The CMS and TOTEM diffractive and forward physics programK. Österberg, High

Energy Physics Division, Department of Physical Sciences, University of Helsinki & Helsinki Institute of

PhysicsLow x meeting, Helsinki 29.8. 1.9.2007

CERN/LHCC 2006039/G124CMS Note2007/002TOTEM Note 065

Diffraction: a window to QCD and proton structure

Double Pomeron Exchange or Central Diffraction:

X

Single Diffraction:

p p p XProton det.

Gap

Central & forward det.

X

p p p X p Proton det.

Proton det.

Gap

Gap

Central & forward det.

characterized by 2 gluon exchange with vacuum quantum numbers (“Pomeron”)

X = anything : dominated by soft physicsMeasurement of inclusive cross sections + their t & MX dependence fundamental measurements of nonperturbative QCD at LHC! X = jets, W, Z, Higgs: hard processes calculable in perturbative QCDProton structure (dPDFs & GPDs), high parton density QCD, rapidity gap survival probability, new physics in exclusive central diffraction

FP420

HF

ZDC

(same as Castor)

Tracking Calorimetry

Roman Pots

Roman Pots

T1: 3.1 < < 4.7

T2: 5.3 < < 6.5

Experimental apparatus at IP5@LHC

CASTOR

10.5 m

14 m

IP5

IP5220 m

147 m

Detect the proton via:its momentum loss (low *) its transverse momentum (high *)

Forward proton measurement: principle

Diffractive protons : hit distribution @ RP220m high L (low *) low L (high *)

10 10 x ~ p/p

y(m

m)

x(mm) x(mm)y(m

m)

y ~ yscatt ~ | ty |

CMS/TOTEM combined acceptanceUnique coverage makes a wide range of physics studies possible from diffraction & proton low-x dynamics to production of SM/MSSM Higgs

Charg

ed p

art

icle

flow

TOTEM CMS TOTEM

En

erg

y fl

ow

Ch

arg

ed

part

icle

flow

Log(

),

=

p/p

Log(t [GeV2])

Acceptance for RP 220 m

* = 1540 * = 90

low *

420 m proton detectors @ low *

Wide coverage in pseudorapidity & proton detection At high L proton detectors @420 m enlarge acceptance to ~ 2 103 For details see B. Cox talk on FP420

pp->pX pp->pjjX pp->pjj (bosons, heavy pp->pXp pp->pjjXp pp->pjjp quarks,Higgs...)

soft diffraction (semi)-hard diffraction hard diffractioncross section luminosity

Accessible physics depends on: luminosity * (i.e. proton acceptance)

mb b nb

* (m)1540 90 2 0.5 L (cm2 s1) 1028 1030 1032 1034

TOTEM runs Standard runs

Running scenario

1p T1/T2

2pT1/T2

1pT1/T2jet(s)

2pT1/T2jet(s)

Estimated Rates (Hz) [acceptance corrected]

L =1030 cm2s1 L =1032 cm2s1

* = 90 m * = 2 m -----------------------------------------------------------------

14 mb 6000 1.4105

1 mb 200 3.5103

1b (pT

jet>20 GeV) 0.2 30nb (pT

jet>50 GeV) 0.01 0.5

60nb (pT

jet>20 GeV) 7103 1.5 nb (pT

jet>50 GeV) 0.03

Triggering on soft & semi-

hard diffraction

Diffraction at low luminosity: soft central diffraction

Differential mass distribution, acceptance corrected

Acc

epta

nce

1

/N

dN

/dM

X [

1/1

0

GeV

]

MX [GeV]

Mass resolution, = 90 m, RP@220 m

low

MX =12s

= ln ()/ ~ 80 % i ET

i ei / s ()/ ~ 100 %

symmetric events

asymmetric events

Study of mass distribution via the 2 protons

measured directly (() ~ 1.6 103 @ = 90 m) or with rapidity gap with calorimeters

Diffraction at high luminosity: central exclusive production

MX [GeV]

(M

X)/

MX

MX [GeV]

New physics searches e.g. (pp p H(120 GeV)[bb] p) ~ 3 fb (KMR)

