1. LHCb-light Meeting –June, 18th 2002 Frédéric MACHEFERT 1 Laboratoire de l’Accélérateur Linéaire (IN2P3-CNRS) Orsay, France Effect of M1-thickness LHCb-light meeting Tuesday, June 18th 2002

2. LHCb-light Meeting –June, 18th 2002 Frédéric MACHEFERT 2 Laboratoire de l’Accélérateur Linéaire (IN2P3-CNRS) Orsay, France 14.4 % X 0 MC Sample Figures based on 17000 B  0  0 LHCb-light as of v241 Brunel v9r1  0 MC considered: p t (  0 )>500MeV and no  merged case selection  : p t (  )>200MeV E PRS > 4 MeV E SPD veto  0 Rec : p t (  0 )>500MeV  0    0   e + e - (z conversion > 8m) #  0 30944 (42.3%)36365 (45.5%) Not seen14.4%76.7%51.9% Seen85.623.3%48.1% Efficiency17.6%17.2%17.9% Purity14.2%2.8% (P(   e + e - )~35 %)   e + e - : p t (e + e - )>200MeV E PRS > 10 MeV E SPD Out of the sweeping region:  0    :  =21.1%  =19.4%  0   e + e -:  =20.1%  =5.8%

3. LHCb-light Meeting –June, 18th 2002 Frédéric MACHEFERT 3 Laboratoire de l’Accélérateur Linéaire (IN2P3-CNRS) Orsay, France Signal - Noise 49.5% 30% 42.3% 45.5% 65% 55%  0    0   e + e - Efficiency Evolution with respect to X 0

4. LHCb-light Meeting –June, 18th 2002 Frédéric MACHEFERT 4 Laboratoire de l’Accélérateur Linéaire (IN2P3-CNRS) Orsay, France X0 variations