Spasimir Balev /CERN/

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20 mrad 3

LKr simulation: – very slow, so only events with interesting topology are fully simulated: –  + with 15 < E < 35 GeV – at least 1  with R<200 cm at IRC – otherwise kill the event CHOD simulation: – NA48 charged HOD – beam pipe added as it is in front of IRC (1 mm thick Al tube with outer radius of 70 mm) – no fins RICH simulation: – Use Giuseppe’s beam pipe inside the RICH according to the new design (thanks!) STRAW simulation: – Use Giuseppe’s private version with proper positioning wrt. the beam (thanks!) LAV simulation: – Not used – The beam pipe in LAV12 responsibility region missing 4

SAC and IRC – total deposited energy in Scintillator layers – E IRC > 40 MeV – E SAC > 40 MeV (double the MIP deposit) LKr – total energy deposit (E LKR ) by cells which: are 10 cm away from the other photon are 20 cm away from  + are with energy E cell >300 MeV – Photon is seen if E LKR > 500 MeV RICH – Number of PMTs with hits – N RICH > 25 CHOD – count number of slabs with total energy deposit > 2 MeV – N CHOD > 8 STRAWS – count the number of straw hits outside 5 mm radius from impact point of  + from K decay – N STRAW > 15 5

6 N CHOD    no interactions interactions  efficiency IRC inefficiency

7 N RICH    no interactions interactions  efficiency IRC inefficiency

N STRAW    no interactions interactions  efficiency IRC inefficiency

114 < Z VTX < 174 m 15 < E  + < 35 GeV  + in CHOD acceptance R  + IRC > 150 mm no    decay at least one photon with R IRC < 200 mm   events generated It is required the other photon to be with R IRC >250 mm The event is classified according to the impact photon’s impact point  x y OUTER RING IRC INNER RING SAC 9

Giuseppe’s selection [as close as possible] The photon is not detected if all of the following is fulfilled: – E LKR 500 MeV) – E SAC <50 MeV – E IRC <50 MeV – N CHOD ≤8 – N RICH ≤25 Inefficiency of shashlyk IRC: (3.7 ± 0.5) x Giuseppe’s inefficiency: (4.6 ± 0.6) x [lead glass; not taking into account the contribution from grazing photons] Efficiency of  : 94.65% “Optimized” cuts (or optimistic?) The photon is not detected if all of the following is fulfilled: – E LKR 300 MeV) – E SAC <40 MeV – E IRC <40 MeV [double the MIP deposit] – N CHOD ≤ 8 – N RICH ≤ 25 – N STRAW ≤ 15 Inefficiency of IRC: (1.5 ± 0.3)x10 -4 Efficiency on  : 92.91% 10

2 out of events are inefficient Both due to PhotoNuclear interactions in RICH. Difficult to recover (rings in RICH? LAV12?) LKr efficiency for photons interacting with RICH with R>150 mm? Inefficiency: 1.6 x event display x, mm y, mm z, mm x, mm y, mm E LKR, MeV , , ,e,others

in IRC of them: 17 inefficient due to PhotoNuclear interactions in RICH 2 inefficient due to conversions in RICH 3 inefficient due to conversions before STRAW 3 Inefficiency: 1.5 x event display x, mm y, mm z, mm x, mm y, mm E LKR, MeV

1905 in the Inner Ring of them: 1 inefficient due to Photonuclear interactions in RICH 23 inefficient due to conversions IRC beam pipe Inefficiency: 1.26% 13 event display x, mm y, mm z, mm x, mm y, mm E SAC, MeV

E IRC (MeV)E SAC (MeV) 14

27748 in SAC acceptance all of them inefficient due to conversions in: IRC  12 STRAW3  15 STRAW4  7 Note: The inefficient events in IRC are always very close to the “inner ring” Effect of G4 stepping? Inefficiency: 1.23 x event display x, mm y, mm z, mm

N STRAW E SAC, MeV 16

Outer ringIRCInner ringSAC Photons Inefficient photons Photonuclear in RICH2171 Conv. before STRAW32 Conv. in RICH3 Conv. in IRC2312 Conv. in STRAW315 Conv. in STRAW47 Inefficiency 1.6 x x % 1.2 x x Total SAV efficiency4.4 x

Drawing by Ferdinand IRC not centered (12 mm shift on X) Stainless steel vessel Vessel windows Mylar 18

New MC generation In addition to the requirements on slide 4 one of the photon should be with R LKR >1400 mm The distribution of the photons going in IRC is very asymmetric. The photons are with E>50 GeV 19 Photon LKR

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IRC – new design Outer ring:< 8 x IRC:<10 -5 Inner ring:1.9% SAC:4.6 x Total SAV inefficiency: 2.6 x IRC – new design in vacuum Outer ring:< 6 x IRC:6.3 x Inner ring:0.3% SAC:1.2 x Total SAV inefficiency: 6.5 x

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1  / 2  SACIRCLKRLAVMISS SAC1.07 x x x x x IRC3.20 x x x x LKR x LAV2.40 x x MISS0 Applied cuts: 114 < Z VTX < 174 m 15 < E  + < 35 GeV  + in CHOD acceptance  + outside radius 15 cm at IRC no    decays Selected events: 2.06 x  in IRC & 1  missed: 1   1.22 x 10 9  0 Probability (1g in IRC & 1 missed in LAVs)  7.8 x Inefficiency of IRC  3 x Missing mass rejection factor  2 x  0 background of such topology: 0.6%

Generated  0 events in 114 < Z < 174 m: 7.68 x 10 7 Selected (see previous slide): x 10 7 Apply weight to each photon = inefficiency of the corresponding subdetector Total sum of the weights: 4.12 Generated  events in 114 < Z < 174 m: Selected  : Missing mass cut rejection according to TD: 2x10 -4 BR(K   ) = 1.7 x Background 3.96% (we quote ~4.3%) Inefficiencies [from Giuseppe’s presentation, ] LAV: – E < 0.2 GeV  1 – 0.2 < E < 0.5 GeV  – E > 0.5 GeV  LKr: – E<1 GeV  1 – 1 < E < 5.5 GeV  to – 5.5 < E < 7.5 GeV  to 5x10 -5 – 7.5 < E < 10 GeV  5x10 -5 to – E > 10 GeV  0.8 x SAC/IRC: – 2.9 x

1 g / 2 gSACIRCLKRLAVMISS SAC1.8 x x x x x IRC5.3 x x x LKR4.3 x LAV MISS0 25 Total: 3.96%

x x x10 -3 Total  0 background % SAC ineff.IRC ineff. In a very pessimistic scenario: ineff(IRC) ~ 4 x ineff(SAC) ~ 1.2 x We get 6.3% total background from  0 (instead of 4%)

Still work in progress IRC and SAC inefficiencies estimated with the new design: – inefficiency of IRC  2.6 x – inefficiency of SAC  1.2 x Preliminary checks with IRC in vacuum Possibility to refine the rejection factor by using STRAW and RICH reconstructions, and LAV Detecting energies/cell ~300 MeV in LKr is very helpful to reduce the inefficiency at small angles SAC and IRC performance for low energetic particles? The   background with the above inefficiencies is ~6% (wrt. ~4% with the intrinsic ones from the SAC prototype test) 27