The authors have measured the doubly differential cross section sd{sup 2}{sigma}/dtdM{sup 2} for the reaction p + p {yields} p + X using 200 GeV incident protons in the external beam at the National Accelerator Laboratory. Here t is the square of the four momentum transfer to the target proton, M{sup 2} is the mass squared of X, and s is the total center of mass energy squared. They cover the region of 0.019 &lt; |t| &lt; 0.19 GeV{sup 2} and 1 &lt; M{sup 2} &lt; 60 GeV{sup 2}. Interesting structure is observed at low |t| and M{sup 2} values

/SUNY, Stony Brook

Childress, S.

Franzini, P.

Lee-Franzini, Juliet

McCarthy, R.

Schamberger, R., Jr.

U., /Columbia

UNT Digital Library

#/'i fIJB-7s-12 L(~£ f-nOI L ! Inelastic P-P Scattering at 200 GeY * S. Childress and P. Franzini Columbia	 University, New York, New York 10027 and J. Lee-Franzini, R. McCarthy, and R. Schamberger, Jr. State	 University of New York at Stony Brook Stony Brook, New York 11790 We have measured the doubly differential cross section sd2cr/dt~ for the reaction p + p + p + X.using 200 GeY incident protons in the ex­ternal beam at the National Accelerator Labora­tory. Here t is the square of the four momentum transfer to the target proton, ~ is the mass squared of X, and s is the total center of mass 'energy squared. We cover the region of 0.019 < 2 2 2It I < 0.19 Gey and 1 < M < 60 GeV • Interes­2ting structure, is observed at low It/ and Mvalues. * Work supported in	 part by the National Science Foundation. , 2 We have studied the reaction p + p + p + X at 200 GeV labora­tory incident energy. We select this reaction by detecting the re­coil proton in one of 18 telescopes each consisting of two solid state detectors. In this way we can identify each proton and measure its kinetic energy T in the range 10 < T < 100 MeV. OUr accuracy in T is typically better than 10 %. The four momentum transfer squared is given by t = 2 MT where M is the proton mass. The measured p p value of T and the telescope angular position e together determine 2M , the square of the mass of X. Each telescope subtends an angu­lar opening in e of 0.460 and accepts a solid angle of approximately 6.4 x 10-5 steradians. The 18 telescopes are uniformly spaced in e between 480 and 890 • Thus our telescopes actually cover only about 20% of the angular range spanned. As a result we have not measured 2the inelastic cross section continuously in M We might thus be missing interesting structure in the cross section vhich we would hopefully cover in the future. In order to obtain the free proton cross section we have used polyethylene (CH )n and carbon targets and performed a subtraction.2The normalization of polyethylene and carbon runs before the sub­traction was obtained by identifying deuterons and tritons from proton-carbon interactions in the two targets. Such deuterons and tritons were counted simultaneously with the proton recoils. The data which we present were obtained during a run of app!oximately 10 hours using the extracted proton beam in the Neutrino Labora­tory at NAL. For many reasons the data were colleeited with large deadtimes. However, our interesting conclusions are not affected by the corrections applied for such effects. l 3 The layout of the experiment is shown in Fig. 1. It should be noted that the detectors are located approximately 100cm from the extracted proton beam which, during the run discussed, had an inten­10sity of 3 x 10 protons/pulse. It was thus very important to obtain an extremely clean beam since interaction of a very small fraction of the beam hundreds of feet upstream of our location would have produced background orders of magrlitude larger than our target signal. The fact that such a beam was made available to us is a tribute to the National Accelerator Laboratory, its accelerator, the beam extrac­tion staff, and the staff of the Neutrino Laboratory. 