diffractive group: experimental summary
DESCRIPTION
Diffractive group: experimental summary. Michele Arneodo Università del Piemonte Orientale, Novara, Italy. o) Diffractive studies at the LHC, including the Higgs o) Input/results from HERA Not an exaustive summary !. See talks by Pierre van Mechelen(*) yesterday - PowerPoint PPT PresentationTRANSCRIPT
1
Diffractive group: experimental summary
Michele ArneodoUniversità del Piemonte Orientale, Novara, Italy
o) Diffractive studies at the LHC, including the Higgs
o) Input/results from HERA
Not an exaustive summary !
See talks by Pierre van Mechelen(*) yesterdayand by Halina Abramowicz on Tuesday !
(*) covers material by K. Borras, A. Bunyatyan, A. Panagiotou
2
Central exclusive production of the Higgs
b, W
b, WH
• Khoze, Martin, Ryskin hep-ph 0111078
• Central system is (to a good approx) 0++
• If you see a new particle produced exclusively with proton tags you know its quantum numbers
• Proton tagging may be the discovery channel in certain regions of the MSSM
• Measuring the protons means excellent mass resolution (~ GeV) irrespective of the decay products of the central system
• Attractive for MH=120-250 GeV
ξ: fractional momentum loss of proton – for 120 GeV Higgs, x~ 1%
t: 4-momentum transfer squared at proton vertex
3
How to measure the protons • At CMS: TOTEM, Roman Pots at 150 and 220m from I.P. Excellent coverage in and t at low luminosity optics (*=90, 1540m)Coverage 0.02<<0.2 at high luminosity optics (*=0.5m) [K.Oesterberg, H.Niewiadomski]
• At ATLAS: FP220Roman Pots at 220 m Coverage similar to TOTEM at high luminosity optics [Ch. Royon]
• At CMS and ATLAS: FP420 R&D project, aim to instrument region at 420m from I.P. 0.002<<0.02 (high luminosity optics only) [S. Watts]
detectors@420m
FP420
TOTEM-
FP220
xL=P’/Pbeam=
Log
Logt
*=0.5
4
TOTEM (or FP220 at ATLAS)FP420
How to measure the protons
K.OesterbergM.GrotheCh. RoyonH. NiewiadomskiA. Pilkington
• Cold region of LHC• Too far for L1 trigger
5
FP420
S. Watts
Replacement ofcryostat @ 420m designed
Moving beam pipe
• R&D phase essentially over
• Proposals to Atlas and CMSimminent• Installation >2009
6
FP420 S. Watts
3D Si detectors: edgeless, rad-hard Successful beam test of 3D detectorsat CERN
Timing detectors to reconstruct vertex
Tracking code available in ATLAS, CMSframeworks (W. Plano, X. Rouby)
7
FP220
Ch. Royon Proposal to Atlas imminent
Acceptance
8
CMS IP T1/T2, Castor ZDC RPs@150m RPs@220m
possibly detectors@420m
T1 (CSC) 3.1 ≤ || ≤ 4.7 HF 3 ≤|| ≤ 5T2 (GEM): 5.3 ≤ || ≤ 6.6Castor 5.3 ≤ || ≤ 6.6
CMS+TOTEM: unprecedented coverage in
Carry out a program of diffractive and forward physics as integral part of the routine data taking at the LHC, i.e. at nominal beam optics and up tothe highest available luminosities.
K.OesterbergM.Grothe
9
Low lumi Rapidity gap selection possibleHF, Castor, BSCs, T1, T2Proton tag selection optionalRPs at 220m and 420 m
Diffraction is about 1/4 of tot
High cross section processes“Soft” diffractionInteresting for start-up runningImportant for understanding pile-up
High lumiNo Rapidity gap selection possibleProton tag selection indispensableRPs at 220m and 420 m
Central exclusive productionDiscovery physics:Light SM HiggsMSSM HiggsExtra dimensions
Gamma-gamma and gamma-proton interactions (QED)Forward energy flow - input to cosmics shower simulationQCD: Diffraction in presence of hard scale Low-x structure of the proton High-density regime (Color glass condensate) Diff PDFs and generalized PDFs Diffractive Drell-Yan
Low
lu
mi
Hig
h lu
mi
“Prospects for diffractive and forward physics at the LHC” CERN/LHCC 2006-039/G-124, CMS Note 2007/002, TOTEM Note 06-5, Dec 2006
K.OesterbergM.GrotheCMS+TOTEM: physics map
1. Trigger is a major limiting factor for selecting diffractive events
2. Background from non-diffractive events that mimic diffractive events because of protons from pile-up events
11
→ CMS trigger thresholds for nominal LHC running too high for diffractive events
→ Use information of forward detectors to lower jet trigger thresholds
→ The CMS trigger menus now foresee a dedicated diffractive trigger stream with 1% of the total bandwidth on L1 and HLT (1 kHz and 1 Hz)
NB Information from 220 detectors crucial for triggering
Much less of a problem is triggering with muons, where L1 threshold for 2-muons is 3 GeV
single-sided 220m conditionwithout and withcut on
Achievable total reduction: 10 (single-sided 220m) x 2 (jet iso) x 2 (2 jets same hemisphere as p) = 40
CMS-TOTEM: diffractive trigger
M.Grothe
12
Trigger is a major limiting factor !
