Forward and low x physics program with CMS at the LHC Pierre Van Mechelen on behalf of the CMS Collaboration

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, Outline This talk: Forward instrumentation around IP5 With emphasis on the status of the very forward calorimeters at CMS The interest of forward physics In particular: what can forward physics do for the study of low x QCD, UE & MI, diffraction,... Other related CMS talks at this workshop: Exclusive dilepton and Upsilon production with CMS (Severine Ovyn) Single diffractive W production with CMS (Antonio Vilela Pereira)

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, What is “Forward” Physics? Experimental definition: All processes in which particles are produced at small polar angles (i.e. large rapidities). Maximal rapidity at the LHC given by: → How to get interesting physics at forward rapidities? Low x QCD − Diffraction − γγ-collisions elastic/diffractive protons most energy is deposited between: 8 < |y| < 9 main ATLAS/CMS calorimeters: |η | < 5 Energy flow at the LHC p p q

Forward instrumentation around IP5

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, Forward instrumentation around IP5 CASTOR Zero Degree Calorimeter (ZDC) CMS central detector Hadronic Forward (HF) FP 420 RP 147 RP 220 T1 T2 IP 5 CMS: blue TOTEM: green

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, The CASTOR calorimeter extends the coverage in forward direction to 5.2 < η < 6.6 → enhances the hermiticity of CMS! m from the interaction point octogonal cylinder with inner radius 3.7cm, outer radius 14cm and total depth 10.5 λ I 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-fold segmentation in φ 14-fold segmentation in z no segmentation in η

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, CASTOR specifications hadronic section  absorber: tungsten plates of 10mm thickness  active material: fused silica plates of 4mm thickness  5 tungsten-quartz sandwiches form 1 reading unit  total interaction length (2+12 r.u.) 10.3 λ I electromagnetic section  absorber: tungsten plates of 5mm thickness  active material: fused silica plates of 2mm thickness  5 tungsten-quartz sandwiches form 1 reading unit  total radiation length (2 reading units) =20.12 X 0

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, CASTOR test beam results 2007 Test Beam: linearity and resolution electrons pions → final analysis forthcoming

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, CASTOR schedule Test Beam June 2008 If LHC allows, installation of ½ calorimeter in beam line: July 2008

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, Zero Degree Calorimeter 140m from interaction point Thungsten/quartz Čerenkov calorimeter with separate e.m. (19 X 0 ) and had.(5.6 λ I ) sections em: 5-fold horizontal segmentation had: 4-fold segmentation in z Acceptance for neutral particles (γ, π 0, n) from η > 8.1 (100% from η > 8.4) Ready for 2008 run Physics programme: evaluation of rapidity gaps Forward energy flow Luminosity calibration Heavy ion and cosmic ray physics

The interest of “Forward Physics”

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, 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 → forward jets from QCD evolution p p rapidity CASTO R CMS

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, Forward hard scattering X can be jets, Drell-Yan pairs, prompt photons, heavy quark pairs,... X goes forward if x 2 ≪ x 1 → access to low- x Bjorken proton structure: → at LHC (for Q ≳ 10 GeV and η = 6): x Bjorken ≳ → x Bjorken decreases approx. by factor 10 for each 2 units in rapidity x1x1 x2x2 X pp

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, qq → γ* → e + e − Proton pdf at low x Forward lepton pairs Shadowing in CASTOR: EHKQS: “saturated” pdf with nonlinear terms in gluon evolution [A. Dainese et al., HERA- LHC Workshop proc.] CASTOR acceptance window PYTHIA DY PYTHIA DY, η 3 or η 4 ∈ CASTOR PYTHIA DY, η 3 and η 4 ∈ CASTOR → no Z 0 from ME in CASTOR (but γ*, J/Ψ,,...) → x-range: CTEQ5L EHKQS 5.2 < η e+,η e− < 6.6 → Cross section reduced by factor 2!

