( Very )Fast simulation of the neutral beam

1. (Very)Fast simulationof the neutralbeam A.Cassese

2. NA48 neutralbeam (1998-99)

3. NA48 neutralbeam (2001)

4. Summary NA48 2001-like • 400 GeV/c insteadof 450: factor0.81 • 2.4 mrad (incidence), ±0.15 mrad (acceptanceseen at 126 m from T10) • 2.4x1012pppinsteadof 1.5x1012ppp: factor1.6 • 4.8s/16.8s duty cycle • Same KL spectrum at 400 and 450 GeV/c: 110 GeV/c mean KL momentum • 0.81x1.6x6.4x106 KL/spill 70<p<170 GeV/c • 8.3x106 KL/spill 70<p<170 GeV/c • 1.4x105 KL decays/spill 70<p<170 GeV/c, 0<z<60 m • 3.6x1010 KL decays/year 70<p<170 GeV/c, 0<z<60 m (1y = 100d, 50% eff)

5. Baseline NA62 neutral • x10 in protonintensity (2.4x1013ppp) • Samemomentum, same inc. angle, same duty cycle,…. as NA48-2001 • Samefinalcollbut at 101 m wrt 126 m (±0.20 mradinsteadof ±0.15 mrad): factor (0.20/0.15)2 = 1.8 • Consider 50<p<200 GeVinsteadof 70<p<170 GeV/c: factor1.6 (slidesworshop 1998) • 10x1.8x1.6x3.6x1010 1x1012 • 1x1012 KL decays/year 50<p<200 GeV/c, 0<z<60 m (1y = 100d, 50% eff)

6. Approach • Take the “working” MC for NA62 (withK+ at 75 GeV/c) • “Replace” a p+withp0 and check the acceptance • Assume 1x1012 KL decay in fiducial volume (105 < z < 165 m) per year • Assume 10-8p0 veto capability (NA62-like)

7. K+→π+KL→π0 • 75 GeV/c kaonmomentum • Replacep+withp0 • 10000 generatedevents • 3616 events105<z(vertex)<165 m • 3733 events 2 gamma in Lkr (anyvertex) • 1681 events 2 gamma in Lkr, 105<z<165 m • p0acceptance on LKr: 46.5%±0.8% • ExpectedsignaleventsKL→π0: Ndecays x BR x Acc = 1x1012x2.4x10-11x46.5% = 11.1 events in 1 year

8. KL→π0

9. K+→π+p0KL→π0p0 • 75 GeV/c kaonmomentum, Replacep+withp0 • 10000 generatedevents • 3633 events 105<z(truevertex)<165 m • 7982 events >=2 gamma in LKr • 3049 2gamma in Lkr • 3499 3gamma in Lkr • 1434 4gamma in Lkr • 6232 events >=2gamma from pi0 (Even) • 67 events >= 2 overlapped gamma (Ngamma>=3), overlap<10cm at Lkr • 105<z(reconstructed)<165 m: EvenOdd(combinatorics) • 2gamma 442 336 • 3gamma 1707 1867 • 4gamma 1217 1896 • Total(couples) 3366 4099 • p0 “effective” acceptance (Even): 3366/3633 = 92.7%±0.4% • Expected background eventsKL→π0p0: Ndecays x BR x Acc x Veto= 1x1012x0.9x10-3x92.7%x10-8 = 8.3 “even” background events in 1 year • p0 “effective” acceptance (Odd): 4099/3633 = 112.8% • Expected background events KL→π0p0: Ndecays x BR x Acc x Veto= 1x1012x0.9x10-3x112.8%x10-8 = 10.1 “odd” background events in 1 year “Even”: 2 gamma from the same pi0 “Odd”: 1γfromone pi0, 1γfrom the otherpi0 All the combinations: 1 in 2gamma, 1 even and 2 odd (3gamma), 2 even and 4 odd (4gamma)

10. KL→π0p0“Even” E and Ptof pi0 reconstructed in Lkr

11. KL→π0p0“Odd” E and Ptof pi0 reconstructed in Lkr

12. 181 overflows KL→π0p0“Even” Angle of the gammasnotusedfor pi0 reconstructedifoutsideLKr 190 overflows KL→π0p0“Odd”

13. KL→π0p0“Even” Enlarged scale Angle of the gammasnotusedfor pi0 reconstructedifoutsideLKr KL→π0p0“Odd”

14. KL→π0p0“Even” Enlarged scale Energy of the pi0 seen in LKr (mimicking the signale) vs Angle of the gammas(notusedfor pi0 reconstruction) outsideLKr KL→π0p0“Odd”

15. Conclusions • Very fast and roughsimulation (75 GeV/c Kaonmomentum) • Expect: 11.1 signalevents in oneyear • Expect: 8.3 background eventsfrom KL->p0p0with the 2 gcomingfrom the samep0(assuming 10-8p0 veto eff.) • Expect: 10.1 background eventsfrom KL->p0p0with the 2 gcomingfromdifferentp0 (assuming 10-8p0 veto eff.) • 10-8 p0 veto eff. Notjustifiedwithpresent LAV coverage: • Prob 1 g q>50 mrad: 181/3366 = (5.4±0.4)% (“Even”) • Prob 1 g q>50 mrad: 190/4099 = (4.6±0.3)% (“Odd”) • Tobecomparedwithfew per mille in NA62 (Ep0>40 GeV) • Only cut applied: reconstructedvertex position (imposing mp0 mass): 105<z<165 m • No cut no Ep0 and PTp0yet