2The targets used were 13mg/cm foils of polyethylene and carbon ap~roximate1y 5mm wide and placed at a 450 angle to the beam. Approxi­4mately 3 x 10- of the beam interacted in our target, the remainder being used by the Neutrino Lab for other experiments. During the run 6 we collected approximately 5 x 10 triggers of which approximately 25% were due to target interactions. The remainder were accidentals due to an extremely lax trigger requirement. Comparison of the energy loss signals in the two detectors of each telescope completely re­moved such accidentals. The first (thin) detector of each telescope is a 500 micron totally depleted silicon' surface barrier detector. The second (thick) is a 5000 micron lithium drifted silicon detector. A specific ioni­zation measurement is performed in the thin detector and the total energy is measured in the thick detector for T up to approximately 30 MeV. For higher energies the proton does not stop in the second detector but a measurement of the energies E1 and E lost in the two2 detectors still allows a good determination of the proton kinetic , -.. 4 energy up to approximately 100 MeV. Scatter plots in the E -El 2 plane for events collected in a few minutes of running are shown in Fig. 2 for two telescopes and two targets. Protons are clearly iden­tified both when stopping and when traversing the thick detector. The proton-proton elastic scattering peaks are clearly visible with the polyethylene targets. Deuterons and tritons are copiously pro­duced and appear in the plot as bands above the proton band. We perform the following steps to obtain the free hydrogen event distribution: (a) Divide the,E -E plane into a rectangular grid.l 2 (b)	 Identify protons, deuterons and tritons by their grid positions. (c)	 Count the deuterons and tritons. (d)	 Determine T of the protons from E and E •l 2(e)	 Normalize the carbon event density in T from the carbon target to the carbon event density from polyethylene using (c). (f)	 Obtain the hydrogen event distribution by sub­tracting the carbon distribution from the poly­etp~lene distribution. This procedure is carried out independently for each telescope. Then a deadtime correction (mentioned previously) is applied to each tele­scope. The final step in the analysisis to compute t ,_ ~ and the 2Jacobian a(e,T)/a(t,M ) from our knowledge of T,6 and the beam momen­tum. At this point the unnormalized differential cross section . d2a/dtd~ is obtained in arbitrary units. 5 The total number of inelastic scattering events on free hydrogen used for the above determination is approximately 35,000. An abso­lute normalization is obtained from the total number of proton-proton elastic scattering events in each telescope which observes the elas­. ak2 t1C pe • Some 45,000 elastic scattering events were observed, the elastic peaks being clearly visible in 5 telescopes. Such elastic 3peaks are also very useful to cross check our energy calibrationsand our ability to correctly measure the t dependence of the cross section. To the accuracy of our data we obtain very good agreement 4with published values for the slope parameter. We find b = 11.6 ± -2L 4 GeV • In Table I and Figs. 3 and 4 we present our measured values of 2 .2 2sd o/dtdMl where s = 377 GeV (square of total center of mass energy). The errors quoted are the statistical errors resulting from the sub­traction. The limits of the It I intervals used are shown in Fig. 4. 2In Fig. 3 we show the M dependence of the cross section in the 2lowest It I interval. Table I presents the inelastic data with 6 GeV2bins in M , coarser binning than used in Fig. 3. The minimum value 2of ~ =7 GeV included in Table I is well outside the region influ­enced by elastic events even for the data at high It1 5. In Fig. 4 we plot the data of Tab:l;e I at the two smallest values of~. The most outstanding fe~ture of the data is the peaking of the cross section at It I ~ . .1 GeV2 and subsequent decrease for lower It I for .2 2 .2 2'­7 < Ml < 19 GeV. Around Ml = 20 GeV there genuinely appears to be a change in the behavior of the cross section dependence versus t. Previous measurements of the proton-proton inelastic cross sec­6 . tion have been performed by Sannes et al. at NAL but at higher values .of It I. Measurements have also been performed by Albrow et al. 7 at , 6 the ISR but for both higher It I and s. Both expertments obtain a .., minimum in the cross section for x = I - rl-/s ::! 0.9. Since our mini­mum for l'tl ::! 0.03 GeV2 occurs at x ::! 