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The CMS/TOTEM Forward Physics Study. Albert De Roeck (CERN) Physics with Forward Proton Taggers at the Tevatron and LHC. Introduction: CMS/TOTEM Study Physics Detectors. The Large Hadron Collider (LHC). PP collisions at  s = 14 TeV 5 experiments 25 ns bunch spacing

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The CMS/TOTEM Forward Physics Study

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The CMS/TOTEM Forward Physics Study

Albert De Roeck (CERN)

Physics with Forward Proton Taggers at the Tevatron and LHC

Introduction: CMS/TOTEM Study



The Large Hadron Collider (LHC)

  • PP collisions at

  • s = 14 TeV

  • 5 experiments

  • 25 ns bunch spacing

  •  2835 bunches

  • 1011 p/bunch

  • Design Luminosity:

  • 1033cm-2s-1 -1034cm-2s-1

  • 100 fb-1/year

    23 inelastic events

    per bunch crossing

In LEP tunnel

(circonf. 26.7 km)


Planned Startup: April 2007

The CMS experiment

  • Tracking

    • Silicon pixels

    • Silicon strips

  • Calorimeters

    • PbW04 crystals

    • for Electro-magn.

    • Scintillator/steel

    • for hadronic part

  • 4T solenoid

  • Instrumented iron

  • for muon detection

  • Coverage

    • Tracking

    • 0 < || < 3

    • Calorimetry

    • 0 < || < 5

A Hugeenterprise !

Main program: EWSB, Beyond SM physics…



The TOTEM Experiment

TOTEM physics program: total pp, elastic & diffractive cross sections

Apparatus: Inelastic Detectors & Roman Pots (2 stations)



150 m

215 m

High * (1540m): Lumi 1028-1030cm-2s-1(few days or weeks)

>90% of all diffractive protons are seen in the Roman Pots.

Proton momentum measured with a resolution ~10-3

Low *: (0.5m): Lumi 1033-1034cm-2s-1

215m: 0.02 <  < 0.2

300/400m: 0.002 <  < 0.2 (RPs in the cold region)

More on TOTEM & acceptance by R. Orava/K. Osterberg

TOTEM inelastic detectors

T1/T2 inelastic event taggers

T1 CSC/RPC tracker (99 LOI)

 T2 GEM or Silicon tracker (TOTEM/New)

 CASTOR Calorimeter (CMS/New)





T1 3<  <5

T2 5< <6.7

CASTOR 9,71 λI

Forward Physics Program

  • Soft & Hard diffraction

    • Total cross section and elastic scattering

    • Gap survival dynamics, multi-gap events, proton light cone (pp3jets+p)

    • Diffractive structure: Production of jets, W, J/, b, t, hard photons

    • Double Pomeron exchange events as a gluon factory (anomalous W,Z production?)

    • Diffractive Higgs production, (diffractive Radion production?)

    • SUSY & other (low mass) exotics & exclusive processes

  • Low-x Dynamics

    • Parton saturation, BFKL/CCFM dynamics, proton structure, multi-parton scattering…

  • New Forward Physics phenomena

    • New phenomena such as DCCs, incoherent pion emission, Centauro’s

  • Strong interest from cosmic rays community

    • Forward energy and particle flows/minimum bias event structure

  • Two-photon interactions and peripheral collisions

  • Forward physics in pA and AA collisions

  • Use QED processes to determine the luminosity to 1% (ppppee, pppp)

Many of these studies can be done best with L ~1033 (or lower)

Diffraction at LHC:

  • PP scattering at highest energy

  • Soft & Hard Diffraction

     < 0.1  O(1) TeV “Pomeron beams“

    E.g. Structure of the Pomeron F(,Q2)

     down to ~ 10-3 & Q2 ~104 GeV2

    Diffraction dynamics?

    Exclusive final states ?

  • Gap dynamics in pp presently not fully


 = proton



Reconstruct 

with roman


DPE:  from Di-jet events

  • Et> 100 GeV/2 figs

Pt>100 GeV/c for different structure functions

d (pb)


H1 fit 6


H1 fit 5


H1 fit 6

H1 fit 4

(x 100)

=jets ET e-/(s) ; from Roman Pots; ET and  from CMS

High  region probed/ clear differences between different SFs

pp  p + jet + jet + p

Petrov et al.

ET > 100 GeV

ET > 10 GeV

|t| (GeV)

|t| dependence  information on shape & size of the interaction region

Evolution in the presence of a short-time perturbation?

