Physics with Tagged Forward Protons and Results from Ultra-Peripheral Collisions at STAR

Transcription

1 Physics with Tagged Forward Protons and Results from Ultra-Peripheral Collisions at STAR (for the STAR Collaboration) Process of diffraction and physics with forward protons - program at RHIC Our program in the context of QCD RHIC program Run 9 PHASE I status of analysis Phase II proposal Results from HI UPC collisions (AuAu) Summary 1

2 The Relativistic Heavy Ion Collider RHIC is a QCD Laboratory: Nucleus- Nucleus collisions (AuAu, CuCu ); Asym. Nucl. (dau); Polarized proton-proton; erhic - Future 2

3 Our Program in the Context of RHIC the QCD Factory Study non perturbative regime of QCD Gluonic degree of freedom in Hadrons exotica (glueballs ) Non-pert. QCD nature of diffractive processes structure of Pomeron, Odderon (color neutral exchange) and its spin dependence The program will naturally include other QCD topics: Spin dependence of the elastic and diffractive scattering in polarized pp collisions in the s up to 500 GeV => hadronic spin flip; Spin averaged elastic scattering (ρ, σ tot, dσ/dt, B-slope); A possibility of new physics of sphaleron production (clustering in multiparticle production) in DPE. 3

4 RHIC-SPIN ACCELERATOR COMPLEX absolute ph polarimeter RHIC RHIC pc CNI polarimeters Former location of pp2pp Siberian Snakes PHENIX Spin Rotators L max = STAR s 1 70% Polarization cm s = GeV 2 Siberian Snakes β * ~ 21 m for pp2pp/star in 2009 Pol. Proton Source LINAC BOOSTER AGS 5% Snake AGS quasi-elastic polarimeter MeV polarimeter RF Dipoles 15% Snake AGS pc CNI polarimeter

5 Processes with Tagged Forward Protons QCD color singlet exchange: C=+1(IP), C=-1(Ο) p + p p + p elastic p + p p + X + p diffractive X= particles, glueballs Discovery Physics p + p p + X SDD 5

6 Central Production in DPE In the double Pomeron exchange process each proton emits a Pomeron and the two Pomerons interact producing a massive system M X M X = ξ 1 ξ 2 s invariant mass p M x where M X = π + π, χ c ( χ b ), qq(jets), H(Higgs boson), gg(glueballs) The massive system could form resonances. We expect that because of the constraints provided by the double Pomeron interaction, glueballs, hybrids, and other states coupling preferentially to gluons, will be produced with much reduced backgrounds compared to standard hadronic production processes. p For each proton vertex one has t four-momentum transfer ξ = Δp/p 6

7 Implementation at RHIC - tag forward protons PP2PP Setup Phys. Lett. B 579 (2004) , Phys. Lett. B 632 (2006) , Phys. Lett. B 647 (2007) p = p ( Θ 1, Θ 1 ) = ( Θ 2, Θ 2 ) 1 2 x y x y 7

8 Implementation at RHIC - Detectors 1. Need detectors to measure forward protons: t - four-momentum transfer, ξ = Δp/p, M X invariant mass and; 2. Detector with good acceptance and particle ID to measure central system Phase I Roman Pots of pp2pp and STAR - use existing equipment Vertical AND Horizontal RP setup for a complete φ coverage 8

9 Implementation at RHIC - STAR Detector Measure recoil system M x EMC Barrel EMC End Cap BBC FMS FPD TPC pp2pp ZDC & ZDCSMD pp2pp ZDC & ZDCSMD PMD Jan. 4-8,

10 Resonance Signal in p+p and Au+Au collisions from STAR p+p K(892) Ξ p+p Σ(1385) Au+Au Au+Au p+p p+p Δ ++ Λ(1520) Au+Au φ(1020) p+p Au+Au 10

11 RUN 9 - Integrated Elastic Triggers Expect about 20-25M elastic events for analysis z-vertex distribution from trigger counters (no corrections) 11

12 Colinearity of candidate elastic events (we have a very good data sample!) The mean is < 1mm Width σ x,y ~ 1.4 mm => σ θ 40 µrad 12

13 Run 9 Candidate Central Production Event 13

14 Glueball Spectrum The glueball spectrum from an anisotropic lattice study Colin Morningstar, Mike Peardon Phys. Rev. D60 (1999)

15 Kinematic filter (dp T ) for gg (F. Close et al./w102) Coupling of the exchange particles to the final state mesons for gluon exchange (small dp T ) and quark exchange (large dp T ) Spin-dependence of the coupling can be studied at RHIC PLB (1997) As predicted by Regge theory the diffractive cross section at RHIC is dominated by the Pomeron (gluonic) exchange, : σ RR ~ s -2 σ RP ~ s -1 σ PP ~ const. or s α where α ~(0.1) Large O(Λ QCD ) Gluon Ladders 15

16 WA102 f 0 (1500) π + π π + π f 1 (1285) F.E.Close and A.Kirk, PLB397, 333 (1997). dp T > 0.5 GeV/c σ(f 1 )= 7 µbarn We are sensitive to this level of cross section σ(f 0 )= 3 µbarn 0.2 GeV < dp T < 0.5 GeV. f 0 (1285) dp T < 0.2 GeV. 16

17 Simulation Performance Plots Simulation done using the beam transport simulator HECTOR Geometrical acceptance dn/dt acceptance Momentum Spectrum Mass Acceptance 17