0.97, apparently the minimum in the cross section moves with It I. It should be pointed out, however, that Albrow et ala have fl. poorer resolution in x than we do which may affect the position of their minimum. Sannes et ala do not quote their resolution. We wish to express our thanks to the NAL accelerator, beam ex­traction and Neutrino Lab staffs. In particular we wish to'thank J. R. Orr, on whom we could always call as a member of our team. E. Blesser and H. Edwards were instrumental in obtaining a clean extracted pro­ton beam. The Nevis machine shop constructed most of our mechanical equipment and some parts of the electronics were built at Nevis. We gratefully acknowledge the help of W. Sippach and Y. Au. We wish to thank our theoretical colleagues, particularly C. QQigg and A. Mueller,-­for their continuous encouragement and interest in our experiment. We also thank Paula and Catfish. , Fig. 1. Fig. 2. Fig. 3. Fig. 4. • FIGURE CAPTIONS Sketch of the apparatus. Scatter plots in the E -E plane for (a) polyehtylene datal 2 at 83° (b) carbon data at 83° (c) polyethylene data at 80° (d) carbon data at 80°. Doubly	 differential cross section versus MF for It I ~ 0.03 2GeV • Doubly differential cross section versus It I for indicated 2M	 • FOOTNOTES	 °1 1.	 S. Childress et al.~ Proceedings of the Vanderbilt Internationsl Conference on New Results from Experiments on High Energy Particle Collisions, Nashville~ 1973. 2.	 We take the elastic differential cross section do/dt to be 26 mb/GeV2 at It\ = 0.1 GeV2 as given by G. Charlton et al.~ "Two and Four Prong pp Interactions at 205 GeV", contribution to the XVI International Conference on High Energy Physics,•	 J Batavia, 1972. The 'accuracy of our absolute normalization should be better than 30%. 3.	 The energy scale for each detector is calibrated with a source producing a particles of 5.477 MeV. 4.	 G. Barbiellini et al., Phys. Letters 39 B~ 663 (1972). The slope parameter is given by b = (a/dt) In (do/dt). 5.	 As can be seen from the elastic peak in Fig. 3 our resolution in 2 2 2M is 1 GeV full width at half maximum for It/ ~ 0.03 GeV. How­ever~ our resolution deteriorates at higher / t I. See reference 1 for details. 6.	 F. Sannes et al.~ Phys. Rev. Lett. 30~ 766 (1973). , 7.	 M.G. Albrow et al., Nuclear Physics B 54, 6 (1973). Table T. sd2U/dtd~ (mb/GeV2) using 6 GeV2 bins in ~ M2 Itl~·03 Itl~·08 Itl~·ll· Itl~·14 Itl~.17 10 36± 63 308±33 229±28 132±23 183±19 16 33± 59 128±24 133±24 78±31 45±15 22 228± 63 125±36 70±31 23±23 55±18 28 274± 64 163±35 133±33 117±31 86±23 34 251± 77 101±31 179±39 117±31 93±23 40 303±127 117±31 126±26 81±24 109±23 3 ~ c Z --t ~ z.A.I \ ~ ~~ '.II~~G) m II ~ -I " 'I 'I 'I 'IQ) 'I 'I" " 'I"'I "-~ m r­." m ::0 c.nO'm ()Z m -I X 0 C 0 --I ""0 mZ -I Z m ;iID (J)~» Zr- -Z '0' »0 m r­» r-- 3: .. » tp '; --t m r-m c.n () 0 .." m (/) -0 r-o ­c.n ~ ~ m 0 m -I m n -I 0 '" Fig. 1. S. Childress et ale I I" I 1.1. "~ .. ,-­u-,, .' .' .', 0 ·. )0 • ·'.. O. · 00 .•' •'t. •• .''''..' ~ .. ....-,.... .;i':: I. ",,:. 'If ., .:e." ~ .~ ~ ... ~. ~ ...... ~ ~I J.­ ••­~ -.. ' .,. : .•.. ... •l:a,I "'., , ~ t ,-­-,. '. .' .,. ,. ", ' '.l' O'. ' ... .. ...e.. .~ '.. '.. .­...."~ ': •. ''f~~ '" .' .••~O ~...' . ...... " } ... .. '..". .t, ... , ". . ( l'l'.",'...' I lr' t I I I I -0-,, -..0-.' 0'.' r I "., . ,•• e,. , ••• e • , I' .. , ,. .. " ,, I , " ,~", a. ' ..~ -.-" . I ...... ' e-li,,,• ~., , · '. • ~.,,. .. , '0 ., I' • .. , " ,, '.. . , . .• . :a , 0 •• . -...... .,...,. ;'".,.... . \~ ~: ..~i :~: .' I o :.I ~ ... ).\ .~ it "~~ " -- ..:\-~..... ~ Title: Inelastic P-P Scattering at 200 GeVFig. 2. S. Childress et ell • • ,---r......;..-...,..----r-~--,---r----.,....:.--0.~ I"-I I (\J III o to ~ I C!>(X) I tf)r() I o 00I 10 I ~I v I • I? I o II o .. -0)v . ~ v o, • II I•I I • ,• II I• II I•I I I•I I I•I I -Ii I•'I 1• IIX 1-10:4'1 ....... ---1 I •I' 1-. , I I--+-t oI 0 II .-... ~ 1•,. 1 (Dill) x r-~I-4;;I--.;--~-j;F~------ + ... r 0 I I -.-a....--~C\J-;--_.....J.----L---L----L---J Q -0I (~l\a8/su.Joq) It\JPtP/.D P S c, ZG ~ M2 =IOGeV2 iJ M2 = 16· .......... >:\J Q) .. ",(9...c E'-'200 .\.1 0.15 - . . Fig. 4. S. Childress et al. Title: Inelastic ~ P-P Scattering at 200 GeV. 

Inelastic p p Scattering at 200-GeV/c

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Inelastic p p Scattering at 200-GeV/c

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