Hadronic physics“experimental” issues

M. Sozzi NA62 Physics Handbook

meetingCERN – 10/12/2009

You said hadronic decays?

Hadron (/hædr:on/): thick, stout, tough, hard, messy, complicated

In principle the place where most interesting things can happen

But hard to make sense of them

General experimental remarks

• In recent times, most “important” hadronic K decay results were obtained from dedicated precision experiments, not as byproducts of experiments designed for something else.

• This is due to what goes under the name of “systematics”

• Some K experiments are more “general-purpose” than others

• An impressive amount of K decaying into the detector is not all

Hadronic K decays in NA62?

A performing and diverse detector is there (to suppress very different decay modes)BUTyou need to trigger on interesting events

NA62 is (being) designed for K+ π+νν decay measurement using an unseparated hadron beam.

Requirements: O(1010) suppression of backgrounds Large control samples for background control Simple trigger conditions (“factorization”)

Aim: trigger on (single) charged-track events with no muons, no photons and no electrons.

K→πνν:17 nm

Kμ2

RICH MUV CEDAR LKRSTRAWS LAV

L0 CTP

GbE switch

PC PC PCPCPC PC PC PCPCPCPCPCPC PC

PC PCPC PC CDRL0 triggerTrigger primitives

Data

EB

1 MHz

1 MHz

1 MHz

O(10 MHz)

O(KHz)

NA62 TDAQ - OVERVIEW

1 MHz

L0L1/2

O(<1ms)

2K 1K200

8K 13K 2.5K 60K

Event rate is comparable to LHC.Trigger rate can be

even higher.

Hadronic K decays?

Hadronic decay modes left through the trigger? HOPEFULLY NONE

So: (1) A second phase of NA62 OR (2) Think hard about trigger improvements to accommodate a few potentially very interesting modes during πνν data-taking (we ARE actively pursuing this) ALSO (3) What about a neutral K high-intensity beam?

K+ hadronic decays

CP/CPT violation in ∆

Need twin beamsNeed absolute flux normalization: probably not possible(but see later for 2πγ)Anyway generally suppressed asymmetries

CP violation in Dalitz plot

Need twin beams∆g not necessarily the best quantity (what is “g”?)Measured interference in ππγ opens up new possibility: Δ(∂σ/∂Eγ)

∆g CPV (NA48/2)

91M events

3.1G events

π±π+π–

π±π0π0

∆g CPV

Significant interest in a 10–4 level experiment (NA48/2)

A 10–5 level experiment: - could possibly be achieved in terms of statistics- would require > x100 control samples- would require a new dedicated design for systematic control- questionable interest? (in view of order-of-magnitude uncertainties in SM predictions, maybe except for ΔgC)

Could think of better observables in the Dalitz plot

K 2πγ

Reminder: INT could give (direct) CPV O(10-4) in SM (among the largest)

Also one of the few places where (exploiting CPT) we might get a combined π+π0 and π+π0 CPV rate asymmetry with cross-normalization

Separation by photon spectrum

K± π±π0

Don’t forget the “usual trick”: K± π±π0e+e–

opening up the possibility for E/M interference (CPV)Added bonus: K+/K– FSI elimination with twin beams

New from NA48/2:

CPV in K±→±

o Asymmetry can manifest itself in rates AN and Dalitz plot AW

o If ≠0 then +≠ the number of events K+→≠ K-→o Theoretical range 2·10-6 to 1·10-5with 50<E

*<170 MeV.

