MC Study on B° J/ ° With J/ ° Jianchun Wang Syracuse University BTeV meeting 03/04/01.

MC Study on B°J/°With J/°

Jianchun Wang

Syracuse University

BTeV meeting03/04/01

03/04/01 Jianchun (JC) Wang 2

Introduction

Test of CPT conservation and measurement of cos(2) ( see Sheldon’s last month talk )

Events per year: 1.14 106

Difficult to detector: c =15.51 m (KL), 2.68 cm (KS)

Generated within (0.5, 0.5, 1.5)m KS : (89.9 0.3)% 1.76

KL : (0.970.01)% 1.11

Total: (1.130.01)% 1.28

B°J/°, J/°

Kaon Decay Time [S]

( KL/KS ~ 580 )


Reconstruction With Missing

Only not reconstructed ( 4 free parameters )

K direction determined by K and J/ vertices ( 2 constraints )

Known K and masses( 2 constraints )

Two solutions

B

(J/)

KS / KL


MC Events

Signal events: 12.8K events with K decay within detection volume, corresponds to one year run

Main background source is real J/from B decay Small J/ width Reject fake J/

Detached vertex criteria Reject prompt J/

Background events: Generic BB events, J/fully decays into

Events preselected after QQ simulation

A quarter of a year events simulated

MCFast simulation used, no multiple interaction yet


Primary Vertex Reconstruction Based on Rob’s primary vertex subroutine, modification

of primary vertex seeds selection Resolution and efficiency improved: eff = 99.2% (90.8%)

11.4 (12.1) m 11.9 (12.5) m 79.9 (89.7) m


Reconstruction of J/ track selection:

Real MC Covariant matrix exists

Num of hits > 20

Silicon hits 4

Applied later: P > 3GeV, max(P) > 8 GeV

At least one has muon hit

Vertex fitting:prob(2, 1) > 0.01

| MM J/| < 3

Mass constraint fit

= 11.7 MeV

Efficiency ~ 20%


B Decay Vertex

Vertex resolution Primary vertex:

(11.4, 11.9, 79.9) m

B (w/o MJ/ constraint): (22.0, 22.9, 163) m

B (with MJ/ constraint): (21.6, 22.2, 154) m

Decay length resolution:L ~ 190 m

Detached vertex: Ldecay / L > 4

B J/ K


K Vertex Reconstruction selection:

Covariant matrix exists

Num of hits > 10

MC real

Selection later has muon hit

DCA > 1 mm, max(DCA) > 2 mm

P > 1 GeV, max(P) > 2GeV

Vertex fitting: prob(2, 1) > 0.01

M < 0.5 GeV, M ~ 2.5 MeV

Vertex Resolution: (62, 52, 450) m

Ldecay/L > 20, ( L ~ 450 m)

°


Determination of K momentum p in K° rest frame = p in Lab frame

cos2 = ( p2 p2) / p2

Selection of two solutions: Matching momentum with vertex direction

Select one with mass close to B

m, p)

K (M, )

Negative due to resolution

Cut: cos2 > 0.2


B° Directions

B directions: Momentum reconstructed

B vertex to primary vertex

Open angle between two directions: B < 20 mrad

The solution with M close to MB selected

Signal is of one year run, background is for ¼ year

B (mrad)

B Signal

Background

cut

With all other cuts applied


J/ Vertex Veto

To reject events with BJ/ + tracks

Add extra track to J/ vertex, require 2 > 10

Track selection: Covariant matrix exists

Silicon hits 4

P > 0.5 GeV

Not from primary vertex

2

B signalBackground

cut

With all other cuts applied


Distribution of MB

MB (GeV)

= 31 MeV

Signal: 132

Background: 14 4

S/N: 2.36


Background Events

5/14 B J/ K X (X = )

7/14 B J/ X, K (from fragmentation, or decay)

1/14 B J/ X, B X, KS

1/14 B J/ X, , KS

Classification of 14 Background Events


Summary

No flavor tagging applied

B mass resolution: 31 MeV

132/year signals for channel only, adding e’s will increase the number by a factor of 2~4

