ? • In addition to a relative luminosity measurement, can they be used to “simply” study backgrounds ? 20

21. Preliminary results: MC Samples • Low angle e+e- -> e+e- (γ) ( Θdown to 0.5o) generated with BHWIDE • Theoretical total Rate = 13120 kHz @ 1033 /cm2/s • Must try lower angles ! • Manuela’s touschek ntuple, lost particles extrapolated back inside the vaccuum chamber • Rate ~ 50 MHz per beam • Manuela’s ntuple corresponds to one beam, single bunch (10 mA). • I multiplied by 120 to get something realistic with full currents. • Correct ? 21

22. Evaluation des bruits de fond… e+ -> <-e+ GEANT-3 x [cm] z [cm] Most of Touschek particles leave the vacuum chamber right in front of the Gamma Monitor, and have to cross QF1 (heavy material). => Big showers covering the gamma monitors… B. VIAUD 12/19/2019 22

23. Starters: a quick look to the signal Just to get an idea of what happens to the signal… • X-Y in a frame attached to the entry face of the detector. • R = distance from the center of the enty face. [ Hz] X [cm] Y [cm] [ Hz] Y [cm] X [cm] [ Hz] Ehit-Egenerated [GeV] Rhit-Rgenerated [cm]

24. Starters: a quick look to the signal Starters: a quick look to the signal Extrapolation of the generated signal photons. Show those that are in the geometrical acceptance of the detector.

25. Starters: a quick look to the signal GEANT hits found on the entry surface of the detector. Red =>Hits due the “clean” signal: Photon associated with the Bhabha vertex by GEANT. Limited interaction with the material between the IP and the photon detector. Characterizing the clean signal can help to find good cuts to reject the bkg, if necessary.

26. Starters: a quick look to the signal Starters: a quick look to the signal Compare the distance R and the energy E of the GEANT hit with those of the extrapo- lated generated photon.

27. Starters: a quick look to the signal Total Rate at generation (Θ in [0.5, 15] degrees) = 13120 kHz “Ideal” Rate = 980 kHz “Hit Rate” = 270 kHz Clean signal = 82 kHz

28. What we see in the Gamma Monitor Number of photons collected in the 4 crystals -- background -- signal -- clean signal window Z Lead [ Hz] beampipe 4 Lead Lead 3 [ Hz] 2 1 [ Hz] Lead

29. What we see in the Gamma Monitor Number of photons collected in the 4 crystals Tot. signal rate = 1312 kHz Tot. bkg rate = 50460 kHz -- background -- signal -- clean signal [ Hz] Rate of events in which at least 1 MeV is left in the photon det. Background : 3278 kHz Signal : 258 kHz Clean Signal : 80 kHz S/B ~ 8% !!!!!! [ Hz] [ Hz]

30. What we see in the Gamma Monitor Let’s have a closer look... The number of photons is higher for the signal (higher energy). => Cuts seem possible. => Have to think about that. => Next slide shows the effect of a simple cut… [ Hz] [ Hz] [ Hz] [ Hz]

31. With some Cuts Background : 35 kHz Signal : 8 kHz Clean Signal : 4.6 kHz S/B ~ 50 % !!!!!! Uncertainty on the background rate could be large, and I need to think a bit to compute it since only a few events, with large weights, survive the selection… Check the effect of one simple cut: #photons in crystal 1 > 50 #photons in crystal 2 > 30 #photons in crystal 3 > 60 #photons in crystal 4 > 120 Total #photons > 3000 Cuts = half the average of the bkg distribution…

32. Conclusion at this point… • Large backgrounds, showing up at a difficult place for the photon detector; • Not easy a priori to get a very small S/B; • With the present state of the simulation, S/B can be as high as 50%; Not that bad (?) • However, the simulation might not be realistic yet; In particular, I’d like to check if the distribution of the #photons / unit of energy is realistic; Some data or beamtest to compare the MC with ? • Also, the signal rate should be bigger at Θ < 0.5 degrees. • Tried last week with 0.05 degrees: BHWIDE crashed • ‘’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’’ 0.1 degrees: signal rate  5, but • I am not sure to trust BHWIDE weights at these angles…

33. Background Characterization Using the Gamma Monitors • We wonder if it is interesting at all to use the Gamma Monitors not only for a fast measurement of the luminosity, but also as a tool to understand backgrounds; • A new master student at LAL could work on this, starting with a GEANT-4 simulation (for pedagogical reasons); One example of what he could do is to simulate the gamma monitors with no signal window in the lead brick and see what precision we can reach if we try to measure observables that characterize the various types of backgrounds… In any case, we need experts guidance: Ideas / suggestions ??

34. Discussion Now, I call for your ideas and/or suggestions: Something obvious I missed ? Something that should have priority ? What shall we drink tonight ? 34

35. Back-up 12/19/2019 35 B. VIAUD

36. Erreurs systématiques dominantes • Positionnement des calorimètres et du SOYUZ à +/- 1mm • Seuil du trigger à +/- 50 MeV • Bruits de fond : incertitude dans la simulation des Touschek + autres bruits de fond (ex: beamgas ) non encore évalués => σ = 100% Ree->ee(γ) = 460 ± 5 ± 35 ± 20 ± 60 Hz(@ L=1032/cm2/s) Ree->ee(γ) = 460 ± 5 ± 70 Hz => Mesure de L à ~ 15% (~5-10% pour la mesure optimisée) B. VIAUD 12/19/2019 36

37. RésultatsOnline 12/19/2019 37 B. VIAUD

38. Luminosité Online L = (1.2 ± 0.2)х 1032 cm-2s-1 X-check: http://www.lnf.infn.it/acceleratori/status/ 12/19/2019 38 B. VIAUD

