Update on Trigger simulation

1. Update on Trigger simulation Spasimir Balev /CERN/ 13.07.2011

2. Introduction The rate with ideal CHOD_Q0 signal was 200 kHz

3. What we learned: • The “default” rate with ideal CHOD_Q0: 200 kHz • The “default” rate with realistic CHOD_Q0: 500 kHz •  We can no longer play with simple kinematics signals • Taking into account the interactions in the trigger simulation is important • All but ~60 kHz of this (500 kHz) rate is junk  decays happening after Z = 165 m. • Realistic and not so realistic solutions: • put SAC and IRC or STRAW at L0  not feasible; • use RICH reconstruction at L0  a drastic improvement which will allow fairly simple cuts in CHOD; • play with CHOD multiplicity  complicated signals; interplay between signal and junk triggers losses; requires well established analysis procedure  getting in shape, but still key ingredients missing… • We can not survive without CHOD: the output L0 rate becomes ~1 MHz, with significant halo contribution (mainly from p+m+ upstream GTK3) • The purpose of this talk: • to get an idea of optimal CHOD design in terms of trigger rates • quantify the effect on L0 output rate with different signals

4. CHOD acceptances • NA48 CHOD Not in |X|,|Y|<130 mm |X|,|Y|<1210 mm + octragon • Analysis CHOD 150 < R < 1080 mm • Trigger CHOD Analysis CHOD R(350 mm,0) < 1080 mm Not in |Y|<130 mm and -130 < X < 400 mmm p+ from pnn @CHOD after all cuts The trigger CHOD cut costs only 0.8% of the signal

5. CHOD pseudo-digitization • At the moment, no digitization is available in NA62FW for CHOD • In order to check the rates, we need to define signals • Kinematic signal  count every charged particle from K+ decay, or halo muon • Realistic signal  see below • The energy deposits are available for each single hit in NA62MC. • One charged particle can produce many “hits” (single energy deposit), which are stored separately with their coordinates, energy, time. • This is useful to study any possible design (given that CHOD consists of two planes with 2 cm thick vinyltoluene) • Recipe for realistic signal construction: • add each energy deposit within a single channel; • define a signal from this channel if the total energy deposit is Etot>2 MeV.

6. Example for the NA48 design Edep, MeV Edep, MeV One pp0 event: p+ and one g reach LKr the other g converts at the end of the RICH See the backsplashes from LKr: y,mm thit – t0, ns Edep, MeV Edep, MeV x,mm

7. The backsplashes thit – t0, ns Complicated time profile of CHOD hits Backsplashes from LKr Backsplashes from IRC CHOD H and V planes Ehit, MeV single charged track pair?

8. Rates calculation • Two designs studied: • the NA48 CHOD with 2 planes of vertical and horizontal slabs (64 + 64) with varying size: 6.5 cm width in the central area and 9.9 cm in the peripheral; • tiles design: 6.5x6.5 cm2 in the central area; 6.5x9.9 and 9.9x9.9 cm2 in the peripheral. • Two types of rates studied: • kinematical rate (for comparison purposes) • real rate (taking into account the interactions) • All the components simulated: • K+ decays downstream GTK3 (6 main decay modes) • p+ beam (with pm decays enabled) after GTK3 • halo and non-halo muons from K± and p± decays upstream GTK3 • Detailed rates by components given at MUV3/CHOD meeting; here – only the summary

9. Rates - Summary kHz kHz Kinematics signals Real signals kHz kHz

10. CHOD optimal design yCHOD, mm xCHOD, mm

11. Signal acceptance • The generated quantities used here (reconstructed in progress) • Total number of generated pnn events: ~105 • Total number in 105 < Z < 165 m range: 79 599 • 15 < P < 35 GeV37.5% • No pm decay 34.7% • 15 < RCHOD < 108 cm 29.6% • !LAV, RICH, LKR, !IRC, !SAC acc. 28.9% • MM2 cut 16.6%

12. p+ interactions Rint, mm Zint, m 8.1% of selected events are with p+ interacting before reaching CHOD

