1. Update on Trigger simulation
Spasimir Balev
/CERN/

2. Introduction
13/7/2011
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
13/7/2011

4. CHOD acceptances p+ from pnn @CHOD after all cuts
NA48 CHOD
Not in |X|,|Y|<130 mm
|X|,|Y|<1210 mm
+ octragon
Analysis CHOD
150 < R < 1080 mm
Trigger CHOD
R(350 mm,0) < 1080 mm
Not in |Y|<130 mm
and -130 < X < 400 mmm
The trigger CHOD cut costs only
0.8% of the signal
13/7/2011

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.
13/7/2011

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
13/7/2011

7. The backsplashes Complicated time profile of CHOD hits
thit – t0, ns
Complicated time
profile of CHOD hits
Backsplashes from LKr
Backsplashes from IRC
CHOD H and V planes
Ehit, MeV
13/7/2011
single charged track
pair?

8. Rates calculation Two designs studied: Two types of rates studied:
the NA48 CHOD with 2 planes of vertical and horizontal slabs ( ) 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
13/7/2011

9. Rates - Summary Kinematics signals Real signals kHz kHz kHz kHz
13/7/2011

10. CHOD optimal design
yCHOD, mm
xCHOD, mm
13/7/2011

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:
15 < P < 35 GeV %
No pm decay %
15 < RCHOD < 108 cm 29.6%
!LAV, RICH, LKR, !IRC, !SAC acc. 28.9%
MM2 cut %
13/7/2011

12. p+ interactions Rint, mm Zint, m 8.1% of selected events are with p+
interacting before reaching CHOD
13/7/2011

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?
13/7/2011
16 crossing points

14. A glimpse to the trigger rates
Default signals: CHOD * !MUV3 * RICH5 * !RICH40 * !LKR * !LAV12
CHOD signal
Rate of signal
[kHz]
L0 rate
Signal loss
[%]
Eout<500 MeV
CHOD_ACC_Q0
9916
212
3.6%
CHOD_ACC_TR_Q0
7928
166
4.5%
CHOD_Q0
11580
489
4.6%
1.9%
CHOD_Q1
9309
258
10.2%
4.9%
CHOD_Q0 * !CHOD_QX
9909
314
6.5%
2.5%
CHOD_TR_Q0
9493
402
5.7%
3.1%
CHOD_TR_Q1
7692
214
10.0%
5.0%
CHOD_TR_Q0 * !CHOD_TR_QX
8212
264
7.1%
3.5%
CHOD_X14
10018
286
9.1%
2.9%
CHOD_X16
10337
315
8.2%
CHOD_NSLABS_10
11496
390
5.8%
1.2%
CHOD_NSLABS_8
10620
324
8.7%
2.2%
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)
13/7/2011

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
13/7/2011

16. Trigger rates
Default signals: CHOD * !MUV3 * RICH5 * !RICH40 * !LKR * !LAV12
CHOD signal
Rate of signal
[kHz]
L0 rate
Signal loss
[%]
Eout<500 MeV
0 < Nt < 3
7812
222
6.9%
2.1%
0 < Nt < 4
8133
241
6.0%
2.0%
0 < Nt < 5
8267
259
5.4%
Nq = 1
7400
202
6.4%
2.4%
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.
13/7/2011

17. CHOD multiplicity rates [summary]
13/7/2011

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 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
13/7/2011

19. S P A R E S
13/7/2011

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)
13/7/2011