18 Acceptance and expected yields in M X We assume the DPE cross section 140 ubarn, and branching ratios as measured at the ISR High-M x reconstruction is limited by PID (π/k separation up to ~ 1.6 GeV/c) Rates for major channels: π + π - π + π - events 27 Hz π + π - events 23 Hz K + K - events 2.3 Hz Event yields for 20 week run at 500 GeV π + π - π + π events π + π events K + K events 18

19 Phase I - ongoing Plan and Timeline Run 11 - five day dedicated run, with longitudinal polarization, β * = 21 m Phase II: Technically driven schedule allows for installation before Run 12: Finish engineering by Summer of 2010; Install DX-D0 vacuum chamber Summer 2011; Finish detectors Fall 2011; Ready for Physics Run

20 Ultra Peripheral Collisions Ultra Peripheral Collisions nuclei miss each other (γγ and γp interactions) Requires b > R A +R B Weizsacker-Williams approach: a field of almost real photons e + e - pair production; MAIN PHYSICS TOPICS Meson spectroscopy: ρ, ω, φ, ρ' state which believed to consist of ρ(1450) and ρ(1700); Transition from soft physics (ρ,ω,φ) to pqcd (J/Ψ, Υ); Fundamental tests of Quantum Mechanics Interference between non overlapping particles. 20

21 Signature and Triggering Signatures: Coherent production dominates Low transverse momentum (p T 2h/RA 60 MeV) Low multiplicity events with vertex Events with nuclear breakup accompanied by forward neutrons Trigger: o o Minimum bias Low multiplicity Neutrons in both ZDCs Topology ToF and TPC: Low multiplicity events Coincidence of North and South Top and Bottom veto cosmics 21

22 The ρ 0 photoproduction cross section Goncalves & Machado (EPJ C29,2003) QCD color dipole approach Nuclear effects and parton saturation phenomena Frankfurt, Strikman & Zhalov (PRC ,2003) Generalized vector dominance (VDM) QCD Gribov-Glauber approach Klein & Nystrand (PR C , 1999) VDM Classical mechanical approach for scattering Klein & Nystrand model agrees well with the data, y <1 does not allow to discriminate based on shape STAR preliminary Red total cross section Blue cross section with mutual excitation. Simulation based on Klein & Nystrand Coherent and incoherent form factors Double exponential fit function σ(incoh)/σ(coh)~ 0.29 ±

23 Photoproduction of π + π π + π arxiv: Expected to be largely through a radially excited Could be ρ(1450) and/or ρ(1700) Studies of the substructure showed low mass pion pairs accompanied by ρ(770) σ coh (π + π π + π - )/σ coh (ρ[770])=13.4 ± 0.8 % no signal for ρ' π + π channel Peak at low p T is due to the coherent production 23

24 UPC Summary Phys. Rev. C 70 (2004) STAR measured e + e - pair production STAR measured ρ 0 photo production cross section: Cross section is in agreement with theoretical models s = 130, 200 GeV Analysis of data at s = 62 GeV is in progress Observed interference effects in ρ 0 production Observed production of π + π π + π final state 24

25 Summary 1. A new rich diffractive physics program with tagged forward protons in polarized proton-proton scattering at RHIC, has been launched and its significant expansion has been proposed. 2. Systematic study of the spin dependence of elastic scattering, of the shape of the differential elastic cross section dσ/dt in unexplored ranges of t and s. 3. It will search for new physics, including glueballs, Odderon and sphalerons. 4. It will search for diffractive production of light and massive systems in double Pomeron exchange process. Possible Pomeron - Odderon interaction => J/ψ production, C odd glueball. RHIC is an exciting, and complementary to other hadron colliders, place to do diffractive physics both in pp and HI New collaborators are welcome! 25

26 BACKUP Jan. 4-8,

27 STAR Experiment MTD EMC Barrel EMC End Cap BBC FMS FHC FPD TPC pp2pp pp2pp PMD trigger computing COMPLET HLT HFT FGT Ongoing R&D

28 Interference In ρ 0 Production ( 2009 ) PRL 102, Impossible to distinguish source of γ and target VM are short lived Decay points are separated in space-time No interference OR The wave function retains amplitudes for all possible decays, long after decay occurs Non-local wave function => Non factorizable Ψπ + π =Ψπ + Ψπ Example of the Einstein-Podolsky-Rosen paradox ρ,ω, φ, J/ψ are J PC = σ ~ A 1(b,y) A 2(b,-y) e ip b 2 where b is impact parameter Suppression at low p T h/<b> Different triggers provide access to different median impact parameter Topology data : median b 46 fm Minimum bias : median b 18 fm (extends interference effects to larger p T ) Fit to the data dn/dt = A exp(-kt)* [1+c(R(t)-1)] Allows to separate nuclear form factor and interference Combined interference c=0.87 ± 0.05 (stat.) ± 0.08 (syst.)% 28

29 Implementation at RHIC - STAR Detector measure recoil system M x EMC Barrel EMC End Cap BBC FMS TPC pp2pp pp2pp 29

30 RHIC Collider Absolute Polarimeter (H jet) RHIC pc Polarimeters Spin Rotators Pol. Proton Source 500 µa, 300 µs PHENIX (p) LINAC BOOSTER L max = 2 10 s = GeV STAR (p) 32 s 1 70% Polarization Partial Siberian Snake Strong AGS Snake cm 2 Siberian Snakes 200 MeV Polarimeter AGS AGS Internal Polarimeter Rf Dipoles AGS pc Polarimeters 30