o SUSY contributions can push the asymmetry to 10-4 in

specific region of the Dalitz plot

o Present experimental knowledge: (0.9±3.3)% PDG08

o NA48/2 limit < 1.4x10-3 90% CL based on 1.08 Million events

INTINT

4224422220

11 )|||(|||)cos(21 WXXmmWXmm

WW MEKEKIB

M. Raggi

CPV in at NA62

• Assuming 1013 K+ K– beam flux (no downscale)• In NA62 events: 150M K+ + 85M K–

• Can measure rate asymmetry down to 10-4 precision

• Can measure Dalitz plot asymmetry T* and W

• Can measure the angle in the interference term • K+/K– ratio measurement can use normalization• Systematic can be pushed down to 10-4 by using 4 ratio

as for

M. Raggi

CPV in K± → ±

• Present PDG have no limit on asymmetry

• NA48/2 can reach a % limit

• NA62 might get (no downscale !!!):– 850000 K+ and 303000 K-– No evidence of systematic limit on the measurement– Can push the asymmetry limit down to 10-3

M. Raggi

K± →π±e+e– K± →π±μ+μ–

• NA48/2 reached a limit of 2.1x10−2 at 90% CL

• NA62 might collect:450000 K+ and 250000 K

• Can reduce present limit by 1 order of magnitude

• The SUSY upper limit on the range of 10-3

• Can measure forward backward asymmetry

M. Raggi

K 3πγ

Dominated by IB at O(p4) for unsuppressed decays (prediction only limited by knowledge of 3π), unlikely to extract direct weak part (low-energy constants)

2π 2π

- The “classic” hard way (Ke4)

- The “new” hard way (cusps)

(see G. Colangelo, B. Bloch and D. Madigojine talks)

However: here also some help from our theory colleagues is needed

What about neutral K ?(the land where CP violation rules)

Nothing very well thought, but NA48 switched from neutral to charged during its life, while keeping most of the setup

In principle an intense neutral beam is possible

Again: when speaking about neutral K non-hadronic modes come to mind: π0νν, π0e+e–, π0μ+μ–.

Each of them (if at all feasible) would be a new experiment in itself

BUT

K0 hadronic decays

KS

KL

K 3π

EM cluster reconstruction inefficiency 0.7% systematic error

KS (CPV): CPLEAR, NA48, KLOE – different techniques

“Trivial” indirect CPV expectedBR(KS 3π0) ≈ BR(KL 3π0) |ε|2 (τS/τL) ≈ 1.9·10−9

Direct CPV small (?) (and however not precisely predictable)

K 2π:

© P. Boyle

12/ˆˆ%5)ˆ( KKK BBB

%5.0||/)( (or <2% Re() semileptonics)

K 2π: ’

χ2=5.3/3, consistency 14%

(was 6.2/3, consistency 10%)

Re(’/) = (16.4 ± 1.9) · 10–4

Including ΔI=3/2 correction [EPJ C36 (2004) 37]

[PDG scaled error]

Direct CPV at ≈ 9σ

Despite the prime importance of this 10%

measurement, it is not (yet) what you would choose as a quantitative test of the SM

CPT

KS

KL

Bell-Steinberger

KLOE+ JHEP12(2006) 011

No direct CPT assumptionπ+π– phase dominatesNo significant contribution from 3π

Guinness Book of Records CPT

Á la CP/T (1999):

SWKK mmm

sin2

0.5% (KTeV, KLOE, NA48) BR

1.5% (KTeV) reg. interference

1.5% using φ00, no dir CPT and no CPV outside 2π, or use Im(x) and Im(η3π) (CPLEAR, NA48, KLOE)0.3% (KTeV) reg. interference

Vacuum interference experiment (hadronic environment close to target, as done in NA48) using π+π– only:pure K0 beam best, e.g. low energy CEX:σ(K+n → K0p) ~ 40mb (120 MeV/c) → 40 μb (12 GeV/c)(CP/T proposal: 25 GeV/c separated K+ beam)

“Planck scale” test of CPTquestionable (but nice and

“durable” result)

CPT limit experiment

As a bonus: Lorentz symmetry violation with high-energy K decays

The Next Great Hadronic K Decay Experimentis not in sight (you knew that)

(Tentative) conclusions

However:

many interesting K measurements were not foreseen at the beginning

Worth keep trying, and you can help on this