Acc

ep

tan

ce

JPC selection (0++...) qq background heavily suppressed Selection: 2 protons + 2 b-jets with consistent mass values Experimental issues: trigger efficiency & pileup background

in some MSSM scenarios much larger, H WW if H heavier

NB! Assu

mes proton detectors @

420 m

Diffraction at high luminosity: triggering on diffraction

dedicated diffractive trigger stream foreseen at L1 & HLT (1 kHz & 1 Hz)

standard trigger thresholds too high for diffraction at nominal optics use information from fwd detectors to lower particular trigger thresholds

L1 trigger threshold [GeV]

Effi

ciency

420m

220m

420+420m

420+220m

L1:● jet ET > 40 GeV ( standard 2jet threshold: ~100 GeV @ L = 2 1033 cm2s1)● 1 (or 2) arm RP@220 m● diffractive topology (fwd rap gaps, jetproton hemisphere correlation …)

HLT (more process dependent):e.g. 420 m proton detectors, mass constraint, b-tagging..

bench mark process: central exclusive H(120 GeV) bbL1: ~ 12 %HLT: ~ 7 %additional ~ 10 % efficiency @ L1 with a 1 jet + 1 (40 GeV, 3 GeV) trigger

Diffraction at high luminosity: reducing pileup background

At high luminosity, non-diffractive events overlaid by soft diffractive events mimic hard diffractive events (“pileup background”)

Pileup event probability with single proton in RP@220m (420m) ~ 6 % (2 %) probability for fake central diffractive signal caused by pileup protons

Pileup background reduction:● correlation & mass measured with central detector & proton detectors ● fast timing detectors to distinguish proton origin & hard scattering vertex from each other (R&D project)

pileup background depends on LHC diffractive proton spectrum rapidity gap survival probability

Lowx physicshigh s @ LHC allows access to quark & gluon densities for small Bjorkenx values: fwd Drell-Yan (jets) sensitive to quarks (gluons)

> 5 & M < 10 GeV x ~ 106107

T2 + CASTOR !!

x of Drell Yan pairs in CASTOR

M2 of Drell Yan pairs in CASTOR

Forward particle & energy flow: validation of hadronicair shower models, possible new phenomena… Study of underlying event & p mediated processes: e.g. exclusive dilepton production

Forward physics

() (true)

rms ~ 10-4

Calibration process for luminosity and energy scale of proton detectors

Allows proton value reconstruction with a 104 resolution < beam energy spreadStriking signature: acoplanarity angle between leptons

known

CMS 2008 diffractive & forward program

First analysis in 2008 most likely based on large rapidity gap selection Even if RP@220 m available need time to understand the data …

Concentrate first analysis on data samples where pileup negligible

Developing rapidity gap trigger with forward calorimeters (HF, CASTOR…)

Program:

“Rediscover” hard diffraction a la Tevatron, for example:● measure fraction of W, Z, dijet and heavy flavour production with large rapidity gap● observe jet-gap-jet and multi-gap topologies

Forward physics with CASTOR● measure forward energy flow, multiplicity, jets & Drell-Yan electrons

& p interactions, for example● observe exclusive di-lepton production

2 RP220 m stations installed into LHC in May-June, remaining by end of summer

First edgeless Si detectors mounted with final VFAT hybrid successfully working with source & in test beam all detector assemblies ready for mounting by April 2008.

Si edgeless detector VFAT hybrid with detector

TOTEM Detectors: Roman Pots

T1 Telescope

Mechanical frames and CSC detectors in production; tests in progress. During 2007 complete CSC production. Plan to have two half-telescopes ready for mounting in April 2008.

