High energy interactions at the...

High energy interactions at the LHCLHC

Krzysztof PIOTRZKOWSKI

Université Catholique de Louvain(CP3 Center)

WE-HERAEUS Summer schoolHeidelberg

September 5-11, 2011

Outline

Part I: Introduction & motivationPart I: Introduction & motivation

Part II: First measurements at the LHCPart II: First measurements at the LHC

Part III: New forward detectors at the LHCPart III: New forward detectors at the LHCsee Friday’s talk by M. Tasevsky

Heidelberg, 6/9/2011 K. Piotrzkowski 2

Outline

Part I: Introduction & motivation (Past)Part I: Introduction & motivation (Past)

Part II: First measurements at the LHC (Present)Part II: First measurements at the LHC (Present)

Part III: New forward detectors at the LHC (Future)Part III: New forward detectors at the LHC (Future)see Friday’s talk by M. Tasevsky


LHC as a High Energy ColliderPhys. Rev. D63 (2001) 071502(R)

pp

Phys. Rev. D63 (2001) 071502(R)hep-ex/0201027

Initial observation:Provided efficient measurement of very forward-scattered protons one can study high-energy collisions at the LHC

Highlights:• CM energy W up to/beyond 1 TeV (and under control)

L h t fl F th f i ifi t l i it• Large photon flux F therefore significant luminosity• Complementary (and clean) physics to pp interactions, eg studies of exclusive production of heavy particles might be possible opens new field high energy (and p) physicspossible opens new field high energy (and p) physics

4K. PiotrzkowskiHeidelberg, 6/9/2011

LHC as a High Energy Collider

pp

T h l i d iTwo photon exclusive production:• Very forward proton scattering large distance interactions• Possibility of detecting whole final state precise kinematics reconstruction; very much like in e+ereconstruction; very much like in e+e

Very different event topologies from typical events at the LHC must exploit that!must exploit that!

5K. PiotrzkowskiHeidelberg, 6/9/2011

DISCLAIMER:

This is NOT meant for studying all photon interactionsy g pat the LHC but those for which the QCD (diffraction!) background can be strongly suppressed, as for example in the exclusive production of pairs of charged non-strongly interacting particles.

This IS meant for studying production of selected final states in photon interactions at the LHC.

Note: At Tevatron available energy too small for EW physics (but enough for lepton pairs – CDF published several measurements of exclusive two‐photon production of these)

First inspiration:


How to measure these events?

Measure ( ) X in the CMS or ATLAS detector andscattered protons using p

HPS

scattered protons using very forward detectors(thanks to proton energy loss)

pp

p beam

scattered p Very forward detectors needed – capable of running at high luminosity, installed as p beam g g yfar (> 100 m) from IP and as close to the beam (2 mm) as possible – expected photon energy resolution of VFDs can be


GeV !

LHC as a colliderE i l t h t i ti (EPA)Equivalent photon approximation (EPA)

…introduced to major event generators as Madgraph, Pythia, Sherpa, Calchepg p , y , p , p


EPA: Kinematics/ LuminosityVirtuality Q2 of colliding photons vary between kinematical minimum = Mp

2x2/(1-x) where x is fraction of proton momentum carried by a photon,and Q2

max ~ 1/proton radius2W2 = s x1 x2

(where W MX)

for x>0.0007, Q2<2GeV2

( X)Photon flux 1/Q2

Q2 Q2min s2/4 Phys. Rev. D63 (2001) 071502(R

protons scattered at `zero-degree’ angle s = 14 TeV

S(W) = f(x1) f(x2)

pp= S dW


dWS=‘pp luminosity’Note: it’s few times larger if one of protons is allowed to break up

Use EPA à la Budnev et al.** error found in the elastic (Q2 integrated) flux for protons!

Tagging two-photon eventsAssume detector stations at ~220 m where approximately x 0 01 range accessibleAssume detector stations at ~220 m where approximately x 0.01 range accessible

Note: If only one forward p detected – single tag, but then non-elastic, p dissociative photon emission is possible

Assume 0.1>x>0.01, and Q2<2 GeV2

photon emission is possibleSingle tags: elastic only, or p-diss. incl. s = 14 TeV

Qand for dissociative mass MN < 20 GeV

S(W) = f(x1) f(x2)

Color: double tags hence elastic scattering only

pp= S p dW

GeV


Color: double-tags, hence elastic scattering only

Problem: Same signature (one or two very forward protons) has also central diffraction (i.e. pomeron-pomeron scattering) in stronginteractions

Both processes weakly interfere, and transverse momentum of the scattered protons are on average much softer intwo photon case Phys Rev D63 (2001) 071502(two-photon case

) `t ’ di t ib ti b)Q2 0.01 GeV2

Phys. Rev. D63 (2001) 071502(

a) true’ distributions; b) distributions smeared due to beam intrinsic pT; all plots normalized for pT

2 < 2 GeV2pT

Diffraction b=4 GeV‐2

Assuming ultimate pTresolution 100 MeV; i.e. neglecting detector effects

pT gives powerful separation handle providedthat size of and pomeron-pomeron cross-sections are not too large...

