4 May 2006 First look to the Ke2 decay ● Interesting for the Ke2/k m 2 ratio ● BR(K ±  e n ) = (1.55 ±0.07)10 -5 ● Large radiative decay BR(K ±  e n ) ~ BR(K ±  e ng ) Kinematically very similar to k m 2, that is 10 5 times more abundant. Exploit m /e discrimination in the calorimeter as much as possible The analisys is a less than premature stage. We beg for suggestions, comments, help....

4 May 2006 R K SM = (  0.001)x10 -5 Extremely well known within SM R K SM = (  0.001)x10 -5 Probe  -e universality: non-universal terms from LFV sources in SUSY extensions Preliminary from NA48/2 R K NA48 = (  stat  syst )x signal events from ’03 run and ’04 stat = 2 x stat(2003) not yet included At KLOE the measurement is extremely challenging:  signal =  tag x  rec x  clu ass ~ 8% A possible  /e discrimination strategy can rely on:  decay kinematics (good separation)  TOF (modest separation, also muons have  ~1)  cluster shape in ECAL (could be fairly good, under study)  dE/dx in the DC (could help, under study) c) R K : Ke2/K  2 i.good reconstruction eff. for signal ii.trigger eff. ~ 1 no autotrigger required iii.but difficult PID due to huge K  2 background O(10 5 ) 4x10 3 events/K 2fb -1 OK TRUE

4 May 2006 Starting point ● Possible realistic accuracy achievable with the KLOE statistic ≈ 2% ● The selection sample can be enlarged tagging with the 2 body decay ( as usual) but also with kaon selected by de/dx. 50% gain wrt the usual k  2 tag ● Tag bias and trigger efficiency (no more auto trigger) can be taken under control at 2% level. ● Control sample ??? (mainly for the calorimetric analysis). Partial sovrapposition of energy range with Ke3. Suggestions are welcome (e + e - 

4 May 2006 Momentum distribution ● We use as starting point a sample of K + e2 (full 2fb statistic) using the usual K - m 2 tag as selection. ● MC 2005 was used with the new charged kaon noise inserted ● K+ decay events, tagged by K-m2, reconstructed with vertex in FV Red = MC blu = ke2 black data Lab momentum Mev/c

4 May 2006 Momentun in K center of mass ● We ask for tracks with associated cluster ● To start rejecting the muons we ask for p e *>240 Mev/c ● Total efficiency on the (Ke2+radiative) decay is 15%. (22% if only Ke2 is considered) ● Then we are left with 1700 ev of signal vs 3.3x10 6 k m 2(mc)

4 May 2006 e/m in Ecal ● We would like to push the ECAL rejection relying on the cluster shape. We used first 3 planes where the difference is larger We use the variables: ●  e i =(E i -E i+1 )/(E i +E i+1 ) ● R=E 3 /E 1, ● ●  e max ●  e min MeV N Plane electron muons

4 May 2006 Cut on DE variables ● We ask for the first 3 planes to be on, with energy> 3MeV, and with the cell time within 60 ns from the TOF ● Then we cut on the normalized  E between plane 1 and 2, and between plane 2 and 3  E12  E23 Blu = ke2 red = km2

4 May 2006 Efficiency signal vs bck Cuts legenda : ● 1= tr. Rec. ● 2= clust. Ass. ● 3= p*>240MeV ● 4=  E 12,  E 23 ≠0 ● 5= DE plane cut red=ke2 blu=bck MC purple=data efficiency

4 May 2006 Data vs MC discrepancy.. DATA vs Ke2(MC)BCK(MC) vs Ke2(MC)

4 May 2006 Data vs MC A contribution electron like is present in the DATA Ke2 BCK (MC) DATA Energy(MeV) Plane Energy(MeV)

4 May 2006 Ratio of Ke2/bck eff Cuts legenda : ● 1= tr. Rec. ● 2= clust. Ass. ● 3= p*>240MeV ● 4=  E 12,  E 23 ≠0 ● 5= DE plane cut Rejection= ratio*eff(ke2) Red= on MC blue= DATA Ratio= eff(ke2)/eff(bck)

4 May 2006 After the ECAL rejection: ● Nothing done yet. 1.4x10 5 ev of bck on DATA survive the ECAL cut ev of signal. ● Some distribution are reported (10 pb -1 of data) to spot the useful variables

4 May 2006 About tof..... ● It is not so powerful, since the muons are almost relativistic ( differently from that one of the semileptonic decay..) ● Red = ke2 ● Blu = BCK(MC) ● Dot = DATA

4 May 2006 How to proceed? ● Cut on the reconstructed kink of the muon decaying into electron ● Exploit (?) TOF ● Neural net or likelihood on the calorimetric variables (control samples from data needed!!) ● Finally emiss-pmiss, if the signal can be seen!!