Evt Gen at Belle Akimasa Ishikawa KEK IPNS
Evt. Gen at Belle Akimasa Ishikawa KEK, IPNS 21 Jan 2005
Evt. Gen p Standard generator at Belle. n n p Both BBbar and continuum events are generated with Evt. Gen. Version 00 -10 -07++ is used. To be updated coming version. Evt. Gen package is included in Belle library. n n Anybody can easily modify Evt. Gen for private purpose by checking out the source codes from Belle CVS. In order to load Evt. Gen from BASF (Belle Analysi. S Framework), shared object module “evtgen” is created. basf<<EOF path create main path add_module main evtgen …. . EOF
Decay Table p We use modified DECAY. DEC and evt. pdl. n n n Only includes tree level b c decays. Other rare decays, which proceed through b u, s, d, annihilation or exchange diagrams, are separated to study rare decay backgrounds. Decay table is basically tuned with PDG and HFAG results and Theory. p n D 0, D+ and Ds spectra are tuned by inclusive measurements. p n Only possible at e+e- B-factory Total width difference between B 0 and B+ is introduced. p n Both exclusive and inclusive measurements. ex. BF(B+ Xln) /BF(B 0 Xln)=1. 08 Some particles are added to evt. pdl p ex. higher N and charmed baryons and X(3872) assuming hc’. Please find the decay tables at http: //www. belle. kek. jp/~akimasa/decaytable/2003/
Branching Fractions p p 7 inclusive decay modes are considered. Determined with inclusive measurements n n n BF(B lepton X)=10. 9% BF(B Ds X)=10. 5% etc. BF B 0 B+ Average DXlnu 0. 209 0. 277 0. 218 DXtaunu 0. 024 0. 026 0. 025 cc. X 0. 024 0. 026 0. 025 Ds. X 0. 101 0. 109 0. 105 DDX 0. 087 0. 083 0. 085 DX 0. 458 0. 436 0. 447 Baryon. X 0. 097 0. 093 0. 095 Total 1. 000 total width difference
D 0, D+ and Ds spectra p Belle has measured inclusive D meson spectra. n n n B(B Ds. X)=11. 7+-0. 1(stat)+-1. 1(syst)+-2. 9(Ds fp) % ary n i B(B D 0 X)=66. 3+-0. 2(stat)+-2. 1(syst)+-1. 5(D 0 Kp) % m reli P B(B D+X)=24. 0+-0. 2(stat)+-0. 9(syst)+-1. 4(D+ Kpp) % Very y Ver D 0 70. 5% D+ 28. 3% Before Ds fixed to 10. 5% D 0 68. 2% After Next Step inclusive charmonia and charmed baryons. flavor specific D mesons and charmed baryons D+ 26. 8%
Pythia, continuum production p Rolf Seuster developed Pythia interface. n n p Now in Evt. Gen. Better representation for heavy flavor fragmentaion. Charm fragmentaion tuning with D 0 and Ds* mesons. n n We use Bowler function D 0 prefers pure Bowler(r. Q=1) but Ds* prefers pure Lund(r. Q=0) r. Q =1 gives minimum combined c 2/ndf. We choose r. Q =1. This analysis was done before obsevations of Ds(2317) and Ds*(2457), so we need to check again. D 0 Red : Bowler Solid : Lund Dot : data Ds*
Event shape p Belle Evt. Gen pythia Q 0 0. 5 1. 0 Q’ 0. 3 0. 8 sq 0. 42 0. 36 LQCD 0. 32 0. 3 0. 62 0. 58 Tuning of event shape is also performed. n 19 event shape variables are put into c 2 and search for minimum by changing the parameters Q 0, Q’: termination of parton shower, sq: transverse momentum, LQCD, Lund a and b. p Thrust, cos. Thurst, Thrust major and minor, oblateness, Planarity, heavy and light Jet Mass, Jet Broadening W and T, A Sphericity, Aplanarity, R 1, R 2, R 3, y 24, CPar, DPar B
Photos p p p We only use photos for semi-leptonic and leptonic decays. However radiative effect is large especially two body decays, B pp. We need to turn on photos for all decay modes. B p+p. DE Eg Mbc events p+p- K+K- without photos 8000+-90 7577+-87 with photos 7474+-87 7282+-85 difference 6. 6+-1. 5% 3. 9+-1. 6%
Interference Weight p p Elisabetta Barberio, who is one of the photos authors, pointed out that interference weight for multi body decay Wmulti is not introduced in Evt. Gen except for two body particle-anti-particle decay, such as B p+p. Wmulti should be introduced.
Speed, Random Generator p Speed n Evt. Gen is about 2. 5 times slower than qq 98. p p 350 Hz and 300 Hz for BBbar and uds events on Pentium 3 1266 MHz, respectively 30 fb-1/day and 11 fb-1/day. 33 days and 90 days to generate 1/ab MC (about 3 x data we have). Need faster CPU or parallel production. True random number generator board for parallel production n n n Pick up thermal noise in semiconductor. Distribute random number via network. About 7 M single precision random numbers/sec 800~900 random numbers to generate BBbar events. ~8 k. Hz for BBbar events 600 fb-1/day A dozen random boards are enough even at Super-B factory. Cost $6000/board http: //www 3. toshiba. co. jp/power/techno/secret/random/index_j. htm In japanese
Platform p OS/compiler n Linux/gcc 2, gcc 3 p n Solaris/gcc 3, Sun. WS 5. 0 cc p n Sun. WS 5. 0 cc does not support template member function, so we cannot compile Evt. Gen with it. Need to switch to Sun one studio 8/9. Free. BSD/gcc 2, gcc 3 p p We will/should use PC Linux to get enough computing power. Some institute at Belle used. We want to try these compiler. n n PGI compiler Intel C/C++ Compiler
What is needed (my opinion) p Decay models should allow that lower resonance decays to higher resonance. n n p Decay models for Higgs mediated B Dtn and B tn decays. n p It is possible if both resonances have large width. Ex. K 1(1270) K 0*(1430)p. One of the inportant decay mode at Super B-factory. Parity (and C-Parity? ) should be defined in evt. pdl.
Summary p p Evt. Gen is standard generator at Belle. We improve the decay table by measuring D meson spectra. n n p p Next target is charmonia and charmed baryons. Next to Next is flavor specific D mesons and charmed baryons. We also tune the continuum production with D mesons and event shapes. Photos should be applied to all decay modes. Interference weight should be introduced. Evt. Gen is not so fast but enough processing speed is possile with parallel production with random generator allows
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History 1999 Signal MC Background MC p p p 2000 2001 2002 2003 2004 2005 qq 98 Evt. Gen ~2000: qq 98 for both signal/BG study. End of 2000: Evt. Gen is implemented to make a better flavor tagging tool and study CPV in b ccs. 2001: Observation of CPV. 2001~2003 some analyses used Evt. Gen for signal study (B pp, B Kll, b uln etc. ). 2004: start background MC mass production with Evt. Gen.
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