Avati, V

Österberg, K

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TOTEM forward measurements: leading proton acceptanceV. Avatia and K. ¤Osterbergba CERN, Geneva, Switzerland and Case Western Reserve University, Cleveland, OH, USAb Department of Physical Sciences, University of Helsinki and Helsinki Institute of Physics, FinlandAbstractWe report about the acceptance of forward leading protons in Roman Pot sta-tions placed along the LHC beam line. The TOTEM stations plus additionaldetectors at 420 m from the interaction point have been considered using thelowβ∗ optics V6.5 for LHC physics runs.1 IntroductionThe TOTEM very forward detectors consist of telescopes of Roman Pots (RP) placed symmetricallyon both sides of the interaction region IP5. The RP stations will be placed at 147 m and 220 m from IP5:each station is composed of two units separated by 2.54 m and each unit is equipped with two verticaland one horizontal silicon detector package. For more details on the TOTEM RPs, please refer to [1].The possibility to add a detector in the cryogenic sections of the LHC is under investigation, therefore,we have included one more RP station at 420 m in these acceptance studies. This work is an update, dueto the release of a new LHC optics, of previous studies done by the TOTEM Collaboration [2].1.1 Low β∗ optics acceptance studyThe transverse displacement (x(s), y(s))1 of a scattered leading proton (with momentum loss ξ =∆P/P < 0) at distance s from the interaction point (IP) is determined by tracking the proton throughthe accelerator lattice using the MAD-X program [3].The new optics version 6.5 for the standard LHC physics runs is used. Notable changes (at IP5)from the previous versions are : β∗= 0.55 m (previously 0.5 m) Beam offset in the horizontal plane = 0.5 mm (previously zero) Horizontal crossing angle = 142 µrad (previously 150 µrad)The protons at the IP are generated with at distributions in the azimuthal angle φ, in Log(−ξ) andin Log(− t) in the kinematically allowed region of the ξt plane, i.e. for physical values of the scatteringangle of the proton. The Mandelstam variable t is dened as t = (porig − pscatt)2, where porig(scatt)is the four-momentum of the incoming (scattered) proton. The scattering angle of the proton is physicalwhen t ≥ t0(ξ), where t0(ξ)is given byt0(ξ)= 2(P2orig +m2p) [√1+(P2orig [ξ2+2ξ])/(P2orig +m2p)− 1]− 2ξP2orig . (1)In Eq. 1, Porig is the momentum of the incoming proton and mp is the proton mass.The transverse vertex position and the scattering angle at the IP are smeared assuming Gaussiandistributions with widths given by the transverse beam size (16 µm) and the beam divergence (30 µrad).1The reference system (x,y,s) defines the reference orbit in the accelerator; the s-axis is tangent to the orbit and positivein the beam direction; the two other axes are perpendicular to the reference orbit. The x-axis (horizontal, bending plane) isnegative toward the center of the ring.452To determine the acceptance of a RP station, the minimum distance of a detector to the beam andconstraints imposed by the beam pipe or beam screen size are considered.The minimum distance of detector approach to the beam is proportional to the beam size:x(y)min = 10σx(y)beam+c , (2)where c is a constant that takes into account the distance from the edge of the sensitive detector area tothe bottom of the RP window (∼ 0.5 mm). For the nominal transverse beam emittance ² = 3.75 µm·radtypical values of the horizontal detector distance are ∼ 1 mm (at 220 m) and ∼ 4 mm (at 420 m). In theresults shown later, the detector shape has not been included. The beam pipe apertures can be found inthe LHCLAYOUT Database [4].1.2 ResultsFigures 13 show the acceptance in Log(−ξ), Log(− t) for the RP stations at 220 and 420 m for theclockwise (beam1) and counterclockwise (beam2) circulating beam.One should note that these results refer to non-physical distributions in the variables ξ and t inorder to have good statistics in each interval and describe all possible processes. To use these results ina general simulation program, the φ dependence has to be taken into account, since it is not negligible inmany kinematical congurations. More detailed analysis such as detector alignment samples, collimatoreffects, etc. can be found in [5].These results have been included in FAMOS (FAst MOntecarlo Simulation of the CMS detector)by M. Tasevsky (Diffractive Higgs production, these proceedings) and they have been used in theCMS/TOTEM studies on triggering a diffractively produced light Higgs boson with the CMS Level-1trigger (Diffractive Higgs: CMS/TOTEM Level-1 Trigger Studies, these proceedings).References[1] The TOTEM collaboration, TOTEM Technical Design Report, CERN-LHCC-2004-002TOTEM-TDR-001 (2004).[2] The TOTEM collaboration, Status Report to the LHCC (http://www.cern.ch/totem)(2002);J. Kalliopuska, J.W. L¤ams¤a, T. M¤aki, N. Marola, R. Orava, K. ¤Osterberg, M. Ottela and S.Tapprogge, TOTEM forward measurements: exclusive central diffraction, these proceedings andJ. Kalliopuska, T. M¤aki, N. Marola, R. Orava, K. ¤Osterberg, M. Ottela and S. Tapprogge,HIP-2003-11/EXP (2003).[3] The MAD-X Program, Methodical Accelerator Design, http://www.cern.ch/mad.[4] LHC Layout, http://lhclayout.web.cern.ch/lhclayout/.[5] V. Avati and K. ¤Osterberg, Acceptance calculations methods for lowβ∗optics,TOTEM Internal Note 05-2 (http://www.cern.ch/totem) (2005).TOTEM FORWARD MEASUREMENTS: LEADING PROTON ACCEPTANCE453Fig. 1: Log(−ξ) acceptance for: beam1 station at 220 m (solid-red) and 420 m (dashed-red) and beam2 station at220 m (dashed-dotted-blue) and 420 m (dotted-blue).Fig. 2: Log(−ξ) vs Log(−t) acceptance for beam1 (left) and beam2 (right) stations at 220 m.Fig. 3: Log(−ξ) vs Log(−t) acceptance for beam1 (left) and beam2 (right) stations at 420 m.V. AVATI AND K. ¨OSTERBERG454

TOTEM forward measurements: leading proton acceptance

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