1. SAC/IRC data analysis Venelin Kozhuharov for the photon veto working group NA62 photon veto meeting

2. SAC/IRC RO
IRC
LAV
FEE
TEL62
4ch
SAC
4ch
To the PC farm
Sums to the CREAM RO
NHOD NewCHOD
L0TP
The TEL62 used by the IRC/SAC was actually hosting few other systems
NHOD, NewCHOD, MUV0
Few changes were made during data taking to optimize the performance

3. SAC/IRC in the last two weeks
The SAC/IRC TDCb changed on 30 November
072 replaced with 0104
TDCb moved from PP2 to PP0 in the TEL62
IRC TDC changed, the mapping became
SAC: TDC 0
MUV0: TDC 2
IRC: TDC 3
Changes are effective from run 3953!

4. First look at the data Run number Intensity Trigger Good bursts
Choosing few “representative” runs
Run number
Intensity
Trigger
Good bursts
4098
60%
Calo/20 [MUV1>5, LKr<5, !SAV]
518
4099
70% 30
4101
80% 59
4109
100%
CALO/20 [MUV1>5,LKr <5]
739
4124
CALO/15 [MUV1>6, LKr<4] & L1 (KTAG)
125
4141
CALO/10 [MUV1>6, LKr <4]
417
4147 (last) 93
Using official reconstruction (latest development version)
Reconstructing a “quasi randomly” chosen single burst

5. Hits multiplicity
SAC
IRC
Run 4147
Run 4147

6. Channel occupancy SAC IRC Run 4147 Run 4147
Uniform occupancy of the SAC and IRC channels

7. Timing of the hits SAC IRC Run 4147 Run 4147
Using the interval -100ns to -20 ns to estimate the hit rate per channel
IRC: ~1.1 MHz
SAC: ~730kHz
Muon rate in IRC is O(10 MHz)

8. Time over threshold
Run 4147
IRC
SAC

9. Time over threshold
SAC
Run 4147
IRC

10. Average number of hits per event
Includes both in time and out of time hits
Run #
Intensity
Trigger
SAC
IRC
4098
60%
Calo/20 [MUV1>5, LKr<5, !SAV]
0.65
2.4
4099
70%
0.76
2.72
4101
80%
0.8
2.83
4109
100%
CALO/20 [MUV1>5,LKr <5]
0.85 3
4124
CALO/15 [MUV1>6, LKr<4] & L1 (KTAG)
0.94
3.23
4141
CALO/10 [MUV1>6, LKr <4]
2.99
4147
0.97
3.38
The problem with the lack of IRC in the NA62 nominal intensity data seem to be related to the usage of wrong config file

11. Small angle veto efficiency
Due to resolution in the extrapolation it is difficult to address the efficiency of a particular part of the small angle veto system
Determine an effective vetoing efficiency as a combination of the SAC, IRC & LKr efficiency at small radius
The efficiency is best to be determined with “minimum bias” data
The strategy:
Reconstruct “clean” K+ →π+π0 events requiring only one of the π0 photons and tagging the impact point of the other
A check on runs 3809 (official reco with r805, 708 bursts/files) and (private reco with correct IRC config file, 93 bursts/files)
% intensity, but anti π+π0 trigger!

12. Tagging selection reminder
15 GeV < Ptrk < 30 GeV
110 m < Zvtx < 180 m
Cluster associated with the track in the LKr
|tcl – tchod|< 10ns, d(trk-cl) < 3cm
0.1 < E/p < 0.8 (assuring the track looks like a pion)
At least one good extra cluster in the LKr (gamma)
Distance to the pion cluster > 20cm
Eg > 3 GeV
|tg – tπ – dt| < 3ns LKr)
Missing mass reconstruction: |(PK – Pπ – Pg)2| < 0.005GeV2/c4
Extrapolated gamma at least 10 cm from the good gamma, 20 cm from the pion cluster, and Eg > 10 GeV.
Dt [ns]

13. K+→p+p0 kinematics K2p events are reconstructed quite well
M [MeV]
M [MeV]
Mmiss [GeV2]
K2p events are reconstructed quite well
No cut on the K-p missing mass in the tagging
Room for improvement
Mmiss [GeV2]

14. Photon tagging
D [mm]
D [mm]
RLKR [mm]
The precision of the extrapolation worsens close to the center of the LKr
At small R the extrapolated position is not a reliable characteristic of the event
No possibility to separate the SAC, IRC or the inner region of the LKr

15. Small angle veto response
The SAC reacts as a single channel detector as expected
Nhits
Nhits
RIRC [mm]
Nhits
Dt [ns]
The cut on the radius of the extrapolated photon was chosen to be 160 mm

16. Small angle veto efficiency
Ncl LKr
10 events out of 3897 do not have extra hits neither in SAV (in time, DT< 5ns) nor in LKr
Inefficiency ~ 3*10-3
Consistent with run 3488
Nhits SAV
However most of them do have extra CHOD/KTAG/LAV hits

17. Small angle veto efficiency
Ncl LKr
10 events out of 3897 do not have extra hits neither in SAV (in time, DT< 5ns) nor in LKr
Inefficiency ~ 3*10-3
Consistent with run 3488
However most of them do have extra CHOD/KTAG/LAV hits
Nhits SAV
Nhits SAV
e.g. RICH
Ptrk [MeV]

18. Small angle veto efficiency
Ncl LKr
10 events out of 3897 do not have extra hits neither in SAV (in time, DT< 5ns) nor in LKr
Inefficiency ~ 3*10-3
Consistent with run 3488
However most of them do have extra CHOD/KTAG/LAV hits
veto on extra activity
Nhits SAV
Nhits SAV
Veto on LAV, CHOD, KTAG and MUV3 results in 1379 tagged events
Only one inefficient event not seen by SAV/LKr
Inefficiency of the inner photon veto of the order of 10-3 (7*10-4)
To be compared with the 1.2*10-3 SAC inefficiency due to conversions in the IRC/STRAW3&4, Spasimir,
# events seen by SAV: 547, if 1 inefficient is due to SAVs: 1/547 = 2*10-3
However the statistic is low to quote a reliable number

19. Conclusion
The SAC and IRC detectors seem to be operating during the last days of the 2015 data taking during the nominal intensity beam period
Data seem to be consistent – i.e. no surprises
Rate (and occupancy) seem to follow the beam intensity
When the other conditions are kept equal
SAC/IRC efficiency estimation possible only when considering all the inner veto system
Preliminary results on run 3809 (r805) consistent with the ones from run (private reco)
Efficiency could be tracked down to ~X*10-3, however methods to increase the statistics under study
Analysis not blind!
0 events tagged in 4147 (LKr<4, necessary for both p+,g tagging)