Diffractive Higgs Production

Exclusive diffractive Higgs production pp p H p : 3-10 fb

Inclusive diffractive Higgs production pp  p+X+H+Y+p : 50-200 fb


E.g. V. Khoze et al

M. Boonekamp et al.

B. Cox et al. …







Advantages Exclusive:

 Jz=0 suppression of ggbb background

 Mass measurement via missing mass






~New: Under study by

many groups


roman pots

roman pots

MSSM Higgs

Kaidalov et al.,


100 fb

Cross section factor

~ 10 larger in MSSM

(high tan)



Study correlations

between the outgoing

protons to analyse the

spin-parity structure of

the produced boson

120 140

 See talk of A. Martin

Beyond Standard Model

Diffractive production of new heavy states pp p + M + p

Particularly if produced in gluon gluon (or ) fusion processes


Light CP violating Higgs Boson MH < 70 GeV

B. Cox et al.

Light MSSM Higgs hbb at large tan 

Light H,A (M<150 GeV) in MSSM with

large tan  (~ 30)  S/B > 10

Medium H,A (M=150-200 GeV) medium tan ?

V. Khoze et al. (see AD Martin talk)

Radion production - couples strongly to gluons

Ryutin, Petrov

Exclusive gluino-gluino production?

Only possible if gluino is light (< 200-250 GeV)

V. Khoze et al.

SM Higgs Studies

Needs Roman Pots at new positions 320 and/or 420 m

Technical challenge: “cold” region of the machine, Trigger signals…







Mass of Higgs

Detectors at 300m/400m

Detectors in this region requires changes in the machine

  • Physics Case

    • Can we expect to see a good signal over background?

       Signal understood (cross section)

       Needs good understanding of the background (inclusive!)

       Needs more complete simulations (resolutions, etc.)

  • Trigger

    • 300m/400m signals of RPs arrive too late for the trigger

       Can we trigger with the central detector only for L1?

      Note: L1 2-jet thresholds ET > ~150 GeV

  • Machine

    • Can detectors (RPs or microstations) be integrated with the machine? Technically there is place available at 330 and 420 m

Some Major Concerns:

Of interest for both ATLAS and CMS

Detectors at 300/400m

  • Initial discussions with the machine group (early 2002; see talk of D Marcina in the May CMS/TOTEM meeting)

  • Cold section: Detectors have to be integrated with cryostat

    No bypass option considered.

TOTEM presently not interested to follow

this up further with the machine.

Common CMS+ATLAS effort needed?

Action is needed soon.

Any change now means paperwork!

Low-x at the LHC

LHC: due to the high energy

can reach small values of Bjorken-x

in structure of the proton F(x,Q2)


 Drell-Yan

 Prompt photon production

 Jet production

 W production

If rapidities below 5 and

masses below 10 GeV can be

covered  x down to 10-6-10-7

Possible with T2 upgrade in TOTEM

(calorimeter, tracker) 5<< 6.7 !

Proton structure at low-x !!

Parton saturation effects?

Low-x at the LHC

Rapidity ranges of jets or leptons vs x range












High Energy Cosmic Rays

Cosmic ray


Dynamics of the

high energy

particle spectrum

is crucial

Interpreting cosmic ray data depends

on hadronic simulation programs

Forward region poorly know/constrained

Models differ by factor 2 or more

Need forward particle/energy measurements

e.g. dE/d…

Model Predictions: proton-proton at the LHC

Predictions in the forward region within the CMS/TOTEM acceptance





Two-photon interactions at the LHC


K. Piotrzkowski

WWA spectrum

Reach high

W values!!

Relative luminosity S = L/Lpp:: ~ 0.1% for W> 200 GeV

Must tag protons at small |t| with good resolution: TOTEM Roman Pots!



Two-photon interactions at the LHC

Sensitivity to Large

Extra Dimensions

total  cross section W~1000 GeV?

New studies: p interactions with 10-100x  Luminosity


Number of Higgs events for single tags and assuming integrated lumi-nosity of 30, 0.3 and 0.03 fb-1 for pp, pAr and ArAr collisions, respectively.


K. Piotrzkowski

Significant production rates and very clean signatures available - both transverse and longitudinal missing energy

Exclusive production!

Range up to 200-250 GeV

for single tags

p interactions at the LHC

K Piotrzkowski

  • 0.01 < x < 0.1, g tagging range

  • 0.005 < x < 0.3, Bjorken-x range


  • • anomalous W and Z production at Wgq  1 TeV

  • top pair production - top charge + threshold scanning?

  • single top production and anomalous Wtb vertex

  • SM BEH - for example,g b  H b, g q H W q

  • SUSY studies (complementary to the nominal ones) -

  • H+ t production (and H++), b and t spairs, t~c pair, ...

  • Exotics: compositness, excited quarks, ...

  • pPhysics



Example of a QED process for luminosity monitoring

D. Bocian

pp  pp e+e-

Electrons are

in forward range

5<  < 8

Cross section ~barns

Tracking important!

EM calorimetry essential

Can get the luminosity to 1-2%?

So far > 5% from W,Z production

Status of the Project

  • Common working group to study diffraction and forward physics at full LHC luminosity approved by CMS and TOTEM (spring 2002)

    (ADR/ K. Eggert organizing)

    Use synergy for e.g. simulation, physics studies & forward detector option studies.