Level-1:~12% efficiency with 2-jets (ET>40GeV) & single-sided 220 m condition
HLT: Jet trigger efficiency ~7%To stay within 1 Hz output rate, needs to either prescale b-tag or add 420 m detectors in trigger
Additional ~10% efficiency by introducing a 1 jet & 1 (40GeV, 3GeV) trigger condition
H(120 GeV) → b bbar
L1 trigger threshold [GeV]
Eff
icie
ncy 420m
220m
420+420m
420+220m
pp pWX1-jet trigger
pp p jj X2-jet trigger
Eff
icie
ncy
L1 trigger threshold [GeV]
no fwd detectorscondition
single-arm 220m
single-arm 420m
Eve
nts
per
pb
-1
CMS-TOTEM: diffractive trigger M.Grothe
13
Eg at 2x 1033 cm-2s-1 10% probability of obtaining a fake 2-proton signature because of pile-up.
Pile-up
• Average number of pile-up events overlaid to any hard scatter 7 @ 2x1033 cm-2s-1, 35 @ 1x1034 cm-2s-1 (not 20…)
• 25% of these events are diffractive, i.e. have a fast proton
• Example: pile-up background to diffr H bb comes from non-diffractive bb production, superimposed to two single- diffractive pile-up events
K.OesterbergM.GrotheM. TasevskyA. PilkingtonV. Khoze
14
Can be reduced by:
Requiring correlation between ξ, M from central detector andξ, M from near-beam detectors
Fast timing detectors to determine if protons came from same vertex as hard scatter(TOF with 10 ps resolution !)
; 1 2 s = M2
(from protons)(
jets
)
CEP H(120) bb incl QCD di-jets + PU
M(2-jets)/(Missing Mass)
Pile-up
K.OesterbergM.GrotheM. TasevskyA. PilkingtonV. Khoze
15
Pile-up
• S/B for SM H bb of order 1 at 2 x 1033 cm-2 s-1
• S/B for MSSM H bb as large as 100-1000
• Pile-up significantly less severe for H WW
H bb
K.OesterbergM.GrotheM. TasevskyA. PilkingtonV. Khoze
A. Pilkington
16
Further upgrades in CMS forward region
A. Bunyatyan, K. Borras
17
• Measurements of diffractive structure function F2D
• QCD fits to F2D and extraction of dPDFs
• How well does QCD hard-diffractive factorisation work ie can use dPDFs to predict cross section of diffractive production of jets or charm ?
• Can we quantify rapidity gap survival probability ? • Leading neutrons and the survival probability
HERA
18
Input from HERA: dPDFs
Diffractive PDF: probability to find a parton of given x in the proton undercondition that proton stays intact – sensitive to low-x partons in proton, complementary to standard PDFs
Obtained from QCD fits to F2D data
IP
p’p
p p’
IP
b, jet
b, jet
dPDF
dPDF
p’p
e
e’
IP dPDF
19
New measurements of F2D from ZEUS
Three methods to select diffraction at ZEUS:
i) Require a leading proton (leading proton spectrometer, LPS)
ii) Require a large rapidity gap (LRG)
iii) Exploit the different shape of MX
for diffractive and non-diffractive events (MX method)
p’p
ee’
IP
X
For the first time, analyse the same set of data with the three methods and try and understand the differences
J. Łukasik Inclusive Diffraction at HERA from the ZEUS experiment
20
ZEUS MX 99-00, ZEUS MX 99-00 (prel.), ZEUS LRG 00 (prel.)
xIPF2D(3) vs. Q2
● reasonable agreement● work on understanding
remaining differences is continuing
ZEUS MX 98-99
ZEUS MX 99-00 (prel.)
