From WANGGL@D0GS03.FNAL.GOV Mon Mar 17 17:49:52 1997 Received: from d0gs03.fnal.gov by nscpmail.physics.umd.edu (AIX 4.1/UCB 5.64/4.03) id AA38226; Mon, 17 Mar 1997 17:49:51 -0500 Date: Mon, 17 Mar 1997 16:49:50 -0600 (CST) From: GUOLIANG WANG To: eno@nscpmail.physics.umd.edu, HOBBS@d0fsub.fnal.gov, LANDSBERG@d0fsub.fnal.gov Cc: MONT@fnal.gov, WEERTS@PA.MSU.EDU, grannis@sbhep.physics.sunysb.edu, "CSA::STROVINK"@d0fsub.fnal.gov, WYATT@d0fsub.fnal.gov, "FSUHEP::HAGOPIAN"@d0fsub.fnal.gov, "FSUHEP::BLESSING"@d0fsub.fnal.gov X-Vmsmail-To: SMTP%"eno@alexander.physics.umd.edu",HOBBS,LANDSBERG X-Vmsmail-Cc: SMTP%"MONT@fnal.gov",SMTP%"WEERTS@PA.MSU.EDU",SMTP%"grannis@sbhep.physics.sunysb.edu",CSA::STROVINK,WYATT,FSUHEP::HAGOPIAN,FSUHEP::BLESSING,FSUHEP::WAHL Message-Id: <970317164950.2160237f@d0fsub.fnal.gov> Subject: why the slq1 mass limit changed from 194 to 175GeV Status: RO Dear All, The following is the description why the scalar lq1 mass limit changed from DPF's 194 GeV to present 175 GeV(all the following mass limit is for beta = 1.0). To describe as clearly and in detail as possible, I wrote step by step on the time axis. If there is anything I didnot make clear or something you think is not correct, please let me know. Best Regards, Guoliang 1. The DPF's 194 GeV number is based on the Run Ib data(93.7pb-1) two candidates, the backgrounds 3.49 +/- 1.10, the signal eff. and the theoretical cross section. The theoretical cross section was got by running Doug Norman's lq cross section program specifying MTLO structure function. Doug told me his method is the same as ISAJET calculation. That's why I made the reference to ISAJET with MTLO structure function. After DPF, the theoretical people in FSU pointed out that MTLO was quite old and was not correct. Since last Oct., I began to think about recalculating the cross section with newer structure function and compared it with the result from ISAJET (Because CDF used ISAJET to calculate the cross section and got higher cross section than ours). By playing with ISAJET, I found a bug in ISAJET and sent email to Frank Paige. He said the bug was that the quark types are messed up for antiprotons and they would fix it in the next release. When I asked if the bug would affect the kinematic distributions or not, he said that he didnot know how much the effect was and said that most of the properties of the event must come from the decay of LQ. By looking up some theoretical papers, I noticed that the theoretical hard scattering cross section for gluon-gluon fusion in Doug's program was wrong because he got it from a paper which was not correct[1][2]. Also Doug's program used the hard scattering theoretical cross section[3] based on the SUSY squark production in which there was the parameter like gluino mass. He let the gluino mass goes to very large and got the asymptotic value as the theoretical value (and divided by two to account for the chiral coupling of LQ). That was the theoretical cross section of scalar lq at DPF. Presently, I folded the Moscow State University(MSU) theoretical group's hard scattering cross section[4] based on the scalar LQ pair production for the gluon-gluon fusion and quark-antiquark annihilation(through gluon). The contribution from the quark-antiquark scattering via exchange of lepton is negligible and is not included. I compared the new result with the MSU's calculation and found the difference is less than 2% (use the same structure function and number of flavors and lambda_QCD)(from now on, I will use the MSU value although the 2% will not contribute to any difference to the mass limit). After I used the new theoretical cross section with CTEQ3M, the mass limits based on the Run Ib luminosity/two candidates, backgrounds 3.49+/1.10 and eff, the mass limit dropped from 194 to 182 GeV. (If I stick to MTLO, the new calculation will drop the mass limit from 194 to 187 GeV). 2. If I use the whole Run I data ( luminosity changed from 93.7 to 117.7pb-1), also two candidates, backgrounds 3.49+/1.10, eff and the new theoretical cross section with CTEQ3M, the mass limit will increase from 182 GeV to 189 GeV. 3. Thanks to John Hobbs check, the electron tracking ineff. was included. This will drop the signal eff. and No. of backgrounds. Using the Run I data, two candidates, backgrounds 2.9+/-1.1, changed eff. and the new theoretical cross section with CTEQ3M, the mass limit will decrease from 189 GeV to 181 GeV. 4. I found a bug in my nt_maker about the electron DE/DX for the vtx track only electron. After fixed this bug, there was one more candidate. Using 3 candidates, backgrounds 2.9+/-1.1, changed eff. and the new theoretical cross section with CTEQ3M, the mass limit will decrease from 181 GeV to 175 GeV. This is the number right now available to the public (La Tuille and Moriond QCD). Pythia (the lq production was implemented into Pythia by the MSU group) was used to simulate the vector lq production. At lq mass = 200GeV, the ISAJET produced scalar lq and Pythia produced vector lq were compared with each other. The Et distribution of the electron and jets and missing Et are the same. This means that the bug in ISAJET will not change the kinematic distribution much. The cross section of the vector lq pair production was from the MSU's program. Summary for the changes of scalar lq1 mass limit(beta=1.0): Cross section recalculation: -12 GeV Luminosity increase: + 7 GeV Electron tracking ineff.: - 8 GeV Additional candidate: - 6 GeV ------------------------------------------------ Total effect: -19 GeV These changed the mass limit from 194 GeV to 175 GeV. Reference: [1] P.R.Harrison and C.H.L.Smith, Nucl. Phys. B213, 223(1983). [2] Errata, P.R.Harrison and C.H.L.Smith, Nucl. Phys. B223, 542(1983). [3] S.Dawson, E.Eichten and C.Quigg, Phys. Rev. D31, 1581(1985). [4] J.Blumlein et al, hep-ph/9610408.