13. p+ interaction example LKR display CHOD display y, mm Ecell, MeV Ehit, MeV x, mm The signal event mimics pp0 decay. What the reconstruction will see? 16 crossing points

14. A glimpse to the trigger rates Default signals: CHOD * !MUV3 * RICH5 * !RICH40 * !LKR * !LAV12 Ideal Real NA48 acc. Real trigger acc. Multiplicity cuts 0  at least 1 quadrant; 1  exactly one quadrant; X  two opposite quadrants X14(X16)  number of crossing points between 1 and 4(6) For signal loss: all cuts applied for the normalization Eout< 500 MeV  energy in LKr outside a circle with 20 cm radius around the p+ (cell threshold 100 MeV)

15. Put CHOD time in the game • Italo’s idea [to be presented at MUV3/CHOD meeting]: • use two planes with horizontal tiles with the same geometry; • in the trigger use the time coincidence of the single tile from the first plane and the corresponding tile in the second plane, or the neighbouring ones; • suppress the rate from backsplashes or interacting photons. • Try simple implementation of the idea with the existing tools: • segment CHOD as in the 32 x 32 “tiles” design (much finer segmentation than what we will have  only to test the effect in extreme case); • for each tile count the minimum time of hits above the threshold (1 MeV); • no resolution smearing applied  times ideally computed by G4 • construct a signal from a given pair of tiles from 1st and 2nd planes (including the neighbouring ones) if Dt < 5 ns • ~1.5% of the selected pnn are without a signal (8.5% if the 2 neighbouring tiles in the second plane are ignored). • Multiplicity signals defined: • Nt  total number of tile pairs • Nq  total number of quadrant with tile pairs giving a signal

16. Trigger rates Default signals: CHOD * !MUV3 * RICH5 * !RICH40 * !LKR * !LAV12 Significantly better separation for signal and background, leading to acceptable rate. However, this is a much finer segmentation than what we will have  to be investigated. No effect from 5 ns  2 ns time difference between the two planes Strong dependency on the Energy threshold due to the way the process of energy loss is simulated.

17. CHOD multiplicity rates [summary]

18. Summary • The design of the new CHOD could be optimized for efficient triggering purpouses a suitable segmentation can allow to exclude areas, not populated by the signal at high intensities. • With more complicated CHOD signals it is possible to keep the L0 output rate at 200-300 kHz for the main trigger, without RICH. It is still mainly junk, however… • This is (almost) the maximum with the tools available at the moment. • To progress further in trigger simulation it is needed: • Overlay MC • reasonable LKr reconstruction • CHOD digitization and reconstruction • multi-ring RICH reconstruction • MUV1/2/3 reconstruction

19. S P A R E S

20. CHOD studies for pnn • 13242 events in analysis cuts: • 1.4% (182 events) with 0 crossings • 92.2% (12208 events) with 1-4 crossings (80% with 1 crossing point) • 6.4% (852 events) with more than 4 crossings • 9% (1231 events) with Eout > 500 MeV • 1083 (8.2%) with interactions before CHOD • 0.5% (61 events) with 0 crossings • 2.5% (329 events) with 1-4 crossings • 5.2% (693 events) with more than 4 crossings: • 0.5% (63 events) are with Eout < 500 MeV • 4.7% (630 events) are with Eout > 500 MeV • 6.3% (863 events) with Eout > 500 MeV • Eout is the total LKr energy outside 20 cm around the impact point of p+ if Ecell > 100 MeV • 12159 (91.8%) w/o interactions before CHOD • 0.9% (121 events) with 0 crossings • 89.5% (11879 events) with 1-4 crossings • 1.2% (159 events) with more than 4 crossings • 2.8% (368 events) with Eout > 500 MeV • Using 1-4 crossing points or Eout > 500 MeV cut, the signal acceptance goes to 15% (from 16.6%) • 18% of the good events are with more than 1 crossing point • To be compared with 30% obtained by Gianluca on 2007 data (1 track + 1 cluster)