11

neglecting detector effectsg…unless special high- running.

Heidelberg, 6/9/2011K. Piotrzkowski

LHC as a collider arXiv:0908.2020

s = 14 TeV


LHC as a colliderT h t l i i d ti tiTwo‐photon exclusive pair production cross‐section is given just by:

• particle charge mass and spinparticle charge, mass and spin

for a given mass and charge it is largest for vector particles , then for fermionsp ,

WW pair production has very sizable cross‐section at the LHC of 100 fb !section at the LHC of 100 fb !

Massive fermions have sizable cross‐sections up fto about 200 GeV masses, for scalars cross‐sections

are about 5 times smaller (but there is H++ case, for example)


p )

Physics with WW (and ZZ)Physics with WW (and ZZ)

WW and ZZ pair as a powerful test bench for WW and ZZ pair as a powerful test bench for the gauge boson sector at the LHC

Search for anomalous quartic couplingsSearch for anomalous quartic couplings


Lagrangian for aQGCsarXiv:0908 2020arXiv:0908.2020


Generic LHC detector acceptance

Note: diffractive CEP of WW is < 1 fb


Setting limits on aQGCs


Unitarity bounds


So far no constrains on W were applied need to watch unitarity bounds!

Unitarity bounds


Improvement of ~4000

Differential distributions

Definitely a lot of space for improvements, but can it be done at high luminosity?


but can it be done at high luminosity?

physics in ion collisionsTo profit from Z4 enhancement in two photon interactionsTo profit from Z4 enhancement in two‐photon interactions one has to fulfill coherence condition: xM 1/(2R), where M and R are the ion mass and radius, respectively.

• Using empirical parameterization of R = 1.25 fm A1/3 one gets 1/(2R) equal to 48 and 20 MeV for oxygen (A=16) and l d (A 208) ti l thi l d t th f ll ilead (A=208) respectively; this leads to the following coherence conditions:

x for oxygen ionsx for oxygen ions(56 TeV beams)

x for lead ions( )(574 TeV beams)

Note: lepton pair production has been measured at RHIC


p p p(using neutrons for tagging, not elastic ions!)


HPS might allow for tagging also ‘zero‐degree’ light ions as Ar or Ca

Heidelberg, 6/9/2011 K. Piotrzkowski 24wrt to 30 fb‐1

p interactions at the LHC - super HERA at CERN

Photon-proton interactions at the LHC have significantly higher energy reach and luminosity yield is expected than for the events

Example assumptions:• 0.01 < x1 < 0.1, photon tagging range• 0.005 < x2 < 0.3, Bjorken-x range for quarks and gluons

+ use MRST2001 (at Q2=104 GeV2) for partons

S(W)= f(x1) fp(x2) , W2=4Ep2x1x2

pp= S p dW


Photon-quark luminosity spectra s = 14 TeVs = 14 TeV

Note: at Wq > 300 GeV photon-quark luminosity is about one third of the


q p q ynominal pp (and still significant beyond 1 TeV)

Photon-gluon luminosity spectra

s = 14 TeV

Note: at Wg > 400 GeV photon-gluon luminosity is about 10% of the


g p g ynominal pp

p Physics Menu - Highlightspb for q Wq at W > 200 GeV

pb !

Wqt t

Note: Quoted at pp level

• anomalous W and Z production at Wq 1 TeV• top pair production and top charge?

Note: Quoted at pp level

• top pair production and top charge?• single top production and anomalous Wtb and tb vertices• exotics: compositeness, excited quarks, ...

Experimentally, more difficult to measure – usually, much weaker signatures and more vulnerable to event pileup…


See more in arXiv:0908.2020

Part IIPart II

What is being done at the LHC now?