ZEUS LRG 00 (prel.)
ZEUS MX vs LRG results
J. Łukasik Inclusive Diffraction at HERA from the ZEUS experiment
21
ZEUS LRG 00 (prel.), ZEUS LPS 00 (prel.)
LPS/LRG=0.82±0.01(stat.)±0.03(sys.)independent of Q2 and β
A measure of the contamination byproton dissociative events in the LRGsample
About 10% normalization uncertainty of the LPS measurement not shown
ZEUS LRG vs LPS results
Np
ee’
IP
X
J. Łukasik Inclusive Diffraction at HERA from the ZEUS experiment
22
xIP = 0.003ZEUS LRG 00 (prel.), H1 LRG
xIP = 0.01ZEUS LRG 00 (prel.), H1 LRG
● Fraction of proton dissociation events for ZEUS and H1 detectors is different
● The ZEUS LRG data are normalized to the H1 LRG data
ZEUS vs H1
H1: (0) = 1.118 ± 0.008 +0.029-0.010
‘ = 0.06 +0.19 -0.06
ZEUS: (0) = 1.117 ± 0.005 +0.024-0.007
' = -0.03 ± 0.07 +0.04 -0.08
23
H1 FH1 F22DD
In best regions, precision ~5% (stat), 5% (syst), 6% (norm),…well described by fit
P.Newman
24
25
`Fit A’ and `Fit B’ DPDFs (linear z scale)`Fit A’ and `Fit B’ DPDFs (linear z scale)
• Lack of sensitivity tohigh z gluon confirmedby dropping (high z) Cg
parameter, so gluon is a constant at starting scale!
•Fit B 2 ~164 / 184 d.o.f.
• Quarks very stable• Gluon similar at low z • Substantial change to gluon at high z
P.Newman
26
QCD factorisation OK
M. Mozer
27
QCD factorisation OK
R. Wolf
28
jet
jet
hard scattering
IP LRG
CDF data
Extrapolationfrom HERA
GPDs and diffractive PDFs measured at HERA cannot be used blindly at LHC or Tevatron:
Digression: rapidity gap survival probability
P.Newman
29
• Proton and anti-proton are large objects, unlike pointlike virtual photon
• In addition to hard diffractive scattering, there may be soft interactions among spectator partons. They fill the rapidity gap and slow down the outgoing p,p – hence reduce the rate of diffractive events. Quantified by rapidity gap survival probability (underlying event !)
CDF data
Predictions basedon rescattering assuming HERA diffractive PDFs
F2D
Kaidalov, Khoze, Martin, Ryskin (2000)
Rapidity gap survival probability
Can we see a similar suppression at HERA by usingresolved photons at Q2=0 ?
30
QCD factorisation OK(but mainly direct component)
I. Melzer (+R. Wolf for H1)
31Unexpected, notunderstood
Hadron-like
QCD factorisationnot OK
32
Leading Neutrons
Kaidalov, Khoze, Martin & Ryskinhave used these data to derivethe rapidity gap survival probability(one pion exchange+absorption+migration)
B. Schmidke
33
Grand summaryLHC:• Diffraction/forward physics has generated several new detectors now on the way – added value for ATLAS and CMS. Diffractive group in CMS !
• Experimental challenges being addressed, eg trigger, pile-up
• Different experiments joining forces: CMS+TOTEM, ATLAS and CMS in FP420
HERA:• Precious input: dPDFs, rapidity gap survival probability, GPDs, experience in operating near-beam detectors
Wish list: • DVCS, J/psi, Y (including t dependence !) for constraining GPDs• H1+ZEUS F2
D, dPDFs• Understanding of gap survival• Leading proton spectra at LHC (crucial for pile-up)
34
RESERVE
35
CDF: evidence for exclusive processes at Fermilab
Search for exclusive 3 candidate events found 1 (+2/-1) predicted from ExHuME MC* background under study
Same type of diagrams as for Higgs Validation of KMR model !D. Goulianos, V. Khoze
36
Diffractive Structure Function:Q2 dependence
ETjet ~ 100 GeV !
Small Q2 dependence in region 100 < Q2 < 10,000 GeV2
Pomeron evolves as the proton!D. Goulianos
37
Diffractive Structure Function:t- dependence
No diffraction dips No Q2 dependence in slope from inclusive to Q2~104 GeV2
Fit d/dt to a double exponential:
Same slope over entire region of 0 < Q2 < 4,500 GeV2
across soft and hard diffraction!
D. Goulianos