Minutes of SUSY meeting Wednesday 1st March 2000

Susy TF results for Winter conferences was shown and something more about new analisys .

Update on long-lived stops (F. Cerutti for G.Sguazzoni):

Fabio presented the update of the analisys  proposed by G. Sguazzoni in the Susy TF Wednesday 16th  February 2000 meeting. The analysis addressed the stop decay to c chi at small deltaM or to u chi, if mstop < mc + mchi ,where the stop is expected to have a  long lifetime. No relation was assumed between Delta-M and the stop decay length (lambda). A bug was found in the efficiency parametrization. The absolute lower limit at 95% of C.L. on stop mass for all deltaM and lambda is 59.3 GeV/c2. In addition a MSSM scan was performed to link the lifetime with the mass difference and the esclusion limit on the plane stop mass-deltaM was shown as obtained with the optimal combination of all analysis. The MSSM absolute lower limit on stop mass for any mu and tanb was 63 GeV/c2 at 95% of C.L..

Impact of stau mixing on charginos searches (G.Vollinga):

Jens presented the update of the study of the impact of the stau mixing on the chargino exclusions at low m0. The optimal combination of existing selection has been identified as a function of deltaM, leptonic branching ratio and tau lepton production probability. The effect of stau mixing angles up to 45 degrees on the masses of  sneutrino and stau has been studied for various combination of the other free parameters.  A new signal Monte Carlo for cha->s-tau+neutrino was used. Generally the effect of mixing becames not negligible around  >30 degrees, as shown in the plane m(chi) vs. m(snu) for various combination of the other free parameters. The lowest escluded chargino mass limit is quite affected by the stau mixing at small m0. In paricular ther is a corridor where the chargino decays mainly into stau nu (other sleptons are heavy) and the stau goes into chi tau with delta-M~Mstau. In this corridor current analyses have no effect. Future plans are to close this corridor (leptonic neutralinos ?)  and go for a publication.
 

More on LSP limit at small m0 (F.Gianotti):

Results about the LSP limit at small m0 are reported. Fabiola  presented the study of  7 points with mchi< 36.8 GeV (this is the limit for m0=500 GeV)  which are not escluded  (these points correspond to m0=120-150 GeV). The slepton-slepton search does not contribute to the esclusion of those points and the cha+cha- one is too weak to be used (light sneutrino). The combination of the neutralino AL and AJ selection does not excludes these 7 points because of the large number of candidates (9 in agreement with GRACE4F expectation)  and NO backround subtraction in the AJ selection. The possibility top subract the background in the AJ neutralino analysis will be investigated before the publucation of these results. The result was a lower limit on LSP of 35.4 GeV for any m0 and tanb.

Impact of Higgs searches on the LSP limit (J.F.Grivaz):

Results of Higgs boson searches are used to improve the limit on the mass of the LSP, assumed to be lightest neutralino. The analysis is conducted within the framework of the MSSM with gaugino and sfermion mass unification. The results for the degenerate stop chi analysis are used to close the loophole h-> stop stop. Assuming: the combination of costraints from chargino, slepton and Higgs boson searches allows a lower limit of 38 GeV/c^2 to be set on the mass of the LSP, indipendent of m0 and tanb. For tanb<3, the lower limit is 45 GeV/c^2. The Higgs results are usefull in improving the LSP limit for tan-beta up to about 3.5. This results are slightly deteriorated  if Mtop is assumed to be 180 GeV OR m0 is assumed to be 2 TeV. If both assumption are done the Higgs exclusion do not contribute anymore to the LSP lower mass limit.

Single sneutrino with RPV up to 202 GeV (C.Curtil):

Christian presented the single sneutrino photo-production (process  e+gamma to sneu_j + l_k). This analysis holds in the range 0< msneu_j <sqrt s. The aim is to study the lambda_1j2 couplings (it is assumed snuj -> e mu decay).  Christian discussed the selection cuts for the direct decay of sneutrino in leptons (e  and mu)  via lambda_1j2 coupling and showed the distribution of  some variables for the background and data. The electron+muon invariant mass calculation uses the reconstructed photons identified as Bremsstrhalung or FSR. All data from 189 to 202 are used  and no background subtraction is performed. The esclusion limit in the plane lambda_1j2 -msneu_j  at 95% C.L. was shown together with another plot with the present limit on lambda_ijk coupling from all other analisys based on pair production and resonant production was realized. It was decided to send a conference note for winter conferences about this topic.
 

More news on stau excess (F. Holldorfer, F.Cerutti and G.Ganis):

Fabio showed the results of stau searches compared to charged Higgs searches. He reported on number of candidates at 192-202 GeV (46 stau+ stau- observed vs 34.2 expected, 36 H+H- observed vs 35.5 expected and 20 events observed in common) and showed the distribution of maximum and minimum tau energy, the maximun lepton momentum, the acollinearity, the visible mass, the missing momentum for the data  and the background (mostly WW production). He compared the H+ selection criteria  with the stau ones, trying  to understand  the origin of stau excess. The difference comes mainly in the intermediate deltaM region: the stau analyses accepts more low energy stuffs than the H+ one (which is correct since Mchi >= Mnu). Some events accepted by the stau analysis are rejected by the H+ analysis because of identified  high energy leptons. A different lepton Id is used in the 2 analyses. The lepton Id is more tight in the stau analyses (less purity but more efficiency) than in the H+ one. No significance inconsistency between the results of the two analyses has been found.

 

Status report on AMSB searches (M.Maggi):

Marcello reported on status of  anomaly supersymmetric breaking searches and of  mass degenerate gauginos one particularly. When  the mass difference between chargino 1 and neutralino 1 (deltaM) is less than few GeV, chargino is almost invisible and difficult to trigger. ISR-tag  analysis (by G.Taylor) was used requiring also extra visible energy. Marcello discussed the modified analysis  criteria and showed the plot of efficiency as function of deltaM for different charginos masses. The comparision between data from 189 and MC background using only ISR-tag showed a mismatch  which was improved rejecting gg and cosmics. Two candidates were observed in data and the background estimate was 1.3 events.  Therefore an esclusion limit at 95% of C.L. in plane deltaM-mcha in gaugino region was derived. Finally Marcello planned to scan the higgsino region, to check the result and to optimize the analysis.
 

RPV LQD 4-jets: Why charged Higgs is better than RPV? (D.Hutchcroft):

David compared the charged Higgs searche in the hadronic channel with RPV 4-jet one. Both analyses need 4-jet reconstruction into 2 (spin 0) equal objects but the current Higgs limit is better (~81 GeV compared to 77 GeV); preselection was similar while Higgs analysis was 45% efficient compared to  35% of RPV one. The difference comes mainly from the way background subtraction was done. In the H+ analysis all the bkg is subtracted while inb th eRPV one only 20% of the WW background is subtracted. An consistent way of subtracting the background between the two analyses must be found


Submitted by: Nicola De Filippis