The CMS and TOTEM diffractive and forward physics program K. Österberg, High Energy Physics...

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