Exclusive physics @ LHC

Early analysis: studying SM physics by imposing exclusivity conditions on the Early analysis: studying SM physics by imposing exclusivity conditions on the central system of CMS Future: Higgs/BSM physics by detecting (both) forward scattered protons with the proposed 'High Precision Spectrometer' (HPS) detectors


p p g p ( )

Exclusive The first measurement focus on the dimuonchannel – standard candle:

* Pure QED process:‐ No PDF to account for‐ Small theoretical uncertainties

* Striking kinematic distributions:‐ due to very small virtuality of the exchanged y y gphotons

* measured in previous experiments to be inagreement with the ME LPAIR generatorg g

• Largest background arises from semi exclusive two photonfrom semi‐exclusive two‐photonproduction due to single and double proton dissociative (or inelastic) photon exchange:


Exclusive

CMS DP 2010 035CMS‐DP‐2010‐035


Exclusive vector mesons

CMS‐DP‐2010‐035CMS DP 2010 035


Question: How to select exclusive events in high pileup environment?

Question: How to select exclusive events in high pileup environment?

Answer: Use tracking only and zoom in onto the vertices!


Exclusivity conditions

In (very) low luminosity era:2 muons and “nothing else“in the tracker and calorimetersin the tracker and calorimeters

In 2010, each event of interest can beaccompanied by extra “PileUp” events

i hi h b h iwithin the same bunch crossing:~ 2‐3 pileup interactions

In 2011, roughly 7‐10 PU per crossing, g y p g

Restricting the analysis to single interactions only would have reduced the data sample % f h l i l i i i ki l


to 20% of the total impose exclusivity using tracking only

Exclusivity selection


Exclusivity selection


CMS PAS FWD‐10‐005

Signal extraction

CMS PAS FWD‐10‐005


Dimuon distributionsCMS PAS FWD 10 005CMS PAS FWD‐10‐005


Drell‐Yan background efficiency

Vetoing the inclusive backgroundsVetoing the inclusive backgrounds very successful with tracking only!… also in high pileup condition.

This opens possibility for exclusive searches using effectively all high g y geven without forward proton detectors.

However only for purely leptonicHowever, only for purely leptonicfinal states.


Part IIIPart III

What can be done more at the LHC?


Brief history:

FP420New forward detectors @ LHCBrief history:

May’05: R&D proposal acknowledged by LHCC

June’08: FP420 ReportFP420

p

Fall’08: Initial proposals to CMS/ATLAS

In 2009: Adding /detectors @ 220/240 m

HPS project in CMS, AFP in ATLAS

43delberg, 6/9/2011 K. Piotrzkowski

JINST 4 (2009) T10001

High Precision Spectrometers: Motivation(1000 Tm bending power p/p~2.10‐4)

Light Higgs boson case is compelling more than everIts exclusive production provides unique information:p p q

• Higgs quantum numbers (spin‐parity filter)• Direct & precise H mass measurement (event‐by‐event);

MHresolution of 2 GeV direct limits on Higgs widthMH resolution of 2 GeV direct limits on Higgs width• Possibility of detecting H bb mode

Detection of SM Higgs boson requires (very) large luminosity fb d h ll d kobs fb and challenging timing detectors to keep backgrounds low (S/B1:2); in case of BSM physics HPS could provide discovery channels for Higgs bosons p y gg

In addition, HPS offers access to ‘guaranteed’ and unique studies like electroweak physics in two‐photon interactions, or

QCD h i l i d i f l


new QCD phenomena in exclusive production, for example.

Optimal places for tagging Central Exclusive Production (CEP)at LHC: @ 220/240m and 420m from IP

K. Piotrzkowski 6

HECTOR: JINST 2, P09005 (2007)For nominal low‐ LHC optics

Heidelberg, 6/9/2011

Forward proton acceptance @ m

HECTOR: JINST 2, P09005 (2007)P09005 (2007)

To detect forward protons for CEP of light Higgs (Mh ~ 120 GeV) one needs HPS420 detectors; Note: Acceptance is mostly drivendetectors; Note: Acceptance is mostly driven by energy loss NOT by scattering angle (pT)

HPS240 essential for triggering + efficiency


for HPS240+HPS420 ~ 2 x HPS420

Measuring (very) forward protonsQuick beam-optics course:• To good approximation beam protons move independently in horizontal and vertical planes• Particle point-to-point transfer can be computed using transport matrices (X=MX0) or, equivalently optics functions and Dor, equivalently optics functions and D

x = x*(*)sinx* cosDE/E

75 mD2Q HPS

Horizontal plane:

IP ~160 m

~75 m


D1

Reconstruction: Chromacity grids

HECTOR

Basic principle:Basic principle:• Three initial variables(position+angle+energy) and two measured (position+angle) assume nominal vertex position (x=0)• (Horizontal and vertical planes independent)

In each arm (&plane) position and angle @ HPS i l d i l @


give energy loss and scattering angle @ IP

10 m per point and ~10 m lever arm result in about 2.10‐4 energy resolution!

