FIRST OPERATION OF THE TPC FACILITY AT PEPLBL, UCLA, UC Riverside , Johns Hopkins , Tokyo, Yale (PEP4 Collaboration)

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Submitted on 1 Jan 1982

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FIRST OPERATION OF THE TPC FACILITY AT PEPLBL, UCLA, UC Riverside , Johns Hopkins ,

Tokyo, Yale (PEP4 Collaboration)

D. Stork

To cite this version:

D. Stork. FIRST OPERATION OF THE TPC FACILITY AT PEPLBL, UCLA, UC Riverside ,

Johns Hopkins , Tokyo, Yale (PEP4 Collaboration). Journal de Physique Colloques, 1982, 43 (C3),

pp.C3-42-C3-42. �10.1051/jphyscol:1982306�. �jpa-00221859�

JOURNAL DE PHYSIQUE

CoZZoque C3, suppZ6ment au n o 12, Tome 43, ddcembre 1982 page C3-42

FIRST OPERATION OF THE TPC F A C I L I T Y AT PEP

LBL, UCLA, UC R i v e r s i d e , J o h n s Hopkins, Tokyo, Yale (PEP4 C o l l a b o r a t i o n ) Presented by D.H. S t o r k

Department of Physics, UCLA, 405 HiZgard Avenue, Los AngeZes, CA 90024, U. S.A.

I n i t s f i r s t o p e r a t i o n a t PEP, t h e TPC f a c i l i t y accumulated 6500 i n v e r s e nano- barns. We have since concentrated on d e t e c t o r performance s t u d i e s based upon s p e c i a l t e s t runs and upon a p a r t i a l and biased sample o f 1000 mu1 t i h a d r o n events. A t y p i c a l event i s i l l u s t r a t e d i n Figure 1 : ( a ) end view o f TPC cathode-pad raw data, ( b ) s i d e view o f the sense w i r e raw data. Not shown i s the side view o f the cathode-pad raw data which completes t h e three-dimensional TPC data readout.

Although TPC d e t e c t o r performance s t u d i e s are f a r from complete, we present here a progress r e p o r t . S p a t i a l r e s o l u t i o n i s c h a r a c t e r i z e d by ax = 195 um i n the bend plane and uz = 450 i n the d r i f t d i r e c t i o n . Track d i s t o r t i o n due t o e l e c t r o s t a t i c and p o s i t i v e i o n e f f e c t s close t o t h e h i g h voltage f i e l d cages has been brought t o a manageable l e v e l by measuring the r a d i a l e l e c t r i c f i e l d component u s i n g the w i r e data, then c o r r e c t i n g t h e bend plane data f o r geometric and ExB e f f e c t s . Momentum r e s o l u t i o n achieved so f a r i s 0 /p = 7% a t 1 GeV f o r t r a c k s w i t h o u t any v e r t e x cons- t r a i n t and i s 3.6% f o r t r a c k s wRen a v e r t e x c o n s t r a i n t i s applied. Momentum r e s o l u - t i o n w i l l be s u b s t a n t i a l l y improved when t r a c k r e c o n s t r u c t i o n i s optimized, when d i s t o r t i o n s are f u l l y corrected, and when d r i f t chamber i n f o r m a t i o n i s included. I n a d d i t i o n , a much g r e a t e r improvement w i l l occur when t h e present 0.4T conventional c o i l i s replaced by a 1.5T superconducting c o i l i n 1983.

A p l o t o f t r a c k i o n i z a t i o n measurements versus momentum f o r multi-hadron events i s shown i n Figure 2. The i o n i z a t i o n i s determined from a t r u n c a t e d mean a l g o r i t h m f o r a l l t r a c k s having a t l e a s t 80 unambiguous w i r e samples o u t o f t h e 183 p o s s i b l e . The dE/dx d i s t r i b u t i o n f o r t h e p i o n band near minimum has cr(dE/dx) ⁼ 4.6%. Bhabha events have a(dE/dx) = 3.2%. Most instrumental e f f e c t s have been c o n t r o l l e d o r c o r r e c t e d t o the 1% l e v e l o r b e t t e r . E f f o r t s are underway t o f u r t h e r reduce the standard d e v i a t i o n t o the value o f 2.8% which was achieved w i t h cosmic rays, compa- r i n g measurements o f t h e same t r a c k i n two sectors o f t h e TPC.

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Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982306