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, jets Forward jets from QCD evolution PYTHIA jets (MSEL=1) central dijet with p T > 60 GeV, |η| < 3 x1x1 p X x2x2 p jet PYTHIA (DGLAP) ARIADNE (CDM) x 2 ≃ x 1 → X can be (di-)jets in central HCAL of HF In BFKL-like QCD-evolution forward jets can have large p T Can also do jet-gap-jet or Mueller-Navelet jets “Jet energy” in CASTOR BFKL: large yield of high E forward jets

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, Multiple interactions Basic partonic cross section → diverges faster than as → eventually exceeds σ tot (even for p ⊥ min > Λ QCD ). Consequence: Multiple parton interactions per event → higher particle multiplicity (additional energy offset in jet profiles) → long distance correlations in rapidity (need to cover forward region!) → additional hard interactions may fake a discovery signal ! (e.g. pp → W H X with H → bb vs. pp → W bb X) pp [T. Sjöstrand, P.Z. Skands hep-ph/ ]

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, Central-forward correlations → forward condition uncovers long range correlations → discriminative power for different M.I. tunes (here: Field and Sandhoff-Skands tunes) [H. Jung] central forward no correlation long rang correlations trigger particle Long-range correlations in multiple interactions models

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, Diffraction One or both protons survive hard interaction (yielding jets, heavy quarks,...) → diffraction (including soft diffraction) makes up 25% of σ tot ! → tool to study (pertubative) QCD and the structure of hadrons → measure diffractive jet, W, Z, heavy quark production and rapidity gap survival Diffractive Higgs production pp -> p H p → particularly clean channel for the study (or discovery) of the Higgs boson → see talks by B. Cox and others... p p p' q q p p H

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, Single diffractive W production Motivation: Sensitive to quark component of diffractive PDF’s Probe Rapidity Gap Survival Probability (S 2 ) – connection to multiple partonic interactions and soft rescattering effects Rapidity gap selection: Based on forward activity (HF, CASTOR) Large Rapidity Gap dPDF … S2S2 Much better rejection of non-diffractive background with CASTOR (S/B -> 20) ZDC reduces diffractive dissociation background by 50% → see talk by A. V. Pereira pp → p W X

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, Exclusive dilepton production pp → pp l + l − Motivations: Nearly pure QED process → luminosity monitoring (precision of 4% is feasible) Study of lepton identification Calibration of forward proton detectors → See talk by S. Ovyn Inelastic background → can be reduced using CASTOR/ZDC

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, ϒ photoproduction pp → pp ϒ, ϒ → l + l − Motivations: Measure gluon distribution in proton at low x Constrain diffractive/QCD models Alignment of forward proton detectors → See talk by S. Ovyn Extraction of slope parameter b from t spectrum

Conclusion

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, Rapidity coverage at CMS CASTORCASTORCASTORCASTOR ZDCZDC CMS = HCAL+HF+CASTOR+ZDC = largest calorimetric η coverage ever! HCAL HFHFHFHF HFHFHFHF

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, Forward physics programme PYTHIA (DGLAP) ARIADNE (CDM) BFKL Saturation UE & MI Exclusive dilepton and Upsilon production p p p' H Diffractive and VBF Higgs Diffractive W production CTEQ5L EHKQS 5.2 < η e+,η e− < 6.6

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, Backup

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, γ (*) γ (*) collisions pp → p γ (*) γ (*) p → p X p → Similar to diffraction, but smaller |t| → X = e + e −, m + m −, γγ, W + W −, Z 0 Z 0, H, t t, SUSY-pairs,... Physics programme: → absolute luminosity calibration (using very well known QED cross sections) → calibration and resolution measurement of forward proton spectrometers → factorisation breaking in hard diffraction p p p' q q → see talk by S. Ovyn

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, AGK cutting rules Relation between diffraction – multiple interactions – low x saturation: Optical theorem: single parton exchange: double parton exchange: diffraction saturation multiple interaction

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, TOTEM-T2 GEM tracking detectors (Ar/CO 2 ) with 10 aligned detector planes 512 strips (width 80 μm, pitch of 400 μm); 65 x 24=1560 pads Acceptance: 5.2 < |η| < 6.5 Resolution: Δφ x Δη = 0.06 x 0.017π Installation 2007?

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, FP420 Cryostat adaptation using movable beampipe Will operate with standard high luminosity optics. Acceptance: < ξ < 0.02 → exclusive central system in mass range 30 < M < 200 GeV 3DSi detectors yielding Δp/p ≈ → δM ≈ 1 GeV Cerenkov timing detector yielding 10 ps resolution → to sort out pile-up Installation (if approved) foreseen during 2008/2009 shutdown

Pierre Van Mechelen - Forward Physics at CMS - DIS Workshop - London - April 9, Jet profiles in CASTOR p T > 0 GeV p T > 10 GeV p T > 20 GeV p T > 0 GeV p T > 10 GeV p T > 20 GeV Hadron level “Detector” level → even low p T jets stand out in CASTOR