S/N = 2.36

To be done: multiple interaction, GEANT


Primary Vertex Reconstruction Based on Rob’s primary vertex subroutine, improvement on primary

vertex seeds selection

Track selections: 4 silicon hits, P > 0.5 GeV, covariance matrix defined, Ntrack>2

Group two tracks together, select about 10 vertices consistent with beam spread: 2 < 5, (x/)2 < 25

Among vertices, reject those far away from majority | Z – Zaverage | < 1.5 (two iterations)

Use tracks from selected vertices as seed, and add all tracks left one by one: (2) < 12

Ntrack 3, 2 / Ntrack < 4.0 99.2%

Resolution: x =11.4 m, y =11.9 m, z = 80 m


Pre-selection of Signal Events Decay channels boosted:

BJ/ K

J/ 5.88

KKS (0.173%), KL (99.827%)

KS/KL 1.36

Event Selection: At least one B in the event

3.96

Primary vertex simulation (moved from MCFast) K vertex within (0.5m, 0.5m, 1.5m) 1.13

One year run 2BB events 12.8 K pre-selected events for further study


Pre-selection of Background Events BB events produced in one year run 2.00

Decay channels boosted: B+, B, BS, b J/C0C1C2 + X 4.23

J/ 5.88

Event Selection: J/: dkl > 400m, P>3 GeV, max(P,P)>8 GeV 1.65

of K: generated within (0.4m, 0.4m, 1.5 m) P > 1GeV, DCA > 1 mm, same side of J/2.77

of K: generated within (0.4m, 0.4m, 1.5 m) P > 1GeV, DCA > 1 mm, same side of J/8.50

and pair: opposite charge, mass() < 0.5 GeV max(P) > 2GeV, max(DCA) > 2 mm 1.50

J/: mass(J/) < 5.5 GeV 7.90

Events selected for one year run 2.24


Lepton Identification With RICH Perfect detection efficiency assumed

Detector size RICH: z ~ 386 cm, 135 cm

square, 2.28 cm inner radius ECAL: z ~ 739 cm, 160cm outer

radius, 9.88 cm square hole MUON: z ~ 890 cm, 240 cm outer

radius , 6 cm inner radius

J/ efficiency improvement, with one lepton identification: (106%): MUON P>5 GeV MUON P>5GeV + RICH 2<p<15GeV e (110%): ECAL

ECAL + RICH p < 17 GeV

J/


Yield of Events Per Year Number of b event cms 10s 100 b 2.00

With B0/B0b 0.4 2 1.60

With B0J/K (8.91.2) 1.42

With J/ (5.880.10) 8.37

With K 1.14

via KS 0.5 4.69

1.96

via KL 0.5 (27.180.25)

1.14

With K decays in (0.5,0.5,1.5)m 1.28

via KS 0.899 (1.76)

via KL (0.970.01) (1.11


Detection of Signal Events Generated and pre-selected events per year (2 arms) 12800 Primary vertex selection (12697+20)

( All tracks detected 1331 Tracks quality (no mu) 1202 )

J/ after primary vertex selection, and after four tracks requirement (!!!) Two tracks pass track quality 2729 Prob > 0.01, 3 mass cut, constraint fit 2482

K° after J/ selection Two tracks pass track quality 1093 Vertex Prob > 0.01 450 M (0.24, 0.70 ) 445 Missing fit cos2 > 0.2 363

Further Cut B decay length: L > 400 um, L/ L > 4 302

B directions from two methods: B < 20 mrad 255 J/ vertex veto 223 J/ p > 3, max(p)>8 GeV 218

K° p > 1, max(p)>2 GeV 192

K° DCA > 1mm, max>2mm (for BKG purpose only) 167

MB within 3 142

Include e modes (2.432), with one arm (/2) 345

MC Study on B° J/ ° With J/ ° Jianchun Wang Syracuse University BTeV meeting 03/04/01.

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Transcript of MC Study on B° J/ ° With J/ ° Jianchun Wang Syracuse University BTeV meeting 03/04/01.