(Very)Fast simulation of the neutral beam

A.Cassese

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NA48 neutral beam (1998-99)

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NA48 neutral beam (2001)

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Summary NA48 2001-like• 400 GeV/c instead of 450: factor 0.81• 2.4 mrad (incidence), ±0.15 mrad (acceptance seen at 126 m from T10)• 2.4x1012 ppp instead of 1.5x1012 ppp: factor 1.6• 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)

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Baseline NA62 neutral

• x10 in proton intensity (2.4x1013 ppp)• Same momentum, same inc. angle, same duty cycle,…. as

NA48-2001• Same final coll but at 101 m wrt 126 m (±0.20 mrad

instead of ±0.15 mrad): factor (0.20/0.15)2 = 1.8• Consider 50<p<200 GeV instead of 70<p<170 GeV/c: factor 1.6 (slides worshop 1998)

• 10x1.8x1.6x3.6x1010 1x1012

• 1x1012 KL decays/year 50<p<200 GeV/c, 0<z<60 m (1y = 100d, 50% eff)

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Approach

• Take the “working” MC for NA62 (with K+ at 75 GeV/c)

• “Replace” a p+ with p0 and check the acceptance

• Assume 1x1012 KL decay in fiducial volume (105 < z < 165 m) per year

• Assume 10-8 p0 veto capability (NA62-like)

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K+→π+ KL→π0

• 75 GeV/c kaon momentum • Replace p+ with p0

• 10000 generated events• 3616 events 105<z(vertex)<165 m• 3733 events 2 gamma in Lkr (any vertex)• 1681 events 2 gamma in Lkr, 105<z<165 m• p0 acceptance on LKr: 46.5%±0.8%• Expected signal events KL→π0: Ndecays x BR x

Acc = 1x1012x2.4x10-11x46.5% = 11.1 events in 1 year

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KL→π0

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• 75 GeV/c kaon momentum, Replace p+ with p0

• 10000 generated events• 3633 events 105<z(true vertex)<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: Even Odd(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 events KL→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

K+→π+p0

KL→π0p0

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“Even”: 2 gamma from the same pi0“Odd”: 1γ from one pi0, 1γ from the other pi0All the combinations: 1 in 2gamma, 1 even and2 odd (3gamma), 2 even and 4 odd (4gamma)

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KL→π0p0

“Even”

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E and Pt of pi0reconstructed in Lkr

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KL→π0p0

“Odd”

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E and Pt of pi0reconstructed in Lkr

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KL→π0p0

“Even”

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KL→π0p0

“Odd”

Angle of the gammas not used for pi0 reconstructed if outside LKr

181 overflows

190 overflows

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KL→π0p0

“Even”

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KL→π0p0

“Odd”

Angle of the gammas not used for pi0 reconstructed if outside LKr

Enlarged scale

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KL→π0p0

“Even”

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KL→π0p0

“Odd”

Energy of the pi0 seen in LKr (mimicking the signale) vs Angle of the gammas (not used for pi0 reconstruction) outside LKr

Enlarged scale

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Conclusions• Very fast and rough simulation (75 GeV/c Kaon momentum)• Expect: 11.1 signal events in one year• Expect: 8.3 background events from KL->p0p0 with the 2 g coming from the

same p0 (assuming 10-8 p0 veto eff.)• Expect: 10.1 background events from KL->p0p0 with the 2 g coming from

different p0 (assuming 10-8 p0 veto eff.)• 10-8 p0 veto eff. Not justified with present 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”) To be compared with few per mille in NA62 (Ep0>40 GeV)

• Only cut applied: reconstructed vertex position (imposing mp0 mass): 105<z<165 m

• No cut no Ep0 and PTp0 yet

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