Calibration with exclusive di-muonspp pp l+l‐ CMS thesis: X. Roubypp pp

~ 700 events in 100 pb‐1

CMS thesis: X. Rouby

• Nearly pure QED processNearly pure QED process

• Calibration/alignment of HPS detectors

(about 40% protons detected!):

Expected resolution of x=E/E is ~5.10‐6 !

Calibration procedure itself can be very well controlledusing Upsilon signal!

BOTTOMLINE:

Heidelberg, 6/9/2011 K. Piotrzkowski49

BOTTOMLINE: Exclusive low‐mass dimuons crucial for HPS

HECTOR: JINST 2,

Proton fluence @ m for 20 fb-1

P09005 (2007)

Small area detectors needed (~several cm2) At nominal luminosity large event rates expected ~10 MHz !! Total fluence of protons cm2


Total fluence of protons cm

Taken on 14/1/2009

CMS

Q6

240m from IP5


Moving Hamburg pipe conceptSuccessfully used at HERA:Robust and simple design, + easy access to detectors

Motorization and movement control to be cloned from LHC collimator design


g

Moving pipe: Detector ‘pockets’Prepared for beam tests:

Thin 300 m entrance and side


windows

Picosecond ToF detectors @ LHCUse very fast ToF detectors to measure longitudinal vertex position by z‐by‐timingy g p y y gfrom forward proton arrival time difference: z = (t1 – t2)/2c

HECTOR: JINST 2, P09005 (2007)

Path length differences are very small for forward protons at LHC, typically 100 di b i d i diff<< 100 m corresponding to sub‐picosecond time differences.

Ultra fast timing detectors are essential for measuring the exclusive productionUltra fast timing detectors are essential for measuring the exclusive production at LHC, like for the Higgs boson case in pp pHp, JINST 4 (2009) T10001Heidelberg, 6/9/2011 54K. Piotrzkowski

HPS (or AFP): Staging

HPS420 detectors are essential for the exclusive Higgs detection but require significant LHC beam‐line modification (2 NCCs for Point 5) long shutdowns and significant costs

HPS240 detectors are important since can provide L1 signals andHPS240 detectors are important since can provide L1 signals and installation require minimal intervention to LHC (NB: HPS detectors are like a couple of new `collimators`… among 100)

Stage One:In 2014 install detectors @220/240 m; with simple trackers and fast ToF detectorsToF detectors Stage Two:In 2018 install detectors @420 m; with final trackers and fast ToF


detectors

Photon@LHC reference: 2008 CERN Workshop on High Energy Photon Collisions @ LHC

> 40 contributions – acrossmany fields – all collidermany fields – all colliderexperiments present

Also comingPHOTON 2011 conference proceedingsproceedings

Heidelberg, 6/9/2011 56K. Piotrzkowski

Extra slides


LHC beam‐line close to 240 m

TOTEM

Available space of m!

From Detlef: • Space above quench resistors (QRs) is not reserved yet• Space between QR and beam pipe ~ 25 cm, and space

between QRs ~ 50 cm


between QRs 50 cm• No problem of heat load

Forward proton detectors @ 420 m(as discussed in FP420 report)

• Installation of Si detectors in cryogenic region of LHC, i.e. cryostat redesign needed

• Strict space limitations rule out Roman Pot technology use movable beampipe insteadtechnology, use movable beampipe instead

• Radiation hardness required of Si is comparable to those at SLHC, use novel 3‐D Silicon technology

• To control pile‐up background use very fast p p g ytiming detectors ( ~ 10ps)

Acceptance: (At nominal LHC β* = 0.5 m)0 002 < ξ < 0 020.002 < ξ < 0.02

Two detector stations per arm

(4 in total): each station contains tracking

and timing detectors


HPS420


Unitarity bounds


Proton fluence at HPS420

HECTORVery high fluence due to protons in singleto protons in single diffraction:

Distribution of protons @ HPS420 in lateral plane:

Small area detectors needed (~several cm2) At nominal luminosity large event rates expected ~10 MHz !!


Total fluence of protons cm2

Heidelberg, 6/9/2011 K. Piotrzkowski 65Also HE photoproduction !

Accidental overlays

Use timing for background suppression


HPS acceptance with newest LHC optics m

Note: 2mm approach introduce some


Note: 2mm approach introduce some shadowing of HPS420

HPS acceptance with newest LHC optics m

Note: Acceptance changes when central system X is constrained ‐ here |rapidity(X)| < 1.5


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