Tagging with Roman Pots at RHIC. Proton tagging at STAR

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1 Tagging with Roman Pots at RHIC Proton tagging at STAR

2 Elastic and Diffractive Processes in High Energy Proton Scattering Elastic scattering Detect protons in very forward direction with Roman Pots (RPs) Single diffractive dissociation Detect one proton with RP and M X in forward STAR detector Central production Detect both protons in forward direction plus M X in central STAR detector (SVT, TPC, )

3 Elastic pp-scattering at RHIC Studies the dynamics and spin dependence of the hadronic interaction through elastic scattering of polarized protons in unexplored cms energy range of 50 GeV < s < 500 GeV, in the range of GeV 2 t 1.5 GeV 2, covering region of Coulomb interaction for t < 10 3 GeV 2 Measure total cross section σ tot and access imaginary part of scattering amplitude via optical theorem Hadronic interaction for GeV 2 t 1 GeV 2 Measure forward diffraction cone slope b STAR M Interference between Coulomb and hadronic interaction (CNI-region) Measure ratio of real and imaginary part of forward scattering amplitude ρ 0 and extract its real part using measured σ tot

4 The RHIC Accelerator PHOBOS Absolute Polarimeter (H jet) Siberian Snakes RHIC pc Polarimeters Siberian Snakes BRAHMS PHENIX Pol. H - Source Spin Rotators (longitudinal polarization) Solenoid Partial Siberian Snake LINAC BOOSTER Helical Partial Siberian Snake 200 MeV Polarimeter AGS AGS Internal Polarimeter Rf Dipole STAR Spin Rotators (longitudinal polarization) AGS pc Polarimeters Strong Helical AGS Snake Spin flipper

5 The RHIC pp Run proton bunches per beam (120 bunch structure) protons per bunch (design ) Luminosity about cm -2 s -1 (large β* = 21 m beam tune) Beam momentum 100 GeV/c (design up to 250 GeV/c) Fill life time about one shift of eight hours

6 Principle of Measurement Elastically forward scattered protons have very small scattering angle θ * Beam transport magnets determine trajectory of beam and scattered protons Scattered protons need to be well separated from the beam protons Need Roman Pot to measure scattered protons close to beam Beam transport equations relate measured position at detector to scattering angle x = a 11 x 0 + L eff θ * x θ x = a 12 x 0 + a 22 θ * x Optimize so that a 11 small and L eff large x 0 can be calculated by measuring θ x (2 nd RP) Similar equations for y-coordinate Neglect terms mixing x- and y-coordinate in above equations x : Position at Detector θ x : Angle at Detector x 0 : Position at Interaction Point θ x : Scattering Angle at IP *

7 Beam Transport RP Positions S. Tepikian

8 Experimental Technique

9 STAR Experimental Setup 2009 Roman Pot above beam to IR Roman Pot below beam

10 Roman Pot Hardware to IR

11 Silicon Detector 400 micron thick silicon, 75 x 45 mm 2 active area Good position resolution with strip pitch ~100 micron Distance between first strip and edge about 500 micron

12 Silicon Detector Efficiency After excluding hot/noisy strips 5 dead strips for ~14,000 strips in active area (acceptance)

13 Elastic Hit Pattern Hit distribution of scattered protons within 3σ - correlation cut reconstructed using the nominal beam transport Top detector Agreement between Monte Carlo simulation and data Inner detector t<0.005 (Gev/c) 2 Outer detector 0.005< t< < t< < t< < t Bottom detector

14 Roman Pots at STAR in Phase II Under construction for 2014/15 Adding Roman Pots between dipole magnets DX and D0 (z = 15 m) Extended kinematic range -t < 1.5 GeV 2 /c 2 for s = 500 GeV

15 Phase II Simulated Kinematic Range for Elastically Scattered Protons Data taking concurrent with standard proton beam tune (using β * = 1 m) Using Hector simulation program (J. de Favereau, X. Rouby) Detector positioned between DX and D0 (around z = 15 m) 200 x 100 mm 2 sensitive silicon detector area (15 mm distance to beam) 100 GeV/c proton beam momentum 250 GeV/c proton beam momentum

16 Polarized 3 He Beams at RHIC & EIC Common detector setup may be used for proton 3 He scattering and electron 3 He scattering Upgraded Phase II Roman Pots usable for RHIC Detect and distinguish scattered nucleons Spectator neutrons (< ~ 3 mrad) detected by current Zero Degree Calorimeter (ZDC) Spectator protons follow magnet lattice Use Roman Pot detectors Minimum scattering angle determined by beam width

17 Polarized 3 He Beams at erhic Simulation for an EIC using DPMJET III (J.H. Lee, BNL) Electron energy 5 GeV and 3 He energy 100 GeV Momentum distribution of spectator protons from 3 He J.H. Lee

18 Polarized 3 He Beams at erhic Ion beam line in interaction region

19 Polarized 3 He Beams at erhic Acceptance at 20 m from the IP About 90% acceptance for spectator protons J.H. Lee

20 Polarized 3 He Beams at erhic Simulation for an EIC using DPMJET III (J.H. Lee, BNL) Electron energy 5 GeV and 3 He energy 100 GeV EIC Roman Pot Setup at 20 m from Interaction Point J.H. Lee

21 Summary Roman Pot detectors enable access to spectator protons with very small scattering angles Presently used at RHIC (and LHC) in proton-proton collisions Planned use at RHIC for proton 3 He collisions Possible use at an EIC also for electron 3 He collisions

22 Additional Slides

23 Analyzing Power Measurement 2009 A N ( t) = t m [ κ c ( 1 ρ δ ) + 2( δ Re r Imr )] 2( Re r ρ Imr ) tc t tc 2 ( ρ + δ ) + ( 1 + ρ ) t t t 5 5 Only statistical errors shown r 5 = m p - t φ had 5 Im ( φ had + )

24 Central Production at STAR In central region use Central Trigger Barrel to veto cosmic events (top and bottom veto) select low multiplicity events in north and south quadrants of STAR From Y. Gorbunov