    Some of this happened e.g. RP & T2 simulation, detector options

  • Detector options being explored

    • Roman Pot/microstations for beampipe detectors

      at 150, 215 , add 310 & 420 m ? (cold section!)

    • Inelastic detectors

      T1 CSC trackers of TOTEM (not usable at CMS lumi)

      Replace T2 with a compact silicon tracker (~ CMS technology) or GEMs

      Add EM/HAD calorimeter (CASTOR) behind T2

      Add Zero degree calorimeter (ZDC) at 140 m

  • Common DAQ/Trigger for CMS & TOTEM

  • Common simulation etc…

New T2 Tracker Proposal (TOTEM)

Silicon tracker or GEM tracker

Distance from IP:13570 mm

T2 inner radius:25 mm + 8 mm = 33mm 

Vacuum chamber inner radius:25 mm

Outer radius:135mm

 Length:400 mm

CMS TRACKER Silicon Strip detectors :

Single side p+ strips on n-type substrate, thickness=320 mm, AC-coupled, pitch 80~205 mm, Radiation hardness up to 1.6x1014 1MeV equ./cm2, Cold enviroment –20oC.

Or an 8 plan GEM detector?

T2 h range : 5.3 < h < 6.5

Under study by TOTEM…

GEMs usable for CMS pp and HI runs?

A Forward Calorimeter

A calorimeter in the range 5.3 << 6.8 (CASTOR)

Position of T2 and Castor (7/2/03)




Tungsten and quartz fibres

Length 152 cm~ 9I

Electromagnetic section

8 sectors/ needs extension


Installation of T2 tracker/CASTOR

CASTOR shielding




ZDC: zero degree calorimeter



Beam pipe splits 140m from IR



M. Murray

Tungsten/ quartz fibre or

PPAC calorimeter

EM and HAD section

Funding pending in DOE


Opportunities for present/new Collaborators

  • CMS central detector

    • Diffractive Gap Trigger (possible in CMS trigger but needs to be studied)

  • T2 region

    • Calorimeter (CASTOR)

      • Add  granularity (silicon, PPAC,…)

      • Castor trigger

      • So far only one side of CMS equipped (500 kCHF)

    • T2 tracker (part of TOTEM, but still in flux…)

      • May need participation from CMS (if silicon option)

      • May need new tracker by CMS (if GEM option)… watch TOTEM TDR

  • Detectors at 300/400m

    • Completely new project

    • Needs new resources (there are interested parties in CMS & ATLAS)

  • ZDC small project but funding not yet garanteed

  • New detectors in the range 7< <9??? (20 m from IP)

     Certainly help welcome on simulation tools, detailed physics studies…

Rapidity Gaps at LHC

Number of overlap events versus LHC luminosity

distribution of number of interactions






1 int. 22% 4%

Doable at startup lumnosity without Roman Pots!

Gap moves farther from outgoing

proton for smaller xPOM

xPomeron < 0.03

xPomeron < 0.02

xPomeron < 0.0075


Hard Single diffraction

 of minimum- particle per event

 G. Snow

rapidity gap trigger study

Groups that expressed interest (my interpretation)

  • Athens : Proposes to built one CASTOR

  • Annecy : Physics and Roman Pot studies/ Hardware participation in T2

  • Belgium : Interest in Roman Pots Hardware (detectors: RD39)

    Detector layout/radiation hardness/occupancy/trigger/integration

    Gamma-gamma /gamma-p studies/Low-x studies/Fast simulation.

  • CERN : Radiation studies

    Physics studies on diffraction and low-x

  • Nebraska: Trigger with gaps including CASTOR, Luminosity

  • Texas Univ: ZDC Hardware

  • UCLA : DAQ (CMS/TOTEM connection), Physics studies in future

  • North-Eastern: APD’s for CASTOR readout

  • Helsinki: Micro stations hardware R&D and Beamline simulation studies

  • Brazil: Diffractive studies & RPs in cold section

  • Saclay: Roman pots in cold section?

  • Protvino : Background calculations for RPs

  • ITEP: Participation in CASTOR via INTAS project

  • Moskou Physics Studies/ CASTOR hardware

  • Karlsruhe: Cosmic ray interest.

  • Buenos Areas: QCD/diffractive studies/ Hardware interest to be defined



  • A study group has been formed to explore the common use of CMS and TOTEM detectors and study the forward region.

    • Physics Interest

      - Hard (& soft) diffraction, QCD and EWSB (Higgs), New Physics

      - Low-x dynamics and proton structure

      - Two-photon physics: QCD and New Physics

      - Special exotics (centauro’s, DCC’s in the forward region)

      - Cosmic Rays, Luminosity measurement, (pA, AA…)

    • Probably initial run at high * (few days/weeks  0.1-1 pb-1 )

    • Runs at low * (10-100 fb-1 )

  • NEW: CMS officially supports forward physics as a project!

    • Expression of interest for the LHCC

    • Opportunities for present/new collaborators to join

       complete forward detectors for initial LHC lumi

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