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CMS forward detectors and their physics potential

This workshop presentation discusses the physics potential of forward detectors in CMS, including forward calorimeters, tracking detectors, and proton taggers. It covers topics such as low x QCD, diffraction, γγ collisions, and elastic/diffractive protons.

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CMS forward detectors and their physics potential

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  1. CMS forward detectors and their physics potential Monika Grothe U Wisconsin Workshop on high-energy photon collisions at the LHC April 2008 • Physics with forward calorimeters and tracking detectors • Physics with !(forward detectors) • Physics with forward proton taggers Monika Grothe, Woekshop on high energy photon processes, CERN, April 2008

  2. q p p What is “Forward” Physics? Energy flow at the LHC Experimental definition: All processes in which particles are produced at small polar angles (i.e. large rapidities). Maximal rapidity at the LHC given by: →Interesting physics where forward rapidities play an essential role ? Low x QCD − Diffraction −γγ-collisions elastic/diffractive protons • most energy is deposited between: 8 < |y| < 9 • main ATLAS/CMS calorimeters: |η| < 5 Monika Grothe, Woekshop on high energy photon processes, CERN, April 2008

  3. Forward instrumentation around CMS IP CMS central detector Hadronic Forward (HF) CASTOR IP 5 T1 T2 Zero Degree Calorimeter (ZDC) RP 147 RP 220 FP 420 IP 5 TOTEM: green CMS: blue Monika Grothe, Woekshop on high energy photon processes, CERN, April 2008

  4. Physics with forward calorimetersand tracking detectors Monika Grothe, Woekshop on high energy photon processes, CERN, April 2008

  5. The CMS CASTOR calorimeter • extends the coverage to 5.2 < η < 6.6 → enhances the hermiticity of CMS! • 14.37 m from the interaction point • octogonal cylinder with inner radius 3.7cm, outer radius 14cm and total depth 10.5 λI • signal collection through Čerenkov photons transmitted to PMTs through aircore lightguides • W absorber & quartz plates sandwich, with 45° inclination with respect to the beam axis • electromagnetic and hadronic sections • 16 seg. in φ, 14 seg in zno segmentation in η Currently funding available only for CASTOR on one side of IP If LHC allows, installation of 1/2 CASTOR on one side of IP 07/2008 Monika Grothe, Woekshop on high energy photon processes, CERN, April 2008

  6. The CMS Zero Degree Calorimeter • 140 m from interaction point in TAN absorber • Thungsten/quartz Čerenkov calorimeter with separate e.m. (19 X0) and had.(5.6 λI) sections • em: 5-fold horizontal seg had: 4-fold seg in z • Acceptance for neutrals (γ, π0, n) from η > 8.1 (100% for η > 8.4) • Ready for 2008 run Monika Grothe, Woekshop on high energy photon processes, CERN, April 2008

  7. 3m Test Beam TOTEM T1 & T2 tracking detectors • Gas Electron Multiplier (GEM) • Mounted in front of CASTOR • 5.3 < | < 6.5 • 10 planes formed by 20 GEM semi-circular modules • Radial position from strips, h, from pads • Resolution strip~70mm • Cathode Strip Chambers (CSC) • Mounted in front of HadronForward calorimeter of CMS • 3.1 < | < 4.7 • 5 planes with 3 coordinates/plane • 6 trapezoidal CSC detectors/plane • Resolution  ~ 0.8mm Monika Grothe, Woekshop on high energy photon processes, CERN, April 2008

  8. p CMS rapidity CASTOR p Proton-proton collisions at low x • Partons from each proton “decelerate” and meet to produce the hard scattering subsystem (ME) • Low x↔ long parton showers • Forward particles can be produced in 2 ways: • Collision between a low- and a high- x parton →hard interaction system goes forward • Collision between two low-x partons →fwd jets from QCD evolution → at LHC (for Q≳10 GeV and η = 6): xBjorken≳ 10-6→ xBjorken decreases by factor ~ 10 for each 2 units in rapidity Monika Grothe, Woekshop on high energy photon processes, CERN, April 2008

  9. PYTHIA DY • PYTHIA DY, η3 or η4∈ CASTOR • PYTHIA DY, η3 and η4∈ CASTOR qq→ γ* → e+e− CASTOR acceptance window Proton pdf at low-x from Drell-Yan Forward lepton pairs EHKQS: “saturated” pdf with nonlinear terms in gluon evolution Kinematic coverage of CMS Castor calorimeter reaches down to <10-6 x1 >> x2 5.2 < ηe+,ηe− < 6.6 CTEQ5L →Cross section reduced by factor 2! EHKQS First time observation of saturation in pp possible ! Monika Grothe, Woekshop on high energy photon processes, CERN, April 2008

  10. PYTHIA jets (MSEL=1)central dijet with pT > 60 GeV, |η| < 3 BFKL: large yield of high E forward jets ARIADNE (CDM) PYTHIA (DGLAP) jets “Jet energy” in CASTOR Forward jets from QCD evolution • x2≃x1 → X can be (di-)jets in central • CMS detector • In BFKL-like QCD-evolution forward jets can have large pT • Also possible: jet-gap-jet events Mueller-Navelet jets Sensitivity to BFKL dynamics Monika Grothe, Woekshop on high energy photon processes, CERN, April 2008

  11. Multiplicity and E flow measurements Titel Can differentiate between certain MC tunes to describe underlying event with CASTOR/T2 Can differentiate between MC models for cosmic rays with CASTOR/T2/ZDC Monika Grothe, Woekshop on high energy photon processes, CERN, April 2008

