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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

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
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
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



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
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
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
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
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
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
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
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
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 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
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
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 lhc1
Low-x at the LHC

Rapidity ranges of jets or leptons vs x range












High energy cosmic rays
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
Model Predictions: proton-proton at the LHC

Predictions in the forward region within the CMS/TOTEM acceptance

Two photon interactions at the lhc





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 lhc1



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
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
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 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
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
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
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
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