39. Luminosité Online L = (1.2 ± 0.2)х 1032 cm-2s-1 Courants: I1 ~ 550 mA I2 ~ 450 mA Avant upgrade: L ~ 1.5 х 1032 cm-2s-1 avec: 12/19/2019 39 B. VIAUD

40. Luminosité Online L = (1.2 ± 0.2)х 1032 cm-2s-1 Courants: I1 ~ 550 mA I2 ~ 450 mA Avant upgrade: L ~ 1.5 х 1032 cm-2s-1 avec: I1 ~ 1430 mA I2 ~ 1430 mA 12/19/2019 40 B. VIAUD

41. Luminosité Online L = 1.2 х 1032 cm-2s-1 Courants: I1 ~ 550 mA I2 ~ 450 mA Avant upgrade: ~ 1/7 !! L ~ 1.5 х 1032 cm-2s-1 avec: I1 ~ 1430 mA I2 ~ 1430 mA 12/19/2019 41 B. VIAUD

42. Ambiance à Frascati • DAΦNE amélioré a déjà rattrapé l’ancien DAΦNE, avec des courants ~ 7 fois plus faibles ! • Les courants vont être progressivement montées jusqu’à 1430 mA Y a-t-il des raisons que la luminosité ne suive pas ? A priori non ! L’effet des sextupoles est normalement purement optique => dépend pas du courant… • Officieusement : test déjà considéré comme un succès. 12/19/2019 42 B. VIAUD

43. Bilan • Une super usine à B est complément crucial au LHC. • Les idées de collision à grand angle et de ‘’Crabbed waists’’ actuellement testées à DAΦNE. • Intense activité au LAL ! • Résultats préliminaires prometteurs. Perspectives • Monter les courants à leur valeur nominale (passer de 0.5 à 1.4 A) • Mesure de la luminosité dans sa configuration optimale. Conclusion du test : fin mai – début juin. • Super B en 2015 à Frascati ??? 12/19/2019 43 B. VIAUD

44. Taux d’événements Bhabha attendu • Cas idéal : juste l’acceptance angulaire des détecteurs (εrec. =100%) σ( e+e- ->e+e-(γ) ) ~ 1/θ3 => En utilisant juste le CALO: Ree->ee(γ) = 550 Hz(@ L=1032/cm2/s) Générateur: BHWIDE Nee->ee(γ) / 0.07o/s => En utilisant le CALO+GEMs Ree->ee(γ) =320 Hz(@ L=1032/cm2/s) --- 1/θ3 --- CALO --- GEM => Mesure de la luminosité (ex: en utilisant juste le CALO) Lmes = (1032/cm2/s) х Rmesee->ee(γ) /(550 Hz) => En réalité ! Lmes -> Lmes/ Eff(reco+selection) θ(e+) [deg.] => Simulation ! B. VIAUD 44 12/19/2019

45. Beam Test des Calorimètres. • L’atténuation optique le long de la tuile • détériore la résolution sur l’énergie • ATT = exp(-d/L1) • Longueur d’atténuation L1 mal connue a priori. • Évaluée entre 1 cm et 12 cm: • => σE entre 21% et 27% (MC) • Peut se corriger grâce au data/MC lors • de la prise de données, mais : • - bruits de fond faisceau • - correspondance imparfaite entre le seuil • appliqué par le trigger et le # coups dans le PM. < # de γ’s > 0 90 180 Φgénéré [deg.] Bruits de fond => Nouvelles contributions au pic de bhabha, difficiles à démêler (surtout avant mise en service des GEMs) => Beam test pour déterminer L1 Evts. triggant 12/19/2019 45 B. VIAUD Nombre de coups

46. Reconstruction : Calorimètre • Reconstruction de l’énergie • Détériorée par la dépendance angulaire Mean~80 RMS~20 σE ~25% 80 γ<=>510 MeV # de γ’s # de γ’s • Nécessitera une correction en cellules (Φrec,θrec) => σE ~20% 20 23 26 θgénéré [deg.] 0 90 180 Φgénéré [deg.] 0 80 160 # de γ’s • θrec : GEM • Φrec : méthode de barycentre • dans le calorimètre. σΦ ~7o 12/19/2019 B. VIAUD 46

47. Reconstruction : Calorimètre • Reconstruction de l’énergie • Détériorée par la dépendance angulaire Mean~80 RMS~20 σE ~25% 80 γ<=>510 MeV # de γ’s # de γ’s • Nécessitera une correction en cellules (Φrec,θrec) => σE ~25% • Necessitera une correction en cellules (Φrec,θrec) 20 23 26 θgénéré [deg.] 0 80 160 # de γ’s Φgénéré [deg.] • θrec : GEM • Φrec : méthode de barycentre • dans le calorimètre. B. VIAUD 12/19/2019 47

48. Reconstruction: GEMs • Dès qu’une trace traverse la couche de dérive de l’une des cellules (Φ,θ) • et dépose ΔE > ~1 keV • => cellule déclenchée • Tirage aléatoire pour simuler les X-talks 12/19/2019 48 B. VIAUD

49. Interaction Simulation - Construction e+ e- • Angle de croisement -> boost • Réduit l’acceptance de la coupure • exigeant 2 cellules back-to-back • dans les GEMs • => Eff(BtoB) ~ 22% au lieu de 99% z Boost x 12/19/2019 49 B. VIAUD

50. Interaction Simulation - Construction Distribution th. des hits sur la surface des GEMs • En décalant les deux GEM de • 0.5 cm dans la direction du • boost : • => Eff(BtoB) ~ 99% ! Droite Gauche <Δx> = 1 cm Gauche si back to back 12/19/2019 50 B. VIAUD Δx [cm]