  12. Physics with !(forward detectors) Monika Grothe, Woekshop on high energy photon processes, CERN, April 2008

  13. S2 … dPDF Diffraction with a hard scale: W prod • pp → p W X, W →sensitive to quark component of dPDFs • Rap gap based selection, i.e. no pile-up • Require absence of activity in the forward calorimeters (HF 3< || < 5, Castor 5.2 < || < 6.6 ) of CMS • For rap gap survival factor of S2 = 5%, arrive at O(100) evts/100pb-1 in the [n(Castor), n (HF)] = [0,0] bin • S/B  20 with Castor veto • Signal enhancement by ~30% due to diffractive dissociation 100pb-1 Other hard diffraction processes possible: Dijets, heavy quarks Monika Grothe, Woekshop on high energy photon processes, CERN, April 2008

  14.  physics: Exclusive dilepton production  talk by J. Hollar Nearly pure QED process • luminosity monitoring with precision of 4% is feasible • Selection via exclusivity condition in central detector + veto on CASTOR & ZDC activity • Calibration/alignment of proton taggers • rejection of 2/3 of p dissociative background with CMS fwd calorimeters pp → pp l+l− ~700  events in 100 pb-1 with dominant background from p dissociative events (~200) Monika Grothe, Woekshop on high energy photon processes, CERN, April 2008

  15. Vectormeson photoproduction  talk by J. Hollar pp→ ppϒ, ϒ→  Possibility to measure pT2 slope: Monika Grothe, Woekshop on high energy photon processes, CERN, April 2008

  16. Physics with near-beam proton taggers Monika Grothe, Woekshop on high energy photon processes, CERN, April 2008

  17. CMS + TOTEM (+ FP420) CMS IP T1/T2, Castor ZDC RPs@150m RPs@220m possibly detectors@420m • TOTEM: • An approved experiment at LHC for measuringtot& elastic, at same IP as CMS • TOTEM aims at start-up on the same timescale as CMS • Expression of wish of CMS + TOTEM to carry out a joint physics program, with joint CMS+TOTEM data taking given to LHCC: “Prospects for diffraction and forward physics at the LHC” CERN LHCC 2006-039 G124, CMS note 2007-02, TOTEM note 06-5 • Possible addition FP420: • Proposal to install high precision silicon tracking and fast timing detectors close to the beams at 420m from the CMS IP • Proposal currently under scrutiny in CMS • If approved, could be installed in 2010 after LHC start-up Monika Grothe, Woekshop on high energy photon processes, CERN, April 2008

  18. Beampipes Proton taggers @ 220m and 420m from IP TOTEM uses Roman pot technique to approach the beam with their Si detectors FP420, because of location in cryogenic region of LHC, uses movable beampipe Extremly rad hard novel Si technology: 3-d Silicon Cherenkov timing detectors with t ~ 10 ps to filter out events with protons from pile-up Monika Grothe, Woekshop on high energy photon processes, CERN, April 2008

  19. CMS + TOTEM (+ FP420): Coverage in  At nominal LHC optics,*=0.5m diffractive peak TOTEM Points are ZEUS data FP420 xL=P’/Pbeam= 1-x Note: Totem RP’s optimized for special optics runs at high* β* is measure for transverse beam size at vertex TOTEM coverage in improves with increasing * Monika Grothe, Woekshop on high energy photon processes, CERN, April 2008

  20. shields color charge of other two gluons Vacuum quantum numbers “Double Pomeron exchange” Physics potential of forward proton tagging Central exclusive production pp pXp: Discovery channel for MSSM Higgs Selection rules: central system is JPC = 0++ (to good approx) Excellent mass resolution (~GeV) from the protons, independent of decay products of the central system For light (~120 GeV) Higgs: Proton tagging improves S/B for SM Higgs dramatically CEP may be the discovery channel in certain regions in MSSM CP quantum numbers and CP violation in Higgs sector directly measurable from azimuthal asymmetry of the protons In addition: Rich QCD program Looking at the proton in QCD through a lens that filters out everything but the vacuum quantum numbers: measure diff PDFs, learn about parton correlations via GPDs, quantify soft multiple scattering effects via diff factorization breaking, ... In addition: Rich program of gamma-gamma mediated processes p in  processes have lower  values than diffractively scattered ones, hence FP420 indispensable Monika Grothe, Woekshop on high energy photon processes, CERN, April 2008

  21. H b, W, τ b, W, τ Discovery potential of CEP of Higgs CEP may be the discovery channel for MSSM Higgs: Heavy Higgs states decouple from gauge bosons, hence preferred search channels at LHC not available But large enhancement of couplings to bb,  at high tan Detailed mapping of discovery potential for pp→p + H,h + p CEP Higgs may also open door to discovery of an NMSSM Higgsin channel h  aa  4 which would be unique at the LHC Monika Grothe, Woekshop on high energy photon processes, CERN, April 2008

  22. Summa Summarum Monika Grothe, Woekshop on high energy photon processes, CERN, April 2008

  23. Map to forward physics in CMS Titel Gamma-gamma and gamma-proton interactions Forward energy flow - input to cosmics shower simulation QCD: Diffraction in presence of hard scale Low-x structure of the proton High-density regime (Color glass condensate) Diffractive PDFs and generalized PDFs Diffractive Drell-Yan Diffraction at low lumi Rapidity gap selection possible HF, Castor, ZDC, T1, T2 Proton tag selection optional Proton taggers at 220m & 420 m Diffraction is about 1/4 of tot High cross section processes “Soft” diffraction Interesting for start-up running Important for understanding pile-up Diffraction at high lumi No Rapidity gap selection possible Proton tag selection indispensable Proton taggers at 220m & 420 m Central exclusive production Discovery physics: MSSM Higgs NMSSM Higgs Low lumi High lumi Current CMS detector Current CMS + proton taggers Monika Grothe, Woekshop on high energy photon processes, CERN, April 2008

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