T2 Telescope

All necessary GEM’s produced (> half tested upto gains of 80000). Energy resolution 20-30 %. The 4 half-telescopes should be ready for mounting in April 2008.

testbeam setup

TOTEM detectors: T1 & T2

Parameters = 2 m(standard step in LHC start-up)

= 90 m(early TOTEM optics)

= 1540 m(final TOTEM optics)

Crossing angle 0.0 0.0 0.0

N of bunches 156 156 43

N of part./bunch (4 – 9) 1010 (4 – 9) 1010 3 1010

Emittance [m ∙ rad] 3.75 3.75 1

10 vertical beam width at RP220 [mm]

~ 3 6.25 1.3

Luminosity [cm-2 s-1] (2 – 11) 1031 (5 – 25) 1029 1.6 1028

* = 90 m ideal for early running:• fits well into the LHC start-up running scenario;• uses standard injection easier to commission than 1540 m optics• wide beam ideal for RP operation training (less sensitive to alignment)

* = 90 m optics proposal submitted to LHCC & well received.

Optics & beam parameters

(x*,y*):vertex position(x

*,y*):emission angle

= p/p

Optics optimized for elastic & diffractive scatteringProton coordinates w.r.t. beam in the RP at 220 m:

* *y y yy L v y

Ly = 265 m (large) vy = 0

* *x x xx L v x D

Lx = 0 vx = – 2

vertical parallel-to-point focusing optimum sensitivity to y

*

i.e. to t (azimuthal symmetry)

D = 23 mm

elimination of x* dependence

enhanced sensitivity to x in diffractive events, horizontal vertex measurement in elastic events

x distribution @ RP220 m x distribution @ RP220 m for elastic

events measurement of horizontal vertex distribution @ IP

Luminosity estimate together with beam parameters if horizontal-vertical beam symmetry assumed

Beam position measurement to ~1 m every minute

= 90 m optics

For early runs: optics with * = 90 m requested from LHCC• Optics commissioning fits well into LHC startup planning• Typical running time: several periods of a few days• Total pp cross section within ± 5% • Luminosity within ± 7%• Soft diffraction with independent proton acceptance (~ 65%)

TOTEM 2008 physics program

proton resolution limited by LHC energy spread

via rapidity gap (T1, T2)

via rapidity gap (CMS)

via rapidity gap (T1, T2)

=

10

0%

via

prot

on (* =

90m

)

SummaryCMS and TOTEM diffractive and forward physics program

CMS+TOTEM provides unique pseudo-rapidity coverageCMS+TOTEM provides unique pseudo-rapidity coverageIntegral part of normal data taking both at nominal & special opticsIntegral part of normal data taking both at nominal & special optics

Low Luminosity (< 10Low Luminosity (< 103232 cm cm-2-2ss-1-1): ): nominal & special opticsnominal & special optics Single & central diffractive cross sections

(inclusive & with jets, rapidity gap studies) Lowx physics Forward Drell-Yan & forward inclusive jets Validation of Hadronic Air Shower Models

Increasing Luminosity (> 10Increasing Luminosity (> 103232 cm cm-2-2ss-1-1): ): nominal opticsnominal optics Single & central diffraction with hard scale

(dijets, W, Z, heavy quarks) dPDF’s, GPD’s, rapidity gap survival probability & p physics

High Luminosity (> 10High Luminosity (> 103333 cm cm-2-2ss-1-1) : nominal optics) : nominal optics Characterise Higgs/new physics in central diffraction?

Running with TOTEM optics: Running with TOTEM optics: large proton acceptancelarge proton acceptance

No pileupNo pileup

Pileup not negligible:Pileup not negligible:important background important background sourcesource

Need additional Need additional proton detectors proton detectors

Ch 1: Introduction

Ch 2: Experimental Set-up

Ch 3: Measurement of Forward Protons

Ch 4: Machine induced background

Ch 5: Diffraction at low and medium luminosity

Ch 6: Triggering on Diffractive Processes

at High Luminosity

Ch 7: Hard diffraction at High Luminosity

Ch 8: Photon-photon and photon-proton physics

Ch 9: Low-x QCD physics

Ch 10: Validation of Hadronic Shower Models used in cosmic ray physics

Includes important experimental issues in measuring forward and diffractive physics but not an exhaustive

physics study

Detailed studies of acceptance & resolutionof forward proton detectors

Trigger

Background

Reconstruction of kinematical variables Several processes studied in detail

An important milestone for collaboration between the 2 experiments

Content of common physics document

1.15 (0.6 - 1.15) 1.150.3 N of part. per bunch

(x 1011)

2 x 1030

2.3

200

3.75

0

156

90

Soft &

semi-hard diffraction

2.4 x 1029

0.29 - 0.57

454 - 880

1 - 3.75

0

156

1540

Soft diffraction

3.6 x 10321.6 (7.3) x 1028Peak luminosity

[cm-2 s-1]

5.280.29 (2.3)RMS beam diverg.

[rad]

95454 (200)RMS beam size at IP [m]

3.751 (3.75)Transv. norm. emitt. [m rad]

1600Half crossing angle

[rad]

280843N of bunches

18, 2, 0.51540 (90)

large |t| elasticlow |t| elastic,

tot ,

min bias

Physics:

*[m]

Running scenarios

Diffraction at low luminosity: rapidity gaps

Measure via rapidity gap: = ln

Achieved resolution: ()/ 80 %

diffractive system Xp2 p1

min max

Gap measurement limit due to acceptance of T2

Gap vs ln () T1+T2+Calorimeters

ln = 2103 2102

* = 90 * = 2 same acceptance / limit

Gap

Diffraction at medium luminosity: semi-hard diffractionass

um

ed

cro

ss s

ect

ion

s

pTjet(GeV)

SD:pp->pjjX

CD:pp->pjjXp

Measure cross sections & their t, MX, pT

jet dependence

Event topology: exclusive vs inclusive jet production

access to dPDF’s and rapidity gap survival probability

N event collected [acceptance included]

* = 90 m ∫L dt = 0.3 pb1

SD: pT>20 GeV 6x104 CD: “ 2000

* = 2 m ∫L dt = 100 pb1 SD: pT>50 GeV 5x105 CD: “ 3x104

d/dpT

(b)

In case of jet activity also determined from calorimeter info:

i ETi ei / s

()/ 40 %

Forward proton measurement: acceptance (@220 m & 420 m)

RP 220m

FP420

* = 1540

* = 2/0.5

* = 90

Log

(),

=

p

/p

Log(t)

*= 0.5 2 m

420 m

220 m

Proton detectors at 420 m would enlarge acceptance range down to = 0.002 at high luminosity (= low *).

Forward proton measurement: momentum resolution (* = 90 m)

Individual contribution to the resolution: Transverse vertex resolution (30 m)

Beam position resolution (50 m)

Detector resolution (10m)

p/p

() total 220 m

Final state dependent; 30 m for light quark & gluon jets

Forward proton measurement: momentum resolution (* = 2/0.5 m)

Individual contribution to the resolution:

Detector resolution (10m)

Beam position resolution (50 m)

Transverse vertex resolution (10 m)

Relative beam energy spread (1.1104)

total

p/p

()

/

* = 90 m vs. * = 2/0.5 m

Better ()/ for * = 2/0.5 m & larger luminosity but limited acceptance ( > 0.02)

Very little final state dependence since transverse IP size is small.

Interpreting cosmic ray data depends on cosmic shower simulation programs Forward hadronic scattering poorly known/constrained Models differ up to a factor 2 or more

Need forward particle/energy measurements at high center-of-mass energy (LHC Elab=1017 eV)

Achievable at low luminosity using T1/T2/HF/Castor

Cosmic ray connection

Inclusive forward “low-ET” jet

(ET ~20-100 GeV) production:

Sensitive to gluons with: x2 ~ 10-4, x1 ~ 10-1

p + p → jet1 + jet2 + X

Large expected yields (~107 at ~20 GeV) !

PYTHIA ~ NLO

1 pb-1

Low-x physics: forward jets

• Diffractive PDFs: probability to find a parton of given x under condition that proton stays intact – sensitive to low-x partons in proton, complementary to standard PDFs

GPD

GPDjet

jet

jet

jet

hard scattering

IP dPDF

• Generalised Parton Distributions (GPD) quantify correlations between parton momenta in the proton

t-dependence sensitive to parton distribution in transverse plane

When x’=x, GPDs are proportional to the square of the usual PDFs

Diffractive PDF’s and GPD’s